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* [Bug tree-optimization/18842] Weak optimization on global references
[not found] <bug-18842-9734@http.gcc.gnu.org/bugzilla/>
@ 2006-03-05 21:30 ` pinskia at gcc dot gnu dot org
2006-07-16 14:23 ` felix dot nawothnig at t-online dot de
` (2 subsequent siblings)
3 siblings, 0 replies; 7+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2006-03-05 21:30 UTC (permalink / raw)
To: gcc-bugs
------- Comment #7 from pinskia at gcc dot gnu dot org 2006-03-05 21:30 -------
(In reply to comment #2)
> This is not a bug. You need IPA to figure out that y is never changed. For
> example:
>
> int x, &y = x, z;
> int bar() { y = z; }
This actually does:
*y = z; and not y = &z;
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18842
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug tree-optimization/18842] Weak optimization on global references
[not found] <bug-18842-9734@http.gcc.gnu.org/bugzilla/>
2006-03-05 21:30 ` [Bug tree-optimization/18842] Weak optimization on global references pinskia at gcc dot gnu dot org
@ 2006-07-16 14:23 ` felix dot nawothnig at t-online dot de
2006-07-16 20:36 ` rguenth at gcc dot gnu dot org
2009-04-22 22:02 ` pinskia at gcc dot gnu dot org
3 siblings, 0 replies; 7+ messages in thread
From: felix dot nawothnig at t-online dot de @ 2006-07-16 14:23 UTC (permalink / raw)
To: gcc-bugs
------- Comment #8 from felix dot nawothnig at t-online dot de 2006-07-16 14:23 -------
Don't know much about GCC internals but shouldn't this be a very trivial
enhancement? I know that this is FOSS so not to annoy anyone, just wondering
why it's still open after >1 year.
(In case someone is wondering why I care - this is the only one thing where
it's still faster to use macros instead of inline functions & references and
this access is a huge bottleneck in my application)
--
felix dot nawothnig at t-online dot de changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |felix dot nawothnig at t-
| |online dot de
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18842
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug tree-optimization/18842] Weak optimization on global references
[not found] <bug-18842-9734@http.gcc.gnu.org/bugzilla/>
2006-03-05 21:30 ` [Bug tree-optimization/18842] Weak optimization on global references pinskia at gcc dot gnu dot org
2006-07-16 14:23 ` felix dot nawothnig at t-online dot de
@ 2006-07-16 20:36 ` rguenth at gcc dot gnu dot org
2009-04-22 22:02 ` pinskia at gcc dot gnu dot org
3 siblings, 0 replies; 7+ messages in thread
From: rguenth at gcc dot gnu dot org @ 2006-07-16 20:36 UTC (permalink / raw)
To: gcc-bugs
------- Comment #9 from rguenth at gcc dot gnu dot org 2006-07-16 20:36 -------
You could try it yourself. But - do you have a testcase that shows how macros
and inline functions come into play here?
--
rguenth at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |rguenth at gcc dot gnu dot
| |org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18842
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug tree-optimization/18842] Weak optimization on global references
[not found] <bug-18842-9734@http.gcc.gnu.org/bugzilla/>
` (2 preceding siblings ...)
2006-07-16 20:36 ` rguenth at gcc dot gnu dot org
@ 2009-04-22 22:02 ` pinskia at gcc dot gnu dot org
3 siblings, 0 replies; 7+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2009-04-22 22:02 UTC (permalink / raw)
To: gcc-bugs
------- Comment #10 from pinskia at gcc dot gnu dot org 2009-04-22 22:02 -------
Fixed in 4.4.0 and above.
--
pinskia at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
Resolution| |FIXED
Target Milestone|--- |4.4.0
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18842
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug tree-optimization/18842] Weak optimization on global references
2004-12-05 8:55 [Bug c++/18842] New: " felix dot nawothnig at t-online dot de
2004-12-05 15:14 ` [Bug tree-optimization/18842] " pinskia at gcc dot gnu dot org
2004-12-05 19:11 ` felix dot nawothnig at t-online dot de
@ 2004-12-05 19:15 ` pinskia at gcc dot gnu dot org
2 siblings, 0 replies; 7+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2004-12-05 19:15 UTC (permalink / raw)
To: gcc-bugs
------- Additional Comments From pinskia at gcc dot gnu dot org 2004-12-05 19:15 -------
(In reply to comment #5)
> Diagnostics? Both files are 100% valid C++ - but since the C++ standard doesn't
> enforce implementation of references as pointers they cause ABI-defined (?)
