[Bug d/105413] New: gdc extended assembler cannot constraints r8 - r15

[Bug d/105413] New: gdc extended assembler cannot constraints r8 - r15

[witold.baryluk+gcc at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105413

            Bug ID: 105413
           Summary: gdc extended assembler cannot constraints r8 - r15
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: d
          Assignee: ibuclaw at gdcproject dot org
          Reporter: witold.baryluk+gcc at gmail dot com
  Target Milestone: ---

gcc in C does not support directly register constraints for x86_64 registers r8
- r15.

In C this can be done however using local register variables and asm
attributes.

https://gcc.gnu.org/onlinedocs/gcc/Local-Register-Variables.html

There is no way to use this in GDC extended assembler.

version (linux) {
version (GNU) {

enum SYSCALL {
  OPENAT = 56,
}

@nogc:
nothrow:

size_t syscall(SYSCALL ident)(size_t arg1, size_t arg2, size_t arg3, size_t
arg4) {
    version (X86_64) {
       asm @nogc nothrow {
         "syscall"
         // output:
         : "=a" (arg1)
         // inputs:
         : "a" (ident),  // rax - syscall number
           "D" (arg1),   // rdi - arg1
           "S" (arg2),   // rsi - arg2
           "d" (arg3),   // rdx - arg3
           "r10" (arg4),  // r10 - arg4
           "m"( *cast(ubyte*)arg1)   // "dummy" input instead of full memory
clobber
         // clobers
         : "c", "r11";  // Clobers rax, and rcx and r11.
       }
       return arg1;
   } else {
       static assert(false, "This platform/architecture is not supported when
using GDC compiler");
   } 
}

}

private int openatdummy() @nogc nothrow {
  return cast(int)syscall!(SYSCALL.OPENAT)(0, 0, 0, 0);
}

}



myio.d: In function ‘syscall’:
myio.d:232:10: error: matching constraint references invalid operand number
  232 |          ;



https://godbolt.org/z/xGzxa6orc

[Bug d/105413] gdc extended assembler cannot constraints r8 - r15

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105413

--- Comment #1 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:91418c42089cd1cbe71edcd6b2f5b26559819372

commit r13-1255-g91418c42089cd1cbe71edcd6b2f5b26559819372
Author: Iain Buclaw <ibuclaw@gdcproject.org>
Date:   Thu Jun 23 18:24:07 2022 +0200

    d: Add `@register' attribute to compiler and library.

    The `@register` attribute specifies that a local or `__gshared` variable
    is to be given a register storage-class in the C sense of the term, and
    will be placed into a register named `registerName`.

    The variable needs to boiled down to a data type that fits the target
    register.  It also cannot have either thread-local or `extern` storage.
    It is an error to take the address of a register variable.

            PR d/105413

    gcc/d/ChangeLog:

            * d-attribs.cc (d_handle_register_attribute): New function.
            (d_langhook_attribute_table): Add register attribute.
            * d-codegen.cc (d_mark_addressable): Error if taken address of
            register variable.
            (build_frame_type): Error if register variable has non-local
            references.
            * d-tree.h (d_mark_addressable): Add complain parameter.
            * decl.cc (get_symbol_decl): Mark register varibles DECL_REGISTER.
            Error when register variable declared thread-local or extern.
            * expr.cc (ExprVisitor::visit (IndexExp *)): Don't complain about
            marking register vectors as addressable in an ARRAY_REF.

    libphobos/ChangeLog:

            * libdruntime/gcc/attributes.d (register): Define.

    gcc/testsuite/ChangeLog:

            * gdc.dg/attr_register1.d: New test.
            * gdc.dg/attr_register2.d: New test.
            * gdc.dg/attr_register3.d: New test.

[Bug d/105413] gdc extended assembler cannot constraints r8 - r15

[ibuclaw at gdcproject dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105413

Iain Buclaw <ibuclaw at gdcproject dot org> changed:

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

--- Comment #2 from Iain Buclaw <ibuclaw at gdcproject dot org> ---
@register attribute has been added, meaning that you can now have the following
as an alternative to your example.

---
import gcc.attributes : register;

@register("rax") SYSCALL rax = ident; // rax - syscall number
@register("rdi") size_t rdi = arg1;   // rdi - arg1
@register("rsi") size_t rsi = arg2;   // rsi - arg2
@register("rdx") size_t rdx = arg3;   // rdx - arg3
@register("r10") size_t r10 = arg4;   // r10 - arg4
asm @nogc nothrow {
  "syscall"
  : "=r" (rax)
  // inputs:
  : "r" (rax),
    "r" (rdi),
    "r" (rsi),
    "r" (rdx),
    "r" (r10),
    "m"( *cast(ubyte*)arg1)   // "dummy" input instead of full memory clobber
  // clobers
  : "rcx", "r11";  // Clobers rax, and rcx and r11.
}
return rax;
---

https://godbolt.org/z/PvnTsea9T

[Bug d/105413] gdc extended assembler cannot constraints r8 - r15

[witold.baryluk+gcc at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105413

--- Comment #3 from Witold Baryluk <witold.baryluk+gcc at gmail dot com> ---
It works. Thank you.

Any chance this will be in gcc 12.x? I work a lot on Debian Linux, and I doubt
I will have gcc trunk or gcc 13 available any time soon.


Also weirdly gcc does not inline this function, unless I add
@attribute("always_inline") on syscall, or @attribute("flatten") on
openatdummy.