[PATCH] D24441: [AA] Add the notion of target-specific alias analyses.

[Justin Lebar via llvm-commits]

jlebar created this revision.
jlebar added a reviewer: chandlerc.
jlebar added subscribers: hfinkel, llvm-commits.
Herald added subscribers: mgorny, beanz, mehdi_amini, jholewinski.

This allows the TTI to specify an alias analysis specifically for its
target.

Example usage (in MyTargetTTI.cpp):

  class MyTargetAAresult : public AAResultBase<MyTargetAAResult> { ... };

  class MyTargetAAResultProvider : public AAResultProvider {
    MyTargetAAResult Result;
  public:
    void addAAResult(AAResults &AAR) override {
      // AAR only keeps a reference to Result; we have to keep it alive.
      AAR.addResult(Result);
    }
  };

  std::unique_ptr<AAResultProvider>
  MyTargetTTI::getAAResultProvider(const Function *) {
    return make_unique<MyTargetAAResultProvider>();
  }

A simpler API (that doesn't end up working) would be to have a different
function on TTI:

  TargetTransformInfo::addAAResult(const Function *, AAResults &)

This would also more closely mirror how external AAs work.

The problem with this is that AAResults::addAAResult takes a reference
to the result it's given, so that object must be stored somewhere.  With
the external AA framework, the external target is expected to register a
pass and store its AAResult in that pass.  But that doesn't work for our
purposes; we have no way to get the TTI to register a pass (nor do I
think that's desirable).

So instead, we essentially have the TTI return a closure which stores
the AAResult and provides access to it via
AAResultProvider::addAAResult.  We use a custom class rather than
std::function for this closure because std::functions must be copyable,
but it's natural for this closure to capture non-copyable objects.

https://reviews.llvm.org/D24441

Files:
  llvm/include/llvm/Analysis/AliasAnalysis.h
  llvm/include/llvm/Analysis/TargetTransformInfo.h
  llvm/include/llvm/Analysis/TargetTransformInfoImpl.h
  llvm/include/llvm/InitializePasses.h
  llvm/lib/Analysis/AliasAnalysis.cpp
  llvm/lib/Analysis/TargetTransformInfo.cpp
  llvm/lib/CodeGen/TargetPassConfig.cpp
  llvm/lib/Target/NVPTX/CMakeLists.txt
  llvm/lib/Transforms/IPO/PassManagerBuilder.cpp

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