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Re: writing patterns
- From: Richard Biener <richard dot guenther at gmail dot com>
- To: Prathamesh Kulkarni <bilbotheelffriend at gmail dot com>
- Cc: GCC Development <gcc at gcc dot gnu dot org>
- Date: Wed, 30 Jul 2014 15:14:16 +0200
- Subject: Re: writing patterns
- Authentication-results: sourceware.org; auth=none
- References: <CAJXstsDfsQbj4e-RVyGC0grF_UDx5J0pYh=M9H9w=VYA-HBY4w at mail dot gmail dot com> <CAFiYyc0mAyTVrn07+ZSzgRT3of=O90iKkM_HVo1MfTvZaJemvw at mail dot gmail dot com> <CAJXstsDeBzQiDeNhXOdQJKuFPvpyN_14q4nqHBmADLaboC_pJQ at mail dot gmail dot com> <CAJXstsB_tjuZY9rbdY5xgMbMitJGSnUcW+ZQrNnsU0JGLSBmdg at mail dot gmail dot com>
On Wed, Jul 30, 2014 at 2:30 PM, Prathamesh Kulkarni
> On Wed, Jul 30, 2014 at 5:55 PM, Prathamesh Kulkarni
> <email@example.com> wrote:
>> On Wed, Jul 30, 2014 at 4:41 PM, Richard Biener
>> <firstname.lastname@example.org> wrote:
>>> On Wed, Jul 30, 2014 at 12:49 PM, Prathamesh Kulkarni
>>> <email@example.com> wrote:
>>>> 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)
>>> (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))
>>> 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.
>> What if we need to capture "value" as well as "type" ?
>> for instance match type with another capture, and value with a
>> different capture ?
>> sth like: (bogus pattern):
>> (plus (minus@T@2 @0 @1) (mult@T @2 @3))
> oops, @T was meant for outermost expression.
> sth like: (plus (minus@T0@2 @0 @1) (mult@T0 @2 @3))
> however this doesn't look good.
Yeah... well. I don't see very many compelling reasons for this
kind of cross-match but didn't think of the matching case initially
(otherwise capturing an expression is a "super-set" of capturing
its type as you can get at its type with TREE_TYPE (@0)).
I guess we can add support when need arises.
>>> 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
>>> with the patterns and do a #include "match-simplify-rotate.pd"
>>> in match.pd. That will make it easier to match the two later.
>> Okay, should I correspondingly split bitwise patterns in
>> match-simplify-bitwise.pd and the rest ?