[Bug d/108763] New: va_arg usage in D doesn't compile

[Bug d/108763] New: va_arg usage in D doesn't compile

[schveiguy at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108763

            Bug ID: 108763
           Summary: va_arg usage in D doesn't compile
           Product: gcc
           Version: 12.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: d
          Assignee: ibuclaw at gdcproject dot org
          Reporter: schveiguy at gmail dot com
  Target Milestone: ---

Compiling a valid D module that uses varargs does not compile. The following is
the source of `test.d`:

```d
import core.vararg;
void foo(...)
{
    ubyte[128] buf;
    foreach(ti; _arguments)
    {
        va_arg(_argptr, ti, buf.ptr);
    }
}
```

This is confirmed a valid module using both other D compilers, dmd and ldc.

The output information of -v is:

COLLECT_GCC=/opt/compiler-explorer/gcc-12.2.0/bin/gdc
Target: x86_64-linux-gnu
Configured with: ../gcc-12.2.0/configure
--prefix=/opt/compiler-explorer/gcc-build/staging --build=x86_64-linux-gnu
--host=x86_64-linux-gnu --target=x86_64-linux-gnu --disable-bootstrap
--enable-multiarch --with-abi=m64 --with-multilib-list=m32,m64,mx32
--enable-multilib --enable-clocale=gnu
--enable-languages=c,c++,fortran,ada,objc,obj-c++,go,d --enable-ld=yes
--enable-gold=yes --enable-libstdcxx-debug --enable-libstdcxx-time=yes
--enable-linker-build-id --enable-lto --enable-plugins --enable-threads=posix
--with-pkgversion=Compiler-Explorer-Build-gcc--binutils-2.38
--enable-libstdcxx-backtrace=yes
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 12.2.0 (Compiler-Explorer-Build-gcc--binutils-2.38) 
COLLECT_GCC_OPTIONS='-fdiagnostics-color=always' '-g' '-o' '/app/output.s'
'-masm=intel' '-S' '-v' '-shared-libgcc' '-mtune=generic' '-march=x86-64'
'-dumpdir' '/app/'

/opt/compiler-explorer/gcc-12.2.0/bin/../libexec/gcc/x86_64-linux-gnu/12.2.0/d21
<source> -quiet -dumpdir /app/ -dumpbase output.d -dumpbase-ext .d -masm=intel
-mtune=generic -march=x86-64 -g -version -fdiagnostics-color=always -o
/app/output.s -imultiarch x86_64-linux-gnu -iprefix
/opt/compiler-explorer/gcc-12.2.0/bin/../lib/gcc/x86_64-linux-gnu/12.2.0/ -v
GNU D (Compiler-Explorer-Build-gcc--binutils-2.38) version 12.2.0
(x86_64-linux-gnu)
        compiled by GNU C version 9.4.0, GMP version 6.2.1, MPFR version 4.1.0,
MPC version 1.2.1, isl version isl-0.24-GMP

GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
GNU D (Compiler-Explorer-Build-gcc--binutils-2.38) version 12.2.0
(x86_64-linux-gnu)
        compiled by GNU C version 9.4.0, GMP version 6.2.1, MPFR version 4.1.0,
MPC version 1.2.1, isl version isl-0.24-GMP

GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
binary   
/opt/compiler-explorer/gcc-12.2.0/bin/../libexec/gcc/x86_64-linux-gnu/12.2.0/d21
version   v2.100.1

predefs   GNU D_Version2 LittleEndian GNU_DWARF2_Exceptions GNU_StackGrowsDown
GNU_InlineAsm D_LP64 assert D_PreConditions D_PostConditions D_Invariants
D_ModuleInfo D_Exceptions D_TypeInfo all X86_64 D_HardFloat Posix linux
CRuntime_Glibc CppRuntime_Gcc

As far as the command line, it would be:

gdc -o test test.d

The compiler output is:


<source>:7:11: error: none of the overloads of template
'core.stdc.stdarg.va_arg' are callable using argument types
'!()(__va_list_tag[1], TypeInfo, ubyte*)'
    7 |     va_arg(_argptr, ti, buf.ptr);
      |           ^
/opt/compiler-explorer/gcc-12.2.0/lib/gcc/x86_64-linux-gnu/12.2.0/include/d/core/stdc/stdarg.d:172:7:
note: Candidates are: 'va_arg(T)(ref va_list ap)'
  172 |     T va_arg(T)(ref va_list ap); // intrinsic
      |       ^
/opt/compiler-explorer/gcc-12.2.0/lib/gcc/x86_64-linux-gnu/12.2.0/include/d/core/stdc/stdarg.d:271:10:
note:                 'va_arg(T)(ref va_list ap, ref T parmn)'
  271 |     void va_arg(T)(ref va_list ap, ref T parmn); // intrinsic
      |          ^

