xref: /freebsd/contrib/llvm-project/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp (revision 6966ac055c3b7a39266fb982493330df7a097997)
1 //===- InstCombineCasts.cpp -----------------------------------------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This file implements the visit functions for cast operations.
10 //
11 //===----------------------------------------------------------------------===//
12 
13 #include "InstCombineInternal.h"
14 #include "llvm/ADT/SetVector.h"
15 #include "llvm/Analysis/ConstantFolding.h"
16 #include "llvm/Analysis/TargetLibraryInfo.h"
17 #include "llvm/IR/DataLayout.h"
18 #include "llvm/IR/DIBuilder.h"
19 #include "llvm/IR/PatternMatch.h"
20 #include "llvm/Support/KnownBits.h"
21 using namespace llvm;
22 using namespace PatternMatch;
23 
24 #define DEBUG_TYPE "instcombine"
25 
26 /// Analyze 'Val', seeing if it is a simple linear expression.
27 /// If so, decompose it, returning some value X, such that Val is
28 /// X*Scale+Offset.
29 ///
30 static Value *decomposeSimpleLinearExpr(Value *Val, unsigned &Scale,
31                                         uint64_t &Offset) {
32   if (ConstantInt *CI = dyn_cast<ConstantInt>(Val)) {
33     Offset = CI->getZExtValue();
34     Scale  = 0;
35     return ConstantInt::get(Val->getType(), 0);
36   }
37 
38   if (BinaryOperator *I = dyn_cast<BinaryOperator>(Val)) {
39     // Cannot look past anything that might overflow.
40     OverflowingBinaryOperator *OBI = dyn_cast<OverflowingBinaryOperator>(Val);
41     if (OBI && !OBI->hasNoUnsignedWrap() && !OBI->hasNoSignedWrap()) {
42       Scale = 1;
43       Offset = 0;
44       return Val;
45     }
46 
47     if (ConstantInt *RHS = dyn_cast<ConstantInt>(I->getOperand(1))) {
48       if (I->getOpcode() == Instruction::Shl) {
49         // This is a value scaled by '1 << the shift amt'.
50         Scale = UINT64_C(1) << RHS->getZExtValue();
51         Offset = 0;
52         return I->getOperand(0);
53       }
54 
55       if (I->getOpcode() == Instruction::Mul) {
56         // This value is scaled by 'RHS'.
57         Scale = RHS->getZExtValue();
58         Offset = 0;
59         return I->getOperand(0);
60       }
61 
62       if (I->getOpcode() == Instruction::Add) {
63         // We have X+C.  Check to see if we really have (X*C2)+C1,
64         // where C1 is divisible by C2.
65         unsigned SubScale;
66         Value *SubVal =
67           decomposeSimpleLinearExpr(I->getOperand(0), SubScale, Offset);
68         Offset += RHS->getZExtValue();
69         Scale = SubScale;
70         return SubVal;
71       }
72     }
73   }
74 
75   // Otherwise, we can't look past this.
76   Scale = 1;
77   Offset = 0;
78   return Val;
79 }
80 
81 /// If we find a cast of an allocation instruction, try to eliminate the cast by
82 /// moving the type information into the alloc.
83 Instruction *InstCombiner::PromoteCastOfAllocation(BitCastInst &CI,
84                                                    AllocaInst &AI) {
85   PointerType *PTy = cast<PointerType>(CI.getType());
86 
87   BuilderTy AllocaBuilder(Builder);
88   AllocaBuilder.SetInsertPoint(&AI);
89 
90   // Get the type really allocated and the type casted to.
91   Type *AllocElTy = AI.getAllocatedType();
92   Type *CastElTy = PTy->getElementType();
93   if (!AllocElTy->isSized() || !CastElTy->isSized()) return nullptr;
94 
95   unsigned AllocElTyAlign = DL.getABITypeAlignment(AllocElTy);
96   unsigned CastElTyAlign = DL.getABITypeAlignment(CastElTy);
97   if (CastElTyAlign < AllocElTyAlign) return nullptr;
98 
99   // If the allocation has multiple uses, only promote it if we are strictly
100   // increasing the alignment of the resultant allocation.  If we keep it the
101   // same, we open the door to infinite loops of various kinds.
102   if (!AI.hasOneUse() && CastElTyAlign == AllocElTyAlign) return nullptr;
103 
104   uint64_t AllocElTySize = DL.getTypeAllocSize(AllocElTy);
105   uint64_t CastElTySize = DL.getTypeAllocSize(CastElTy);
106   if (CastElTySize == 0 || AllocElTySize == 0) return nullptr;
107 
108   // If the allocation has multiple uses, only promote it if we're not
109   // shrinking the amount of memory being allocated.
110   uint64_t AllocElTyStoreSize = DL.getTypeStoreSize(AllocElTy);
111   uint64_t CastElTyStoreSize = DL.getTypeStoreSize(CastElTy);
112   if (!AI.hasOneUse() && CastElTyStoreSize < AllocElTyStoreSize) return nullptr;
113 
114   // See if we can satisfy the modulus by pulling a scale out of the array
115   // size argument.
116   unsigned ArraySizeScale;
117   uint64_t ArrayOffset;
118   Value *NumElements = // See if the array size is a decomposable linear expr.
119     decomposeSimpleLinearExpr(AI.getOperand(0), ArraySizeScale, ArrayOffset);
120 
121   // If we can now satisfy the modulus, by using a non-1 scale, we really can
122   // do the xform.
123   if ((AllocElTySize*ArraySizeScale) % CastElTySize != 0 ||
124       (AllocElTySize*ArrayOffset   ) % CastElTySize != 0) return nullptr;
125 
126   unsigned Scale = (AllocElTySize*ArraySizeScale)/CastElTySize;
127   Value *Amt = nullptr;
128   if (Scale == 1) {
129     Amt = NumElements;
130   } else {
131     Amt = ConstantInt::get(AI.getArraySize()->getType(), Scale);
132     // Insert before the alloca, not before the cast.
133     Amt = AllocaBuilder.CreateMul(Amt, NumElements);
134   }
135 
136   if (uint64_t Offset = (AllocElTySize*ArrayOffset)/CastElTySize) {
137     Value *Off = ConstantInt::get(AI.getArraySize()->getType(),
138                                   Offset, true);
139     Amt = AllocaBuilder.CreateAdd(Amt, Off);
140   }
141 
142   AllocaInst *New = AllocaBuilder.CreateAlloca(CastElTy, Amt);
143   New->setAlignment(AI.getAlignment());
144   New->takeName(&AI);
145   New->setUsedWithInAlloca(AI.isUsedWithInAlloca());
146 
147   // If the allocation has multiple real uses, insert a cast and change all
148   // things that used it to use the new cast.  This will also hack on CI, but it
149   // will die soon.
150   if (!AI.hasOneUse()) {
151     // New is the allocation instruction, pointer typed. AI is the original
152     // allocation instruction, also pointer typed. Thus, cast to use is BitCast.
153     Value *NewCast = AllocaBuilder.CreateBitCast(New, AI.getType(), "tmpcast");
154     replaceInstUsesWith(AI, NewCast);
155   }
156   return replaceInstUsesWith(CI, New);
157 }
158 
159 /// Given an expression that CanEvaluateTruncated or CanEvaluateSExtd returns
160 /// true for, actually insert the code to evaluate the expression.
161 Value *InstCombiner::EvaluateInDifferentType(Value *V, Type *Ty,
162                                              bool isSigned) {
163   if (Constant *C = dyn_cast<Constant>(V)) {
164     C = ConstantExpr::getIntegerCast(C, Ty, isSigned /*Sext or ZExt*/);
165     // If we got a constantexpr back, try to simplify it with DL info.
166     if (Constant *FoldedC = ConstantFoldConstant(C, DL, &TLI))
167       C = FoldedC;
168     return C;
169   }
170 
171   // Otherwise, it must be an instruction.
172   Instruction *I = cast<Instruction>(V);
173   Instruction *Res = nullptr;
174   unsigned Opc = I->getOpcode();
175   switch (Opc) {
176   case Instruction::Add:
177   case Instruction::Sub:
178   case Instruction::Mul:
179   case Instruction::And:
180   case Instruction::Or:
181   case Instruction::Xor:
182   case Instruction::AShr:
183   case Instruction::LShr:
184   case Instruction::Shl:
185   case Instruction::UDiv:
186   case Instruction::URem: {
187     Value *LHS = EvaluateInDifferentType(I->getOperand(0), Ty, isSigned);
188     Value *RHS = EvaluateInDifferentType(I->getOperand(1), Ty, isSigned);
189     Res = BinaryOperator::Create((Instruction::BinaryOps)Opc, LHS, RHS);
190     break;
191   }
192   case Instruction::Trunc:
193   case Instruction::ZExt:
194   case Instruction::SExt:
195     // If the source type of the cast is the type we're trying for then we can
196     // just return the source.  There's no need to insert it because it is not
197     // new.
198     if (I->getOperand(0)->getType() == Ty)
199       return I->getOperand(0);
200 
201     // Otherwise, must be the same type of cast, so just reinsert a new one.
202     // This also handles the case of zext(trunc(x)) -> zext(x).
203     Res = CastInst::CreateIntegerCast(I->getOperand(0), Ty,
204                                       Opc == Instruction::SExt);
205     break;
206   case Instruction::Select: {
207     Value *True = EvaluateInDifferentType(I->getOperand(1), Ty, isSigned);
208     Value *False = EvaluateInDifferentType(I->getOperand(2), Ty, isSigned);
209     Res = SelectInst::Create(I->getOperand(0), True, False);
210     break;
211   }
212   case Instruction::PHI: {
213     PHINode *OPN = cast<PHINode>(I);
214     PHINode *NPN = PHINode::Create(Ty, OPN->getNumIncomingValues());
215     for (unsigned i = 0, e = OPN->getNumIncomingValues(); i != e; ++i) {
216       Value *V =
217           EvaluateInDifferentType(OPN->getIncomingValue(i), Ty, isSigned);
218       NPN->addIncoming(V, OPN->getIncomingBlock(i));
219     }
220     Res = NPN;
221     break;
222   }
223   default:
224     // TODO: Can handle more cases here.
225     llvm_unreachable("Unreachable!");
226   }
227 
228   Res->takeName(I);
229   return InsertNewInstWith(Res, *I);
230 }
231 
232 Instruction::CastOps InstCombiner::isEliminableCastPair(const CastInst *CI1,
233                                                         const CastInst *CI2) {
234   Type *SrcTy = CI1->getSrcTy();
235   Type *MidTy = CI1->getDestTy();
236   Type *DstTy = CI2->getDestTy();
237 
238   Instruction::CastOps firstOp = CI1->getOpcode();
239   Instruction::CastOps secondOp = CI2->getOpcode();
240   Type *SrcIntPtrTy =
241       SrcTy->isPtrOrPtrVectorTy() ? DL.getIntPtrType(SrcTy) : nullptr;
242   Type *MidIntPtrTy =
243       MidTy->isPtrOrPtrVectorTy() ? DL.getIntPtrType(MidTy) : nullptr;
244   Type *DstIntPtrTy =
245       DstTy->isPtrOrPtrVectorTy() ? DL.getIntPtrType(DstTy) : nullptr;
246   unsigned Res = CastInst::isEliminableCastPair(firstOp, secondOp, SrcTy, MidTy,
247                                                 DstTy, SrcIntPtrTy, MidIntPtrTy,
248                                                 DstIntPtrTy);
249 
250   // We don't want to form an inttoptr or ptrtoint that converts to an integer
251   // type that differs from the pointer size.
252   if ((Res == Instruction::IntToPtr && SrcTy != DstIntPtrTy) ||
253       (Res == Instruction::PtrToInt && DstTy != SrcIntPtrTy))
254     Res = 0;
255 
256   return Instruction::CastOps(Res);
257 }
258 
259 /// Implement the transforms common to all CastInst visitors.
260 Instruction *InstCombiner::commonCastTransforms(CastInst &CI) {
261   Value *Src = CI.getOperand(0);
262 
263   // Try to eliminate a cast of a cast.
264   if (auto *CSrc = dyn_cast<CastInst>(Src)) {   // A->B->C cast
265     if (Instruction::CastOps NewOpc = isEliminableCastPair(CSrc, &CI)) {
266       // The first cast (CSrc) is eliminable so we need to fix up or replace
267       // the second cast (CI). CSrc will then have a good chance of being dead.
268       auto *Ty = CI.getType();
269       auto *Res = CastInst::Create(NewOpc, CSrc->getOperand(0), Ty);
270       // Point debug users of the dying cast to the new one.
271       if (CSrc->hasOneUse())
272         replaceAllDbgUsesWith(*CSrc, *Res, CI, DT);
273       return Res;
274     }
275   }
276 
277   if (auto *Sel = dyn_cast<SelectInst>(Src)) {
278     // We are casting a select. Try to fold the cast into the select, but only
279     // if the select does not have a compare instruction with matching operand
280     // types. Creating a select with operands that are different sizes than its
281     // condition may inhibit other folds and lead to worse codegen.
282     auto *Cmp = dyn_cast<CmpInst>(Sel->getCondition());
283     if (!Cmp || Cmp->getOperand(0)->getType() != Sel->getType())
284       if (Instruction *NV = FoldOpIntoSelect(CI, Sel)) {
285         replaceAllDbgUsesWith(*Sel, *NV, CI, DT);
286         return NV;
287       }
288   }
289 
290   // If we are casting a PHI, then fold the cast into the PHI.
291   if (auto *PN = dyn_cast<PHINode>(Src)) {
292     // Don't do this if it would create a PHI node with an illegal type from a
293     // legal type.
294     if (!Src->getType()->isIntegerTy() || !CI.getType()->isIntegerTy() ||
295         shouldChangeType(CI.getType(), Src->getType()))
296       if (Instruction *NV = foldOpIntoPhi(CI, PN))
297         return NV;
298   }
299 
300   return nullptr;
301 }
302 
303 /// Constants and extensions/truncates from the destination type are always
304 /// free to be evaluated in that type. This is a helper for canEvaluate*.
305 static bool canAlwaysEvaluateInType(Value *V, Type *Ty) {
306   if (isa<Constant>(V))
307     return true;
308   Value *X;
309   if ((match(V, m_ZExtOrSExt(m_Value(X))) || match(V, m_Trunc(m_Value(X)))) &&
310       X->getType() == Ty)
311     return true;
312 
313   return false;
314 }
315 
316 /// Filter out values that we can not evaluate in the destination type for free.
317 /// This is a helper for canEvaluate*.
318 static bool canNotEvaluateInType(Value *V, Type *Ty) {
319   assert(!isa<Constant>(V) && "Constant should already be handled.");
320   if (!isa<Instruction>(V))
321     return true;
322   // We don't extend or shrink something that has multiple uses --  doing so
323   // would require duplicating the instruction which isn't profitable.
324   if (!V->hasOneUse())
325     return true;
326 
327   return false;
328 }
329 
330 /// Return true if we can evaluate the specified expression tree as type Ty
331 /// instead of its larger type, and arrive with the same value.
332 /// This is used by code that tries to eliminate truncates.
333 ///
334 /// Ty will always be a type smaller than V.  We should return true if trunc(V)
335 /// can be computed by computing V in the smaller type.  If V is an instruction,
336 /// then trunc(inst(x,y)) can be computed as inst(trunc(x),trunc(y)), which only
337 /// makes sense if x and y can be efficiently truncated.
