[Ping] [PATCH, 10/10] aarch64: Handle ccmp in ifcvt to make it work with cmov

[Richard Henderson]

On 09/22/2014 11:46 PM, Zhenqiang Chen wrote:
> @@ -2375,10 +2387,21 @@ noce_get_condition (rtx_insn *jump, rtx_insn **earliest, bool then_else_reversed
>        return cond;
>      }
>  
> +  /* For conditional compare, set ALLOW_CC_MODE to TRUE.  */
> +  if (targetm.gen_ccmp_first)
> +    {
> +      rtx prev = prev_nonnote_nondebug_insn (jump);
> +      if (prev
> +	  && NONJUMP_INSN_P (prev)
> +	  && BLOCK_FOR_INSN (prev) == BLOCK_FOR_INSN (jump)
> +	  && ccmp_insn_p (prev))
> +	allow_cc_mode = true;
> +    }
> +
>    /* Otherwise, fall back on canonicalize_condition to do the dirty
>       work of manipulating MODE_CC values and COMPARE rtx codes.  */
>    tmp = canonicalize_condition (jump, cond, reverse, earliest,
> -				NULL_RTX, false, true);
> +				NULL_RTX, allow_cc_mode, true);

This needs a lot more explanation.  Why it it ok to allow a cc_mode when the
source is a ccmp, and not for any other comparison?

The issue is going to be how we use the comparison once we've finished with the
transformation.  Is it going to be able to be properly handled by
emit_conditional_move?

If the target doesn't have cbranchcc4, I think that prep_cmp_insn will fail.
But as you show from

> +++ b/gcc/config/aarch64/aarch64.md
> @@ -2589,15 +2589,19 @@
>  			   (match_operand:ALLI 3 "register_operand" "")))]
>    ""
>    {
> -    rtx ccreg;
>      enum rtx_code code = GET_CODE (operands[1]);
>  
>      if (code == UNEQ || code == LTGT)
>        FAIL;
>  
> -    ccreg = aarch64_gen_compare_reg (code, XEXP (operands[1], 0),
> -				  XEXP (operands[1], 1));
> -    operands[1] = gen_rtx_fmt_ee (code, VOIDmode, ccreg, const0_rtx);
> +    if (!ccmp_cc_register (XEXP (operands[1], 0),
> +			   GET_MODE (XEXP (operands[1], 0))))
> +      {
> +	rtx ccreg;
> +	ccreg = aarch64_gen_compare_reg (code, XEXP (operands[1], 0),
> +					 XEXP (operands[1], 1));
> +	operands[1] = gen_rtx_fmt_ee (code, VOIDmode, ccreg, const0_rtx);
> +      }

this change, even more than that may be required.


r~