Global Register Variables (64 bit)

[Akko]

I recently stumbled over gcc's global register variables. Tried them and my interpreter program ran on steroids.  :-)
Speed factor 2-3 !!

F.ex. simply changed a variable declaration (there are others) from
int64_t mftos; // top-of-stack
to
register int64_t mftos asm ("r12"); // register-cached top-of-stack

Available registers are within the setjmp buffer frame:
// extract from GCC-W64 setjmp.h:
typedef struct _JUMP_BUFFER {
    __MINGW_EXTENSION unsigned __int64 Frame;
    __MINGW_EXTENSION unsigned __int64 Rbx;
    __MINGW_EXTENSION unsigned __int64 Rsp;
    __MINGW_EXTENSION unsigned __int64 Rbp;
    __MINGW_EXTENSION unsigned __int64 Rsi;
    __MINGW_EXTENSION unsigned __int64 Rdi;
    __MINGW_EXTENSION unsigned __int64 R12;
    __MINGW_EXTENSION unsigned __int64 R13;
    __MINGW_EXTENSION unsigned __int64 R14;
    __MINGW_EXTENSION unsigned __int64 R15;
    __MINGW_EXTENSION unsigned __int64 Rip;
    __MINGW_EXTENSION unsigned __int64 Spare;
    SETJMP_FLOAT128 Xmm6;
    SETJMP_FLOAT128 Xmm7;
    SETJMP_FLOAT128 Xmm8;
    SETJMP_FLOAT128 Xmm9;
    SETJMP_FLOAT128 Xmm10;
    SETJMP_FLOAT128 Xmm11;
    SETJMP_FLOAT128 Xmm12;
    SETJMP_FLOAT128 Xmm13;
    SETJMP_FLOAT128 Xmm14;
    SETJMP_FLOAT128 Xmm15;
  } _JUMP_BUFFER;

It would be nice to have this feature also in Pelles C. Unfortunately its setjmp.h doesn't tell much.
I don't know if it would be hard to build a wrapper around the Windows library's jmp_buf structure,
and to reserve some CPU registers for it, like gcc seems to do.

Best regards

[Pelle]

1) I think this would be useful to very few programs/people.
2) It sounds like an extremely dangerous feature, likely leading to long and hard debugging sessions. For starters, imagine linking one object module with this feature and another module without it...