Merge metadata in the AliasSetTracker (and refactor merging)

[hfinkel]

Summary

Refactor how AA metadata merging is done, and allow the AliasSetTracker to merge non-equal metadata when merging access sets instead of just dropping all AA metadata when unequal.

I no longer have an in-tree test case for this change, so I'll need to try making one.

[reames]

include/llvm/IR/Metadata.h

549

Documentation?

lib/Analysis/TypeBasedAliasAnalysis.cpp

626

Given the implementation, I'd be tempted to have this return a new merged AAMDNodes structure. e.g.
AAMDNodes merge(const AAMDNodes &LHS, const AAMDNodes& RHS) { .. }

include/llvm/Analysis/AliasSetTracker.h

public:
 
     void updateSizeAndAAInfo(uint64_t NewSize, const AAMDNodes &NewAAInfo) {
       if (NewSize > Size) Size = NewSize;
 
       if (AAInfo == DenseMapInfo<AAMDNodes>::getEmptyKey())
         // We don't have a AAInfo yet. Set it to NewAAInfo.
         AAInfo = NewAAInfo;
       else if (AAInfo != NewAAInfo)
-        // NewAAInfo conflicts with AAInfo.
-        AAInfo = DenseMapInfo<AAMDNodes>::getTombstoneKey();
+        AAInfo.merge(NewAAInfo);
     }
 
     uint64_t getSize() const { return Size; }
 
     /// getAAInfo - Return the AAInfo, or null if there is no
     /// information or conflicting information.
     AAMDNodes getAAInfo() const {
       // If we have missing or conflicting AAInfo, return null.

include/llvm/IR/Metadata.h

struct AAMDNodes {
   bool operator==(const AAMDNodes &A) const {
     return TBAA == A.TBAA && Scope == A.Scope && NoAlias == A.NoAlias;
   }
 
   bool operator!=(const AAMDNodes &A) const { return !(*this == A); }
 
   explicit operator bool() const { return TBAA || Scope || NoAlias; }
 
+  void merge(const AAMDNodes &N);
+
   /// \brief The tag for type-based alias analysis.
   MDNode *TBAA;
 
   /// \brief The tag for alias scope specification (used with noalias).
   MDNode *Scope;
 
   /// \brief The tag specifying the noalias scope.
   MDNode *NoAlias;

lib/Analysis/TypeBasedAliasAnalysis.cpp

if (!Ret)
     return nullptr;
   // We need to convert from a type node to a tag node.
   Type *Int64 = IntegerType::get(A->getContext(), 64);
   Metadata *Ops[3] = {Ret, Ret,
                       ConstantAsMetadata::get(ConstantInt::get(Int64, 0))};
   return MDNode::get(A->getContext(), Ops);
 }
 
+void AAMDNodes::merge(const AAMDNodes &N) {
+  TBAA = MDNode::getMostGenericTBAA(TBAA, N.TBAA);
+  Scope = MDNode::getMostGenericAliasScope(Scope, N.Scope);
+  NoAlias = MDNode::intersect(NoAlias, N.NoAlias);
+}
+
 void Instruction::getAAMetadata(AAMDNodes &N, bool Merge) const {
-  if (Merge)
-    N.TBAA =
-        MDNode::getMostGenericTBAA(N.TBAA, getMetadata(LLVMContext::MD_tbaa));
-  else
-    N.TBAA = getMetadata(LLVMContext::MD_tbaa);
+  if (Merge) {
+    AAMDNodes M;
+    getAAMetadata(M);
+    N.merge(M);
+    return;
+  }
 
-  if (Merge)
-    N.Scope = MDNode::getMostGenericAliasScope(
-        N.Scope, getMetadata(LLVMContext::MD_alias_scope));
-  else
-    N.Scope = getMetadata(LLVMContext::MD_alias_scope);
-
-  if (Merge)
-    N.NoAlias =
-        MDNode::intersect(N.NoAlias, getMetadata(LLVMContext::MD_noalias));
-  else
-    N.NoAlias = getMetadata(LLVMContext::MD_noalias);
+  N.TBAA = getMetadata(LLVMContext::MD_tbaa);
 }