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/Constant are skipped because they may not be Bool 82 // type. For CallInst, their positions are defined by ABI. 83 if (CurrUser && !isa<CallInst>(Curr) && !isa<Constant>(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 assert(V->getType() == Type::getInt1Ty(V->getContext()) && 94 "Expect an i1 value"); 95 96 Type *IntTy = ST->isPPC64() ? Type::getInt64Ty(V->getContext()) 97 : Type::getInt32Ty(V->getContext()); 98 99 if (auto *C = dyn_cast<Constant>(V)) 100 return ConstantExpr::getZExt(C, IntTy); 101 if (auto *P = dyn_cast<PHINode>(V)) { 102 // Temporarily set the operands to 0. We'll fix this later in 103 // runOnUse. 104 Value *Zero = Constant::getNullValue(IntTy); 105 PHINode *Q = 106 PHINode::Create(IntTy, P->getNumIncomingValues(), P->getName(), P); 107 for (unsigned i = 0; i < P->getNumOperands(); ++i) 108 Q->addIncoming(Zero, P->getIncomingBlock(i)); 109 return Q; 110 } 111 112 auto *A = dyn_cast<Argument>(V); 113 auto *I = dyn_cast<Instruction>(V); 114 assert((A || I) && "Unknown value type"); 115 116 auto InstPt = 117 A ? &*A->getParent()->getEntryBlock().begin() : I->getNextNode(); 118 return new ZExtInst(V, IntTy, "", InstPt); 119 } 120 121 typedef SmallPtrSet<const PHINode *, 8> PHINodeSet; 122 123 // A PHINode is Promotable if: 124 // 1. Its type is i1 AND 125 // 2. All of its uses are ReturnInt, CallInst, PHINode, or DbgInfoIntrinsic 126 // AND 127 // 3. All of its operands are Constant or Argument or 128 // CallInst or PHINode AND 129 // 4. All of its PHINode uses are Promotable AND 130 // 5. All of its PHINode operands are Promotable 131 static PHINodeSet getPromotablePHINodes(const Function &F) { 132 PHINodeSet Promotable; 133 // Condition 1 134 for (auto &BB : F) 135 for (auto &I : BB) 136 if (const auto *P = dyn_cast<PHINode>(&I)) 137 if (P->getType()->isIntegerTy(1)) 138 Promotable.insert(P); 139 140 SmallVector<const PHINode *, 8> ToRemove; 141 for (const PHINode *P : Promotable) { 142 // Condition 2 and 3 143 auto IsValidUser = [] (const Value *V) -> bool { 144 return isa<ReturnInst>(V) || isa<CallInst>(V) || isa<PHINode>(V) || 145 isa<DbgInfoIntrinsic>(V); 146 }; 147 auto IsValidOperand = [] (const Value *V) -> bool { 148 return isa<Constant>(V) || isa<Argument>(V) || isa<CallInst>(V) || 149 isa<PHINode>(V); 150 }; 151 const auto &Users = P->users(); 152 const auto &Operands = P->operands(); 153 if (!llvm::all_of(Users, IsValidUser) || 154 !llvm::all_of(Operands, IsValidOperand)) 155 ToRemove.push_back(P); 156 } 157 158 // Iterate to convergence 159 auto IsPromotable = [&Promotable] (const Value *V) -> bool { 160 const auto *Phi = dyn_cast<PHINode>(V); 161 return !Phi || Promotable.count(Phi); 162 }; 163 while (!ToRemove.empty()) { 164 for (auto &User : ToRemove) 165 Promotable.erase(User); 166 ToRemove.clear(); 167 168 for (const PHINode *P : Promotable) { 169 // Condition 4 and 5 170 const auto &Users = P->users(); 171 const auto &Operands = P->operands(); 172 if (!llvm::all_of(Users, IsPromotable) || 173 !llvm::all_of(Operands, IsPromotable)) 174 ToRemove.push_back(P); 175 } 176 } 177 178 return Promotable; 179 } 180 181 typedef DenseMap<Value *, Value *> B2IMap; 182 183 public: 184 static char ID; 185 186 PPCBoolRetToInt() : FunctionPass(ID) { 187 initializePPCBoolRetToIntPass(*PassRegistry::getPassRegistry()); 