Introduce "expect" intrinsic instructions.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@134516 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/Utils/LowerExpectIntrinsic.cpp

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