Enable -frename-registers at -O2.

	PR rtl-optimization/57193
	* opts.c (default_options_table): Add OPT_frename_registers at -O2
	and above.
	* doc/invoke.texi (-frename-registers, -O2): Update documentation.

From-SVN: r235442

gcc/ChangeLog

+2016-04-26  Bernd Schmidt  <bschmidt@redhat.com>
+
+	PR rtl-optimization/57193
+	* opts.c (default_options_table): Add OPT_frename_registers at -O2
+	and above.
+	* doc/invoke.texi (-frename-registers, -O2): Update documentation.
+
 2016-04-26  Bin Cheng  <bin.cheng@arm.com>
 
 	* tree-if-conv.c (any_pred_load_store): New static variable.

gcc/doc/invoke.texi

@@ -6255,6 +6255,7 @@ also turns on the following optimization flags:
 -foptimize-strlen @gol
 -fpartial-inlining @gol
 -fpeephole2 @gol
+-frename-registers @gol
 -freorder-blocks-algorithm=stc @gol
 -freorder-blocks-and-partition -freorder-functions @gol
 -frerun-cse-after-loop  @gol
@@ -8562,7 +8563,8 @@ debug information format adopted by the target, however, it can
 make debugging impossible, since variables no longer stay in
 a ``home register''.
 
-Enabled by default with @option{-funroll-loops} and @option{-fpeel-loops}.
+Enabled by default with @option{-funroll-loops} and @option{-fpeel-loops},
+and also enabled at levels @option{-O2} and @option{-O3}.
 
 @item -fschedule-fusion
 @opindex fschedule-fusion

gcc/opts.c

@@ -498,6 +498,7 @@ static const struct default_options default_options_table[] =
     { OPT_LEVELS_2_PLUS, OPT_fstrict_overflow, NULL, 1 },
     { OPT_LEVELS_2_PLUS_SPEED_ONLY, OPT_freorder_blocks_algorithm_, NULL,
       REORDER_BLOCKS_ALGORITHM_STC },
+    { OPT_LEVELS_2_PLUS, OPT_frename_registers, NULL, 1 },
     { OPT_LEVELS_2_PLUS, OPT_freorder_functions, NULL, 1 },
     { OPT_LEVELS_2_PLUS, OPT_ftree_vrp, NULL, 1 },
     { OPT_LEVELS_2_PLUS, OPT_ftree_pre, NULL, 1 },