338 ///
339 /// This function works on both vectors and scalars.
340 ///
341 static bool canEvaluateTruncated(Value *V, Type *Ty, InstCombiner &IC,
342                                  Instruction *CxtI) {
343   if (canAlwaysEvaluateInType(V, Ty))
344     return true;
345   if (canNotEvaluateInType(V, Ty))
346     return false;
347 
348   auto *I = cast<Instruction>(V);
349   Type *OrigTy = V->getType();
350   switch (I->getOpcode()) {
351   case Instruction::Add:
352   case Instruction::Sub:
353   case Instruction::Mul:
354   case Instruction::And:
355   case Instruction::Or:
356   case Instruction::Xor:
357     // These operators can all arbitrarily be extended or truncated.
358     return canEvaluateTruncated(I->getOperand(0), Ty, IC, CxtI) &&
359            canEvaluateTruncated(I->getOperand(1), Ty, IC, CxtI);
360 
361   case Instruction::UDiv:
362   case Instruction::URem: {
363     // UDiv and URem can be truncated if all the truncated bits are zero.
364     uint32_t OrigBitWidth = OrigTy->getScalarSizeInBits();
365     uint32_t BitWidth = Ty->getScalarSizeInBits();
366     assert(BitWidth < OrigBitWidth && "Unexpected bitwidths!");
367     APInt Mask = APInt::getBitsSetFrom(OrigBitWidth, BitWidth);
368     if (IC.MaskedValueIsZero(I->getOperand(0), Mask, 0, CxtI) &&
369         IC.MaskedValueIsZero(I->getOperand(1), Mask, 0, CxtI)) {
370       return canEvaluateTruncated(I->getOperand(0), Ty, IC, CxtI) &&
371              canEvaluateTruncated(I->getOperand(1), Ty, IC, CxtI);
372     }
373     break;
374   }
375   case Instruction::Shl: {
376     // If we are truncating the result of this SHL, and if it's a shift of a
377     // constant amount, we can always perform a SHL in a smaller type.
378     const APInt *Amt;
379     if (match(I->getOperand(1), m_APInt(Amt))) {
380       uint32_t BitWidth = Ty->getScalarSizeInBits();
381       if (Amt->getLimitedValue(BitWidth) < BitWidth)
382         return canEvaluateTruncated(I->getOperand(0), Ty, IC, CxtI);
383     }
384     break;
385   }
386   case Instruction::LShr: {
387     // If this is a truncate of a logical shr, we can truncate it to a smaller
388     // lshr iff we know that the bits we would otherwise be shifting in are
389     // already zeros.
390     const APInt *Amt;
391     if (match(I->getOperand(1), m_APInt(Amt))) {
392       uint32_t OrigBitWidth = OrigTy->getScalarSizeInBits();
393       uint32_t BitWidth = Ty->getScalarSizeInBits();
394       if (Amt->getLimitedValue(BitWidth) < BitWidth &&
395           IC.MaskedValueIsZero(I->getOperand(0),
396             APInt::getBitsSetFrom(OrigBitWidth, BitWidth), 0, CxtI)) {
397         return canEvaluateTruncated(I->getOperand(0), Ty, IC, CxtI);
398       }
399     }
400     break;
401   }
402   case Instruction::AShr: {
403     // If this is a truncate of an arithmetic shr, we can truncate it to a
404     // smaller ashr iff we know that all the bits from the sign bit of the
405     // original type and the sign bit of the truncate type are similar.
406     // TODO: It is enough to check that the bits we would be shifting in are
407     //       similar to sign bit of the truncate type.
408     const APInt *Amt;
409     if (match(I->getOperand(1), m_APInt(Amt))) {
410       uint32_t OrigBitWidth = OrigTy->getScalarSizeInBits();
411       uint32_t BitWidth = Ty->getScalarSizeInBits();
412       if (Amt->getLimitedValue(BitWidth) < BitWidth &&
413           OrigBitWidth - BitWidth <
414               IC.ComputeNumSignBits(I->getOperand(0), 0, CxtI))
415         return canEvaluateTruncated(I->getOperand(0), Ty, IC, CxtI);
416     }
417     break;
418   }
419   case Instruction::Trunc:
420     // trunc(trunc(x)) -> trunc(x)
421     return true;
422   case Instruction::ZExt:
423   case Instruction::SExt:
424     // trunc(ext(x)) -> ext(x) if the source type is smaller than the new dest
425     // trunc(ext(x)) -> trunc(x) if the source type is larger than the new dest
426     return true;
427   case Instruction::Select: {
428     SelectInst *SI = cast<SelectInst>(I);
429     return canEvaluateTruncated(SI->getTrueValue(), Ty, IC, CxtI) &&
430            canEvaluateTruncated(SI->getFalseValue(), Ty, IC, CxtI);
431   }
432   case Instruction::PHI: {
433     // We can change a phi if we can change all operands.  Note that we never
434     // get into trouble with cyclic PHIs here because we only consider
435     // instructions with a single use.
436     PHINode *PN = cast<PHINode>(I);
437     for (Value *IncValue : PN->incoming_values())
438       if (!canEvaluateTruncated(IncValue, Ty, IC, CxtI))
439         return false;
440     return true;
441   }
442   default:
443     // TODO: Can handle more cases here.
444     break;
445   }
446 
447   return false;
448 }
449 
450 /// Given a vector that is bitcast to an integer, optionally logically
451 /// right-shifted, and truncated, convert it to an extractelement.
452 /// Example (big endian):
453 ///   trunc (lshr (bitcast <4 x i32> %X to i128), 32) to i32
454 ///   --->
455 ///   extractelement <4 x i32> %X, 1
456 static Instruction *foldVecTruncToExtElt(TruncInst &Trunc, InstCombiner &IC) {
457   Value *TruncOp = Trunc.getOperand(0);
458   Type *DestType = Trunc.getType();
459   if (!TruncOp->hasOneUse() || !isa<IntegerType>(DestType))
460     return nullptr;
461 
462   Value *VecInput = nullptr;
463   ConstantInt *ShiftVal = nullptr;
464   if (!match(TruncOp, m_CombineOr(m_BitCast(m_Value(VecInput)),
465                                   m_LShr(m_BitCast(m_Value(VecInput)),
466                                          m_ConstantInt(ShiftVal)))) ||
467       !isa<VectorType>(VecInput->getType()))
468     return nullptr;
469 
470   VectorType *VecType = cast<VectorType>(VecInput->getType());
471   unsigned VecWidth = VecType->getPrimitiveSizeInBits();
472   unsigned DestWidth = DestType->getPrimitiveSizeInBits();
473   unsigned ShiftAmount = ShiftVal ? ShiftVal->getZExtValue() : 0;
474 
475   if ((VecWidth % DestWidth != 0) || (ShiftAmount % DestWidth != 0))
476     return nullptr;
477 
478   // If the element type of the vector doesn't match the result type,
479   // bitcast it to a vector type that we can extract from.
480   unsigned NumVecElts = VecWidth / DestWidth;
481   if (VecType->getElementType() != DestType) {
482     VecType = VectorType::get(DestType, NumVecElts);
483     VecInput = IC.Builder.CreateBitCast(VecInput, VecType, "bc");
484   }
485 
486   unsigned Elt = ShiftAmount / DestWidth;
487   if (IC.getDataLayout().isBigEndian())
488     Elt = NumVecElts - 1 - Elt;
489 
490   return ExtractElementInst::Create(VecInput, IC.Builder.getInt32(Elt));
491 }
492 
493 /// Rotate left/right may occur in a wider type than necessary because of type
494 /// promotion rules. Try to narrow the inputs and convert to funnel shift.
495 Instruction *InstCombiner::narrowRotate(TruncInst &Trunc) {
496   assert((isa<VectorType>(Trunc.getSrcTy()) ||
497           shouldChangeType(Trunc.getSrcTy(), Trunc.getType())) &&
498          "Don't narrow to an illegal scalar type");
499 
500   // Bail out on strange types. It is possible to handle some of these patterns
501   // even with non-power-of-2 sizes, but it is not a likely scenario.
502   Type *DestTy = Trunc.getType();
503   unsigned NarrowWidth = DestTy->getScalarSizeInBits();
504   if (!isPowerOf2_32(NarrowWidth))
505     return nullptr;
506 
507   // First, find an or'd pair of opposite shifts with the same shifted operand:
508   // trunc (or (lshr ShVal, ShAmt0), (shl ShVal, ShAmt1))
509   Value *Or0, *Or1;
510   if (!match(Trunc.getOperand(0), m_OneUse(m_Or(m_Value(Or0), m_Value(Or1)))))
511     return nullptr;
512 
513   Value *ShVal, *ShAmt0, *ShAmt1;
514   if (!match(Or0, m_OneUse(m_LogicalShift(m_Value(ShVal), m_Value(ShAmt0)))) ||
515       !match(Or1, m_OneUse(m_LogicalShift(m_Specific(ShVal), m_Value(ShAmt1)))))
516     return nullptr;
517 
518   auto ShiftOpcode0 = cast<BinaryOperator>(Or0)->getOpcode();
519   auto ShiftOpcode1 = cast<BinaryOperator>(Or1)->getOpcode();
520   if (ShiftOpcode0 == ShiftOpcode1)
521     return nullptr;
522 
523   // Match the shift amount operands for a rotate pattern. This always matches
524   // a subtraction on the R operand.
525   auto matchShiftAmount = [](Value *L, Value *R, unsigned Width) -> Value * {
526     // The shift amounts may add up to the narrow bit width:
527     // (shl ShVal, L) | (lshr ShVal, Width - L)
528     if (match(R, m_OneUse(m_Sub(m_SpecificInt(Width), m_Specific(L)))))
529       return L;
530 
531     // The shift amount may be masked with negation:
532     // (shl ShVal, (X & (Width - 1))) | (lshr ShVal, ((-X) & (Width - 1)))
533     Value *X;
534     unsigned Mask = Width - 1;
535     if (match(L, m_And(m_Value(X), m_SpecificInt(Mask))) &&
536         match(R, m_And(m_Neg(m_Specific(X)), m_SpecificInt(Mask))))
537       return X;
538 
539     // Same as above, but the shift amount may be extended after masking:
540     if (match(L, m_ZExt(m_And(m_Value(X), m_SpecificInt(Mask)))) &&
541         match(R, m_ZExt(m_And(m_Neg(m_Specific(X)), m_SpecificInt(Mask)))))
542       return X;
543 
544     return nullptr;
545   };
546 
547   Value *ShAmt = matchShiftAmount(ShAmt0, ShAmt1, NarrowWidth);
548   bool SubIsOnLHS = false;
549   if (!ShAmt) {
550     ShAmt = matchShiftAmount(ShAmt1, ShAmt0, NarrowWidth);
551     SubIsOnLHS = true;
552   }
553   if (!ShAmt)
554     return nullptr;
555 
556   // The shifted value must have high zeros in the wide type. Typically, this
557   // will be a zext, but it could also be the result of an 'and' or 'shift'.
558   unsigned WideWidth = Trunc.getSrcTy()->getScalarSizeInBits();
559   APInt HiBitMask = APInt::getHighBitsSet(WideWidth, WideWidth - NarrowWidth);
560   if (!MaskedValueIsZero(ShVal, HiBitMask, 0, &Trunc))
561     return nullptr;
562 
563   // We have an unnecessarily wide rotate!
564   // trunc (or (lshr ShVal, ShAmt), (shl ShVal, BitWidth - ShAmt))
565   // Narrow the inputs and convert to funnel shift intrinsic:
566   // llvm.fshl.i8(trunc(ShVal), trunc(ShVal), trunc(ShAmt))
567   Value *NarrowShAmt = Builder.CreateTrunc(ShAmt, DestTy);
568   Value *X = Builder.CreateTrunc(ShVal, DestTy);
569   bool IsFshl = (!SubIsOnLHS && ShiftOpcode0 == BinaryOperator::Shl) ||
570                 (SubIsOnLHS && ShiftOpcode1 == BinaryOperator::Shl);
571   Intrinsic::ID IID = IsFshl ? Intrinsic::fshl : Intrinsic::fshr;
572   Function *F = Intrinsic::getDeclaration(Trunc.getModule(), IID, DestTy);
573   return IntrinsicInst::Create(F, { X, X, NarrowShAmt });
574 }
575 
576 /// Try to narrow the width of math or bitwise logic instructions by pulling a
577 /// truncate ahead of binary operators.
578 /// TODO: Transforms for truncated shifts should be moved into here.
579 Instruction *InstCombiner::narrowBinOp(TruncInst &Trunc) {
580   Type *SrcTy = Trunc.getSrcTy();
581   Type *DestTy = Trunc.getType();
582   if (!isa<VectorType>(SrcTy) && !shouldChangeType(SrcTy, DestTy))
583     return nullptr;
584 
585   BinaryOperator *BinOp;
586   if (!match(Trunc.getOperand(0), m_OneUse(m_BinOp(BinOp))))
587     return nullptr;
588 
589   Value *BinOp0 = BinOp->getOperand(0);
590   Value *BinOp1 = BinOp->getOperand(1);
591   switch (BinOp->getOpcode()) {
592   case Instruction::And:
593   case Instruction::Or:
594   case Instruction::Xor:
595   case Instruction::Add:
596   case Instruction::Sub:
597   case Instruction::Mul: {
598     Constant *C;
599     if (match(BinOp0, m_Constant(C))) {
600       // trunc (binop C, X) --> binop (trunc C', X)
601       Constant *NarrowC = ConstantExpr::getTrunc(C, DestTy);
602       Value *TruncX = Builder.CreateTrunc(BinOp1, DestTy);
603       return BinaryOperator::Create(BinOp->getOpcode(), NarrowC, TruncX);
604     }
605     if (match(BinOp1, m_Constant(C))) {
606       // trunc (binop X, C) --> binop (trunc X, C')
607       Constant *NarrowC = ConstantExpr::getTrunc(C, DestTy);
608       Value *TruncX = Builder.CreateTrunc(BinOp0, DestTy);
609       return BinaryOperator::Create(BinOp->getOpcode(), TruncX, NarrowC);
610     }
611     Value *X;
612     if (match(BinOp0, m_ZExtOrSExt(m_Value(X))) && X->getType() == DestTy) {
613       // trunc (binop (ext X), Y) --> binop X, (trunc Y)
614       Value *NarrowOp1 = Builder.CreateTrunc(BinOp1, DestTy);
615       return BinaryOperator::Create(BinOp->getOpcode(), X, NarrowOp1);
616     }
617     if (match(BinOp1, m_ZExtOrSExt(m_Value(X))) && X->getType() == DestTy) {
618       // trunc (binop Y, (ext X)) --> binop (trunc Y), X
619       Value *NarrowOp0 = Builder.CreateTrunc(BinOp0, DestTy);
620       return BinaryOperator::Create(BinOp->getOpcode(), NarrowOp0, X);
621     }
622     break;
623   }
624 
625   default: break;
626   }
627 
628   if (Instruction *NarrowOr = narrowRotate(Trunc))
629     return NarrowOr;
630 
631   return nullptr;
632 }
633 
634 /// Try to narrow the width of a splat shuffle. This could be generalized to any
635 /// shuffle with a constant operand, but we limit the transform to avoid
636 /// creating a shuffle type that targets may not be able to lower effectively.
