[Serialization] Add support for @execution attribute

Author: xedin

lib/Serialization/Deserialization.cpp

@@ -5736,6 +5736,14 @@ llvm::Error DeclDeserializer::deserializeDeclCommon() {
       DeclAttribute *Attr = nullptr;
       bool skipAttr = false;
       switch (recordID) {
+      case decls_block::Execution_DECL_ATTR: {
+        unsigned behavior;
+        serialization::decls_block::ExecutionDeclAttrLayout::readRecord(
+            scratch, behavior);
+        Attr = new (ctx) ExecutionAttr(static_cast<ExecutionKind>(behavior),
+                                       /*Implicit=*/false);
+        break;
+      }
       case decls_block::ABI_DECL_ATTR: {
         bool isImplicit;
         DeclID abiDeclID;

lib/Serialization/ModuleFormat.h

@@ -58,7 +58,7 @@ const uint16_t SWIFTMODULE_VERSION_MAJOR = 0;
 /// describe what change you made. The content of this comment isn't important;
 /// it just ensures a conflict if two people change the module format.
 /// Don't worry about adhering to the 80-column limit for this line.
-const uint16_t SWIFTMODULE_VERSION_MINOR = 913; // @safe removal
+const uint16_t SWIFTMODULE_VERSION_MINOR = 914; // @execution attribute
 
 /// A standard hash seed used for all string hashes in a serialized module.
 ///
@@ -2355,6 +2355,11 @@ namespace decls_block {
     BCFixed<2>  // exclusivity mode
   >;
 
+  using ExecutionDeclAttrLayout = BCRecordLayout<
+    Execution_DECL_ATTR,
+    BCFixed<1>  // execution behavior kind
+  >;
+
   using ABIDeclAttrLayout = BCRecordLayout<
     ABI_DECL_ATTR,
     BCFixed<1>, // implicit flag

lib/Serialization/Serialization.cpp

@@ -2891,6 +2891,14 @@ class Serializer::DeclSerializer : public DeclVisitor<DeclSerializer> {
   }
 #include "swift/AST/DeclAttr.def"
 
+    case DeclAttrKind::Execution: {
+      auto *theAttr = cast<ExecutionAttr>(DA);
+      auto abbrCode = S.DeclTypeAbbrCodes[ExecutionDeclAttrLayout::Code];
+      ExecutionDeclAttrLayout::emitRecord(S.Out, S.ScratchRecord, abbrCode,
+                                          (unsigned)theAttr->getKind());
+      return;
+    }
+
     case DeclAttrKind::ABI: {
       auto *theAttr = cast<ABIAttr>(DA);
       auto abbrCode = S.DeclTypeAbbrCodes[ABIDeclAttrLayout::Code];