Re: [PATCH] Remove dead labels to increase superblock scope

[Tom de Vries <Tom_deVries at mentor dot com>]

On 27/11/11 23:59, Eric Botcazou wrote:
>> No, DELETED_LABEL notes still work just fine. It depends on how you
>> remove the label and replace it with a note, and Tom isn't showing
>> what he did, so...
> 
> I agree that there is no obvious reason why just calling delete_insn would not 
> work, so this should be investigated first.
> 

The reason it didn't work, is because after turning a label into a
NOTE_INSN_DELETED_LABEL, one needs to move it to after the NOTE_INSN_BASIC_BLOCK
as in cfgcleanup.c:try_optimize_cfg():
...
		  delete_insn_chain (label, label, false);
		  /* If the case label is undeletable, move it after the
		     BASIC_BLOCK note.  */
		  if (NOTE_KIND (BB_HEAD (b)) == NOTE_INSN_DELETED_LABEL)
		    {
		      rtx bb_note = NEXT_INSN (BB_HEAD (b));

		      reorder_insns_nobb (label, label, bb_note);
		      BB_HEAD (b) = bb_note;
		      if (BB_END (b) == bb_note)
			BB_END (b) = label;
		    }
...

Attached patch factors out this piece of code and reuses it in fixup_reorder_chain.

Bootstrapped and reg-tested on x86_64.

OK for next stage1?

Thanks,
- Tom

2011-12-01  Tom de Vries  <tom@codesourcery.com>

	* cfgcleanup.c (fixup_deleted_label): New function, factored out of ...
	(try_optimize_cfg): Use fixup_deleted_label.
	* cfglayout.c (fixup_reorder_chain): Delete unused label, and fixup
	using fixup_deleted_label.

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

Index: gcc/cfgcleanup.c
===================================================================
--- gcc/cfgcleanup.c (revision 181652)
+++ gcc/cfgcleanup.c (working copy)
@@ -2518,6 +2518,27 @@ trivially_empty_bb_p (basic_block bb)
     }
 }
 
+/* Move a DELETED_LABEL note after the BASIC_BLOCK note of BB.  */
+
+void
+fixup_deleted_label (basic_block bb)
+{
+  rtx deleted_label = BB_HEAD (bb), bb_note;
+
+  if (deleted_label == NULL_RTX
+      || !NOTE_P (deleted_label)
+      || NOTE_KIND (deleted_label) != NOTE_INSN_DELETED_LABEL)
+    return;
+
+  bb_note = NEXT_INSN (deleted_label);
+  gcc_assert (bb_note != NULL_RTX && NOTE_INSN_BASIC_BLOCK_P (bb_note));
+
+  reorder_insns_nobb (deleted_label, deleted_label, bb_note);
+  BB_HEAD (bb) = bb_note;
+  if (BB_END (bb) == bb_note)
+    BB_END (bb) = deleted_label;
+}
+
 /* Do simple CFG optimizations - basic block merging, simplifying of jump
    instructions etc.  Return nonzero if changes were made.  */
 
@@ -2637,15 +2658,7 @@ try_optimize_cfg (int mode)
 		  delete_insn_chain (label, label, false);
 		  /* If the case label is undeletable, move it after the
 		     BASIC_BLOCK note.  */
-		  if (NOTE_KIND (BB_HEAD (b)) == NOTE_INSN_DELETED_LABEL)
-		    {
-		      rtx bb_note = NEXT_INSN (BB_HEAD (b));
-
-		      reorder_insns_nobb (label, label, bb_note);
-		      BB_HEAD (b) = bb_note;
-		      if (BB_END (b) == bb_note)
-			BB_END (b) = label;
-		    }
+		  fixup_deleted_label (b);
 		  if (dump_file)
 		    fprintf (dump_file, "Deleted label in block %i.\n",
 			     b->index);
Index: gcc/cfglayout.c
===================================================================
--- gcc/cfglayout.c (revision 181652)
+++ gcc/cfglayout.c (working copy)
@@ -857,6 +857,12 @@ fixup_reorder_chain (void)
 				       (e_taken->src, e_taken->dest));
 		  e_taken->flags |= EDGE_FALLTHRU;
 		  update_br_prob_note (bb);
+		  if (LABEL_NUSES (ret_label) == 0
+		      && single_pred_p (e_taken->dest))
+		    {
+		      delete_insn (ret_label);
+		      fixup_deleted_label (e_taken->dest);
+		    }
 		  continue;
 		}
 	    }
Index: gcc/basic-block.h
===================================================================
--- gcc/basic-block.h (revision 181652)
+++ gcc/basic-block.h (working copy)
@@ -813,6 +813,7 @@ extern void rtl_make_eh_edge (sbitmap, b
 enum replace_direction { dir_none, dir_forward, dir_backward, dir_both };
 
 /* In cfgcleanup.c.  */
+extern void fixup_deleted_label (basic_block);
 extern bool cleanup_cfg (int);
 extern int flow_find_cross_jump (basic_block, basic_block, rtx *, rtx *,
                                  enum replace_direction*);
Index: gcc/testsuite/gcc.dg/superblock.c
===================================================================
--- /dev/null (new file)
+++ gcc/testsuite/gcc.dg/superblock.c (revision 0)
@@ -0,0 +1,23 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fno-asynchronous-unwind-tables -fsched2-use-superblocks -fdump-rtl-sched2 -fdump-rtl-bbro" } */
+
+typedef int aligned __attribute__ ((aligned (64)));
+extern void abort (void);
+
+int bar (void *p);
+
+void
+foo (void)
+{
+  char *p = __builtin_alloca (13);
+  aligned i;
+
+  if (bar (p) || bar (&i))
+    abort ();
+}
+
+/* { dg-final { scan-rtl-dump-times "0 uses" 0 "bbro"} } */
+/* { dg-final { scan-rtl-dump-times "ADVANCING TO" 2 "sched2"} } */
+/* { dg-final { cleanup-rtl-dump "bbro" } } */
+/* { dg-final { cleanup-rtl-dump "sched2" } } */
+