637 static Instruction *shrinkSplatShuffle(TruncInst &Trunc,
638                                        InstCombiner::BuilderTy &Builder) {
639   auto *Shuf = dyn_cast<ShuffleVectorInst>(Trunc.getOperand(0));
640   if (Shuf && Shuf->hasOneUse() && isa<UndefValue>(Shuf->getOperand(1)) &&
641       Shuf->getMask()->getSplatValue() &&
642       Shuf->getType() == Shuf->getOperand(0)->getType()) {
643     // trunc (shuf X, Undef, SplatMask) --> shuf (trunc X), Undef, SplatMask
644     Constant *NarrowUndef = UndefValue::get(Trunc.getType());
645     Value *NarrowOp = Builder.CreateTrunc(Shuf->getOperand(0), Trunc.getType());
646     return new ShuffleVectorInst(NarrowOp, NarrowUndef, Shuf->getMask());
647   }
648 
649   return nullptr;
650 }
651 
652 /// Try to narrow the width of an insert element. This could be generalized for
653 /// any vector constant, but we limit the transform to insertion into undef to
654 /// avoid potential backend problems from unsupported insertion widths. This
655 /// could also be extended to handle the case of inserting a scalar constant
656 /// into a vector variable.
657 static Instruction *shrinkInsertElt(CastInst &Trunc,
658                                     InstCombiner::BuilderTy &Builder) {
659   Instruction::CastOps Opcode = Trunc.getOpcode();
660   assert((Opcode == Instruction::Trunc || Opcode == Instruction::FPTrunc) &&
661          "Unexpected instruction for shrinking");
662 
663   auto *InsElt = dyn_cast<InsertElementInst>(Trunc.getOperand(0));
664   if (!InsElt || !InsElt->hasOneUse())
665     return nullptr;
666 
667   Type *DestTy = Trunc.getType();
668   Type *DestScalarTy = DestTy->getScalarType();
669   Value *VecOp = InsElt->getOperand(0);
670   Value *ScalarOp = InsElt->getOperand(1);
671   Value *Index = InsElt->getOperand(2);
672 
673   if (isa<UndefValue>(VecOp)) {
674     // trunc   (inselt undef, X, Index) --> inselt undef,   (trunc X), Index
675     // fptrunc (inselt undef, X, Index) --> inselt undef, (fptrunc X), Index
676     UndefValue *NarrowUndef = UndefValue::get(DestTy);
677     Value *NarrowOp = Builder.CreateCast(Opcode, ScalarOp, DestScalarTy);
678     return InsertElementInst::Create(NarrowUndef, NarrowOp, Index);
679   }
680 
681   return nullptr;
682 }
683 
684 Instruction *InstCombiner::visitTrunc(TruncInst &CI) {
685   if (Instruction *Result = commonCastTransforms(CI))
686     return Result;
687 
688   Value *Src = CI.getOperand(0);
689   Type *DestTy = CI.getType(), *SrcTy = Src->getType();
690 
691   // Attempt to truncate the entire input expression tree to the destination
692   // type.   Only do this if the dest type is a simple type, don't convert the
693   // expression tree to something weird like i93 unless the source is also
694   // strange.
695   if ((DestTy->isVectorTy() || shouldChangeType(SrcTy, DestTy)) &&
696       canEvaluateTruncated(Src, DestTy, *this, &CI)) {
697 
698     // If this cast is a truncate, evaluting in a different type always
699     // eliminates the cast, so it is always a win.
700     LLVM_DEBUG(
701         dbgs() << "ICE: EvaluateInDifferentType converting expression type"
702                   " to avoid cast: "
703                << CI << '\n');
704     Value *Res = EvaluateInDifferentType(Src, DestTy, false);
705     assert(Res->getType() == DestTy);
706     return replaceInstUsesWith(CI, Res);
707   }
708 
709   // Test if the trunc is the user of a select which is part of a
710   // minimum or maximum operation. If so, don't do any more simplification.
711   // Even simplifying demanded bits can break the canonical form of a
712   // min/max.
713   Value *LHS, *RHS;
714   if (SelectInst *SI = dyn_cast<SelectInst>(CI.getOperand(0)))
715     if (matchSelectPattern(SI, LHS, RHS).Flavor != SPF_UNKNOWN)
716       return nullptr;
717 
718   // See if we can simplify any instructions used by the input whose sole
719   // purpose is to compute bits we don't care about.
720   if (SimplifyDemandedInstructionBits(CI))
721     return &CI;
722 
723   if (DestTy->getScalarSizeInBits() == 1) {
724     Value *Zero = Constant::getNullValue(Src->getType());
725     if (DestTy->isIntegerTy()) {
726       // Canonicalize trunc x to i1 -> icmp ne (and x, 1), 0 (scalar only).
727       // TODO: We canonicalize to more instructions here because we are probably
728       // lacking equivalent analysis for trunc relative to icmp. There may also
729       // be codegen concerns. If those trunc limitations were removed, we could
730       // remove this transform.
731       Value *And = Builder.CreateAnd(Src, ConstantInt::get(SrcTy, 1));
732       return new ICmpInst(ICmpInst::ICMP_NE, And, Zero);
733     }
734 
735     // For vectors, we do not canonicalize all truncs to icmp, so optimize
736     // patterns that would be covered within visitICmpInst.
737     Value *X;
738     const APInt *C;
739     if (match(Src, m_OneUse(m_LShr(m_Value(X), m_APInt(C))))) {
740       // trunc (lshr X, C) to i1 --> icmp ne (and X, C'), 0
741       APInt MaskC = APInt(SrcTy->getScalarSizeInBits(), 1).shl(*C);
742       Value *And = Builder.CreateAnd(X, ConstantInt::get(SrcTy, MaskC));
743       return new ICmpInst(ICmpInst::ICMP_NE, And, Zero);
744     }
745     if (match(Src, m_OneUse(m_c_Or(m_LShr(m_Value(X), m_APInt(C)),
746                                    m_Deferred(X))))) {
747       // trunc (or (lshr X, C), X) to i1 --> icmp ne (and X, C'), 0
748       APInt MaskC = APInt(SrcTy->getScalarSizeInBits(), 1).shl(*C) | 1;
749       Value *And = Builder.CreateAnd(X, ConstantInt::get(SrcTy, MaskC));
750       return new ICmpInst(ICmpInst::ICMP_NE, And, Zero);
751     }
752   }
753 
754   // FIXME: Maybe combine the next two transforms to handle the no cast case
755   // more efficiently. Support vector types. Cleanup code by using m_OneUse.
756 
757   // Transform trunc(lshr (zext A), Cst) to eliminate one type conversion.
758   Value *A = nullptr; ConstantInt *Cst = nullptr;
759   if (Src->hasOneUse() &&
760       match(Src, m_LShr(m_ZExt(m_Value(A)), m_ConstantInt(Cst)))) {
761     // We have three types to worry about here, the type of A, the source of
762     // the truncate (MidSize), and the destination of the truncate. We know that
763     // ASize < MidSize   and MidSize > ResultSize, but don't know the relation
764     // between ASize and ResultSize.
765     unsigned ASize = A->getType()->getPrimitiveSizeInBits();
766 
767     // If the shift amount is larger than the size of A, then the result is
768     // known to be zero because all the input bits got shifted out.
769     if (Cst->getZExtValue() >= ASize)
770       return replaceInstUsesWith(CI, Constant::getNullValue(DestTy));
771 
772     // Since we're doing an lshr and a zero extend, and know that the shift
773     // amount is smaller than ASize, it is always safe to do the shift in A's
774     // type, then zero extend or truncate to the result.
775     Value *Shift = Builder.CreateLShr(A, Cst->getZExtValue());
776     Shift->takeName(Src);
777     return CastInst::CreateIntegerCast(Shift, DestTy, false);
778   }
779 
780   // FIXME: We should canonicalize to zext/trunc and remove this transform.
781   // Transform trunc(lshr (sext A), Cst) to ashr A, Cst to eliminate type
782   // conversion.
783   // It works because bits coming from sign extension have the same value as
784   // the sign bit of the original value; performing ashr instead of lshr
785   // generates bits of the same value as the sign bit.
786   if (Src->hasOneUse() &&
787       match(Src, m_LShr(m_SExt(m_Value(A)), m_ConstantInt(Cst)))) {
788     Value *SExt = cast<Instruction>(Src)->getOperand(0);
789     const unsigned SExtSize = SExt->getType()->getPrimitiveSizeInBits();
790     const unsigned ASize = A->getType()->getPrimitiveSizeInBits();
791     const unsigned CISize = CI.getType()->getPrimitiveSizeInBits();
792     const unsigned MaxAmt = SExtSize - std::max(CISize, ASize);
793     unsigned ShiftAmt = Cst->getZExtValue();
794 
795     // This optimization can be only performed when zero bits generated by
796     // the original lshr aren't pulled into the value after truncation, so we
797     // can only shift by values no larger than the number of extension bits.
798     // FIXME: Instead of bailing when the shift is too large, use and to clear
799     // the extra bits.
800     if (ShiftAmt <= MaxAmt) {
801       if (CISize == ASize)
802         return BinaryOperator::CreateAShr(A, ConstantInt::get(CI.getType(),
803                                           std::min(ShiftAmt, ASize - 1)));
804       if (SExt->hasOneUse()) {
805         Value *Shift = Builder.CreateAShr(A, std::min(ShiftAmt, ASize - 1));
806         Shift->takeName(Src);
807         return CastInst::CreateIntegerCast(Shift, CI.getType(), true);
808       }
809     }
810   }
811 
812   if (Instruction *I = narrowBinOp(CI))
813     return I;
814 
815   if (Instruction *I = shrinkSplatShuffle(CI, Builder))
816     return I;
817 
818   if (Instruction *I = shrinkInsertElt(CI, Builder))
819     return I;
820 
821   if (Src->hasOneUse() && isa<IntegerType>(SrcTy) &&
822       shouldChangeType(SrcTy, DestTy)) {
823     // Transform "trunc (shl X, cst)" -> "shl (trunc X), cst" so long as the
824     // dest type is native and cst < dest size.
825     if (match(Src, m_Shl(m_Value(A), m_ConstantInt(Cst))) &&
826         !match(A, m_Shr(m_Value(), m_Constant()))) {
827       // Skip shifts of shift by constants. It undoes a combine in
828       // FoldShiftByConstant and is the extend in reg pattern.
829       const unsigned DestSize = DestTy->getScalarSizeInBits();
830       if (Cst->getValue().ult(DestSize)) {
831         Value *NewTrunc = Builder.CreateTrunc(A, DestTy, A->getName() + ".tr");
832 
833         return BinaryOperator::Create(
834           Instruction::Shl, NewTrunc,
835           ConstantInt::get(DestTy, Cst->getValue().trunc(DestSize)));
836       }
837     }
838   }
839 
840   if (Instruction *I = foldVecTruncToExtElt(CI, *this))
841     return I;
842 
843   return nullptr;
844 }
845 
846 Instruction *InstCombiner::transformZExtICmp(ICmpInst *ICI, ZExtInst &CI,
847                                              bool DoTransform) {
848   // If we are just checking for a icmp eq of a single bit and zext'ing it
849   // to an integer, then shift the bit to the appropriate place and then
850   // cast to integer to avoid the comparison.
851   const APInt *Op1CV;
852   if (match(ICI->getOperand(1), m_APInt(Op1CV))) {
853 
854     // zext (x <s  0) to i32 --> x>>u31      true if signbit set.
855     // zext (x >s -1) to i32 --> (x>>u31)^1  true if signbit clear.
856     if ((ICI->getPredicate() == ICmpInst::ICMP_SLT && Op1CV->isNullValue()) ||
857         (ICI->getPredicate() == ICmpInst::ICMP_SGT && Op1CV->isAllOnesValue())) {
858       if (!DoTransform) return ICI;
859 
860       Value *In = ICI->getOperand(0);
861       Value *Sh = ConstantInt::get(In->getType(),
862                                    In->getType()->getScalarSizeInBits() - 1);
863       In = Builder.CreateLShr(In, Sh, In->getName() + ".lobit");
864       if (In->getType() != CI.getType())
865         In = Builder.CreateIntCast(In, CI.getType(), false /*ZExt*/);
866 
867       if (ICI->getPredicate() == ICmpInst::ICMP_SGT) {
868         Constant *One = ConstantInt::get(In->getType(), 1);
869         In = Builder.CreateXor(In, One, In->getName() + ".not");
870       }
871 
872       return replaceInstUsesWith(CI, In);
873     }
874 
875     // zext (X == 0) to i32 --> X^1      iff X has only the low bit set.
876     // zext (X == 0) to i32 --> (X>>1)^1 iff X has only the 2nd bit set.
877     // zext (X == 1) to i32 --> X        iff X has only the low bit set.
878     // zext (X == 2) to i32 --> X>>1     iff X has only the 2nd bit set.
879     // zext (X != 0) to i32 --> X        iff X has only the low bit set.
880     // zext (X != 0) to i32 --> X>>1     iff X has only the 2nd bit set.
881     // zext (X != 1) to i32 --> X^1      iff X has only the low bit set.
882     // zext (X != 2) to i32 --> (X>>1)^1 iff X has only the 2nd bit set.
883     if ((Op1CV->isNullValue() || Op1CV->isPowerOf2()) &&
884         // This only works for EQ and NE
885         ICI->isEquality()) {
886       // If Op1C some other power of two, convert:
887       KnownBits Known = computeKnownBits(ICI->getOperand(0), 0, &CI);
888 
889       APInt KnownZeroMask(~Known.Zero);
890       if (KnownZeroMask.isPowerOf2()) { // Exactly 1 possible 1?
891         if (!DoTransform) return ICI;
892 
893         bool isNE = ICI->getPredicate() == ICmpInst::ICMP_NE;
894         if (!Op1CV->isNullValue() && (*Op1CV != KnownZeroMask)) {
895           // (X&4) == 2 --> false
896           // (X&4) != 2 --> true
897           Constant *Res = ConstantInt::get(CI.getType(), isNE);
898           return replaceInstUsesWith(CI, Res);
899         }
900 
901         uint32_t ShAmt = KnownZeroMask.logBase2();
902         Value *In = ICI->getOperand(0);
903         if (ShAmt) {
904           // Perform a logical shr by shiftamt.
905           // Insert the shift to put the result in the low bit.
906           In = Builder.CreateLShr(In, ConstantInt::get(In->getType(), ShAmt),
907                                   In->getName() + ".lobit");
908         }
909 
910         if (!Op1CV->isNullValue() == isNE) { // Toggle the low bit.
911           Constant *One = ConstantInt::get(In->getType(), 1);
912           In = Builder.CreateXor(In, One);
913         }
914 
915         if (CI.getType() == In->getType())
916           return replaceInstUsesWith(CI, In);
917 
918         Value *IntCast = Builder.CreateIntCast(In, CI.getType(), false);
919         return replaceInstUsesWith(CI, IntCast);
920       }
921     }
922   }
923 
924   // icmp ne A, B is equal to xor A, B when A and B only really have one bit.
925   // It is also profitable to transform icmp eq into not(xor(A, B)) because that
926   // may lead to additional simplifications.
