[Bug c++/95222] New: GCC 10.1 x86 issue with function pointers with calling convention attribute and template specialization

[Bug c++/95222] New: GCC 10.1 x86 issue with function pointers with calling convention attribute and template specialization

[raptorfactor at raptorfactor dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95222

            Bug ID: 95222
           Summary: GCC 10.1 x86 issue with function pointers with calling
                    convention attribute and template specialization
           Product: gcc
           Version: 10.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: raptorfactor at raptorfactor dot com
  Target Milestone: ---

The following code (which is a simplified repro from a much larger function
introspection library) used to work with GCC 9.x, but does not with the update
to 10.1. Is this a compiler/toolchain bug or is there something incorrect about
the code that I'm missing (obviously it's non-standard and relying on the
behavior of vendor extensions)?

>>>>>>>>>>>>>>>

#if defined(_MSC_VER)
#define CC_FASTCALL __fastcall
#define CC_STDCALL __stdcall
#else
#define CC_FASTCALL __attribute__((fastcall))
#define CC_STDCALL __attribute__((stdcall))
#endif

template <typename FuncT>
struct FuncResult;

template <typename R, typename... Args>
struct FuncResult<R(*)(Args...)>
{
    using type = R;
};

template <typename R, typename... Args>
struct FuncResult<R(CC_FASTCALL*)(Args...)>
{
    using type = R;
};

template <typename R, typename... Args>
struct FuncResult<R(CC_STDCALL*)(Args...)>
{
    using type = R;
};

template <typename FuncT>
auto wrap(FuncT f) -> typename FuncResult<FuncT>::type
{
    return f(1, 2, 3);
}

int CC_FASTCALL func1(int x, int y, int z)
{
    return x + y + z;
}

int CC_STDCALL func2(int x, int y, int z)
{
    return x + y + z;
}

int main()
{
    return wrap(&func1) + wrap(&func2);
}

>>>>>>>>>>>>>>>

With the calling convention specific specialization:

>>>>>>>>>>>>>>>

main.cpp:19:8: error: redefinition of 'struct FuncResult<R (*)(Args ...)>'
   19 | struct FuncResult<R(CC_FASTCALL*)(Args...)>
      |        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
main.cpp:13:8: note: previous definition of 'struct FuncResult<R (*)(Args
...)>'
   13 | struct FuncResult<R(*)(Args...)>
      |        ^~~~~~~~~~~~~~~~~~~~~~~~~

>>>>>>>>>>>>>>>

Without the calling convention specific specialization:

>>>>>>>>>>>>>>>

main.cpp:50:23: error: no matching function for call to 'wrap(int
(__attribute__((fastcall)) *)(int, int, int))'
   50 |     return wrap(&func1) + wrap(&func2);
      |                       ^
main.cpp:33:6: note: candidate: 'template<class FuncT> typename
FuncResult<FuncT>::type wrap(FuncT)'
   33 | auto wrap(FuncT f) -> typename FuncResult<FuncT>::type
      |      ^~~~
main.cpp:33:6: note:   template argument deduction/substitution failed:
main.cpp: In substitution of 'template<class FuncT> typename
FuncResult<FuncT>::type wrap(FuncT) [with FuncT = int
(__attribute__((fastcall)) *)(int, int, int)]':
main.cpp:50:23:   required from here
main.cpp:33:6: error: invalid use of incomplete type 'struct FuncResult<int
(__attribute__((fastcall)) *)(int, int, int)>'
main.cpp:10:8: note: declaration of 'struct FuncResult<int
(__attribute__((fastcall)) *)(int, int, int)>'
   10 | struct FuncResult;
      |        ^~~~~~~~~~

>>>>>>>>>>>>>>>

Damned if you do, damned if you don't. Is anyone aware of a workaround for
this? It's blocking my build and I can't figure out an easy workaround.

Thanks.

