[LLVMdev] implicit Pass Type dependencies between Analysis Pass and Transformation Pass

[Chuck Zhao]

i am organizing my LLVM Passes into an Analysis Pass and a few 
Optimization Passes, which takes the result from analysis pass to guide 
their transformations.

I found a surprising pass type dependency between the analysis pass and 
optimization passes.

E.g.
Analysis-Pass Type                Optimization-Pass Type                
         Status in Optimization Pass when adding the Analysis Pass
Function Pass                         Function Pass                    
                         Fine
Module Pass                          Module Pass                        
                        Fine

Module Pass                          Function Pass                    
                          Stuck
Function Pass                         Module Pass                        
                       Stuck

Function Pass                         Loop Pass                        
                            Stuck
Module Pass                          Loop Pass                        
                            Stuck
...

The "stuck" situation happens when calling 
AU.addRequired<AnalysisPass>() inside the OptimizationPass's 
getAnalysisUsage() function.
The opt tool seems to run into an infinite loop (on trivial testcases, 
which should finish in a flash of a second).

Seems the Pass type between Analysis Pass and Optimization Pass has to 
match.
I wonder if this is documented somewhere?
Is there a simple rule to guide this?

E.g.
if the Optimization Pass needs to be a LoopPass, does it mean the 
AnalysisPass _has to_ be a Loop Pass as well?


Thank you

Chuck