[Vm-dev] Fwd: [Pharo-project] Could not load VMMaker in 10315

Eliot Miranda eliot.miranda at gmail.com
Sun May 24 20:44:52 UTC 2009

On Sun, May 24, 2009 at 1:13 PM, John M McIntosh <
johnmci at smalltalkconsulting.com> wrote:

> Begin forwarded message:
>  From: Stéphane Ducasse <stephane.ducasse at inria.fr>
>> Date: May 24, 2009 1:35:01 AM PDT (CA)
>> To: Pharo Development <Pharo-project at lists.gforge.inria.fr>
>> Subject: [Pharo-project] Could not load VMMaker in 10315
>> Reply-To: Pharo-project at lists.gforge.inria.fr
>> Hi
>> I did
>> ScriptLoader loadFFI
>> Then loaded VMMaker-dtl.122
>> Then proceeded when asked about klatt.
>> And I got Cannot compile -- stack including temps is too deep
>> what did I miss?
Nothing.  There is a method in the GeniePlugin who's stack is too deep to
compile with closures.  Here are some workarounds and solutions in
increasing levels of difficulty:

1. since the GeniePlugin is inessential simply move it to another package
and ignore the problem (this is what we have done at Qwaq).

2a. Since the method is never executed one can temporarily change the stack
limit (e.g. CompiledMethod classPool at: #LargeFrame put: 57) and load the
package, reverting the stack limit after loading (Compiledmethod classPool
at: #LargeFrame put: 56)

2b. change CompiledMethod>>needsFrame: so that proceeding from the error
still creates a compiled method (i.e. remove the ^ return from the method so
that it reads
        needsFrameSize: newFrameSize
                 "Set the largeFrameBit to accomodate the newFrameSize"
                 | largeFrameBit header |
                 largeFrameBit *:=* 16r20000.
                 (self numTemps + newFrameSize) > LargeFrame ifTrue:
                          [self error: 'Cannot compile -- stack including
temps is too deep'].
                 header *:=* self objectAt: 1.
                 (header bitAnd: largeFrameBit) ~= 0
                          ifTrue: [header *:=* header - largeFrameBit].
                 self objectAt: 1 put: header
                                   + ((self numTemps + newFrameSize) >
                                                     ifTrue: [largeFrameBit]

                                                     ifFalse: [0])

then file-in the method and proceed through the warning.
Both of these are tedious but since you're probably not going to be changing
the method and since Monticello won't recompile it once it is loaded it'll
sit there quite happily once compiled.

3. refactor the GeniePlugin method into an outer args parser and an inner
engine method and solve the problem.  Since VMMaker will inline anyway this
shouldn't make performance worse.  I haven't done this because I'm not the
author and it is quite a complex method.

4. modify the Closure compiler so that it reuses temporaries in optimized
blocks.  The method compiles with the BlueBook compiler because in
1 to: n do: [:i| .......].
1 to: n do: [:i| .......].
the two block variables "i" are the same "physical" variable stored in the
same location in the home context (because BlueBook blocks do not have local
arguments or temporaries).
But in the Closure compiler they are logically distinct variables and if the
blocks were real and not optimized they would occupy different "physical"
locations.  Since they are optimized blocks their temporaries do get
allocated in the home context, but they occupy different locations, and
hence the stack size is larger in the Closure compiler.  The Closure
compiler could be modified to use a more sophisticated temporary variable
scope analysis that would allow it to determine that the first block's "i"
is out of scope when the second block is compiled and hence that the
location can be reused.
This is non-trivial because it requires rewriting much of the temporary
scope management (see TempVariableNode>>scope[:] & senders of scope:).  If I
had hit the stack limit in more than this one method I probably would have
tried to solve this but for now there are fatter fish to fry.

I plan that eventually the Cog VM will support a CompiledMethod format that
will have a higher argument, temp and total frame size limit, but this isn't
a priority right now.


>> Stef
>> _______________________________________________
>> Pharo-project mailing list
>> Pharo-project at lists.gforge.inria.fr
>> http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project
> --
> =
> =
> =
> ========================================================================
> John M. McIntosh <johnmci at smalltalkconsulting.com>   Twitter:
>  squeaker68882
> Corporate Smalltalk Consulting Ltd.  http://www.smalltalkconsulting.com
> ===========================================================================
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