[LLVMdev] about AnalysisUsage

[Chris Lattner]

On Fri, 29 Apr 2005, Sameer D. Sahasrabuddhe wrote:

> On Fri, Apr 29, 2005 at 08:10:17AM -0500, Chris Lattner wrote:
>
>>     AU.addRequiredID(LoopSimplifyID);
>>
>> "LoopSimplifyID" is a marker that is used to identify the pass, which is
>> exported from the .cpp file.
>
> I'll have to declare a PassInfo* called LoopSimplifyID inside
> namespace llvm, in order for that to compile correctly, right? I was
> wondering why not simply make it available for AU.addRequired instead.

It's already available by #including llvm/Transforms/Scalar.h.  For 
example see lib/Transforms/Scalar/LICM.cpp which requires loop simplify.

> I guess that AU.addRequired will not be sufficient because
> LoopSimplify is not an analysis that the PassManager can update when
> some other pass changes the CFG. So the only way for my pass to ensure
> that the loops are simplified is to explicitly invoke LoopSimplify ...
> is that correct?

We could definitely expose the pass class itself, but there are no 
implementation details or any other state that is useful.  Following the 
principle of information hiding, it seemed better just to expose the fact 
that we need the loops to be simplified rather than to tightly couple the 
users to the class definition.

-Chris

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