Home | History | Annotate | Download | only in Utils 
      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 }
    175