[Vm-dev] VM Maker: VMMaker.oscog-eem.1972.mcz

[Eliot Miranda]

Hi Nicolas,

On Mon, Oct 31, 2016 at 3:38 PM, Nicolas Cellier <
nicolas.cellier.aka.nice at gmail.com> wrote:

>
>
>
> 2016-10-31 22:42 GMT+01:00 <commits at source.squeak.org>:
>
>>
>> Eliot Miranda uploaded a new version of VMMaker to project VM Maker:
>> http://source.squeak.org/VMMaker/VMMaker.oscog-eem.1972.mcz
>>
>> ==================== Summary ====================
>>
>> Name: VMMaker.oscog-eem.1972
>> Author: eem
>> Time: 31 October 2016, 2:42:12.362675 pm
>> UUID: 0e6a54ad-d62f-4b69-9f0d-7b66f8350984
>> Ancestors: VMMaker.oscog-eem.1971
>>
>> Redo fixing extB sign extension in NewsqueakV4 & SistaV1
>> extPushIntegerBytecode & extUnconditionalJump in interpreter and Cogit
>> using bitShift: 8 instead of << 8.  Slang seems to generate the correct
>> code with bitAShift:, but not with <<.
>>
>>
> Hi Eliot,
> it would have worked if you would have used bitOr: instead of +
> I'd say bitOr: better fits the intention:
> you want to assemble the bits, you do not really want to perform
> arithmetic here.
>

OK, but in 2's complement they do the same thing, so + sdeems just as good
for me.


>
> Also, the result we are after is a signed int, so consider that << is
> doing the right thing, it gives you a signed int.
>

That's not what Slang generated.  It generated a cast to usqInt.


> The expression you propose is unsigned. It works OK in this context,
> because we assign immediately to a signed int.
> But for a more general usage, it could deceive the inliner (for example if
> variable is automatically typed or eliminated...)
>

Well, we have signed right shifts, but no signed left shifts.  What I
really want is a signed left shift but chose not to introduce e.g. <<<.
For me I would make left shift maintain the signedness of the left-hand,
generating a warning if the type couldn't be determined.  That's closest to
what Smalltalk does.


=============== Diff against VMMaker.oscog-eem.1971 ===============
>>
>> Item was changed:
>>   ----- Method: SimpleStackBasedCogit>>genExtPushIntegerBytecode (in
>> category 'bytecode generators') -----
>>   genExtPushIntegerBytecode
>>         "NewsqueakV4:   229             11100101        iiiiiiii
>> Push Integer #iiiiiiii (+ Extend B * 256, where bbbbbbbb = sddddddd, e.g.
>> -32768 = i=0, a=0, s=1)
>>         SistaV1:                232             11101000        iiiiiiii
>>       Push Integer #iiiiiiii (+ Extend B * 256, where bbbbbbbb = sddddddd,
>> e.g. -32768 = i=0, a=0, s=1)"
>>         | value |
>> +       value := byte1 + ((extB > 127 ifTrue: [extB - 256] ifFalse:
>> [extB]) bitShift: 8).
>> -       value := byte1 + ((extB > 127 ifTrue: [extB - 256] ifFalse:
>> [extB]) << 8).
>>         extB := 0.
>>         ^self genPushLiteral: (objectMemory integerObjectOf: value)!
>>
>> Item was changed:
>>   ----- Method: SimpleStackBasedCogit>>genExtUnconditionalJump (in
>> category 'bytecode generators') -----
>>   genExtUnconditionalJump
>>         "242            11110010        i i i i i i i i Jump i i i i i i
>> i i (+ Extend B * 256, where bbbbbbbb = sddddddd, e.g. -32768 = i=0, a=0,
>> s=1)"
>>         | distance target |
>> +       distance := byte1 + ((extB > 127 ifTrue: [extB - 256] ifFalse:
>> [extB]) bitShift: 8).
>> -       distance := byte1 + ((extB > 127 ifTrue: [extB - 256] ifFalse:
>> [extB]) << 8).
>>         self assert: distance = (self v4: (self generatorAt: byte0)
>>                                                                 Long:
>> bytecodePC
>>                                                                 Branch:
>> (extA ~= 0 ifTrue: [1] ifFalse: [0]) + (extB ~= 0 ifTrue: [1] ifFalse: [0])
>>                                                                 Distance:
>> methodObj).
>>         extB := 0.
>>         target := distance + 2 + bytecodePC.
>>         distance < 0 ifTrue:
>>                 [^self genJumpBackTo: target].
>>         self genJumpTo: target.
>>         "The bytecode must be mapped since it can be either forward or
>> backward, and
>>           backwards branches must be mapped. So if forward, we need to
>> map."
>>         self annotateBytecode: self lastOpcode.
>>         ^0!
>>
>> Item was changed:
>>   ----- Method: SimpleStackBasedCogit>>v4:Long:Branch:Distance: (in
>> category 'span functions') -----
>>   v4: descriptor Long: pc Branch: nExts Distance: aMethodObj
>>         "242            11110010        i i i i i i i i Jump i i i i i i
>> i i (+ Extend B * 256, where bbbbbbbb = sddddddd, e.g. -32768 = i=0, a=0,
>> s=1)"
>>         <var: #descriptor type: #'BytecodeDescriptor *'>
>>         | extBValue |
>>         self assert: nExts >= 0.
>>         self parseV4Exts: nExts priorTo: pc in: aMethodObj into: [:ea
>> :eb| extBValue := eb].
>>         ^(objectMemory fetchByte: pc + 1 ofObject: aMethodObj)
>> +       + (extBValue bitShift: 8)!
>> -       + (extBValue << 8)!
>>
>> Item was changed:
>>   ----- Method: StackInterpreter>>extPushIntegerBytecode (in category
>> 'stack bytecodes') -----
>>   extPushIntegerBytecode
>>         "229            11100101        i i i i i i i i Push Integer
>> #iiiiiiii (+ Extend B * 256, where bbbbbbbb = sddddddd, e.g. -32768 = i=0,
>> a=0, s=1)"
>>         | value |
>> +       value := self fetchByte + ((extB > 127 ifTrue: [extB - 256]
>> ifFalse: [extB]) bitShift: 8).
>> -       value := self fetchByte + ((extB > 127 ifTrue: [extB - 256]
>> ifFalse: [extB]) << 8).
>>         self fetchNextBytecode.
>>         extB := 0.
>>         self internalPush: (objectMemory integerObjectOf: value)!
>>
>> Item was changed:
>>   ----- Method: StackInterpreter>>extUnconditionalJump (in category
>> 'jump bytecodes') -----
>>   extUnconditionalJump
>>         "242            11110010        i i i i i i i i Jump i i i i i i
>> i i (+ Extend B * 256, where bbbbbbbb = sddddddd, e.g. -32768 = i=0, a=0,
>> s=1)"
>>         | byte offset |
>>         byte := self fetchByte.
>> +       offset := byte + ((extB > 127 ifTrue: [extB - 256] ifFalse:
>> [extB]) bitShift: 8).
>> -       offset := byte + ((extB > 127 ifTrue: [extB - 256] ifFalse:
>> [extB]) << 8).
>>         extB := 0.
>>         localIP := localIP + offset.
>>         self ifBackwardsCheckForEvents: offset.
>>         self fetchNextBytecode!
>>
>>
>
>


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