1 //===- PromoteMemoryToRegister.cpp - Convert allocas to registers ---------===//
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 promotes memory references to be register references. It promotes
10 // alloca instructions which only have loads and stores as uses. An alloca is
11 // transformed by using iterated dominator frontiers to place PHI nodes, then
12 // traversing the function in depth-first order to rewrite loads and stores as
13 // appropriate.
14 //
15 //===----------------------------------------------------------------------===//
16
17 #include "llvm/ADT/ArrayRef.h"
18 #include "llvm/ADT/DenseMap.h"
19 #include "llvm/ADT/STLExtras.h"
20 #include "llvm/ADT/SmallPtrSet.h"
21 #include "llvm/ADT/SmallVector.h"
22 #include "llvm/ADT/Statistic.h"
23 #include "llvm/ADT/Twine.h"
24 #include "llvm/Analysis/AssumptionCache.h"
25 #include "llvm/Analysis/InstructionSimplify.h"
26 #include "llvm/Analysis/IteratedDominanceFrontier.h"
27 #include "llvm/Analysis/ValueTracking.h"
28 #include "llvm/IR/BasicBlock.h"
29 #include "llvm/IR/CFG.h"
30 #include "llvm/IR/Constant.h"
31 #include "llvm/IR/Constants.h"
32 #include "llvm/IR/DIBuilder.h"
33 #include "llvm/IR/DebugInfo.h"
34 #include "llvm/IR/DebugProgramInstruction.h"
35 #include "llvm/IR/Dominators.h"
36 #include "llvm/IR/Function.h"
37 #include "llvm/IR/InstrTypes.h"
38 #include "llvm/IR/Instruction.h"
39 #include "llvm/IR/Instructions.h"
40 #include "llvm/IR/IntrinsicInst.h"
41 #include "llvm/IR/Intrinsics.h"
42 #include "llvm/IR/LLVMContext.h"
43 #include "llvm/IR/Module.h"
44 #include "llvm/IR/Operator.h"
45 #include "llvm/IR/Type.h"
46 #include "llvm/IR/User.h"
47 #include "llvm/Support/Casting.h"
48 #include "llvm/Transforms/Utils/Local.h"
49 #include "llvm/Transforms/Utils/PromoteMemToReg.h"
50 #include <algorithm>
51 #include <cassert>
52 #include <iterator>
53 #include <utility>
54 #include <vector>
55
56 using namespace llvm;
57
58 #define DEBUG_TYPE "mem2reg"
59
60 STATISTIC(NumLocalPromoted, "Number of alloca's promoted within one block");
61 STATISTIC(NumSingleStore, "Number of alloca's promoted with a single store");
62 STATISTIC(NumDeadAlloca, "Number of dead alloca's removed");
63 STATISTIC(NumPHIInsert, "Number of PHI nodes inserted");
64
isAllocaPromotable(const AllocaInst * AI)65 bool llvm::isAllocaPromotable(const AllocaInst *AI) {
66 // Only allow direct and non-volatile loads and stores...
67 for (const User *U : AI->users()) {
68 if (const LoadInst *LI = dyn_cast<LoadInst>(U)) {
69 // Note that atomic loads can be transformed; atomic semantics do
70 // not have any meaning for a local alloca.
71 if (LI->isVolatile() || LI->getType() != AI->getAllocatedType())
72 return false;
73 } else if (const StoreInst *SI = dyn_cast<StoreInst>(U)) {
74 if (SI->getValueOperand() == AI ||
75 SI->getValueOperand()->getType() != AI->getAllocatedType())
76 return false; // Don't allow a store OF the AI, only INTO the AI.
77 // Note that atomic stores can be transformed; atomic semantics do
78 // not have any meaning for a local alloca.
79 if (SI->isVolatile())
80 return false;
81 } else if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(U)) {
82 if (!II->isLifetimeStartOrEnd() && !II->isDroppable())
83 return false;
84 } else if (const BitCastInst *BCI = dyn_cast<BitCastInst>(U)) {
85 if (!onlyUsedByLifetimeMarkersOrDroppableInsts(BCI))
86 return false;
87 } else if (const GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(U)) {
88 if (!GEPI->hasAllZeroIndices())
89 return false;
90 if (!onlyUsedByLifetimeMarkersOrDroppableInsts(GEPI))
91 return false;
92 } else if (const AddrSpaceCastInst *ASCI = dyn_cast<AddrSpaceCastInst>(U)) {
93 if (!onlyUsedByLifetimeMarkers(ASCI))
94 return false;
95 } else {
96 return false;
97 }
98 }
99
100 return true;
101 }
102
103 namespace {
104
createDebugValue(DIBuilder & DIB,Value * NewValue,DILocalVariable * Variable,DIExpression * Expression,const DILocation * DI,DbgVariableRecord * InsertBefore)105 static void createDebugValue(DIBuilder &DIB, Value *NewValue,
106 DILocalVariable *Variable,
107 DIExpression *Expression, const DILocation *DI,
108 DbgVariableRecord *InsertBefore) {
109 // FIXME: Merge these two functions now that DIBuilder supports
110 // DbgVariableRecords. We neeed the API to accept DbgVariableRecords as an
111 // insert point for that to work.
112 (void)DIB;
113 DbgVariableRecord::createDbgVariableRecord(NewValue, Variable, Expression, DI,
114 *InsertBefore);
115 }
createDebugValue(DIBuilder & DIB,Value * NewValue,DILocalVariable * Variable,DIExpression * Expression,const DILocation * DI,Instruction * InsertBefore)116 static void createDebugValue(DIBuilder &DIB, Value *NewValue,
117 DILocalVariable *Variable,
118 DIExpression *Expression, const DILocation *DI,
119 Instruction *InsertBefore) {
120 DIB.insertDbgValueIntrinsic(NewValue, Variable, Expression, DI, InsertBefore);
121 }
122
123 /// Helper for updating assignment tracking debug info when promoting allocas.
124 class AssignmentTrackingInfo {
125 /// DbgAssignIntrinsics linked to the alloca with at most one per variable
126 /// fragment. (i.e. not be a comprehensive set if there are multiple
127 /// dbg.assigns for one variable fragment).
128 SmallVector<DbgVariableIntrinsic *> DbgAssigns;
129 SmallVector<DbgVariableRecord *> DVRAssigns;
130
131 public:
init(AllocaInst * AI)132 void init(AllocaInst *AI) {
133 SmallSet<DebugVariable, 2> Vars;
134 for (DbgAssignIntrinsic *DAI : at::getAssignmentMarkers(AI)) {
135 if (Vars.insert(DebugVariable(DAI)).second)
136 DbgAssigns.push_back(DAI);
137 }
138 for (DbgVariableRecord *DVR : at::getDVRAssignmentMarkers(AI)) {
139 if (Vars.insert(DebugVariable(DVR)).second)
140 DVRAssigns.push_back(DVR);
141 }
142 }
143
144 /// Update assignment tracking debug info given for the to-be-deleted store
145 /// \p ToDelete that stores to this alloca.
updateForDeletedStore(StoreInst * ToDelete,DIBuilder & DIB,SmallSet<DbgAssignIntrinsic *,8> * DbgAssignsToDelete,SmallSet<DbgVariableRecord *,8> * DVRAssignsToDelete) const146 void updateForDeletedStore(
147 StoreInst *ToDelete, DIBuilder &DIB,
148 SmallSet<DbgAssignIntrinsic *, 8> *DbgAssignsToDelete,
149 SmallSet<DbgVariableRecord *, 8> *DVRAssignsToDelete) const {
150 // There's nothing to do if the alloca doesn't have any variables using
151 // assignment tracking.
