1 //===- PPCBoolRetToInt.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 converting i1 values to i32/i64 if they could be more 10 // profitably allocated as GPRs rather than CRs. This pass will become totally 11 // unnecessary if Register Bank Allocation and Global Instruction Selection ever 12 // go upstream. 13 // 14 // Presently, the pass converts i1 Constants, and Arguments to i32/i64 if the 15 // transitive closure of their uses includes only PHINodes, CallInsts, and 16 // ReturnInsts. The rational is that arguments are generally passed and returned 17 // in GPRs rather than CRs, so casting them to i32/i64 at the LLVM IR level will 18 // actually save casts at the Machine Instruction level. 19 // 20 // It might be useful to expand this pass to add bit-wise operations to the list 21 // of safe transitive closure types. Also, we miss some opportunities when LLVM 22 // represents logical AND and OR operations with control flow rather than data 23 // flow. For example by lowering the expression: return (A && B && C) 24 // 25 // as: return A ? true : B && C. 26 // 27 // There's code in SimplifyCFG that code be used to turn control flow in data 28 // flow using SelectInsts. Selects are slow on some architectures (P7/P8), so 29 // this probably isn't good in general, but for the special case of i1, the 30 // Selects could be further lowered to bit operations that are fast everywhere. 31 // 32 //===----------------------------------------------------------------------===// 33 34 #include "PPC.h" 35 #include "PPCTargetMachine.h" 36 #include "llvm/ADT/DenseMap.h" 37 #include "llvm/ADT/STLExtras.h" 38 #include "llvm/ADT/SmallPtrSet.h" 39 #include "llvm/ADT/SmallVector.h" 40 #include "llvm/ADT/Statistic.h" 41 #include "llvm/IR/Argument.h" 42 #include "llvm/IR/Constants.h" 43 #include "llvm/IR/Dominators.h" 44 #include "llvm/IR/Function.h" 45 #include "llvm/IR/Instruction.h" 46 #include "llvm/IR/Instructions.h" 47 #include "llvm/IR/IntrinsicInst.h" 48 #include "llvm/IR/OperandTraits.h" 49 #include "llvm/IR/Type.h" 50 #include "llvm/IR/Use.h" 51 #include "llvm/IR/User.h" 52 #include "llvm/IR/Value.h" 53 #include "llvm/Pass.h" 54 #include "llvm/CodeGen/TargetPassConfig.h" 55 #include "llvm/Support/Casting.h" 56 #include <cassert> 57 58 using namespace llvm; 59 60 namespace { 61 62 #define DEBUG_TYPE "bool-ret-to-int" 63 64 STATISTIC(NumBoolRetPromotion, 65 "Number of times a bool feeding a RetInst was promoted to an int"); 66 STATISTIC(NumBoolCallPromotion, 67 "Number of times a bool feeding a CallInst was promoted to an int"); 68 STATISTIC(NumBoolToIntPromotion, 69 "Total number of times a bool was promoted to an int"); 70 71 class PPCBoolRetToInt : public FunctionPass { 72 static SmallPtrSet<Value *, 8> findAllDefs(Value *V) { 73 SmallPtrSet<Value *, 8> Defs; 74 SmallVector<Value *, 8> WorkList; 75 WorkList.push_back(V); 76 Defs.insert(V); 77 while (!WorkList.empty()) { 78 Value *Curr = WorkList.back(); 79 WorkList.pop_back(); 80 auto *CurrUser = dyn_cast<User>(Curr); 81 // Operands of CallInst are skipped because they may not be Bool type, 82 // and their positions are defined by ABI. 83 if (CurrUser && !isa<CallInst>(Curr)) 84 for (auto &Op : CurrUser->operands()) 