[PATCH] Limit path splitting to loops we optimize for speed

* doc/invoke.texi (-O2 options): Remove -fsplit-paths.
	(-O3 options): Add -fsplit-paths.
	* gimple-ssa-split-paths.c: Include predict.h
	(split_paths): Only split paths in a loop that should be
	optimized for speed.
	* opts.c (default_options_table): Move -fsplit-paths from -O2 to
	-O3.

	* gcc.dg/tree-ssa/split-path-1.c: Explicitly ask for path
	splitting optimizations.

From-SVN: r231790

gcc/ChangeLog

@@ -1,3 +1,13 @@
+2015-12-17  Jeff Law  <law@redhat.com>
+
+	* doc/invoke.texi (-O2 options): Remove -fsplit-paths.
+	(-O3 options): Add -fsplit-paths.
+	* gimple-ssa-split-paths.c: Include predict.h
+	(split_paths): Only split paths in a loop that should be
+	optimized for speed.
+	* opts.c (default_options_table): Move -fsplit-paths from -O2 to
+	-O3.
+
 2015-12-17  Nathan Sidwell  <nathan@acm.org>
 
 	* ipa-icf.c (sem_item_optimizer::merge): Don't pick 'main' as the

gcc/doc/invoke.texi

@@ -7836,7 +7836,6 @@ also turns on the following optimization flags:
 -frerun-cse-after-loop  @gol
 -fsched-interblock  -fsched-spec @gol
 -fschedule-insns  -fschedule-insns2 @gol
--fsplit-paths @gol
 -fstrict-aliasing -fstrict-overflow @gol
 -ftree-builtin-call-dce @gol
 -ftree-switch-conversion -ftree-tail-merge @gol
@@ -7853,7 +7852,7 @@ Optimize yet more.  @option{-O3} turns on all optimizations specified
 by @option{-O2} and also turns on the @option{-finline-functions},
 @option{-funswitch-loops}, @option{-fpredictive-commoning},
 @option{-fgcse-after-reload}, @option{-ftree-loop-vectorize},
-@option{-ftree-loop-distribute-patterns},
+@option{-ftree-loop-distribute-patterns}, @option{-fsplit-paths}
 @option{-ftree-slp-vectorize}, @option{-fvect-cost-model},
 @option{-ftree-partial-pre} and @option{-fipa-cp-clone} options.
 

gcc/gimple-ssa-split-paths.c

@@ -29,6 +29,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "cfgloop.h"
 #include "gimple-iterator.h"
 #include "tracer.h"
+#include "predict.h"
 
 /* Given LATCH, the latch block in a loop, see if the shape of the
    path reaching LATCH is suitable for being split by duplication.
@@ -180,9 +181,14 @@ split_paths ()
 
   FOR_EACH_LOOP (loop, LI_FROM_INNERMOST)
     {
+      /* Only split paths if we are optimizing this loop for speed.  */
+      if (!optimize_loop_for_speed_p (loop))
+	continue;
+
       /* See if there is a block that we can duplicate to split the
 	 path to the loop latch.  */
-      basic_block bb = find_block_to_duplicate_for_splitting_paths (loop->latch);
+      basic_block bb
+	= find_block_to_duplicate_for_splitting_paths (loop->latch);
 
       /* BB is the merge point for an IF-THEN-ELSE we want to transform.
 

gcc/opts.c

@@ -523,11 +523,11 @@ static const struct default_options default_options_table[] =
     { OPT_LEVELS_2_PLUS, OPT_fisolate_erroneous_paths_dereference, NULL, 1 },
     { OPT_LEVELS_2_PLUS, OPT_fipa_ra, NULL, 1 },
     { OPT_LEVELS_2_PLUS, OPT_flra_remat, NULL, 1 },
-    { OPT_LEVELS_2_PLUS, OPT_fsplit_paths, NULL, 1 },
 
     /* -O3 optimizations.  */
     { OPT_LEVELS_3_PLUS, OPT_ftree_loop_distribute_patterns, NULL, 1 },
     { OPT_LEVELS_3_PLUS, OPT_fpredictive_commoning, NULL, 1 },
+    { OPT_LEVELS_3_PLUS, OPT_fsplit_paths, NULL, 1 },
     /* Inlining of functions reducing size is a good idea with -Os
        regardless of them being declared inline.  */
     { OPT_LEVELS_3_PLUS_AND_SIZE, OPT_finline_functions, NULL, 1 },

gcc/testsuite/ChangeLog

@@ -1,3 +1,8 @@
+2015-12-17  Jeff Law  <law@redhat.com>
+
+	* gcc.dg/tree-ssa/split-path-1.c: Explicitly ask for path
+	splitting optimizations.
+
 2015-12-17  Nathan Sidwell  <nathan@acm.org>
 
 	* gcc.dg/ipa/ipa-icf-merge-1.c: New.

gcc/testsuite/gcc.dg/tree-ssa/split-path-1.c

@@ -1,5 +1,5 @@
 /* { dg-do run } */
-/* { dg-options "-O2 -fdump-tree-split-paths-details " } */
+/* { dg-options "-O2 -fsplit-paths -fdump-tree-split-paths-details " } */
 
 #include <stdio.h>
 #include <stdlib.h>