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[PATCH i386] Enable -freorder-blocks-and-partition


This patch enables -freorder-blocks-and-partition by default for x86
at -O2 and up. It is showing some modest gains in cpu2006 performance
with profile feedback and -O2 on an Intel Westmere system. Specifically,
I am seeing consistent improvements in 401.bzip2 (1.5-3%), 483.xalancbmk
(1.5-3%), and 453.povray (2.5-3%), and no apparent regressions.

Bootstrapped and tested on x86-64-unknown-linux-gnu with a normal
bootstrap, a profiledbootstrap and an LTO profiledbootstrap. All were
configured with --enable-languages=all,obj-c++ and tested for both
32 and 64-bit with RUNTESTFLAGS="--target_board=unix\{-m32,-m64\}".

It would be good to enable this for additional targets as a follow on,
but it needs more testing for both correctness and performance on those
other targets (i.e for correctness because I see a number of places
in other config/*/*.c files that do some special handling under this
option for different targets or simply disable it, so I am not sure
how well-tested it is under different architectural constraints).

Ok for trunk?

Thanks,
Teresa

2013-11-19  Teresa Johnson  <tejohnson@google.com>

        * common/config/i386/i386-common.c: Enable
        -freorder-blocks-and-partition at -O2 and up for x86.
        * opts.c (finish_options): Only warn if -freorder-blocks-and-
        partition was set on command line.

Index: common/config/i386/i386-common.c
===================================================================
--- common/config/i386/i386-common.c    (revision 205001)
+++ common/config/i386/i386-common.c    (working copy)
@@ -789,6 +789,8 @@ static const struct default_options ix86_option_op
   {
     /* Enable redundant extension instructions removal at -O2 and higher.  */
     { OPT_LEVELS_2_PLUS, OPT_free, NULL, 1 },
+    /* Enable function splitting at -O2 and higher.  */
+    { OPT_LEVELS_2_PLUS, OPT_freorder_blocks_and_partition, NULL, 1 },
     /* Turn off -fschedule-insns by default.  It tends to make the
        problem with not enough registers even worse.  */
     { OPT_LEVELS_ALL, OPT_fschedule_insns, NULL, 0 },
Index: opts.c
===================================================================
--- opts.c      (revision 205001)
+++ opts.c      (working copy)
@@ -737,9 +737,10 @@ finish_options (struct gcc_options *opts, struct g
       && opts->x_flag_reorder_blocks_and_partition
       && (ui_except == UI_SJLJ || ui_except >= UI_TARGET))
     {
-      inform (loc,
-             "-freorder-blocks-and-partition does not work "
-             "with exceptions on this architecture");
+      if (opts_set->x_flag_reorder_blocks_and_partition)
+        inform (loc,
+                "-freorder-blocks-and-partition does not work "
+                "with exceptions on this architecture");
       opts->x_flag_reorder_blocks_and_partition = 0;
       opts->x_flag_reorder_blocks = 1;
     }
@@ -752,9 +753,10 @@ finish_options (struct gcc_options *opts, struct g
       && opts->x_flag_reorder_blocks_and_partition
       && (ui_except == UI_SJLJ || ui_except >= UI_TARGET))
     {
-      inform (loc,
-             "-freorder-blocks-and-partition does not support "
-             "unwind info on this architecture");
+      if (opts_set->x_flag_reorder_blocks_and_partition)
+        inform (loc,
+                "-freorder-blocks-and-partition does not support "
+                "unwind info on this architecture");
       opts->x_flag_reorder_blocks_and_partition = 0;
       opts->x_flag_reorder_blocks = 1;
     }
@@ -769,9 +771,10 @@ finish_options (struct gcc_options *opts, struct g
              && targetm_common.unwind_tables_default
              && (ui_except == UI_SJLJ || ui_except >= UI_TARGET))))
     {
-      inform (loc,
-             "-freorder-blocks-and-partition does not work "
-             "on this architecture");
+      if (opts_set->x_flag_reorder_blocks_and_partition)
+        inform (loc,
+                "-freorder-blocks-and-partition does not work "
+                "on this architecture");
       opts->x_flag_reorder_blocks_and_partition = 0;
       opts->x_flag_reorder_blocks = 1;
     }


-- 
Teresa Johnson | Software Engineer | tejohnson@google.com | 408-460-2413


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