152 if (DbgAssigns.empty() && DVRAssigns.empty())
153 return;
154
155 // Insert a dbg.value where the linked dbg.assign is and remember to delete
156 // the dbg.assign later. Demoting to dbg.value isn't necessary for
157 // correctness but does reduce compile time and memory usage by reducing
158 // unnecessary function-local metadata. Remember that we've seen a
159 // dbg.assign for each variable fragment for the untracked store handling
160 // (after this loop).
161 SmallSet<DebugVariableAggregate, 2> VarHasDbgAssignForStore;
162 auto InsertValueForAssign = [&](auto *DbgAssign, auto *&AssignList) {
163 VarHasDbgAssignForStore.insert(DebugVariableAggregate(DbgAssign));
164 AssignList->insert(DbgAssign);
165 createDebugValue(DIB, DbgAssign->getValue(), DbgAssign->getVariable(),
166 DbgAssign->getExpression(), DbgAssign->getDebugLoc(),
167 DbgAssign);
168 };
169 for (auto *Assign : at::getAssignmentMarkers(ToDelete))
170 InsertValueForAssign(Assign, DbgAssignsToDelete);
171 for (auto *Assign : at::getDVRAssignmentMarkers(ToDelete))
172 InsertValueForAssign(Assign, DVRAssignsToDelete);
173
174 // It's possible for variables using assignment tracking to have no
175 // dbg.assign linked to this store. These are variables in DbgAssigns that
176 // are missing from VarHasDbgAssignForStore. Since there isn't a dbg.assign
177 // to mark the assignment - and the store is going to be deleted - insert a
178 // dbg.value to do that now. An untracked store may be either one that
179 // cannot be represented using assignment tracking (non-const offset or
180 // size) or one that is trackable but has had its DIAssignID attachment
181 // dropped accidentally.
182 auto ConvertUnlinkedAssignToValue = [&](auto *Assign) {
183 if (VarHasDbgAssignForStore.contains(DebugVariableAggregate(Assign)))
184 return;
185 ConvertDebugDeclareToDebugValue(Assign, ToDelete, DIB);
186 };
187 for_each(DbgAssigns, ConvertUnlinkedAssignToValue);
188 for_each(DVRAssigns, ConvertUnlinkedAssignToValue);
189 }
190
191 /// Update assignment tracking debug info given for the newly inserted PHI \p
192 /// NewPhi.
updateForNewPhi(PHINode * NewPhi,DIBuilder & DIB) const193 void updateForNewPhi(PHINode *NewPhi, DIBuilder &DIB) const {
194 // Regardless of the position of dbg.assigns relative to stores, the
195 // incoming values into a new PHI should be the same for the (imaginary)
196 // debug-phi.
197 for (auto *DAI : DbgAssigns)
198 ConvertDebugDeclareToDebugValue(DAI, NewPhi, DIB);
199 for (auto *DVR : DVRAssigns)
200 ConvertDebugDeclareToDebugValue(DVR, NewPhi, DIB);
201 }
202
clear()203 void clear() {
204 DbgAssigns.clear();
205 DVRAssigns.clear();
206 }
empty()207 bool empty() { return DbgAssigns.empty() && DVRAssigns.empty(); }
208 };
209
210 struct AllocaInfo {
211 using DbgUserVec = SmallVector<DbgVariableIntrinsic *, 1>;
212 using DPUserVec = SmallVector<DbgVariableRecord *, 1>;
213
214 SmallVector<BasicBlock *, 32> DefiningBlocks;
215 SmallVector<BasicBlock *, 32> UsingBlocks;
216
217 StoreInst *OnlyStore;
218 BasicBlock *OnlyBlock;
219 bool OnlyUsedInOneBlock;
220
221 /// Debug users of the alloca - does not include dbg.assign intrinsics.
222 DbgUserVec DbgUsers;
223 DPUserVec DPUsers;
224 /// Helper to update assignment tracking debug info.
225 AssignmentTrackingInfo AssignmentTracking;
226
clear__anon4233e3b50111::AllocaInfo227 void clear() {
228 DefiningBlocks.clear();
229 UsingBlocks.clear();
230 OnlyStore = nullptr;
231 OnlyBlock = nullptr;
232 OnlyUsedInOneBlock = true;
233 DbgUsers.clear();
234 DPUsers.clear();
235 AssignmentTracking.clear();
236 }
237
238 /// Scan the uses of the specified alloca, filling in the AllocaInfo used
239 /// by the rest of the pass to reason about the uses of this alloca.
AnalyzeAlloca__anon4233e3b50111::AllocaInfo240 void AnalyzeAlloca(AllocaInst *AI) {
241 clear();
242
243 // As we scan the uses of the alloca instruction, keep track of stores,
244 // and decide whether all of the loads and stores to the alloca are within
245 // the same basic block.
246 for (User *U : AI->users()) {
247 Instruction *User = cast<Instruction>(U);
248
249 if (StoreInst *SI = dyn_cast<StoreInst>(User)) {
250 // Remember the basic blocks which define new values for the alloca
251 DefiningBlocks.push_back(SI->getParent());
252 OnlyStore = SI;
253 } else {
254 LoadInst *LI = cast<LoadInst>(User);
255 // Otherwise it must be a load instruction, keep track of variable
256 // reads.
257 UsingBlocks.push_back(LI->getParent());
258 }
259
260 if (OnlyUsedInOneBlock) {
261 if (!OnlyBlock)
262 OnlyBlock = User->getParent();
263 else if (OnlyBlock != User->getParent())
264 OnlyUsedInOneBlock = false;
265 }
266 }
267 DbgUserVec AllDbgUsers;
268 SmallVector<DbgVariableRecord *> AllDPUsers;
269 findDbgUsers(AllDbgUsers, AI, &AllDPUsers);
270 std::copy_if(AllDbgUsers.begin(), AllDbgUsers.end(),
271 std::back_inserter(DbgUsers), [](DbgVariableIntrinsic *DII) {
272 return !isa<DbgAssignIntrinsic>(DII);
273 });
274 std::copy_if(AllDPUsers.begin(), AllDPUsers.end(),
275 std::back_inserter(DPUsers),
276 [](DbgVariableRecord *DVR) { return !DVR->isDbgAssign(); });
277 AssignmentTracking.init(AI);
278 }
279 };
280
281 /// Data package used by RenamePass().
282 struct RenamePassData {
283 using ValVector = std::vector<Value *>;
284 using LocationVector = std::vector<DebugLoc>;
285
RenamePassData__anon4233e3b50111::RenamePassData286 RenamePassData(BasicBlock *B, BasicBlock *P, ValVector V, LocationVector L)
287 : BB(B), Pred(P), Values(std::move(V)), Locations(std::move(L)) {}
288
289 BasicBlock *BB;
290 BasicBlock *Pred;
291 ValVector Values;
292 LocationVector Locations;
293 };
294
295 /// This assigns and keeps a per-bb relative ordering of load/store
296 /// instructions in the block that directly load or store an alloca.
297 ///
298 /// This functionality is important because it avoids scanning large basic
299 /// blocks multiple times when promoting many allocas in the same block.
300 class LargeBlockInfo {
301 /// For each instruction that we track, keep the index of the
302 /// instruction.
303 ///
304 /// The index starts out as the number of the instruction from the start of
305 /// the block.
