[Vm-dev] Making a Slower VM
Nicolas Cellier
nicolas.cellier.aka.nice at gmail.com
Mon Feb 10 21:12:32 UTC 2014
Hi David,
do you realize that Eliot is (ab)using this in COG in order to eliminate
some direct cCode: '...' inclusion?
So setFoo: is not an option (or i misunderstood something)
2014-02-10 21:51 GMT+01:00 David T. Lewis <lewis at mail.msen.com>:
>
> I was looking at the trunk VMM yesterday and found that most of the issues
> were just caused by accessor methods, where #foo and #foo: generate
> conflicting foo(void) and foo(aParameter). In most cases, a convention of
> #setFoo: rather than #foo: takes care of the problem. There were a few
> other miscellaneous issues as well, but nothing that looked serious.
>
> The variable 'memory' is a challenge because it is used extensively both
> directly and through #memory and #memory:. I was considering changing the
> variable name to something like memoryBase, and leaving the accessors
> alone though I'm not sure that would be a very good idea.
>
> I ran out of time yesterday and did not pursue it beyond this.
>
> Dave
>
> >
> >
> > On 10-02-2014, at 11:53 AM, Eliot Miranda <eliot.miranda at gmail.com>
> wrote:
> >>
> >> I *think* the issue is the internal/external split brought abut by the
> >> introduction of the localFoo variables, such as localSP and localIP.
> >
> > It's really hard to be sure but I suspect that this isn't the (only)
> > issue. IIRC we used to be able to make non-inlined VMs at one point and
> > that was well after the internalFoo code was added.
> >
> > OK, some quick email searching reveals some work done in '03 by johnMcI,
> > Craig & me.
> > Craig found the following code helped -
> >
> > !'From Squeak3.6alpha of ''17 March 2003'' [latest update: #5325] on 21
> > July 2003 at 1:11:25 pm'!
> >
> > !Interpreter methodsFor: 'contexts' stamp: 'crl 7/19/2003 15:59'!
> > primitiveFindNextUnwindContext
> > "Primitive. Search up the context stack for the next method context
> > marked for unwind handling from the receiver up to but not including the
> > argument. Return nil if none found."
> > | thisCntx nilOop aContext isUnwindMarked header meth pIndex |
> > aContext _ self popStack.
> > thisCntx _ self fetchPointer: SenderIndex ofObject: self popStack.
> > nilOop _ nilObj.
> >
> > [(thisCntx = aContext) or: [thisCntx = nilOop]] whileFalse: [
> >
> > header _ self baseHeader: aContext.
> >
> > (self isMethodContextHeader: header)
> > ifTrue: [
> > meth _ self fetchPointer: MethodIndex ofObject:
> aContext.
> > pIndex _ self primitiveIndexOf: meth.
> > isUnwindMarked _ pIndex == 198]
> > ifFalse: [isUnwindMarked _ false].
> > isUnwindMarked ifTrue:[
> > self push: thisCntx.
> > ^nil].
> > thisCntx _ self fetchPointer: SenderIndex ofObject:
> thisCntx].
> >
> > ^self push: nilOop! !
> >
> > !Interpreter methodsFor: 'interpreter shell' stamp: 'crl 7/19/2003
> 15:33'!
> > interpret
> > "This is the main interpreter loop. It normally loops forever,
> fetching
> > and executing bytecodes. When running in the context of a browser plugin
> > VM, however, it must return control to the browser periodically. This
> > should done only when the state of the currently running Squeak thread is
> > safely stored in the object heap. Since this is the case at the moment
> > that a check for interrupts is performed, that is when we return to the
> > browser if it is time to do so. Interrupt checks happen quite
> > frequently."
> >
> > "record entry time when running as a browser plug-in"
> > "self browserPluginInitialiseIfNeeded"
> > self internalizeIPandSP.
> > self fetchNextBytecode.
> > [true] whileTrue: [self dispatchOn: currentBytecode in:
> BytecodeTable].
> > localIP _ localIP - 1. "undo the pre-increment of IP before
> returning"
> > self externalizeIPandSP.
> > ! !
> >
> > !Interpreter methodsFor: 'return bytecodes' stamp: 'crl 7/19/2003 16:05'!
