[Bug c++/61214] New: [4.9 regression] Weird interaction between -fvisibility-inlines-hidden, inline virtuals and devirtualization

[Bug c++/61214] New: [4.9 regression] Weird interaction between -fvisibility-inlines-hidden, inline virtuals and devirtualization

[delroth@dolphin-emu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61214

            Bug ID: 61214
           Summary: [4.9 regression] Weird interaction between
                    -fvisibility-inlines-hidden, inline virtuals and
                    devirtualization
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: delroth@dolphin-emu.org

Created attachment 32814
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=32814&action=edit
Small test case reproducing this issue

A shared library (libtest.so) is compiled using -fvisibility=hidden
-fvisibility-inlines-hidden. This library exports (visibility=default) a class
hierarchy with virtual inline methods:

struct VISIBILITY_DEFAULT Base { virtual Base* clone() { return new Base(); }};
struct VISIBILITY_DEFAULT Foo { virtual Base* clone() { return new Foo(); }};
// + at least one method that is defined in a compilation unit, along with the
vtable, typeinfo, etc.

The code that uses libtest.so looks like this:
Base* obj = new Foo();
obj->clone();

When this is compiled to libtest.so, Base::clone and Foo::clone are not present
among the exported symbols. This did not cause issues before g++4.9 because g++
was not smart enough to determine that "obj" is always a Foo. It always issued
a call through the vtable, which *is* exported by libtest.so (and contains a
valid entry for Foo::clone).

Now, with g++4.9 and (better) devirtualization, g++ tries to generate a direct
call to Foo::clone. But instead of instantiating the inline function, it
assumes the inline function is already instantiated. This fails at link time
because no definition of Foo::clone can be found.

Small test case attached (with Makefile, reproduces the bug on g++4.9 on Linux
x86_64). In practice, s/libtest/wxWidgets/,
s/Foo::clone/wxCommandEvent::Clone/. Whether this is a bug of wxWidgets that
should not be using -fvisibility-inlines-hidden or a bug of g++4.9 that should
be instantiating the inline function, is something you will have to debate :)
>From gcc-bugs-return-451836-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Sun May 18 03:26:09 2014
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From: "sandra at codesourcery dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug libstdc++/60758] Infinite backtrace in  __cxa_end_cleanup
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id`758

Sandra Loosemore <sandra at codesourcery dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |sandra at codesourcery dot com

--- Comment #5 from Sandra Loosemore <sandra at codesourcery dot com> ---
The patch committed as r210215 is broken for -mthumb on arm-none-eabi:

libtool: compile:
/scratch/sandra/arm-fsf/obj/gcc-mainline-0-arm-none-eabi-i686-pc-linux-gnu/./gcc/xgcc
-shared-libgcc
-B/scratch/sandra/arm-fsf/obj/gcc-mainline-0-arm-none-eabi-i686-pc-linux-gnu/./gcc
-nostdinc++
-L/scratch/sandra/arm-fsf/obj/gcc-mainline-0-arm-none-eabi-i686-pc-linux-gnu/arm-none-eabi/thumb/libstdc++-v3/src
-L/scratch/sandra/arm-fsf/obj/gcc-mainline-0-arm-none-eabi-i686-pc-linux-gnu/arm-none-eabi/thumb/libstdc++-v3/src/.libs
-L/scratch/sandra/arm-fsf/obj/gcc-mainline-0-arm-none-eabi-i686-pc-linux-gnu/arm-none-eabi/thumb/libstdc++-v3/libsupc++/.libs
-B/scratch/sandra/arm-fsf/install/arm-none-eabi/bin/
-B/scratch/sandra/arm-fsf/install/arm-none-eabi/lib/ -isystem
/scratch/sandra/arm-fsf/install/arm-none-eabi/include -isystem
/scratch/sandra/arm-fsf/install/arm-none-eabi/sys-include -mthumb
-I/scratch/sandra/arm-fsf/src/gcc-mainline/libstdc++-v3/../libgcc
-I/scratch/sandra/arm-fsf/obj/gcc-mainline-0-arm-none-eabi-i686-pc-linux-gnu/arm-none-eabi/thumb/libstdc++-v3/include/arm-none-eabi
-I/scratch/sandra/arm-fsf/obj/gcc-mainline-0-arm-none-eabi-i686-pc-linux-gnu/arm-none-eabi/thumb/libstdc++-v3/include
-I/scratch/sandra/arm-fsf/src/gcc-mainline/libstdc++-v3/libsupc++
-fno-implicit-templates -Wall -Wextra -Wwrite-strings -Wcast-qual -Wabi
-fdiagnostics-show-location=once -ffunction-sections -fdata-sections
-frandom-seed=eh_arm.lo -g -O2 -mthumb -c
/scratch/sandra/arm-fsf/src/gcc-mainline/libstdc++-v3/libsupc++/eh_arm.cc -o
eh_arm.o
/tmp/cchJLQxH.s: Assembler messages:
/tmp/cchJLQxH.s:26: Error: invalid register list to push/pop instruction --
`pop {r1,r2,r3,lr}'

