RTL alias analysis

[Jan Hubicka]

> Steven Bosscher wrote:
> > Hi rth,
> > 
> > The stack space sharing you added to cfgexpand.c breaks RTL alias
> > analysis.
> > 
> > For example, the attached test case breaks for pentiumpro at -O2. 
> > The problem apparently is that the second store to c is moved up
> > before before the load.
> 
> My guess at a solution is that when A (with alias set S_a) and B (with
> alias set S_b) are given the same stack slot, we should create a new
> alias set S_c which is a subset of both S_a and S_b, and give the
> combined stack slot that aliase set.

This won't work for the indirect accesses via pointers, like in the
testcase.

Honza
> 
> -- 
> Mark Mitchell
> CodeSourcery, LLC
> mark@codesourcery.com
> (650) 331-3385 x713