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* [Bug tree-optimization/104539] New: Failed to inline a very simple template function when it's explicit instantiated.
@ 2022-02-15 4:34 cassio.neri at gmail dot com
2022-02-15 4:35 ` [Bug tree-optimization/104539] " cassio.neri at gmail dot com
` (6 more replies)
0 siblings, 7 replies; 8+ messages in thread
From: cassio.neri at gmail dot com @ 2022-02-15 4:34 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104539
Bug ID: 104539
Summary: Failed to inline a very simple template function when
it's explicit instantiated.
Product: gcc
Version: 11.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: cassio.neri at gmail dot com
Target Milestone: ---
Consider:
template <int>
//inline
int f() {
return 0;
}
int g() {
return f<0>() + 1;
}
Using -O3, I'd expect f to be inlined in g and this is indeed the case:
g():
mov eax, 1
ret
However, if f is explicit instantiated:
template unsigned f<0>();
then we get a function call (or a jmp if tail call optimisation is possible)
g():
sub rsp, 8
call int f<0>()
add rsp, 8
add eax, 1
ret
A (quite unusual, IMHO) workaround is declaring f as inline:
template <unsigned n>
inline
unsigned f() {
return n;
}
https://godbolt.org/z/TarsTY3zb
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug tree-optimization/104539] Failed to inline a very simple template function when it's explicit instantiated.
2022-02-15 4:34 [Bug tree-optimization/104539] New: Failed to inline a very simple template function when it's explicit instantiated cassio.neri at gmail dot com
@ 2022-02-15 4:35 ` cassio.neri at gmail dot com
2022-02-15 8:13 ` [Bug c++/104539] " rguenth at gcc dot gnu.org
` (5 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: cassio.neri at gmail dot com @ 2022-02-15 4:35 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104539
--- Comment #1 from Cassio Neri <cassio.neri at gmail dot com> ---
Sorry, the last snippet above should be
template <int>
inline
int f() {
return 0;
}
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug c++/104539] Failed to inline a very simple template function when it's explicit instantiated.
2022-02-15 4:34 [Bug tree-optimization/104539] New: Failed to inline a very simple template function when it's explicit instantiated cassio.neri at gmail dot com
2022-02-15 4:35 ` [Bug tree-optimization/104539] " cassio.neri at gmail dot com
@ 2022-02-15 8:13 ` rguenth at gcc dot gnu.org
2022-02-17 5:11 ` jason at gcc dot gnu.org
` (4 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: rguenth at gcc dot gnu.org @ 2022-02-15 8:13 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104539
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |missed-optimization
Last reconfirmed| |2022-02-15
Component|tree-optimization |c++
Ever confirmed|0 |1
CC| |hubicka at gcc dot gnu.org,
| |jason at gcc dot gnu.org
Status|UNCONFIRMED |NEW
Known to fail| |12.0
--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
t.ii:9:20: missed: not inlinable: int g()/1 -> int f() [with int <anonymous>
= 0]/0, function body can be overwritten at link time
so the issue seems to be that explicitely instantiating changes
_Z1fILi0EEiv/1 (int f() [with int <anonymous> = 0]) @0x7ffff6697220
Type: function definition analyzed
Visibility: semantic_interposition public weak comdat
comdat_group:_Z1fILi0EEiv one_only
Aux: @0x42d7d00
References:
Referring:
Function flags: body
Called by: _Z1gv/0
Calls:
to
_Z1fILi0EEiv/0 (int f() [with int <anonymous> = 0]) @0x7ffff6697000
Type: function definition analyzed
Visibility: forced_by_abi semantic_interposition public weak
comdat_group:_Z1fILi0EEiv one_only
Aux: @0x7ffff6697220
References:
Referring:
Function flags: body
Called by: _Z1gv/1 (can throw external)
Calls:
the explicit instantiation lacks COMDAT (but has comdat_group) and it
has forced_by_abi.
I'm not sure the C++ standard calls out any semantic difference for
explicit vs. implicit instantiations but maybe the Itanium ABI does.
Jason? Honza?
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug c++/104539] Failed to inline a very simple template function when it's explicit instantiated.
2022-02-15 4:34 [Bug tree-optimization/104539] New: Failed to inline a very simple template function when it's explicit instantiated cassio.neri at gmail dot com
2022-02-15 4:35 ` [Bug tree-optimization/104539] " cassio.neri at gmail dot com
2022-02-15 8:13 ` [Bug c++/104539] " rguenth at gcc dot gnu.org
@ 2022-02-17 5:11 ` jason at gcc dot gnu.org
2022-02-17 18:29 ` jason at gcc dot gnu.org
` (3 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: jason at gcc dot gnu.org @ 2022-02-17 5:11 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104539
--- Comment #3 from Jason Merrill <jason at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #2)
> the explicit instantiation lacks COMDAT (but has comdat_group) and it
> has forced_by_abi.
>
> I'm not sure the C++ standard calls out any semantic difference for
> explicit vs. implicit instantiations but maybe the Itanium ABI does.