927   if (ICI->isEquality() && CI.getType() == ICI->getOperand(0)->getType()) {
928     if (IntegerType *ITy = dyn_cast<IntegerType>(CI.getType())) {
929       Value *LHS = ICI->getOperand(0);
930       Value *RHS = ICI->getOperand(1);
931 
932       KnownBits KnownLHS = computeKnownBits(LHS, 0, &CI);
933       KnownBits KnownRHS = computeKnownBits(RHS, 0, &CI);
934 
935       if (KnownLHS.Zero == KnownRHS.Zero && KnownLHS.One == KnownRHS.One) {
936         APInt KnownBits = KnownLHS.Zero | KnownLHS.One;
937         APInt UnknownBit = ~KnownBits;
938         if (UnknownBit.countPopulation() == 1) {
939           if (!DoTransform) return ICI;
940 
941           Value *Result = Builder.CreateXor(LHS, RHS);
942 
943           // Mask off any bits that are set and won't be shifted away.
944           if (KnownLHS.One.uge(UnknownBit))
945             Result = Builder.CreateAnd(Result,
946                                         ConstantInt::get(ITy, UnknownBit));
947 
948           // Shift the bit we're testing down to the lsb.
949           Result = Builder.CreateLShr(
950                Result, ConstantInt::get(ITy, UnknownBit.countTrailingZeros()));
951 
952           if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
953             Result = Builder.CreateXor(Result, ConstantInt::get(ITy, 1));
954           Result->takeName(ICI);
955           return replaceInstUsesWith(CI, Result);
956         }
957       }
958     }
959   }
960 
961   return nullptr;
962 }
963 
964 /// Determine if the specified value can be computed in the specified wider type
965 /// and produce the same low bits. If not, return false.
966 ///
967 /// If this function returns true, it can also return a non-zero number of bits
968 /// (in BitsToClear) which indicates that the value it computes is correct for
969 /// the zero extend, but that the additional BitsToClear bits need to be zero'd
970 /// out.  For example, to promote something like:
971 ///
972 ///   %B = trunc i64 %A to i32
973 ///   %C = lshr i32 %B, 8
974 ///   %E = zext i32 %C to i64
975 ///
976 /// CanEvaluateZExtd for the 'lshr' will return true, and BitsToClear will be
977 /// set to 8 to indicate that the promoted value needs to have bits 24-31
978 /// cleared in addition to bits 32-63.  Since an 'and' will be generated to
979 /// clear the top bits anyway, doing this has no extra cost.
980 ///
981 /// This function works on both vectors and scalars.
982 static bool canEvaluateZExtd(Value *V, Type *Ty, unsigned &BitsToClear,
983                              InstCombiner &IC, Instruction *CxtI) {
984   BitsToClear = 0;
985   if (canAlwaysEvaluateInType(V, Ty))
986     return true;
987   if (canNotEvaluateInType(V, Ty))
988     return false;
989 
990   auto *I = cast<Instruction>(V);
991   unsigned Tmp;
992   switch (I->getOpcode()) {
993   case Instruction::ZExt:  // zext(zext(x)) -> zext(x).
994   case Instruction::SExt:  // zext(sext(x)) -> sext(x).
995   case Instruction::Trunc: // zext(trunc(x)) -> trunc(x) or zext(x)
996     return true;
997   case Instruction::And:
998   case Instruction::Or:
999   case Instruction::Xor:
1000   case Instruction::Add:
1001   case Instruction::Sub:
1002   case Instruction::Mul:
1003     if (!canEvaluateZExtd(I->getOperand(0), Ty, BitsToClear, IC, CxtI) ||
1004         !canEvaluateZExtd(I->getOperand(1), Ty, Tmp, IC, CxtI))
1005       return false;
1006     // These can all be promoted if neither operand has 'bits to clear'.
1007     if (BitsToClear == 0 && Tmp == 0)
1008       return true;
1009 
1010     // If the operation is an AND/OR/XOR and the bits to clear are zero in the
1011     // other side, BitsToClear is ok.
1012     if (Tmp == 0 && I->isBitwiseLogicOp()) {
1013       // We use MaskedValueIsZero here for generality, but the case we care
1014       // about the most is constant RHS.
1015       unsigned VSize = V->getType()->getScalarSizeInBits();
1016       if (IC.MaskedValueIsZero(I->getOperand(1),
1017                                APInt::getHighBitsSet(VSize, BitsToClear),
1018                                0, CxtI)) {
1019         // If this is an And instruction and all of the BitsToClear are
1020         // known to be zero we can reset BitsToClear.
1021         if (I->getOpcode() == Instruction::And)
1022           BitsToClear = 0;
1023         return true;
1024       }
1025     }
1026 
1027     // Otherwise, we don't know how to analyze this BitsToClear case yet.
1028     return false;
1029 
1030   case Instruction::Shl: {
1031     // We can promote shl(x, cst) if we can promote x.  Since shl overwrites the
1032     // upper bits we can reduce BitsToClear by the shift amount.
1033     const APInt *Amt;
1034     if (match(I->getOperand(1), m_APInt(Amt))) {
1035       if (!canEvaluateZExtd(I->getOperand(0), Ty, BitsToClear, IC, CxtI))
1036         return false;
1037       uint64_t ShiftAmt = Amt->getZExtValue();
1038       BitsToClear = ShiftAmt < BitsToClear ? BitsToClear - ShiftAmt : 0;
1039       return true;
1040     }
1041     return false;
1042   }
1043   case Instruction::LShr: {
1044     // We can promote lshr(x, cst) if we can promote x.  This requires the
1045     // ultimate 'and' to clear out the high zero bits we're clearing out though.
1046     const APInt *Amt;
1047     if (match(I->getOperand(1), m_APInt(Amt))) {
1048       if (!canEvaluateZExtd(I->getOperand(0), Ty, BitsToClear, IC, CxtI))
1049         return false;
1050       BitsToClear += Amt->getZExtValue();
1051       if (BitsToClear > V->getType()->getScalarSizeInBits())
1052         BitsToClear = V->getType()->getScalarSizeInBits();
1053       return true;
1054     }
1055     // Cannot promote variable LSHR.
1056     return false;
1057   }
1058   case Instruction::Select:
1059     if (!canEvaluateZExtd(I->getOperand(1), Ty, Tmp, IC, CxtI) ||
1060         !canEvaluateZExtd(I->getOperand(2), Ty, BitsToClear, IC, CxtI) ||
1061         // TODO: If important, we could handle the case when the BitsToClear are
1062         // known zero in the disagreeing side.
1063         Tmp != BitsToClear)
1064       return false;
1065     return true;
1066 
1067   case Instruction::PHI: {
1068     // We can change a phi if we can change all operands.  Note that we never
1069     // get into trouble with cyclic PHIs here because we only consider
1070     // instructions with a single use.
1071     PHINode *PN = cast<PHINode>(I);
1072     if (!canEvaluateZExtd(PN->getIncomingValue(0), Ty, BitsToClear, IC, CxtI))
1073       return false;
1074     for (unsigned i = 1, e = PN->getNumIncomingValues(); i != e; ++i)
1075       if (!canEvaluateZExtd(PN->getIncomingValue(i), Ty, Tmp, IC, CxtI) ||
1076           // TODO: If important, we could handle the case when the BitsToClear
1077           // are known zero in the disagreeing input.
1078           Tmp != BitsToClear)
1079         return false;
1080     return true;
1081   }
1082   default:
1083     // TODO: Can handle more cases here.
1084     return false;
1085   }
1086 }
1087 
1088 Instruction *InstCombiner::visitZExt(ZExtInst &CI) {
1089   // If this zero extend is only used by a truncate, let the truncate be
1090   // eliminated before we try to optimize this zext.
1091   if (CI.hasOneUse() && isa<TruncInst>(CI.user_back()))
1092     return nullptr;
1093 
1094   // If one of the common conversion will work, do it.
1095   if (Instruction *Result = commonCastTransforms(CI))
1096     return Result;
1097 
1098   Value *Src = CI.getOperand(0);
1099   Type *SrcTy = Src->getType(), *DestTy = CI.getType();
1100 
1101   // Try to extend the entire expression tree to the wide destination type.
1102   unsigned BitsToClear;
1103   if (shouldChangeType(SrcTy, DestTy) &&
1104       canEvaluateZExtd(Src, DestTy, BitsToClear, *this, &CI)) {
1105     assert(BitsToClear <= SrcTy->getScalarSizeInBits() &&
1106            "Can't clear more bits than in SrcTy");
1107 
1108     // Okay, we can transform this!  Insert the new expression now.
1109     LLVM_DEBUG(
1110         dbgs() << "ICE: EvaluateInDifferentType converting expression type"
1111                   " to avoid zero extend: "
1112                << CI << '\n');
1113     Value *Res = EvaluateInDifferentType(Src, DestTy, false);
1114     assert(Res->getType() == DestTy);
1115 
1116     // Preserve debug values referring to Src if the zext is its last use.
1117     if (auto *SrcOp = dyn_cast<Instruction>(Src))
1118       if (SrcOp->hasOneUse())
1119         replaceAllDbgUsesWith(*SrcOp, *Res, CI, DT);
1120 
1121     uint32_t SrcBitsKept = SrcTy->getScalarSizeInBits()-BitsToClear;
1122     uint32_t DestBitSize = DestTy->getScalarSizeInBits();
1123 
1124     // If the high bits are already filled with zeros, just replace this
1125     // cast with the result.
1126     if (MaskedValueIsZero(Res,
1127                           APInt::getHighBitsSet(DestBitSize,
1128                                                 DestBitSize-SrcBitsKept),
1129                              0, &CI))
1130       return replaceInstUsesWith(CI, Res);
1131 
1132     // We need to emit an AND to clear the high bits.
1133     Constant *C = ConstantInt::get(Res->getType(),
1134                                APInt::getLowBitsSet(DestBitSize, SrcBitsKept));
1135     return BinaryOperator::CreateAnd(Res, C);
1136   }
1137 
1138   // If this is a TRUNC followed by a ZEXT then we are dealing with integral
1139   // types and if the sizes are just right we can convert this into a logical
1140   // 'and' which will be much cheaper than the pair of casts.
1141   if (TruncInst *CSrc = dyn_cast<TruncInst>(Src)) {   // A->B->C cast
1142     // TODO: Subsume this into EvaluateInDifferentType.
1143 
1144     // Get the sizes of the types involved.  We know that the intermediate type
1145     // will be smaller than A or C, but don't know the relation between A and C.
1146     Value *A = CSrc->getOperand(0);
1147     unsigned SrcSize = A->getType()->getScalarSizeInBits();
1148     unsigned MidSize = CSrc->getType()->getScalarSizeInBits();
1149     unsigned DstSize = CI.getType()->getScalarSizeInBits();
1150     // If we're actually extending zero bits, then if
1151     // SrcSize <  DstSize: zext(a & mask)
1152     // SrcSize == DstSize: a & mask
1153     // SrcSize  > DstSize: trunc(a) & mask
1154     if (SrcSize < DstSize) {
1155       APInt AndValue(APInt::getLowBitsSet(SrcSize, MidSize));
1156       Constant *AndConst = ConstantInt::get(A->getType(), AndValue);
1157       Value *And = Builder.CreateAnd(A, AndConst, CSrc->getName() + ".mask");
1158       return new ZExtInst(And, CI.getType());
1159     }
1160 
1161     if (SrcSize == DstSize) {
1162       APInt AndValue(APInt::getLowBitsSet(SrcSize, MidSize));
1163       return BinaryOperator::CreateAnd(A, ConstantInt::get(A->getType(),
1164                                                            AndValue));
1165     }
1166     if (SrcSize > DstSize) {
1167       Value *Trunc = Builder.CreateTrunc(A, CI.getType());
1168       APInt AndValue(APInt::getLowBitsSet(DstSize, MidSize));
1169       return BinaryOperator::CreateAnd(Trunc,
1170                                        ConstantInt::get(Trunc->getType(),
1171                                                         AndValue));
1172     }
1173   }
1174 
1175   if (ICmpInst *ICI = dyn_cast<ICmpInst>(Src))
1176     return transformZExtICmp(ICI, CI);
1177 
1178   BinaryOperator *SrcI = dyn_cast<BinaryOperator>(Src);
1179   if (SrcI && SrcI->getOpcode() == Instruction::Or) {
1180     // zext (or icmp, icmp) -> or (zext icmp), (zext icmp) if at least one
1181     // of the (zext icmp) can be eliminated. If so, immediately perform the
1182     // according elimination.
1183     ICmpInst *LHS = dyn_cast<ICmpInst>(SrcI->getOperand(0));
1184     ICmpInst *RHS = dyn_cast<ICmpInst>(SrcI->getOperand(1));
1185     if (LHS && RHS && LHS->hasOneUse() && RHS->hasOneUse() &&
1186         (transformZExtICmp(LHS, CI, false) ||
1187          transformZExtICmp(RHS, CI, false))) {
1188       // zext (or icmp, icmp) -> or (zext icmp), (zext icmp)
1189       Value *LCast = Builder.CreateZExt(LHS, CI.getType(), LHS->getName());
1190       Value *RCast = Builder.CreateZExt(RHS, CI.getType(), RHS->getName());
1191       BinaryOperator *Or = BinaryOperator::Create(Instruction::Or, LCast, RCast);
1192 
1193       // Perform the elimination.
1194       if (auto *LZExt = dyn_cast<ZExtInst>(LCast))
1195         transformZExtICmp(LHS, *LZExt);
1196       if (auto *RZExt = dyn_cast<ZExtInst>(RCast))
1197         transformZExtICmp(RHS, *RZExt);
1198 
1199       return Or;
1200     }
1201   }
1202 
1203   // zext(trunc(X) & C) -> (X & zext(C)).
1204   Constant *C;
1205   Value *X;
1206   if (SrcI &&
1207       match(SrcI, m_OneUse(m_And(m_Trunc(m_Value(X)), m_Constant(C)))) &&
1208       X->getType() == CI.getType())
1209     return BinaryOperator::CreateAnd(X, ConstantExpr::getZExt(C, CI.getType()));
1210 
1211   // zext((trunc(X) & C) ^ C) -> ((X & zext(C)) ^ zext(C)).
1212   Value *And;
1213   if (SrcI && match(SrcI, m_OneUse(m_Xor(m_Value(And), m_Constant(C)))) &&
1214       match(And, m_OneUse(m_And(m_Trunc(m_Value(X)), m_Specific(C)))) &&
1215       X->getType() == CI.getType()) {
1216     Constant *ZC = ConstantExpr::getZExt(C, CI.getType());
1217     return BinaryOperator::CreateXor(Builder.CreateAnd(X, ZC), ZC);
1218   }
1219 
1220   return nullptr;
1221 }
1222 
1223 /// Transform (sext icmp) to bitwise / integer operations to eliminate the icmp.
1224 Instruction *InstCombiner::transformSExtICmp(ICmpInst *ICI, Instruction &CI) {
1225   Value *Op0 = ICI->getOperand(0), *Op1 = ICI->getOperand(1);
1226   ICmpInst::Predicate Pred = ICI->getPredicate();
1227 
1228   // Don't bother if Op1 isn't of vector or integer type.
