[Bug tree-optimization/38865] missing FRE with VIEW_CONVERT_EXPR

["rguenther at suse dot de" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #4 from rguenther at suse dot de  2009-01-16 09:36 -------
Subject: Re:  missing FRE with
 VIEW_CONVERT_EXPR

On Fri, 16 Jan 2009, pinskia at gcc dot gnu dot org wrote:

> ------- Comment #2 from pinskia at gcc dot gnu dot org  2009-01-16 02:33 -------
> Mine. Simple patch which implements it in vn_reference_lookup, Since VCE is
> both a reference and really a bit-wise cast, we can do the normal lookup and
> then do a lookup if the VCE was not there.  I have not seen if this improves
> any testcases yet though but I thought I remembering seeing code like this in
> the benchmark we have internally.

Can you use the same trick as for union loads/stores and adjust
how we record V_C_Es instead and use the needs_insertion stuff?

Richard.

> Index: tree-ssa-sccvn.c
> ===================================================================
> --- tree-ssa-sccvn.c    (revision 143413)
> +++ tree-ssa-sccvn.c    (working copy)
> @@ -1041,6 +1041,19 @@ vn_reference_lookup (tree op, VEC (tree,
>    vr1.operands = valueize_refs (shared_reference_ops_from_ref (op));
>    vr1.hashcode = vn_reference_compute_hash (&vr1);
>    result = vn_reference_lookup_1 (&vr1, vnresult);
> +  
> +  /* If we don't get the result right away for a VIEW_CONVERT_EXPR, try again
> +     with the original expression.  */
> +  if (!result && TREE_CODE (op) == VIEW_CONVERT_EXPR)
> +    {
> +      vr1.vuses = valueize_vuses (vuses);
> +      vr1.operands = valueize_refs (shared_reference_ops_from_ref
> (TREE_OPERAND (op, 0)));
> +      vr1.hashcode = vn_reference_compute_hash (&vr1);
> +      result = vn_reference_lookup_1 (&vr1, vnresult);
> +      /* Convert it back to the original type */
> +      if (result)
> +       fold_build1 (VIEW_CONVERT_EXPR, TREE_TYPE (op), result);
> +    }
> 
>    /* If there is a single defining statement for all virtual uses, we can
>       use that, following virtual use-def chains.  */
> 
> 
> 


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38865