Bug#560812: gcc-4.4: Incorrect 3DNow! code generated

[Catalin Ionescu <catalin.ionescu@radioconsult.ro>]

Package: gcc-4.4
Version: 4.4.2-4
Severity: important

*** Please type your report below this line ***

With the following simple test file, the 3DNow! generated code is
incorrect, with final _m_pfsub generated as pfsubr %mm0,%mm0, thus
producing completely incorrect result.

*** main.c
#include <mm3dnow.h>

void Butterfly_3(__m64 *D,__m64 SC,unsigned int IStep,unsigned int Off)
{ __m64 T,T1,T2;

  T=_m_pfmul(D[Off+1],SC);
  T1=D[Off+0];D[Off+0]=_m_pfadd(T1,T);D[Off+1]=_m_pfsub(T1,T);
}
***

The command line is:

gcc -march=athlon -S -O3 main.c

The generated code is:

*** main.s
    .file    "main.c"
    .text
    .p2align 4,,15
.globl Butterfly_3
    .type    Butterfly_3, @function
Butterfly_3:
    pushl    %ebp
    movl    %esp, %ebp
    movl    8(%ebp), %edx
    movl    16(%ebp), %ecx
    leal    8(%edx,%ecx,8), %eax
    leal    (%edx,%ecx,8), %edx
    pfmul    (%eax), %mm0
    movq    (%edx), %mm1
    movq    %mm1, %mm2
    pfadd    %mm0, %mm2
    pfsubr    %mm0, %mm0
    movq    %mm2, (%edx)
    movq    %mm0, (%eax)
    leave
    ret
    .size    Butterfly_3, .-Butterfly_3
    .ident    "GCC: (Debian 4.4.2-4) 4.4.2"
    .section    .note.GNU-stack,"",@progbits
***

The problem exists in all current Debian releases (stable, testing,
unstable).
Without optimizations the problem is still there, but it's a lot more
difficult to follow.

This is the simplest test code that I could extract. The basic principle
is used in a large
cross-platform library and all GCC variants for x86 that I have used
(Debian, Cygwin, MinGW, TDM)
generate essentially the same code.

-- System Information:
Debian Release: squeeze/sid
  APT prefers unstable
  APT policy: (500, 'unstable')
Architecture: i386 (i686)

Kernel: Linux 2.6.31-1-686 (SMP w/1 CPU core)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash

Versions of packages gcc-4.4 depends on:
ii  binutils                      2.20-4     The GNU assembler, linker
and bina
ii  cpp-4.4                       4.4.2-4    The GNU C preprocessor
ii  gcc-4.4-base                  4.4.2-4    The GNU Compiler Collection
(base
ii  libc6                         2.10.2-2   GNU C Library: Shared libraries
ii  libgcc1                       1:4.4.2-4  GCC support library
ii  libgomp1                      4.4.2-4    GCC OpenMP (GOMP) support
library

Versions of packages gcc-4.4 recommends:
ii  libc6-dev                     2.10.2-2   GNU C Library: Development
Librari

Versions of packages gcc-4.4 suggests:
pn  gcc-4.4-doc                   <none>     (no description available)
pn  gcc-4.4-locales               <none>     (no description available)
pn  gcc-4.4-multilib              <none>     (no description available)
pn  libcloog-ppl0                 <none>     (no description available)
pn  libgcc1-dbg                   <none>     (no description available)
pn  libgomp1-dbg                  <none>     (no description available)
pn  libmudflap0-4.4-dev           <none>     (no description available)
pn  libmudflap0-dbg               <none>     (no description available)
pn  libppl-c2                     <none>     (no description available)
pn  libppl7                       <none>     (no description available)

-- no debconf information