[Vm-dev] Slang's type inference and typing

Wed Dec 18 02:52:48 UTC 2019

Hi Pierre,

On Tue, Dec 17, 2019 at 9:50 AM pierre misse <pierre_misse25 at msn.com> wrote:

>
>
> Hi,
>
> I saw my previous mistake, and corrected this.
> This is a sample test, for a very simple inference.
>
> testReturnFloatConstantNode
>     | ccg tMethod |
>     ccg := CCodeGenerator new.
>     ccg addClass: SlangTypeInferenceTestsClass.
>     ccg inferTypesForImplicitlyTypedVariablesAndMethods.
>     tMethod := ccg methodNamed: #returnAFloatConstantNode.
>
>     self assert: tMethod isNotNil.
>     self assert: (ccg typeFor: tMethod statements first in: tMethod)
> equals: #double.
>     self assert: tMethod returnType equals: #double
>

 And perhaps have SlangTypeInferenceTestsClass inherit from
StackInterpreter or InterpreterPrimitives.  That will give you much more
context.

 I need to work on ones with ambiguity.
>
>
>  The instability I saw was in getErrorObjectFromPrimFailCode; its two
locals clone & errObj are sometimes typed as squint and sometimes as
usqInt.  Some times numPointerSlotsOf ends up with a return type of usqInt,
some times as sqInt.  I've recently had success in another project
substituting OrderedDictionary et al for Dictionary.  So I'm sure that
solutions can be found easily.

> Pierre
>
>
> On 17/12/2019 07:49, pierre misse wrote:
>
>
> My first approach is very simple
>
> create a CCodeGenerator
> add only my current class with independent methods
> infer the type
> check the types.
>
> testConstantInt32
>     | ccg tMethod |
>     ccg := CCodeGenerator new.
>     ccg addClass: self class.
>     tMethod := ccg compileToTMethodSelector: #anInt32 in: self class.
>     ccg inferTypesForImplicitlyTypedVariablesAndMethods.
>     ccg typeFor: tMethod statements first expression variable in: tMethod.
> "#sqInt"
>     tMethod inferReturnTypeFromReturnsIn: ccg."a TMethod
> (SlangTypeInferenceTests>>anInt32)"
>     tMethod returnType."nil"
>
> Applied in this case to:
>
> anInt32
>     | a |
>     ^ a := 30
>
> Maybe I misunderstood the type Inference that I read so far, but based on
> #TMethod >> #typeFor:in:,
> I would expect the ccg to keep the type information somewhere, which
> doesn't seem to be the case.
>
> Maybe it's because my set up is wrong?
>
> This part of the comment puzzles me "deferring to aCodeGen (which defers
> to the vmClass)", gonna dig into this method.
>
>
> Thank you,
>
> Pierre
>
>
>
> On 17/12/2019 07:33, Eliot Miranda wrote:
>
>
> Hi Pierre, and welcome.
>
> On Dec 16, 2019, at 10:19 PM, pierre misse <pierre_misse25 at msn.com>
> <pierre_misse25 at msn.com> wrote:
>
> 
>
> Hi Eliot,
>
>
> Thanks for the detailed answer and all the pointers !
>
> I must have misunderstood
> #inferTypesForImplicitlyTypedVariablesAndMethods when I first came across
> it.
>
>
> Have a nice day :)
>
>
> thank you :)
>
> Pierre
> On 17/12/2019 01:14, Eliot Miranda wrote:
>
>
> Hi Pierre,
>
> On Mon, Dec 16, 2019 at 4:07 AM pierre misse <pierre_misse25 at msn.com>
> wrote:
>
>> Hi,
>>
>> I'm currently trying to understand Slang's type inference, and to do so
>> trying to write tests.
>>
> Is it your intention to contribute those tests back to VMMaker.oscog on
> source.squeak.org?
>
> If I am able to, it is my intention.
>
>
> Thank you. It be warmly appreciated.
>
> One thing yo look at in your tests is instabilities in the algorithm,
> typically caused by the use of hashed collections (eg Set) that have
> different enumerations from run to run, usually due to hashes being
> pseudo-randomly computed.  If you look at the last commit of the Spur
> cointerp.c’s you’ll see one variable that changes type from sqInt to
> usqInt. This points to such a bug. I’ll try and provide you with specifics
> soon.
>
> Thanks for the warning. I was actually already aware of this bug, but now
> I also know the cause !
>
>
> I'm using CCodeGenerator >> #compileToTMethodSelector:in: to get the
>> TMethod, but i cannot seem to find how to use the type inference on this
>> TMethod (or in the instance of CCodeGenerator).
>>
>
> Here's some doit that run Slang including type inference:
>
>
> https://github.com/OpenSmalltalk/opensmalltalk-vm/blob/Cog/image/Slang%20Test%20Workspace.text
>
> If you use
> https://github.com/OpenSmalltalk/opensmalltalk-vm/blob/Cog/image/buildspurtrunkvmmaker64image.sh
> to build a VMMaker image it'll create an image containing g this and other
> useful workspaces that contain doit to launch a VM under the simulator, etc.
>
> Type inference is driven by this loop in
> CCodeGeneraror>>inferTypesForImplicitlyTypedVariablesAndMethods which
> iterates, inferring types until no more types can b e inferred (until the
> algorithm has reached a fixed point).
>
> "now iterate until we reach a fixed point"
> [| changedReturnType |
> changedReturnType := false.
> allMethods do:
> [:m|
> m inferTypesForImplicitlyTypedVariablesIn: self.
> (m inferReturnTypeIn: self) ifTrue:
> [changedReturnType := true]].
> changedReturnType] whileTrue.
>
> Type information is derived from explicit return types in methods (the
> <returnTypeC: > pragma), types for "kernel" sends from
> CCodeGenerator>>#returnTypeForSend:in:ifNil:, and for types propagated to
> returns from variables that themselves are either explicitly typed using
> <var: ... type: ...> and <var: ... declareC: ...> pragmas, or get their
> types in assignments of the results of methods, where the type they acquire
> is the return types of those methods.
>
>> Also, I have been wondering what is the semantic of sqInt. I found out it
>> was an alias for a long, but i couldn't find better than that.
>>
> #sqInt is first of all a pun for "squint"
>
> nice , I was wondering if that was the case too :D
>
> , a shortening of Squeak Integer.  It is an integer type of the same size
> as an "ordinary object pointer", or "oop". #usqInt, #sqLong & #usqLong are
> other important types.  #sqLong & #usqLong are 64-bit types.  #sqInt &
> #usqInt are 32-bit types in 32-bit VMs and 64-bit types in 64-bit VMs.
>
>> Are there offsets to find objects in the object memory?
>>
> A #sqInt is typically used to hold the oop for an object and indeed it
> points to the header word of the object.  The object is preceded by an
> overflow header word if it has more than 254 slots.
>
>> Are there cast as pointers?
>>
> Yes.  See the functions and macros in platforms/Cross/vm/sqMemoryAccess.h.
>
>> Thank you in advance :)
>>
>> Pierre.
>>
> _,,,^..^,,,_
>
> best, Eliot
>
>
> Cheers
>
>

-- 
_,,,^..^,,,_
best, Eliot
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