Mark all subsequent decls used.

In the source

  static void f();
  static void f();
  template<typename T>
  static void g() {
    f();
  }
  static void f() {
  }
  void h() {
    g<int>();
  }

the call to f refers to the second decl, but it is only marked used at the end
of the translation unit during instantiation, after the third f decl has been
linked in.

With this patch we mark all subsequent decls used, so that it is easy to check
if a symbol is used or not.

llvm-svn: 171888

clang/lib/Sema/Sema.cpp

@@ -328,11 +328,7 @@ CastKind Sema::ScalarTypeToBooleanCastKind(QualType ScalarTy) {
 
 /// \brief Used to prune the decls of Sema's UnusedFileScopedDecls vector.
 static bool ShouldRemoveFromUnused(Sema *SemaRef, const DeclaratorDecl *D) {
-  // Template instantiation can happen at the end of the translation unit
-  // and it sets the canonical (first) decl to used. Normal uses set the last
-  // decl at the time to used and subsequent decl inherit the flag. The net
-  // result is that we need to check both ends of the decl chain.
-  if (D->isUsed() || D->getMostRecentDecl()->isUsed())
+  if (D->getMostRecentDecl()->isUsed())
     return true;
 
   if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(D)) {

clang/lib/Sema/SemaExpr.cpp

@@ -10495,7 +10495,18 @@ void Sema::MarkFunctionReferenced(SourceLocation Loc, FunctionDecl *Func) {
     if (old.isInvalid()) old = Loc;
   }
 
-  Func->setUsed(true);
+  // Normally the must current decl is marked used while processing the use and
+  // any subsequent decls are marked used by decl merging. This fails with
+  // template instantiation since marking can happen at the end of the file
+  // and, because of the two phase lookup, this function is called with at
+  // decl in the middle of a decl chain. We loop to maintain the invariant
+  // that once a decl is used, all decls after it are also used.
+  for (FunctionDecl *F = Func->getMostRecentDecl();;) {
+    F->setUsed(true);
+    if (F == Func)
+      break;
+    F = F->getPreviousDecl();
+  }
 }
 
 static void

clang/test/SemaCXX/warn-func-not-needed.cpp

@@ -28,3 +28,17 @@ namespace test3 {
     g<int>();
   }
 }
+
+namespace test4 {
+  static void f();
+  static void f();
+  template<typename T>
+  static void g() {
+    f();
+  }
+  static void f() {
+  }
+  void h() {
+    g<int>();
+  }
+}