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[InstCombine] Handle ssubo always overflow 

Following D60483 and D60497, this adds support for AlwaysOverflows
handling for ssubo. This is the last case we can handle right now.

Differential Revision: https://reviews.llvm.org/D60518

llvm-svn: 358100
This commit is contained in:
Nikita Popov 2019-04-10 16:32:15 +00:00
parent 7a543c3758
commit 0a8228fd28
2 changed files with 6 additions and 5 deletions
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6
llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
View File

@ -3997,15 +3997,15 @@ bool InstCombiner::OptimizeOverflowCheck(OverflowCheckFlavor OCF, Value *LHS,
if (OR == OverflowResult::NeverOverflows)
return SetResult(Builder.CreateNUWSub(LHS, RHS), Builder.getFalse(),
true);
if (OR == OverflowResult::AlwaysOverflows)
return SetResult(Builder.CreateSub(LHS, RHS), Builder.getTrue(), true);
} else {
OR = computeOverflowForSignedSub(LHS, RHS, &OrigI);
if (OR == OverflowResult::NeverOverflows)
return SetResult(Builder.CreateNSWSub(LHS, RHS), Builder.getFalse(),
true);
}
if (OR == OverflowResult::AlwaysOverflows)
return SetResult(Builder.CreateSub(LHS, RHS), Builder.getTrue(), true);
break;
}

5
llvm/test/Transforms/InstCombine/with_overflow.ll
View File

@ -582,8 +582,9 @@ define { i8, i1 } @ssub_always_overflow(i8 %x) nounwind {
; CHECK-LABEL: @ssub_always_overflow(
; CHECK-NEXT: [[C:%.*]] = icmp sgt i8 [[X:%.*]], 29
; CHECK-NEXT: [[Y:%.*]] = select i1 [[C]], i8 [[X]], i8 29
; CHECK-NEXT: [[A:%.*]] = call { i8, i1 } @llvm.ssub.with.overflow.i8(i8 -100, i8 [[Y]])
; CHECK-NEXT: ret { i8, i1 } [[A]]
; CHECK-NEXT: [[A:%.*]] = sub nuw i8 -100, [[Y]]
; CHECK-NEXT: [[TMP1:%.*]] = insertvalue { i8, i1 } { i8 undef, i1 true }, i8 [[A]], 0
; CHECK-NEXT: ret { i8, i1 } [[TMP1]]
;
%c = icmp sgt i8 %x, 29
%y = select i1 %c, i8 %x, i8 29