Re: [PATCH] LoongArch: Use finer-grained DBAR hints

[chenglulu <chenglulu@loongson.cn>]

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在 2023/11/14 上午7:18, Xi Ruoyao 写道:
/* snip */
>   (define_insn "mem_thread_fence_1"
>     [(set (match_operand:BLK 0 "" "")
>   	(unspec:BLK [(match_dup 0)] UNSPEC_MEMORY_BARRIER))
>      (match_operand:SI 1 "const_int_operand" "")] ;; model
>     ""
> -  "dbar\t0")
> +  {
> +    enum memmodel model = memmodel_base (INTVAL (operands[1]));
> +
> +    switch (model)
> +      {
> +      case MEMMODEL_ACQUIRE:
> +      case MEMMODEL_CONSUME:

Hi,

  * Before calling this template, the function get_memmodel is called to
    process memmodel, which has a piece of code:
  *

    /* Workaround for Bugzilla 59448. GCC doesn't track consume
    properly, so be conservative and promote consume to acquire. */ if
    (val == MEMMODEL_CONSUME) val = MEMMODEL_ACQUIRE;

  *


  * So I think MEMMODEL_CONSUME don't need to be processed here either.

Otherwise is OK.

  * Thanks.

> +	/* Consume is implemented using the stronger acquire memory order
> +	   because of a deficiency in C++11's semantics.  */
> +	return "dbar\t0b10100";
> +      case MEMMODEL_RELEASE:
> +	return "dbar\t0b10010";
> +      case MEMMODEL_ACQ_REL:
> +      case MEMMODEL_SEQ_CST:
> +	return "dbar\t0b10000";
> +      default:
> +	/* GCC internal: "For the '__ATOMIC_RELAXED' model no instructions
> +	   need to be issued and this expansion is not invoked."
> +	   Other values should not be returned by memmodel_base.  */
> +	gcc_unreachable ();
> +      }
> +  })
>   
>   ;; Atomic memory operations.
>