85 if (Defs.insert(Op).second) 86 WorkList.push_back(Op); 87 } 88 return Defs; 89 } 90 91 // Translate a i1 value to an equivalent i32/i64 value: 92 Value *translate(Value *V) { 93 Type *IntTy = ST->isPPC64() ? Type::getInt64Ty(V->getContext()) 94 : Type::getInt32Ty(V->getContext()); 95 96 if (auto *C = dyn_cast<Constant>(V)) 97 return ConstantExpr::getZExt(C, IntTy); 98 if (auto *P = dyn_cast<PHINode>(V)) { 99 // Temporarily set the operands to 0. We'll fix this later in 100 // runOnUse. 101 Value *Zero = Constant::getNullValue(IntTy); 102 PHINode *Q = 103 PHINode::Create(IntTy, P->getNumIncomingValues(), P->getName(), P); 104 for (unsigned i = 0; i < P->getNumOperands(); ++i) 105 Q->addIncoming(Zero, P->getIncomingBlock(i)); 106 return Q; 107 } 108 109 auto *A = dyn_cast<Argument>(V); 110 auto *I = dyn_cast<Instruction>(V); 111 assert((A || I) && "Unknown value type"); 112 113 auto InstPt = 114 A ? &*A->getParent()->getEntryBlock().begin() : I->getNextNode(); 115 return new ZExtInst(V, IntTy, "", InstPt); 116 } 117 118 typedef SmallPtrSet<const PHINode *, 8> PHINodeSet; 119 120 // A PHINode is Promotable if: 121 // 1. Its type is i1 AND 122 // 2. All of its uses are ReturnInt, CallInst, PHINode, or DbgInfoIntrinsic 123 // AND 124 // 3. All of its operands are Constant or Argument or 125 // CallInst or PHINode AND 126 // 4. All of its PHINode uses are Promotable AND 127 // 5. All of its PHINode operands are Promotable 128 static PHINodeSet getPromotablePHINodes(const Function &F) { 129 PHINodeSet Promotable; 130 // Condition 1 131 for (auto &BB : F) 132 for (auto &I : BB) 133 if (const auto *P = dyn_cast<PHINode>(&I)) 134 if (P->getType()->isIntegerTy(1)) 135 Promotable.insert(P); 136 137 SmallVector<const PHINode *, 8> ToRemove; 138 for (const PHINode *P : Promotable) { 139 // Condition 2 and 3 140 auto IsValidUser = [] (const Value *V) -> bool { 141 return isa<ReturnInst>(V) || isa<CallInst>(V) || isa<PHINode>(V) || 142 isa<DbgInfoIntrinsic>(V); 143 }; 144 auto IsValidOperand = [] (const Value *V) -> bool { 145 return isa<Constant>(V) || isa<Argument>(V) || isa<CallInst>(V) || 146 isa<PHINode>(V); 147 }; 148 const auto &Users = P->users(); 149 const auto &Operands = P->operands(); 150 if (!llvm::all_of(Users, IsValidUser) || 151 !llvm::all_of(Operands, IsValidOperand)) 152 ToRemove.push_back(P); 153 } 154 155 // Iterate to convergence 156 auto IsPromotable = [&Promotable] (const Value *V) -> bool { 157 const auto *Phi = dyn_cast<PHINode>(V); 158 return !Phi || Promotable.count(Phi); 159 }; 160 while (!ToRemove.empty()) { 161 for (auto &User : ToRemove) 162 Promotable.erase(User); 163 ToRemove.clear(); 164 165 for (const PHINode *P : Promotable) { 166 // Condition 4 and 5 167 const auto &Users = P->users(); 168 const auto &Operands = P->operands(); 169 if (!llvm::all_of(Users, IsPromotable) || 170 !llvm::all_of(Operands, IsPromotable)) 171 ToRemove.push_back(P); 172 } 173 } 174 175 return Promotable; 176 } 177 178 typedef DenseMap<Value *, Value *> B2IMap; 179 180 public: 181 static char ID; 182 183 PPCBoolRetToInt() : FunctionPass(ID) { 184 initializePPCBoolRetToIntPass(*PassRegistry::getPassRegistry()); 185 } 186 187 bool runOnFunction(Function &F) override { 188 if (skipFunction(F)) 189 return false; 190 191 auto *TPC = getAnalysisIfAvailable<TargetPassConfig>(); 192 if (!TPC) 193 return false; 194 195 auto &TM = TPC->getTM<PPCTargetMachine>(); 196 ST = TM.getSubtargetImpl(F); 197 198 PHINodeSet PromotablePHINodes = getPromotablePHINodes(F); 199 B2IMap Bool2IntMap; 200 bool Changed = false; 201 for (auto &BB : F) { 202 for (auto &I : BB) { 203 if (auto *R = dyn_cast<ReturnInst>(&I)) 204 if (F.getReturnType()->isIntegerTy(1)) 205 Changed |= 206 runOnUse(R->getOperandUse(0), PromotablePHINodes, Bool2IntMap); 207 208 if (auto *CI = dyn_cast<CallInst>(&I)) 209 for (auto &U : CI->operands()) 210 if (U->getType()->isIntegerTy(1)) 211 Changed |= runOnUse(U, PromotablePHINodes, Bool2IntMap); 212 } 213 } 214 215 return Changed; 216 } 217 218 bool runOnUse(Use &U, const PHINodeSet &PromotablePHINodes, 219 B2IMap &BoolToIntMap) { 220 auto Defs = findAllDefs(U); 221 222 // If the values are all Constants or Arguments, don't bother 223 if (llvm::none_of(Defs, [](Value *V) { return isa<Instruction>(V); })) 224 return false; 225 226 // Presently, we only know how to handle PHINode, Constant, Arguments and 227 // CallInst. Potentially, bitwise operations (AND, OR, XOR, NOT) and sign 228 // extension could also be handled in the future. 229 for (Value *V : Defs) 230 if (!isa<PHINode>(V) && !isa<Constant>(V) && 231 !isa<Argument>(V) && !isa<CallInst>(V)) 232 return false; 233 234 for (Value *V : Defs) 235 if (const auto *P = dyn_cast<PHINode>(V)) 236 if (!PromotablePHINodes.count(P)) 237 return false; 238 239 if (isa<ReturnInst>(U.getUser())) 240 ++NumBoolRetPromotion; 241 if (isa<CallInst>(U.getUser())) 242 ++NumBoolCallPromotion; 243 ++NumBoolToIntPromotion; 244 245 for (Value *V : Defs) 246 if (!BoolToIntMap.count(V)) 247 BoolToIntMap[V] = translate(V); 248 249 // Replace the operands of the translated instructions. They were set to 250 // zero in the translate function. 251 for (auto &Pair : BoolToIntMap) { 252 auto *First = dyn_cast<User>(Pair.first); 253 auto *Second = dyn_cast<User>(Pair.second); 254 assert((!First || Second) && "translated from user to non-user!?"); 255 // Operands of CallInst are skipped because they may not be Bool type, 256 // and their positions are defined by ABI. 257 if (First && !isa<CallInst>(First)) 258 for (unsigned i = 0; i < First->getNumOperands(); ++i) 259 Second->setOperand(i, BoolToIntMap[First->getOperand(i)]); 260 } 261 262 Value *IntRetVal = BoolToIntMap[U]; 263 Type *Int1Ty = Type::getInt1Ty(U->getContext()); 264 auto *I = cast<Instruction>(U.getUser()); 265 Value *BackToBool = new TruncInst(IntRetVal, Int1Ty, "backToBool", I); 266 U.set(BackToBool); 267 268 return true; 269 } 270 271 void getAnalysisUsage(AnalysisUsage &AU) const override { 272 AU.addPreserved<DominatorTreeWrapperPass>(); 273 FunctionPass::getAnalysisUsage(AU); 274 } 275 276 private: 277 const PPCSubtarget *ST; 278 }; 279 280 } // end anonymous namespace 281 282 char PPCBoolRetToInt::ID = 0; 283 INITIALIZE_PASS(PPCBoolRetToInt, "bool-ret-to-int", 284 "Convert i1 constants to i32/i64 if they are returned", 285 false, false) 286 287 FunctionPass *llvm::createPPCBoolRetToIntPass() { return new PPCBoolRetToInt(); } 288