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[InstCombine] Fold abs(-x) -> abs(x)

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Negating the input doesn't matter. I left a FIXME to copy the nsw flag if its present on the neg but not on the abs.

Reviewed By: nikic

Differential Revision: https://reviews.llvm.org/D85055
This commit is contained in:
Craig Topper 2020-08-01 09:59:09 -07:00
parent ab94d6392d
commit 8ed321d822
2 changed files with 30 additions and 0 deletions
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10
lib/Transforms/InstCombine/InstCombineCalls.cpp
View File

@ -769,6 +769,16 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
if (Value *V = lowerObjectSizeCall(II, DL, &TLI, /*MustSucceed=*/false))
return replaceInstUsesWith(CI, V);
return nullptr;
case Intrinsic::abs: {
Value *IIOperand = II->getArgOperand(0);
// abs(-x) -> abs(x)
// TODO: Copy nsw if it was present on the neg?
Value *X;
if (match(IIOperand, m_Neg(m_Value(X))))
return replaceOperand(*II, 0, X);
break;
}
case Intrinsic::bswap: {
Value *IIOperand = II->getArgOperand(0);
Value *X = nullptr;

20
test/Transforms/InstCombine/abs-intrinsic.ll
View File

@ -165,3 +165,23 @@ define <4 x i1> @abs_known_not_int_min_vec(<4 x i32> %x) {
%c2 = icmp sge <4 x i32> %abs, zeroinitializer
ret <4 x i1> %c2
}
define i32 @abs_of_neg(i32 %x) {
; CHECK-LABEL: @abs_of_neg(
; CHECK-NEXT: [[B:%.*]] = call i32 @llvm.abs.i32(i32 [[X:%.*]], i1 false)
; CHECK-NEXT: ret i32 [[B]]
;
%a = sub i32 0, %x
%b = call i32 @llvm.abs.i32(i32 %a, i1 false)
ret i32 %b
}
define <4 x i32> @abs_of_neg_vec(<4 x i32> %x) {
; CHECK-LABEL: @abs_of_neg_vec(
; CHECK-NEXT: [[B:%.*]] = call <4 x i32> @llvm.abs.v4i32(<4 x i32> [[X:%.*]], i1 false)
; CHECK-NEXT: ret <4 x i32> [[B]]
;
%a = sub nsw <4 x i32> zeroinitializer, %x
%b = call <4 x i32> @llvm.abs.v4i32(<4 x i32> %a, i1 false)
ret <4 x i32> %b
}