[deserialization] Add ClassDecl -> VTable map to SILModule.

Swift SVN r15545

include/swift/SIL/SILModule.h

@@ -125,6 +125,9 @@ private:
   llvm::DenseMap<const NormalProtocolConformance *, SILWitnessTable *>
   WitnessTableLookupCache;
 
+  /// Lookup table for SIL vtables from class decls.
+  llvm::DenseMap<const ClassDecl *, SILVTable *> VTableLookupTable;
+
   /// This is a cache of intrinsic Function declarations to numeric ID mappings.
   llvm::DenseMap<Identifier, IntrinsicInfo> IntrinsicIDCache;
 
@@ -314,6 +317,9 @@ public:
   std::pair<SILWitnessTable *, ArrayRef<Substitution>>
   lookUpWitnessTable(const ProtocolConformance *C);
 
+  /// Look up the VTable mapped to the given ClassDecl. Returns null on failure.
+  SILVTable *lookUpVTable(const ClassDecl *C);
+
   // Given a protocol conformance, attempt to create a witness table declaration
   // for it.
   SILWitnessTable *

lib/SIL/SILModule.cpp

@@ -479,3 +479,11 @@ void SILModule::linkAllWitnessTables() {
 void SILModule::linkAllVTables() {
   SILLoader->getAllVTables();
 }
+
+SILVTable *SILModule::lookUpVTable(const ClassDecl *C) {
+  auto R = VTableLookupTable.find(C);
+  if (R == VTableLookupTable.end())
+    return nullptr;
+
+  return R->second;
+}

lib/SIL/SILVTable.cpp

@@ -32,6 +32,7 @@ SILVTable *SILVTable::create(SILModule &M, ClassDecl *Class,
                          alignof(SILVTable));
   SILVTable *vt = ::new (buf) SILVTable(Class, Entries);
   M.vtables.push_back(vt);
+  M.VTableLookupTable[Class] = vt;
   return vt;
 }