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From: "pskocik at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/114011] New: Feature request: __goto__
Date: Tue, 20 Feb 2024 12:43:30 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D114011

            Bug ID: 114011
           Summary: Feature request: __goto__
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pskocik at gmail dot com
  Target Milestone: ---

Gcc has __volatile__.
I can only assume the rationale for it is so that inline asm macros can
do __asm __volatile__ and not have to worry about user-redefines of the
volatile keyword (which while not quite approved by the standard, is someti=
mes
practically useful).
While the __asm syntax also allows the goto keyword, there's currently no
__goto__ counterpart to __volatile__, which could similarly protect against
goto redefines.
Adding it is trivial and consistent with the already existing
volatile/__volatile__ pair. Would you consider it?

(
Why am I redefining goto? I'm basically doing it within the confines of a m=
acro
framework to force a static context check on gotos to prevent gotos out of
scopes where doing it would be an error.
Something like:

enum { DISALLOW_GOTO_HERE =3D 0 }; //normally, goto is allowed
#define goto while(_Generic((int(*)[!DISALLOW_GOTO_HERE])0, int(*)[1]:1)) g=
oto
//statically checked goto
int main(void){
    goto next; next:; //OK, not disallowed in this context

    #if 0 //would fail to compile
    enum {DISALLOW_GOTO_HERE=3D1}; //disallowed in this context
    goto next2; next2:;
    #endif
}

While this redefine does not syntactically disturb C, it does disturb `__asm
goto()`, which I, unfortunately, have one very frequently used instance of,=
 and
since there's no way to suppress an object macro redefine, I'd like to be a=
ble
to change it to `__asm __goto__` and have it peacefully coexist with the go=
to
redefine.
)=