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[InstCombine] fix use check when canonicalizing abs/nabs 

We were checking for extra uses of the negated operand even
if we were not going to create it as part of this canonicalization.

This was showing up as a regression when we limit EarlyCSE as
proposed in D74285.
This commit is contained in:
Sanjay Patel 2020-02-10 14:50:51 -05:00
parent 93073e52b1
commit 62ce7e650a
2 changed files with 13 additions and 12 deletions
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9
llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
View File

@ -1073,10 +1073,11 @@ static Instruction *canonicalizeAbsNabs(SelectInst &Sel, ICmpInst &Cmp,
if (CmpCanonicalized && RHSCanonicalized)
return nullptr;
// If RHS is used by other instructions except compare and select, don't
// canonicalize it to not increase the instruction count.
if (!(RHS->hasOneUse() || (RHS->hasNUses(2) && CmpUsesNegatedOp)))
return nullptr;
// If RHS is not canonical but is used by other instructions, don't
// canonicalize it and potentially increase the instruction count.
if (!RHSCanonicalized)
if (!(RHS->hasOneUse() || (RHS->hasNUses(2) && CmpUsesNegatedOp)))
return nullptr;
// Create the canonical compare: icmp slt LHS 0.
if (!CmpCanonicalized) {

16
llvm/test/Transforms/InstCombine/abs-1.ll
View File

@ -573,8 +573,8 @@ define i8 @abs_swapped(i8 %a) {
; CHECK-LABEL: @abs_swapped(
; CHECK-NEXT: [[NEG:%.*]] = sub i8 0, [[A:%.*]]
; CHECK-NEXT: call void @extra_use(i8 [[NEG]])
; CHECK-NEXT: [[CMP1:%.*]] = icmp sgt i8 [[A]], 0
; CHECK-NEXT: [[M1:%.*]] = select i1 [[CMP1]], i8 [[A]], i8 [[NEG]]
; CHECK-NEXT: [[CMP1:%.*]] = icmp slt i8 [[A]], 0
; CHECK-NEXT: [[M1:%.*]] = select i1 [[CMP1]], i8 [[NEG]], i8 [[A]]
; CHECK-NEXT: ret i8 [[M1]]
;
%neg = sub i8 0, %a
@ -588,8 +588,8 @@ define i8 @nabs_swapped(i8 %a) {
; CHECK-LABEL: @nabs_swapped(
; CHECK-NEXT: [[NEG:%.*]] = sub i8 0, [[A:%.*]]
; CHECK-NEXT: call void @extra_use(i8 [[NEG]])
; CHECK-NEXT: [[CMP2:%.*]] = icmp sgt i8 [[A]], 0
; CHECK-NEXT: [[M2:%.*]] = select i1 [[CMP2]], i8 [[NEG]], i8 [[A]]
; CHECK-NEXT: [[CMP2:%.*]] = icmp slt i8 [[A]], 0
; CHECK-NEXT: [[M2:%.*]] = select i1 [[CMP2]], i8 [[A]], i8 [[NEG]]
; CHECK-NEXT: ret i8 [[M2]]
;
%neg = sub i8 0, %a
@ -603,8 +603,8 @@ define i8 @abs_different_constants(i8 %a) {
; CHECK-LABEL: @abs_different_constants(
; CHECK-NEXT: [[NEG:%.*]] = sub i8 0, [[A:%.*]]
; CHECK-NEXT: call void @extra_use(i8 [[NEG]])
; CHECK-NEXT: [[CMP1:%.*]] = icmp sgt i8 [[A]], -1
; CHECK-NEXT: [[M1:%.*]] = select i1 [[CMP1]], i8 [[A]], i8 [[NEG]]
; CHECK-NEXT: [[CMP1:%.*]] = icmp slt i8 [[A]], 0
; CHECK-NEXT: [[M1:%.*]] = select i1 [[CMP1]], i8 [[NEG]], i8 [[A]]
; CHECK-NEXT: ret i8 [[M1]]
;
%neg = sub i8 0, %a
@ -618,8 +618,8 @@ define i8 @nabs_different_constants(i8 %a) {
; CHECK-LABEL: @nabs_different_constants(
; CHECK-NEXT: [[NEG:%.*]] = sub i8 0, [[A:%.*]]
; CHECK-NEXT: call void @extra_use(i8 [[NEG]])
; CHECK-NEXT: [[CMP2:%.*]] = icmp sgt i8 [[A]], -1
; CHECK-NEXT: [[M2:%.*]] = select i1 [[CMP2]], i8 [[NEG]], i8 [[A]]
; CHECK-NEXT: [[CMP2:%.*]] = icmp slt i8 [[A]], 0
; CHECK-NEXT: [[M2:%.*]] = select i1 [[CMP2]], i8 [[A]], i8 [[NEG]]
; CHECK-NEXT: ret i8 [[M2]]
;
%neg = sub i8 0, %a