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[InstCombine] Handle usubo always overflow 

Check AlwaysOverflow condition for usubo. The implementation is the
same as the existing handling for uaddo and umulo. Handling for saddo
and ssubo will follow (smulo doesn't have the necessary ValueTracking
support).

Differential Revision: https://reviews.llvm.org/D60483

llvm-svn: 358052
This commit is contained in:
Nikita Popov 2019-04-10 07:10:53 +00:00
parent 596cbeb705
commit 09020ec2a7
2 changed files with 6 additions and 2 deletions
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3
llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
View File

@ -3997,6 +3997,9 @@ 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)

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

@ -544,8 +544,9 @@ define { i8, i1 } @uadd_always_overflow(i8 %x) nounwind {
define { i8, i1 } @usub_always_overflow(i8 %x) nounwind {
; CHECK-LABEL: @usub_always_overflow(
; CHECK-NEXT: [[Y:%.*]] = or i8 [[X:%.*]], 64
; CHECK-NEXT: [[A:%.*]] = call { i8, i1 } @llvm.usub.with.overflow.i8(i8 63, i8 [[Y]])
; CHECK-NEXT: ret { i8, i1 } [[A]]
; CHECK-NEXT: [[A:%.*]] = sub nsw i8 63, [[Y]]
; CHECK-NEXT: [[TMP1:%.*]] = insertvalue { i8, i1 } { i8 undef, i1 true }, i8 [[A]], 0
; CHECK-NEXT: ret { i8, i1 } [[TMP1]]
;
%y = or i8 %x, 64
%a = call { i8, i1 } @llvm.usub.with.overflow.i8(i8 63, i8 %y)