Re: [PATCH v3] Modify combine pattern by a pseudo AND with its nonzero bits [PR93453]

[HAO CHEN GUI <guihaoc@linux.ibm.com>]

Hi Segher,
  Really appreciate your review comments.

On 11/8/2022 上午 1:38, Segher Boessenkool wrote:
> Hi!
> 
> Sorry for the tardiness.
> 
> On Fri, Jul 22, 2022 at 03:07:55PM +0800, HAO CHEN GUI wrote:
>>   This patch creates a new function - change_pseudo_and_mask. If recog fails,
>> the function converts a single pseudo to the pseudo AND with a mask if the
>> outer operator is IOR/XOR/PLUS and inner operator is ASHIFT or AND. The
>> conversion helps pattern to match rotate and mask insn on some targets.
> 
> The name isn't so clear.  It isn't changing a mask, to start with.
How about setting function name to change_pseudo? It converts a pseudo to
the pseudo AND with a mask in a particular situation.

> 
>> +/* When the outer code of set_src is IOR/XOR/PLUS and the inner code is
>> +   ASHIFT/AND,
> 
> "When the outercode of the SET_SRC of PAT is ..."
Yeah, I will change it.

> 
>> convert a pseudo to pseudo AND with a mask if its nonzero_bits
>> +   is less than its mode mask.  The nonzero_bits in later passes is not a
>> +   superset of what is known in combine pass.  So an insn with nonzero_bits
>> +   can't be recoged later.  */
> 
> Can this not be done with a splitter in the machine description?
> 
Sorry, I don't quite understand it. Do you mean if the conversion can be done in
split pass?

If a pseudo has DImode and stem from a char, we get nonzero_bits as 0xff in combine
pass. But in split pass, it's nonzero_bits is 0xffffffffffffffff. So the conversion
can only be done in combine pass.

Thanks
Gui Haochen