[Bug c++/95222] GCC 10.1 x86 issue with function pointers with calling convention attribute and template specialization

[raptorfactor at raptorfactor dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95222

--- Comment #1 from raptorfactor at raptorfactor dot com ---
$ g++ -v
Using built-in specs.
COLLECT_GCC=C:\Redacted\msys2-x86_64-rolling\mingw32\bin\g++.exe
COLLECT_LTO_WRAPPER=C:/Redacted/msys2-x86_64-rolling/mingw32/bin/../lib/gcc/i686-w64-mingw32/10.1.0/lto-wrapper.exe
Target: i686-w64-mingw32
Configured with: ../gcc-10.1.0/configure --prefix=/mingw32
--with-local-prefix=/mingw32/local --build=i686-w64-mingw32
--host=i686-w64-mingw32 --target=i686-w64-mingw32
--with-native-system-header-dir=/mingw32/i686-w64-mingw32/include
--libexecdir=/mingw32/lib --enable-bootstrap --with-arch=i686
--with-tune=generic --enable-languages=c,lto,c++,fortran,ada,objc,obj-c++
--enable-shared --enable-static --enable-libatomic --enable-threads=posix
--enable-graphite --enable-fully-dynamic-string
--enable-libstdcxx-filesystem-ts=yes --enable-libstdcxx-time=yes
--disable-libstdcxx-pch --disable-libstdcxx-debug --disable-isl-version-check
--enable-lto --enable-libgomp --disable-multilib --enable-checking=release
--disable-rpath --disable-win32-registry --disable-nls --disable-werror
--disable-symvers --disable-plugin --with-libiconv --with-system-zlib
--with-gmp=/mingw32 --with-mpfr=/mingw32 --with-mpc=/mingw32
--with-isl=/mingw32 --with-pkgversion='Rev2, Built by MSYS2 project'
--with-bugurl=https://sourceforge.net/projects/msys2 --with-gnu-as
--with-gnu-ld --disable-sjlj-exceptions --with-dwarf2
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 10.1.0 (Rev2, Built by MSYS2 project)

[Bug c++/95222] [10/11 Regression] GCC 10.1 x86 issue with function pointers with calling convention attribute and template specialization

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95222

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|GCC 10.1 x86 issue with     |[10/11 Regression] GCC 10.1
                   |function pointers with      |x86 issue with function
                   |calling convention          |pointers with calling
                   |attribute and template      |convention attribute and
                   |specialization              |template specialization
   Target Milestone|---                         |10.2
             Target|                            |x86_64-*-* i?86-*-*
           Keywords|                            |needs-bisection,
                   |                            |rejects-valid

[Bug c++/95222] [10/11 Regression] GCC 10.1 x86 issue with function pointers with calling convention attribute and template specialization

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95222

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
           Keywords|needs-bisection             |
   Last reconfirmed|                            |2020-05-23
     Ever confirmed|0                           |1
                 CC|                            |jakub at gcc dot gnu.org,
                   |                            |jason at gcc dot gnu.org

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Rejected since r10-7998-g5f1cd1da1a805c3d00332da45c3ab78a3931af63 , on Linux
needs -m32.

[Bug c++/95222] [10/11 Regression] GCC 10.1 x86 issue with function pointers with calling convention attribute and template specialization

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95222

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

[Bug c++/95222] [10/11 Regression] GCC 10.1 x86 issue with function pointers with calling convention attribute and template specialization

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95222

--- Comment #3 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:7e7d9fcff56385812764cba63e1ebf6f4c6c0320

commit r11-662-g7e7d9fcff56385812764cba63e1ebf6f4c6c0320
Author: Jason Merrill <jason@redhat.com>
Date:   Mon May 25 19:04:05 2020 -0400

    c++: Fix stdcall attribute in template. [PR95222]

    Another case that breaks with my fix for PR90750: we shouldn't move type
    attributes in TYPENAME context either, as there's no decl for them to move
    to.

    gcc/cp/ChangeLog:

            PR c++/95222
            * decl.c (grokdeclarator): Don't shift attributes in TYPENAME
            context.

    gcc/testsuite/ChangeLog:

            PR c++/95222
            * g++.dg/ext/tmplattr10.C: New test.

