Re: [RFC PATCH] Handle sequence in reg_set_p

[Jeff Law <law at redhat dot com>]

On 01/08/15 05:23, Oleg Endo wrote:
> Hi,
>
> Currently reg_set_p doesn't handle sequence rtx, which I've identified
> as the root cause of PR 64479.  There is another alternative fix for the
> PR, but I'd like to get some comments regarding letting reg_set_p also
> handle sequence rtx:
>
> Index: gcc/rtlanal.c
> ===================================================================
> --- gcc/rtlanal.c	(revision 218544)
> +++ gcc/rtlanal.c	(working copy)
> @@ -875,17 +875,24 @@
>   {
>     /* We can be passed an insn or part of one.  If we are passed an insn,
>        check if a side-effect of the insn clobbers REG.  */
> -  if (INSN_P (insn)
> -      && (FIND_REG_INC_NOTE (insn, reg)
> -	  || (CALL_P (insn)
> -	      && ((REG_P (reg)
> -		   && REGNO (reg) < FIRST_PSEUDO_REGISTER
> -		   && overlaps_hard_reg_set_p (regs_invalidated_by_call,
> -					       GET_MODE (reg), REGNO (reg)))
> -		  || MEM_P (reg)
> -		  || find_reg_fusage (insn, CLOBBER, reg)))))
> -    return 1;
> +  if (INSN_P (insn) && FIND_REG_INC_NOTE (insn, reg))
> +    return true;
>
> +  /* After delay slot handling, call and branch insns might be in a
> +     sequence.  Check all the elements there.  */
> +  if (INSN_P (insn) && GET_CODE (PATTERN (insn)) == SEQUENCE)
> +    for (int i = 0; i < XVECLEN (PATTERN (insn), 0); ++i)
> +      if (reg_set_p (reg, XVECEXP (PATTERN (insn), 0, i)))
> +	return true;
> +
> +  if (CALL_P (insn)
> +      && ((REG_P (reg) && REGNO (reg) < FIRST_PSEUDO_REGISTER
> +	   && overlaps_hard_reg_set_p (regs_invalidated_by_call,
> +				       GET_MODE (reg), REGNO (reg)))
> +	  || MEM_P (reg)
> +	  || find_reg_fusage (insn, CLOBBER, reg)))
> +	return true;
> +
>     return set_of (reg, insn) != NULL_RTX;
>   }
>
>
> Would that be OK to do if it passes testing, or is there something that
> could potentially/obviously blow up?
It looks reasonable to me.

Any particular reason why the SEQUENCE handling isn't done first, then 
the REG_INC and CALL insn handling?  I'd probably explicitly return 
false if we had a sequence and none of its elements returned true. 
There's no need to check anything on the toplevel SEQUENCE to the best 
of my knowledge.

jeff