[Newcompiler] How to decompile #while{True,False}

Wed Sep 5 12:45:58 UTC 2007

Hi Klaus

Thanks

On Sep 5, 2007, at 7:12 AM, Klaus D. Witzel wrote:

> Hi Math,
>
> when the old decompiler decompiles #sweep: it finds

He can find the #ifTrue:ifFalse: because he keep the push true or false.

>
> [(ind := ind + 1) > list size
> 		ifTrue: [false]
> 		ifFalse: [(parts at: ind) first asLowercase = projectName
> 				and: [versions
> 						add: (parts at: ind).
> 					true]]] whileTrue.
>
> which is what can be expected, the inner #ifTrue:ifFalse: is  
> rendered as an #and: (... ifFalse: [false]).
>
> The place where a #not message send is inserted is  
> IRDecompiler>>#endAndOr2: (reducing the jump structures).

Yes I know that but I don't know where the NewCompiler remove the  
pushConstant: true.
It should be somewhere where when the IRJumpIf is interpret but I  
cant find it.

The old compiler don't  remove the push true:

> 199 <14> pushTemp: 4
> 200 <76> pushConstant: 1
> 201 <B0> send: +
> 202 <81 44> storeIntoTemp: 4
> 204 <12> pushTemp: 2
> 205 <C2> send: size
> 206 <B3> send: >
> 207 <9A> jumpFalse: 211 "First ifTrue ifFalse"
>
> ''(ind := ind + 1) > list size  ifTrue:  [false]"
> 208 <72> pushConstant: false
> 209 <A4 15> jumpTo: 232
>
> ''(ind := ind + 1) > list size  ifFalse:  [...]"
> 211 <13> pushTemp: 3
> 212 <14> pushTemp: 4
> 213 <C0> send: at:
> 214 <83 15> send: first
> 216 <83 14> send: asLowercase
> 218 <16> pushTemp: 6
> 219 <B6> send: =
> 220 <AC 09> jumpFalse: 231   "Second ifTrue ifFalse"
>
> "(parts at: ind) first asLowercase = projectName ifTrue: [..]"
> 222 <17> pushTemp: 7
> 223 <13> pushTemp: 3
> 224 <14> pushTemp: 4
> 225 <C0> send: at:
> 226 <83 37> send: add:
> 228 <87> pop
> 229 <71> pushConstant: true
> 230 <90> jumpTo: 232
>
> "(parts at: ind) first asLowercase = projectName ifFalse: [false]"
> 231 <72> pushConstant: false
> 232 <99> jumpFalse: 235

You can see the 208 229 and 231 bytecode. There are remove with the  
NewCompiler.
I don't think that is usefull to make dose optimization.

	Mth

>
> HTH.
>
> Cheers
> Klaus
>
> On Wed, 05 Sep 2007 00:06:55 +0200, Mathieu Suen wrote:
>
>> Hi
>>
>> In a very particular case the compiler optimize the #whileTrue in  
>> a way that the Decompiler can't find the roght code.
>>
>> This particular case is:
>>
>> [
>> self somthings
>>
>> aTest
>> 	ifTrue:[ok anOtherThings
>> 		ifTrue:[here doSomthings. true]
>> 		ifFalse:[false]]
>> 	ifFalse:[false]
>> ] whileTrue
>>
>> The typical exemple is from  Project class>>#sweep: :
>>
>>> 		…
>>> 		[(ind _ ind + 1) > list size
>>> 			ifFalse: [(parts at: ind) first asLowercase = projectName
>>> 				ifTrue: [versions add: (parts at: ind).  true]
>>> 				ifFalse: [false]]
>>> 			ifTrue: [false]] whileTrue.
>>> 		…
>>
>> The corresponding bytecode is:
>>
>>> 199 <14> pushTemp: 4
>>> 200 <76> pushConstant: 1
>>> 201 <B0> send: +
>>> 202 <81 44> storeIntoTemp: 4
>>> 204 <12> pushTemp: 2
>>> 205 <C2> send: size
>>> 206 <B3> send: >
>>> 207 <A8 16> jumpTrue: 231
>>>
>>> 209 <13> pushTemp: 3
>>> 210 <14> pushTemp: 4
>>> 211 <C0> send: at:
>>> 212 <83 14> send: first
>>> 214 <83 15> send: asLowercase
>>> 216 <16> pushTemp: 6
>>> 217 <B6> send: =
>>> 218 <AC 0B> jumpFalse: 231
>>>
>>> 220 <17> pushTemp: 7
>>> 221 <13> pushTemp: 3
>>> 222 <14> pushTemp: 4
>>> 223 <C0> send: at:
>>> 224 <83 37> send: add:
>>> 226 <87> pop
>>> 227 <71> pushConstant: true
>>> 228 <99> jumpFalse: 231
>>>
>>> 229 <A3 E0> jumpTo: 199
>>
>>
>> So the first #ifFlase:ifTrue: has been compact to a single jump:
>> 207 <A8 16> jumpTrue: 231
>>
>> This avoid pushing false and make an unconditional jump to the end  
>> of the nearly end of the block.
>> We also have the same optimazation for the inner #iTrue:ifFalse:  
>> message (i.e. at bytecode: 218 and: 228).
>>
>> We can rewrite the code to produce the same flow :
>>
>>> [((ind _ ind + 1) > list size) not
>>> 			or: [(parts at: ind) first asLowercase = projectName
>>> 				and: [versions add: (parts at: ind)]]]] whileTrue
>>
>> This is what the decompiler found out.
>> But this do not produce the same bytecode:
>>
>>> 203 <14> pushTemp: 4
>>> 204 <76> pushConstant: 1
>>> 205 <B0> send: +
>>> 206 <81 44> storeIntoTemp: 4
>>> 208 <12> pushTemp: 2
>>> 209 <C2> send: size
>>> 210 <B3> send: >
>>> 211 <83 18> send: not
>>> 213 <A8 12> jumpTrue: 233
>>>
>>> 215 <13> pushTemp: 3
>>> 216 <14> pushTemp: 4
>>> 217 <C0> send: at:
>>> 218 <83 14> send: first
>>> 220 <83 15> send: asLowercase
>>> 222 <16> pushTemp: 6
>>> 223 <B6> send: =
>>> 224 <AC 09> jumpFalse: 235
>>>
>>> 226 <17> pushTemp: 7
>>> 227 <13> pushTemp: 3
>>> 228 <14> pushTemp: 4
>>> 229 <C0> send: at:
>>> 230 <83 37> send: add:
>>> 232 <99> jumpFalse: 235
>>>
>>> 233 <A3 E0> jumpTo: 203
>>
>> The only difference is in the bytecode 211 and 213:
>> A "send: not" is added and the jump don't have the same destination.
>>
>> The old compiler dose not make this smart optimization.
>> So I have several  question.
>>
>> Do we want the decompiler produce different bytecode (i.e. adding  
>> a "send: not"…)?
>> Should we do such optimization? (IMO I don't thinks so.)
>> where dose the optimization take place? I can't figure out where  
>> it is. I get lost inside ASTTranslator and IRTranslator.
>>
>>
>> Thanks
>>
>> 	Mth
>>
>>
>>
>
>

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