[Bug c++/95222] [10/11 Regression] GCC 10.1 x86 issue with function pointers with calling convention attribute and template specialization

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95222

--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-10 branch has been updated by Jason Merrill
<jason@gcc.gnu.org>:

https://gcc.gnu.org/g:0c473d8f32510fcc96d584ee5099b856cfd3d8d6

commit r10-8189-g0c473d8f32510fcc96d584ee5099b856cfd3d8d6
Author: Jason Merrill <jason@redhat.com>
Date:   Mon May 25 19:04:05 2020 -0400

    c++: Fix stdcall attribute in template. [PR95222]

    Another case that breaks with my fix for PR90750: we shouldn't move type
    attributes in TYPENAME context either, as there's no decl for them to move
    to.

    gcc/cp/ChangeLog:

            PR c++/95222
            * decl.c (grokdeclarator): Don't shift attributes in TYPENAME
            context.

    gcc/testsuite/ChangeLog:

            PR c++/95222
            * g++.dg/ext/tmplattr10.C: New test.

    (cherry picked from commit 7e7d9fcff56385812764cba63e1ebf6f4c6c0320)

[Bug c++/95222] [10/11 Regression] GCC 10.1 x86 issue with function pointers with calling convention attribute and template specialization

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95222

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

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

--- Comment #5 from Jason Merrill <jason at gcc dot gnu.org> ---
Fixed for 10.2/11.

[Bug c++/95222] [10/11 Regression] GCC 10.1 x86 issue with function pointers with calling convention attribute and template specialization

[ro at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95222

Rainer Orth <ro at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ro at gcc dot gnu.org
             Status|RESOLVED                    |REOPENED
         Resolution|FIXED                       |---

--- Comment #6 from Rainer Orth <ro at gcc dot gnu.org> ---
The new testcase FAILs on 32-bit Solaris/x86:

+FAIL: g++.dg/ext/tmplattr10.C  -std=c++98 (test for excess errors)

Excess errors:
/vol/gcc/src/hg/master/local/gcc/testsuite/g++.dg/ext/tmplattr10.C:15:31:
error: variadic templates only available with '-std=c++11' or '-std=gnu++11'
/vol/gcc/src/hg/master/local/gcc/testsuite/g++.dg/ext/tmplattr10.C:16:28:
error: variadic templates only available with '-std=c++11' or '-std=gnu++11'
/vol/gcc/src/hg/master/local/gcc/testsuite/g++.dg/ext/tmplattr10.C:18:11:
error: expected nested-name-specifier before 'type'
/vol/gcc/src/hg/master/local/gcc/testsuite/g++.dg/ext/tmplattr10.C:21:31:
error: variadic templates only available with '-std=c++11' or '-std=gnu++11'
/vol/gcc/src/hg/master/local/gcc/testsuite/g++.dg/ext/tmplattr10.C:22:39:
error: variadic templates only available with '-std=c++11' or '-std=gnu++11'
/vol/gcc/src/hg/master/local/gcc/testsuite/g++.dg/ext/tmplattr10.C:24:11:
error: expected nested-name-specifier before 'type'
/vol/gcc/src/hg/master/local/gcc/testsuite/g++.dg/ext/tmplattr10.C:27:31:
error: variadic templates only available with '-std=c++11' or '-std=gnu++11'
/vol/gcc/src/hg/master/local/gcc/testsuite/g++.dg/ext/tmplattr10.C:28:38:
error: variadic templates only available with '-std=c++11' or '-std=gnu++11'
/vol/gcc/src/hg/master/local/gcc/testsuite/g++.dg/ext/tmplattr10.C:30:11:
error: expected nested-name-specifier before 'type'
/vol/gcc/src/hg/master/local/gcc/testsuite/g++.dg/ext/tmplattr10.C:34:6: error:
ISO C++ forbids declaration of 'wrap' with no type [-fpermissive]
/vol/gcc/src/hg/master/local/gcc/testsuite/g++.dg/ext/tmplattr10.C:34:1: error:
top-level declaration of 'wrap' specifies 'auto'
/vol/gcc/src/hg/master/local/gcc/testsuite/g++.dg/ext/tmplattr10.C:34:51:
error: trailing return type only available with '-std=c++11' or '-std=gnu++11'
/vol/gcc/src/hg/master/local/gcc/testsuite/g++.dg/ext/tmplattr10.C:51:12:
error: 'wrap' was not declared in this scope

[Bug c++/95222] [10/11 Regression] GCC 10.1 x86 issue with function pointers with calling convention attribute and template specialization

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95222

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

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

--- Comment #7 from Jason Merrill <jason at gcc dot gnu.org> ---
Testcase fixed.

