[PATCH 2/4] match.pd: Add x & ~(x & y) -> x & ~y pattern

[Rasmus Villemoes]

On Thu, Jan 22 2015, Richard Biener <richard.guenther@gmail.com> wrote:

> On Wed, Jan 21, 2015 at 9:00 PM, Marc Glisse <marc.glisse@inria.fr> wrote:
>> Hello,
>>
>> (sorry for the broken thread, for some reason I haven't received any email
>> from gcc since about 10am, I'll investigate later)
>>
>> +/* x & ~(x & y) -> x & ~y */
>> +(simplify
>> + (bit_and:c @0 (bit_not (bit_and:c@2 @0 @1)))
>> + (if (TREE_CODE (@2) != SSA_NAME || has_single_use (@2))
>> +  (bit_and @0 (bit_not @1))))
>>
>> Wouldn't it make more sense to put @2 on bit_not? If bit_and is used
>> multiple times, the transformation is neutral so it should be done as a
>> canonicalization. On the other hand, if bit_not is used multiple times, the
>> transformation adds an extra bit_not (which might be free when there is an
>> andn insn). So I believe the 2 main options are:
>> - move @2 on the bit_not
>> - don't test has_single_use at all
>
> I tend to favor not testing has_single_use at all.

Does this apply only to this pattern, to this pattern and its dual
(3/4), or to all four?

Rasmus