[Bug tree-optimization/46590] [4.6/4.7/4.8 Regression] long compile time with -O2 and many loops

[rguenther at suse dot de]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46590

--- Comment #24 from rguenther at suse dot de <rguenther at suse dot de> 2012-08-21 09:59:41 UTC ---
On Tue, 21 Aug 2012, steven at gcc dot gnu.org wrote:

> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46590
> 
> Steven Bosscher <steven at gcc dot gnu.org> changed:
> 
>            What    |Removed                     |Added
> ----------------------------------------------------------------------------
>                  CC|                            |steven at gcc dot gnu.org
> 
> --- Comment #23 from Steven Bosscher <steven at gcc dot gnu.org> 2012-08-21 09:42:42 UTC ---
> (In reply to comment #13)
> > The I/O parts of the FRE cost are due to value-numbering stores in
> > visit_reference_op_store.  They can be drastically cut by an equivalent
> > of (not generating code)
> > 
> > Index: trans-io.c
> > ===================================================================
> > --- trans-io.c  (revision 167111)
> > +++ trans-io.c  (working copy)
> > @@ -1670,6 +1670,7 @@ build_dt (tree function, gfc_code * code
> >    gfc_init_block (&post_iu_block);
> > 
> >    var = gfc_create_var (st_parameter[IOPARM_ptype_dt].type, "dt_parm");
> > +  gfc_add_modify (&block, var, build_constructor (TREE_TYPE (var), NULL));
> > 
> >    set_error_locus (&block, var, &code->loc);
> > 
> 
> You didn't post/commit this, but it looks like a reasonable change to me.

I think this is obsolete now with Michas change to have CLOBBERs.  Or
if still useful, the above should be a CLOBBER now.

Richard.