Re: [PATCH, rs6000] Disable gimple fold for float or double vec_minmax when fast-math is not set

[Richard Biener <richard.guenther@gmail.com>]

On Tue, Oct 12, 2021 at 10:59 AM HAO CHEN GUI via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> Hi,
>
>     This patch disables gimple folding for float or double vec_min/max when fast-math is not set. It makes vec_min/max conform with the guide.
>
> Bootstrapped and tested on powerpc64le-linux with no regressions. Is this okay for trunk? Any recommendations? Thanks a lot.
>
>     I re-send the patch as previous one is messed up in email thread. Sorry for that.

If the VSX/altivec min/max instructions conform to IEEE behavior then
you could instead fold
to .F{MIN,MAX} internal functions and define the f{min,max} optabs.

Otherwise the patch looks correct to me - MIN_EXPR and MAX_EXPR are
not IEEE conforming.
Note a better check would be to use HONOR_NANS/HONOR_SIGNED_ZEROS on
the argument type
(that also works for the integer types with the obvious answer).

Richard.

> ChangeLog
>
> 2021-08-25 Haochen Gui <guihaoc@linux.ibm.com>
>
> gcc/
>          * config/rs6000/rs6000-call.c (rs6000_gimple_fold_builtin):
>          Modify the VSX_BUILTIN_XVMINDP, ALTIVEC_BUILTIN_VMINFP,
>          VSX_BUILTIN_XVMAXDP, ALTIVEC_BUILTIN_VMAXFP expansions.
>
> gcc/testsuite/
>          * gcc.target/powerpc/vec-minmax-1.c: New test.
>          * gcc.target/powerpc/vec-minmax-2.c: Likewise.
>
>
> patch.diff
>
> diff --git a/gcc/config/rs6000/rs6000-call.c b/gcc/config/rs6000/rs6000-call.c
> index b4e13af4dc6..90527734ceb 100644
> --- a/gcc/config/rs6000/rs6000-call.c
> +++ b/gcc/config/rs6000/rs6000-call.c
> @@ -12159,6 +12159,11 @@ rs6000_gimple_fold_builtin (gimple_stmt_iterator *gsi)
>         return true;
>       /* flavors of vec_min.  */
>       case VSX_BUILTIN_XVMINDP:
> +    case ALTIVEC_BUILTIN_VMINFP:
> +      if (!flag_finite_math_only || flag_signed_zeros)
> +       return false;
> +      /* Fall through to MIN_EXPR.  */
> +      gcc_fallthrough ();
>       case P8V_BUILTIN_VMINSD:
>       case P8V_BUILTIN_VMINUD:
>       case ALTIVEC_BUILTIN_VMINSB:
> @@ -12167,7 +12172,6 @@ rs6000_gimple_fold_builtin (gimple_stmt_iterator *gsi)
>       case ALTIVEC_BUILTIN_VMINUB:
>       case ALTIVEC_BUILTIN_VMINUH:
>       case ALTIVEC_BUILTIN_VMINUW:
> -    case ALTIVEC_BUILTIN_VMINFP:
>         arg0 = gimple_call_arg (stmt, 0);
>         arg1 = gimple_call_arg (stmt, 1);
>         lhs = gimple_call_lhs (stmt);
> @@ -12177,6 +12181,11 @@ rs6000_gimple_fold_builtin (gimple_stmt_iterator *gsi)
>         return true;
>       /* flavors of vec_max.  */
>       case VSX_BUILTIN_XVMAXDP:
> +    case ALTIVEC_BUILTIN_VMAXFP:
> +      if (!flag_finite_math_only || flag_signed_zeros)
> +       return false;
> +      /* Fall through to MAX_EXPR.  */
> +      gcc_fallthrough ();
>       case P8V_BUILTIN_VMAXSD:
>       case P8V_BUILTIN_VMAXUD:
>       case ALTIVEC_BUILTIN_VMAXSB:
> @@ -12185,7 +12194,6 @@ rs6000_gimple_fold_builtin (gimple_stmt_iterator *gsi)
>       case ALTIVEC_BUILTIN_VMAXUB:
>       case ALTIVEC_BUILTIN_VMAXUH:
>       case ALTIVEC_BUILTIN_VMAXUW:
> -    case ALTIVEC_BUILTIN_VMAXFP:
>         arg0 = gimple_call_arg (stmt, 0);
>         arg1 = gimple_call_arg (stmt, 1);
>         lhs = gimple_call_lhs (stmt);
> diff --git a/gcc/testsuite/gcc.target/powerpc/vec-minmax-1.c b/gcc/testsuite/gcc.target/powerpc/vec-minmax-1.c
> new file mode 100644
