> On Oct 26, 2020, at 3:33 PM, Uros Bizjak <ubiz...@gmail.com> wrote:
>
> On Mon, Oct 26, 2020 at 9:05 PM Uros Bizjak <ubiz...@gmail.com> wrote:
>>
>> 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.
>
> Please compile the following testcase with "-m32 -mmmx":
>
> --cut here--
> #include <stdio.h>
>
> typedef int __v2si __attribute__ ((vector_size (8)));
>
> __v2si zzz;
>
> void
> __attribute__ ((noinline))
> mmx (__v2si a, __v2si b, __v2si c)
> {
> __v2si res;
>
> res = __builtin_ia32_paddd (a, b);
> zzz = __builtin_ia32_paddd (res, c);
>
> __builtin_ia32_emms ();
> }
>
>
> int main ()
> {
> __v2si a = { 123, 345 };
> __v2si b = { 234, 456 };
> __v2si c = { 345, 567 };
>
> mmx (a, b, c);
>
> printf ("%i, %i\n", zzz[0], zzz[1]);
>
> return 0;
> }
> --cut here--
>
> at the end of mmx() function:
>
> 0x080491ed in mmx ()
> (gdb) disass
> Dump of assembler code for function mmx:
> 0x080491e0 <+0>: paddd %mm1,%mm0
> 0x080491e3 <+3>: paddd %mm2,%mm0
> 0x080491e6 <+6>: movq %mm0,0x804c020
> => 0x080491ed <+13>: emms
> 0x080491ef <+15>: ret
> End of assembler dump.
> (gdb) i r flo
> st0 <invalid float value> (raw 0xffff00000558000002be)
> st1 <invalid float value> (raw 0xffff000001c8000000ea)
> st2 <invalid float value> (raw 0xffff0000023700000159)
> st3 0 (raw 0x00000000000000000000)
> st4 0 (raw 0x00000000000000000000)
> st5 0 (raw 0x00000000000000000000)
> st6 0 (raw 0x00000000000000000000)
> st7 0 (raw 0x00000000000000000000)
> fctrl 0x37f 895
> fstat 0x0 0
> ftag 0x556a 21866
> fiseg 0x0 0
> fioff 0x0 0
> foseg 0x0 0
> fooff 0x0 0
> fop 0x0 0
>
> There are still values in the MMX registers. However, we are in x87
> mode, so the whole stack has to be cleared.
Yes. And I just tried, my current implementation behaved correctly.
>
> Now, what to do if the function uses x87 registers and exits in MMX
> mode? I guess we have to clear all MMX registers (modulo return value
> reg).
Need to add this part.
thanks.
Qing
>
> Uros.
