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Subject: [Bug rtl-optimization/56175] Issue with combine phase on x86.
Date: Sat, 02 Feb 2013 12:02:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56175

--- Comment #2 from Uros Bizjak <ubizjak at gmail dot com> 2013-02-02 12:01:56 UTC ---
(In reply to comment #1)
> Created attachment 29330 [details]
> testcase
> 
> This test must be compiled with the following options:
> "-O2 -ffast-math -msse2 -mfpmath=sse -m32 -march=atom -mtune=atom
> -ftree-loop-if-convert"

Compiling attached test with above flags, I got:

foo:
        movl    4(%esp), %eax
        movl    8(%esp), %edx
        testb   %al, %al
        je      .L3
        testw   %dx, %dx
        je      .L3
        shrb    %al
        shrw    %dx
        xorl    %edx, %eax
        andl    $1, %eax
        ret
.L3:
        xorl    %eax, %eax
        ret

which looks the same as your optimal assembly in Description - maybe due to the
fact that the attached test source is the same as the source in Description.

BTW: This is probably the case of missing CSE in tree optimizers. Combine pass
is not powerful enough to figure out optimal sequence, it more-or-less blindly
combines various patterns.

Please provide the test that exposes this missing optimization.