Re: [PATCH] rs6000: Don't use TFmode for 128 bits fp constant in toc [PR110011]

[David Edelsohn <dje.gcc@gmail.com>]

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On Tue, Jun 6, 2023 at 5:20 AM Kewen.Lin <linkw@linux.ibm.com> wrote:

> Hi,
>
> As PR110011 shows, when encoding 128 bits fp constant into
> toc, we adopts REAL_VALUE_TO_TARGET_LONG_DOUBLE which is
> to find the first float mode with LONG_DOUBLE_TYPE_SIZE
> bits of precision, it would be TFmode here.  But the 128
> bits fp constant can be with mode IFmode or KFmode, which
> doesn't necessarily have the same underlying float format
> as the one of TFmode, like this PR exposes, with option
> -mabi=ibmlongdouble TFmode has ibm_extended_format while
> KFmode has ieee_quad_format, mixing up the formats (the
> encoding/decoding ways) would cause unexpected results.
>
> This patch is to make it use constant's own mode instead
> of TFmode for real_to_target call.
>
> Bootstrapped and regtested on powerpc64-linux-gnu P7/P8/P9 and
> powerpc64le-linux-gnu P9 and P10.
>
> I'll push this next week if no objections.
>
> BR,
> Kewen
> -----
>         PR target/110011
>
> gcc/ChangeLog:
>
>         * config/rs6000/rs6000.cc (output_toc): Use its own mode of the
>         128-bit float constant for real_to_target call.
>

The comment wording can be worded better.  Maybe

Use the mode of the 128-bit floating constant itself for real_to_target
call.

This is okay.

Thanks, David


> gcc/testsuite/ChangeLog:
>
>         * gcc.target/powerpc/pr110011.c: New test.
> ---
>  gcc/config/rs6000/rs6000.cc                 |  2 +-
>  gcc/testsuite/gcc.target/powerpc/pr110011.c | 42 +++++++++++++++++++++
>  2 files changed, 43 insertions(+), 1 deletion(-)
>  create mode 100644 gcc/testsuite/gcc.target/powerpc/pr110011.c
>
> diff --git a/gcc/config/rs6000/rs6000.cc b/gcc/config/rs6000/rs6000.cc
> index 3f129ea37d2..330c6a6fa5f 100644
> --- a/gcc/config/rs6000/rs6000.cc
> +++ b/gcc/config/rs6000/rs6000.cc
> @@ -17314,7 +17314,7 @@ output_toc (FILE *file, rtx x, int labelno,
> machine_mode mode)
>        if (DECIMAL_FLOAT_MODE_P (GET_MODE (x)))
>         REAL_VALUE_TO_TARGET_DECIMAL128 (*CONST_DOUBLE_REAL_VALUE (x), k);
>        else
> -       REAL_VALUE_TO_TARGET_LONG_DOUBLE (*CONST_DOUBLE_REAL_VALUE (x), k);
> +       real_to_target (k, CONST_DOUBLE_REAL_VALUE (x), GET_MODE (x));
>
>        if (TARGET_64BIT)
>         {
> diff --git a/gcc/testsuite/gcc.target/powerpc/pr110011.c
> b/gcc/testsuite/gcc.target/powerpc/pr110011.c
> new file mode 100644
> index 00000000000..5b04d3e298a
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/powerpc/pr110011.c
> @@ -0,0 +1,42 @@
> +/* { dg-do run } */
> +/* { dg-require-effective-target float128_runtime } */
> +/* Force long double to be with IBM format here, to verify
> +   _Float128 constant still uses its own format (IEEE) for
> +   encoding rather than IBM format.  */
> +/* { dg-options "-mfp-in-toc -mabi=ibmlongdouble" } */
> +/* { dg-add-options float128 } */
> +
> +#define MPFR_FLOAT128_MAX 0x1.ffffffffffffffffffffffffffffp+16383f128
> +
> +__attribute__ ((noipa))
> +_Float128 f128_max ()
> +{
> +  return MPFR_FLOAT128_MAX;
> +}
> +
> +typedef union
> +{
> +  int w[4];
> +  _Float128 f128;
> +} U;
> +
> +int main ()
> +{
> +
> +  U umax;
> +  umax.f128 = f128_max ();
> +  /* ieee float128 max:
> +     7ffeffff ffffffff ffffffff ffffffff.  */
> +  if (umax.w[1] != 0xffffffff || umax.w[2] != 0xffffffff)
> +    __builtin_abort ();
> +#ifdef __LITTLE_ENDIAN__
> +  if (umax.w[0] != 0xffffffff || umax.w[3] != 0x7ffeffff)
> +    __builtin_abort ();
> +#else
> +  if (umax.w[3] != 0xffffffff || umax.w[0] != 0x7ffeffff)
> +    __builtin_abort ();
> +#endif
> +
> +  return 0;
> +}
> +
> --
> 2.31.1
>