1229   if (!Op1->getType()->isIntOrIntVectorTy())
1230     return nullptr;
1231 
1232   if ((Pred == ICmpInst::ICMP_SLT && match(Op1, m_ZeroInt())) ||
1233       (Pred == ICmpInst::ICMP_SGT && match(Op1, m_AllOnes()))) {
1234     // (x <s  0) ? -1 : 0 -> ashr x, 31        -> all ones if negative
1235     // (x >s -1) ? -1 : 0 -> not (ashr x, 31)  -> all ones if positive
1236     Value *Sh = ConstantInt::get(Op0->getType(),
1237                                  Op0->getType()->getScalarSizeInBits() - 1);
1238     Value *In = Builder.CreateAShr(Op0, Sh, Op0->getName() + ".lobit");
1239     if (In->getType() != CI.getType())
1240       In = Builder.CreateIntCast(In, CI.getType(), true /*SExt*/);
1241 
1242     if (Pred == ICmpInst::ICMP_SGT)
1243       In = Builder.CreateNot(In, In->getName() + ".not");
1244     return replaceInstUsesWith(CI, In);
1245   }
1246 
1247   if (ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) {
1248     // If we know that only one bit of the LHS of the icmp can be set and we
1249     // have an equality comparison with zero or a power of 2, we can transform
1250     // the icmp and sext into bitwise/integer operations.
1251     if (ICI->hasOneUse() &&
1252         ICI->isEquality() && (Op1C->isZero() || Op1C->getValue().isPowerOf2())){
1253       KnownBits Known = computeKnownBits(Op0, 0, &CI);
1254 
1255       APInt KnownZeroMask(~Known.Zero);
1256       if (KnownZeroMask.isPowerOf2()) {
1257         Value *In = ICI->getOperand(0);
1258 
1259         // If the icmp tests for a known zero bit we can constant fold it.
1260         if (!Op1C->isZero() && Op1C->getValue() != KnownZeroMask) {
1261           Value *V = Pred == ICmpInst::ICMP_NE ?
1262                        ConstantInt::getAllOnesValue(CI.getType()) :
1263                        ConstantInt::getNullValue(CI.getType());
1264           return replaceInstUsesWith(CI, V);
1265         }
1266 
1267         if (!Op1C->isZero() == (Pred == ICmpInst::ICMP_NE)) {
1268           // sext ((x & 2^n) == 0)   -> (x >> n) - 1
1269           // sext ((x & 2^n) != 2^n) -> (x >> n) - 1
1270           unsigned ShiftAmt = KnownZeroMask.countTrailingZeros();
1271           // Perform a right shift to place the desired bit in the LSB.
1272           if (ShiftAmt)
1273             In = Builder.CreateLShr(In,
1274                                     ConstantInt::get(In->getType(), ShiftAmt));
1275 
1276           // At this point "In" is either 1 or 0. Subtract 1 to turn
1277           // {1, 0} -> {0, -1}.
1278           In = Builder.CreateAdd(In,
1279                                  ConstantInt::getAllOnesValue(In->getType()),
1280                                  "sext");
1281         } else {
1282           // sext ((x & 2^n) != 0)   -> (x << bitwidth-n) a>> bitwidth-1
1283           // sext ((x & 2^n) == 2^n) -> (x << bitwidth-n) a>> bitwidth-1
1284           unsigned ShiftAmt = KnownZeroMask.countLeadingZeros();
1285           // Perform a left shift to place the desired bit in the MSB.
1286           if (ShiftAmt)
1287             In = Builder.CreateShl(In,
1288                                    ConstantInt::get(In->getType(), ShiftAmt));
1289 
1290           // Distribute the bit over the whole bit width.
1291           In = Builder.CreateAShr(In, ConstantInt::get(In->getType(),
1292                                   KnownZeroMask.getBitWidth() - 1), "sext");
1293         }
1294 
1295         if (CI.getType() == In->getType())
1296           return replaceInstUsesWith(CI, In);
1297         return CastInst::CreateIntegerCast(In, CI.getType(), true/*SExt*/);
1298       }
1299     }
1300   }
1301 
1302   return nullptr;
1303 }
1304 
1305 /// Return true if we can take the specified value and return it as type Ty
1306 /// without inserting any new casts and without changing the value of the common
1307 /// low bits.  This is used by code that tries to promote integer operations to
1308 /// a wider types will allow us to eliminate the extension.
1309 ///
1310 /// This function works on both vectors and scalars.
1311 ///
1312 static bool canEvaluateSExtd(Value *V, Type *Ty) {
1313   assert(V->getType()->getScalarSizeInBits() < Ty->getScalarSizeInBits() &&
1314          "Can't sign extend type to a smaller type");
1315   if (canAlwaysEvaluateInType(V, Ty))
1316     return true;
1317   if (canNotEvaluateInType(V, Ty))
1318     return false;
1319 
1320   auto *I = cast<Instruction>(V);
1321   switch (I->getOpcode()) {
1322   case Instruction::SExt:  // sext(sext(x)) -> sext(x)
1323   case Instruction::ZExt:  // sext(zext(x)) -> zext(x)
1324   case Instruction::Trunc: // sext(trunc(x)) -> trunc(x) or sext(x)
1325     return true;
1326   case Instruction::And:
1327   case Instruction::Or:
1328   case Instruction::Xor:
1329   case Instruction::Add:
1330   case Instruction::Sub:
1331   case Instruction::Mul:
1332     // These operators can all arbitrarily be extended if their inputs can.
1333     return canEvaluateSExtd(I->getOperand(0), Ty) &&
1334            canEvaluateSExtd(I->getOperand(1), Ty);
1335 
1336   //case Instruction::Shl:   TODO
1337   //case Instruction::LShr:  TODO
1338 
1339   case Instruction::Select:
1340     return canEvaluateSExtd(I->getOperand(1), Ty) &&
1341            canEvaluateSExtd(I->getOperand(2), Ty);
1342 
1343   case Instruction::PHI: {
1344     // We can change a phi if we can change all operands.  Note that we never
1345     // get into trouble with cyclic PHIs here because we only consider
1346     // instructions with a single use.
1347     PHINode *PN = cast<PHINode>(I);
1348     for (Value *IncValue : PN->incoming_values())
1349       if (!canEvaluateSExtd(IncValue, Ty)) return false;
1350     return true;
1351   }
1352   default:
1353     // TODO: Can handle more cases here.
1354     break;
1355   }
1356 
1357   return false;
1358 }
1359 
1360 Instruction *InstCombiner::visitSExt(SExtInst &CI) {
1361   // If this sign extend is only used by a truncate, let the truncate be
1362   // eliminated before we try to optimize this sext.
1363   if (CI.hasOneUse() && isa<TruncInst>(CI.user_back()))
1364     return nullptr;
1365 
1366   if (Instruction *I = commonCastTransforms(CI))
1367     return I;
1368 
1369   Value *Src = CI.getOperand(0);
1370   Type *SrcTy = Src->getType(), *DestTy = CI.getType();
1371 
1372   // If we know that the value being extended is positive, we can use a zext
1373   // instead.
1374   KnownBits Known = computeKnownBits(Src, 0, &CI);
1375   if (Known.isNonNegative())
1376     return CastInst::Create(Instruction::ZExt, Src, DestTy);
1377 
1378   // Try to extend the entire expression tree to the wide destination type.
1379   if (shouldChangeType(SrcTy, DestTy) && canEvaluateSExtd(Src, DestTy)) {
1380     // Okay, we can transform this!  Insert the new expression now.
1381     LLVM_DEBUG(
1382         dbgs() << "ICE: EvaluateInDifferentType converting expression type"
1383                   " to avoid sign extend: "
1384                << CI << '\n');
1385     Value *Res = EvaluateInDifferentType(Src, DestTy, true);
1386     assert(Res->getType() == DestTy);
1387 
1388     uint32_t SrcBitSize = SrcTy->getScalarSizeInBits();
1389     uint32_t DestBitSize = DestTy->getScalarSizeInBits();
1390 
1391     // If the high bits are already filled with sign bit, just replace this
1392     // cast with the result.
1393     if (ComputeNumSignBits(Res, 0, &CI) > DestBitSize - SrcBitSize)
1394       return replaceInstUsesWith(CI, Res);
1395 
1396     // We need to emit a shl + ashr to do the sign extend.
1397     Value *ShAmt = ConstantInt::get(DestTy, DestBitSize-SrcBitSize);
1398     return BinaryOperator::CreateAShr(Builder.CreateShl(Res, ShAmt, "sext"),
1399                                       ShAmt);
1400   }
1401 
1402   // If the input is a trunc from the destination type, then turn sext(trunc(x))
1403   // into shifts.
1404   Value *X;
1405   if (match(Src, m_OneUse(m_Trunc(m_Value(X)))) && X->getType() == DestTy) {
1406     // sext(trunc(X)) --> ashr(shl(X, C), C)
1407     unsigned SrcBitSize = SrcTy->getScalarSizeInBits();
1408     unsigned DestBitSize = DestTy->getScalarSizeInBits();
1409     Constant *ShAmt = ConstantInt::get(DestTy, DestBitSize - SrcBitSize);
1410     return BinaryOperator::CreateAShr(Builder.CreateShl(X, ShAmt), ShAmt);
1411   }
1412 
1413   if (ICmpInst *ICI = dyn_cast<ICmpInst>(Src))
1414     return transformSExtICmp(ICI, CI);
1415 
1416   // If the input is a shl/ashr pair of a same constant, then this is a sign
1417   // extension from a smaller value.  If we could trust arbitrary bitwidth
1418   // integers, we could turn this into a truncate to the smaller bit and then
1419   // use a sext for the whole extension.  Since we don't, look deeper and check
1420   // for a truncate.  If the source and dest are the same type, eliminate the
1421   // trunc and extend and just do shifts.  For example, turn:
1422   //   %a = trunc i32 %i to i8
1423   //   %b = shl i8 %a, 6
1424   //   %c = ashr i8 %b, 6
1425   //   %d = sext i8 %c to i32
1426   // into:
1427   //   %a = shl i32 %i, 30
1428   //   %d = ashr i32 %a, 30
1429   Value *A = nullptr;
1430   // TODO: Eventually this could be subsumed by EvaluateInDifferentType.
1431   ConstantInt *BA = nullptr, *CA = nullptr;
1432   if (match(Src, m_AShr(m_Shl(m_Trunc(m_Value(A)), m_ConstantInt(BA)),
1433                         m_ConstantInt(CA))) &&
1434       BA == CA && A->getType() == CI.getType()) {
1435     unsigned MidSize = Src->getType()->getScalarSizeInBits();
1436     unsigned SrcDstSize = CI.getType()->getScalarSizeInBits();
1437     unsigned ShAmt = CA->getZExtValue()+SrcDstSize-MidSize;
1438     Constant *ShAmtV = ConstantInt::get(CI.getType(), ShAmt);
1439     A = Builder.CreateShl(A, ShAmtV, CI.getName());
1440     return BinaryOperator::CreateAShr(A, ShAmtV);
1441   }
1442 
1443   return nullptr;
1444 }
1445 
1446 
1447 /// Return a Constant* for the specified floating-point constant if it fits
1448 /// in the specified FP type without changing its value.
1449 static bool fitsInFPType(ConstantFP *CFP, const fltSemantics &Sem) {
1450   bool losesInfo;
1451   APFloat F = CFP->getValueAPF();
1452   (void)F.convert(Sem, APFloat::rmNearestTiesToEven, &losesInfo);
1453   return !losesInfo;
1454 }
1455 
1456 static Type *shrinkFPConstant(ConstantFP *CFP) {
1457   if (CFP->getType() == Type::getPPC_FP128Ty(CFP->getContext()))
1458     return nullptr;  // No constant folding of this.
1459   // See if the value can be truncated to half and then reextended.
1460   if (fitsInFPType(CFP, APFloat::IEEEhalf()))
1461     return Type::getHalfTy(CFP->getContext());
1462   // See if the value can be truncated to float and then reextended.
1463   if (fitsInFPType(CFP, APFloat::IEEEsingle()))
1464     return Type::getFloatTy(CFP->getContext());
1465   if (CFP->getType()->isDoubleTy())
1466     return nullptr;  // Won't shrink.
1467   if (fitsInFPType(CFP, APFloat::IEEEdouble()))
1468     return Type::getDoubleTy(CFP->getContext());
1469   // Don't try to shrink to various long double types.
1470   return nullptr;
1471 }
1472 
1473 // Determine if this is a vector of ConstantFPs and if so, return the minimal
1474 // type we can safely truncate all elements to.
1475 // TODO: Make these support undef elements.
1476 static Type *shrinkFPConstantVector(Value *V) {
1477   auto *CV = dyn_cast<Constant>(V);
1478   if (!CV || !CV->getType()->isVectorTy())
1479     return nullptr;
1480 
1481   Type *MinType = nullptr;
1482 
1483   unsigned NumElts = CV->getType()->getVectorNumElements();
1484   for (unsigned i = 0; i != NumElts; ++i) {
1485     auto *CFP = dyn_cast_or_null<ConstantFP>(CV->getAggregateElement(i));
1486     if (!CFP)
1487       return nullptr;
1488 
1489     Type *T = shrinkFPConstant(CFP);
1490     if (!T)
1491       return nullptr;
1492 
1493     // If we haven't found a type yet or this type has a larger mantissa than
1494     // our previous type, this is our new minimal type.
1495     if (!MinType || T->getFPMantissaWidth() > MinType->getFPMantissaWidth())
1496       MinType = T;
1497   }
1498 
1499   // Make a vector type from the minimal type.
1500   return VectorType::get(MinType, NumElts);
1501 }
1502 
1503 /// Find the minimum FP type we can safely truncate to.
1504 static Type *getMinimumFPType(Value *V) {
1505   if (auto *FPExt = dyn_cast<FPExtInst>(V))
1506     return FPExt->getOperand(0)->getType();
1507 
1508   // If this value is a constant, return the constant in the smallest FP type
1509   // that can accurately represent it.  This allows us to turn
1510   // (float)((double)X+2.0) into x+2.0f.
1511   if (auto *CFP = dyn_cast<ConstantFP>(V))
1512     if (Type *T = shrinkFPConstant(CFP))
1513       return T;
1514 
1515   // Try to shrink a vector of FP constants.
1516   if (Type *T = shrinkFPConstantVector(V))
1517     return T;
1518 
1519   return V->getType();
1520 }
1521 
1522 Instruction *InstCombiner::visitFPTrunc(FPTruncInst &FPT) {
1523   if (Instruction *I = commonCastTransforms(FPT))
1524     return I;
1525 
1526   // If we have fptrunc(OpI (fpextend x), (fpextend y)), we would like to
1527   // simplify this expression to avoid one or more of the trunc/extend
1528   // operations if we can do so without changing the numerical results.
1529   //
1530   // The exact manner in which the widths of the operands interact to limit
1531   // what we can and cannot do safely varies from operation to operation, and
1532   // is explained below in the various case statements.
