On 4/10/23 01:10, Jakub Jelinek wrote:
> On Sat, Apr 08, 2023 at 06:25:32PM -0600, Jeff Law wrote:
>>
>>
>> On 4/6/23 08:21, Eric Botcazou wrote:
>>
>>>> So, perhaps just in the return op0; case add further code for
>>>> WORD_REGISTER_OPERATIONS and sub-word modes which will call nonzero_bits
>>>> again for the word mode and decide if it is still safe.
>>>
>>> Does it work to just replace mode by word_mode in the calls to nonzero_bits?
>> It helps marginally -- basically we defer mucking up the code a bit.  We
>> then hit this in simplify_and_const_int_1:
>>
>>
>>    /* See what bits may be nonzero in VAROP.  Unlike the general case of
>>       a call to nonzero_bits, here we don't care about bits outside
>>       MODE.  */
>>
>>    nonzero = nonzero_bits (varop, mode) & GET_MODE_MASK (mode);
>>
>> That just seems wrong for WORD_REGISTER_OPERATIONS targets.
>>
>>
>> Hacking both locations in a similar manner fixes the test.
> 
> If so, can you post that in patch form and can we go with that version
> plus the testcase (e.g. from the first patch I've posted where I've changed
> dse)?
So as I mentioned in IRC, I haven't really looked closely at 
simplify_and_const_int_1.  I don't have a high degree of confidence this 
patch is complete, even though it does fix the test for 108947 and 109040.

I did bootstrap on riscv, but not a regression test, that's spinning 
right now.

Jeff