It looks to me like lr is valid in the reglist for PUSH but not POP on Thumb.

Since this breaks builds, please either fix ASAP or revert the broken patch.

[Bug c++/61214] [4.9/4.10 regression] Weird interaction between -fvisibility-inlines-hidden, inline virtuals and devirtualization

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61214

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |hubicka at gcc dot gnu.org,
                   |                            |jason at gcc dot gnu.org
   Target Milestone|---                         |4.9.1
            Summary|[4.9 regression] Weird      |[4.9/4.10 regression] Weird
                   |interaction between         |interaction between
                   |-fvisibility-inlines-hidden |-fvisibility-inlines-hidden
                   |, inline virtuals and       |, inline virtuals and
                   |devirtualization            |devirtualization
>From gcc-bugs-return-451892-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Mon May 19 10:39:46 2014
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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug ipa/61211] [4.9/4.10 Regression] ICE: verify_cgraph_node failed: edge points to wrong declaration with -O3 -fno-inline
Date: Mon, 19 May 2014 10:39:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?ida211

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |hubicka at gcc dot gnu.org,
                   |                            |jamborm at gcc dot gnu.org
   Target Milestone|---                         |4.9.1

[Bug c++/61214] [4.9/4.10 regression] Weird interaction between -fvisibility-inlines-hidden, inline virtuals and devirtualization

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61214

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2014-06-03
     Ever confirmed|0                           |1

--- Comment #1 from Jason Merrill <jason at gcc dot gnu.org> ---
The current trunk (r211157) doesn't devirtualize the call to Foo::clone; it
goes through the vtable even though we know which vtable we're dealing with.  I
would guess that this is due to a change to can_refer_decl_in_current_unit_p.

[Bug c++/61214] [4.9/4.10 regression] Weird interaction between -fvisibility-inlines-hidden, inline virtuals and devirtualization

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61214

--- Comment #2 from Jason Merrill <jason at gcc dot gnu.org> ---
I wonder why we don't inline Foo::clone, though.

[Bug c++/61214] [4.9/4.10 regression] Weird interaction between -fvisibility-inlines-hidden, inline virtuals and devirtualization

[delroth@dolphin-emu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61214

--- Comment #3 from Pierre Bourdon <delroth@dolphin-emu.org> ---
I'm more wondering why Foo::clone is not being instantiated by the code that
calls it.

Does C++ specify that virtual inline functions are guaranteed to be
instantiated in the compilation unit that contains the vtable? It looks like
this is the assumption made by GCC at the moment.

