[LLVMdev] llvm-java

[Fernando Magno Quintao Pereira]

It is certainly useful in other optimizations:

1) Type check elimination in dynamically typed languages: if you know that 
i is int, then you don't have to check its type before performing integer 
operations on it.

2) Constant propagation:
if (!i) then x = i else x = 13 => if (i) then x = 0 else x = 13

3) Bitwidth analysis:
if (x < 128) then ... => if (x < 128) then "x has at most 7 bits"

4) Dead code elimination:
if (x > 10) then if (x < 9) then... else S => if (x <= 10) then S

etc

That is why we need a modular design: a client pass gives some 
variables to the SSI module, which will convert those variables to SSI.

Fernando

> Dear All,
>
> Perhaps a related issue is whether SSI form is valuable for other
> transformations or analysis passes.  If it is, then it might be worth
> building general SSA->SSI and SSI->SSA transforms so that any LLVM pass
> wishing to have the code in SSI form can do so.
>
> -- John T.
>
> Nicolas Geoffray wrote:
>> [snip]
>>
>> OK. Is it possible to do SSI Transformation --> Array Bounds
>> Optimization --> SSI undo Transformation? Or would that render useless
>> the speed gained with O(1) queries?
>>
>> I think the LLVM philosophy is to favor O(1) queries, and the SSI is
>> probably not increasing the program size that much. Besides, if we can
>> undo, that's the approach I'd recommend.
>>
>> Thanks,
>> Nicolas
>>
>>
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