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[Fortran] Make -Ofast imply -fstack-arrays

Message ID 4DCE2BE7.4030708@net-b.de
State New
Headers show

Commit Message

Tobias Burnus May 14, 2011, 7:14 a.m. UTC 
As title says: Make -Ofast imply -fstack-arrays

(For Polyhedron shows, -fstack-arrays improves performance by 7% to 10%. 
Cf. 
https://userpage.physik.fu-berlin.de/~tburnus/gcc-trunk/benchmark/iff/#rt )

Build on x86-64-linux.
OK for the trunk?

Tobias

Comments

Janne Blomqvist May 14, 2011, 8:53 a.m. UTC | #1 
On Sat, May 14, 2011 at 10:14, Tobias Burnus <burnus@net-b.de> wrote:
> As title says: Make -Ofast imply -fstack-arrays
>
> (For Polyhedron shows, -fstack-arrays improves performance by 7% to 10%. Cf.
> https://userpage.physik.fu-berlin.de/~tburnus/gcc-trunk/benchmark/iff/#rt )
>
> Build on x86-64-linux.
> OK for the trunk?

Ok.
Toon Moene May 14, 2011, 2:39 p.m. UTC | #2 
On 05/14/2011 09:14 AM, Tobias Burnus wrote:

> As title says: Make -Ofast imply -fstack-arrays

I haven't commented on this before, but everyone should realize that 
automatic arrays were allocated on the stack *always* by g77.

I never even bothered to study how gfortran did it, because I assumed it 
would just have copied g77's behavior.

Duh.
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Patch

2011-05-14  Tobias Burnus  <burnus@net-b.de>

	* doc/invoke.texi (-Ofast): Also enables -fstack-arrays.

2011-05-14  Tobias Burnus  <burnus@net-b.de>

	* options.c (gfc_init_options, gfc_post_options): Enable
	-fstack-arrays by default if -Ofast is used.
	* invoke.texi (-fstack-arrays): Document this.

diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index aee1e6b..6ed289e 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -6000,7 +6000,7 @@  Disregard strict standards compliance.  @option{-Ofast} enables all
 @option{-O3} optimizations.  It also enables optimizations that are not
 valid for all standard compliant programs.
 It turns on @option{-ffast-math} and the Fortran-specific
-@option{-fno-protect-parens}.
+@option{-fno-protect-parens} and @option{-fstack-arrays}.
 
 If you use multiple @option{-O} options, with or without level numbers,
 the last such option is the one that is effective.
diff --git a/gcc/fortran/invoke.texi b/gcc/fortran/invoke.texi
index 9f02239..f0ee096 100644
--- a/gcc/fortran/invoke.texi
+++ b/gcc/fortran/invoke.texi
@@ -1385,7 +1385,9 @@  The default value for @var{n} is 32768.
 Adding this option will make the fortran compiler put all local arrays,
 even those of unknown size onto stack memory.  If your program uses very
 large local arrays it's possible that you'll have to extend your runtime
-limits for stack memory on some operating systems.
+limits for stack memory on some operating systems. This flag is enabled
+by default at optimization level @option{-Ofast}.
+
 
 @item -fpack-derived
 @opindex @code{fpack-derived}
diff --git a/gcc/fortran/options.c b/gcc/fortran/options.c
index c67d109..8e352ae 100644
--- a/gcc/fortran/options.c
+++ b/gcc/fortran/options.c
@@ -125,7 +125,7 @@  gfc_init_options (unsigned int decoded_options_count,
 
   /* Default value of flag_max_stack_var_size is set in gfc_post_options.  */
   gfc_option.flag_max_stack_var_size = -2;
-  gfc_option.flag_stack_arrays = 0;
+  gfc_option.flag_stack_arrays = -1;
 
   gfc_option.flag_range_check = 1;
   gfc_option.flag_pack_derived = 0;
@@ -275,6 +275,9 @@  gfc_post_options (const char **pfilename)
   if (gfc_option.flag_protect_parens == -1)
     gfc_option.flag_protect_parens = !optimize_fast;
 
+  if (gfc_option.flag_stack_arrays == -1)
+    gfc_option.flag_stack_arrays = optimize_fast;
+
   /* By default, disable (re)allocation during assignment for -std=f95,
      and enable it for F2003/F2008/GNU/Legacy. */
   if (gfc_option.flag_realloc_lhs == -1)