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[InstSimplify] fsub 0.0, (fsub -0.0, X) ==> X is only safe if signed zeros are ignored. 

Only allow fsub -0.0, (fsub -0.0, X) ==> X without nsz. PR26746.

llvm-svn: 262212
This commit is contained in:
Benjamin Kramer 2016-02-29 11:12:23 +00:00
parent 27ba83fd45
commit f5b2a47ac6
2 changed files with 31 additions and 10 deletions
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15
llvm/lib/Analysis/InstructionSimplify.cpp
View File

@ -833,14 +833,15 @@ static Value *SimplifyFSubInst(Value *Op0, Value *Op1, FastMathFlags FMF,
(FMF.noSignedZeros() || CannotBeNegativeZero(Op0)))
return Op0;
// fsub 0, (fsub -0.0, X) ==> X
// fsub -0.0, (fsub -0.0, X) ==> X
Value *X;
if (match(Op0, m_AnyZero())) {
if (match(Op1, m_FSub(m_NegZero(), m_Value(X))))
return X;
if (FMF.noSignedZeros() && match(Op1, m_FSub(m_AnyZero(), m_Value(X))))
return X;
}
if (match(Op0, m_NegZero()) && match(Op1, m_FSub(m_NegZero(), m_Value(X))))
return X;
// fsub 0.0, (fsub 0.0, X) ==> X if signed zeros are ignored.
if (FMF.noSignedZeros() && match(Op0, m_NegZero()) &&
match(Op1, m_FSub(m_AnyZero(), m_Value(X))))
return X;
// fsub nnan x, x ==> 0.0
if (FMF.noNaNs() && Op0 == Op1)

26
llvm/test/Transforms/InstSimplify/floating-point-arithmetic.ll
View File

@ -1,8 +1,8 @@
; RUN: opt < %s -instsimplify -S | FileCheck %s
; fsub 0, (fsub 0, X) ==> X
; CHECK-LABEL: @fsub_0_0_x(
define float @fsub_0_0_x(float %a) {
; fsub -0.0, (fsub -0.0, X) ==> X
; CHECK-LABEL: @fsub_-0_-0_x(
define float @fsub_-0_-0_x(float %a) {
%t1 = fsub float -0.0, %a
%ret = fsub float -0.0, %t1
@ -10,6 +10,26 @@ define float @fsub_0_0_x(float %a) {
ret float %ret
}
; fsub 0.0, (fsub -0.0, X) != X
; CHECK-LABEL: @fsub_0_-0_x(
define float @fsub_0_-0_x(float %a) {
%t1 = fsub float 0.0, %a
%ret = fsub float -0.0, %t1
; CHECK-NOT: ret float %a
ret float %ret
}
; fsub -0.0, (fsub 0.0, X) != X
; CHECK-LABEL: @fsub_-0_0_x(
define float @fsub_-0_0_x(float %a) {
%t1 = fsub float -0.0, %a
%ret = fsub float 0.0, %t1
; CHECK-NOT: ret float %a
ret float %ret
}
; fsub X, 0 ==> X
; CHECK-LABEL: @fsub_x_0(
define float @fsub_x_0(float %a) {