The ABI says nothing about explicit vs. implicit instantiations.
mark_decl_instantiated cleared DECL_COMDAT to fix PR10968, where we failed to
emit an explicit instantiation. But that was before mark_needed; now that we
have that, I'd think it makes sense to have DECL_COMDAT set on explicit
instantiations just like implicit ones.
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug c++/104539] Failed to inline a very simple template function when it's explicit instantiated.
2022-02-15 4:34 [Bug tree-optimization/104539] New: Failed to inline a very simple template function when it's explicit instantiated cassio.neri at gmail dot com
` (2 preceding siblings ...)
2022-02-17 5:11 ` jason at gcc dot gnu.org
@ 2022-02-17 18:29 ` jason at gcc dot gnu.org
2022-02-17 22:51 ` cvs-commit at gcc dot gnu.org
` (2 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: jason at gcc dot gnu.org @ 2022-02-17 18:29 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104539
Jason Merrill <jason at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |ASSIGNED
Assignee|unassigned at gcc dot gnu.org |jason at gcc dot gnu.org
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug c++/104539] Failed to inline a very simple template function when it's explicit instantiated.
2022-02-15 4:34 [Bug tree-optimization/104539] New: Failed to inline a very simple template function when it's explicit instantiated cassio.neri at gmail dot com
` (3 preceding siblings ...)
2022-02-17 18:29 ` jason at gcc dot gnu.org
@ 2022-02-17 22:51 ` cvs-commit at gcc dot gnu.org
2022-02-17 22:52 ` jason at gcc dot gnu.org
2024-03-18 7:08 ` pinskia at gcc dot gnu.org
6 siblings, 0 replies; 8+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2022-02-17 22:51 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104539
--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jason Merrill <jason@gcc.gnu.org>:
https://gcc.gnu.org/g:2c9b7077b72529fbbe896212a0088bff6025c5e7
commit r12-7288-g2c9b7077b72529fbbe896212a0088bff6025c5e7
Author: Jason Merrill <jason@redhat.com>
Date: Thu Feb 17 00:04:21 2022 -0500
c++: inlining explicit instantiations [PR104539]
The PR10968 fix cleared DECL_COMDAT to force output of explicit
instantiations. Then the PR59469 fix added a call to mark_needed, after
which we no longer need to clear DECL_COMDAT, and leaving it set allows us
to inline explicit instantiations without worrying about symbol
interposition.
I suppose there's an argument to be made that an explicit instantiation
declaration (extern template) should clear DECL_COMDAT, since that suggests
that there will be only a single instantiation somewhere that could be
subject to interposition, but that doesn't change the 'inline' semantics,
and it seems cleaner to treat template instantiations uniformly.
PR c++/104539
gcc/cp/ChangeLog:
* pt.cc (mark_decl_instantiated): Don't clear DECL_COMDAT.
gcc/testsuite/ChangeLog:
* g++.dg/ipa/inline-4.C: New test.
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug c++/104539] Failed to inline a very simple template function when it's explicit instantiated.
2022-02-15 4:34 [Bug tree-optimization/104539] New: Failed to inline a very simple template function when it's explicit instantiated cassio.neri at gmail dot com
` (4 preceding siblings ...)
2022-02-17 22:51 ` cvs-commit at gcc dot gnu.org
@ 2022-02-17 22:52 ` jason at gcc dot gnu.org
2024-03-18 7:08 ` pinskia at gcc dot gnu.org
6 siblings, 0 replies; 8+ messages in thread
From: jason at gcc dot gnu.org @ 2022-02-17 22:52 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104539
Jason Merrill <jason at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Known to fail|12.0 |
Known to work| |12.0
Status|ASSIGNED |RESOLVED
Target Milestone|--- |12.0
Resolution|--- |FIXED
--- Comment #5 from Jason Merrill <jason at gcc dot gnu.org> ---
Fixed for GCC 12.
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug c++/104539] Failed to inline a very simple template function when it's explicit instantiated.
2022-02-15 4:34 [Bug tree-optimization/104539] New: Failed to inline a very simple template function when it's explicit instantiated cassio.neri at gmail dot com
` (5 preceding siblings ...)
2022-02-17 22:52 ` jason at gcc dot gnu.org
@ 2024-03-18 7:08 ` pinskia at gcc dot gnu.org
6 siblings, 0 replies; 8+ messages in thread
From: pinskia at gcc dot gnu.org @ 2024-03-18 7:08 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104539
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |programmerjake at gmail dot com
--- Comment #6 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
*** Bug 71587 has been marked as a duplicate of this bug. ***
^ permalink raw reply [flat|nested] 8+ messages in thread
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2022-02-15 4:34 [Bug tree-optimization/104539] New: Failed to inline a very simple template function when it's explicit instantiated cassio.neri at gmail dot com
2022-02-15 4:35 ` [Bug tree-optimization/104539] " cassio.neri at gmail dot com
2022-02-15 8:13 ` [Bug c++/104539] " rguenth at gcc dot gnu.org
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2022-02-17 18:29 ` jason at gcc dot gnu.org
2022-02-17 22:51 ` cvs-commit at gcc dot gnu.org
2022-02-17 22:52 ` jason at gcc dot gnu.org
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