* [Bug ipa/61190] [4.8/4.9/4.10 Regression] g++.old-deja/g++.mike/p4736b.C FAILs at -O2/-Os/-O3
2014-05-14 20:14 [Bug ipa/61190] New: [4.8/4.9/4.10 Regression] g++.old-deja/g++.mike/p4736b.C FAILs at -O2/-Os/-O3 zsojka at seznam dot cz
@ 2014-05-26 14:02 ` rguenth at gcc dot gnu.org
2014-05-30 20:57 ` bernd.edlinger at hotmail dot de
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From: rguenth at gcc dot gnu.org @ 2014-05-26 14:02 UTC (permalink / raw)
To: gcc-bugs
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Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|--- |4.8.4
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2014-05-14 20:14 [Bug ipa/61190] New: [4.8/4.9/4.10 Regression] g++.old-deja/g++.mike/p4736b.C FAILs at -O2/-Os/-O3 zsojka at seznam dot cz
2014-05-26 14:02 ` [Bug ipa/61190] " rguenth at gcc dot gnu.org
@ 2014-05-30 20:57 ` bernd.edlinger at hotmail dot de
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From: bernd.edlinger at hotmail dot de @ 2014-05-30 20:57 UTC (permalink / raw)
To: gcc-bugs
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Bernd Edlinger <bernd.edlinger at hotmail dot de> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |bernd.edlinger at hotmail dot de
--- Comment #1 from Bernd Edlinger <bernd.edlinger at hotmail dot de> ---
Created attachment 32879
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=32879&action=edit
slightly reduced test case
Acutally also -O1 produces wrong code, and happens to not crash by chance.
Only -O0 and -Og produce correct code.
The constructor Main::Main() first inlined and then completely optimized
away in the dce1 pass.
But even with -fno-tree-dce the constructor seems to be removed in the rtl
passes.
However when I use -fno-ipa-pure-const the sample works at all optimization
levels.
So should we blame "ipa-pure-const"?
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2014-05-14 20:14 [Bug ipa/61190] New: [4.8/4.9/4.10 Regression] g++.old-deja/g++.mike/p4736b.C FAILs at -O2/-Os/-O3 zsojka at seznam dot cz
2014-05-26 14:02 ` [Bug ipa/61190] " rguenth at gcc dot gnu.org
2014-05-30 20:57 ` bernd.edlinger at hotmail dot de
@ 2014-06-01 22:58 ` bernd.edlinger at hotmail dot de
2014-07-08 8:42 ` jakub at gcc dot gnu.org
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From: bernd.edlinger at hotmail dot de @ 2014-06-01 22:58 UTC (permalink / raw)
To: gcc-bugs
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--- Comment #2 from Bernd Edlinger <bernd.edlinger at hotmail dot de> ---
Created attachment 32883
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=32883&action=edit
possible fix
Well, the problem seems to be, that the thunk code is
not emitted in the normal way using gimple code,
but instead by the i386 back-end with a callback.
This makes the thunk invisible to the ipa-pure-const pass,
which assumes that all values just flow straight thu the thunk.
See ipa-pure-const.c (analyze_function):
if (fn->thunk.thunk_p || fn->alias)
{
/* Thunk gets propagated through, so nothing interesting happens. */
gcc_assert (ipa);
return l;
}
But this is not true for a virtual base class:
The thunk itself references the vtable, so if nothing else might need
the vtable, the optimizer may remove the initalization of the vtable,
which happened in this example.
The most simple work around would be the attached patch, which
simply falls back to emitting gimple code, if virtual base classes
are used.
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From: jakub at gcc dot gnu.org @ 2014-07-08 8:42 UTC (permalink / raw)
To: gcc-bugs
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Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |jakub at gcc dot gnu.org
--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
That looks like a too ugly hack. Much better is just to teach the
ipa-pure-const pass about thunks IMHO, what they can and can't access.
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2014-05-14 20:14 [Bug ipa/61190] New: [4.8/4.9/4.10 Regression] g++.old-deja/g++.mike/p4736b.C FAILs at -O2/-Os/-O3 zsojka at seznam dot cz
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From: bernd.edlinger at hotmail dot de @ 2014-07-10 20:41 UTC (permalink / raw)
To: gcc-bugs
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Bernd Edlinger <bernd.edlinger at hotmail dot de> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |hubicka at gcc dot gnu.org
--- Comment #4 from Bernd Edlinger <bernd.edlinger at hotmail dot de> ---
(In reply to Jakub Jelinek from comment #3)
> That looks like a too ugly hack. Much better is just to teach the
> ipa-pure-const pass about thunks IMHO, what they can and can't access.
yes, sigh, I know...
But OTOH this patch not only fixes the test case, but also
allows several optimizations on the thunk,
that were not possible before:
- inlining the function into the thunk
- inlining the thunk into the caller
- versioning on the thunk
- general optimizations on the thunk
this means, in this example:
the thunk's access to the vtable is optimized away
and then the constructor is also optimized away.
=> everything is just fine!
And, if inlining of the function into the thunk is
not possible for any reason, then I still see a
tail-call optimization.
Well I have still a few days off, to work on this.
What I tried so far is this:
Following Honzas advice, I tried this:
Index: ipa-pure-const.c
===================================================================
--- ipa-pure-const.c (revision 212426)
+++ ipa-pure-const.c (working copy)
@@ -735,6 +735,8 @@ analyze_function (struct cgraph_node *fn, bool ipa
l->looping_previously_known = true;
l->looping = false;
l->can_throw = false;
+ if (fn->thunk.thunk_p && fn->thunk.virtual_offset_p)
+ l->pure_const_state = IPA_NEITHER;
state_from_flags (&l->state_previously_known, &l->looping_previously_known,
flags_from_decl_or_type (fn->decl),
cgraph_node_cannot_return (fn));
BUT it does not fix the test case. I frankly admit I do not fully
understand why... Any insight here, might be helpful.