[Bug c++/95222] [10/11 Regression] GCC 10.1 x86 issue with function pointers with calling convention attribute and template specialization

[puetzk at puetzk dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95222

Kevin Puetz <puetzk at puetzk dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |puetzk at puetzk dot org

--- Comment #8 from Kevin Puetz <puetzk at puetzk dot org> ---
This bug can also manifest as wrong-code, e.g.

>>>>>>>>>>>>>>>

template<bool bIsStdcall, typename T> struct func_ptr_t;

template<typename T> struct func_ptr_t<false,T> {
        using type = void(*)(T);
};

template<typename T> struct func_ptr_t<true,T> {
#if 1
        using type = void(__attribute__((__stdcall__))*)(T);
#else
        using type = void(__attribute__((__stdcall__))*)(int); // this works,
using T is important somehow
#endif
};

#if 1
        using foo_stdcall_ptr = func_ptr_t<true,int>::type;
        using foo_cdecl_ptr = func_ptr_t<false,int>::type;
#else
        using foo_stdcall_ptr = void(__attribute__((__stdcall__))*)(int,int);
        using foo_cdecl_ptr = void(*)(int,int);
#endif

foo_stdcall_ptr foo_stdcall;
foo_cdecl_ptr foo_cdecl;

void bar_stdcall() {
        foo_stdcall(1);
}

void bar_cdecl() {
        foo_cdecl(1);
}

>>>>>>>>>>>>>>>

Should compile so that the bar_stdcall versions pops fewer bytes off the stack
(as foo_stdcall already cleaned up its own arguments).

>>>>>>>>>>>>>>>

--- bar_cdecl.S 2021-03-09 00:54:58.404022904 +0000
+++ bar_stdcall.S       2021-03-09 00:52:07.900015002 +0000
@@ -1,15 +1,15 @@
-<bar_cdecl()>:
+<bar_stdcall()>:
    0:  f3 0f 1e fb             endbr32 
    4:  55                      push   %ebp
    5:  89 e5                   mov    %esp,%ebp
    7:  83 ec 08                sub    $0x8,%esp
-   a:  e8 fc ff ff ff          call   32 <bar_cdecl()+0xb>
+   a:  e8 fc ff ff ff          call   b <bar_stdcall()+0xb>
    f:  05 01 00 00 00          add    $0x1,%eax
   14:  8b 80 00 00 00 00       mov    0x0(%eax),%eax
   1a:  83 ec 0c                sub    $0xc,%esp
   1d:  6a 01                   push   $0x1
   1f:  ff d0                   call   *%eax
-  21:  83 c4 10                add    $0x10,%esp
+  21:  83 c4 0c                add    $0xc,%esp
   24:  90                      nop
   25:  c9                      leave  
   26:  c3                      ret    


>>>>>>>>>>>>>>>

But doesn't in 9.4, 10.0, and 10.1 (seems to be fixed again in 10.2+,
presumably per this fix). I mention this only because I finally found this
relevant PR, and perhaps knowing it might affect decisions about which branches
should get fixed - e.g. 9.x is in stage 4 but this is a 9.3.0->9.4.0 regression
(presumably PR090750), and also wrong-code. But we were able to work around it,
and so I'm not directly arguing for (or against) a backport to 

Ubuntu 20.04 compiler **is** affected despite claiming to be 9.3.0 - Ubuntu has
seemingly backported the gcc 9 branch through 4ad02cfb768 (git-updates.patch in
gcc-9_9.3.0-17ubuntu1~20.04.debian.tar.xz). But I'll raise that separately in
their bug tracker.

[Bug c++/95222] [10/11 Regression] GCC 10.1 x86 issue with function pointers with calling convention attribute and template specialization

[puetzk at puetzk dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95222

--- Comment #9 from Kevin Puetz <puetzk at puetzk dot org> ---
I accidentally dropped a word, meant to say:
I'm not directly arguing for (or against) a backport to (a hypothetical 9.5.0)

Just noting that this issue could also manifest as wrong-code, for
consideration in case there's going to be one.