1533   Type *Ty = FPT.getType();
1534   BinaryOperator *OpI = dyn_cast<BinaryOperator>(FPT.getOperand(0));
1535   if (OpI && OpI->hasOneUse()) {
1536     Type *LHSMinType = getMinimumFPType(OpI->getOperand(0));
1537     Type *RHSMinType = getMinimumFPType(OpI->getOperand(1));
1538     unsigned OpWidth = OpI->getType()->getFPMantissaWidth();
1539     unsigned LHSWidth = LHSMinType->getFPMantissaWidth();
1540     unsigned RHSWidth = RHSMinType->getFPMantissaWidth();
1541     unsigned SrcWidth = std::max(LHSWidth, RHSWidth);
1542     unsigned DstWidth = Ty->getFPMantissaWidth();
1543     switch (OpI->getOpcode()) {
1544       default: break;
1545       case Instruction::FAdd:
1546       case Instruction::FSub:
1547         // For addition and subtraction, the infinitely precise result can
1548         // essentially be arbitrarily wide; proving that double rounding
1549         // will not occur because the result of OpI is exact (as we will for
1550         // FMul, for example) is hopeless.  However, we *can* nonetheless
1551         // frequently know that double rounding cannot occur (or that it is
1552         // innocuous) by taking advantage of the specific structure of
1553         // infinitely-precise results that admit double rounding.
1554         //
1555         // Specifically, if OpWidth >= 2*DstWdith+1 and DstWidth is sufficient
1556         // to represent both sources, we can guarantee that the double
1557         // rounding is innocuous (See p50 of Figueroa's 2000 PhD thesis,
1558         // "A Rigorous Framework for Fully Supporting the IEEE Standard ..."
1559         // for proof of this fact).
1560         //
1561         // Note: Figueroa does not consider the case where DstFormat !=
1562         // SrcFormat.  It's possible (likely even!) that this analysis
1563         // could be tightened for those cases, but they are rare (the main
1564         // case of interest here is (float)((double)float + float)).
1565         if (OpWidth >= 2*DstWidth+1 && DstWidth >= SrcWidth) {
1566           Value *LHS = Builder.CreateFPTrunc(OpI->getOperand(0), Ty);
1567           Value *RHS = Builder.CreateFPTrunc(OpI->getOperand(1), Ty);
1568           Instruction *RI = BinaryOperator::Create(OpI->getOpcode(), LHS, RHS);
1569           RI->copyFastMathFlags(OpI);
1570           return RI;
1571         }
1572         break;
1573       case Instruction::FMul:
1574         // For multiplication, the infinitely precise result has at most
1575         // LHSWidth + RHSWidth significant bits; if OpWidth is sufficient
1576         // that such a value can be exactly represented, then no double
1577         // rounding can possibly occur; we can safely perform the operation
1578         // in the destination format if it can represent both sources.
1579         if (OpWidth >= LHSWidth + RHSWidth && DstWidth >= SrcWidth) {
1580           Value *LHS = Builder.CreateFPTrunc(OpI->getOperand(0), Ty);
1581           Value *RHS = Builder.CreateFPTrunc(OpI->getOperand(1), Ty);
1582           return BinaryOperator::CreateFMulFMF(LHS, RHS, OpI);
1583         }
1584         break;
1585       case Instruction::FDiv:
1586         // For division, we use again use the bound from Figueroa's
1587         // dissertation.  I am entirely certain that this bound can be
1588         // tightened in the unbalanced operand case by an analysis based on
1589         // the diophantine rational approximation bound, but the well-known
1590         // condition used here is a good conservative first pass.
1591         // TODO: Tighten bound via rigorous analysis of the unbalanced case.
1592         if (OpWidth >= 2*DstWidth && DstWidth >= SrcWidth) {
1593           Value *LHS = Builder.CreateFPTrunc(OpI->getOperand(0), Ty);
1594           Value *RHS = Builder.CreateFPTrunc(OpI->getOperand(1), Ty);
1595           return BinaryOperator::CreateFDivFMF(LHS, RHS, OpI);
1596         }
1597         break;
1598       case Instruction::FRem: {
1599         // Remainder is straightforward.  Remainder is always exact, so the
1600         // type of OpI doesn't enter into things at all.  We simply evaluate
1601         // in whichever source type is larger, then convert to the
1602         // destination type.
1603         if (SrcWidth == OpWidth)
1604           break;
1605         Value *LHS, *RHS;
1606         if (LHSWidth == SrcWidth) {
1607            LHS = Builder.CreateFPTrunc(OpI->getOperand(0), LHSMinType);
1608            RHS = Builder.CreateFPTrunc(OpI->getOperand(1), LHSMinType);
1609         } else {
1610            LHS = Builder.CreateFPTrunc(OpI->getOperand(0), RHSMinType);
1611            RHS = Builder.CreateFPTrunc(OpI->getOperand(1), RHSMinType);
1612         }
1613 
1614         Value *ExactResult = Builder.CreateFRemFMF(LHS, RHS, OpI);
1615         return CastInst::CreateFPCast(ExactResult, Ty);
1616       }
1617     }
1618   }
1619 
1620   // (fptrunc (fneg x)) -> (fneg (fptrunc x))
1621   Value *X;
1622   Instruction *Op = dyn_cast<Instruction>(FPT.getOperand(0));
1623   if (Op && Op->hasOneUse()) {
1624     if (match(Op, m_FNeg(m_Value(X)))) {
1625       Value *InnerTrunc = Builder.CreateFPTrunc(X, Ty);
1626 
1627       // FIXME: Once we're sure that unary FNeg optimizations are on par with
1628       // binary FNeg, this should always return a unary operator.
1629       if (isa<BinaryOperator>(Op))
1630         return BinaryOperator::CreateFNegFMF(InnerTrunc, Op);
1631       return UnaryOperator::CreateFNegFMF(InnerTrunc, Op);
1632     }
1633   }
1634 
1635   if (auto *II = dyn_cast<IntrinsicInst>(FPT.getOperand(0))) {
1636     switch (II->getIntrinsicID()) {
1637     default: break;
1638     case Intrinsic::ceil:
1639     case Intrinsic::fabs:
1640     case Intrinsic::floor:
1641     case Intrinsic::nearbyint:
1642     case Intrinsic::rint:
1643     case Intrinsic::round:
1644     case Intrinsic::trunc: {
1645       Value *Src = II->getArgOperand(0);
1646       if (!Src->hasOneUse())
1647         break;
1648 
1649       // Except for fabs, this transformation requires the input of the unary FP
1650       // operation to be itself an fpext from the type to which we're
1651       // truncating.
1652       if (II->getIntrinsicID() != Intrinsic::fabs) {
1653         FPExtInst *FPExtSrc = dyn_cast<FPExtInst>(Src);
1654         if (!FPExtSrc || FPExtSrc->getSrcTy() != Ty)
1655           break;
1656       }
1657 
1658       // Do unary FP operation on smaller type.
1659       // (fptrunc (fabs x)) -> (fabs (fptrunc x))
1660       Value *InnerTrunc = Builder.CreateFPTrunc(Src, Ty);
1661       Function *Overload = Intrinsic::getDeclaration(FPT.getModule(),
1662                                                      II->getIntrinsicID(), Ty);
1663       SmallVector<OperandBundleDef, 1> OpBundles;
1664       II->getOperandBundlesAsDefs(OpBundles);
1665       CallInst *NewCI =
1666           CallInst::Create(Overload, {InnerTrunc}, OpBundles, II->getName());
1667       NewCI->copyFastMathFlags(II);
1668       return NewCI;
1669     }
1670     }
1671   }
1672 
1673   if (Instruction *I = shrinkInsertElt(FPT, Builder))
1674     return I;
1675 
1676   return nullptr;
1677 }
1678 
1679 Instruction *InstCombiner::visitFPExt(CastInst &CI) {
1680   return commonCastTransforms(CI);
1681 }
1682 
1683 // fpto{s/u}i({u/s}itofp(X)) --> X or zext(X) or sext(X) or trunc(X)
1684 // This is safe if the intermediate type has enough bits in its mantissa to
1685 // accurately represent all values of X.  For example, this won't work with
1686 // i64 -> float -> i64.
1687 Instruction *InstCombiner::FoldItoFPtoI(Instruction &FI) {
1688   if (!isa<UIToFPInst>(FI.getOperand(0)) && !isa<SIToFPInst>(FI.getOperand(0)))
1689     return nullptr;
1690   Instruction *OpI = cast<Instruction>(FI.getOperand(0));
1691 
1692   Value *SrcI = OpI->getOperand(0);
1693   Type *FITy = FI.getType();
1694   Type *OpITy = OpI->getType();
1695   Type *SrcTy = SrcI->getType();
1696   bool IsInputSigned = isa<SIToFPInst>(OpI);
1697   bool IsOutputSigned = isa<FPToSIInst>(FI);
1698 
1699   // We can safely assume the conversion won't overflow the output range,
1700   // because (for example) (uint8_t)18293.f is undefined behavior.
1701 
1702   // Since we can assume the conversion won't overflow, our decision as to
1703   // whether the input will fit in the float should depend on the minimum
1704   // of the input range and output range.
1705 
1706   // This means this is also safe for a signed input and unsigned output, since
1707   // a negative input would lead to undefined behavior.
1708   int InputSize = (int)SrcTy->getScalarSizeInBits() - IsInputSigned;
1709   int OutputSize = (int)FITy->getScalarSizeInBits() - IsOutputSigned;
1710   int ActualSize = std::min(InputSize, OutputSize);
1711 
1712   if (ActualSize <= OpITy->getFPMantissaWidth()) {
1713     if (FITy->getScalarSizeInBits() > SrcTy->getScalarSizeInBits()) {
1714       if (IsInputSigned && IsOutputSigned)
1715         return new SExtInst(SrcI, FITy);
1716       return new ZExtInst(SrcI, FITy);
1717     }
1718     if (FITy->getScalarSizeInBits() < SrcTy->getScalarSizeInBits())
1719       return new TruncInst(SrcI, FITy);
1720     if (SrcTy == FITy)
1721       return replaceInstUsesWith(FI, SrcI);
1722     return new BitCastInst(SrcI, FITy);
1723   }
1724   return nullptr;
1725 }
1726 
1727 Instruction *InstCombiner::visitFPToUI(FPToUIInst &FI) {
1728   Instruction *OpI = dyn_cast<Instruction>(FI.getOperand(0));
1729   if (!OpI)
1730     return commonCastTransforms(FI);
1731 
1732   if (Instruction *I = FoldItoFPtoI(FI))
1733     return I;
1734 
1735   return commonCastTransforms(FI);
1736 }
1737 
1738 Instruction *InstCombiner::visitFPToSI(FPToSIInst &FI) {
1739   Instruction *OpI = dyn_cast<Instruction>(FI.getOperand(0));
1740   if (!OpI)
1741     return commonCastTransforms(FI);
1742 
1743   if (Instruction *I = FoldItoFPtoI(FI))
1744     return I;
1745 
1746   return commonCastTransforms(FI);
1747 }
1748 
1749 Instruction *InstCombiner::visitUIToFP(CastInst &CI) {
1750   return commonCastTransforms(CI);
1751 }
1752 
1753 Instruction *InstCombiner::visitSIToFP(CastInst &CI) {
1754   return commonCastTransforms(CI);
1755 }
1756 
1757 Instruction *InstCombiner::visitIntToPtr(IntToPtrInst &CI) {
1758   // If the source integer type is not the intptr_t type for this target, do a
1759   // trunc or zext to the intptr_t type, then inttoptr of it.  This allows the
1760   // cast to be exposed to other transforms.
1761   unsigned AS = CI.getAddressSpace();
1762   if (CI.getOperand(0)->getType()->getScalarSizeInBits() !=
1763       DL.getPointerSizeInBits(AS)) {
1764     Type *Ty = DL.getIntPtrType(CI.getContext(), AS);
1765     if (CI.getType()->isVectorTy()) // Handle vectors of pointers.
1766       Ty = VectorType::get(Ty, CI.getType()->getVectorNumElements());
1767 
1768     Value *P = Builder.CreateZExtOrTrunc(CI.getOperand(0), Ty);
1769     return new IntToPtrInst(P, CI.getType());
1770   }
1771 
1772   if (Instruction *I = commonCastTransforms(CI))
1773     return I;
1774 
1775   return nullptr;
1776 }
1777 
1778 /// Implement the transforms for cast of pointer (bitcast/ptrtoint)
1779 Instruction *InstCombiner::commonPointerCastTransforms(CastInst &CI) {
1780   Value *Src = CI.getOperand(0);
1781 
1782   if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Src)) {
1783     // If casting the result of a getelementptr instruction with no offset, turn
1784     // this into a cast of the original pointer!
1785     if (GEP->hasAllZeroIndices() &&
1786         // If CI is an addrspacecast and GEP changes the poiner type, merging
1787         // GEP into CI would undo canonicalizing addrspacecast with different
1788         // pointer types, causing infinite loops.
1789         (!isa<AddrSpaceCastInst>(CI) ||
1790          GEP->getType() == GEP->getPointerOperandType())) {
1791       // Changing the cast operand is usually not a good idea but it is safe
1792       // here because the pointer operand is being replaced with another
1793       // pointer operand so the opcode doesn't need to change.
1794       Worklist.Add(GEP);
1795       CI.setOperand(0, GEP->getOperand(0));
1796       return &CI;
1797     }
1798   }
1799 
1800   return commonCastTransforms(CI);
1801 }
1802 
1803 Instruction *InstCombiner::visitPtrToInt(PtrToIntInst &CI) {
1804   // If the destination integer type is not the intptr_t type for this target,
1805   // do a ptrtoint to intptr_t then do a trunc or zext.  This allows the cast
1806   // to be exposed to other transforms.
1807 
1808   Type *Ty = CI.getType();
1809   unsigned AS = CI.getPointerAddressSpace();
1810 
1811   if (Ty->getScalarSizeInBits() == DL.getIndexSizeInBits(AS))
1812     return commonPointerCastTransforms(CI);
1813 
1814   Type *PtrTy = DL.getIntPtrType(CI.getContext(), AS);
1815   if (Ty->isVectorTy()) // Handle vectors of pointers.
1816     PtrTy = VectorType::get(PtrTy, Ty->getVectorNumElements());
1817 
1818   Value *P = Builder.CreatePtrToInt(CI.getOperand(0), PtrTy);
1819   return CastInst::CreateIntegerCast(P, Ty, /*isSigned=*/false);
1820 }
1821 
1822 /// This input value (which is known to have vector type) is being zero extended
1823 /// or truncated to the specified vector type.
1824 /// Try to replace it with a shuffle (and vector/vector bitcast) if possible.
1825 ///
1826 /// The source and destination vector types may have different element types.
1827 static Instruction *optimizeVectorResize(Value *InVal, VectorType *DestTy,
1828                                          InstCombiner &IC) {
1829   // We can only do this optimization if the output is a multiple of the input
1830   // element size, or the input is a multiple of the output element size.
1831   // Convert the input type to have the same element type as the output.
1832   VectorType *SrcTy = cast<VectorType>(InVal->getType());
1833 
1834   if (SrcTy->getElementType() != DestTy->getElementType()) {
1835     // The input types don't need to be identical, but for now they must be the
1836     // same size.  There is no specific reason we couldn't handle things like
1837     // <4 x i16> -> <4 x i32> by bitcasting to <2 x i32> but haven't gotten
1838     // there yet.