306 DenseMap<const Instruction *, unsigned> InstNumbers;
307
308 public:
309
310 /// This code only looks at accesses to allocas.
isInterestingInstruction(const Instruction * I)311 static bool isInterestingInstruction(const Instruction *I) {
312 return (isa<LoadInst>(I) && isa<AllocaInst>(I->getOperand(0))) ||
313 (isa<StoreInst>(I) && isa<AllocaInst>(I->getOperand(1)));
314 }
315
316 /// Get or calculate the index of the specified instruction.
getInstructionIndex(const Instruction * I)317 unsigned getInstructionIndex(const Instruction *I) {
318 assert(isInterestingInstruction(I) &&
319 "Not a load/store to/from an alloca?");
320
321 // If we already have this instruction number, return it.
322 DenseMap<const Instruction *, unsigned>::iterator It = InstNumbers.find(I);
323 if (It != InstNumbers.end())
324 return It->second;
325
326 // Scan the whole block to get the instruction. This accumulates
327 // information for every interesting instruction in the block, in order to
328 // avoid gratuitus rescans.
329 const BasicBlock *BB = I->getParent();
330 unsigned InstNo = 0;
331 for (const Instruction &BBI : *BB)
332 if (isInterestingInstruction(&BBI))
333 InstNumbers[&BBI] = InstNo++;
334 It = InstNumbers.find(I);
335
336 assert(It != InstNumbers.end() && "Didn't insert instruction?");
337 return It->second;
338 }
339
deleteValue(const Instruction * I)340 void deleteValue(const Instruction *I) { InstNumbers.erase(I); }
341
clear()342 void clear() { InstNumbers.clear(); }
343 };
344
345 struct PromoteMem2Reg {
346 /// The alloca instructions being promoted.
347 std::vector<AllocaInst *> Allocas;
348
349 DominatorTree &DT;
350 DIBuilder DIB;
351
352 /// A cache of @llvm.assume intrinsics used by SimplifyInstruction.
353 AssumptionCache *AC;
354
355 const SimplifyQuery SQ;
356
357 /// Reverse mapping of Allocas.
358 DenseMap<AllocaInst *, unsigned> AllocaLookup;
359
360 /// The PhiNodes we're adding.
361 ///
362 /// That map is used to simplify some Phi nodes as we iterate over it, so
363 /// it should have deterministic iterators. We could use a MapVector, but
364 /// since we already maintain a map from BasicBlock* to a stable numbering
365 /// (BBNumbers), the DenseMap is more efficient (also supports removal).
366 DenseMap<std::pair<unsigned, unsigned>, PHINode *> NewPhiNodes;
367
368 /// For each PHI node, keep track of which entry in Allocas it corresponds
369 /// to.
370 DenseMap<PHINode *, unsigned> PhiToAllocaMap;
371
372 /// For each alloca, we keep track of the dbg.declare intrinsic that
373 /// describes it, if any, so that we can convert it to a dbg.value
374 /// intrinsic if the alloca gets promoted.
375 SmallVector<AllocaInfo::DbgUserVec, 8> AllocaDbgUsers;
376 SmallVector<AllocaInfo::DPUserVec, 8> AllocaDPUsers;
377
378 /// For each alloca, keep an instance of a helper class that gives us an easy
379 /// way to update assignment tracking debug info if the alloca is promoted.
380 SmallVector<AssignmentTrackingInfo, 8> AllocaATInfo;
381 /// A set of dbg.assigns to delete because they've been demoted to
382 /// dbg.values. Call cleanUpDbgAssigns to delete them.
383 SmallSet<DbgAssignIntrinsic *, 8> DbgAssignsToDelete;
384 SmallSet<DbgVariableRecord *, 8> DVRAssignsToDelete;
385
386 /// The set of basic blocks the renamer has already visited.
387 SmallPtrSet<BasicBlock *, 16> Visited;
388
389 /// Contains a stable numbering of basic blocks to avoid non-determinstic
390 /// behavior.
391 DenseMap<BasicBlock *, unsigned> BBNumbers;
392
393 /// Lazily compute the number of predecessors a block has.
394 DenseMap<const BasicBlock *, unsigned> BBNumPreds;
395
396 /// Whether the function has the no-signed-zeros-fp-math attribute set.
397 bool NoSignedZeros = false;
398
399 public:
PromoteMem2Reg__anon4233e3b50111::PromoteMem2Reg400 PromoteMem2Reg(ArrayRef<AllocaInst *> Allocas, DominatorTree &DT,
401 AssumptionCache *AC)
402 : Allocas(Allocas.begin(), Allocas.end()), DT(DT),
403 DIB(*DT.getRoot()->getParent()->getParent(), /*AllowUnresolved*/ false),
404 AC(AC), SQ(DT.getRoot()->getDataLayout(),
405 nullptr, &DT, AC) {}
406
407 void run();
408
409 private:
RemoveFromAllocasList__anon4233e3b50111::PromoteMem2Reg410 void RemoveFromAllocasList(unsigned &AllocaIdx) {
411 Allocas[AllocaIdx] = Allocas.back();
412 Allocas.pop_back();
413 --AllocaIdx;
414 }
415
getNumPreds__anon4233e3b50111::PromoteMem2Reg416 unsigned getNumPreds(const BasicBlock *BB) {
417 unsigned &NP = BBNumPreds[BB];
418 if (NP == 0)
419 NP = pred_size(BB) + 1;
420 return NP - 1;
421 }
422
423 void ComputeLiveInBlocks(AllocaInst *AI, AllocaInfo &Info,
424 const SmallPtrSetImpl<BasicBlock *> &DefBlocks,
425 SmallPtrSetImpl<BasicBlock *> &LiveInBlocks);
426 void RenamePass(BasicBlock *BB, BasicBlock *Pred,
427 RenamePassData::ValVector &IncVals,
428 RenamePassData::LocationVector &IncLocs,
429 std::vector<RenamePassData> &Worklist);
430 bool QueuePhiNode(BasicBlock *BB, unsigned AllocaIdx, unsigned &Version);
431
432 /// Delete dbg.assigns that have been demoted to dbg.values.
cleanUpDbgAssigns__anon4233e3b50111::PromoteMem2Reg433 void cleanUpDbgAssigns() {
434 for (auto *DAI : DbgAssignsToDelete)
435 DAI->eraseFromParent();
436 DbgAssignsToDelete.clear();
437 for (auto *DVR : DVRAssignsToDelete)
438 DVR->eraseFromParent();
439 DVRAssignsToDelete.clear();
440 }
441 };
442
443 } // end anonymous namespace
444
445 /// Given a LoadInst LI this adds assume(LI != null) after it.
addAssumeNonNull(AssumptionCache * AC,LoadInst * LI)446 static void addAssumeNonNull(AssumptionCache *AC, LoadInst *LI) {
447 Function *AssumeIntrinsic =
448 Intrinsic::getDeclaration(LI->getModule(), Intrinsic::assume);
449 ICmpInst *LoadNotNull = new ICmpInst(ICmpInst::ICMP_NE, LI,
450 Constant::getNullValue(LI->getType()));
451 LoadNotNull->insertAfter(LI);
452 CallInst *CI = CallInst::Create(AssumeIntrinsic, {LoadNotNull});
453 CI->insertAfter(LoadNotNull);
454 AC->registerAssumption(cast<AssumeInst>(CI));
455 }
456
convertMetadataToAssumes(LoadInst * LI,Value * Val,const DataLayout & DL,AssumptionCache * AC,const DominatorTree * DT)457 static void convertMetadataToAssumes(LoadInst *LI, Value *Val,
458 const DataLayout &DL, AssumptionCache *AC,
459 const DominatorTree *DT) {
460 if (isa<UndefValue>(Val) && LI->hasMetadata(LLVMContext::MD_noundef)) {
461 // Insert non-terminator unreachable.
