Patchwork Fix PR55833 + cheaper checking

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Submitter Marek Polacek
Date Jan. 14, 2013, 7:11 p.m.
Message ID <20130114191131.GC5414@redhat.com>
Download mbox | patch
Permalink /patch/211864/
State New
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Comments

Marek Polacek - Jan. 14, 2013, 7:11 p.m.
On Mon, Jan 14, 2013 at 06:51:54PM +0100, Zdenek Dvorak wrote:
> Hi,
> 
> > On Thu, Jan 10, 2013 at 11:19:43PM +0100, Zdenek Dvorak wrote:
> > > I agree -- at the very least, unswitch_single_loop should check whether there
> > > is any possiblity it could have affected irreducible loops information (this
> > > should only be the case when some already existing irreducible loop is altered
> > > in the progress).  Which is what it (or more precisely, remove_path function
> > > used by it) tries to do -- so is should be sufficient to check why this fails
> > > for the considered testcase, and make sure the situation is correctly detected,
> > 
> > Actually, in this case, we don't call remove_path from unswitch_single_loop
> > at all.
> 
> I am not quite sure what you mean by that -- remove_path is called unconditionally
> in unswitch_loop (and fix_loop_placement is only called through remove_path).

Yeah, that's right, what I meant was that in unswitch_single_loop, we
call remove_path only conditionally (and for this particular TC that's
not the case).

> > So, here's another stab at it.  In this version, we will call
> > mark_irreducible_loops only in case where we're removing a loop
> > from loop hierarchy tree.  Because when we do that (and we're in some
> > irreducible region), the edge that connects those two loops
> > should be marked as EDGE_IRREDUCIBLE_LOOP.  And the preheader BB
> > eventually as BB_IRREDUCIBLE_LOOP.  Does this look any better?
> > I'm not actually checking whether we really are in a irreducible
> > region, should that be done (how?)?
> 
> Yes, you should check whether you are in an irreducible loop.  This is done by
> testing EDGE_IRREDUCIBLE_LOOP flag,

Alright, I was wondering whether there's any other way.  Unfortunately,
here I couldn't do something like

if (loop_preheader_edge (loop)->flags & EDGE_IRREDUCIBLE_LOOP)
  ...
because we're natural loop in a subloop, so I abused the loop exits of
this loop.  Hopefully I'm not doing something evil.

Updated patch attached.  Ok if testing passes?  Thanks,

2013-01-14  Richard Biener  <rguenther@suse.de>
	    Marek Polacek  <polacek@redhat.com>

	PR rtl-optimization/55833
	* loop-unswitch.c (unswitch_loops): Move loop verification...
	(unswitch_single_loop): ...here.  Call mark_irreducible_loops.
	* cfgloopmanip.c (fix_loop_placement): Add IRRED_INVALIDATED parameter.
	Set it to true when we're removing a loop from hierarchy tree in
	an irreducible region.
	(fix_bb_placements): Adjust caller.
	(fix_loop_placements): Likewise.

	* gcc.dg/pr55833.c: New test.


	Marek
Zdenek Dvorak - Jan. 15, 2013, 10:21 p.m.
Hi,

> > Yes, you should check whether you are in an irreducible loop.  This is done by
> > testing EDGE_IRREDUCIBLE_LOOP flag,
> 
> Alright, I was wondering whether there's any other way.  Unfortunately,
> here I couldn't do something like
> 
> if (loop_preheader_edge (loop)->flags & EDGE_IRREDUCIBLE_LOOP)
>   ...
> because we're natural loop in a subloop, so I abused the loop exits of
> this loop.  Hopefully I'm not doing something evil.
> 
> Updated patch attached.  Ok if testing passes?  Thanks,

yes, this is OK,

Zdenek

> 2013-01-14  Richard Biener  <rguenther@suse.de>
> 	    Marek Polacek  <polacek@redhat.com>
> 
> 	PR rtl-optimization/55833
> 	* loop-unswitch.c (unswitch_loops): Move loop verification...
> 	(unswitch_single_loop): ...here.  Call mark_irreducible_loops.
> 	* cfgloopmanip.c (fix_loop_placement): Add IRRED_INVALIDATED parameter.
> 	Set it to true when we're removing a loop from hierarchy tree in
> 	an irreducible region.
> 	(fix_bb_placements): Adjust caller.
> 	(fix_loop_placements): Likewise.
> 
> 	* gcc.dg/pr55833.c: New test.

