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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>, GCC Development <gcc at gcc dot gnu dot org>
- Date: Wed, 30 Jul 2014 13:11:12 +0200
- Subject: Re: writing patterns
- Authentication-results: sourceware.org; auth=none
- References: <CAJXstsDfsQbj4e-RVyGC0grF_UDx5J0pYh=M9H9w=VYA-HBY4w at mail dot gmail dot com>
On Wed, Jul 30, 2014 at 12:49 PM, Prathamesh Kulkarni
> 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))))
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
with the patterns and do a #include "match-simplify-rotate.pd"
in match.pd. That will make it easier to match the two later.