On Mon, Oct 26, 2020 at 8:10 PM Qing Zhao <qing.z...@oracle.com> wrote:
>
>
>
> > On Oct 26, 2020, at 1:42 PM, Uros Bizjak <ubiz...@gmail.com> wrote:
> >
> > On Mon, Oct 26, 2020 at 6:30 PM Qing Zhao <qing.z...@oracle.com> wrote:
> >>
> >>
> >> The following is the current change in i386.c, could you check whether the
> >> logic is good?
> >
> > x87 handling looks good to me.
> >
> > One remaining question: If the function uses MMX regs (either
> > internally or as an argument register), but exits in x87 mode, does
> > your logic clear the x87 stack?
>
> Yes but not completely yes.
>
> FIRST, As following:
>
> /* Then, decide which mode (MMX mode or x87 mode) the function exit with.
> In order to decide whether we need to clear the MMX registers or the
> stack registers. */
> bool exit_with_mmx_mode = false;
>
> exit_with_mmx_mode = ((GET_CODE (crtl->return_rtx) == REG)
> && (MMX_REG_P (crtl->return_rtx)));
>
> /* then, let's see whether we can zero all st registers togeter. */
> if (!exit_with_mmx_mode)
> st_zeroed = zero_all_st_registers (need_zeroed_hardregs);
>
>
> We first check whether this routine exit with mmx mode, if Not then it’s X87
> mode
> (at exit, “EMMS” should already been called per ABI), then
> The st/mm registers will be cleared as x87 stack registers.
>
> However, within the routine “zero_all_st_registers”:
>
> static bool
> zero_all_st_registers (HARD_REG_SET need_zeroed_hardregs)
> {
> unsigned int num_of_st = 0;
> for (unsigned int regno = 0; regno < FIRST_PSEUDO_REGISTER; regno++)
> if (STACK_REGNO_P (regno)
> && TEST_HARD_REG_BIT (need_zeroed_hardregs, regno))
> {
> num_of_st++;
> break;
> }
>
> if (num_of_st == 0)
> return false;
>
>
> In the above, I currently only check whether any “Stack” registers need to be
> zeroed or not.
> But looks like we should also check any “MMX” register need to be zeroed or
> not too. If there is any
> “MMX” register need to be zeroed, we still need to clear the whole X87 stack?
I think so, but I have to check the details
> BTW, is it convenient for you to provide me 3 small testing cases for the
> following situation:
>
> 1. Return with MMX register;
> 2. Return with x87 stack register;
> 3. Return with 2 x87 stack register (i.e the complex value).
>
> Then it will be much easy for me to verify my implementation is good or not
> at my side.
--cut here--
typedef int __v2si __attribute__ ((vector_size (8)));
__v2si ret_mmx (void)
{
return (__v2si) { 123, 345 };
}
long double ret_x87 (void)
{
return 1.1L;
}
_Complex long double ret_x87_cplx (void)
{
return 1.1L + 1.2iL;
}
--cut here--
Please compile this with "-m32 -mmmx".
ret_mmx returns value in MMX register.
ret_x87 returns value in x87 register.
ret_x87_cplx returns value in memory.
"-m64"
ret_mmx returns value in XMM register.
ret_x87 returns value in x87 register.
ret_x87_cplx returns value in two x87 registers.
Uros.
