writing patterns

[Prathamesh Kulkarni]

On Tue, Aug 5, 2014 at 3:15 PM, Richard Biener
<richard.guenther@gmail.com> wrote:
> On Mon, Aug 4, 2014 at 4:44 PM, Prathamesh Kulkarni
> <bilbotheelffriend@gmail.com> wrote:
>> On Mon, Aug 4, 2014 at 2:59 PM, Richard Biener
>> <richard.guenther@gmail.com> wrote:
>>> On Mon, Aug 4, 2014 at 12:16 AM, Prathamesh Kulkarni
>>> <bilbotheelffriend@gmail.com> wrote:
>>>> On Thu, Jul 31, 2014 at 2:49 PM, Prathamesh Kulkarni
>>>> <bilbotheelffriend@gmail.com> wrote:
>>>>> On Thu, Jul 31, 2014 at 2:44 PM, Richard Biener
>>>>> <richard.guenther@gmail.com> wrote:
>>>>>> On Thu, Jul 31, 2014 at 11:09 AM, Prathamesh Kulkarni
>>>>>> <bilbotheelffriend@gmail.com> wrote:
>>>>>>> On Thu, Jul 31, 2014 at 2:15 PM, Richard Biener
>>>>>>> <richard.guenther@gmail.com> wrote:
>>>>>>>> On Thu, Jul 31, 2014 at 7:41 AM, Prathamesh Kulkarni
>>>>>>>> <bilbotheelffriend@gmail.com> wrote:
>>>>>>>>> On Wed, Jul 30, 2014 at 11:49 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.
>>>>>>>>>> Would it be better to have syntax (say using ?) for denoting that an
>>>>>>>>>> operator is optional ?
>>>>>>>>>> operator should be unary, and it's operand must be an expression.
>>>>>>>>>>
>>>>>>>>>> so the pattern becomes sth like:
>>>>>>>>>> (plus@2 (convert? (lshift@0 (convert? X) CNT1))
>>>>>>>>>>              (convert? (rshift@1 (convert? X) CNT2)))
>>>>>>>>>>
>>>>>>>>> Let me rephrase it.
>>>>>>>>> An operator can be marked optional, if
>>>>>>>>> a) it's unary
>>>>>>>>> b) if in outermost-expr, the operand must be an expression
>>>>>>>>>
>>>>>>>>> I want to reject case like:
>>>>>>>>> (negate? @0)
>>>>>>>>>
>>>>>>>>> (op? operand)
>>>>>>>>> generates code :
>>>>>>>>> match (op)
>>>>>>>>>    match (operand)
>>>>>>>>>
>>>>>>>>> and once without op
>>>>>>>>> match (operand)
>>>>>>>>>
>>>>>>>>> Implementation-wise I think, we could duplicate the AST, like we do
>>>>>>>>> for "for pattern".
>>>>>>>>> Would that be okay ?
>>>>>>>>
>>>>>>>> I thought of something similar but how exactly would you do the
>>>>>>>> duplication in the above example?  The point is that we know
>>>>>>>> that the conversions will exist in pairs, that is, either
>>>>>>>> the two outer and no inner or no outer and both inner or
>>>>>>>> both outer and both inner.  You can express that with the
>>>>>>>> nested for - with just a '?' you can't do that.  Of course you could
>>>>>>>> do sth like
>>>>>>>>
>>>>>>>> (plus@2 (convert?1 (lshift@0 (convert?2 X) CNT1))
>>>>>>>>              (convert?1 (rshift@1 (convert?2 X) CNT2)))
>>>>>>>>
>>>>>>>> that is, add an index to ?s and tie them together.  We want to
>>>>>>>> avoid generating useless patterns - in this case 4 are sufficient
>>>>>>>> but if we generate all possible combinations we'd have an additional
>>>>>>>> 12 useless patterns.
>>>>>>> Ah yes, didn't realize that, thanks.
>>>>>>>>
>>>>>>>> But using '?' indeed looks better than (ab)using 'for'.  Note that
>>>>>>>> it is _only_ 'convert' that I can see this useful for (or can you
>>>>>>>> think of other cases?).  So maybe we instead want to make
>>>>>>>> it a special operator like
>>>>>>>>
>>>>>>>> (plus@2 (opt_convert 1 (lshift@0 (opt_convert 2 X) CNT1))
>>>>>>>>              (opt_convert 1 (rshift@1 (opt_convert 2 X) CONT2)))
>>>>>>>>
>>>>>>>> with an additional operand specifying the group (or simply
>>>>>>>> have opt_convert1 and opt_convert2 operands - hoping for
>>>>>>>> more "groups" to never happen ;)).
>>>>>>>>
>>>>>>>> Actually I like opt_convert[123] most.
>>>>>>> I like opt_convert[123] too.
>>>>>>> Implementation-wise I don't think it would be more difficult to
>>>>>>> generalize it for other operators ...
>>>>>>
>>>>>> Of course, but I don't see the need for that.  Conversions are really
>>>>>> special in this regard.
>>>>>>
>>>>>>> I was thinking about this ... Instead of grouping by indexes,
>>>>>>> how about defining operator aliases ?
>>>>>>> sth like:
>>>>>>> (define_op cvt1 convert)
>>>>>>> (define_op cvt2 convert)
>>>>>>>
>>>>>>> and then the pattern becomes:
>>>>>>>
>>>>>>> (plus@2 (cvt1? (lshift@0 (cvt2? X) CNT1))
>>>>>>>              (cvt1? (rshift@1 (cvt2? X) CNT2)))
>>>>>>>
>>>>>>> that would avoid generating useless patterns (since cvt1, cvt2 are
>>>>>>> "different"), however during code-gen
>>>>>>> both shall map to CONVERT_EXPR (and once without it since its optional).
>>>>>>
>>>>>> Yeah, that would work if we'd implement it that way.  Still I don't like
