D538 and compiler performance spec

[Alan & Kim Zimmerman]

Ok, I backed it out for all but the compound cases and the performance test
once more passes, and I can round-trip compound RdrNames.

On Fri, Dec 12, 2014 at 11:30 PM, Alan & Kim Zimmerman <alan.zimm at gmail.com>
wrote:
>
> On reflection, I can try to make it work with annotations just for those
> fairly rare cases where there are parens/backquotes, and use the location
> span otherwise.
>
> On Fri, Dec 12, 2014 at 11:20 PM, Alan & Kim Zimmerman <
> alan.zimm at gmail.com> wrote:
>>
>> The problem is round-tripping cases like this, which are valid
>>
>>     (     ///     ) :: Int -> Int -> Int
>>     a /// b = 3
>>
>>     baz :: Int -> Int -> Int
>>     a `     baz     ` b = 4
>>
>> There can be arbitrary spaces between the surrounding parens and the
>> operator name, and between the backquotes and the identifier in the infix
>> version.
>>
>> In each case we simply get a RdrName, which in turn is wrapped in HsVar
>> or whatever.
>>
>> The D538 productions are of the form
>>
>>     var     :: { Located RdrName }
>>             : varid                 { $1 }
>>             | '(' varsym ')'        {% ams (sLL $1 $> (unLoc $2))
>>                                            [mo $1,mj AnnVal $2,mc $3] }
>>
>> and
>>
>>     tyvarop :: { Located RdrName }
>>     tyvarop : '`' tyvarid '`'       {% ams (sLL $1 $> (unLoc $2))
>>                                            [mj AnnBackquote $1,mj AnnVal
>> $2
>>                                            ,mj AnnBackquote $3] }
>>
>> So the location tracks the entire span, but we need annotations for the
>> three individual parts.
>>
>> Note: I did not check how far close to the limit the performance was
>> prior to this change, it may have been the last 1% to take it over.
>>
>> Alan
>>
>>
>> On Fri, Dec 12, 2014 at 11:03 PM, Simon Peyton Jones <
>> simonpj at microsoft.com> wrote:
>>>
>>>   I am now adding an `AnnVal` to every RdrName, to be able to separate
>>> it out from any decoration, such as surrounding backticks or parens.
>>>
>>>
>>>
>>> That seems like overkill to me.  (a `op` b) is an HsOpApp, and must of
>>> course have backticks unless op is an operator like (a + b), in which case
>>> it doesn’t.
>>>
>>>
>>>
>>> The corner case is something like ((`op`) a b), which will parse as
>>> (HsApp (HsApp (HsVar op) (HsVar a)) (HsVar b)).  But it would be silly for
>>> us to get bent out of shape because of such a vanishingly rare corner
>>> case.  Instead, if you really want to reflect it faithfully, add a new
>>> constructor for “parens around backticks”).
>>>
>>>
>>>
>>> Let’s only take these overheads when there is real reason to do so.
>>>
>>>
>>>
>>> Simon
>>>
>>>
>>>
>>> *From:* ghc-devs [mailto:ghc-devs-bounces at haskell.org] *On Behalf Of *Alan
>>> & Kim Zimmerman
>>> *Sent:* 12 December 2014 14:22
>>> *To:* ghc-devs at haskell.org
>>> *Subject:* D538 and compiler performance spec
>>>
>>>
>>>
>>> For API annotations I am working in the details of RdrNames, which come
>>> in a bewildering variety of syntactic forms.
>>>
>>> My latest change causes perf/compiler to fail, with
>>>
>>> bytes allocated value is too high:
>>>     Expected    parsing001(normal) bytes allocated: 587079016 +/-5%
>>>     Lower bound parsing001(normal) bytes allocated: 557725065
>>>     Upper bound parsing001(normal) bytes allocated: 616432967
>>>     Actual      parsing001(normal) bytes allocated: 704940512
>>>     Deviation   parsing001(normal) bytes allocated:      20.1 %
>>>
>>> I am now adding an `AnnVal` to every RdrName, to be able to separate it
>>> out from any decoration, such as surrounding backticks or parens.
>>>
>>> Is this a problem? The alternative would be to add a SourceText field to
>>> RdrName.
>>>
>>> Alan
>>>
>>
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