[LLVMdev] SCCP

[Nick Lewycky]

Chris Lattner wrote:
> On Tue, 9 May 2006, Nick Lewycky wrote:
> 
>>>> For an analysis pass, I'm interested in reading the lattice values
>>>> calculated by SCCP. Should I split the current SCCP optimization
>>>> into an
>>>> analysis piece and the optimization that depends on it, so that I can
>>>> use its analysis results?
>>>
>>>
>>> SCCP is already split into an SCCPSolver class that is used by the SCCP
>>> and IPSCCP classes.  You should just be able to use SCCPSolver.  Note
>>> that it is not a pass, just a class you can use.
>>
>>
>> Thanks. I thought SCCPSolver was just a helper. I suppose then I should
>> just move its class declaration into a header so it can be seen from
>> outside SCCP.cpp. Would creating a new include/llvm/Transforms/SCCP.h be
>> the right idea?
> 
> You could do that, but SCCPSolver isn't really useful to mainline LLVM
> for anything other than SCCP and IPSCCP, so we don't need it in a public
> header.  Out of curiosity, what are you looking to use the latice values
> for?  Why not just run SCCP and then look at the transformed code?

I was planning to write an analysis pass that checks the expression at
every conditional statement to see whether the value is underdefined or
not. This would be after SCCP and other optimizations have already been
run, so conditional statements with constant expressions would already
be eliminated. (Am I being silly? There isn't a pass to eliminate
conditionals on underdefined variables is there?)

It would be fine for my purposes to just copy the class declaration into
my own code.

Nick