Serialization and deserialization support for layout requirements.

include/swift/Serialization/ModuleFormat.h

@@ -252,6 +252,18 @@ enum GenericRequirementKind : uint8_t {
 };
 using GenericRequirementKindField = BCFixed<2>;
 
+// These IDs must \em not be renumbered or reordered without incrementing
+// VERSION_MAJOR.
+enum LayoutRequirementKind : uint8_t {
+  UnknownLayout = 0,
+  TrivialOfExactSize = 1,
+  TrivialOfAtMostSize = 2,
+  Trivial = 3,
+  RefCountedObject = 4,
+  NativeRefCountedObject = 5,
+};
+using LayoutRequirementKindField = BCFixed<3>;
+
 // These IDs must \em not be renumbered or reordered without incrementing
 // VERSION_MAJOR.
 enum Associativity : uint8_t {
@@ -1102,6 +1114,14 @@ namespace decls_block {
     TypeIDField                  // same-type; one for value witness marker)
   >;
 
+  using LayoutRequirementLayout = BCRecordLayout<
+    LAYOUT_REQUIREMENT,
+    LayoutRequirementKindField,  // requirement kind
+    TypeIDField,                 // type being constrained
+    BCFixed<24>,                 // size
+    BCFixed<32>                  // alignment
+  >;
+
   /// Specifies the private discriminator string for a private declaration. This
   /// identifies the declaration's original source file in some opaque way.
   using PrivateDiscriminatorLayout = BCRecordLayout<