Re: [PATCH] Do not simplify "(and (reg) (const bit))" to if_then_else.

[Bernd Schmidt <bschmidt@redhat.com>]

On 11/21/2016 01:36 PM, Dominik Vogt wrote:
> diff --git a/gcc/combine.c b/gcc/combine.c
> index b22a274..457fe8a 100644
> --- a/gcc/combine.c
> +++ b/gcc/combine.c
> @@ -5575,10 +5575,23 @@ combine_simplify_rtx (rtx x, machine_mode op0_mode, int in_dest,
>  	{
>  	  rtx cop1 = const0_rtx;
>  	  enum rtx_code cond_code = simplify_comparison (NE, &cond, &cop1);
> +	  unsigned HOST_WIDE_INT nz;
>
>  	  if (cond_code == NE && COMPARISON_P (cond))
>  	    return x;
>
> +	  /* If the operation is an AND wrapped in a SIGN_EXTEND or ZERO_EXTEND
> +	     with either operand being just a constant single bit value, do
> +	     nothing since IF_THEN_ELSE is likely to increase the expression's
> +	     complexity.  */
> +	  if (HWI_COMPUTABLE_MODE_P (mode)
> +	      && pow2p_hwi (nz = nonzero_bits (x, mode))
> +	      && ! ((code == SIGN_EXTEND || code == ZERO_EXTEND)
> +		    && GET_CODE (XEXP (x, 0)) == AND
> +		    && CONST_INT_P (XEXP (XEXP (x, 0), 0))
> +		    && UINTVAL (XEXP (XEXP (x, 0), 0)) == nz))
> +	    return x;

It looks like this doesn't actually use cond or true/false_rtx. So this 
could be placed just above the call to if_then_else_cond to avoid 
unnecessary work. Ok if that works.


Bernd