implement a simple instcombine xform that has been in the
readme forever.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@94318 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/InstCombine/InstCombineShifts.cpp b/lib/Transforms/InstCombine/InstCombineShifts.cpp
index 321c91d..9dd60dd 100644
--- a/lib/Transforms/InstCombine/InstCombineShifts.cpp
+++ b/lib/Transforms/InstCombine/InstCombineShifts.cpp
@@ -12,6 +12,7 @@
//===----------------------------------------------------------------------===//
#include "InstCombine.h"
+#include "llvm/IntrinsicInst.h"
#include "llvm/Support/PatternMatch.h"
using namespace llvm;
using namespace PatternMatch;
@@ -69,10 +70,9 @@
if (Op1->uge(TypeBits)) {
if (I.getOpcode() != Instruction::AShr)
return ReplaceInstUsesWith(I, Constant::getNullValue(Op0->getType()));
- else {
- I.setOperand(1, ConstantInt::get(I.getType(), TypeBits-1));
- return &I;
- }
+ // ashr i32 X, 32 --> ashr i32 X, 31
+ I.setOperand(1, ConstantInt::get(I.getType(), TypeBits-1));
+ return &I;
}
// ((X*C1) << C2) == (X * (C1 << C2))
@@ -387,7 +387,29 @@
}
Instruction *InstCombiner::visitLShr(BinaryOperator &I) {
- return commonShiftTransforms(I);
+ if (Instruction *R = commonShiftTransforms(I))
+ return R;
+
+ Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
+
+ if (ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1))
+ if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(Op0)) {
+ // ctlz.i32(x)>>5 --> zext(x == 0)
+ // cttz.i32(x)>>5 --> zext(x == 0)
+ // ctpop.i32(x)>>5 --> zext(x == -1)
+ if ((II->getIntrinsicID() == Intrinsic::ctlz ||
+ II->getIntrinsicID() == Intrinsic::cttz ||
+ II->getIntrinsicID() == Intrinsic::ctpop) &&
+ (1ULL << Op1C->getZExtValue()) ==
+ Op0->getType()->getScalarSizeInBits()) {
+ bool isCtPop = II->getIntrinsicID() == Intrinsic::ctpop;
+ Constant *RHS = ConstantInt::getSigned(Op0->getType(), isCtPop ? -1 : 0);
+ Value *Cmp = Builder->CreateICmpEQ(II->getOperand(1), RHS);
+ return new ZExtInst(Cmp, II->getType());
+ }
+ }
+
+ return 0;
}
Instruction *InstCombiner::visitAShr(BinaryOperator &I) {