> behaviour at/after linkage, just as...
Yes both files are valid C++ but when you link them together they become invalid C++ and yes
the C++ defines this as invalid with no diagnostic required. In fact your example is also invalid C++
but since the standard says we don't have to provide diagnostic as it is a hard problem to actually
provide the diagnostic.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18842
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug tree-optimization/18842] Weak optimization on global references
2004-12-05 8:55 [Bug c++/18842] New: " felix dot nawothnig at t-online dot de
2004-12-05 15:14 ` [Bug tree-optimization/18842] " pinskia at gcc dot gnu dot org
@ 2004-12-05 19:11 ` felix dot nawothnig at t-online dot de
2004-12-05 19:15 ` pinskia at gcc dot gnu dot org
2 siblings, 0 replies; 7+ messages in thread
From: felix dot nawothnig at t-online dot de @ 2004-12-05 19:11 UTC (permalink / raw)
To: gcc-bugs
------- Additional Comments From felix dot nawothnig at t-online dot de 2004-12-05 19:10 -------
Diagnostics? Both files are 100% valid C++ - but since the C++ standard doesn't
enforce implementation of references as pointers they cause ABI-defined (?)
behaviour at/after linkage, just as...
extern int x;
void main() { foo(); assert(x == 5); }
---
float x;
void foo() { x = 5; }
...isn't guaranteed to "work" either. (but is still valid C)
Reading the reference over a pointer would still work because we can't remove
the reference itself from the object since someone might do "extern int &y;" in
another file - but it's evil. (non-portable)
*And* they are guaranteed to be const by the standard.
So, yes, safe to optimize. I think. :)
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18842
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug tree-optimization/18842] Weak optimization on global references
2004-12-05 8:55 [Bug c++/18842] New: " felix dot nawothnig at t-online dot de
@ 2004-12-05 15:14 ` pinskia at gcc dot gnu dot org
2004-12-05 19:11 ` felix dot nawothnig at t-online dot de
2004-12-05 19:15 ` pinskia at gcc dot gnu dot org
2 siblings, 0 replies; 7+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2004-12-05 15:14 UTC (permalink / raw)
To: gcc-bugs
------- Additional Comments From pinskia at gcc dot gnu dot org 2004-12-05 15:14 -------
Consider these two TUs:
extern int *y, x, z;
int foo();
extern "C" void abort();
int main()
{
foo();
if (*y!=42)
abort();
if (y!=&x)
abort();
y = &z;
foo ();
if (*y!=42)
abort();
if (y!=&z)
abort();
return 0;
}
-----
int x, &y = x, z;
int foo() { y = 42; }
-----
Now I think the above is invalid C++ but we don't have to diagnostic since the standard allows us not
to but since the standard allows the correct way, we can optimizate global references now.
--
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Component|c++ |tree-optimization
Ever Confirmed| |1
Keywords| |missed-optimization
Last reconfirmed|0000-00-00 00:00:00 |2004-12-05 15:14:15
date| |
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18842
^ permalink raw reply [flat|nested] 7+ messages in thread
end of thread, other threads:[~2009-04-22 22:02 UTC | newest]
Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
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[not found] <bug-18842-9734@http.gcc.gnu.org/bugzilla/>
2006-03-05 21:30 ` [Bug tree-optimization/18842] Weak optimization on global references pinskia at gcc dot gnu dot org
2006-07-16 14:23 ` felix dot nawothnig at t-online dot de
2006-07-16 20:36 ` rguenth at gcc dot gnu dot org
2009-04-22 22:02 ` pinskia at gcc dot gnu dot org
2004-12-05 8:55 [Bug c++/18842] New: " felix dot nawothnig at t-online dot de
2004-12-05 15:14 ` [Bug tree-optimization/18842] " pinskia at gcc dot gnu dot org
2004-12-05 19:11 ` felix dot nawothnig at t-online dot de
2004-12-05 19:15 ` pinskia at gcc dot gnu dot org
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