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Re: [PATCH, combine] Fix host-specific behavior in simplify_compare_const()


> In other words, any 32-bit target with 'need_64bit_hwint=yes' in config.gcc
> is not able to have benefit from this optimization because it never
> passes the condition test.
> 
> 
> My solution is to use GET_MODE_MASK(mode) to filter out all bits not
> in target mode. The following is my patch:

The patch is OK for 4.9 once stage #1 is open if it passes bootstrap/regtest.

> gcc/ChangLog:
> 
>         * gcc/combine.c: Use GET_MODE_MASK() to filter out
>         unnecessary bits in simplify_compare_const().

This should be

	* combine.c (simplify_compare_const): Use GET_MODE_MASK to filter out
	unnecessary bits in the constant power of two case.

> 
> diff --git a/gcc/combine.c b/gcc/combine.c
> index 67bd776..8c8cb92 100644
> --- a/gcc/combine.c
> +++ b/gcc/combine.c
> @@ -10917,8 +10917,8 @@ simplify_compare_const (enum rtx_code code,
> rtx op0, rtx *pop1)
>        && (code == EQ || code == NE || code == GE || code == GEU
> 
>           || code == LT || code == LTU)
> 
>        && mode_width <= HOST_BITS_PER_WIDE_INT
> -      && exact_log2 (const_op) >= 0
> -      && nonzero_bits (op0, mode) == (unsigned HOST_WIDE_INT) const_op)
> +      && exact_log2 (const_op & GET_MODE_MASK (mode)) >= 0
> +      && nonzero_bits (op0, mode) == (unsigned HOST_WIDE_INT)
> (const_op & GET_MODE_MASK (mode)))
>      {
>        code = (code == EQ || code == GE || code == GEU ? NE : EQ);
>        const_op = 0;

The line is too long, write

     && nonzero_bits (op0, mode)
        == (unsigned HOST_WIDE_INT) (const_op & GET_MODE_MASK (mode)))

instead.

-- 
Eric Botcazou


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