462 LLVMContext &Ctx = LI->getContext();
463 new StoreInst(ConstantInt::getTrue(Ctx),
464 PoisonValue::get(PointerType::getUnqual(Ctx)),
465 /*isVolatile=*/false, Align(1), LI);
466 return;
467 }
468
469 // If the load was marked as nonnull we don't want to lose that information
470 // when we erase this Load. So we preserve it with an assume. As !nonnull
471 // returns poison while assume violations are immediate undefined behavior,
472 // we can only do this if the value is known non-poison.
473 if (AC && LI->getMetadata(LLVMContext::MD_nonnull) &&
474 LI->getMetadata(LLVMContext::MD_noundef) &&
475 !isKnownNonZero(Val, SimplifyQuery(DL, DT, AC, LI)))
476 addAssumeNonNull(AC, LI);
477 }
478
removeIntrinsicUsers(AllocaInst * AI)479 static void removeIntrinsicUsers(AllocaInst *AI) {
480 // Knowing that this alloca is promotable, we know that it's safe to kill all
481 // instructions except for load and store.
482
483 for (Use &U : llvm::make_early_inc_range(AI->uses())) {
484 Instruction *I = cast<Instruction>(U.getUser());
485 if (isa<LoadInst>(I) || isa<StoreInst>(I))
486 continue;
487
488 // Drop the use of AI in droppable instructions.
489 if (I->isDroppable()) {
490 I->dropDroppableUse(U);
491 continue;
492 }
493
494 if (!I->getType()->isVoidTy()) {
495 // The only users of this bitcast/GEP instruction are lifetime intrinsics.
496 // Follow the use/def chain to erase them now instead of leaving it for
497 // dead code elimination later.
498 for (Use &UU : llvm::make_early_inc_range(I->uses())) {
499 Instruction *Inst = cast<Instruction>(UU.getUser());
500
501 // Drop the use of I in droppable instructions.
502 if (Inst->isDroppable()) {
503 Inst->dropDroppableUse(UU);
504 continue;
505 }
506 Inst->eraseFromParent();
507 }
508 }
509 I->eraseFromParent();
510 }
511 }
512
513 /// Rewrite as many loads as possible given a single store.
514 ///
515 /// When there is only a single store, we can use the domtree to trivially
516 /// replace all of the dominated loads with the stored value. Do so, and return
517 /// true if this has successfully promoted the alloca entirely. If this returns
518 /// false there were some loads which were not dominated by the single store
519 /// and thus must be phi-ed with undef. We fall back to the standard alloca
520 /// promotion algorithm in that case.
521 static bool
rewriteSingleStoreAlloca(AllocaInst * AI,AllocaInfo & Info,LargeBlockInfo & LBI,const DataLayout & DL,DominatorTree & DT,AssumptionCache * AC,SmallSet<DbgAssignIntrinsic *,8> * DbgAssignsToDelete,SmallSet<DbgVariableRecord *,8> * DVRAssignsToDelete)522 rewriteSingleStoreAlloca(AllocaInst *AI, AllocaInfo &Info, LargeBlockInfo &LBI,
523 const DataLayout &DL, DominatorTree &DT,
524 AssumptionCache *AC,
525 SmallSet<DbgAssignIntrinsic *, 8> *DbgAssignsToDelete,
526 SmallSet<DbgVariableRecord *, 8> *DVRAssignsToDelete) {
527 StoreInst *OnlyStore = Info.OnlyStore;
528 Value *ReplVal = OnlyStore->getOperand(0);
529 // Loads may either load the stored value or uninitialized memory (undef).
530 // If the stored value may be poison, then replacing an uninitialized memory
531 // load with it would be incorrect. If the store dominates the load, we know
532 // it is always initialized.
533 bool RequireDominatingStore =
534 isa<Instruction>(ReplVal) || !isGuaranteedNotToBePoison(ReplVal);
535 BasicBlock *StoreBB = OnlyStore->getParent();
536 int StoreIndex = -1;
537
538 // Clear out UsingBlocks. We will reconstruct it here if needed.
539 Info.UsingBlocks.clear();
540
541 for (User *U : make_early_inc_range(AI->users())) {
542 Instruction *UserInst = cast<Instruction>(U);
543 if (UserInst == OnlyStore)
544 continue;
545 LoadInst *LI = cast<LoadInst>(UserInst);
546
547 // Okay, if we have a load from the alloca, we want to replace it with the
548 // only value stored to the alloca. We can do this if the value is
549 // dominated by the store. If not, we use the rest of the mem2reg machinery
550 // to insert the phi nodes as needed.
551 if (RequireDominatingStore) {
552 if (LI->getParent() == StoreBB) {
553 // If we have a use that is in the same block as the store, compare the
554 // indices of the two instructions to see which one came first. If the
555 // load came before the store, we can't handle it.
556 if (StoreIndex == -1)
557 StoreIndex = LBI.getInstructionIndex(OnlyStore);
558
559 if (unsigned(StoreIndex) > LBI.getInstructionIndex(LI)) {
560 // Can't handle this load, bail out.
561 Info.UsingBlocks.push_back(StoreBB);
562 continue;
563 }
564 } else if (!DT.dominates(StoreBB, LI->getParent())) {
565 // If the load and store are in different blocks, use BB dominance to
566 // check their relationships. If the store doesn't dom the use, bail
567 // out.
568 Info.UsingBlocks.push_back(LI->getParent());
569 continue;
570 }
571 }
572
573 // Otherwise, we *can* safely rewrite this load.
574 // If the replacement value is the load, this must occur in unreachable
575 // code.
576 if (ReplVal == LI)
577 ReplVal = PoisonValue::get(LI->getType());
578
579 convertMetadataToAssumes(LI, ReplVal, DL, AC, &DT);
580 LI->replaceAllUsesWith(ReplVal);
581 LI->eraseFromParent();
582 LBI.deleteValue(LI);
583 }
584
585 // Finally, after the scan, check to see if the store is all that is left.
586 if (!Info.UsingBlocks.empty())
587 return false; // If not, we'll have to fall back for the remainder.
588
589 DIBuilder DIB(*AI->getModule(), /*AllowUnresolved*/ false);
590 // Update assignment tracking info for the store we're going to delete.
591 Info.AssignmentTracking.updateForDeletedStore(
592 Info.OnlyStore, DIB, DbgAssignsToDelete, DVRAssignsToDelete);
593
594 // Record debuginfo for the store and remove the declaration's
595 // debuginfo.
596 auto ConvertDebugInfoForStore = [&](auto &Container) {
597 for (auto *DbgItem : Container) {
598 if (DbgItem->isAddressOfVariable()) {
599 ConvertDebugDeclareToDebugValue(DbgItem, Info.OnlyStore, DIB);
600 DbgItem->eraseFromParent();
601 } else if (DbgItem->getExpression()->startsWithDeref()) {
602 DbgItem->eraseFromParent();
603 }
604 }
605 };
606 ConvertDebugInfoForStore(Info.DbgUsers);
607 ConvertDebugInfoForStore(Info.DPUsers);
608
609 // Remove dbg.assigns linked to the alloca as these are now redundant.