1839     if (SrcTy->getElementType()->getPrimitiveSizeInBits() !=
1840         DestTy->getElementType()->getPrimitiveSizeInBits())
1841       return nullptr;
1842 
1843     SrcTy = VectorType::get(DestTy->getElementType(), SrcTy->getNumElements());
1844     InVal = IC.Builder.CreateBitCast(InVal, SrcTy);
1845   }
1846 
1847   // Now that the element types match, get the shuffle mask and RHS of the
1848   // shuffle to use, which depends on whether we're increasing or decreasing the
1849   // size of the input.
1850   SmallVector<uint32_t, 16> ShuffleMask;
1851   Value *V2;
1852 
1853   if (SrcTy->getNumElements() > DestTy->getNumElements()) {
1854     // If we're shrinking the number of elements, just shuffle in the low
1855     // elements from the input and use undef as the second shuffle input.
1856     V2 = UndefValue::get(SrcTy);
1857     for (unsigned i = 0, e = DestTy->getNumElements(); i != e; ++i)
1858       ShuffleMask.push_back(i);
1859 
1860   } else {
1861     // If we're increasing the number of elements, shuffle in all of the
1862     // elements from InVal and fill the rest of the result elements with zeros
1863     // from a constant zero.
1864     V2 = Constant::getNullValue(SrcTy);
1865     unsigned SrcElts = SrcTy->getNumElements();
1866     for (unsigned i = 0, e = SrcElts; i != e; ++i)
1867       ShuffleMask.push_back(i);
1868 
1869     // The excess elements reference the first element of the zero input.
1870     for (unsigned i = 0, e = DestTy->getNumElements()-SrcElts; i != e; ++i)
1871       ShuffleMask.push_back(SrcElts);
1872   }
1873 
1874   return new ShuffleVectorInst(InVal, V2,
1875                                ConstantDataVector::get(V2->getContext(),
1876                                                        ShuffleMask));
1877 }
1878 
1879 static bool isMultipleOfTypeSize(unsigned Value, Type *Ty) {
1880   return Value % Ty->getPrimitiveSizeInBits() == 0;
1881 }
1882 
1883 static unsigned getTypeSizeIndex(unsigned Value, Type *Ty) {
1884   return Value / Ty->getPrimitiveSizeInBits();
1885 }
1886 
1887 /// V is a value which is inserted into a vector of VecEltTy.
1888 /// Look through the value to see if we can decompose it into
1889 /// insertions into the vector.  See the example in the comment for
1890 /// OptimizeIntegerToVectorInsertions for the pattern this handles.
1891 /// The type of V is always a non-zero multiple of VecEltTy's size.
1892 /// Shift is the number of bits between the lsb of V and the lsb of
1893 /// the vector.
1894 ///
1895 /// This returns false if the pattern can't be matched or true if it can,
1896 /// filling in Elements with the elements found here.
1897 static bool collectInsertionElements(Value *V, unsigned Shift,
1898                                      SmallVectorImpl<Value *> &Elements,
1899                                      Type *VecEltTy, bool isBigEndian) {
1900   assert(isMultipleOfTypeSize(Shift, VecEltTy) &&
1901          "Shift should be a multiple of the element type size");
1902 
1903   // Undef values never contribute useful bits to the result.
1904   if (isa<UndefValue>(V)) return true;
1905 
1906   // If we got down to a value of the right type, we win, try inserting into the
1907   // right element.
1908   if (V->getType() == VecEltTy) {
1909     // Inserting null doesn't actually insert any elements.
1910     if (Constant *C = dyn_cast<Constant>(V))
1911       if (C->isNullValue())
1912         return true;
1913 
1914     unsigned ElementIndex = getTypeSizeIndex(Shift, VecEltTy);
1915     if (isBigEndian)
1916       ElementIndex = Elements.size() - ElementIndex - 1;
1917 
1918     // Fail if multiple elements are inserted into this slot.
1919     if (Elements[ElementIndex])
1920       return false;
1921 
1922     Elements[ElementIndex] = V;
1923     return true;
1924   }
1925 
1926   if (Constant *C = dyn_cast<Constant>(V)) {
1927     // Figure out the # elements this provides, and bitcast it or slice it up
1928     // as required.
1929     unsigned NumElts = getTypeSizeIndex(C->getType()->getPrimitiveSizeInBits(),
1930                                         VecEltTy);
1931     // If the constant is the size of a vector element, we just need to bitcast
1932     // it to the right type so it gets properly inserted.
1933     if (NumElts == 1)
1934       return collectInsertionElements(ConstantExpr::getBitCast(C, VecEltTy),
1935                                       Shift, Elements, VecEltTy, isBigEndian);
1936 
1937     // Okay, this is a constant that covers multiple elements.  Slice it up into
1938     // pieces and insert each element-sized piece into the vector.
1939     if (!isa<IntegerType>(C->getType()))
1940       C = ConstantExpr::getBitCast(C, IntegerType::get(V->getContext(),
1941                                        C->getType()->getPrimitiveSizeInBits()));
1942     unsigned ElementSize = VecEltTy->getPrimitiveSizeInBits();
1943     Type *ElementIntTy = IntegerType::get(C->getContext(), ElementSize);
1944 
1945     for (unsigned i = 0; i != NumElts; ++i) {
1946       unsigned ShiftI = Shift+i*ElementSize;
1947       Constant *Piece = ConstantExpr::getLShr(C, ConstantInt::get(C->getType(),
1948                                                                   ShiftI));
1949       Piece = ConstantExpr::getTrunc(Piece, ElementIntTy);
1950       if (!collectInsertionElements(Piece, ShiftI, Elements, VecEltTy,
1951                                     isBigEndian))
1952         return false;
1953     }
1954     return true;
1955   }
1956 
1957   if (!V->hasOneUse()) return false;
1958 
1959   Instruction *I = dyn_cast<Instruction>(V);
1960   if (!I) return false;
1961   switch (I->getOpcode()) {
1962   default: return false; // Unhandled case.
1963   case Instruction::BitCast:
1964     return collectInsertionElements(I->getOperand(0), Shift, Elements, VecEltTy,
1965                                     isBigEndian);
1966   case Instruction::ZExt:
1967     if (!isMultipleOfTypeSize(
1968                           I->getOperand(0)->getType()->getPrimitiveSizeInBits(),
1969                               VecEltTy))
1970       return false;
1971     return collectInsertionElements(I->getOperand(0), Shift, Elements, VecEltTy,
1972                                     isBigEndian);
1973   case Instruction::Or:
1974     return collectInsertionElements(I->getOperand(0), Shift, Elements, VecEltTy,
1975                                     isBigEndian) &&
1976            collectInsertionElements(I->getOperand(1), Shift, Elements, VecEltTy,
1977                                     isBigEndian);
1978   case Instruction::Shl: {
1979     // Must be shifting by a constant that is a multiple of the element size.
1980     ConstantInt *CI = dyn_cast<ConstantInt>(I->getOperand(1));
1981     if (!CI) return false;
1982     Shift += CI->getZExtValue();
1983     if (!isMultipleOfTypeSize(Shift, VecEltTy)) return false;
1984     return collectInsertionElements(I->getOperand(0), Shift, Elements, VecEltTy,
1985                                     isBigEndian);
1986   }
1987 
1988   }
1989 }
1990 
1991 
1992 /// If the input is an 'or' instruction, we may be doing shifts and ors to
1993 /// assemble the elements of the vector manually.
1994 /// Try to rip the code out and replace it with insertelements.  This is to
1995 /// optimize code like this:
1996 ///
1997 ///    %tmp37 = bitcast float %inc to i32
1998 ///    %tmp38 = zext i32 %tmp37 to i64
1999 ///    %tmp31 = bitcast float %inc5 to i32
2000 ///    %tmp32 = zext i32 %tmp31 to i64
2001 ///    %tmp33 = shl i64 %tmp32, 32
2002 ///    %ins35 = or i64 %tmp33, %tmp38
2003 ///    %tmp43 = bitcast i64 %ins35 to <2 x float>
2004 ///
2005 /// Into two insertelements that do "buildvector{%inc, %inc5}".
2006 static Value *optimizeIntegerToVectorInsertions(BitCastInst &CI,
2007                                                 InstCombiner &IC) {
2008   VectorType *DestVecTy = cast<VectorType>(CI.getType());
2009   Value *IntInput = CI.getOperand(0);
2010 
2011   SmallVector<Value*, 8> Elements(DestVecTy->getNumElements());
2012   if (!collectInsertionElements(IntInput, 0, Elements,
2013                                 DestVecTy->getElementType(),
2014                                 IC.getDataLayout().isBigEndian()))
2015     return nullptr;
2016 
2017   // If we succeeded, we know that all of the element are specified by Elements
2018   // or are zero if Elements has a null entry.  Recast this as a set of
2019   // insertions.
2020   Value *Result = Constant::getNullValue(CI.getType());
2021   for (unsigned i = 0, e = Elements.size(); i != e; ++i) {
2022     if (!Elements[i]) continue;  // Unset element.
2023 
2024     Result = IC.Builder.CreateInsertElement(Result, Elements[i],
2025                                             IC.Builder.getInt32(i));
2026   }
2027 
2028   return Result;
2029 }
2030 
2031 /// Canonicalize scalar bitcasts of extracted elements into a bitcast of the
2032 /// vector followed by extract element. The backend tends to handle bitcasts of
2033 /// vectors better than bitcasts of scalars because vector registers are
2034 /// usually not type-specific like scalar integer or scalar floating-point.
2035 static Instruction *canonicalizeBitCastExtElt(BitCastInst &BitCast,
2036                                               InstCombiner &IC) {
2037   // TODO: Create and use a pattern matcher for ExtractElementInst.
2038   auto *ExtElt = dyn_cast<ExtractElementInst>(BitCast.getOperand(0));
2039   if (!ExtElt || !ExtElt->hasOneUse())
2040     return nullptr;
2041 
2042   // The bitcast must be to a vectorizable type, otherwise we can't make a new
2043   // type to extract from.
2044   Type *DestType = BitCast.getType();
2045   if (!VectorType::isValidElementType(DestType))
2046     return nullptr;
2047 
2048   unsigned NumElts = ExtElt->getVectorOperandType()->getNumElements();
2049   auto *NewVecType = VectorType::get(DestType, NumElts);
2050   auto *NewBC = IC.Builder.CreateBitCast(ExtElt->getVectorOperand(),
2051                                          NewVecType, "bc");
2052   return ExtractElementInst::Create(NewBC, ExtElt->getIndexOperand());
2053 }
2054 
2055 /// Change the type of a bitwise logic operation if we can eliminate a bitcast.
2056 static Instruction *foldBitCastBitwiseLogic(BitCastInst &BitCast,
2057                                             InstCombiner::BuilderTy &Builder) {
2058   Type *DestTy = BitCast.getType();
2059   BinaryOperator *BO;
2060   if (!DestTy->isIntOrIntVectorTy() ||
2061       !match(BitCast.getOperand(0), m_OneUse(m_BinOp(BO))) ||
2062       !BO->isBitwiseLogicOp())
2063     return nullptr;
2064 
2065   // FIXME: This transform is restricted to vector types to avoid backend
2066   // problems caused by creating potentially illegal operations. If a fix-up is
2067   // added to handle that situation, we can remove this check.
2068   if (!DestTy->isVectorTy() || !BO->getType()->isVectorTy())
2069     return nullptr;
2070 
2071   Value *X;
2072   if (match(BO->getOperand(0), m_OneUse(m_BitCast(m_Value(X)))) &&
2073       X->getType() == DestTy && !isa<Constant>(X)) {
2074     // bitcast(logic(bitcast(X), Y)) --> logic'(X, bitcast(Y))
2075     Value *CastedOp1 = Builder.CreateBitCast(BO->getOperand(1), DestTy);
2076     return BinaryOperator::Create(BO->getOpcode(), X, CastedOp1);
2077   }
2078 
2079   if (match(BO->getOperand(1), m_OneUse(m_BitCast(m_Value(X)))) &&
2080       X->getType() == DestTy && !isa<Constant>(X)) {
2081     // bitcast(logic(Y, bitcast(X))) --> logic'(bitcast(Y), X)
2082     Value *CastedOp0 = Builder.CreateBitCast(BO->getOperand(0), DestTy);
2083     return BinaryOperator::Create(BO->getOpcode(), CastedOp0, X);
2084   }
2085 
2086   // Canonicalize vector bitcasts to come before vector bitwise logic with a
2087   // constant. This eases recognition of special constants for later ops.
2088   // Example:
2089   // icmp u/s (a ^ signmask), (b ^ signmask) --> icmp s/u a, b
2090   Constant *C;
2091   if (match(BO->getOperand(1), m_Constant(C))) {
2092     // bitcast (logic X, C) --> logic (bitcast X, C')
2093     Value *CastedOp0 = Builder.CreateBitCast(BO->getOperand(0), DestTy);
2094     Value *CastedC = ConstantExpr::getBitCast(C, DestTy);
2095     return BinaryOperator::Create(BO->getOpcode(), CastedOp0, CastedC);
2096   }
2097 
2098   return nullptr;
2099 }
2100 
2101 /// Change the type of a select if we can eliminate a bitcast.
2102 static Instruction *foldBitCastSelect(BitCastInst &BitCast,
2103                                       InstCombiner::BuilderTy &Builder) {
2104   Value *Cond, *TVal, *FVal;
2105   if (!match(BitCast.getOperand(0),
2106              m_OneUse(m_Select(m_Value(Cond), m_Value(TVal), m_Value(FVal)))))
2107     return nullptr;
2108 
2109   // A vector select must maintain the same number of elements in its operands.
2110   Type *CondTy = Cond->getType();
2111   Type *DestTy = BitCast.getType();
2112   if (CondTy->isVectorTy()) {
2113     if (!DestTy->isVectorTy())
2114       return nullptr;
2115     if (DestTy->getVectorNumElements() != CondTy->getVectorNumElements())
2116       return nullptr;
2117   }
2118 
2119   // FIXME: This transform is restricted from changing the select between
2120   // scalars and vectors to avoid backend problems caused by creating
2121   // potentially illegal operations. If a fix-up is added to handle that
2122   // situation, we can remove this check.
2123   if (DestTy->isVectorTy() != TVal->getType()->isVectorTy())
2124     return nullptr;
2125 
2126   auto *Sel = cast<Instruction>(BitCast.getOperand(0));
2127   Value *X;
2128   if (match(TVal, m_OneUse(m_BitCast(m_Value(X)))) && X->getType() == DestTy &&
2129       !isa<Constant>(X)) {
2130     // bitcast(select(Cond, bitcast(X), Y)) --> select'(Cond, X, bitcast(Y))
2131     Value *CastedVal = Builder.CreateBitCast(FVal, DestTy);
2132     return SelectInst::Create(Cond, X, CastedVal, "", nullptr, Sel);
2133   }
2134 
2135   if (match(FVal, m_OneUse(m_BitCast(m_Value(X)))) && X->getType() == DestTy &&
2136       !isa<Constant>(X)) {
2137     // bitcast(select(Cond, Y, bitcast(X))) --> select'(Cond, bitcast(Y), X)
2138     Value *CastedVal = Builder.CreateBitCast(TVal, DestTy);
2139     return SelectInst::Create(Cond, CastedVal, X, "", nullptr, Sel);
2140   }
2141 
2142   return nullptr;
2143 }
2144 
2145 /// Check if all users of CI are StoreInsts.
