AST: Introduce a ValueDecl convenience for looking up the renamed decl.

Wrap `RenamedDeclRequest` instead of evaluating it directly.

Author: tshortli

include/swift/AST/Decl.h

@@ -3262,6 +3262,10 @@ class ValueDecl : public Decl {
   /// @_dynamicReplacement(for: ...), compute the original declaration
   /// that this declaration dynamically replaces.
   ValueDecl *getDynamicallyReplacedDecl() const;
+
+  /// Performs a request to look up the decl that this decl has been renamed to
+  /// if `attr` indicates that it has been renamed.
+  ValueDecl *getRenamedDecl(const AvailableAttr *attr) const;
 };
 
 /// This is a common base class for declarations which declare a type.

lib/AST/Decl.cpp

@@ -4231,6 +4231,11 @@ bool ValueDecl::canInferObjCFromRequirement(ValueDecl *requirement) {
   return false;
 }
 
+ValueDecl *ValueDecl::getRenamedDecl(const AvailableAttr *attr) const {
+  return evaluateOrDefault(getASTContext().evaluator,
+                           RenamedDeclRequest{this, attr}, nullptr);
+}
+
 SourceLoc Decl::getAttributeInsertionLoc(bool forModifier) const {
   // Some decls have a parent/child split where the introducer keyword is on the
   // parent, but the attributes are on the children. If this is a child in such
@@ -9259,8 +9264,7 @@ AbstractFunctionDecl *AbstractFunctionDecl::getAsyncAlternative() const {
     }
   }
 
-  auto *renamedDecl = evaluateOrDefault(
-      getASTContext().evaluator, RenamedDeclRequest{this, avAttr}, nullptr);
+  auto *renamedDecl = getRenamedDecl(avAttr);
   auto *alternative = dyn_cast_or_null<AbstractFunctionDecl>(renamedDecl);
   if (!alternative || !alternative->hasAsync())
     return nullptr;

lib/PrintAsClang/DeclAndTypePrinter.cpp

@@ -1835,8 +1835,7 @@ class DeclAndTypePrinter::Implementation
                           const ValueDecl *D, bool includeQuotes) {
     assert(!AvAttr->Rename.empty());
 
-    auto *renamedDecl = evaluateOrDefault(
-        getASTContext().evaluator, RenamedDeclRequest{D, AvAttr}, nullptr);
+    auto *renamedDecl = D->getRenamedDecl(AvAttr);
     if (renamedDecl) {
       assert(shouldInclude(renamedDecl) &&
              "ObjC printer logic mismatch with renamed decl");