[Bug other/57202] New: Please make the intrinsics headers like immintrin.h be usable without compiler flags

["thiago at kde dot org" <gcc-bugzilla@gcc.gnu.org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57202

             Bug #: 57202
           Summary: Please make the intrinsics headers like immintrin.h be
                    usable without compiler flags
    Classification: Unclassified
           Product: gcc
           Version: 4.8.1
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: other
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: thiago@kde.org


Please make all headers for intrinsics be includable without special compiler
flags.

In other words, I want the following to work:

$ gcc -fsyntax-only -include smmintrin.h -xc /dev/null
In file included from <command-line>:0:0:
/usr/lib/gcc/x86_64-redhat-linux/4.7.2/include/smmintrin.h:31:3: error: #error
"SSE4.1 instruction set not enabled"

Note it works with ICC:
$ icc -fsyntax-only -include smmintrin.h -xc /dev/null && echo works
works


Not only that, please make all the intrinsics functions be defined and ready to
be used.

This is necessary so that the following source file could compile even if
-msse4.1 is not passed on the command-line (adapted from
http://gcc.gnu.org/gcc-4.8/changes.html):

#include <smmintrin.h>

 __attribute__ ((target ("default")))
int foo(void)
{
  return 1;
}

__attribute__ ((target ("sse4.2")))
int foo(void)
{
  __m128i v;
  _mm_blendv_epi8(v, v, v);
  return 2;
}

There are several reasons for that, number one among them that it makes the GCC
4.8 feature above actually useful for non-trivial code. Also, passing extra
options on the command-line are simply not an option for C++ code (where the
feature above is useful) if that code is moderately complex and uses inline
functions, and those options cannot be used if LTO is to be used (bug 54231).