Re: [PATCH] x86_64: fix 'gather' avx2 builtin names

[Sergei Trofimovich <slyich at gmail dot com>]

On Sun, 25 Sep 2016 19:01:14 +0200
Jakub Jelinek <jakub@redhat.com> wrote:

> On Sun, Sep 25, 2016 at 02:48:19PM +0100, Sergei Trofimovich wrote:
> > From: Sergei Trofimovich <siarheit@google.com>
> > 
> > Today I traced AVX2 optimisation bug in gcc and
> > distilled it down to '__builtin_ia32_gatheraltdiv4si256'
> > generated by gcc.
> > 
> > When I attempted to use this builtin directly
> > in a simple program gcc refused to recognise
> > it as known:
> > 
> >   #include <immintrin.h>
> > 
> >   void a (void) {
> >     __builtin_ia32_gatheraltdiv4si256 (1);
> >   }
> > 
> >   $ LANG=C gcc -c -march=core-avx2 a.c
> >     a.c: In function 'a':
> >     a.c:4:5: warning: implicit declaration of function
> >         '__builtin_ia32_gatheraltdiv4si256' [-Wimplicit-function-declaration]
> > 
> > The cause is trailing whitespace in builtin definition:
> > 
> >       def_builtin (OPTION_MASK_ISA_AVX2, "__builtin_ia32_gatheraltdiv4si256 ",
> > 
> > Fixed by dropping trailing whitespace.  
> 
> No, that isn't a fix, adding such characters has been an older way to
> express internal only builtins that aren't ever meant to be available to
> users (these days we'd use internal-fn.* stuff, except we don't have support
> for backends adding their own internal functions).

Aha, got it. Having a seemingly callable name is very confusing.

I did grab the name from one of -fdump-tree-all outputs
(bug.c.165t.optimized) which looked as:

  vect_.16_59 = VIEW_CONVERT_EXPR<vector(4) long long int>(vect_var_.12_56);
  vect_var_.14_60 = __builtin_ia32_gatheraltdiv4si256  ({ -1, -1, -1, -1, -1, -1, -1, -1 }, &PERMS, vect_.16_59, { -1, -1, -1, 
-1, -1, -1, -1, -1 }, 4);
  vect_.17_61 = VIEW_CONVERT_EXPR<vector(4) long long int>(vect_var_.12_57);
  vect_var_.14_62 = __builtin_ia32_gatheraltdiv4si256  ({ -1, -1, -1, -1, -1, -1, -1, -1 }, &PERMS, vect_.17_61, { -1, -1, -1, 
-1, -1, -1, -1, -1 }, 4);

and I assumed that builtin can be used directly to reproduce
smaller example. Sorry for the noise.

-- 

  Sergei

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