188 } 189 190 bool runOnFunction(Function &F) override { 191 if (skipFunction(F)) 192 return false; 193 194 auto *TPC = getAnalysisIfAvailable<TargetPassConfig>(); 195 if (!TPC) 196 return false; 197 198 auto &TM = TPC->getTM<PPCTargetMachine>(); 199 ST = TM.getSubtargetImpl(F); 200 201 PHINodeSet PromotablePHINodes = getPromotablePHINodes(F); 202 B2IMap Bool2IntMap; 203 bool Changed = false; 204 for (auto &BB : F) { 205 for (auto &I : BB) { 206 if (auto *R = dyn_cast<ReturnInst>(&I)) 207 if (F.getReturnType()->isIntegerTy(1)) 208 Changed |= 209 runOnUse(R->getOperandUse(0), PromotablePHINodes, Bool2IntMap); 210 211 if (auto *CI = dyn_cast<CallInst>(&I)) 212 for (auto &U : CI->operands()) 213 if (U->getType()->isIntegerTy(1)) 214 Changed |= runOnUse(U, PromotablePHINodes, Bool2IntMap); 215 } 216 } 217 218 return Changed; 219 } 220 221 bool runOnUse(Use &U, const PHINodeSet &PromotablePHINodes, 222 B2IMap &BoolToIntMap) { 223 auto Defs = findAllDefs(U); 224 225 // If the values are all Constants or Arguments, don't bother 226 if (llvm::none_of(Defs, [](Value *V) { return isa<Instruction>(V); })) 227 return false; 228 229 // Presently, we only know how to handle PHINode, Constant, Arguments and 230 // CallInst. Potentially, bitwise operations (AND, OR, XOR, NOT) and sign 231 // extension could also be handled in the future. 232 for (Value *V : Defs) 233 if (!isa<PHINode>(V) && !isa<Constant>(V) && 234 !isa<Argument>(V) && !isa<CallInst>(V)) 235 return false; 236 237 for (Value *V : Defs) 238 if (const auto *P = dyn_cast<PHINode>(V)) 239 if (!PromotablePHINodes.count(P)) 240 return false; 241 242 if (isa<ReturnInst>(U.getUser())) 243 ++NumBoolRetPromotion; 244 if (isa<CallInst>(U.getUser())) 245 ++NumBoolCallPromotion; 246 ++NumBoolToIntPromotion; 247 248 for (Value *V : Defs) 249 if (!BoolToIntMap.count(V)) 250 BoolToIntMap[V] = translate(V); 251 252 // Replace the operands of the translated instructions. They were set to 253 // zero in the translate function. 254 for (auto &Pair : BoolToIntMap) { 255 auto *First = dyn_cast<User>(Pair.first); 256 auto *Second = dyn_cast<User>(Pair.second); 257 assert((!First || Second) && "translated from user to non-user!?"); 258 // Operands of CallInst/Constant are skipped because they may not be Bool 259 // type. For CallInst, their positions are defined by ABI. 260 if (First && !isa<CallInst>(First) && !isa<Constant>(First)) 261 for (unsigned i = 0; i < First->getNumOperands(); ++i) 262 Second->setOperand(i, BoolToIntMap[First->getOperand(i)]); 263 } 264 265 Value *IntRetVal = BoolToIntMap[U]; 266 Type *Int1Ty = Type::getInt1Ty(U->getContext()); 267 auto *I = cast<Instruction>(U.getUser()); 268 Value *BackToBool = new TruncInst(IntRetVal, Int1Ty, "backToBool", I); 269 U.set(BackToBool); 270 271 return true; 272 } 273 274 void getAnalysisUsage(AnalysisUsage &AU) const override { 275 AU.addPreserved<DominatorTreeWrapperPass>(); 276 FunctionPass::getAnalysisUsage(AU); 277 } 278 279 private: 280 const PPCSubtarget *ST; 281 }; 282 283 } // end anonymous namespace 284 285 char PPCBoolRetToInt::ID = 0; 286 INITIALIZE_PASS(PPCBoolRetToInt, "bool-ret-to-int", 287 "Convert i1 constants to i32/i64 if they are returned", 288 false, false) 289 290 FunctionPass *llvm::createPPCBoolRetToIntPass() { return new PPCBoolRetToInt(); } 291