Add an "addUsedAAAnalyses" helper function

[sanjoy]

Summary

Passes that call getAnalysisIfAvailable<T> also need to call
addUsedIfAvailable<T> in getAnalysisUsage to indicate to the
legacy pass manager that it uses T. This contract was being
violated by passes that used createLegacyPMAAResults. This change
fixes this by exposing a helper in AliasAnalysis.h,
addUsedAAAnalyses, that is complementary to createLegacyPMAAResults
and does the right thing when called from getAnalysisUsage.

[chandlerc]

LGTM, minor suggestion below.

Not a huge fan of the name, but no better ideas, and it doesn't matter much.

lib/Analysis/AliasAnalysis.cpp

568–572

Add a comment here and above indicating how these should be kept in sync? Minor.

include/llvm/Analysis/AliasAnalysis.h

 /// function, and the AAResults object to populate. This should be used when
 /// setting up a custom pass pipeline to inject a hook into the AA results.
 ImmutablePass *createExternalAAWrapperPass(
     std::function<void(Pass &, Function &, AAResults &)> Callback);
 
 /// A helper for the legacy pass manager to create a \c AAResults
 /// object populated to the best of our ability for a particular function when
 /// inside of a \c ModulePass or a \c CallGraphSCCPass.
+///
+/// If a \c ModulePass or a \c CallGraphSCCPass calls \p
+/// createLegacyPMAAResults, it also needs to call \p addUsedAAAnalyses in \p
+/// getAnalysisUsage.
 AAResults createLegacyPMAAResults(Pass &P, Function &F, BasicAAResult &BAR);
 
+/// A helper for the legacy pass manager to populate \p AU to add uses to make
+/// sure the analyses required by \p createLegacyPMAAResults are available.
+void addUsedAAAnalyses(AnalysisUsage &AU);
+
 } // End llvm namespace
 
 #endif

lib/Analysis/AliasAnalysis.cpp

bool llvm::isIdentifiedObject(const Value *V) {
   if (const Argument *A = dyn_cast<Argument>(V))
     return A->hasNoAliasAttr() || A->hasByValAttr();
   return false;
 }
 
 bool llvm::isIdentifiedFunctionLocal(const Value *V) {
   return isa<AllocaInst>(V) || isNoAliasCall(V) || isNoAliasArgument(V);
 }
+
+void llvm::addUsedAAAnalyses(AnalysisUsage &AU) {
+  AU.addUsedIfAvailable<ScopedNoAliasAAWrapperPass>();
+  AU.addUsedIfAvailable<TypeBasedAAWrapperPass>();
+  AU.addUsedIfAvailable<objcarc::ObjCARCAAWrapperPass>();
+  AU.addUsedIfAvailable<GlobalsAAWrapperPass>();
+  AU.addUsedIfAvailable<CFLAAWrapperPass>();
+}

lib/Transforms/IPO/ArgumentPromotion.cpp

 
 namespace {
   /// ArgPromotion - The 'by reference' to 'by value' argument promotion pass.
   ///
   struct ArgPromotion : public CallGraphSCCPass {
     void getAnalysisUsage(AnalysisUsage &AU) const override {
       AU.addRequired<AssumptionCacheTracker>();
       AU.addRequired<TargetLibraryInfoWrapperPass>();
+      addUsedAAAnalyses(AU);
       CallGraphSCCPass::getAnalysisUsage(AU);
     }
 
     bool runOnSCC(CallGraphSCC &SCC) override;
     static char ID; // Pass identification, replacement for typeid
     explicit ArgPromotion(unsigned maxElements = 3)
         : CallGraphSCCPass(ID), maxElements(maxElements) {
       initializeArgPromotionPass(*PassRegistry::getPassRegistry());

lib/Transforms/IPO/FunctionAttrs.cpp

struct PostOrderFunctionAttrs : public CallGraphSCCPass {
   }
 
   bool runOnSCC(CallGraphSCC &SCC) override;
 
   void getAnalysisUsage(AnalysisUsage &AU) const override {
     AU.setPreservesCFG();
     AU.addRequired<AssumptionCacheTracker>();
     AU.addRequired<TargetLibraryInfoWrapperPass>();
+    addUsedAAAnalyses(AU);
     CallGraphSCCPass::getAnalysisUsage(AU);
   }
 
 private:
   TargetLibraryInfo *TLI;
 };
 }
 

lib/Transforms/IPO/Inliner.cpp

Inliner::Inliner(char &ID, bool InsertLifetime)
     : CallGraphSCCPass(ID), InsertLifetime(InsertLifetime) {}
 
 /// For this class, we declare that we require and preserve the call graph.
 /// If the derived class implements this method, it should
 /// always explicitly call the implementation here.
 void Inliner::getAnalysisUsage(AnalysisUsage &AU) const {
   AU.addRequired<AssumptionCacheTracker>();
   AU.addRequired<TargetLibraryInfoWrapperPass>();
+  addUsedAAAnalyses(AU);
   CallGraphSCCPass::getAnalysisUsage(AU);
 }
 
 
 typedef DenseMap<ArrayType*, std::vector<AllocaInst*> >
 InlinedArrayAllocasTy;
 
 /// If it is possible to inline the specified call site,

test/Analysis/alias-analysis-uses.ll

+; RUN: opt -debug-pass=Executions -globals-aa -functionattrs -disable-output < %s 2>&1 | FileCheck %s
+
+; CHECK: Executing Pass 'Globals Alias Analysis'
+; CHECK-NOT: Freeing Pass 'Globals Alias Analysis'
+; CHECK: Executing Pass 'Deduce function attributes'
+; CHECK: Freeing Pass 'Globals Alias Analysis'
+
+define void @test(i8* %p) {
+  ret void
+}