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

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It's always safe to pick the earlier abs regardless of the nsw flag. We'll just lose it if it is on the outer abs but not the inner abs.

Differential Revision: https://reviews.llvm.org/D85053
This commit is contained in:
Craig Topper 2020-08-01 10:01:58 -07:00
parent 8ed321d822
commit 183d6fbbe7
2 changed files with 45 additions and 0 deletions
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5
lib/Analysis/InstructionSimplify.cpp
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@ -5256,6 +5256,11 @@ static Value *simplifyBinaryIntrinsic(Function *F, Value *Op0, Value *Op1,
unsigned BitWidth = ReturnType->getScalarSizeInBits();
switch (IID) {
case Intrinsic::abs:
// abs(abs(x)) -> abs(x). We don't need to worry about the nsw arg here.
// It is always ok to pick the earlier abs. We'll just lose nsw if its only
// on the outer abs.
if (match(Op0, m_Intrinsic<Intrinsic::abs>(m_Value(), m_Value())))
return Op0;
// If the sign bit is clear already, then abs does not do anything.
if (isKnownNonNegative(Op0, Q.DL, 0, Q.AC, Q.CxtI, Q.DT))
return Op0;

40
test/Transforms/InstSimplify/call.ll
View File

@ -5,6 +5,46 @@
declare i32 @llvm.abs.i32(i32, i1)
declare <3 x i82> @llvm.abs.v3i82(<3 x i82>, i1)
define i32 @test_abs_abs_0(i32 %x) {
; CHECK-LABEL: @test_abs_abs_0(
; CHECK-NEXT: [[A:%.*]] = call i32 @llvm.abs.i32(i32 [[X:%.*]], i1 false)
; CHECK-NEXT: ret i32 [[A]]
;
%a = call i32 @llvm.abs.i32(i32 %x, i1 false)
%b = call i32 @llvm.abs.i32(i32 %a, i1 false)
ret i32 %b
}
define i32 @test_abs_abs_1(i32 %x) {
; CHECK-LABEL: @test_abs_abs_1(
; CHECK-NEXT: [[A:%.*]] = call i32 @llvm.abs.i32(i32 [[X:%.*]], i1 true)
; CHECK-NEXT: ret i32 [[A]]
;
%a = call i32 @llvm.abs.i32(i32 %x, i1 true)
%b = call i32 @llvm.abs.i32(i32 %a, i1 false)
ret i32 %b
}
define i32 @test_abs_abs_2(i32 %x) {
; CHECK-LABEL: @test_abs_abs_2(
; CHECK-NEXT: [[A:%.*]] = call i32 @llvm.abs.i32(i32 [[X:%.*]], i1 false)
; CHECK-NEXT: ret i32 [[A]]
;
%a = call i32 @llvm.abs.i32(i32 %x, i1 false)
%b = call i32 @llvm.abs.i32(i32 %a, i1 true)
ret i32 %b
}
define i32 @test_abs_abs_3(i32 %x) {
; CHECK-LABEL: @test_abs_abs_3(
; CHECK-NEXT: [[A:%.*]] = call i32 @llvm.abs.i32(i32 [[X:%.*]], i1 true)
; CHECK-NEXT: ret i32 [[A]]
;
%a = call i32 @llvm.abs.i32(i32 %x, i1 true)
%b = call i32 @llvm.abs.i32(i32 %a, i1 true)
ret i32 %b
}
; If the sign bit is known zero, the abs is not needed.
define i32 @zext_abs(i31 %x) {