>>>>>> a general '?' facility unless we come up with really good uses apart from
>>>>>> conversions.
>>>>> Agreed. I will start with implementing opt_convert.
>>>> I have attached patch, that implements opt_convert.
>>>> The implementation is not very efficient (i hope we can combine
>>>> replace_opt_convert and lower_opt_convert).
>>>>
>>>> Some issues with implementation:
>>>> a) since OPT_CONVERT is not defined in tree.def, i added it after
>>>> #include tree.def in enum tree_code.
>>>> So our enum tree_code becomes different from the usual enum tree_code.
>>>>
>>>> b) checks if there's any opt_convert remaining before lowering it to CONVERT
>>>> and once removing it (this leads to walking AST thrice per each group).
>>>> We can probably combine lower_opt_convert, remove_opt_convert and
>>>> has_opt_convert into one function.
>>>>
>>>> c) opt_convert cannot be captured, for instance doesn't make sense
>>>> when it's operand is not an expression
>>>> eg - (opt_convert 1 @0)
>>>> Or maybe allow capturing if the operand is expression ?
>>>
>>> Hmm.  Capturing the convert may be necessary though as we usually
>>> have to constrain allowed conversions.  Like
>>>
>>>  (convert?@0 @1)
>>>  if (TYPE_PRECISION (TREE_TYPE (@0)) > TYPE_PRECISION (TREE_TYPE (@1))
>>>
>>> to allow an optional widening convertsion.  But yes, we can't
>>> possibly evaluate that if-expression if the convert is not there.
>>>
>>> Bummer.
>>>
>>> That rules out this way of doing a conditional conversion.
>>>
>>> OTOH we can simply make the capturing of the conversion
>>> capture its operand if it is not there?
>> I am not sure if I understood this.
>> eg: (foo (convert?@0 @1))  where foo's any operator.
>> gets lowered to:
>> a) (foo (convert@0 @1))
>> b) (foo @1)
>
> b) (foo @0@1)
>
> that is, both captures capture the same
>
>> in case a), @0 captures (convert @1).
>> in case b), when there's no convert, what should @0 capture ?
>> It cannot capture foo, (foo@0 @1) since foo's in outermost-expr,
>> so should @0 be same as @1 for this case ?
>
> Yes.
>
>>>
>>>> d) Use of opt_convert inside for operator-list is rejected.
>>>> eg - (for op in convert opt_convert bit_not)
>>>>
>>>> * Changing syntax:
>>>> I was wondering if instead of having new operator like opt_convert, we
>>>> could reuse convert ?
>>>> convert becomes optional if it's followed with '?'
>>>> eg:
>>>> (convert? 1 @0) is "optional convert".
>>>> or maybe use colon ?
>>>> (convert:1 @0) ?
>>>> (IMHO '?' is slightly better since it's typically used to denote
>>>> "optional" in regexp, but
>>>> '? number' looks somewhat out of place in the pattern, ': number' looks better).
>>>
>>> Hmm, then if we resort to predicate/flag syntax why not do
>>> convert:?1 or convert:? convert:?? convert:??? with the number
>>> of ?s also providing the match-number.  Of course that makes
>>> it look like a generic flag when we should only accept it on converts.
>>>
>>> Or do convert1?  I don't like the binary form or the number following
>>> the ? (looks too much like a capture).  Note that convert1? lexes
>>> as one identifier followed by a ? though.
>>>
>>>> the above pattern becomes:
>>>> (plus@2 (convert? 1 (lshift@0 (convert? 2 X) CNT1))
>>>>              (convert? 1 (rshift@1 (convert? 2 X) CNT2)))
>>>>
>>>> "optional" converts won't be allowed to get captured (non-optional convert yes).
>>>
>>> See above - we should capture its operand if it is not there.
>>>
>>> So I think let's go with convert1? and allow capturing.  Doing that
>>> with appending CONVERT1, CONVERT2, ... to tree.def works for me.
>> Thanks, I would do that.
>> I was wondering whether it would be okay to change tree.def for this
>> purpose though ?
>> since convert1, convert2 would be having no other use.
>
> No, not changing tree.def but its use as you did in your first proposed
> patch.
I have got it done except for capturing optional converts.
for instance (negate (convert1@0 @1)) does not work.
This is because of insertion in decision tree (insert::operand).
Since captures were always predicate or expressions,
ie, the corresponding dt-node->type was dt_node::DT_OPERAND,
i could hard-code for a search on dt_node::DT_OPERAND.
This changes when capture itself can be captured (dt_node::DT_TRUE/DT_MATCH),
and there's no easy way right now to obtain corresponding
dt-node from a given operand node.