> > returnValueTo
> > "Note: Assumed to be inlined into the dispatch loop."
> >
> > | nilOop thisCntx contextOfCaller localCntx localVal isUnwindMarked
> > header meth pIndex |
> > self inline: true.
> > self sharedCodeNamed: 'commonReturn' inCase: 120.
> >
> > nilOop _ nilObj. "keep in a register"
> > thisCntx _ activeContext.
> > localCntx _ cntx.
> > localVal _ val.
> >
> > "make sure we can return to the given context"
> > ((localCntx = nilOop) or:
> > [(self fetchPointer: InstructionPointerIndex ofObject: localCntx)
> =
> > nilOop]) ifTrue: [
> > "error: sender's instruction pointer or context is nil;
> cannot return"
> > ^self internalCannotReturn: localVal].
> >
> > "If this return is not to our immediate predecessor (i.e. from a
> method
> > to its sender, or from a block to its caller), scan the stack for the
> > first unwind marked context and inform this context and let it deal with
> > it. This provides a chance for ensure unwinding to occur."
> > thisCntx _ self fetchPointer: SenderIndex ofObject: activeContext.
> >
> > "Just possibly a faster test would be to compare the homeContext
> and
> > activeContext - they are of course different for blocks. Thus we might be
> > able to optimise a touch by having a different returnTo for the
> > blockreteurn (since we know that must return to caller) and then if
> > active ~= home we must be doing a non-local return. I think. Maybe."
> > [thisCntx = localCntx] whileFalse: [
> > thisCntx = nilObj ifTrue:[
> > "error: sender's instruction pointer or context is
> nil; cannot return"
> > ^self internalCannotReturn: localVal].
> > "Climb up stack towards localCntx. Break out to a send of
> > #aboutToReturn:through: if an unwind marked context is found"
> > header _ self baseHeader: thisCntx.
> >
> > (self isMethodContextHeader: header)
> > ifTrue: [
> > meth _ self fetchPointer: MethodIndex ofObject:
> thisCntx.
> > pIndex _ self primitiveIndexOf: meth.
> > isUnwindMarked _ pIndex == 198]
> > ifFalse: [isUnwindMarked _ false].
> >
> > isUnwindMarked ifTrue:[
> > "context is marked; break out"
> > ^self internalAboutToReturn: localVal through:
> thisCntx].
> > thisCntx _ self fetchPointer: SenderIndex ofObject:
> thisCntx.
> > ].
> >
> > "If we get here there is no unwind to worry about. Simply
> terminate the
> > stack up to the localCntx - often just the sender of the method"
> > thisCntx _ activeContext.
> > [thisCntx = localCntx]
> > whileFalse:
> > ["climb up stack to localCntx"
> > contextOfCaller _ self fetchPointer: SenderIndex ofObject:
> thisCntx.
> >
> > "zap exited contexts so any future attempted use will be
> caught"
> > self storePointerUnchecked: SenderIndex ofObject: thisCntx
> withValue:
> > nilOop.
> > self storePointerUnchecked: InstructionPointerIndex
> ofObject: thisCntx
> > withValue: nilOop.
> > reclaimableContextCount > 0 ifTrue:
> > ["try to recycle this context"
> > reclaimableContextCount _ reclaimableContextCount
> - 1.
> > self recycleContextIfPossible: thisCntx].
> > thisCntx _ contextOfCaller].
> >
> > activeContext _ thisCntx.
> > (thisCntx < youngStart) ifTrue: [ self beRootIfOld: thisCntx ].
> >
> > self internalFetchContextRegisters: thisCntx. "updates local IP
> and SP"
> > self fetchNextBytecode.
> > self internalPush: localVal.
> > ! !
> >
> > Shortly after that I released the VMMaker3.6 with a note that it couldn't
> > produce a completely non-inlined VM because of a problem in fetchByte if
> > globalstruct was enabled, and some odd problems in B2DPlugin. When
> > VMMaker3.7 was released a year late (march 04) I apparently thought it
> > could make the core vm non-inlined. Since this is all a bazillion years
> > ago I can't remember any context to help extend the history.
> >
> > tim
> > --
> > tim Rowledge; tim at rowledge.org; http://www.rowledge.org/tim
> > Science is imagination equipped with grappling hooks.
> >
>
>
>
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