Re: PATCH: PR target/42542: Vectorizer produces incorrect results on max of signed intergers

[Uros Bizjak <ubizjak at gmail dot com>]

On 01/05/2010 08:47 PM, H.J. Lu wrote:

> > > Subtracting 0x80000000 from a number in the range 0 to 0xFFFFFFFF will
> > > produce a result in the range -0x80000000 to 0x7FFFFFFF which is exactly
> > > two's complement. ïXOR just happens to give the same result.
> > >
> > > It's a very well known trick IMNSHO. ïPlease provide a counterexample if
> > > you think there is one.
> > >        
> > I don't have one. 0x8000000 was all that worried me.
> >
> > H.J., can you please revert your patch and fix the PR with Paolo's proposed
> > solution?
> >
> >      
> Here is the patch. OK for trunk?
>    

> 2010-01-05 Paolo Bonzini <bonzinI@gnu.rg> H.J. Lu 
> <hongjiu.lu@intel.com> PR target/42542 * config/i386/i386.c 
> (ix86_expand_int_vcond): Convert GTU to GT for V4SI and V2DI by 
> subtracting (-(INT MAX) - 1) from both operands to make them signed. * 
> config/i386/sse.md (umaxv4si3): Revert the last change. (umin<mode>3): 
> Likewise. (uminv8hi3): Removed. (uminv4si3): Likewise. gcc/testsuite/ 
> 2010-01-05 H.J. Lu <hongjiu.lu@intel.com> * 
> gcc.target/i386/pr42542-1.c (res): Make it 8 elements.
>    

This is OK for mainline and release branches after a couple of days 
without problems.

I guess that ia64 maintainer wants to apply the same fix to ia64, as 
noted by Paolo.

Thanks,
Uros.