610 at::deleteAssignmentMarkers(AI);
611
612 // Remove the (now dead) store and alloca.
613 Info.OnlyStore->eraseFromParent();
614 LBI.deleteValue(Info.OnlyStore);
615
616 AI->eraseFromParent();
617 return true;
618 }
619
620 /// Many allocas are only used within a single basic block. If this is the
621 /// case, avoid traversing the CFG and inserting a lot of potentially useless
622 /// PHI nodes by just performing a single linear pass over the basic block
623 /// using the Alloca.
624 ///
625 /// If we cannot promote this alloca (because it is read before it is written),
626 /// return false. This is necessary in cases where, due to control flow, the
627 /// alloca is undefined only on some control flow paths. e.g. code like
628 /// this is correct in LLVM IR:
629 /// // A is an alloca with no stores so far
630 /// for (...) {
631 /// int t = *A;
632 /// if (!first_iteration)
633 /// use(t);
634 /// *A = 42;
635 /// }
636 static bool
promoteSingleBlockAlloca(AllocaInst * AI,const AllocaInfo & Info,LargeBlockInfo & LBI,const DataLayout & DL,DominatorTree & DT,AssumptionCache * AC,SmallSet<DbgAssignIntrinsic *,8> * DbgAssignsToDelete,SmallSet<DbgVariableRecord *,8> * DVRAssignsToDelete)637 promoteSingleBlockAlloca(AllocaInst *AI, const AllocaInfo &Info,
638 LargeBlockInfo &LBI, const DataLayout &DL,
639 DominatorTree &DT, AssumptionCache *AC,
640 SmallSet<DbgAssignIntrinsic *, 8> *DbgAssignsToDelete,
641 SmallSet<DbgVariableRecord *, 8> *DVRAssignsToDelete) {
642 // The trickiest case to handle is when we have large blocks. Because of this,
643 // this code is optimized assuming that large blocks happen. This does not
644 // significantly pessimize the small block case. This uses LargeBlockInfo to
645 // make it efficient to get the index of various operations in the block.
646
647 // Walk the use-def list of the alloca, getting the locations of all stores.
648 using StoresByIndexTy = SmallVector<std::pair<unsigned, StoreInst *>, 64>;
649 StoresByIndexTy StoresByIndex;
650
651 for (User *U : AI->users())
652 if (StoreInst *SI = dyn_cast<StoreInst>(U))
653 StoresByIndex.push_back(std::make_pair(LBI.getInstructionIndex(SI), SI));
654
655 // Sort the stores by their index, making it efficient to do a lookup with a
656 // binary search.
657 llvm::sort(StoresByIndex, less_first());
658
659 // Walk all of the loads from this alloca, replacing them with the nearest
660 // store above them, if any.
661 for (User *U : make_early_inc_range(AI->users())) {
662 LoadInst *LI = dyn_cast<LoadInst>(U);
663 if (!LI)
664 continue;
665
666 unsigned LoadIdx = LBI.getInstructionIndex(LI);
667
668 // Find the nearest store that has a lower index than this load.
669 StoresByIndexTy::iterator I = llvm::lower_bound(
670 StoresByIndex,
671 std::make_pair(LoadIdx, static_cast<StoreInst *>(nullptr)),
672 less_first());
673 Value *ReplVal;
674 if (I == StoresByIndex.begin()) {
675 if (StoresByIndex.empty())
676 // If there are no stores, the load takes the undef value.
677 ReplVal = UndefValue::get(LI->getType());
678 else
679 // There is no store before this load, bail out (load may be affected
680 // by the following stores - see main comment).
681 return false;
682 } else {
683 // Otherwise, there was a store before this load, the load takes its
684 // value.
685 ReplVal = std::prev(I)->second->getOperand(0);
686 }
687
688 convertMetadataToAssumes(LI, ReplVal, DL, AC, &DT);
689
690 // If the replacement value is the load, this must occur in unreachable
691 // code.
692 if (ReplVal == LI)
693 ReplVal = PoisonValue::get(LI->getType());
694
695 LI->replaceAllUsesWith(ReplVal);
696 LI->eraseFromParent();
697 LBI.deleteValue(LI);
698 }
699
700 // Remove the (now dead) stores and alloca.
701 DIBuilder DIB(*AI->getModule(), /*AllowUnresolved*/ false);
702 while (!AI->use_empty()) {
703 StoreInst *SI = cast<StoreInst>(AI->user_back());
704 // Update assignment tracking info for the store we're going to delete.
705 Info.AssignmentTracking.updateForDeletedStore(SI, DIB, DbgAssignsToDelete,
706 DVRAssignsToDelete);
707 // Record debuginfo for the store before removing it.
708 auto DbgUpdateForStore = [&](auto &Container) {
709 for (auto *DbgItem : Container) {
710 if (DbgItem->isAddressOfVariable()) {
711 ConvertDebugDeclareToDebugValue(DbgItem, SI, DIB);
712 }
713 }
714 };
715 DbgUpdateForStore(Info.DbgUsers);
716 DbgUpdateForStore(Info.DPUsers);
717
718 SI->eraseFromParent();
719 LBI.deleteValue(SI);
720 }
721
722 // Remove dbg.assigns linked to the alloca as these are now redundant.
723 at::deleteAssignmentMarkers(AI);
724 AI->eraseFromParent();
725
726 // The alloca's debuginfo can be removed as well.
727 auto DbgUpdateForAlloca = [&](auto &Container) {
728 for (auto *DbgItem : Container)
729 if (DbgItem->isAddressOfVariable() ||
730 DbgItem->getExpression()->startsWithDeref())
731 DbgItem->eraseFromParent();
732 };
733 DbgUpdateForAlloca(Info.DbgUsers);
734 DbgUpdateForAlloca(Info.DPUsers);
735
736 ++NumLocalPromoted;
737 return true;
738 }
739
run()740 void PromoteMem2Reg::run() {
741 Function &F = *DT.getRoot()->getParent();
742
743 AllocaDbgUsers.resize(Allocas.size());
744 AllocaATInfo.resize(Allocas.size());
745 AllocaDPUsers.resize(Allocas.size());
746
747 AllocaInfo Info;
748 LargeBlockInfo LBI;
749 ForwardIDFCalculator IDF(DT);
750
751 NoSignedZeros = F.getFnAttribute("no-signed-zeros-fp-math").getValueAsBool();
752
753 for (unsigned AllocaNum = 0; AllocaNum != Allocas.size(); ++AllocaNum) {
754 AllocaInst *AI = Allocas[AllocaNum];
755
756 assert(isAllocaPromotable(AI) && "Cannot promote non-promotable alloca!");
757 assert(AI->getParent()->getParent() == &F &&
758 "All allocas should be in the same function, which is same as DF!");
759
760 removeIntrinsicUsers(AI);
761
762 if (AI->use_empty()) {
763 // If there are no uses of the alloca, just delete it now.
764 AI->eraseFromParent();
765
766 // Remove the alloca from the Allocas list, since it has been processed
767 RemoveFromAllocasList(AllocaNum);
768 ++NumDeadAlloca;
769 continue;
770 }
771
772 // Calculate the set of read and write-locations for each alloca. This is
773 // analogous to finding the 'uses' and 'definitions' of each variable.
774 Info.AnalyzeAlloca(AI);
775
776 // If there is only a single store to this value, replace any loads of
777 // it that are directly dominated by the definition with the value stored.
