Problems with g++ and __attribute__((regparm(3)))

[Rimantas Plaipa]

Documentation of gcc doesn't specify where function attributes have to
placed in declarations. All examples in the official docs have them after
the name of function, but the placement before the name works too. Such a
form is essential for compatibility with other compilers for Windows,
because it allows to use headers for them by defining 

-D__stdcall=__attribute__((__stdcall__))

and so on.

But when the other popular attribute - __fastcall - is used in such a way a
disaster happens.

===== test.cpp ======

void* a(void* p, int i);

void*  __attribute__((regparm(3))) b(void* p, int i);

void* b(void* p, int i){
	return a(p,i);
}
======================
Compilation with g++ 2.95.2

g++ -O -fomit-frame-pointer -S test.cpp

gives:

_b__FPvi:
        subl $12,%esp
        call _a__FPvi
        addl $12,%esp
        ret

Function a(void*,int) (no attributes) is called as __fastcall !

If the attribute is placed after the name :

void*  b(void* p, int i) __attribute__((regparm(3)));

or before the type of function:

__attribute__((regparm(3))) void*  b(void* p, int i);

everything is OK:

_b__FPvi:
        subl $12,%esp
        addl $-8,%esp
        pushl %edx
        pushl %eax
        call _a__FPvi
        addl $16,%esp
        addl $12,%esp
        ret

g++ snapshot 20001104 have this bug too.


Rimantas Plaipa,

Department of Biochemistry and Biophysics,
Vilnius University,
Ciurlionio 21/27, Vilnius 2009, Lithuania.

E-mail: rp010gf@voruta.vu.lt
Phone: (370-2)-650381 
Fax: (370-2)-236660