[Vm-dev] Fix for label duplications in Slang's case expansion

Guillermo Polito guillermopolito at gmail.com
Fri Jan 24 15:58:55 UTC 2020


Of course, for the test to run, it needs these other two methods :)

methodWithCases

	self dispatchOn: currentBytecode in: #( expanded expanded expanded )


expanded
	<expandCases>
	^ (currentBytecode bitAnd: 15) << 2

> El 24 ene 2020, a las 16:57, Guillermo Polito <guillermopolito at gmail.com> escribió:
> 
> Hi all,
> 
> with Federico, a student from Argentina, we have found a problem in the label generation inside expanded cases in Slang.
> The problem comes from the fact that expanded cases (using the pragma <expandCase>, typically used for bytecodes), duplicate the entire tree with its inlines too, also duplicating labels inside it, which generates compilation errors due to label redefinition.
> 
> I’ve written a test for the case:
> 
> 	| translation method codeGenerator |
> 	method := self class >> #methodWithCases.
> 	translation := method asTranslationMethodOfClass: TMethod.
> 	codeGenerator := CCodeGeneratorGlobalStructure new.
> 	codeGenerator addMethod: ((self class >> #expanded) asTranslationMethodOfClass: TMethod).
> 	codeGenerator addMethod: translation.
> 
> 	codeGenerator prepareMethods.
> 	codeGenerator inlineDispatchesInMethodNamed: #methodWithCases localizingVars: #().
> 	self assert: translation statements first cases first statements last isLabel.
> 	self assert: translation statements first cases third statements last isLabel.
> 
> 	self
> 		deny: translation statements first cases first statements last label
> 		equals: translation statements first cases third statements last label.
> 
> 
> 
> And I’ve made a fix that renames labels on each expanded case, to ensure non shared labels are unique within each case.
> I’ve put it in vmmaker's inbox. I hope there are no problems regarding timestamps, I’ve been careful about that ^^.
> 
> Commit + commit message below:
> 
> Name: VMMaker.oscog-GuillermoPolito.2676
> Author: GuillermoPolito
> Time: 24 January 2020, 4:27:09.847804 pm
> UUID: 49bcc820-4659-0d00-b258-043c01043dd2
> Ancestors: VMMaker.oscog-eem.2675
> 
> Fix in slang case statement expansion labels.
> 
> During expansion in case statements, trees are duplicated and expanded.
> However, labels inside those trees are duplicated using the same name, producing compilation problems due to label conflicts/redefinition.
> 
> This fix uses #renameLabelsForInliningInto: when expanding case statements to rewrite labels generating unique labels.
> 
> Cheers,
> Guille



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