FYI, a more "real" testcase: if you build wxWidgets 3.0 with
-fvisibility=hidden -fvisibility-inlines-hidden (the default, afaict), the
following will work on gcc 4.8 but not 4.9:

$ cat >testcase.cpp <<EOF
#include <wx/event.h>

int main()
{
wxEvent* evt = new wxNotifyEvent();
evt->Clone();
return 0;
}
EOF
$ g++ -std=c++11 -O3 $(wx-config --cxxflags --libs) testcase.cpp

[Bug c++/61214] [4.9/4.10 regression] Weird interaction between -fvisibility-inlines-hidden, inline virtuals and devirtualization

[vz-gcc at zeitlins dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61214

Vadim Zeitlin <vz-gcc at zeitlins dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |vz-gcc at zeitlins dot org

--- Comment #4 from Vadim Zeitlin <vz-gcc at zeitlins dot org> ---
I'd be grateful for any workaround suggestions in the meanwhile. We have one
patch at http://trac.wxwidgets.org/ticket/16359 but it is rather ugly, so it
would be great if someone could propose something better. TIA!

BTW, -O3 is not necessary to see the bug, compiling the test case with just -O
(or -O1, -O2, ...) is enough, it only links without any optimizations at all.

[Bug c++/61214] [4.9/4.10 regression] Weird interaction between -fvisibility-inlines-hidden, inline virtuals and devirtualization

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61214

--- Comment #5 from Jason Merrill <jason at gcc dot gnu.org> ---
(In reply to Vadim Zeitlin from comment #4)
> I'd be grateful for any workaround suggestions in the meanwhile.

-fno-devirtualize should avoid the problem.

[Bug c++/61214] [4.9/4.10 regression] Weird interaction between -fvisibility-inlines-hidden, inline virtuals and devirtualization

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61214

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.9.1                       |4.9.2

--- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 4.9.1 has been released.

[Bug c++/61214] [4.9/5 regression] Weird interaction between -fvisibility-inlines-hidden, inline virtuals and devirtualization

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61214

--- Comment #7 from Jason Merrill <jason at gcc dot gnu.org> ---
Author: jason
Date: Wed Aug 20 01:54:40 2014
New Revision: 214208

URL: https://gcc.gnu.org/viewcvs?rev=214208&root=gcc&view=rev
Log:
    PR c++/61214
    PR tree-optimization/62091
    * decl2.c (decl_needed_p): Return true for virtual functions when
    devirtualizing.

Added:
    branches/gcc-4_9-branch/gcc/testsuite/g++.dg/ipa/devirt-39.C
Modified:
    branches/gcc-4_9-branch/gcc/cp/ChangeLog
    branches/gcc-4_9-branch/gcc/cp/decl2.c

[Bug c++/61214] [4.9/5 regression] Weird interaction between -fvisibility-inlines-hidden, inline virtuals and devirtualization

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61214

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED

--- Comment #8 from Jason Merrill <jason at gcc dot gnu.org> ---
Fixed for 4.9.2 and trunk.

[Bug c++/61214] [4.9/5 regression] Weird interaction between -fvisibility-inlines-hidden, inline virtuals and devirtualization

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61214

--- Comment #9 from Jason Merrill <jason at gcc dot gnu.org> ---
Author: jason
Date: Tue Sep  9 11:57:25 2014
New Revision: 215061

URL: https://gcc.gnu.org/viewcvs?rev=215061&root=gcc&view=rev
Log:
    PR c++/61214
    PR c++/62224
gcc/
    * gimple-fold.c (can_refer_decl_in_current_unit_p): Don't allow
    reference to a DECL_EXTERNAL COMDAT.
gcc/cp/
    * decl2.c (decl_needed_p): Revert virtual functions change.

Added:
    branches/gcc-4_9-branch/gcc/testsuite/g++.dg/ipa/devirt-40.C
Modified:
    branches/gcc-4_9-branch/gcc/ChangeLog
    branches/gcc-4_9-branch/gcc/cp/ChangeLog
    branches/gcc-4_9-branch/gcc/cp/decl2.c
    branches/gcc-4_9-branch/gcc/gimple-fold.c
    branches/gcc-4_9-branch/gcc/testsuite/g++.dg/ipa/devirt-39.C

[Bug c++/61214] [4.9/5 regression] Weird interaction between -fvisibility-inlines-hidden, inline virtuals and devirtualization

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61214

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |rafael at espindo dot la

--- Comment #10 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
*** Bug 58045 has been marked as a duplicate of this bug. ***