The expected function should be implemented as identified in the D library
here: https://dlang.org/phobos/core_vararg.html#.va_arg

[Bug d/108763] va_arg usage in D doesn't compile

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108763

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
https://github.com/dlang/dmd/blob/master/druntime/src/core/vararg.d

version (GNU) { /* TypeInfo-based va_arg overload unsupported */ }

...

[Bug d/108763] va_arg usage in D doesn't compile

[schveiguy at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108763

--- Comment #2 from Steven Schveighoffer <schveiguy at gmail dot com> ---
(In reply to Andrew Pinski from comment #1)
> https://github.com/dlang/dmd/blob/master/druntime/src/core/vararg.d
> 
> version (GNU) { /* TypeInfo-based va_arg overload unsupported */ }
> 
> ...

oof. This is somewhat of a problem, because the undead package
(https://github.com/dlang/undead) uses it inside doformat, and this means that
anyone wanting to use those packages cannot do so with GDC.

The undead package is a collection of modules that are no longer in mainline D,
and so the point is to be able to use older modules with older code.

If this is deemed to be unsupportable, then people will just have to live with
not being able to use GDC for programs using that package. I also can look at
possibly disabling the offending code for GDC users, and then people can use
the other parts of undead (e.g. undead.xml)

Thanks for pointing that out!

[Bug d/108763] va_arg usage in D doesn't compile

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108763

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Reading the code on I think it would need some huge work to get it working on
GDC really. Especially on aarch64. Mainly because the way var_args is defined
is something which is very much target specific. and GCC implements var_args
internally to optimize some cases sometimes.

[Bug d/108763] va_arg usage in D doesn't compile

[schveiguy at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108763

--- Comment #4 from Steven Schveighoffer <schveiguy at gmail dot com> ---
I don't think it's worth a major effort. Nobody is using this kind of varargs
in D these days, it's mostly for legacy code (newer code will use template
varargs).

When I filed this bug, it was because I thought there was just a missing piece
in the library, I did not expect it to be a conscious decision to omit this
feature.

I'm OK with closing this if the effort is great. Don't spend time on it,
projects can avoid doformat pretty easily. I was hoping for a quick fix!

[Bug d/108763] va_arg usage in D doesn't compile

[ibuclaw at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108763

ibuclaw at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ibuclaw at gcc dot gnu.org

--- Comment #5 from ibuclaw at gcc dot gnu.org ---
I abandoned the idea of supporting RTTI-based variadics years ago. Even the
current reference implementation only supports a subset of the x86_64 ABI in
its current incarnation as far as I recall.

I had considered maybe libffi might allow us to do this, but I didn't see
anything that would allow me to say "retrieve the next variadic argument of
size SIZE and mode MODE". But I could not see anything that looked exactly as
that, even though as I understand there is limited support for constructing a
variadic call to a C function.

[Bug d/108763] va_arg usage in D doesn't compile

[ibuclaw at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108763

--- Comment #6 from ibuclaw at gcc dot gnu.org ---
I'll add it as a note to the deviations page.

https://gcc.gnu.org/onlinedocs/gdc/Missing-Features.html#Missing-Features

I'd actually forgotten about this.

[Bug d/108763] va_arg usage in D doesn't compile

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108763

--- Comment #7 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Iain Buclaw <ibuclaw@gcc.gnu.org>:

https://gcc.gnu.org/g:1f83aee5864129c4147a95c1a4e35d37c7eb7e59

commit r13-6463-g1f83aee5864129c4147a95c1a4e35d37c7eb7e59
Author: Iain Buclaw <ibuclaw@gdcproject.org>
Date:   Fri Mar 3 20:39:59 2023 +0100

    d: Document that TypeInfo-based va_arg is not implemented

            PR d/108763

    gcc/d/ChangeLog:

            * implement-d.texi (Missing Features): Document that TypeInfo-based
            va_arg is not implemented.

[Bug d/108763] va_arg usage in D doesn't compile

[ibuclaw at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108763

ibuclaw at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |WONTFIX
             Status|UNCONFIRMED                 |RESOLVED

--- Comment #8 from ibuclaw at gcc dot gnu.org ---
Added note on the missing features page.