cfgloop.c (mark_loop_for_removal): Record former header when ENABLE_CHECKING.

2014-09-05  Richard Biener  <rguenther@suse.de>

	* cfgloop.c (mark_loop_for_removal): Record former header
	when ENABLE_CHECKING.
	* cfgloop.h (strut loop): Add former_header member when
	ENABLE_CHECKING.
	* loop-init.c (fix_loop_structure): Sanity check loops
	marked for removal if they re-appeared.

From-SVN: r214957

gcc/ChangeLog

+2014-09-05  Richard Biener  <rguenther@suse.de>
+
+	* cfgloop.c (mark_loop_for_removal): Record former header
+	when ENABLE_CHECKING.
+	* cfgloop.h (strut loop): Add former_header member when
+	ENABLE_CHECKING.
+	* loop-init.c (fix_loop_structure): Sanity check loops
+	marked for removal if they re-appeared.
+
 2014-09-05  Alan Lawrence  <alan.lawrence@arm.com>
 
 	* config/aarch64/arm_neon.h (int32x1_t, int16x1_t, int8x1_t,

gcc/cfgloop.c

@@ -1927,7 +1927,11 @@ bb_loop_depth (const_basic_block bb)
 void
 mark_loop_for_removal (loop_p loop)
 {
+#ifdef ENABLE_CHECKING
+  loop->former_header = loop->header;
+#endif
   loop->header = NULL;
   loop->latch = NULL;
   loops_state_set (LOOPS_NEED_FIXUP);
 }
+

gcc/cfgloop.h

@@ -193,6 +193,14 @@ struct GTY ((chain_next ("%h.next"))) loop {
 
   /* Number of iteration analysis data for RTL.  */
   struct niter_desc *simple_loop_desc;
+
+#ifdef ENABLE_CHECKING
+  /* For sanity checking during loop fixup we record here the former
+     loop header for loops marked for removal.  Note that this prevents
+     the basic-block from being collected but its index can still be
+     reused.  */
+  basic_block former_header;
+#endif
 };
 
 /* Flags for state of loop structure.  */

gcc/loop-init.c

@@ -245,6 +245,12 @@ fix_loop_structure (bitmap changed_bbs)
 	}
 
       /* Remove the loop.  */
+#ifdef ENABLE_CHECKING
+      if (loop->header)
+	loop->former_header = loop->header;
+      else
+	gcc_assert (loop->former_header != NULL);
+#endif
       loop->header = NULL;
       flow_loop_tree_node_remove (loop);
     }
@@ -272,6 +278,35 @@ fix_loop_structure (bitmap changed_bbs)
   FOR_EACH_VEC_ELT (*get_loops (cfun), i, loop)
     if (loop && loop->header == NULL)
       {
+#ifdef ENABLE_CHECKING
+	if (dump_file
+	    && ((unsigned) loop->former_header->index
+		< basic_block_info_for_fn (cfun)->length ()))
+	  {
+	    basic_block former_header
+	      = BASIC_BLOCK_FOR_FN (cfun, loop->former_header->index);
+	    /* If the old header still exists we want to check if the
+	       original loop is re-discovered or the old header is now
+	       part of a newly discovered loop.
+	       In both cases we should have avoided removing the loop.  */
+	    if (former_header == loop->former_header)
+	      {
+		if (former_header->loop_father->header == former_header)
+		  fprintf (dump_file, "fix_loop_structure: rediscovered "
+			   "removed loop %d as loop %d with old header %d\n",
+			   loop->num, former_header->loop_father->num,
+			   former_header->index);
+		else if ((unsigned) former_header->loop_father->num
+			 >= old_nloops)
+		  fprintf (dump_file, "fix_loop_structure: header %d of "
+			   "removed loop %d is part of the newly "
+			   "discovered loop %d with header %d\n",
+			   former_header->index, loop->num,
+			   former_header->loop_father->num,
+			   former_header->loop_father->header->index);
+	      }
+	  }
+#endif
 	(*get_loops (cfun))[i] = NULL;
 	flow_loop_free (loop);
       }