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[InstCombine] Handle GEP inbounds in select op replacement (PR47730)

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When retrying the "simplify with operand replaced" select
optimization without poison flags, also handle inbounds on GEPs.

Of course, this particular example would also be safe to transform
while keeping inbounds, but the underlying machinery does not
know this (yet).
This commit is contained in:
Nikita Popov 2020-10-05 21:13:02 +02:00
parent 1f54eb0252
commit 2071b043eb
2 changed files with 10 additions and 5 deletions
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8
lib/Transforms/InstCombine/InstCombineSelect.cpp
View File

@ -1200,7 +1200,7 @@ Instruction *InstCombinerImpl::foldSelectValueEquivalence(SelectInst &Sel,
// InstSimplify already performed this fold if it was possible subject to
// current poison-generating flags. Try the transform again with
// poison-generating flags temporarily dropped.
bool WasNUW = false, WasNSW = false, WasExact = false;
bool WasNUW = false, WasNSW = false, WasExact = false, WasInBounds = false;
if (auto *OBO = dyn_cast<OverflowingBinaryOperator>(FalseVal)) {
WasNUW = OBO->hasNoUnsignedWrap();
WasNSW = OBO->hasNoSignedWrap();
@ -1211,6 +1211,10 @@ Instruction *InstCombinerImpl::foldSelectValueEquivalence(SelectInst &Sel,
WasExact = PEO->isExact();
FalseInst->setIsExact(false);
}
if (auto *GEP = dyn_cast<GetElementPtrInst>(FalseVal)) {
WasInBounds = GEP->isInBounds();
GEP->setIsInBounds(false);
}
// Try each equivalence substitution possibility.
// We have an 'EQ' comparison, so the select's false value will propagate.
@ -1230,6 +1234,8 @@ Instruction *InstCombinerImpl::foldSelectValueEquivalence(SelectInst &Sel,
FalseInst->setHasNoSignedWrap();
if (WasExact)
FalseInst->setIsExact();
if (WasInBounds)
cast<GetElementPtrInst>(FalseInst)->setIsInBounds();
return nullptr;
}

7
test/Transforms/InstCombine/select.ll
View File

@ -2725,12 +2725,11 @@ define i32 @select_replacement_loop2(i32 %arg, i32 %arg2) {
ret i32 %sel
}
; TODO: Dropping the inbounds flag should not be necessary for this fold.
define i8* @select_replacement_gep_inbounds(i8* %base, i64 %offset) {
; CHECK-LABEL: @select_replacement_gep_inbounds(
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i64 [[OFFSET:%.*]], 0
; CHECK-NEXT: [[GEP:%.*]] = getelementptr inbounds i8, i8* [[BASE:%.*]], i64 [[OFFSET]]
; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i8* [[BASE]], i8* [[GEP]]
; CHECK-NEXT: ret i8* [[SEL]]
; CHECK-NEXT: [[GEP:%.*]] = getelementptr i8, i8* [[BASE:%.*]], i64 [[OFFSET:%.*]]
; CHECK-NEXT: ret i8* [[GEP]]
;
%cmp = icmp eq i64 %offset, 0
%gep = getelementptr inbounds i8, i8* %base, i64 %offset