On Thu, 29 Sep 2016, Richard Biener wrote:
> 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.
Committed as follows.
Bootstrapped / tested on x86_64-unknown-linux-gnu.
Richard.
2016-09-29 Richard Biener <rguent...@suse.de>
PR middle-end/55152
* match.pd: Add max(a,-a) -> abs(a) pattern.
* tree-ssa-phiopt.c (minmax_replacement): Disable for
HONOR_SIGNED_ZEROS types.
* gcc.dg/pr55152.c: New testcase.
* gcc.dg/tree-ssa/phi-opt-5.c: Adjust.
Index: gcc/match.pd
===================================================================
--- gcc/match.pd (revision 240565)
+++ gcc/match.pd (working copy)
@@ -1271,6 +1284,13 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
(simplify
(max:c (min:c @0 @1) @1)
@1)
+/* max(a,-a) -> abs(a). */
+(simplify
+ (max:c @0 (negate @0))
+ (if (TREE_CODE (type) != COMPLEX_TYPE
+ && (! ANY_INTEGRAL_TYPE_P (type)
+ || TYPE_OVERFLOW_UNDEFINED (type)))
+ (abs @0)))
(simplify
(min @0 @1)
(switch
Index: gcc/tree-ssa-phiopt.c
===================================================================
--- gcc/tree-ssa-phiopt.c (revision 240565)
+++ gcc/tree-ssa-phiopt.c (working copy)
@@ -1075,7 +1075,7 @@ minmax_replacement (basic_block cond_bb,
type = TREE_TYPE (PHI_RESULT (phi));
/* The optimization may be unsafe due to NaNs. */
- if (HONOR_NANS (type))
+ if (HONOR_NANS (type) || HONOR_SIGNED_ZEROS (type))
return false;
cond = as_a <gcond *> (last_stmt (cond_bb));
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 -fno-signed-zeros -fstrict-overflow
-fdump-tree-optimized" } */
+
+double g (double a)
+{
+ return (a>=-a)?a:-a;
+}
+int f(int a)
+{
+ return (a>=-a)?a:-a;
+}
+
+/* { dg-final { scan-tree-dump-times "ABS_EXPR" 2 "optimized" } } */
Index: gcc/testsuite/gcc.dg/tree-ssa/phi-opt-5.c
===================================================================
--- gcc/testsuite/gcc.dg/tree-ssa/phi-opt-5.c (revision 240612)
+++ gcc/testsuite/gcc.dg/tree-ssa/phi-opt-5.c (working copy)
@@ -1,5 +1,5 @@
/* { dg-do compile } */
-/* { dg-options "-O1 -ffinite-math-only -fdump-tree-phiopt1" } */
+/* { dg-options "-O1 -ffinite-math-only -fno-signed-zeros -fdump-tree-phiopt1"
} */
float repl1 (float varx)
{
