[Bug target/59390] New: presence of __attribute__((target("fma"))) declaration breaks __builtin_fma

["jtaylor.debian at googlemail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59390

            Bug ID: 59390
           Summary: presence of  __attribute__((target("fma")))
                    declaration breaks __builtin_fma
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jtaylor.debian at googlemail dot com

compiling this code leads to a compilation error on -O3:


#include "math.h"
void fun() __attribute__((target("fma")));

void 
other_fun(double *restrict out, double * restrict a, double * restrict b,
double * restrict c, int n)
{
    int i;
    for (i = 0; i < n; i++) {
        out[i] = fma(a[i], b[i], c[i]);
    }   
}

$ cc-4.9 fma.c -c -std=c99 -O3
fma.c: In function âother_funâ:
fma.c:9:21: error: â__builtin_ia32_vfmaddpdâ needs isa option -m32 -mfma4 -mfma
         out[i] = fma(a[i], b[i], c[i]);
                     ^

removing the attribute from the unused declaration fixes it, as does using
-fno-builtin or a lower optimization level.

$ gcc-4.9 -v
Using built-in specs.
COLLECT_GCC=/home/jtaylor/tmp/gcc-local/bin/../bin/gcc
COLLECT_LTO_WRAPPER=/home/jtaylor/tmp/gcc-local/libexec/gcc/x86_64-unknown-linux-gnu/4.9.0/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: /home/jtaylor/tmp/gcc/configure
--enable-languages=c,c++,fortran --enable-tls
--prefix=/home/jtaylor/tmp/gcc-local --with-gmp=/usr --with-mpfr=/usr
--with-mpc=/usr --with-cloog=/usr --with-ppl=/usr --with-isl=/usr
Thread model: posix
gcc version 4.9.0 20131204 (experimental) (GCC)

also affects gcc 4.8.1