Re: [PATCH v1] LoongArch: testsuite:Add the "-ffast-math" compilation option for the file vect-fmin-3.c.

[Richard Sandiford <richard.sandiford@arm.com>]

chenxiaolong <chenxiaolong@loongson.cn> writes:
> After the detection of maximum reduction is enabled on LoongArch architecture,
> the regression test of GCC finds that vect-fmin-3.c fails. Currently, in the
> target-supports.exp file, only aarch64,arm,riscv, and LoongArch architectures
> are supported. Through analysis, the "-ffast-math" compilation option needs to
> be added to the test case in order to successfully reduce using vectorization.
> The original patch was submitted by author Richard Sandiford.
>
> The initial patch information submitted is as follows:
>
> commit e32b9eb32d7cd2d39bf9c70497890ac61b9ee14c
>
> gcc/testsuite/ChangeLog:
>
> 	* gcc.dg/vect/vect-fmin-3.c:Adding an extra "-ffast-math" to the
>         compilation option ensures that the loop can be reduced to maximum
>         success.

This shouldn't be necessary.  The test does:

  for (int i = 0; i < n; i += 2)
    {
      x0 = __builtin_fmin (x0, ptr[i + 0]);
      x1 = __builtin_fmin (x1, ptr[i + 1]);
    }
  res[0] = x0;
  res[1] = x1;

__builtin_fmin is an FP minimum operation that corresponds directly to
the fmin*3 optab (or reduc_fmin_scal_* for reductions).  It is naturally
associative, so doesn't need -ffast-math for that.

Does LoongArch provide reduc_min_scal_* but not reduc_fmin_scal_*?
If so, we probably need a new target selector for fmin/fmax reduction.

Thanks,
Richard


> ---
>  gcc/testsuite/gcc.dg/vect/vect-fmin-3.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/gcc/testsuite/gcc.dg/vect/vect-fmin-3.c b/gcc/testsuite/gcc.dg/vect/vect-fmin-3.c
> index 2e282ba6878..edef57925c1 100644
> --- a/gcc/testsuite/gcc.dg/vect/vect-fmin-3.c
> +++ b/gcc/testsuite/gcc.dg/vect/vect-fmin-3.c
> @@ -1,4 +1,5 @@
>  /* { dg-require-effective-target vect_float } */
> +/* { dg-additional-options "-ffast-math" } */
>  
>  #include "tree-vect.h"