IRGen/Runtime: Use only the 'layout' subset of the vwtable to perform value type layout.

Full type metadata isn't necessary to calculate the runtime layout of a dependent struct or enum; we only need the non-function data from the value witness table (size, alignment, extra inhabitant count, and POD/BT/etc. flags). This can be generated more efficiently than the type metadata for many types--if we know a specific instantiation is fixed-layout, we can regenerate the layout information, or if we know the type has the same layout as another well-known type, we can get the layout from a common value witness table. This breaks a deadlock in most (but not all) cases where a value type is recursive using classes or fixed-layout indirected structs like UnsafePointer. rdar://problem/19898165

This time, factor out the ObjC-dependent parts of the tests so they only run with ObjC interop.

Swift SVN r30266

lib/IRGen/IRGenModule.h

@@ -24,6 +24,7 @@
 #include "swift/Basic/SuccessorMap.h"
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/DenseSet.h"
+#include "llvm/ADT/Hashing.h"
 #include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringMap.h"
@@ -105,6 +106,7 @@ namespace irgen {
   class ClangTypeConverter;
   class EnumImplStrategy;
   class ExplosionSchema;
+  class FixedTypeInfo;
   class FormalType;
   class IRGenDebugInfo;
   class LinkEntity;
@@ -547,9 +549,20 @@ private:
     /// protocol record.
     llvm::WeakVH ref;
   };
-  
+
   llvm::DenseMap<ProtocolDecl*, ObjCProtocolPair> ObjCProtocols;
-  llvm::SmallVector<ProtocolDecl*, 4> LazyObjCProtocolDefinitions;  
+  llvm::SmallVector<ProtocolDecl*, 4> LazyObjCProtocolDefinitions;
+
+  /// Uniquing key for a fixed type layout record.
+  struct FixedLayoutKey {
+    unsigned size;
+    unsigned numExtraInhabitants;
+    unsigned align: 16;
+    unsigned pod: 1;
+    unsigned bitwiseTakable: 1;
+  };
+  friend struct ::llvm::DenseMapInfo<swift::irgen::IRGenModule::FixedLayoutKey>;
+  llvm::DenseMap<FixedLayoutKey, llvm::Constant *> PrivateFixedLayouts;
 
   /// A mapping from order numbers to the LLVM functions which we
   /// created for the SIL functions with those orders.
@@ -630,7 +643,8 @@ public:
   void emitSILFunction(SILFunction *f);
   void emitSILWitnessTable(SILWitnessTable *wt);
   void emitSILStaticInitializer();
-  
+  llvm::Constant *emitFixedTypeLayout(CanType t, const FixedTypeInfo &ti);
+
   void emitNestedTypeDecls(DeclRange members);
   void emitClangDecl(clang::Decl *decl);
   void finalizeClangCodeGen();
@@ -728,4 +742,33 @@ public:
 } // end namespace irgen
 } // end namespace swift
 
+namespace llvm {
+
+template<>
+struct DenseMapInfo<swift::irgen::IRGenModule::FixedLayoutKey> {
+  using FixedLayoutKey = swift::irgen::IRGenModule::FixedLayoutKey;
+
+  static inline FixedLayoutKey getEmptyKey() {
+    return {0, 0xFFFFFFFFu, 0, 0, 0};
+  }
+
+  static inline FixedLayoutKey getTombstoneKey() {
+    return {0, 0xFFFFFFFEu, 0, 0, 0};
+  }
+
+  static unsigned getHashValue(const FixedLayoutKey &key) {
+    return hash_combine(key.size, key.numExtraInhabitants, key.align,
+                        (bool)key.pod, (bool)key.bitwiseTakable);
+  }
+  static bool isEqual(const FixedLayoutKey &a, const FixedLayoutKey &b) {
+    return a.size == b.size
+      && a.numExtraInhabitants == b.numExtraInhabitants
+      && a.align == b.align
+      && a.pod == b.pod
+      && a.bitwiseTakable == b.bitwiseTakable;
+  }
+};
+
+}
+
 #endif