Re: Re: Re: Fwd: Re: More precise values in Analyzer

Le 16/07/2010 00:25, Joshua Warner a écrit :
> Eugene,
>
> I looked at SourceValue and SourceInterpreter, and it appears that 
> when a SourceValue comes from a parameter (or this pointer or 
> exception variable), it just reports the source as an empty set.
>
> Maybe some more background will help:
>
> The goal of this project is to make an optimizing ahead-of-time 
> compiler for the Avian virtual machine (oss.readytalk.com 
> <http://oss.readytalk.com>).  I want to take in a list of class files, 
> and spit out lots of llvm assembly.  The input and output would look 
> roughly like this (as part of a larger program):
>
> [javap style assembly]
> public int returnFirstParameter(int i)
> Code:
> 0:  iload 1
> 1:  ireturn
>
> [llvm assembly]
> define i32 @TestClasS_returnFirstParameter(i32 %i) nounwind {
> entry:
>   ret i32 %i;
> }
>
> LLVM (low-level virtual machine, llvm.org <http://llvm.org> - 
> essentially a compiler / optimizer infrastructure) stores its IR 
> completely in SSA form.  This requires naming the parameters to a 
> method, and tracking their uses.
>
> Just using the variable slot number to detect a parameter may not be 
> sufficient, because a java program could (though they don't usually) 
> decide to overwrite its own arguments.  In this case, this 
> overwritting value would be detected as the original parameter, when 
> in fact it is a new value.  I need something that is correct 100% of 
> the time, not just in the (very) common cases.

Why not tracking store ? i.e each store create a new variable.
This is the usual algorithm to convert into SSA form.

>
> Even if this would work, I don't see a way to get the specific local 
> variables index that a certain value originated in (particularly in 
> the case of Values allocated with Interpreter.newValue(...).  Am I 
> missing something?
>
> I've read significant portions of "ASM 3.0 A Java bytecode engineering 
> library <http://download.forge.objectweb.org/asm/asm-guide.pdf>", and 
> I didn't see anything that could help me with this particular 
> problem.  Do you have a certain section that you are thinking of?
>
> Thanks,
>
> Joshua

There is also already a llvm project that implement a basic bytecode 
frontend:
https://llvm.org/svn/llvm-project/java/trunk/docs/java-frontend.txt

cheers,
Rémi

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