778 if (Info.DefiningBlocks.size() == 1) {
779 if (rewriteSingleStoreAlloca(AI, Info, LBI, SQ.DL, DT, AC,
780 &DbgAssignsToDelete, &DVRAssignsToDelete)) {
781 // The alloca has been processed, move on.
782 RemoveFromAllocasList(AllocaNum);
783 ++NumSingleStore;
784 continue;
785 }
786 }
787
788 // If the alloca is only read and written in one basic block, just perform a
789 // linear sweep over the block to eliminate it.
790 if (Info.OnlyUsedInOneBlock &&
791 promoteSingleBlockAlloca(AI, Info, LBI, SQ.DL, DT, AC,
792 &DbgAssignsToDelete, &DVRAssignsToDelete)) {
793 // The alloca has been processed, move on.
794 RemoveFromAllocasList(AllocaNum);
795 continue;
796 }
797
798 // If we haven't computed a numbering for the BB's in the function, do so
799 // now.
800 if (BBNumbers.empty()) {
801 unsigned ID = 0;
802 for (auto &BB : F)
803 BBNumbers[&BB] = ID++;
804 }
805
806 // Remember the dbg.declare intrinsic describing this alloca, if any.
807 if (!Info.DbgUsers.empty())
808 AllocaDbgUsers[AllocaNum] = Info.DbgUsers;
809 if (!Info.AssignmentTracking.empty())
810 AllocaATInfo[AllocaNum] = Info.AssignmentTracking;
811 if (!Info.DPUsers.empty())
812 AllocaDPUsers[AllocaNum] = Info.DPUsers;
813
814 // Keep the reverse mapping of the 'Allocas' array for the rename pass.
815 AllocaLookup[Allocas[AllocaNum]] = AllocaNum;
816
817 // Unique the set of defining blocks for efficient lookup.
818 SmallPtrSet<BasicBlock *, 32> DefBlocks(Info.DefiningBlocks.begin(),
819 Info.DefiningBlocks.end());
820
821 // Determine which blocks the value is live in. These are blocks which lead
822 // to uses.
823 SmallPtrSet<BasicBlock *, 32> LiveInBlocks;
824 ComputeLiveInBlocks(AI, Info, DefBlocks, LiveInBlocks);
825
826 // At this point, we're committed to promoting the alloca using IDF's, and
827 // the standard SSA construction algorithm. Determine which blocks need phi
828 // nodes and see if we can optimize out some work by avoiding insertion of
829 // dead phi nodes.
830 IDF.setLiveInBlocks(LiveInBlocks);
831 IDF.setDefiningBlocks(DefBlocks);
832 SmallVector<BasicBlock *, 32> PHIBlocks;
833 IDF.calculate(PHIBlocks);
834 llvm::sort(PHIBlocks, [this](BasicBlock *A, BasicBlock *B) {
835 return BBNumbers.find(A)->second < BBNumbers.find(B)->second;
836 });
837
838 unsigned CurrentVersion = 0;
839 for (BasicBlock *BB : PHIBlocks)
840 QueuePhiNode(BB, AllocaNum, CurrentVersion);
841 }
842
843 if (Allocas.empty()) {
844 cleanUpDbgAssigns();
845 return; // All of the allocas must have been trivial!
846 }
847 LBI.clear();
848
849 // Set the incoming values for the basic block to be null values for all of
850 // the alloca's. We do this in case there is a load of a value that has not
851 // been stored yet. In this case, it will get this null value.
852 RenamePassData::ValVector Values(Allocas.size());
853 for (unsigned i = 0, e = Allocas.size(); i != e; ++i)
854 Values[i] = UndefValue::get(Allocas[i]->getAllocatedType());
855
856 // When handling debug info, treat all incoming values as if they have unknown
857 // locations until proven otherwise.
858 RenamePassData::LocationVector Locations(Allocas.size());
859
860 // Walks all basic blocks in the function performing the SSA rename algorithm
861 // and inserting the phi nodes we marked as necessary
862 std::vector<RenamePassData> RenamePassWorkList;
863 RenamePassWorkList.emplace_back(&F.front(), nullptr, std::move(Values),
864 std::move(Locations));
865 do {
866 RenamePassData RPD = std::move(RenamePassWorkList.back());
867 RenamePassWorkList.pop_back();
868 // RenamePass may add new worklist entries.
869 RenamePass(RPD.BB, RPD.Pred, RPD.Values, RPD.Locations, RenamePassWorkList);
870 } while (!RenamePassWorkList.empty());
871
872 // The renamer uses the Visited set to avoid infinite loops. Clear it now.
873 Visited.clear();
874
875 // Remove the allocas themselves from the function.
876 for (Instruction *A : Allocas) {
877 // Remove dbg.assigns linked to the alloca as these are now redundant.
878 at::deleteAssignmentMarkers(A);
879 // If there are any uses of the alloca instructions left, they must be in
880 // unreachable basic blocks that were not processed by walking the dominator
881 // tree. Just delete the users now.
882 if (!A->use_empty())
883 A->replaceAllUsesWith(PoisonValue::get(A->getType()));
884 A->eraseFromParent();
885 }
886
887 // Remove alloca's dbg.declare intrinsics from the function.
888 auto RemoveDbgDeclares = [&](auto &Container) {
889 for (auto &DbgUsers : Container) {
890 for (auto *DbgItem : DbgUsers)
891 if (DbgItem->isAddressOfVariable() ||
892 DbgItem->getExpression()->startsWithDeref())
893 DbgItem->eraseFromParent();
894 }
895 };
896 RemoveDbgDeclares(AllocaDbgUsers);
897 RemoveDbgDeclares(AllocaDPUsers);
898
899 // Loop over all of the PHI nodes and see if there are any that we can get
900 // rid of because they merge all of the same incoming values. This can
901 // happen due to undef values coming into the PHI nodes. This process is
902 // iterative, because eliminating one PHI node can cause others to be removed.
903 bool EliminatedAPHI = true;
904 while (EliminatedAPHI) {
905 EliminatedAPHI = false;
906
907 // Iterating over NewPhiNodes is deterministic, so it is safe to try to
908 // simplify and RAUW them as we go. If it was not, we could add uses to
909 // the values we replace with in a non-deterministic order, thus creating
910 // non-deterministic def->use chains.
911 for (DenseMap<std::pair<unsigned, unsigned>, PHINode *>::iterator
912 I = NewPhiNodes.begin(),
913 E = NewPhiNodes.end();
914 I != E;) {
915 PHINode *PN = I->second;
916
917 // If this PHI node merges one value and/or undefs, get the value.
918 if (Value *V = simplifyInstruction(PN, SQ)) {
919 PN->replaceAllUsesWith(V);
920 PN->eraseFromParent();
921 NewPhiNodes.erase(I++);
922 EliminatedAPHI = true;
923 continue;
924 }
925 ++I;
926 }
927 }
928
929 // At this point, the renamer has added entries to PHI nodes for all reachable
930 // code. Unfortunately, there may be unreachable blocks which the renamer
931 // hasn't traversed. If this is the case, the PHI nodes may not
932 // have incoming values for all predecessors. Loop over all PHI nodes we have
933 // created, inserting poison values if they are missing any incoming values.
934 for (DenseMap<std::pair<unsigned, unsigned>, PHINode *>::iterator
935 I = NewPhiNodes.begin(),
936 E = NewPhiNodes.end();
937 I != E; ++I) {
938 // We want to do this once per basic block. As such, only process a block
939 // when we find the PHI that is the first entry in the block.
