[Bug target/13144] New: Bad memory-to-memory code for SSE

["hjl at lucon dot org" <gcc-bugzilla at gcc dot gnu dot org>]

When SSE is enabled, gcc generatea bad memory-to-memory code.

[hjl@gnu-1 memcpy]$ cat foo.c
char buf1 [64];
char buf2 [64];
 
 
void
bar ()
{
  memcpy (buf1, buf2, sizeof (buf1));
}
[hjl@gnu-1 memcpy]$ /usr/gcc-3.4/bin/gcc -msse -S -O2 foo.c
[hjl@gnu-1 memcpy]$ cat foo.s
        .file   "foo.c"
        .text
        .p2align 4,,15
.globl bar
        .type   bar, @function
bar:
        pushl   %ebp
        movl    buf2, %eax
        movl    %esp, %ebp
        popl    %ebp
        movl    %eax, buf1
        movl    buf2+4, %eax
        movl    %eax, buf1+4
        movl    buf2+8, %eax
        movl    %eax, buf1+8
        movl    buf2+12, %eax
        movl    %eax, buf1+12
        movl    buf2+16, %eax
        movl    %eax, buf1+16
        movl    buf2+20, %eax
        movl    %eax, buf1+20
        movl    buf2+24, %eax
        movl    %eax, buf1+24
        movl    buf2+28, %eax
        movl    %eax, buf1+28
        movl    buf2+32, %eax
        movl    %eax, buf1+32
        movl    buf2+36, %eax
        movl    %eax, buf1+36
        movl    buf2+40, %eax
        movl    %eax, buf1+40
        movl    buf2+44, %eax
        movl    %eax, buf1+44
        movl    buf2+48, %eax
        movl    %eax, buf1+48
        movl    buf2+52, %eax
        movl    %eax, buf1+52
        movl    buf2+56, %eax
        movl    %eax, buf1+56
        movl    buf2+60, %eax
        movl    %eax, buf1+60
        ret
        .size   bar, .-bar
        .comm   buf1,64,32
        .comm   buf2,64,32
        .section        .note.GNU-stack,"",@progbits
        .ident  "GCC: (GNU) 3.4 20031105 (experimental)"

It is because move_by_pieces_ninsns assumes TImode can be accessed
with 8 bit alignment. But the i386 backend won't do it. Should i386
define SLOW_UNALIGNED_ACCESS for TImode and move_by_pieces_ninsns
check the widest mode instead of word_mode for slow unaligned access?

-- 
           Summary: Bad memory-to-memory code for SSE
           Product: gcc
           Version: 3.4
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: target
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: hjl at lucon dot org
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=13144