2146 static bool hasStoreUsersOnly(CastInst &CI) {
2147   for (User *U : CI.users()) {
2148     if (!isa<StoreInst>(U))
2149       return false;
2150   }
2151   return true;
2152 }
2153 
2154 /// This function handles following case
2155 ///
2156 ///     A  ->  B    cast
2157 ///     PHI
2158 ///     B  ->  A    cast
2159 ///
2160 /// All the related PHI nodes can be replaced by new PHI nodes with type A.
2161 /// The uses of \p CI can be changed to the new PHI node corresponding to \p PN.
2162 Instruction *InstCombiner::optimizeBitCastFromPhi(CastInst &CI, PHINode *PN) {
2163   // BitCast used by Store can be handled in InstCombineLoadStoreAlloca.cpp.
2164   if (hasStoreUsersOnly(CI))
2165     return nullptr;
2166 
2167   Value *Src = CI.getOperand(0);
2168   Type *SrcTy = Src->getType();         // Type B
2169   Type *DestTy = CI.getType();          // Type A
2170 
2171   SmallVector<PHINode *, 4> PhiWorklist;
2172   SmallSetVector<PHINode *, 4> OldPhiNodes;
2173 
2174   // Find all of the A->B casts and PHI nodes.
2175   // We need to inspect all related PHI nodes, but PHIs can be cyclic, so
2176   // OldPhiNodes is used to track all known PHI nodes, before adding a new
2177   // PHI to PhiWorklist, it is checked against and added to OldPhiNodes first.
2178   PhiWorklist.push_back(PN);
2179   OldPhiNodes.insert(PN);
2180   while (!PhiWorklist.empty()) {
2181     auto *OldPN = PhiWorklist.pop_back_val();
2182     for (Value *IncValue : OldPN->incoming_values()) {
2183       if (isa<Constant>(IncValue))
2184         continue;
2185 
2186       if (auto *LI = dyn_cast<LoadInst>(IncValue)) {
2187         // If there is a sequence of one or more load instructions, each loaded
2188         // value is used as address of later load instruction, bitcast is
2189         // necessary to change the value type, don't optimize it. For
2190         // simplicity we give up if the load address comes from another load.
2191         Value *Addr = LI->getOperand(0);
2192         if (Addr == &CI || isa<LoadInst>(Addr))
2193           return nullptr;
2194         if (LI->hasOneUse() && LI->isSimple())
2195           continue;
2196         // If a LoadInst has more than one use, changing the type of loaded
2197         // value may create another bitcast.
2198         return nullptr;
2199       }
2200 
2201       if (auto *PNode = dyn_cast<PHINode>(IncValue)) {
2202         if (OldPhiNodes.insert(PNode))
2203           PhiWorklist.push_back(PNode);
2204         continue;
2205       }
2206 
2207       auto *BCI = dyn_cast<BitCastInst>(IncValue);
2208       // We can't handle other instructions.
2209       if (!BCI)
2210         return nullptr;
2211 
2212       // Verify it's a A->B cast.
2213       Type *TyA = BCI->getOperand(0)->getType();
2214       Type *TyB = BCI->getType();
2215       if (TyA != DestTy || TyB != SrcTy)
2216         return nullptr;
2217     }
2218   }
2219 
2220   // For each old PHI node, create a corresponding new PHI node with a type A.
2221   SmallDenseMap<PHINode *, PHINode *> NewPNodes;
2222   for (auto *OldPN : OldPhiNodes) {
2223     Builder.SetInsertPoint(OldPN);
2224     PHINode *NewPN = Builder.CreatePHI(DestTy, OldPN->getNumOperands());
2225     NewPNodes[OldPN] = NewPN;
2226   }
2227 
2228   // Fill in the operands of new PHI nodes.
2229   for (auto *OldPN : OldPhiNodes) {
2230     PHINode *NewPN = NewPNodes[OldPN];
2231     for (unsigned j = 0, e = OldPN->getNumOperands(); j != e; ++j) {
2232       Value *V = OldPN->getOperand(j);
2233       Value *NewV = nullptr;
2234       if (auto *C = dyn_cast<Constant>(V)) {
2235         NewV = ConstantExpr::getBitCast(C, DestTy);
2236       } else if (auto *LI = dyn_cast<LoadInst>(V)) {
2237         Builder.SetInsertPoint(LI->getNextNode());
2238         NewV = Builder.CreateBitCast(LI, DestTy);
2239         Worklist.Add(LI);
2240       } else if (auto *BCI = dyn_cast<BitCastInst>(V)) {
2241         NewV = BCI->getOperand(0);
2242       } else if (auto *PrevPN = dyn_cast<PHINode>(V)) {
2243         NewV = NewPNodes[PrevPN];
2244       }
2245       assert(NewV);
2246       NewPN->addIncoming(NewV, OldPN->getIncomingBlock(j));
2247     }
2248   }
2249 
2250   // Traverse all accumulated PHI nodes and process its users,
2251   // which are Stores and BitcCasts. Without this processing
2252   // NewPHI nodes could be replicated and could lead to extra
2253   // moves generated after DeSSA.
2254   // If there is a store with type B, change it to type A.
2255 
2256 
2257   // Replace users of BitCast B->A with NewPHI. These will help
2258   // later to get rid off a closure formed by OldPHI nodes.
2259   Instruction *RetVal = nullptr;
2260   for (auto *OldPN : OldPhiNodes) {
2261     PHINode *NewPN = NewPNodes[OldPN];
2262     for (User *V : OldPN->users()) {
2263       if (auto *SI = dyn_cast<StoreInst>(V)) {
2264         if (SI->isSimple() && SI->getOperand(0) == OldPN) {
2265           Builder.SetInsertPoint(SI);
2266           auto *NewBC =
2267             cast<BitCastInst>(Builder.CreateBitCast(NewPN, SrcTy));
2268           SI->setOperand(0, NewBC);
2269           Worklist.Add(SI);
2270           assert(hasStoreUsersOnly(*NewBC));
2271         }
2272       }
2273       else if (auto *BCI = dyn_cast<BitCastInst>(V)) {
2274         // Verify it's a B->A cast.
2275         Type *TyB = BCI->getOperand(0)->getType();
2276         Type *TyA = BCI->getType();
2277         if (TyA == DestTy && TyB == SrcTy) {
2278           Instruction *I = replaceInstUsesWith(*BCI, NewPN);
2279           if (BCI == &CI)
2280             RetVal = I;
2281         }
2282       }
2283     }
2284   }
2285 
2286   return RetVal;
2287 }
2288 
2289 Instruction *InstCombiner::visitBitCast(BitCastInst &CI) {
2290   // If the operands are integer typed then apply the integer transforms,
2291   // otherwise just apply the common ones.
2292   Value *Src = CI.getOperand(0);
2293   Type *SrcTy = Src->getType();
2294   Type *DestTy = CI.getType();
2295 
2296   // Get rid of casts from one type to the same type. These are useless and can
2297   // be replaced by the operand.
2298   if (DestTy == Src->getType())
2299     return replaceInstUsesWith(CI, Src);
2300 
2301   if (PointerType *DstPTy = dyn_cast<PointerType>(DestTy)) {
2302     PointerType *SrcPTy = cast<PointerType>(SrcTy);
2303     Type *DstElTy = DstPTy->getElementType();
2304     Type *SrcElTy = SrcPTy->getElementType();
2305 
2306     // Casting pointers between the same type, but with different address spaces
2307     // is an addrspace cast rather than a bitcast.
2308     if ((DstElTy == SrcElTy) &&
2309         (DstPTy->getAddressSpace() != SrcPTy->getAddressSpace()))
2310       return new AddrSpaceCastInst(Src, DestTy);
2311 
2312     // If we are casting a alloca to a pointer to a type of the same
2313     // size, rewrite the allocation instruction to allocate the "right" type.
2314     // There is no need to modify malloc calls because it is their bitcast that
2315     // needs to be cleaned up.
2316     if (AllocaInst *AI = dyn_cast<AllocaInst>(Src))
2317       if (Instruction *V = PromoteCastOfAllocation(CI, *AI))
2318         return V;
2319 
2320     // When the type pointed to is not sized the cast cannot be
2321     // turned into a gep.
2322     Type *PointeeType =
2323         cast<PointerType>(Src->getType()->getScalarType())->getElementType();
2324     if (!PointeeType->isSized())
2325       return nullptr;
2326 
2327     // If the source and destination are pointers, and this cast is equivalent
2328     // to a getelementptr X, 0, 0, 0...  turn it into the appropriate gep.
2329     // This can enhance SROA and other transforms that want type-safe pointers.
2330     unsigned NumZeros = 0;
2331     while (SrcElTy != DstElTy &&
2332            isa<CompositeType>(SrcElTy) && !SrcElTy->isPointerTy() &&
2333            SrcElTy->getNumContainedTypes() /* not "{}" */) {
2334       SrcElTy = cast<CompositeType>(SrcElTy)->getTypeAtIndex(0U);
2335       ++NumZeros;
2336     }
2337 
2338     // If we found a path from the src to dest, create the getelementptr now.
2339     if (SrcElTy == DstElTy) {
2340       SmallVector<Value *, 8> Idxs(NumZeros + 1, Builder.getInt32(0));
2341       return GetElementPtrInst::CreateInBounds(SrcPTy->getElementType(), Src,
2342                                                Idxs);
2343     }
2344   }
2345 
2346   if (VectorType *DestVTy = dyn_cast<VectorType>(DestTy)) {
2347     if (DestVTy->getNumElements() == 1 && !SrcTy->isVectorTy()) {
2348       Value *Elem = Builder.CreateBitCast(Src, DestVTy->getElementType());
2349       return InsertElementInst::Create(UndefValue::get(DestTy), Elem,
2350                      Constant::getNullValue(Type::getInt32Ty(CI.getContext())));
2351       // FIXME: Canonicalize bitcast(insertelement) -> insertelement(bitcast)
2352     }
2353 
2354     if (isa<IntegerType>(SrcTy)) {
2355       // If this is a cast from an integer to vector, check to see if the input
2356       // is a trunc or zext of a bitcast from vector.  If so, we can replace all
2357       // the casts with a shuffle and (potentially) a bitcast.
2358       if (isa<TruncInst>(Src) || isa<ZExtInst>(Src)) {
2359         CastInst *SrcCast = cast<CastInst>(Src);
2360         if (BitCastInst *BCIn = dyn_cast<BitCastInst>(SrcCast->getOperand(0)))
2361           if (isa<VectorType>(BCIn->getOperand(0)->getType()))
2362             if (Instruction *I = optimizeVectorResize(BCIn->getOperand(0),
2363                                                cast<VectorType>(DestTy), *this))
2364               return I;
2365       }
2366 
2367       // If the input is an 'or' instruction, we may be doing shifts and ors to
2368       // assemble the elements of the vector manually.  Try to rip the code out
2369       // and replace it with insertelements.
2370       if (Value *V = optimizeIntegerToVectorInsertions(CI, *this))
2371         return replaceInstUsesWith(CI, V);
2372     }
2373   }
2374 
2375   if (VectorType *SrcVTy = dyn_cast<VectorType>(SrcTy)) {
2376     if (SrcVTy->getNumElements() == 1) {
2377       // If our destination is not a vector, then make this a straight
2378       // scalar-scalar cast.
2379       if (!DestTy->isVectorTy()) {
2380         Value *Elem =
2381           Builder.CreateExtractElement(Src,
2382                      Constant::getNullValue(Type::getInt32Ty(CI.getContext())));
2383         return CastInst::Create(Instruction::BitCast, Elem, DestTy);
2384       }
2385 
2386       // Otherwise, see if our source is an insert. If so, then use the scalar
2387       // component directly:
2388       // bitcast (inselt <1 x elt> V, X, 0) to <n x m> --> bitcast X to <n x m>
2389       if (auto *InsElt = dyn_cast<InsertElementInst>(Src))
2390         return new BitCastInst(InsElt->getOperand(1), DestTy);
2391     }
2392   }
2393 
2394   if (ShuffleVectorInst *SVI = dyn_cast<ShuffleVectorInst>(Src)) {
2395     // Okay, we have (bitcast (shuffle ..)).  Check to see if this is
2396     // a bitcast to a vector with the same # elts.
2397     if (SVI->hasOneUse() && DestTy->isVectorTy() &&
2398         DestTy->getVectorNumElements() == SVI->getType()->getNumElements() &&
2399         SVI->getType()->getNumElements() ==
2400         SVI->getOperand(0)->getType()->getVectorNumElements()) {
2401       BitCastInst *Tmp;
2402       // If either of the operands is a cast from CI.getType(), then
2403       // evaluating the shuffle in the casted destination's type will allow
2404       // us to eliminate at least one cast.
2405       if (((Tmp = dyn_cast<BitCastInst>(SVI->getOperand(0))) &&
2406            Tmp->getOperand(0)->getType() == DestTy) ||
2407           ((Tmp = dyn_cast<BitCastInst>(SVI->getOperand(1))) &&
2408            Tmp->getOperand(0)->getType() == DestTy)) {
2409         Value *LHS = Builder.CreateBitCast(SVI->getOperand(0), DestTy);
2410         Value *RHS = Builder.CreateBitCast(SVI->getOperand(1), DestTy);
2411         // Return a new shuffle vector.  Use the same element ID's, as we
2412         // know the vector types match #elts.
2413         return new ShuffleVectorInst(LHS, RHS, SVI->getOperand(2));
2414       }
2415     }
2416   }
2417 
2418   // Handle the A->B->A cast, and there is an intervening PHI node.
2419   if (PHINode *PN = dyn_cast<PHINode>(Src))
2420     if (Instruction *I = optimizeBitCastFromPhi(CI, PN))
2421       return I;
2422 
2423   if (Instruction *I = canonicalizeBitCastExtElt(CI, *this))
2424     return I;
2425 
2426   if (Instruction *I = foldBitCastBitwiseLogic(CI, Builder))
2427     return I;
2428 
2429   if (Instruction *I = foldBitCastSelect(CI, Builder))
2430     return I;
2431 
2432   if (SrcTy->isPointerTy())
2433     return commonPointerCastTransforms(CI);
2434   return commonCastTransforms(CI);
2435 }
2436 
2437 Instruction *InstCombiner::visitAddrSpaceCast(AddrSpaceCastInst &CI) {
2438   // If the destination pointer element type is not the same as the source's
2439   // first do a bitcast to the destination type, and then the addrspacecast.
2440   // This allows the cast to be exposed to other transforms.
2441   Value *Src = CI.getOperand(0);
2442   PointerType *SrcTy = cast<PointerType>(Src->getType()->getScalarType());
2443   PointerType *DestTy = cast<PointerType>(CI.getType()->getScalarType());
2444 
2445   Type *DestElemTy = DestTy->getElementType();
2446   if (SrcTy->getElementType() != DestElemTy) {
2447     Type *MidTy = PointerType::get(DestElemTy, SrcTy->getAddressSpace());
2448     if (VectorType *VT = dyn_cast<VectorType>(CI.getType())) {
2449       // Handle vectors of pointers.
2450       MidTy = VectorType::get(MidTy, VT->getNumElements());
2451     }
2452 
2453     Value *NewBitCast = Builder.CreateBitCast(Src, MidTy);
2454     return new AddrSpaceCastInst(NewBitCast, CI.getType());
2455   }
2456 
2457   return commonPointerCastTransforms(CI);
2458 }
2459