lib/Transforms/Utils/LowerExpectIntrinsic.cpp

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