[PATCH GCC8][30/33]Fold more type conversion into binary arithmetic operations

[Bin.Cheng]

On Thu, May 11, 2017 at 11:54 AM, Richard Biener
<richard.guenther@gmail.com> wrote:
> On Tue, Apr 18, 2017 at 12:53 PM, Bin Cheng <Bin.Cheng@arm.com> wrote:
>> Hi,
>> Simplification of (T1)(X *+- CST) is already implemented in aff_combination_expand,
>> this patch moves it to tree_to_aff_combination.  It also supports unsigned types
>> if range information allows the transformation, as well as special case (T1)(X + X).
>> Is it OK?
>
> Can you first please simply move it?
>
> +           /* In case X's type has wrapping overflow behavior, we can still
> +              convert (T1)(X - CST) into (T1)X - (T1)CST if X - CST doesn't
> +              overflow by range information.  Also Convert (T1)(X + CST) as
> +              if it's (T1)(X - (-CST)).  */
> +           if (TYPE_UNSIGNED (itype)
> +               && TYPE_OVERFLOW_WRAPS (itype)
> +               && TREE_CODE (op0) == SSA_NAME
> +               && TREE_CODE (op1) == INTEGER_CST
> +               && (icode == PLUS_EXPR || icode == MINUS_EXPR)
> +               && get_range_info (op0, &minv, &maxv) == VR_RANGE)
> +             {
> +               if (icode == PLUS_EXPR)
> +                 op1 = fold_build1 (NEGATE_EXPR, itype, op1);
>
> Negating -INF will produce -INF(OVF) which we don't want to have in our IL,
> I suggest to use
>
>                   op1 = wide_int_to_tree (itype, wi::neg (op1));
>
> instead.
>
> +               if (wi::geu_p (minv, op1))
> +                 {
> +                   op0 = fold_convert (otype, op0);
> +                   op1 = fold_convert (otype, op1);
> +                   expr = fold_build2 (MINUS_EXPR, otype, op0, op1);
> +                   tree_to_aff_combination (expr, type, comb);
> +                   return;
> +                 }
> +             }
>
> I think this is similar to a part of what Robin Dapp (sp?) is
> proposing as fix for PR69526?
>
> The same trick should work for (int)((unsigned)X - CST) with different
> overflow checks
> (you need to make sure the resulting expr does not overflow).
Hi,
As suggested, I separated the patch into three.  Other review comments
are also addressed.
I read Robin's PR and patch, I think it's two different issues sharing
some aspects, for example, the overflow check using range information
are quite the same.  In effect, this should also captures the result
of Robin's patch because we don't want to fold (T1)(x +- CST) in
general, but here in tree-affine.

Bootstrap and test, is it OK?

Part1:
2017-04-11  Bin Cheng  <bin.cheng@arm.com>

    (aff_combination_expand): Move (T1)(X *+- CST) simplification to ...
    (tree_to_aff_combination): ... here.

Part2:
2017-04-11  Bin Cheng  <bin.cheng@arm.com>

    * tree-affine.c (tree_to_aff_combination): Handle (T1)(X + X).

Part3:
2017-04-11  Bin Cheng  <bin.cheng@arm.com>

    * tree-affine.c (ssa.h): Include header file.
    (tree_to_aff_combination): Handle (T1)(X - CST) when inner type
    has wrapping overflow behavior.

Thanks,
bin
>
> Richard.
>
>
>> Thanks,
>> bin
>> 2017-04-11  Bin Cheng  <bin.cheng@arm.com>
>>
>>         * tree-affine.c: Include header file.
>>         (aff_combination_expand): Move (T1)(X *+- CST) simplification to ...
>>         (tree_to_aff_combination): ... here.  Support (T1)(X + X) case, and
>>         unsigned type case if range information allows.
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