940 PHINode *SomePHI = I->second;
941 BasicBlock *BB = SomePHI->getParent();
942 if (&BB->front() != SomePHI)
943 continue;
944
945 // Only do work here if there the PHI nodes are missing incoming values. We
946 // know that all PHI nodes that were inserted in a block will have the same
947 // number of incoming values, so we can just check any of them.
948 if (SomePHI->getNumIncomingValues() == getNumPreds(BB))
949 continue;
950
951 // Get the preds for BB.
952 SmallVector<BasicBlock *, 16> Preds(predecessors(BB));
953
954 // Ok, now we know that all of the PHI nodes are missing entries for some
955 // basic blocks. Start by sorting the incoming predecessors for efficient
956 // access.
957 auto CompareBBNumbers = [this](BasicBlock *A, BasicBlock *B) {
958 return BBNumbers.find(A)->second < BBNumbers.find(B)->second;
959 };
960 llvm::sort(Preds, CompareBBNumbers);
961
962 // Now we loop through all BB's which have entries in SomePHI and remove
963 // them from the Preds list.
964 for (unsigned i = 0, e = SomePHI->getNumIncomingValues(); i != e; ++i) {
965 // Do a log(n) search of the Preds list for the entry we want.
966 SmallVectorImpl<BasicBlock *>::iterator EntIt = llvm::lower_bound(
967 Preds, SomePHI->getIncomingBlock(i), CompareBBNumbers);
968 assert(EntIt != Preds.end() && *EntIt == SomePHI->getIncomingBlock(i) &&
969 "PHI node has entry for a block which is not a predecessor!");
970
971 // Remove the entry
972 Preds.erase(EntIt);
973 }
974
975 // At this point, the blocks left in the preds list must have dummy
976 // entries inserted into every PHI nodes for the block. Update all the phi
977 // nodes in this block that we are inserting (there could be phis before
978 // mem2reg runs).
979 unsigned NumBadPreds = SomePHI->getNumIncomingValues();
980 BasicBlock::iterator BBI = BB->begin();
981 while ((SomePHI = dyn_cast<PHINode>(BBI++)) &&
982 SomePHI->getNumIncomingValues() == NumBadPreds) {
983 Value *PoisonVal = PoisonValue::get(SomePHI->getType());
984 for (BasicBlock *Pred : Preds)
985 SomePHI->addIncoming(PoisonVal, Pred);
986 }
987 }
988
989 NewPhiNodes.clear();
990 cleanUpDbgAssigns();
991 }
992
993 /// Determine which blocks the value is live in.
994 ///
995 /// These are blocks which lead to uses. Knowing this allows us to avoid
996 /// inserting PHI nodes into blocks which don't lead to uses (thus, the
997 /// inserted phi nodes would be dead).
ComputeLiveInBlocks(AllocaInst * AI,AllocaInfo & Info,const SmallPtrSetImpl<BasicBlock * > & DefBlocks,SmallPtrSetImpl<BasicBlock * > & LiveInBlocks)998 void PromoteMem2Reg::ComputeLiveInBlocks(
999 AllocaInst *AI, AllocaInfo &Info,
1000 const SmallPtrSetImpl<BasicBlock *> &DefBlocks,
1001 SmallPtrSetImpl<BasicBlock *> &LiveInBlocks) {
1002 // To determine liveness, we must iterate through the predecessors of blocks
1003 // where the def is live. Blocks are added to the worklist if we need to
1004 // check their predecessors. Start with all the using blocks.
1005 SmallVector<BasicBlock *, 64> LiveInBlockWorklist(Info.UsingBlocks.begin(),
1006 Info.UsingBlocks.end());
1007
1008 // If any of the using blocks is also a definition block, check to see if the
1009 // definition occurs before or after the use. If it happens before the use,
1010 // the value isn't really live-in.
1011 for (unsigned i = 0, e = LiveInBlockWorklist.size(); i != e; ++i) {
1012 BasicBlock *BB = LiveInBlockWorklist[i];
1013 if (!DefBlocks.count(BB))
1014 continue;
1015
1016 // Okay, this is a block that both uses and defines the value. If the first
1017 // reference to the alloca is a def (store), then we know it isn't live-in.
1018 for (BasicBlock::iterator I = BB->begin();; ++I) {
1019 if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
1020 if (SI->getOperand(1) != AI)
1021 continue;
1022
1023 // We found a store to the alloca before a load. The alloca is not
1024 // actually live-in here.
1025 LiveInBlockWorklist[i] = LiveInBlockWorklist.back();
1026 LiveInBlockWorklist.pop_back();
1027 --i;
1028 --e;
1029 break;
1030 }
1031
1032 if (LoadInst *LI = dyn_cast<LoadInst>(I))
1033 // Okay, we found a load before a store to the alloca. It is actually
1034 // live into this block.
1035 if (LI->getOperand(0) == AI)
1036 break;
1037 }
1038 }
1039
1040 // Now that we have a set of blocks where the phi is live-in, recursively add
1041 // their predecessors until we find the full region the value is live.
1042 while (!LiveInBlockWorklist.empty()) {
1043 BasicBlock *BB = LiveInBlockWorklist.pop_back_val();
1044
1045 // The block really is live in here, insert it into the set. If already in
1046 // the set, then it has already been processed.
1047 if (!LiveInBlocks.insert(BB).second)
1048 continue;
1049
1050 // Since the value is live into BB, it is either defined in a predecessor or
1051 // live into it to. Add the preds to the worklist unless they are a
1052 // defining block.
1053 for (BasicBlock *P : predecessors(BB)) {
1054 // The value is not live into a predecessor if it defines the value.
1055 if (DefBlocks.count(P))
1056 continue;
1057
1058 // Otherwise it is, add to the worklist.
1059 LiveInBlockWorklist.push_back(P);
1060 }
1061 }
1062 }
1063
1064 /// Queue a phi-node to be added to a basic-block for a specific Alloca.
1065 ///
1066 /// Returns true if there wasn't already a phi-node for that variable
QueuePhiNode(BasicBlock * BB,unsigned AllocaNo,unsigned & Version)1067 bool PromoteMem2Reg::QueuePhiNode(BasicBlock *BB, unsigned AllocaNo,
1068 unsigned &Version) {
1069 // Look up the basic-block in question.
1070 PHINode *&PN = NewPhiNodes[std::make_pair(BBNumbers[BB], AllocaNo)];
1071
1072 // If the BB already has a phi node added for the i'th alloca then we're done!
1073 if (PN)
1074 return false;
1075
1076 // Create a PhiNode using the dereferenced type... and add the phi-node to the
1077 // BasicBlock.
1078 PN = PHINode::Create(Allocas[AllocaNo]->getAllocatedType(), getNumPreds(BB),
1079 Allocas[AllocaNo]->getName() + "." + Twine(Version++));
1080 PN->insertBefore(BB->begin());
1081 ++NumPHIInsert;
1082 PhiToAllocaMap[PN] = AllocaNo;
1083 return true;
1084 }
1085
1086 /// Update the debug location of a phi. \p ApplyMergedLoc indicates whether to
1087 /// create a merged location incorporating \p DL, or to set \p DL directly.
updateForIncomingValueLocation(PHINode * PN,DebugLoc DL,bool ApplyMergedLoc)1088 static void updateForIncomingValueLocation(PHINode *PN, DebugLoc DL,
1089 bool ApplyMergedLoc) {
1090 if (ApplyMergedLoc)
1091 PN->applyMergedLocation(PN->getDebugLoc(), DL);
1092 else
1093 PN->setDebugLoc(DL);
1094 }
1095
1096 /// Recursively traverse the CFG of the function, renaming loads and
1097 /// stores to the allocas which we are promoting.
