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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c++/102548] [9/10/11/12 Regression] ICE with cdecl attribute on
 a builtin function
Date: Thu, 30 Sep 2021 22:45:18 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102548

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |ice-on-valid-code
            Summary|gcc segmentation fault in   |[9/10/11/12 Regression] ICE
                   |cc1plus (with repro case)   |with cdecl attribute on a
                   |                            |builtin function
   Target Milestone|---                         |9.5

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
sometime between GCC 6 and GCC 7, the ICE was introduced before this was
rejected:
<source>: In function 'void f()':
<source>:12:35: error: invalid conversion from 'size_t
(__attribute__((__cdecl__)) *)(char*, size_t, const char*, const tm*) {aka
unsigned int (__attribute__((__cdecl__)) *)(char*, unsigned int, const char=
*,
const tm*)}' to 'T {aka unsigned int (__attribute__((__stdcall__)) *)(char*,
unsigned int, const char*, const tm*)}' [-fpermissive]
   static T strftime =3D loadStrftime();
                       ~~~~~~~~~~~~^~


Note using auto instead of the type T, the ICE shows up still:

typedef decltype(sizeof(0)) size_t;
struct tm;
extern "C"
size_t __attribute__((__cdecl__)) strftime(char *  _Buf,size_t
_SizeInBytes,const char *  _Format,const struct tm *  _Tm);
void f(void)
{
  auto g =3D strftime;
}

And was accepted in GCC 6.
So this is a regression from GCC6.

Looks like it has to do with builtin functions too.=