Qing Zhao <qing.z...@oracle.com> writes:
>> On Sep 25, 2020, at 10:28 AM, Richard Sandiford <richard.sandif...@arm.com>
>> wrote:
>>
>> Qing Zhao <qing.z...@oracle.com <mailto:qing.z...@oracle.com>> writes:
>>>> On Sep 25, 2020, at 7:53 AM, Richard Sandiford <richard.sandif...@arm.com>
>>>> wrote:
>>>>
>>>> Qing Zhao <qing.z...@oracle.com> writes:
>>>>> Hi, Richard,
>>>>>
>>>>> As you suggested, I added a default implementation of the target hook
>>>>> “zero_cal_used_regs (HARD_REG_SET)” as following in my latest patch
>>>>>
>>>>>
>>>>> /* The default hook for TARGET_ZERO_CALL_USED_REGS. */
>>>>>
>>>>> void
>>>>> default_zero_call_used_regs (HARD_REG_SET need_zeroed_hardregs)
>>>>
>>>> FWIW, I was suggesting to return the set of registers that are actually
>>>> cleared too. Here you have the hook emit the asm statement, but IMO the
>>>> way we generate the asm for a given set of registers should be entirely
>>>> target-independent, and happen outside the hook.
>>>>
>>>> So the hook returning the set of cleared registers does two things:
>>>>
>>>> (1) It indicates which registers should be clobbered by the asm
>>>> (which would be generated after calling the hook, but emitted
>>>> before the sequence of instructions generated by the hook).
>>>
>>> For this purpose, this hook should return a Set of RTX that hold the
>>> cleared registers, a HARD_REG_SET is not enough.
>>>
>>> Since in the ASM_OPERANDS, we will need the RTX for the register (not the
>>> REGNO).
>>>
>>> Which data structure in GCC should be used here to hold this returned value
>>> as Set of RTX ?
>>
>> A HARD_REG_SET is enough. All the caller needs to know is: which registers
>> were clobbered? It can then represent a clobber of R with a clobber of
>> reg_regno_rtx[R].
>
> I did not find reg_regno_rtx in the current gcc source, not sure how to use
> it?
Sorry, I misremembered the name, it's regno_reg_rtx (which makes
more sense than what I wrote).
>>
>> The mode isn't important for single-register clobbers: clobbering a single
>> register in one mode is equivalent to clobbering it in another mode.
>> None of the register contents survive the clobber.
>
> Okay, I see.
>
> Then is the following good enough:
>
> /* Generate asm volatile("" : : : "memory") as a memory blockage, at the
> same time clobbering the register set specified by ZEROED_REGS. */
>
> void
> expand_asm_memory_blockage_clobber_regs (HARD_REG_SET zeroed_regs)
> {
> rtx asm_op, clob_mem, clob_reg;
>
> /* first get the number of registers that have been zeroed from ZEROED_REGS
> set. */
> unsigned int num_of_regs = ….;
>
> asm_op = gen_rtx_ASM_OPERANDS (VOIDmode, "", "", 0,
> rtvec_alloc (0), rtvec_alloc (0),
> rtvec_alloc (0), UNKNOWN_LOCATION);
> MEM_VOLATILE_P (asm_op) = 1;
>
> rtvec v = rtvec_alloc (num_of_regs + 2);
>
> clob_mem = gen_rtx_SCRATCH (VOIDmode);
> clob_mem = gen_rtx_MEM (BLKmode, clob_mem);
> clob_mem = gen_rtx_CLOBBER (VOIDmode, clob_mem);
>
> RTVEC_ELT (v,0) = asm_op;
> RTVEC_ELT (v,1) = clob_mem;
>
> for (unsigned int I = 0; i < FIRST_PSEUDO_REGISTER; i++)
> If (TEST_HARD_REG_BIT (zeroed_regs, i))
> {
> clob_reg = gen_rtx_CLOBBER (VOIDmode, reg_regno_rtx[i]);
> RTVEC_ELT (v,i+2) = clob_reg;
> }
>
> emit_insn (gen_rtx_PARALLEL (VOIDmode, v));
> }
Yeah, looks like it should work.
Thanks,
Richard