> index 00000000000..547798fd65c
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/powerpc/vec-minmax-1.c
> @@ -0,0 +1,53 @@
> +/* { dg-do compile { target { powerpc*-*-* } } } */
> +/* { dg-require-effective-target powerpc_p9vector_ok } */
> +/* { dg-options "-O2 -mdejagnu-cpu=power9" } */
> +/* { dg-final { scan-assembler-times {\mxvmaxdp\M} 1 } } */
> +/* { dg-final { scan-assembler-times {\mxvmaxsp\M} 1 } } */
> +/* { dg-final { scan-assembler-times {\mxvmindp\M} 1 } } */
> +/* { dg-final { scan-assembler-times {\mxvminsp\M} 1 } } */
> +
> +/* This test verifies that float or double vec_min/max are bound to
> +   xv[min|max][d|s]p instructions when fast-math is not set.  */
> +
> +
> +#include <altivec.h>
> +
> +#ifdef _BIG_ENDIAN
> +   const int PREF_D = 0;
> +#else
> +   const int PREF_D = 1;
> +#endif
> +
> +double vmaxd (double a, double b)
> +{
> +  vector double va = vec_promote (a, PREF_D);
> +  vector double vb = vec_promote (b, PREF_D);
> +  return vec_extract (vec_max (va, vb), PREF_D);
> +}
> +
> +double vmind (double a, double b)
> +{
> +  vector double va = vec_promote (a, PREF_D);
> +  vector double vb = vec_promote (b, PREF_D);
> +  return vec_extract (vec_min (va, vb), PREF_D);
> +}
> +
> +#ifdef _BIG_ENDIAN
> +   const int PREF_F = 0;
> +#else
> +   const int PREF_F = 3;
> +#endif
> +
> +float vmaxf (float a, float b)
> +{
> +  vector float va = vec_promote (a, PREF_F);
> +  vector float vb = vec_promote (b, PREF_F);
> +  return vec_extract (vec_max (va, vb), PREF_F);
> +}
> +
> +float vminf (float a, float b)
> +{
> +  vector float va = vec_promote (a, PREF_F);
> +  vector float vb = vec_promote (b, PREF_F);
> +  return vec_extract (vec_min (va, vb), PREF_F);
> +}
> diff --git a/gcc/testsuite/gcc.target/powerpc/vec-minmax-2.c b/gcc/testsuite/gcc.target/powerpc/vec-minmax-2.c
> new file mode 100644
> index 00000000000..4c6f4365830
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/powerpc/vec-minmax-2.c
> @@ -0,0 +1,51 @@
> +/* { dg-do compile { target { powerpc*-*-* } } } */
> +/* { dg-require-effective-target powerpc_p9vector_ok } */
> +/* { dg-options "-O2 -mdejagnu-cpu=power9 -ffast-math" } */
> +/* { dg-final { scan-assembler-times {\mxsmaxcdp\M} 2 } } */
> +/* { dg-final { scan-assembler-times {\mxsmincdp\M} 2 } } */
> +
> +/* This test verifies that float or double vec_min/max can be converted
> +   to scalar comparison when fast-math is set.  */
> +
> +
> +#include <altivec.h>
> +
> +#ifdef _BIG_ENDIAN
> +   const int PREF_D = 0;
> +#else
> +   const int PREF_D = 1;
> +#endif
> +
> +double vmaxd (double a, double b)
> +{
> +  vector double va = vec_promote (a, PREF_D);
> +  vector double vb = vec_promote (b, PREF_D);
> +  return vec_extract (vec_max (va, vb), PREF_D);
> +}
> +
> +double vmind (double a, double b)
> +{
> +  vector double va = vec_promote (a, PREF_D);
> +  vector double vb = vec_promote (b, PREF_D);
> +  return vec_extract (vec_min (va, vb), PREF_D);
> +}
> +
> +#ifdef _BIG_ENDIAN
> +   const int PREF_F = 0;
> +#else
> +   const int PREF_F = 3;
> +#endif
> +
> +float vmaxf (float a, float b)
> +{
> +  vector float va = vec_promote (a, PREF_F);
> +  vector float vb = vec_promote (b, PREF_F);
> +  return vec_extract (vec_max (va, vb), PREF_F);
> +}
> +
> +float vminf (float a, float b)
> +{
> +  vector float va = vec_promote (a, PREF_F);
> +  vector float vb = vec_promote (b, PREF_F);
> +  return vec_extract (vec_min (va, vb), PREF_F);
> +}
>