Uros Bizjak <ubiz...@gmail.com> writes:
> On Tue, Sep 5, 2017 at 12:35 PM, Alexander Monakov <amona...@ispras.ru> wrote:
>> On Tue, 5 Sep 2017, Uros Bizjak wrote:
>>> This patch allows to emit memory_blockage pattern instead of default
>>> asm volatile as a memory blockage. This patch is needed, so targets
>>> (e.g. x86) can define and emit more optimal memory blockage pseudo
>>> insn.
>>
>> Optimal in what sense? What pattern do you intend to use on x86, and
>> would any target be able to use the same?
>
> You don't have to emit a generic asm-like pattern. This is the same
> situation as with blockage insn, where targets can emit "blockage"
> instead of generic asm insn.
>
> x86 defines memory_blockage as:
>
> (define_expand "memory_blockage"
> [(set (match_dup 0)
> (unspec:BLK [(match_dup 0)] UNSPEC_MEMORY_BLOCKAGE))]
> ""
> {
> operands[0] = gen_rtx_MEM (BLKmode, gen_rtx_SCRATCH (Pmode));
> MEM_VOLATILE_P (operands[0]) = 1;
> })
>
> However, this definition can't be generic, since unspec is used.
If all ports have switched over to define_c_enum for unspecs
(haven't checked), we could probably define something like this
in common.md.
Thanks,
Richard
