Re: [RFC] Enable saliasing for structs with arrays

[Zdenek Dvorak <rakdver at atrey dot karlin dot mff dot cuni dot cz>]

Hello,

> > >     if (!var)
> > >       return NULL_TREE;
> > >   
> > > *************** rewrite_use (struct ivopts_data *data,
> > > *** 5745,5750 ****
> > > --- 5760,5766 ----
> > >   	gcc_unreachable ();
> > >       }
> > >     update_stmt (use->stmt);
> > > +   mark_new_vars_to_rename (use->stmt);
> > >   }
> > 
> > This should not be necessary with the correct approach -- the alias info
> > should be completely preserved, thus the virtual operands of the
> > statement should not change at all.
> 
> It's necessary because of the below change.

regardless of what you do elsewhere, if you cause the virtual operands
of a statement to change in ivopts, then something went wrong.

I think that currently there is no way how to represent subvars info
on TARGET_MEM_REFs correctly.  I am trying to do something about it.

Zdenek

> > > Index: tree-ssa-operands.c
> > > ===================================================================
> > > RCS file: /cvs/gcc/gcc/gcc/tree-ssa-operands.c,v
> > > retrieving revision 2.97
> > > diff -c -3 -p -r2.97 tree-ssa-operands.c
> > > *** tree-ssa-operands.c	20 Jul 2005 01:18:26 -0000	2.97
> > > --- tree-ssa-operands.c	21 Jul 2005 12:24:35 -0000
> > > *************** get_tmr_operands (tree stmt, tree expr, 
> > > *** 1698,1704 ****
> > >       }
> > >   
> > >     if (tag)
> > > !     add_stmt_operand (&tag, stmt_ann (stmt), flags);
> > >     else
> > >       /* Something weird, so ensure that we will be careful.  */
> > >       stmt_ann (stmt)->has_volatile_ops = true;
> > > --- 1698,1709 ----
> > >       }
> > >   
> > >     if (tag)
> > > !     {
> > > !       if (TREE_CODE (tag) == SSA_NAME)
> > > !         add_stmt_operand (&tag, stmt_ann (stmt), flags);
> > > !       else
> > > !         get_expr_operands (stmt, &tag, flags);
> > > !     }
> > >     else
> > >       /* Something weird, so ensure that we will be careful.  */
> > >       stmt_ann (stmt)->has_volatile_ops = true;
> > 
> > Why is this change necessary?  And, how it can happen that TMR_TAG is an
> > SSA name?
> 
> We need to call get_expr_operands on the tag, if it is a VAR_DECL
> (I reversed the condition - maybe I goofed and should just use != VAR_DECL
> here).  This is because get_expr_operands takes care inserting all subvars
> here, if necessary.  Maybe we can do this unconditionally - but I do
> understand too little about all the interworkings, so I'm just trying.
> 
> Richard.