User account creation filtered due to spam.

Bug 37565 - __optimize__ attribute doesn't work correctly
Summary: __optimize__ attribute doesn't work correctly
Status: NEW
Alias: None
Product: gcc
Classification: Unclassified
Component: middle-end (show other bugs)
Version: 4.4.0
: P3 normal
Target Milestone: ---
Assignee: Not yet assigned to anyone
URL: http://gcc.gnu.org/ml/gcc-patches/200...
Keywords:
Depends on:
Blocks: 39787 39840 45478 46143 47315 53776 37394 38018 41206 45325 52555
  Show dependency treegraph
 
Reported: 2008-09-17 19:54 UTC by H.J. Lu
Modified: 2012-08-15 14:32 UTC (History)
4 users (show)

See Also:
Host:
Target:
Build:
Known to work:
Known to fail:
Last reconfirmed: 2010-08-18 20:59:09


Attachments

Note You need to log in before you can comment on or make changes to this bug.
Description H.J. Lu 2008-09-17 19:54:49 UTC
Many backends need to override optimization options after
we have processed all optimization options.  It is done
in OVERRIDE_OPTIONS. But it is only called once for a given
input. We do have OPTIMIZATION_OPTIONS, which is executed
when the optimization options are changed via "pragma GCC optimize"
or by using the "optimize" attribute. But OPTIMIZATION_OPTIONS
isn't enough. On Linux/x86-64, it gives

[hjl@gnu-6 gcc]$ cat /tmp/x.i
void foo (void) __attribute__ ((__optimize__(2,"omit-frame-pointer")));
void
foo (void)
{
}
[hjl@gnu-6 gcc]$ ./xgcc -B./ -S  /tmp/x.i -mno-accumulate-outgoing-args  -fomit-frame-pointer
/tmp/x.i:1: warning: unwind tables currently require either a frame pointer or -maccumulate-outgoing-args for correctness
[hjl@gnu-6 gcc]$ ./xgcc -B./ -S  /tmp/x.i -mno-accumulate-outgoing-args
[hjl@gnu-6 gcc]$ 

That means we may silently generate wrong codes. To properly support
"pragma GCC optimize" and the "optimize" attribute, we need a way for
a backend to override the optimization options whenever they are
changed.
Comment 1 Andrew Pinski 2008-09-17 20:07:07 UTC
This is a target bug as the warning happens in the back-end.
Comment 2 H.J. Lu 2008-09-17 20:07:47 UTC
Here is one approach to add OVERRIDE_OPTIMIZATION_OPTIONS so
that a backend can have a chance to override optimization
options.

--- gcc/config/i386/i386.h.override	2008-09-11 16:48:39.000000000 -0700
+++ gcc/config/i386/i386.h	2008-09-17 13:02:45.000000000 -0700
@@ -482,6 +482,8 @@ enum calling_abi
 
 #define OVERRIDE_OPTIONS override_options (true)
 
+#define OVERRIDE_OPTIMIZATION_OPTIONS override_options (false)
+
 /* Define this to change the optimizations performed by default.  */
 #define OPTIMIZATION_OPTIONS(LEVEL, SIZE) \
   optimization_options ((LEVEL), (SIZE))
--- gcc/opts.c.override	2008-09-15 08:44:27.000000000 -0700
+++ gcc/opts.c	2008-09-17 13:00:58.000000000 -0700
@@ -1105,8 +1105,14 @@ decode_options (unsigned int argc, const
     }
 #endif
 
+#ifndef OVERRIDE_OPTIMIZATION_OPTIONS
+#define OVERRIDE_OPTIMIZATION_OPTIONS do { } while (0)
+#endif
+
   /* Save the current optimization options if this is the first call.  */
-  if (first_time_p)
+  if (!first_time_p)
+    OVERRIDE_OPTIMIZATION_OPTIONS;
+  else
     {
       optimization_default_node = build_optimization_node ();
       optimization_current_node = optimization_default_node;
Comment 3 H.J. Lu 2008-09-17 20:13:39 UTC
(In reply to comment #1)
> This is a target bug as the warning happens in the back-end.
> 

But there is no chance for a backend to do anything about it.
It can happen to any backends which check flag_XXX in
OVERRIDE_OPTIONS.

Comment 4 Andrew Pinski 2008-09-17 20:16:15 UTC
(In reply to comment #3)
> (In reply to comment #1)
> > This is a target bug as the warning happens in the back-end.
> > 
> 
> But there is no chance for a backend to do anything about it.
> It can happen to any backends which check flag_XXX in
> OVERRIDE_OPTIONS.

But what does C front-end have to do it then?  Nothing.
Comment 5 H.J. Lu 2008-09-17 20:24:17 UTC
If the  __optimize__ attribute is handled properly, we
may be able to fold the __target__ attribute into the
__optimize__ attribute and all backends can support
function specific -mXXX options like

void foo (void) __attribute__ ((__optimize__(2,"omit-frame-pointer,-mtune=core2")));
Comment 6 Andrew Pinski 2008-09-17 20:26:28 UTC
Then lets say it is a middle-end issue.  Still nowhere has you touched the C front-end.
Comment 7 Steve Ellcey 2008-11-17 18:41:47 UTC
This also causes the failure of gcc.dg/pr37106-1.c on ia64-*-* targets.
Comment 8 H.J. Lu 2008-11-19 18:09:06 UTC
I think we need to break OVERRIDE_OPTIONS into 2 parts:

1. Execute only once for a given input.
2. Execute every time after all optimization options
are processed.

with things like OVERRIDE_OPTIONS_ONCE and OVERRIDE_OPTIONS_ALWAYS.
Then OVERRIDE_OPTIONS can be defined as

#define OVERRIDE_OPTIONS \
  OVERRIDE_OPTIONS_ALWAYS; \
  OVERRIDE_OPTIONS_ONCE
Comment 9 Steve Ellcey 2009-10-29 16:44:27 UTC
Subject: Bug 37565

Author: sje
Date: Thu Oct 29 16:44:02 2009
New Revision: 153714

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=153714
Log:
2009-10-29  Steve Ellcey  <sje@cup.hp.com>

	PR middle-end/37565
	PR target/38018
	* doc/tm.texi (OVERRIDE_OPTIONS): Update.
	(TARGET_OVERRIDE_OPTIONS_AFTER_CHANGE): New.
	* optc-gen.awk (cl_target_option_restore): Include call to 
	targetm.override_options_after_change.
	* target-def.h (TARGET_OVERRIDE_OPTIONS_AFTER_CHANGE): New.
	* target.h (override_options_after_change): New.
	* c-common.c (parse_optimize_options): Call
	targetm.override_options_after_change.
	* config/ia64/ia64.c (TARGET_OVERRIDE_OPTIONS_AFTER_CHANGE): New.
	(ia64_override_options_after_change): New.
	(ia64_override_options) Add call to above.


Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/c-common.c
    trunk/gcc/config/ia64/ia64.c
    trunk/gcc/doc/tm.texi
    trunk/gcc/optc-gen.awk
    trunk/gcc/target-def.h
    trunk/gcc/target.h

Comment 10 Steve Ellcey 2009-10-29 17:03:49 UTC
The patch I checked in provides the infrastructure to fix this problem and I have fixed the IA64 instance of it but other targets (like x86) will need to define TARGET_OVERRIDE_OPTIONS_AFTER_CHANGE as well to completely resolve this defect.