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Re: [PATCH] Fix PR target/28946


On Tue, Sep 05, 2006 at 07:20:02AM -0600, Roger Sayle wrote:
> 
> On Tue, 5 Sep 2006, Uros Bizjak wrote:
> > 2006-09-06 Uros Bizjak <uros@kss-loka.si>
> >
> > 	PR target/28946
> > 	* combine.c (try_combine): Force PARALLEL of comparison and
> > 	arithmetic insn even if arithmetic result is not used.
> >
> >       * gcc.target/i386/pr28946.c: New test.
> 
> I was going to point out tht a generic change to combine like this
> really needs more testing that C & C++ on x86, especially during
> stage 3.  However, from your latest comments in the bugzilla PR it

As I have pointed out in the bug report, some recent processors need
the extra "testl   %eax, %eax" here

       shrl    $5, %eax
       testl   %eax, %eax

to avoid partial flag register stall since a shift instruction may
not set flag register since shift count may be 0.


H.J.


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