[clang-tidy] Don't warn implicit variables in peformance-unnecessary-copy-initialization.

Summary:

This will prevent the check warning the variables which have been
implicitly added by compiler, like the following case (in for-range loop):

  the variable '__end' is copy-constructed from a const reference...

Reviewers: alexfh

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D25911

llvm-svn: 286186

clang-tools-extra/clang-tidy/performance/UnnecessaryCopyInitialization.cpp

@@ -57,6 +57,7 @@ void UnnecessaryCopyInitialization::registerMatchers(MatchFinder *Finder) {
                    declStmt(
                        has(varDecl(hasLocalStorage(),
                                    hasType(matchers::isExpensiveToCopy()),
+                                   unless(isImplicit()),
                                    hasInitializer(
                                        cxxConstructExpr(
                                            hasDeclaration(cxxConstructorDecl(

clang-tools-extra/test/clang-tidy/performance-unnecessary-copy-initialization.cpp

@@ -368,3 +368,22 @@ void WarningOnlyMultiDeclStmt() {
   // CHECK-MESSAGES: [[@LINE-1]]:23: warning: local copy 'copy' of the variable 'orig' is never modified; consider avoiding the copy [performance-unnecessary-copy-initialization]
   // CHECK-FIXES: ExpensiveToCopyType copy = orig, copy2;
 }
+
+class Element {};
+class Container {
+public:
+  class Iterator {
+  public:
+    void operator++();
+    Element operator*();
+    bool operator!=(const Iterator &);
+    WeirdCopyCtorType c;
+  };
+  const Iterator &begin() const;
+  const Iterator &end() const;
+};
+
+void implicitVarFalsePositive() {
+  for (const Element &E : Container()) {
+  }
+}