[llvm] [Transforms] Remove one-time check if other logic operand (Y) is constant (PR #77973)
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Fri Jan 12 12:18:03 PST 2024
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-llvm-transforms
Author: AtariDreams (AtariDreams)
<details>
<summary>Changes</summary>
By using isa<Constant>(W), we do not need to worry about one-time use anymore.
---
Full diff: https://github.com/llvm/llvm-project/pull/77973.diff
1 Files Affected:
- (modified) llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp (+8-4)
``````````diff
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp b/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
index b7958978c450c9..8614aad529eb4a 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
@@ -368,10 +368,14 @@ static Instruction *foldShiftOfShiftedBinOp(BinaryOperator &I,
// Find a matching one-use shift by constant. The fold is not valid if the sum
// of the shift values equals or exceeds bitwidth.
- // TODO: Remove the one-use check if the other logic operand (Y) is constant.
Value *X, *Y;
- auto matchFirstShift = [&](Value *V) {
+ auto matchFirstShift = [&](Value *V, Value *W) {
APInt Threshold(Ty->getScalarSizeInBits(), Ty->getScalarSizeInBits());
+ if (isa<Constant>(W)) {
+ return match(V, (m_BinOp(ShiftOpcode, m_Value(X), m_Constant(C0)))) &&
+ match(ConstantExpr::getAdd(C0, C1),
+ m_SpecificInt_ICMP(ICmpInst::ICMP_ULT, Threshold));
+ }
return match(V,
m_OneUse(m_BinOp(ShiftOpcode, m_Value(X), m_Constant(C0)))) &&
match(ConstantExpr::getAdd(C0, C1),
@@ -382,9 +386,9 @@ static Instruction *foldShiftOfShiftedBinOp(BinaryOperator &I,
// is not so we cannot reoder if we match operand(1) and need to keep the
// operands in their original positions.
bool FirstShiftIsOp1 = false;
- if (matchFirstShift(BinInst->getOperand(0)))
+ if (matchFirstShift(BinInst->getOperand(0), BinInst->getOperand(1)))
Y = BinInst->getOperand(1);
- else if (matchFirstShift(BinInst->getOperand(1))) {
+ else if (matchFirstShift(BinInst->getOperand(1), BinInst->getOperand(0))) {
Y = BinInst->getOperand(0);
FirstShiftIsOp1 = BinInst->getOpcode() == Instruction::Sub;
} else
``````````
</details>
https://github.com/llvm/llvm-project/pull/77973
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