On Sun, 25 Sep 2016 19:01:14 +0200 Jakub Jelinek <ja...@redhat.com> wrote:
> On Sun, Sep 25, 2016 at 02:48:19PM +0100, Sergei Trofimovich wrote:
> > From: Sergei Trofimovich <siarh...@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
pgpmQcY54o8k2.pgp
Description: Цифровая подпись OpenPGP
