1 //===- LowerExpectIntrinsic.cpp - Lower expect intrinsic ------------------===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 // 10 // This pass lowers the 'expect' intrinsic to LLVM metadata. 11 // 12 //===----------------------------------------------------------------------===// 13 14 #define DEBUG_TYPE "lower-expect-intrinsic" 15 #include "llvm/Constants.h" 16 #include "llvm/Function.h" 17 #include "llvm/BasicBlock.h" 18 #include "llvm/LLVMContext.h" 19 #include "llvm/Instructions.h" 20 #include "llvm/Intrinsics.h" 21 #include "llvm/Metadata.h" 22 #include "llvm/Pass.h" 23 #include "llvm/Transforms/Scalar.h" 24 #include "llvm/Support/CommandLine.h" 25 #include "llvm/Support/Debug.h" 26 #include "llvm/ADT/Statistic.h" 27 #include <vector> 28 29 using namespace llvm; 30 31 STATISTIC(IfHandled, "Number of 'expect' intrinsic intructions handled"); 32 33 static cl::opt<uint32_t> 34 LikelyBranchWeight("likely-branch-weight", cl::Hidden, cl::init(64), 35 cl::desc("Weight of the branch likely to be taken (default = 64)")); 36 static cl::opt<uint32_t> 37 UnlikelyBranchWeight("unlikely-branch-weight", cl::Hidden, cl::init(4), 38 cl::desc("Weight of the branch unlikely to be taken (default = 4)")); 39 40 namespace { 41 42 class LowerExpectIntrinsic : public FunctionPass { 43 44 bool HandleSwitchExpect(SwitchInst *SI); 45 46 bool HandleIfExpect(BranchInst *BI); 47 48 public: 49 static char ID; 50 LowerExpectIntrinsic() : FunctionPass(ID) { 51 initializeLowerExpectIntrinsicPass(*PassRegistry::getPassRegistry()); 52 } 53 54 bool runOnFunction(Function &F); 55 }; 56 } 57 58 59 bool LowerExpectIntrinsic::HandleSwitchExpect(SwitchInst *SI) { 60 CallInst *CI = dyn_cast<CallInst>(SI->getCondition()); 61 if (!CI) 62 return false; 63 64 Function *Fn = CI->getCalledFunction(); 65 if (!Fn || Fn->getIntrinsicID() != Intrinsic::expect) 66 return false; 67 68 Value *ArgValue = CI->getArgOperand(0); 69 ConstantInt *ExpectedValue = dyn_cast<ConstantInt>(CI->getArgOperand(1)); 70 if (!ExpectedValue) 71 return false; 72 73 LLVMContext &Context = CI->getContext(); 74 Type *Int32Ty = Type::getInt32Ty(Context); 75 76 unsigned caseNo = SI->findCaseValue(ExpectedValue); 77 std::vector<Value *> Vec; 78 unsigned n = SI->getNumCases(); 79 Vec.resize(n + 1); // +1 for MDString 80 81 Vec[0] = MDString::get(Context, "branch_weights"); 82 for (unsigned i = 0; i < n; ++i) { 83 Vec[i + 1] = ConstantInt::get(Int32Ty, i == caseNo ? LikelyBranchWeight : UnlikelyBranchWeight); 84 } 85 86 MDNode *WeightsNode = llvm::MDNode::get(Context, Vec); 87 SI->setMetadata(LLVMContext::MD_prof, WeightsNode); 88 89 SI->setCondition(ArgValue); 90 return true; 91 } 92 93 94 bool LowerExpectIntrinsic::HandleIfExpect(BranchInst *BI) { 95 if (BI->isUnconditional()) 96 return false; 97 98 // Handle non-optimized IR code like: 99 // %expval = call i64 @llvm.expect.i64.i64(i64 %conv1, i64 1) 100 // %tobool = icmp ne i64 %expval, 0 101 // br i1 %tobool, label %if.then, label %if.end 102 103 ICmpInst *CmpI = dyn_cast<ICmpInst>(BI->getCondition()); 104 if (!CmpI || CmpI->getPredicate() != CmpInst::ICMP_NE) 105 return false; 106 107 CallInst *CI = dyn_cast<CallInst>(CmpI->getOperand(0)); 108 if (!CI) 109 return false; 110 111 Function *Fn = CI->getCalledFunction(); 112 if (!Fn || Fn->getIntrinsicID() != Intrinsic::expect) 113 return false; 114 115 Value *ArgValue = CI->getArgOperand(0); 116 ConstantInt *ExpectedValue = dyn_cast<ConstantInt>(CI->getArgOperand(1)); 117 if (!ExpectedValue) 118 return false; 119 120 LLVMContext &Context = CI->getContext(); 121 Type *Int32Ty = Type::getInt32Ty(Context); 122 bool Likely = ExpectedValue->isOne(); 123 124 // If expect value is equal to 1 it means that we are more likely to take 125 // branch 0, in other case more likely is branch 1. 126 Value *Ops[] = { 127 MDString::get(Context, "branch_weights"), 128 ConstantInt::get(Int32Ty, Likely ? LikelyBranchWeight : UnlikelyBranchWeight), 129 ConstantInt::get(Int32Ty, Likely ? UnlikelyBranchWeight : LikelyBranchWeight) 130 }; 131 132 MDNode *WeightsNode = MDNode::get(Context, Ops); 133 BI->setMetadata(LLVMContext::MD_prof, WeightsNode); 134 135 CmpI->setOperand(0, ArgValue); 136 return true; 137 } 138 139 140 bool LowerExpectIntrinsic::runOnFunction(Function &F) { 141 for (Function::iterator I = F.begin(), E = F.end(); I != E;) { 142 BasicBlock *BB = I++; 143 144 // Create "block_weights" metadata. 145 if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) { 146 if (HandleIfExpect(BI)) 147 IfHandled++; 148 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) { 149 if (HandleSwitchExpect(SI)) 150 IfHandled++; 151 } 152 153 // remove llvm.expect intrinsics. 154 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); 155 BI != BE; ) { 156 CallInst *CI = dyn_cast<CallInst>(BI++); 157 if (!CI) 158 continue; 159 160 Function *Fn = CI->getCalledFunction(); 161 if (Fn && Fn->getIntrinsicID() == Intrinsic::expect) { 162 Value *Exp = CI->getArgOperand(0); 163 CI->replaceAllUsesWith(Exp); 164 CI->eraseFromParent(); 165 } 166 } 167 } 168 169 return false; 170 } 171 172 173 char LowerExpectIntrinsic::ID = 0; 174 INITIALIZE_PASS(LowerExpectIntrinsic, "lower-expect", "Lower 'expect' " 175 "Intrinsics", false, false) 176 177 FunctionPass *llvm::createLowerExpectIntrinsicPass() { 178 return new LowerExpectIntrinsic(); 179 } 180
