Re: Not pulling out obvious non-aliasing global from the loop

[Andrew Pinski <pinskia at physics dot uc dot edu>]

On Aug 30, 2004, at 4:01 PM, Andrew Pinski wrote:

> On Aug 25, 2004, at 8:33 PM, Andrew Pinski wrote:
>
> > While working on a loop pass, I noticed that we were not pulling out 
> > the load
> > from a global variable from a loop where it obviously cannot alias 
> > anything in
> > the loop.  This seems like it would hurt the vectorizer also.
> >
> > This example comes from bzip2:
> > unsigned short *q;
> > #define NOSB 10
> > void h1(int last)
> > {
> >   int i;
> >   for (i=0;i<last+NOSB;i++)
> >     q[i] = 0;
> > }
> >
> > Tree after lim:
>
>
> I looked at this again with respect to lim and found that lim was doing
> invariant load motion because the cost was not high enough,  I think
> we need to change the cost for this case even though it increases
> register pressure as we then can do other optimizations on the loop 
> which
> actually decrease it and maybe even vectorize the loop.

And here is the patch which I am testing to fix this.
Is this the right approach or is something else needed?

Thanks,
Andrew Pinski

ChangeLog:

	* tree-ssa-loop-im.c (stmt_cost): Gimple variables should be
	pulled out too as they cause memory accesses.

Index: tree-ssa-loop-im.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/tree-ssa-loop-im.c,v
retrieving revision 2.7
diff -u -p -r2.7 tree-ssa-loop-im.c
--- tree-ssa-loop-im.c	25 Aug 2004 21:21:17 -0000	2.7
+++ tree-ssa-loop-im.c	31 Aug 2004 02:10:12 -0000
@@ -350,7 +350,7 @@ stmt_cost (tree stmt)
   /* Hoisting memory references out should almost surely be a win.  */
   if (!is_gimple_variable (lhs))
     cost += 20;
-  if (is_gimple_addressable (rhs) && !is_gimple_variable (rhs))
+  if (is_gimple_addressable (rhs))
     cost += 20;

   switch (TREE_CODE (rhs))