[PassManager] add setupAnalysis() to customize analyses registered in AnalysisManager

[fedor.sergeev]

Summary

One of the problems we have in customization of compilation pipeline is inability to construct
a customized analysis. Currently the only way to customize is to use a global option.
This does not work when per-compilation-context or per-module customization is required
(say, in JIT scenario).

Our current downstream need is to customize MemoryDependenceAnalysis with a different
block scan limit (to make compile-time/run-time tradeoff choice per individual JIT compilation).

Plan is to register analysis normally (through e.g. PassBuilder) and then run:

   FAM.setupAnalysis([](MemoryDependenceAnalysis& MDep) {
	 MDep.setDefaultBlockScanLimit(NonDefaultBlockScanLimit);
   }

[fedor.sergeev]

( D65805 is not really a parent, just showing parts of the changes supporting my usecase )

[fedor.sergeev]

and yes, this is more of a request for feedback than anything else...

[fedor.sergeev]

Had a chat with @ppf and there is a feeling that we are getting too many ways of customizing the pass (global command line options, explicit arguments passed to constructors, command line parsing etc).
If there is a need to customize passes/analyzes in a way similar to this patch then it should better be done by introducing a generic notion of PassSettings, handled in somewhat general manner through PassManager/PassBuilder.

Yet, as this particular patch and this particular need is concerned, colleague of mine just found a way to customize the analysis during the registration time.
Apparently, it is allowed to "pre-register" analysis by doing PM.addPass(ParticularAnalysis(parameters)) before registering all the "standard" PassRegistry.def analyses.
Then "standard" analysis will just be skipped (as AnalysisManager::addPass just skips analyses that are already registered).
This approach, while being a bit fragile to my tastes, completely solves our current need of customized analysis without any PassManager changes.

llvm/include/llvm/IR/PassManager.h

if (PassPtr)
       // Already registered this pass type!
       return false;
 
     // Construct a new model around the instance returned by the builder.
     PassPtr.reset(new PassModelT(PassBuilder()));
     return true;
   }
 
+  /// Setup an analysis pass previously registered with the manager.
+  ///
+  /// The parameter is a callable taking a pointer to \p PassT and returning bool.
+  /// This allows passing in a lambda to modify the analysis behavior after
+  /// it has been registered.
+  template <typename PassT, typename CallableT>
+  bool setupAnalysis(CallableT Setup) {
+    auto &PassPtr = AnalysisPasses[PassT::ID()];
+    if (PassPtr)
+      return Setup(PassPtr.get());
+    return false;
+  }
+
   /// Invalidate a specific analysis pass for an IR module.
   ///
   /// Note that the analysis result can disregard invalidation, if it determines
   /// it is in fact still valid.
   template <typename PassT> void invalidate(IRUnitT &IR) {
     assert(AnalysisPasses.count(PassT::ID()) &&
            "This analysis pass was not registered prior to being invalidated");
     invalidateImpl(PassT::ID(), IR);