When I look at the code in ipa-pure-const.c,
I noticed, that cgraph_function_body_availability is called in many
places, and it may be able to influence lots of things.
So I tried this:
Index: cgraph.c
===================================================================
--- cgraph.c (revision 212426)
+++ cgraph.c (working copy)
@@ -2133,6 +2133,8 @@ cgraph_function_body_availability (struct cgraph_n
avail = AVAIL_LOCAL;
else if (node->alias && node->weakref)
cgraph_function_or_thunk_node (node, &avail);
+ else if (node->thunk.thunk_p && node->thunk.virtual_offset_p)
+ avail = AVAIL_OVERWRITABLE;
else if (lookup_attribute ("ifunc", DECL_ATTRIBUTES (node->decl)))
avail = AVAIL_OVERWRITABLE;
else if (!node->externally_visible)
And yes, this fixes the test case!
Returning AVAIL_OVERWRITABLE in this case means in my own words:
"this thunk can do anything, and you can not assume anything,
it may be even replaced by someting completely different, by the back-end."
However I don't know if this is a better soulution at all...
The resulting code, at -O2 is worse than with my first hacky patch,
because the constructor is now fully expanded, and can no longer be
optimized away, but it seems to work.
IMHO this issue clearly needs to be fixed, one way or the other...
What would be your ideas, how to fix it?
Thanks
Bernd.
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2014-11-26 18:23 ` [Bug ipa/61190] [4.8/4.9 " edlinger at gcc dot gnu.org
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From: edlinger at gcc dot gnu.org @ 2014-11-26 18:11 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61190
--- Comment #5 from Bernd Edlinger <edlinger at gcc dot gnu.org> ---
Author: edlinger
Date: Wed Nov 26 18:10:29 2014
New Revision: 218091
URL: https://gcc.gnu.org/viewcvs?rev=218091&root=gcc&view=rev
Log:
2014-11-26 Bernd Edlinger <bernd.edlinger@hotmail.de>
PR ipa/61190
* cgraph.h (symtab_node::call_for_symbol_and_aliases): Fix comment.
(cgraph_node::function_or_virtual_thunk_symbol): New function.
(cgraph_node::call_for_symbol_and_aliases): Fix comment.
(cgraph_node::call_for_symbol_thunks_and_aliases): Adjust comment.
Add new optional parameter exclude_virtual_thunks.
* cgraph.c (cgraph_node::call_for_symbol_thunks_and_aliases): Add new
optional parameter exclude_virtual_thunks.
(cgraph_node::set_const_flag): Don't propagate to virtual thunks.
(cgraph_node::set_pure_flag): Likewise.
(cgraph_node::function_symbol): Simplified.
(cgraph_node::function_or_virtual_thunk_symbol): New function.
* ipa-pure-const.c (analyze_function): For virtual thunks set
pure_const_state to IPA_NEITHER.
(propagate_pure_const): Use function_or_virtual_thunk_symbol.
testsuite/ChangeLog:
2014-11-26 Bernd Edlinger <bernd.edlinger@hotmail.de>
PR ipa/61190
* g++.old-deja/g++.mike/p4736b.C: Use -O2.
Modified:
trunk/gcc/ChangeLog
trunk/gcc/cgraph.c
trunk/gcc/cgraph.h
trunk/gcc/ipa-pure-const.c
trunk/gcc/testsuite/ChangeLog
trunk/gcc/testsuite/g++.old-deja/g++.mike/p4736b.C
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2014-11-26 18:11 ` [Bug ipa/61190] [4.8/4.9/5 " edlinger at gcc dot gnu.org
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From: edlinger at gcc dot gnu.org @ 2014-11-26 18:23 UTC (permalink / raw)
To: gcc-bugs
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Bernd Edlinger <edlinger at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Last reconfirmed| |2014-11-26
Known to work| |5.0
Summary|[4.8/4.9/5 Regression] |[4.8/4.9 Regression]
|g++.old-deja/g++.mike/p4736 |g++.old-deja/g++.mike/p4736
|b.C FAILs at -O2/-Os/-O3 |b.C FAILs at -O2/-Os/-O3
Ever confirmed|0 |1
Known to fail|4.10.0 |
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2014-11-26 18:23 ` [Bug ipa/61190] [4.8/4.9 " edlinger at gcc dot gnu.org
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From: rguenth at gcc dot gnu.org @ 2014-12-10 13:00 UTC (permalink / raw)
To: gcc-bugs
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Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Priority|P3 |P2
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From: jakub at gcc dot gnu.org @ 2014-12-19 13:32 UTC (permalink / raw)
To: gcc-bugs
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Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|4.8.4 |4.8.5
--- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 4.8.4 has been released.
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From: rguenth at gcc dot gnu.org @ 2015-06-23 8:24 UTC (permalink / raw)
To: gcc-bugs
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Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|4.8.5 |4.9.3
--- Comment #7 from Richard Biener <rguenth at gcc dot gnu.org> ---
The gcc-4_8-branch is being closed, re-targeting regressions to 4.9.3.
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From: jakub at gcc dot gnu.org @ 2015-06-26 20:01 UTC (permalink / raw)
To: gcc-bugs
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--- Comment #8 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 4.9.3 has been released.
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From: jakub at gcc dot gnu.org @ 2015-06-26 20:30 UTC (permalink / raw)
To: gcc-bugs
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Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|4.9.3 |4.9.4
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