[Performance Hints] Restrict analysis to primary source files

When Swift code is compiled or analyzed under whole module compilation mode, the
compiler receives all the imported files along with the source file being
compiled (the primary source file). Currently, the performance assistant runs on
all of these files, repeating analysis work, since the non-primary source files
will be treated as primary in separate runs. Furthermore, declarations in
non-primary source files don't have type information, leading to crashes, since
performance hint generation require type information. In this commit, we have
restricted the performance hint analysis to run only on primary source files.

Author: aviralg

lib/Sema/PerformanceHints.cpp

@@ -168,6 +168,8 @@ class PerformanceHintDiagnosticWalker final : public ASTWalker {
 
 evaluator::SideEffect EmitPerformanceHints::evaluate(Evaluator &evaluator,
                                                      SourceFile *SF) const {
+  assert(SF->isPrimary() &&
+         "Performance hints can only be generated for primary source files!");
   PerformanceHintDiagnosticWalker::check(SF);
   return {};
 }

lib/Sema/TypeChecker.cpp

@@ -385,7 +385,7 @@ TypeCheckPrimaryFileRequest::evaluate(Evaluator &eval, SourceFile *SF) const {
       CheckInconsistentWeakLinkedImportsRequest{SF->getParentModule()}, {});
 
   // Opt-in performance hint diagnostics for performance-critical code.
-  if (performanceHintDiagnosticsEnabled(Ctx))
+  if (performanceHintDiagnosticsEnabled(Ctx) && SF->isPrimary())
     evaluateOrDefault(Ctx.evaluator, EmitPerformanceHints{SF}, {});
 
   // Perform various AST transforms we've been asked to perform.

test/PerformanceHints/primary-file.swift

@@ -0,0 +1,15 @@
+// RUN: %empty-directory(%t)
+// RUN: %{python} %utils/split_file.py -o %t %s
+// RUN: %target-swift-frontend -typecheck -primary-file %t/a.swift %t/b.swift -Wwarning PerformanceHints -diagnostic-style llvm -verify
+
+// BEGIN a.swift
+func foo() -> [Int] {  // expected-warning {{Performance: 'foo()' returns an array, leading to implicit copies. Consider using an 'inout' parameter instead.}}
+  return [1, 2, 3, 4, 5, 6]
+}
+
+// BEGIN b.swift
+protocol Animal {
+  var Name: String { get }
+}
+
+typealias AnyAnimal = any Animal