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Introduce "expect" intrinsic instructions.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@134516 91177308-0d34-0410-b5e6-96231b3b80d8
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163
lib/Transforms/Utils/LowerExpectIntrinsic.cpp
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163
lib/Transforms/Utils/LowerExpectIntrinsic.cpp
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#define DEBUG_TYPE "lower-expect-intrinsic"
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#include "llvm/Constants.h"
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#include "llvm/Function.h"
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#include "llvm/BasicBlock.h"
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#include "llvm/LLVMContext.h"
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#include "llvm/Instructions.h"
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#include "llvm/Intrinsics.h"
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#include "llvm/Metadata.h"
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#include "llvm/Pass.h"
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#include "llvm/Transforms/Scalar.h"
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#include "llvm/Support/CommandLine.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/ADT/Statistic.h"
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#include <vector>
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using namespace llvm;
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STATISTIC(IfHandled, "Number of 'expect' intrinsic intructions handled");
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static cl::opt<uint32_t>
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LikelyBranchWeight("likely-branch-weight", cl::Hidden, cl::init(64),
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cl::desc("Weight of the branch likely to be taken (default = 64)"));
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static cl::opt<uint32_t>
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UnlikelyBranchWeight("unlikely-branch-weight", cl::Hidden, cl::init(4),
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cl::desc("Weight of the branch unlikely to be taken (default = 4)"));
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namespace {
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class LowerExpectIntrinsic : public FunctionPass {
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bool HandleSwitchExpect(SwitchInst *SI);
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bool HandleIfExpect(BranchInst *BI);
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public:
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static char ID;
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LowerExpectIntrinsic() : FunctionPass(ID) {
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initializeLowerExpectIntrinsicPass(*PassRegistry::getPassRegistry());
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}
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bool runOnFunction(Function &F);
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};
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}
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bool LowerExpectIntrinsic::HandleSwitchExpect(SwitchInst *SI) {
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CallInst *CI = dyn_cast<CallInst>(SI->getCondition());
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if (!CI)
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return false;
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Function *Fn = CI->getCalledFunction();
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if (!Fn || Fn->getIntrinsicID() != Intrinsic::expect)
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return false;
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Value *ArgValue = CI->getArgOperand(0);
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ConstantInt *ExpectedValue = dyn_cast<ConstantInt>(CI->getArgOperand(1));
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if (!ExpectedValue)
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return false;
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LLVMContext &Context = CI->getContext();
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const Type *Int32Ty = Type::getInt32Ty(Context);
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unsigned caseNo = SI->findCaseValue(ExpectedValue);
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std::vector<Value *> Vec;
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unsigned n = SI->getNumCases();
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Vec.resize(n + 1); // +1 for MDString
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Vec[0] = MDString::get(Context, "branch_weights");
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for (unsigned i = 0; i < n; ++i) {
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Vec[i + 1] = ConstantInt::get(Int32Ty, i == caseNo ? LikelyBranchWeight : UnlikelyBranchWeight);
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}
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MDNode *WeightsNode = llvm::MDNode::get(Context, Vec);
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SI->setMetadata(LLVMContext::MD_prof, WeightsNode);
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SI->setCondition(ArgValue);
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return true;
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}
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bool LowerExpectIntrinsic::HandleIfExpect(BranchInst *BI) {
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if (BI->isUnconditional())
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return false;
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// Handle non-optimized IR code like:
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// %expval = call i64 @llvm.expect.i64.i64(i64 %conv1, i64 1)
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// %tobool = icmp ne i64 %expval, 0
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// br i1 %tobool, label %if.then, label %if.end
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ICmpInst *CmpI = dyn_cast<ICmpInst>(BI->getCondition());
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if (!CmpI || CmpI->getPredicate() != CmpInst::ICMP_NE)
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return false;
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CallInst *CI = dyn_cast<CallInst>(CmpI->getOperand(0));
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if (!CI)
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return false;
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Function *Fn = CI->getCalledFunction();
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if (!Fn || Fn->getIntrinsicID() != Intrinsic::expect)
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return false;
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Value *ArgValue = CI->getArgOperand(0);
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ConstantInt *ExpectedValue = dyn_cast<ConstantInt>(CI->getArgOperand(1));
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if (!ExpectedValue)
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return false;
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LLVMContext &Context = CI->getContext();
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const Type *Int32Ty = Type::getInt32Ty(Context);
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bool Likely = ExpectedValue->isOne();
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// If expect value is equal to 1 it means that we are more likely to take
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// branch 0, in other case more likely is branch 1.
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Value *Ops[] = {
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MDString::get(Context, "branch_weights"),
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ConstantInt::get(Int32Ty, Likely ? LikelyBranchWeight : UnlikelyBranchWeight),
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ConstantInt::get(Int32Ty, Likely ? UnlikelyBranchWeight : LikelyBranchWeight)
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};
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MDNode *WeightsNode = MDNode::get(Context, ArrayRef<Value *>(Ops, 3));
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BI->setMetadata(LLVMContext::MD_prof, WeightsNode);
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CmpI->setOperand(0, ArgValue);
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return true;
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}
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bool LowerExpectIntrinsic::runOnFunction(Function &F) {
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for (Function::iterator I = F.begin(), E = F.end(); I != E;) {
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BasicBlock *BB = I++;
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// Create "block_weights" metadata.
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if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
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if (HandleIfExpect(BI))
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IfHandled++;
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} else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
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if (HandleSwitchExpect(SI))
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IfHandled++;
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}
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// remove llvm.expect intrinsics.
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for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
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BI != BE; ) {
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CallInst *CI = dyn_cast<CallInst>(BI++);
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if (!CI)
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continue;
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Function *Fn = CI->getCalledFunction();
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if (Fn && Fn->getIntrinsicID() == Intrinsic::expect)
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CI->eraseFromParent();
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}
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}
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return false;
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}
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char LowerExpectIntrinsic::ID = 0;
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INITIALIZE_PASS(LowerExpectIntrinsic, "lower-expect", "Lower 'expect' "
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"Intrinsics", false, false)
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FunctionPass *llvm::createLowerExpectIntrinsicPass() {
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return new LowerExpectIntrinsic();
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}
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