1098 ///
1099 /// IncomingVals indicates what value each Alloca contains on exit from the
1100 /// predecessor block Pred.
RenamePass(BasicBlock * BB,BasicBlock * Pred,RenamePassData::ValVector & IncomingVals,RenamePassData::LocationVector & IncomingLocs,std::vector<RenamePassData> & Worklist)1101 void PromoteMem2Reg::RenamePass(BasicBlock *BB, BasicBlock *Pred,
1102 RenamePassData::ValVector &IncomingVals,
1103 RenamePassData::LocationVector &IncomingLocs,
1104 std::vector<RenamePassData> &Worklist) {
1105 NextIteration:
1106 // If we are inserting any phi nodes into this BB, they will already be in the
1107 // block.
1108 if (PHINode *APN = dyn_cast<PHINode>(BB->begin())) {
1109 // If we have PHI nodes to update, compute the number of edges from Pred to
1110 // BB.
1111 if (PhiToAllocaMap.count(APN)) {
1112 // We want to be able to distinguish between PHI nodes being inserted by
1113 // this invocation of mem2reg from those phi nodes that already existed in
1114 // the IR before mem2reg was run. We determine that APN is being inserted
1115 // because it is missing incoming edges. All other PHI nodes being
1116 // inserted by this pass of mem2reg will have the same number of incoming
1117 // operands so far. Remember this count.
1118 unsigned NewPHINumOperands = APN->getNumOperands();
1119
1120 unsigned NumEdges = llvm::count(successors(Pred), BB);
1121 assert(NumEdges && "Must be at least one edge from Pred to BB!");
1122
1123 // Add entries for all the phis.
1124 BasicBlock::iterator PNI = BB->begin();
1125 do {
1126 unsigned AllocaNo = PhiToAllocaMap[APN];
1127
1128 // Update the location of the phi node.
1129 updateForIncomingValueLocation(APN, IncomingLocs[AllocaNo],
1130 APN->getNumIncomingValues() > 0);
1131
1132 // Add N incoming values to the PHI node.
1133 for (unsigned i = 0; i != NumEdges; ++i)
1134 APN->addIncoming(IncomingVals[AllocaNo], Pred);
1135
1136 // For the sequence `return X > 0.0 ? X : -X`, it is expected that this
1137 // results in fabs intrinsic. However, without no-signed-zeros(nsz) flag
1138 // on the phi node generated at this stage, fabs folding does not
1139 // happen. So, we try to infer nsz flag from the function attributes to
1140 // enable this fabs folding.
1141 if (isa<FPMathOperator>(APN) && NoSignedZeros)
1142 APN->setHasNoSignedZeros(true);
1143
1144 // The currently active variable for this block is now the PHI.
1145 IncomingVals[AllocaNo] = APN;
1146 AllocaATInfo[AllocaNo].updateForNewPhi(APN, DIB);
1147 auto ConvertDbgDeclares = [&](auto &Container) {
1148 for (auto *DbgItem : Container)
1149 if (DbgItem->isAddressOfVariable())
1150 ConvertDebugDeclareToDebugValue(DbgItem, APN, DIB);
1151 };
1152 ConvertDbgDeclares(AllocaDbgUsers[AllocaNo]);
1153 ConvertDbgDeclares(AllocaDPUsers[AllocaNo]);
1154
1155 // Get the next phi node.
1156 ++PNI;
1157 APN = dyn_cast<PHINode>(PNI);
1158 if (!APN)
1159 break;
1160
1161 // Verify that it is missing entries. If not, it is not being inserted
1162 // by this mem2reg invocation so we want to ignore it.
1163 } while (APN->getNumOperands() == NewPHINumOperands);
1164 }
1165 }
1166
1167 // Don't revisit blocks.
1168 if (!Visited.insert(BB).second)
1169 return;
1170
1171 for (BasicBlock::iterator II = BB->begin(); !II->isTerminator();) {
1172 Instruction *I = &*II++; // get the instruction, increment iterator
1173
1174 if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
1175 AllocaInst *Src = dyn_cast<AllocaInst>(LI->getPointerOperand());
1176 if (!Src)
1177 continue;
1178
1179 DenseMap<AllocaInst *, unsigned>::iterator AI = AllocaLookup.find(Src);
1180 if (AI == AllocaLookup.end())
1181 continue;
1182
1183 Value *V = IncomingVals[AI->second];
1184 convertMetadataToAssumes(LI, V, SQ.DL, AC, &DT);
1185
1186 // Anything using the load now uses the current value.
1187 LI->replaceAllUsesWith(V);
1188 LI->eraseFromParent();
1189 } else if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
1190 // Delete this instruction and mark the name as the current holder of the
1191 // value
1192 AllocaInst *Dest = dyn_cast<AllocaInst>(SI->getPointerOperand());
1193 if (!Dest)
1194 continue;
1195
1196 DenseMap<AllocaInst *, unsigned>::iterator ai = AllocaLookup.find(Dest);
1197 if (ai == AllocaLookup.end())
1198 continue;
1199
1200 // what value were we writing?
1201 unsigned AllocaNo = ai->second;
1202 IncomingVals[AllocaNo] = SI->getOperand(0);
1203
1204 // Record debuginfo for the store before removing it.
1205 IncomingLocs[AllocaNo] = SI->getDebugLoc();
1206 AllocaATInfo[AllocaNo].updateForDeletedStore(SI, DIB, &DbgAssignsToDelete,
1207 &DVRAssignsToDelete);
1208 auto ConvertDbgDeclares = [&](auto &Container) {
1209 for (auto *DbgItem : Container)
1210 if (DbgItem->isAddressOfVariable())
1211 ConvertDebugDeclareToDebugValue(DbgItem, SI, DIB);
1212 };
1213 ConvertDbgDeclares(AllocaDbgUsers[ai->second]);
1214 ConvertDbgDeclares(AllocaDPUsers[ai->second]);
1215 SI->eraseFromParent();
1216 }
1217 }
1218
1219 // 'Recurse' to our successors.
1220 succ_iterator I = succ_begin(BB), E = succ_end(BB);
1221 if (I == E)
1222 return;
1223
1224 // Keep track of the successors so we don't visit the same successor twice
1225 SmallPtrSet<BasicBlock *, 8> VisitedSuccs;
1226
1227 // Handle the first successor without using the worklist.
1228 VisitedSuccs.insert(*I);
1229 Pred = BB;
1230 BB = *I;
1231 ++I;
1232
1233 for (; I != E; ++I)
1234 if (VisitedSuccs.insert(*I).second)
1235 Worklist.emplace_back(*I, Pred, IncomingVals, IncomingLocs);
1236
1237 goto NextIteration;
1238 }
1239
PromoteMemToReg(ArrayRef<AllocaInst * > Allocas,DominatorTree & DT,AssumptionCache * AC)1240 void llvm::PromoteMemToReg(ArrayRef<AllocaInst *> Allocas, DominatorTree &DT,
1241 AssumptionCache *AC) {
1242 // If there is nothing to do, bail out...
1243 if (Allocas.empty())
1244 return;
1245
1246 PromoteMem2Reg(Allocas, DT, AC).run();
1247 }
1248