Re: writing patterns

[Richard Biener <richard dot guenther at gmail dot com>]

On Wed, Jul 30, 2014 at 2:25 PM, Prathamesh Kulkarni
<bilbotheelffriend@gmail.com> wrote:
> On Wed, Jul 30, 2014 at 4:49 PM, Richard Biener
> <richard.guenther@gmail.com> wrote:
>> On Wed, Jul 30, 2014 at 1:11 PM, Richard Biener
>> <richard.guenther@gmail.com> wrote:
>>> On Wed, Jul 30, 2014 at 12:49 PM, Prathamesh Kulkarni
>>> <bilbotheelffriend@gmail.com> wrote:
>>>> Hi,
>>>>    Sorry to ask a stupid question, but I am having issues writing patterns
>>>> involving casts. I am trying to write patterns from simplify_rotate.
>>>>
>>>> Could you show me how to write a patterns that involve
>>>> casts ?
>>>> for eg:
>>>> ((T) ((T2) X << CNT1)) + ((T) ((T2) X >> CNT2))     iff CNT1 + CNT2 == B
>>>> T -> some unsigned type with bitsize B, and some type T2 wider than T.
>>>> How to express this in the pattern ?
>>>
>>> [copying gcc@ because of the syntax stuff]
>>>
>>> for example with (leaving captures as the appear in the pattern above)
>>>
>>> (match_and_simplify
>>>    (plus (convert@2 (lshift (convert@0 X) CNT1))
>>>            (convert (rshift (convert@1 X) CNT2)))
>>>     /* Types T2 have to match */
>>>    (if (types_compatible_p (TREE_TYPE (@0), TREE_TYPE (@1))
>>>         /* Type T should be unsigned.  */
>>>        && TYPE_UNSIGNED (TREE_TYPE (@2))
>>>        /* T2 should be wider than T.  */
>>>        && TYPE_PRECISION (TREE_TYPE (@0)) > TYPE_PRECISION (TREE_TYPE (@2))
>>>        /* CNT1 + CNT2 == B */
>>>        && wi::eq_p (TYPE_PRECISION (TREE_TYPE (@2)),
>>>                            wi::add (CNT1, CNT2))))
>>>    (lrotate CNT1))
>>
>> Note that this will _explicitely_ require a conversion.  That is, if T == T2
>> it won't match because the conversion to T will not be there, nor if X
>> is already of type T2.
>>
>> Which means that we want to match multiple variants of this
>> (with conversions in place or not).  Hmm.  Maybe with extending 'for' like
>>
>> (for cvt1 in convert *
>>   (fot cvt2 in convert *
>>     (plus@2 (cvt1 (lshift@0 (cvt2 X) CNT1))
>>                  (cvt1 (rshift@1 (cvt2 X) CNT2)))
>> ...
>>
>> adding an "empty" operator to the list of operators to substitute for cvt1
>> and allowing nested for.  The "empty" operator would necessarily be
>> unary and be just un-wrapped.
> um can't we use nop for "empty" operator ?

Unfortunately "nop" is already taken (NOP_EXPR).  we could use
"nil".

>>
>> Extending for in this way avoids treating conversions specially
>> (I don't see an easy way to do very good at that automagically).  We
>> need multiple patterns in the decision tree here anyway.
>>
>> Now guess sth fancy in place of '*' ...
>>
>> Lisp style would be less free-form like
>>
>> (for cvt (convert ())
>>
>> where we could use an empty list for the "empty" operator.
>>
>> Is nested for support already implemented?
> Yes.

Great.

Thanks,
Richard.

> Thanks,
> Prathamesh
>>
>> Thanks,
>> Richard.
>>
>>> which suggests that we may want to add some type capturing / matching
>>> so we can maybe write
>>>
>>>   (plus (convert@T (lshift (convert@T2 X) CNT1))
>>>           (convert (rshift (convert@T2 X) CNT2)))
>>>   (if (/* T2s will be matched automagically */
>>>        && TYPE_UNSIGNED (@T)
>>>        && TYPE_PRECISION (@T2) > TYPE_PRECISION (@T)
>>>        && wi::eq_p (TYPE_PRECISION (@T), wi::add (CNT1, CNT2))))
>>>
>>> which is less to type and supports requiring matching types.  Maybe
>>> require @T[0-9]+ here thus use @T0 and disallow plain @T.  We could
>>> then also use @T for the implicitely "captured" outermost type we
>>> refer to as plain 'type' right now.
>>>
>>> I suggest to go ahead without a new syntax for now and see if it
>>> gets unwieldingly ugly without first.
>>>
>>>> For this week, I have planned:
>>>> a) writing patterns from simplify_rotate
>>>> b) replacing op in c_expr
>>>> c) writing more test-cases.
>>>>
>>>> If there's anything else you would like me to do, I would be happy
>>>> to know.
>>>
>>> Just keep an eye open for things like above - easy ways to reduce
>>> typing for patterns.
>>>
>>> Btw, I suggest to split up match.pd by code you converted from.  Thus
>>> for simplify_rotate add
>>>
>>>   match-simplify-rotate.pd
>>>
>>> with the patterns and do a #include "match-simplify-rotate.pd"
>>> in match.pd.  That will make it easier to match the two later.
>>>
>>> Thanks,
>>> Richard.
>>>
>>>
>>>> Thanks,
>>>> Prathamesh