From patchwork Fri Jun 11 19:18:44 2010
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Subject: [PR44181] skip debug insns when inserting IV updates
Date: Fri, 11 Jun 2010 09:18:44 -0000
From: Alexandre Oliva <aoliva@redhat.com>
X-Patchwork-Id: 55350
Message-Id: <oriq5pml7v.fsf@livre.localdomain>
To: gcc-patches@gcc.gnu.org

A number of graphite -fcompare-debug bug reports were fixed with this
patch.  The problem was that we inserted induction variable increment
stmts before the last stmt in the block, but if the block ended with a
fall-through, the insert would be before a non-debug stmt in the non-VTA
case, whereas in the VTA case it could be before a debug stmt, after the
non-debug stmt.  Skipping trailing debug stmts so that we insert before
the last non-debug stmt removed the codegen differences.

Bootstrapped the compiler, along with the upcoming patch for PR43656, on
x86_64-linux-gnu, with the following options:

-O2 -g -fschedule-insns -fsched-pressure -funroll-loops -fgraphite-identity

for stage2 and stage3 host, and for stage3 libs (also -fcompare-debug)

I got build failures on zlib and libada, presumably because of this
unusual combination of flags, but no -fcompare-debug errors.

Ok to install?


for  gcc/ChangeLog
from  Alexandre Oliva  <aoliva@redhat.com>

	PR debug/43650
	PR debug/44181
	PR debug/44247
	* tree-ssa-loop-manip.c (tree_transform_and_unroll_loop): Skip
	debug stmts.
	(canonicalize_loop_ivs): Likewise.

Index: gcc/tree-ssa-loop-manip.c
===================================================================
--- gcc/tree-ssa-loop-manip.c.orig	2010-06-11 09:16:28.000000000 -0300
+++ gcc/tree-ssa-loop-manip.c	2010-06-11 09:17:38.000000000 -0300
@@ -1081,7 +1081,7 @@ tree_transform_and_unroll_loop (struct l
 
   /* Finally create the new counter for number of iterations and add the new
      exit instruction.  */
-  bsi = gsi_last_bb (exit_bb);
+  bsi = gsi_last_nondebug_bb (exit_bb);
   exit_if = gsi_stmt (bsi);
   create_iv (exit_base, exit_step, NULL_TREE, loop,
 	     &bsi, false, &ctr_before, &ctr_after);
@@ -1217,7 +1217,7 @@ canonicalize_loop_ivs (struct loop *loop
 	gsi_insert_seq_on_edge_immediate (loop_preheader_edge (loop), stmts);
     }
 
-  gsi = gsi_last_bb (bump_in_latch ? loop->latch : loop->header);
+  gsi = gsi_last_nondebug_bb (bump_in_latch ? loop->latch : loop->header);
   create_iv (build_int_cst_type (type, 0), build_int_cst (type, 1), NULL_TREE,
 	     loop, &gsi, bump_in_latch, &var_before, NULL);