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[InstCombine] Preserve 'exact' in -(X >>u 31) -> (X >>s 31) fold 

https://rise4fun.com/Alive/yR4

llvm-svn: 373363
This commit is contained in:
Roman Lebedev 2019-10-01 17:50:09 +00:00
parent f273fc793a
commit 65144149d0
2 changed files with 8 additions and 4 deletions
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8
llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
View File

@ -1676,12 +1676,16 @@ Instruction *InstCombiner::visitSub(BinaryOperator &I) {
if (match(Op1, m_LShr(m_Value(X), m_APInt(ShAmt))) &&
*ShAmt == BitWidth - 1) {
Value *ShAmtOp = cast<Instruction>(Op1)->getOperand(1);
return BinaryOperator::CreateAShr(X, ShAmtOp);
Instruction *NewShift = BinaryOperator::CreateAShr(X, ShAmtOp);
NewShift->copyIRFlags(Op1);
return NewShift;
}
if (match(Op1, m_AShr(m_Value(X), m_APInt(ShAmt))) &&
*ShAmt == BitWidth - 1) {
Value *ShAmtOp = cast<Instruction>(Op1)->getOperand(1);
return BinaryOperator::CreateLShr(X, ShAmtOp);
Instruction *NewShift = BinaryOperator::CreateLShr(X, ShAmtOp);
NewShift->copyIRFlags(Op1);
return NewShift;
}
if (Op1->hasOneUse()) {

4
llvm/test/Transforms/InstCombine/high-bit-signmask.ll
View File

@ -12,7 +12,7 @@ define i64 @t0(i64 %x) {
}
define i64 @t0_exact(i64 %x) {
; CHECK-LABEL: @t0_exact(
; CHECK-NEXT: [[R:%.*]] = ashr i64 [[X:%.*]], 63
; CHECK-NEXT: [[R:%.*]] = ashr exact i64 [[X:%.*]], 63
; CHECK-NEXT: ret i64 [[R]]
;
%t0 = lshr exact i64 %x, 63
@ -30,7 +30,7 @@ define i64 @t2(i64 %x) {
}
define i64 @t3_exact(i64 %x) {
; CHECK-LABEL: @t3_exact(
; CHECK-NEXT: [[R:%.*]] = lshr i64 [[X:%.*]], 63
; CHECK-NEXT: [[R:%.*]] = lshr exact i64 [[X:%.*]], 63
; CHECK-NEXT: ret i64 [[R]]
;
%t0 = ashr exact i64 %x, 63