Re: [PATCH] [i386] Fix _mm256_zeroupper to notify LRA that vzeroupper will kill sse registers. [PR target/82735]

[Jakub Jelinek <jakub@redhat.com>]

On Thu, May 27, 2021 at 01:07:09PM +0800, Hongtao Liu via Gcc-patches wrote:
> +  /* Flag used for call_insn indicates it's a fake call.  */
> +  RTX_FLAG (insn, used) = 1;

> +      /* CALL_INSN use "used" flag to indicate it's a fake call.  */
> +      if (i == STACK_POINTER_REGNUM
> +	  && !RTX_FLAG (insn_info->insn, used))

> -	  && ! SIBLING_CALL_P (insn))
> +	  && ! SIBLING_CALL_P (insn)
> +	  && !RTX_FLAG (insn, used))

> -      /* For all other RTXes clear the used flag on the copy.  */
> -      RTX_FLAG (copy, used) = 0;
> +      /* For all other RTXes clear the used flag on the copy.
> +	 CALL_INSN use "used" flag to indicate it's a fake call.  */
> +      if (!INSN_P (orig))
> +	RTX_FLAG (copy, used) = 0;
>        break;
>      }
>    return copy;
> @@ -57,7 +57,8 @@ requires_stack_frame_p (rtx_insn *insn, HARD_REG_SET prologue_used,
>    HARD_REG_SET hardregs;
>    unsigned regno;
>  
> -  if (CALL_P (insn))
> +  /* CALL_INSN use "used" flag to indicate it's a fake call.  */
> +  if (CALL_P (insn) && !RTX_FLAG (insn, used))
>      return !SIBLING_CALL_P (insn);

Please define a macro for this in rtl.h (and mention it above used;
member too in a comment, see all the other comments in there), like:
/* 1 if RTX is a call_insn for a fake call.  */
#define FAKE_CALL_P(RTX)					\
  (RTL_FLAG_CHECK1 ("FAKE_CALL_P", (RTX), CALL_INSN)->used)
Though, I'm also not sure if used can be actually used for this,
because it is used e.g. in emit-rtl.c for verification of RTL sharing.
Though, it seems no other rtl flag is free for CALL_INSN.
Could this fake call flag sit on the CALL rtx instead?

	Jakub