[Bug other/25277] New: missed optimization for simple mmx code.

["pluto at agmk dot net" <gcc-bugzilla at gcc dot gnu dot org>]

#include <mmintrin.h>
__v8qi foo(const __v8qi x, const __v8qi y){return x+y;}
__v8qi bar(const __v8qi x, const __v8qi y){return __builtin_ia32_paddb(x,y);}

$ gcc tmp.c -S -O2 -mmmx

3.3.6 produces the same code for foo() and bar():

foo:    movq    4(%esp), %mm0
        paddb   12(%esp), %mm0
        movq    %mm0, (%eax)
        ret

bar:    movq    4(%esp), %mm0
        paddb   12(%esp), %mm0
        movq    %mm0, (%eax)
        ret

4.2.0 produces horrible code for foo():

foo:    pushl   %edi
        pushl   %esi
        pushl   %ebx
        subl    $24, %esp
        movq    %mm0, (%esp)
        movl    (%esp), %ebx
        movl    4(%esp), %esi
        movl    %ebx, %edi
        movq    %mm1, (%esp)
        movl    (%esp), %eax
        movl    4(%esp), %edx
        movl    %eax, %ecx
        movl    %esi, %ebx
        movl    %edi, %eax
        xorl    %ecx, %eax
        andl    $-2139062144, %eax
        andl    $2139062143, %ecx
        andl    $2139062143, %edi
        addl    %edi, %ecx
        xorl    %ecx, %eax
        pxor    %mm0, %mm0
        movq    %mm0, 16(%esp)
        movl    %eax, 16(%esp)
        movl    %esi, %ecx
        xorl    %edx, %ecx
        andl    $-2139062144, %ecx
        andl    $2139062143, %edx
        andl    $2139062143, %ebx
        addl    %ebx, %edx
        xorl    %edx, %ecx
        movl    16(%esp), %eax
        movl    %eax, 8(%esp)
        movl    %ecx, 12(%esp)
        movq    8(%esp), %mm0
        addl    $24, %esp
        popl    %ebx
        popl    %esi
        popl    %edi
        ret

bar:    paddb   %mm1, %mm0
        ret


-- 
           Summary: missed optimization for simple mmx code.
           Product: gcc
           Version: 4.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: other
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: pluto at agmk dot net
 GCC build triplet: i686-pld-linux
  GCC host triplet: i686-pld-linux
GCC target triplet: i686-pld-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25277