https://issues.dlang.org/show_bug.cgi?id=20838

--- Comment #1 from mw <mingwu@gmail.com> ---
BTW, I only tested on x86_64 Linux, I think this bug on other platform too MacOS, Windows (on modern x86_64 CPUs with CX16 support).

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https://issues.dlang.org/show_bug.cgi?id=20838

Mathias LANG <pro.mathias.lang@gmail.com> changed:

           What    |Removed                     |Added
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                 CC|                            |pro.mathias.lang@gmail.com

--- Comment #2 from Mathias LANG <pro.mathias.lang@gmail.com> ---
Doesn't affect OSX (used objdump, grepped for cmpxchg).

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https://issues.dlang.org/show_bug.cgi?id=20838

--- Comment #3 from mw <mingwu@gmail.com> ---
Yes, verified, not on MacOS.

Thank you (at least there is a system I can use now).


$ objdump -disassemble-all c.o > c.o.asm
$ grep -i cmpxchg  c.o.asm
     80a:       49 0f c7 08     cmpxchg16b      (%r8)

$ uname -a
Darwin 19.4.0 Darwin Kernel Version 19.4.0: Wed Mar  4 22:28:40 PST 2020;
root:xnu-6153.101.6~15/RELEASE_X86_64 x86_64

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https://issues.dlang.org/show_bug.cgi?id=20838

Seb <greeenify@gmail.com> changed:

           What    |Removed                     |Added
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                 CC|                            |greeenify@gmail.com

--- Comment #4 from Seb <greeenify@gmail.com> ---
> at least there is a system I can use now).

Well, you could just use LDC like almost everyone else ;-)

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https://issues.dlang.org/show_bug.cgi?id=20838

--- Comment #5 from mw <mingwu@gmail.com> ---
LDC ? did I miss sth?

--------------------------------------------------------------------------------
$ ldc2 -m64 -c c.d
$ obj2asm c.o > c.o.asm
$ grep -i xchg  c.o.asm
                cmpxchg8b       [RSI]
                cmpxchg8b       [RSI]
                cmpxchg8b       [RSI]
                cmpxchg8b       [RSI]
                cmpxchg8b       [RSI]
.data._D100TypeInfo_S3ldc10intrinsics__T13CmpXchgResultTS4core8internal6atomic__T11_AtomicTypeTS1c1NZ5UCentZQCq6__initZ
segment
_D100TypeInfo_S3ldc10intrinsics__T13CmpXchgResultTS4core8internal6atomic__T11_AtomicTypeTS1c1NZ5UCentZQCq6__initZ:
.data._D100TypeInfo_S3ldc10intrinsics__T13CmpXchgResultTS4core8internal6atomic__T11_AtomicTypeTS1c1NZ5UCentZQCq6__initZ
ends


$ ldc2 --version
LDC - the LLVM D compiler (1.21.0):
  based on DMD v2.091.1 and LLVM 10.0.0
  built with LDC - the LLVM D compiler (1.21.0)
  Default target: x86_64-unknown-linux-gnu
  Host CPU: skylake
  http://dlang.org - http://wiki.dlang.org/LDC
--------------------------------------------------------------------------------

Want to file a bug against LDC ?

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https://issues.dlang.org/show_bug.cgi?id=20838

kinke <kinke@gmx.net> changed:

           What    |Removed                     |Added
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                 CC|                            |kinke@gmx.net

--- Comment #6 from kinke <kinke@gmx.net> ---
(In reply to mw from comment #5)
> Want to file a bug against LDC ?

No need, cmpxchg16 is used for all x86_64 CPUs: https://d.godbolt.org/z/HesA24

For the few old CPUs not supporting it, it can be disabled via `-mattr=-cx16` (but then it doesn't fall back to cmpxchg8 anway, so no idea how your results came about).

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https://issues.dlang.org/show_bug.cgi?id=20838

--- Comment #7 from mw <mingwu@gmail.com> ---
Hi kinke,

> so no idea how your results came about

I downloaded directly from:

https://github.com/ldc-developers/ldc/releases/download/v1.21.0/ldc2-1.21.0-linux-x86_64.tar.xz


And I just downloaded 1.20, which is on the d.godbolt.org page you mentioned, but the result is the same:

--------------------------------------------------------------------------------
$ wget https://github.com/ldc-developers/ldc/releases/download/v1.20.0/ldc2-1.20.0-linux-x86_64.tar.xz

$ ldc2 -m64 -c c.d
$ obj2asm c.o > c.o.asm
$ grep -i xchg  c.o.asm
                cmpxchg8b       [RSI]
                cmpxchg8b       [RSI]
                cmpxchg8b       [RSI]
                cmpxchg8b       [RSI]
                cmpxchg8b       [RSI]
.data._D100TypeInfo_S3ldc10intrinsics__T13CmpXchgResultTS4core8internal6atomic__T11_AtomicTypeTS1c1NZ5UCentZQCq6__initZ
segment
_D100TypeInfo_S3ldc10intrinsics__T13CmpXchgResultTS4core8internal6atomic__T11_AtomicTypeTS1c1NZ5UCentZQCq6__initZ:
.data._D100TypeInfo_S3ldc10intrinsics__T13CmpXchgResultTS4core8internal6atomic__T11_AtomicTypeTS1c1NZ5UCentZQCq6__initZ
ends

$ ldc2 --version
LDC - the LLVM D compiler (1.20.0):
  based on DMD v2.090.1 and LLVM 9.0.1
  built with LDC - the LLVM D compiler (1.20.0)
  Default target: x86_64-unknown-linux-gnu
  Host CPU: skylake
  http://dlang.org - http://wiki.dlang.org/LDC

$ uname -a
Linux titan 4.15.0-99-generic #100-Ubuntu SMP Wed Apr 22 20:32:56 UTC 2020
x86_64 x86_64 x86_64 GNU/Linux
--------------------------------------------------------------------------------


What else should I check?

Or, can try my step on a Linux box?

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https://issues.dlang.org/show_bug.cgi?id=20838

--- Comment #8 from mw <mingwu@gmail.com> ---
And for GDC:

--------------------------------------------------------------------------------
$ gdc-10 -m64 -c c.d
$ obj2asm c.o > c.o.asm
$ grep -i xch  c.o.asm
        extrn   __atomic_compare_exchange
                call      __atomic_compare_exchange@PLT32

--------------------------------------------------------------------------------

On this page:  https://d.godbolt.org/z/HesA24

I changed the compiler to "gdc 9.2.0", and searched the window, and search for 'xch':

        mov     rsi, rax
        mov     edi, 16
        call    __atomic_compare_exchange
        mov     BYTE PTR [rbp-1], al
        .loc 3 1413 9
        movzx   eax, BYTE PTR [rbp-1]


I'm not an asm guy, can someone help to read where is this __atomic_compare_exchange? and confirm it's calling the correct CMPXCHG16B?


Thanks.

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https://issues.dlang.org/show_bug.cgi?id=20838

--- Comment #9 from mw <mingwu@gmail.com> ---
Oh,

$ gdc-10 --version
gdc-10 (Debian 10.1.0-1) 10.1.0
Copyright (C) 2020 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

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https://issues.dlang.org/show_bug.cgi?id=20838

--- Comment #10 from kinke <kinke@gmx.net> ---
(In reply to mw from comment #7)
> What else should I check?

Wrt. LDC, I'm almost certain this is solely an issue with your 'workflow' involving obj2asm. - Godbolt runs on Linux (but you can inspect the produced assembly for any target using LDC's -mtriple option).

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