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Dominance related breakage, was Re: [PATCH] PR71275 ira.c bb_loop_depth

Message ID 20160528003303.GL3300@bubble.grove.modra.org
State New
Headers show

Commit Message

Alan Modra May 28, 2016, 12:33 a.m. UTC 
On Thu, May 26, 2016 at 11:04:41PM -0400, Vladimir Makarov wrote:
> On 05/26/2016 10:14 PM, Alan Modra wrote:
> >On Thu, May 26, 2016 at 10:12:14AM -0400, Vladimir Makarov wrote:
> >>On 05/26/2016 07:02 AM, Alan Modra wrote:
> >>>This fixes lack of bb_loop_depth info in some of the early parts of
> >>>ira, which has been the case for quite some time.  All active branches
> >>>return 0 from bb_loop_depth() in update_equiv_regs, but whether that
> >>>actually causes mis-optimization anywhere but trunk is yet to be
> >>>determined.
> >>>
> >>>I played a little with trying to consolidate this loop_optimizer_init
> >>>call with one that occurs a little later, but ran into ICEs.  (We now
> >>>have four calls to loop_optimizer_init in ira.c.)
> >>>
> >>>Bootstrapped and regression tested powerpc64le-linux and x86_64-linux.
> >>>OK to apply?
> >>>
> >>Yes.  Thank you, Alan.
> >Hi Vlad,
> >Sorry to do this to you and others, but the patch (committed as
> >r236789) may be wrong.  I didn't see any problems on trunk but when
> >I backported to gcc-5, I hit an error in stage2 compiling
> >insn-recog.c "dominator of 10 status unknown" from if_after_reload.
> >
> >On gcc-5, the error disappears by adding a call to
> >   free_dominance_info (CDI_DOMINATORS);
> >after the newly added call to loop_optimizer_finalize.
> >
> >I'm not sure yet what is going on.  Does anyone know whether the
> >free_dominance_info call is needed on trunk?
> >
> That is ok.  It is always a discovery.  I am not sure but I think I saw this
> problem when I wrote IRA.
> 
> Looking at the dominance code, I seems to me that it can reuse the previous
> info if it was not cleared.  So I guess free_dominance_info is important.

Given your comment, I've committed the following after running
a full regression check.

	PR rtl-optimization/71275
	* ira.c (ira): Free dominance info.
diff mbox

Patch

diff --git a/gcc/ira.c b/gcc/ira.c
index 1b269ea..3c4e3b6 100644
--- a/gcc/ira.c
+++ b/gcc/ira.c
@@ -5188,6 +5188,7 @@  ira (FILE *f)
     add_store_equivs ();
 
   loop_optimizer_finalize ();
+  free_dominance_info (CDI_DOMINATORS);
   end_alias_analysis ();
   free (reg_equiv);