[patch] for PR23509

Zdenek Dvorak rakdver@atrey.karlin.mff.cuni.cz
Sat Aug 27 19:01:00 GMT 2005


Hello,

> > > >we lose the VUSE, which could in worst case lead to misscompilations.
> > > >In this particular case it only confuses ivopts that expect 
> > > >name_mem_tag
> > > >or type_mem_tag to be set for every dereferenced pointer, and leads to
> > > >ICE.
> > > 
> > > Then how does copy prop works?  This is exactly what copy prop does
> > > and I don't see we losing VUSE there.
> > 
> > copy propagation merges the alias information (see
> > tree-ssa-copy.c:merge_alias_info).  Which of course is an
> > alternative solution for the problem; I may prepare a patch to
> > use it if preferable.
> 
> I'm not sure i understand:
> Why is it preferrable to not do the propagation at all here when the
> other places in the compiler simply merge the alias info?

the proposed patch is more conservative and safer; but, given that
actually exactly the same problem is solved on other places in the
compiler and that a well tested function to do it is available,
this is not too strong argument.  I am testing new patch now.

Zdenek



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