On Wed, 28 Sep 2016, Joseph Myers wrote:
> On Wed, 28 Sep 2016, Richard Biener wrote:
>
> > Index: gcc/testsuite/gcc.dg/pr55152.c
> > ===================================================================
> > --- gcc/testsuite/gcc.dg/pr55152.c (revision 0)
> > +++ gcc/testsuite/gcc.dg/pr55152.c (working copy)
> > @@ -0,0 +1,13 @@
> > +/* { dg-do compile } */
> > +/* { dg-options "-O -ffinite-math-only -fstrict-overflow
> > -fdump-tree-optimized" } */
> > +
> > +double g (double a)
> > +{
> > + return (a>=-a)?a:-a;
>
> You should need -fno-signed-zeros for this (that is, for the
> transformation to MAX_EXPR), not -ffinite-math-only. For a == -0, that
> function should return -0, but abs would produce +0.
This means that tree-ssa-phiopt.c has a bug:
static bool
minmax_replacement (basic_block cond_bb, basic_block middle_bb,
edge e0, edge e1, gimple *phi,
tree arg0, tree arg1)
{
...
/* The optimization may be unsafe due to NaNs. */
if (HONOR_NANS (type))
return false;
and it should check HONOR_SIGNED_ZEROS as well.
I'll fix that as a followup.
Thanks,
Richard.
