[LLVMdev] Analysis Passes

[Marc de Kruijf]

Could somebody please explain exactly what an "analysis pass" is?  I've
spent some time trying to understand this and I just don't get it.  Right
now my understanding is the following:  if a pass is an "analysis" pass, the
"print" function is called when giving the "-analyze" switch to opt.  Is
there more to it than that?

If I've got it wrong, here are some potentially clarifying questions:

1.  If a pass is an analysis pass, does it necessarily not alter the CFG?
2.  Does a pass need to be an analysis pass if it is used by another pass
calling getAnalysisUsage?
3.  How does whether or not a pass is an analysis pass or not affect the
pass's execution?

Marc
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