Should we keep a mapping (hash_map/std::map) from operand * to dt_node * ?
That will also get rid of dt_node::parent (but we need to then
introduce parent in AST).

Other cases where convert1, convert2 are not captured work
fine.
(bit_not (convert1 @0) (convert2 @1))
I have attached patch for reference (don't intend to get it committed).

Thanks,
Prathamesh
>
> Richard.
>
>> Thanks,
>> Prathamesh
>>>
>>> Richard.
>>>
>>>>
>>>> * genmatch.c (enum tree_code): New value OPT_CONVERT.
>>>>       (e_operation): New member unsigned group_index.
>>>>       (e_operation::e_operation): Add new default argument.
>>>>                                               Adjust to changes in e_operation.
>>>>       (remove_opt_convert): New function.
>>>>       (has_opt_convert): Likewise.
>>>>       (lower_opt_convert): Likewise.
>>>>       (lower_opt_convert): New overloaded function.
>>>>       (lower_opt_convert): Likewise.
>>>>       (parse_expr): Adjust to parse opt_convert.
>>>>       (parse_for): Reject opt_convert in opers.
>>>>       (main): Call lower_opt_convert.
>>>>
>>>> Thanks,
>>>> Prathamesh
>>>>>
>>>>> Thanks,
>>>>> Prathamesh.
>>>>>>
>>>>>> Richard.
>>>>>>
>>>>>>> Thanks,
>>>>>>> Prathamesh
>>>>>>>
>>>>>>>>
>>>>>>>> Richard.
>>>>>>>>
>>>>>>>>> Thanks,
>>>>>>>>> Prathamesh
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>> Thanks,
>>>>>>>>>> Prathamesh
>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> 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?
>>>>>>>>>>>
>>>>>>>>>>> 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
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