Re: [PATCH] Improve handling of threads which cross over the current loops header

[Jeff Law <law at redhat dot com>]

On 11/22/13 08:56, Richard Biener wrote:
> > So the issue here is we can create irreducible regions & new nested
> > loops.  Does just setting the header,latch fields for the current loop
> > handle those cases?
>
> Yes.
Fixed via the attached patch.

Bootstrapped and regression tested on x86_64-unknown-linux-gnu.  Also 
tested by removing the requirement that the loop header contain a 
multi-way branch, bootstrapping and testing that compiler as well. 
Installed on the trunk.

Jeff


	* tree-ssa-threadupdate.c (thread_through_all_blocks): Selectively
	invalidate loop information.



diff --git a/gcc/tree-ssa-threadupdate.c b/gcc/tree-ssa-threadupdate.c
index ee0c838..1a52e47 100644
--- a/gcc/tree-ssa-threadupdate.c
+++ b/gcc/tree-ssa-threadupdate.c
@@ -1579,7 +1579,6 @@ thread_through_all_blocks (bool may_peel_loop_headers)
   bitmap_iterator bi;
   bitmap threaded_blocks;
   struct loop *loop;
-  bool totally_clobbered_loops = false;
 
   /* We must know about loops in order to preserve them.  */
   gcc_assert (current_loops != NULL);
@@ -1675,9 +1674,15 @@ thread_through_all_blocks (bool may_peel_loop_headers)
 		/* Our path is still valid, thread it.  */
 	        if (e->aux)
 		  {
-		    totally_clobbered_loops
-		      |= thread_block ((*path)[0]->e->dest, false);
+		    struct loop *loop = (*path)[0]->e->dest->loop_father;
+
+		    retval |= thread_block ((*path)[0]->e->dest, false);
 		    e->aux = NULL;
+
+		    /* This jump thread likely totally scrambled this loop.
+		       So arrange for it to be fixed up.  */
+		    loop->header = NULL;
+		    loop->latch = NULL;
 		  }
 	      }
 	   else
@@ -1700,32 +1705,7 @@ thread_through_all_blocks (bool may_peel_loop_headers)
   threaded_blocks = NULL;
   paths.release ();
 
-  /* If we made changes to the CFG that might have totally messed
-     up the loop structure, then drop the old loop structure and
-     rebuild.  */
-  if (totally_clobbered_loops)
-    {
-      /* Release the current loop structures, they are totally
-	 clobbered at this point.  */
-      loop_optimizer_finalize ();
-      current_loops = NULL;
-
-      /* Similarly for dominance information.  */
-      free_dominance_info (CDI_DOMINATORS);
-      free_dominance_info (CDI_POST_DOMINATORS);
-
-      /* Before we can rebuild the loop structures, we need dominators,
-	 which requires no unreachable code.  So remove unreachable code.  */
-      delete_unreachable_blocks ();
-
-      /* Now rebuild the loop structures.  */
-      cfun->curr_properties &= ~PROP_loops;
-      loop_optimizer_init (AVOID_CFG_MODIFICATIONS);
-      cfun->curr_properties |= PROP_loops;
-      retval = 1;
-    }
-
-  if (retval && current_loops)
+  if (retval)
     loops_state_set (LOOPS_NEED_FIXUP);
 
   return retval;