[Bug rtl-optimization/48696] Horrible bitfield code generation on x86

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48696

--- Comment #5 from Richard Guenther <rguenth at gcc dot gnu.org> 2011-04-20 12:15:14 UTC ---
(In reply to comment #4)
> (In reply to comment #3)
> > So something changed between 4.0.3 and 4.0.4?  Or maybe a typo?
> 
> I only have 32bit compilers for both and see, for 4.0.3:
> 
> show_bug:
>         pushl   %ebp
>         movl    %esp, %ebp
>         movl    8(%ebp), %edx
>         movl    (%edx), %eax
>         andl    $-64, %eax
>         movl    %eax, (%edx)
>         shrl    $6, %eax
>         popl    %ebp
>         movzwl  %ax, %eax
>         ret
> 
> and for 4.0.4:
> 
> show_bug:
>         pushl   %ebp
>         movl    %esp, %ebp
>         movl    8(%ebp), %eax
>         andb    $-64, (%eax)
>         movl    (%eax), %eax
>         leave
>         shrl    $6, %eax
>         movzwl  %ax, %eax
>         ret

Actually the 4.0.4 compiler is x86_64, the code with -m32.  The 4.0.3
compiler is i586.

 /space/rguenther/install/gcc-4.0.3/libexec/gcc/i686-pc-linux-gnu/4.0.3/cc1
-quiet -v t.c -quiet -dumpbase t.c -m32 -mtune=pentiumpro -auxbase t -O2
-version -o t.s


/space/rguenther/install/gcc-4.0.4/libexec/gcc/x86_64-unknown-linux-gnu/4.0.4/cc1
-quiet -v t.c -quiet -dumpbase t.c -m32 -mtune=k8 -auxbase t -O2 -version -o
t.s

but no -march/tune combination makes the bug vanish for the 4.0.4 compiler
(maybe a HWI dependent "optimization")