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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/107727] error: multiversioning needs 'ifunc' which
 is not supported on this target (x86_64-w64-mingw32 target)
Date: Wed, 16 Nov 2022 21:50:15 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107727

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
              Build|x86_64-linux-gnu            |
     Ever confirmed|0                           |1
           Severity|normal                      |enhancement
             Target|x86_64-w64-mingw32          |ones which don't support
                   |                            |ifunc
   Last reconfirmed|                            |2022-11-16
               Host|x86_64-linux-gnu            |
          Component|target                      |middle-end

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
What they do is basically have the resolver always called:
        callq   __cpu_indicator_init
        movl    __cpu_model+12(%rip), %eax
        andl    $1024, %eax                     # imm =3D 0x400
        cmpl    $1024, %eax                     # imm =3D 0x400
        sete    %al
        andb    $1, %al
        testb   $1, %al
        jne     .LBB1_1
        jmp     .LBB1_2
.LBB1_1:
        addq    $40, %rsp
        jmp     _Z3foov.avx2                    # TAILCALL
.LBB1_2:
        nop
        addq    $40, %rsp
        jmp     _Z3foov                         # TAILCALL

Not the fastest way of implementing this either.
A faster way to caching the result of the resolver.

Anyways we currently don't support multiversioning for non-ifuncs supported
targets. Someone will need to program up that support but it might be years
unless you pay someone to do it.=