Seems it can't happen then without breaking desired beahaviour of superclasses, unless the class in question does actually override all relevant inherited methods...

Seems one must make a decision to (at compile time) universally inline certain selectors or not.

Regards, Gary.
  ----- Original Message ----- 
  From: Eliot Miranda 
  To: The general-purpose Squeak developers list 
  Sent: Wednesday, November 19, 2008 8:31 PM
  Subject: Re: [squeak-dev] Lightweight Classes





  On Wed, Nov 19, 2008 at 12:13 PM, Gary Chambers <gazzaguru2 at btinternet.com> wrote:

    Perhaps the compiler could ask the class (or meta) of the method being compiled as to whether to inline a selector. All after the fact until a full recompile of the class, of course...


  Doesn't really help.  One wants the property to be of the receiver, not of the sending context.  Inheritance gets in the way also since a subclass that overrides the setting would need to reimplement all methods that send class to get its own setting, and even then super sends could invoke inherited code compiled with the wrong setting.  Alas this idea doesn't work.



    Regards, Gary.

    ----- Original Message ----- From: "Igor Stasenko" <siguctua at gmail.com>
    To: "The general-purpose Squeak developers list" <squeak-dev at lists.squeakfoundation.org>
    Sent: Wednesday, November 19, 2008 8:03 PM
    Subject: Re: [squeak-dev] Lightweight Classes




      2008/11/19 Eliot Miranda <eliot.miranda at gmail.com>:



        On Sun, Nov 16, 2008 at 7:11 PM, Igor Stasenko <siguctua at gmail.com> wrote:


          2008/11/17 Hernán Morales Durand <hernan.morales at gmail.com>:
          > Dear all,
          >   In the attachment you will find an implementation of Lightweight
          > Classes
          > for Squeak that follows the original paper "Debugging Objects" of > Hinkle
          > et
          > al. However I was unable to set up the #class method in the
          > LightweightClass
          > to answer the real class of the lightwighted object, is this possible
          > currently in Squeak?.
          >
          > What I did:
          > -Created the LightweightClass as in the old VisualWorks > implementation.
          > The
          > only difference here was CompiledMethod's cannot be copied, so I used
          > #clone.
          > -Created and installed an UnstoredMethod (a CompiledMethod subclass) > in
          > the
          > LightweightClass's methodDictionary. Since I want to store the source
          > code
          > but not through the changes log, I borrowed the MethodWrappers idea of
          > storing the state (sourceCode) in a class instance variable, and > compile
          > without logging. The methods I borrowed from MW are:
          >
          > -#copyWithTrailerBytes: - I think the superimplementor in > CompiledMethod
          > could use "self class" to avoid reimplementors.
          > -#tweakClassFormat - which set the format but I don't know why and
          > cannot
          > find documentation on this.
          > -#objectAt: I suspected the class literal was stored in the literal
          > frame
          > everytime I accepted a method, but for the simple test below still
          > answer
          > the LightweightClass and not the real class.
          >
          > Here is the test:
          >
          > | aDate |
          > aDate := Date today.
          > aDate becomeLightweight.
          > aDate dispatchingClass compile: 'day ^43' notifying: nil.
          > aDate day. " 43 (works) "
          > aDate perform: #class. " Date ------> (works) "
          > aDate class. " {Date} ------> LightweightClass (wrong) "
          >

          The only cause of this can be compiler.
          Instead of generating an instruction for sending #class message, it
          generates a bytecode to fetch the class from receiver oop , instead of
          sending real message.


        IMO the bug is in the VM.  The compiler generates bytecode 199, the special
        selector class send.  But it is the VM that decides to short-cut this send
        and implement it by accessing the receiver's class directly instead of
        actually sending the message.  I doubt very much this short-circuiting has
        any impact on performance (VisualWorks has never inlined this special
        selector send), and it is very easy to fix in the VM.  A number of other
        special selector bytecodes become ordinary sends (e.g. next nextPut: etc).
        If class were important for performance one could implement something
        analogous to the at cache that speeds up at:, at:put: and size for special
        selectors.  The special selector bytecode would check that the receiver of
        the class message had the standard implementation (primitive in Object) and
        answer the class directly.  But this isn't going to save significant time.
        To fix this change
        bytecodePrimClass
        | rcvr |
        rcvr := self internalStackTop.
        self internalPop: 1 thenPush: (self fetchClassOf: rcvr).
        self fetchNextBytecode.
        to
        bytecodePrimClass
        messageSelector := self specialSelector: 23.
        argumentCount := 0.
        self normalSend.



      Agreed, it seem a VM feature, kind of :)
      As  temporary workaround, one could modify compiler to generate a
      normal send bytecode instead of using a short bytecode for special
      selector which #class is. I'm not sure how easy/hard such modification
      could be made.

      And i agree, that such optimization buys a little. I didn't seen a
      code which does a heavy numerical crunching, where speed is essential,
      and at same time needs a #class sends. To my sense a #class appears in
      places where we need to deal with polymorphism or doing something on
      meta levels - but in such areas, a correctess is far more important
      than speed.


          > Any hint would be appreciated.
          > Best regards.
          >
          > Hernán
          >
          > PS: Just to avoid duplicate efforts, I wrote a LightweightClasses
          > Browser
          > which will be available as soon as I find a solution to the problem
          > above.
          >

          --
          Best regards,
          Igor Stasenko AKA sig.




      -- 
      Best regards,
      Igor Stasenko AKA sig.





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