Some day the backend may handle instruction-level fast math flags and make
this transform unnecessary, but it's still better practice to use the canonical
representation of fneg when possible (use a -0.0).
This is a partial fix for PR20870 ( http://llvm.org/bugs/show_bug.cgi?id=20870 ).
See also http://reviews.llvm.org/D6723.
Differential Revision: http://reviews.llvm.org/D6731
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@225050
91177308-0d34-0410-b5e6-
96231b3b80d8
TLI, DT, AT))
return ReplaceInstUsesWith(I, V);
+ // fsub nsz 0, X ==> fsub nsz -0.0, X
+ if (I.getFastMathFlags().noSignedZeros() && match(Op0, m_Zero())) {
+ // Subtraction from -0.0 is the canonical form of fneg.
+ Instruction *NewI = BinaryOperator::CreateFNeg(Op1);
+ NewI->copyFastMathFlags(&I);
+ return NewI;
+ }
+
if (isa<Constant>(Op0))
if (SelectInst *SI = dyn_cast<SelectInst>(Op1))
if (Instruction *NV = FoldOpIntoSelect(I, SI))
; CHECK: fmul float %f1, %f2
}
+define float @fneg2(float %x) {
+ %sub = fsub nsz float 0.0, %x
+ ret float %sub
+; CHECK-LABEL: @fneg2(
+; CHECK-NEXT: fsub nsz float -0.000000e+00, %x
+; CHECK-NEXT: ret float
+}
+
; =========================================================================
;
; Testing-cases about div