Patch

--- gcc/loop-unswitch.c.mp	2013-01-10 16:50:28.899559875 +0100
+++ gcc/loop-unswitch.c	2013-01-14 19:04:21.675418957 +0100
@@ -145,12 +144,7 @@  unswitch_loops (void)
   /* Go through inner loops (only original ones).  */
 
   FOR_EACH_LOOP (li, loop, LI_ONLY_INNERMOST)
-    {
-      unswitch_single_loop (loop, NULL_RTX, 0);
-#ifdef ENABLE_CHECKING
-      verify_loop_structure ();
-#endif
-    }
+    unswitch_single_loop (loop, NULL_RTX, 0);
 
   iv_analysis_done ();
 }
@@ -370,6 +364,10 @@  unswitch_single_loop (struct loop *loop,
   nloop = unswitch_loop (loop, bbs[i], copy_rtx_if_shared (cond), cinsn);
   gcc_assert (nloop);
 
+#ifdef ENABLE_CHECKING
+  verify_loop_structure ();
+#endif
+
   /* Invoke itself on modified loops.  */
   unswitch_single_loop (nloop, rconds, num + 1);
   unswitch_single_loop (loop, conds, num + 1);
--- gcc/cfgloopmanip.c.mp	2013-01-14 14:42:52.502002650 +0100
+++ gcc/cfgloopmanip.c	2013-01-14 19:55:47.330356459 +0100
@@ -111,10 +111,13 @@  fix_bb_placement (basic_block bb)
 /* Fix placement of LOOP inside loop tree, i.e. find the innermost superloop
    of LOOP to that leads at least one exit edge of LOOP, and set it
    as the immediate superloop of LOOP.  Return true if the immediate superloop
-   of LOOP changed.  */
+   of LOOP changed.
+
+   IRRED_INVALIDATED is set to true if a change in the loop structures might
+   invalidate the information about irreducible regions.  */
 
 static bool
-fix_loop_placement (struct loop *loop)
+fix_loop_placement (struct loop *loop, bool *irred_invalidated)
 {
   unsigned i;
   edge e;
@@ -139,7 +142,12 @@  fix_loop_placement (struct loop *loop)
       /* The exit edges of LOOP no longer exits its original immediate
 	 superloops; remove them from the appropriate exit lists.  */
       FOR_EACH_VEC_ELT (exits, i, e)
-	rescan_loop_exit (e, false, false);
+	{
+	  /* We may need to recompute irreducible loops.  */
+	  if (e->flags & EDGE_IRREDUCIBLE_LOOP)
+	    *irred_invalidated = true;
+	  rescan_loop_exit (e, false, false);
+	}
 
       ret = true;
     }
@@ -212,7 +220,7 @@  fix_bb_placements (basic_block from,
       if (from->loop_father->header == from)
 	{
 	  /* Subloop header, maybe move the loop upward.  */
-	  if (!fix_loop_placement (from->loop_father))
+	  if (!fix_loop_placement (from->loop_father, irred_invalidated))
 	    continue;
 	  target_loop = loop_outer (from->loop_father);
 	}
@@ -965,7 +973,7 @@  fix_loop_placements (struct loop *loop,
   while (loop_outer (loop))
     {
       outer = loop_outer (loop);
-      if (!fix_loop_placement (loop))
+      if (!fix_loop_placement (loop, irred_invalidated))
 	break;
 
       /* Changing the placement of a loop in the loop tree may alter the
--- gcc/testsuite/gcc.dg/pr55833.c.mp	2013-01-10 17:23:26.016102692 +0100
+++ gcc/testsuite/gcc.dg/pr55833.c	2013-01-10 17:23:15.898073384 +0100
@@ -0,0 +1,28 @@ 
+/* PR rtl-optimization/55833 */
+/* { dg-do compile } */
+/* { dg-options "-O3" } */
+
+int a, b, c;
+
+void foo()
+{
+    unsigned d, l, *p, k = 1;
+
+    if(bar())
+    {
+label:
+      	if((a = a <= 0))
+        {
+            if(c)
+                d = b;
+
+            if (b || d ? l : k ? : 0)
+                a = d = 0;
+
+            goto label;
+       	}
+    }
+
+    while(*p++)
+        goto label;
+}