Hi.
Still trying to make a "fastcall" calling convention work on m68k. I
want functions marked as __attribute__((fastcall)) to pass arguments
in d0-2/a0-a1, this works for me.
I also want d2 to be properly marked as clobbered by "fastcall" calls.
This does not work for me. Or rather it works for the first call to a
function, but not for any further calls.
I have used the i386 port as the basis for my hack, thus only updating
call_used_regs from TARGET_CONDITIONAL_REGISTER_USAGE. I also
re-implemted TARGET_SET_CURRENT_FUNCTION and TARGET_EXPAND_TO_RTL_HOOK
to call reinit_regs() and reinit_target() as per i386.
Still it looks to me like upon completing the expansion of a function
call the call_used_regs of the current function is restored, and not
set again if calling the same function again.
Consider this C-code to compile:
#define FASTCALL __attribute__((fastcall))
#define MUL_ASSERT(a, b, c) my_assert(mul(a, b), a * b, c)
FASTCALL
int mul(int a, int b) {
return a * b;
}
FASTCALL
void my_assert(int v, int e, int f) {
if (v != e) {
__asm__ __volatile__
(
"illegal\n\t"
: /* outputs */
: /* inputs */
: /* clobbered regs */
);
}
}
int answer() {
return 42;
}
int main(int argc, char* argv[])
{
int a = answer(); // Default ABI d0-d1,a0-a1 used.
MUL_ASSERT(0,0, a); // "fastcall" ABI d0-d2,a0-a1 used
MUL_ASSERT(1,0, a); // ditto
return 0;
}
====
This is the generated assembly for the main function:
_main:
movem.l #12336,-(%sp)
jsr ___main
jar _answer
move.l %d0,%d3 | result from anser() stored in d3, d2 is
correctly assumed clobbered later here.
lea _mul,%a3
moveq #0,%d1
moveq #0,%d0
jsr (%a3) | Calling mul(int,int) here, d0-2/a0-1 clobbered, thi
is where d2 becomes clobbered.
lea _my_assert,%a2
move.l %d3,%d2 | For first call to my_assert() d3 correctly moved
down to d2 for arg passing.
moveq #0,%d1
jsr (%a2) | Calling my_assert(), will clobber d0-d2/a0-a1
moveq #0,%d1
moveq #1,%d0
jsr (%a3) | Calling mul() again, will clobber.
moveq #0,%d1
jsr (%a2) | This call to my_assert() d2 is incorrectly assumed to
be still valid from previous call. HOW can I fix this?
moveq #0,%d0
movem.l (%sp)+,#3084
rts
// Fredrik Olsson
