Re: Use OEP_ADDRESS_OF in emit-rtl.c

[Jan Hubicka <hubicka at ucw dot cz>]

> 
> Did you audit all callers of mem_attrs_eq_p to see if they really
> only care about that?  After all MEM_EXPR, via access paths, encode
> type-based alias info and thus replacing one with the other (cse.c use
> or ifcvt.c use) is only valid if that doesn't break dependences.

Hmm, expr is used by ao_ref_from_mem and nonoverlapping_memrefs_p.
The alias set of the access is not taken from expr, but from alias set info
stored in the memory attribute itself (and it is checked by those to match)

I still think it is an address of the expression that matters, not the value.
I think operand_equal_p may, for example, consider two different VAR_DECL equivalent
if their constructors are, because the value is (it doesn't do that), but their
addresses differ.

I will look more into nonoverlapping_memrefs_p and ao_ref_from_mem. The first
one may need some update to tree-alias infrastructure....

Honza
> 
> So I don't believe this is safe.
> 
> Thanks,
> Richard.
> 
> > Honza
> > 
> > 	* emit-rtl.c (mem_attrs_eq_p, mem_expr_equal_p): Pass OEP_ADDRESS_OF
> > 	to operand_equal_p.
> > 
> > Index: emit-rtl.c
> > ===================================================================
> > --- emit-rtl.c	(revision 228131)
> > +++ emit-rtl.c	(working copy)
> > @@ -334,7 +334,7 @@ mem_attrs_eq_p (const struct mem_attrs *
> >  	  && p->addrspace == q->addrspace
> >  	  && (p->expr == q->expr
> >  	      || (p->expr != NULL_TREE && q->expr != NULL_TREE
> > -		  && operand_equal_p (p->expr, q->expr, 0))));
> > +		  && operand_equal_p (p->expr, q->expr, OEP_ADDRESS_OF))));
> >  }
> >  
> >  /* Set MEM's memory attributes so that they are the same as ATTRS.  */
> > @@ -1657,7 +1657,7 @@ mem_expr_equal_p (const_tree expr1, cons
> >    if (TREE_CODE (expr1) != TREE_CODE (expr2))
> >      return 0;
> >  
> > -  return operand_equal_p (expr1, expr2, 0);
> > +  return operand_equal_p (expr1, expr2, OEP_ADDRESS_OF);
> >  }
> >  
> >  /* Return OFFSET if XEXP (MEM, 0) - OFFSET is known to be ALIGN
> > 
> > 
> 
> -- 
> Richard Biener <rguenther@suse.de>
> SUSE LINUX GmbH, GF: Felix Imendoerffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nuernberg)