Re: Ping ^ 2: [PATCH] rs6000: Expand fmod and remainder when built with fast-math [PR97142]

[Segher Boessenkool <segher@kernel.crashing.org>]

Hi!

On Mon, Sep 06, 2021 at 04:59:27PM +0800, Xionghu Luo wrote:
> On 2021/9/4 05:44, Segher Boessenkool wrote:
> >>+/* { dg-final { scan-assembler-not {\mbl fmod\M} } } */
> >>+/* { dg-final { scan-assembler-not {\mbl fmodf\M} } } */
> >>+/* { dg-final { scan-assembler-not {\mbl remainder\M} } } */
> >>+/* { dg-final { scan-assembler-not {\mbl remainderf\M} } } */
> >
> >These are negative tests, so won't spuriously fail, but this does not
> >test for the function prefixes we can have.  See
> >gcc.target/powerpc/builtins-1.c for example.
> 
> Thanks.  Verified that different calls are generated on different platforms
> without this patch.
> 
> P8BE-64: bl __fmodf_finite
> P8BE-32: b __fmodf_finite
> P8LE-64:  bl fmodf

Ah, it won't use the "dot-names" here, okay.  I think for Darwin you
need to allow a single underscore, but you'll find out (or Iain will,
most likely ;-) )

> "l", "__" and "_finite" are optional, so is it OK to check them with below 
> patterns?
> 
> +/* { dg-final { scan-assembler-not {\mbl? (__)?fmod(_finite)?\M} } } */
> +/* { dg-final { scan-assembler-not {\mbl? (__)?fmodf(_finite)?\M} } } */
> +/* { dg-final { scan-assembler-not {\mbl? (__)?remainder(_finite)?\M} } } 
> */
> +/* { dg-final { scan-assembler-not {\mbl? (__)?remainderf(_finite)?\M} } } 
> */

You could even do

/* { dg-final { scan-assembler-not {(?n)\mb.*fmod} } } */
/* { dg-final { scan-assembler-not {(?n)\mb.*remainder} } } */

or even

/* { dg-final { scan-assembler-not {fmod} } } */
/* { dg-final { scan-assembler-not {remainder} } } */

(and the testcase name will not accidentally match either of those REs
either, I checked :-) )

And yeah, on some subtargets the calls will be tail-optimised, good
find.  You can get around that (in general, on any target) by doing

float test1 (float x, float y)
{
  float z = fmodf (x, y);
  asm (""); // to prevent tail calls
  return z;
}

but what you do is fine as well, and much more elegant.

Please pick (and test ;-) ) whichever option you like best.  Thanks!


Segher