let app invariant failure, HALP Re: how to write a ghc primop that acts on an unevaluated argument?

[Carter Schonwald]

woot, solved it, at least in a way thats OK for now.

if I mark the prefetchValue operations as has_side_effects=True, the core
lint failure goes away! I'm not sure if thats the right semantics in the
long term, but it does give me a simple way to make sure it works safely
for 7.10

pardon all the noise
-Carter

On Sun, Nov 23, 2014 at 4:26 PM, Carter Schonwald <
carter.schonwald at gmail.com> wrote:

> ok, i'm getting a let/app invariant failure when i build my test case with
> O1 or O2 but not without
>
> http://lpaste.net/114881
>
> any help would be appreciated on how to address that
>
> On Sun, Nov 23, 2014 at 4:13 PM, Carter Schonwald <
> carter.schonwald at gmail.com> wrote:
>
>> yup, i have that!
>>
>>     wrapFetch prefetchValue0# (error "this shouldn't get evaluated")
>>
>> in the test suite!
>>
>> in contrast
>>     wrapFetch prefetchValue0# $! (error "this shouldn't get evaluated")
>> does explode
>>
>> shall I add a "should fail" test with the latter? (it doesn't seem
>> worthwhile)
>>
>> On Sun, Nov 23, 2014 at 3:53 PM, Edward Kmett <ekmett at gmail.com> wrote:
>>
>>> Maybe test for laziness in the argument by just putting something in
>>> that goes boom when forced, e.g. 'undefined'?
>>>
>>>
>>> On Sun, Nov 23, 2014 at 2:04 PM, Carter Schonwald <
>>> carter.schonwald at gmail.com> wrote:
>>>
>>>> Hey All,
>>>> as part of trying to get some fixups for how prefetch works into 7.10,
>>>> i'm adding a "prefetchValue" primop that prefetchs the memory location
>>>> of a lifted heap value
>>>>
>>>> namely
>>>>
>>>> several operations of the following form
>>>>
>>>> primop PrefetchValueOp1 "prefetchValue1#" GenPrimOp
>>>>    a -> State# s -> State# s
>>>>    with strictness  = { \ _arity -> mkClosedStrictSig [botDmd, topDmd]
>>>> topRes }
>>>>
>>>> I'd like some feedback on the strictness information design by someone
>>>> who's familiar with how that piece of GHC. the idea being that
>>>> prefetchValue is lazy in its polymorphic argument (it doesn't force it, it
>>>> just does a prefetch on the heap location, which may or may not be
>>>> evaluated).
>>>>
>>>> https://phabricator.haskell.org/D350
>>>>
>>>> is the code in question. And i *believe* i'm testing for being lazy in
>>>> that argument correctly.
>>>>
>>>> thoughts?
>>>>
>>>> many thanks!
>>>> -Carter
>>>>
>>>>
>>>> _______________________________________________
>>>> ghc-devs mailing list
>>>> ghc-devs at haskell.org
>>>> http://www.haskell.org/mailman/listinfo/ghc-devs
>>>>
>>>>
>>>
>>
>
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