Move some shift transforms out of instcombine and into InstructionSimplify.
While there, I noticed that the transform "undef >>a X -> undef" was wrong.
For example if X is 2 then the top two bits must be equal, so the result can
not be anything. I fixed this in the constant folder as well. Also, I made
the transform for "X << undef" stronger: it now folds to undef always, even
though X might be zero. This is in accordance with the LangRef, but I must
admit that it is fairly aggressive. Also, I added "i32 X << 32 -> undef"
following the LangRef and the constant folder, likewise fairly aggressive.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@123417 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/InstCombine/InstCombineShifts.cpp b/lib/Transforms/InstCombine/InstCombineShifts.cpp
index a0c5ef5..fe791dd 100644
--- a/lib/Transforms/InstCombine/InstCombineShifts.cpp
+++ b/lib/Transforms/InstCombine/InstCombineShifts.cpp
@@ -13,6 +13,7 @@
#include "InstCombine.h"
#include "llvm/IntrinsicInst.h"
+#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Support/PatternMatch.h"
using namespace llvm;
using namespace PatternMatch;
@@ -21,25 +22,6 @@
assert(I.getOperand(1)->getType() == I.getOperand(0)->getType());
Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
- // shl X, 0 == X and shr X, 0 == X
- // shl 0, X == 0 and shr 0, X == 0
- if (Op1 == Constant::getNullValue(Op1->getType()) ||
- Op0 == Constant::getNullValue(Op0->getType()))
- return ReplaceInstUsesWith(I, Op0);
-
- if (isa<UndefValue>(Op0)) {
- if (I.getOpcode() == Instruction::AShr) // undef >>s X -> undef
- return ReplaceInstUsesWith(I, Op0);
- else // undef << X -> 0, undef >>u X -> 0
- return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
- }
- if (isa<UndefValue>(Op1)) {
- if (I.getOpcode() == Instruction::AShr) // X >>s undef -> X
- return ReplaceInstUsesWith(I, Op0);
- else // X << undef, X >>u undef -> 0
- return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
- }
-
// See if we can fold away this shift.
if (SimplifyDemandedInstructionBits(I))
return &I;
@@ -635,10 +617,15 @@
}
Instruction *InstCombiner::visitShl(BinaryOperator &I) {
+ if (Value *V = SimplifyShlInst(I.getOperand(0), I.getOperand(1), TD))
+ return ReplaceInstUsesWith(I, V);
return commonShiftTransforms(I);
}
Instruction *InstCombiner::visitLShr(BinaryOperator &I) {
+ if (Value *V = SimplifyLShrInst(I.getOperand(0), I.getOperand(1), TD))
+ return ReplaceInstUsesWith(I, V);
+
if (Instruction *R = commonShiftTransforms(I))
return R;
@@ -665,17 +652,14 @@
}
Instruction *InstCombiner::visitAShr(BinaryOperator &I) {
+ if (Value *V = SimplifyAShrInst(I.getOperand(0), I.getOperand(1), TD))
+ return ReplaceInstUsesWith(I, V);
+
if (Instruction *R = commonShiftTransforms(I))
return R;
Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
-
- if (ConstantInt *CSI = dyn_cast<ConstantInt>(Op0)) {
- // ashr int -1, X = -1 (for any arithmetic shift rights of ~0)
- if (CSI->isAllOnesValue())
- return ReplaceInstUsesWith(I, CSI);
- }
-
+
if (ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) {
// If the input is a SHL by the same constant (ashr (shl X, C), C), then we
// have a sign-extend idiom.