Sema/AST support for attribute used. Patch by Anders Johnson (with small tweaks & test case)!

llvm-svn: 64478

clang/include/clang/AST/Attr.h

@@ -50,6 +50,7 @@ public:
     TransparentUnion,
     Unavailable,
     Unused,    
+    Used,
     Visibility,
     Weak,
     Blocks,
@@ -266,6 +267,15 @@ public:
   static bool classof(const UnusedAttr *A) { return true; }
 };  
   
+class UsedAttr : public Attr {
+public:
+  UsedAttr() : Attr(Used) {}
+  
+  // Implement isa/cast/dyncast/etc.
+  static bool classof(const Attr *A) { return A->getKind() == Used; }  
+  static bool classof(const UsedAttr *A) { return true; }
+};  
+  
 class WeakAttr : public Attr {
 public:
   WeakAttr() : Attr(Weak) {}

clang/include/clang/Parse/AttributeList.h

@@ -70,6 +70,7 @@ public:
     AT_transparent_union,
     AT_unavailable,
     AT_unused,
+    AT_used,
     AT_vector_size,
     AT_visibility,
     AT_warn_unused_result,

clang/lib/Parse/AttributeList.cpp

@@ -56,6 +56,7 @@ AttributeList::Kind AttributeList::getKind(const IdentifierInfo *Name) {
     if (!memcmp(Str, "weak", 4)) return AT_weak;
     if (!memcmp(Str, "pure", 4)) return AT_pure;
     if (!memcmp(Str, "mode", 4)) return AT_mode;
+    if (!memcmp(Str, "used", 4)) return AT_used;
     break;
   case 5:
     if (!memcmp(Str, "alias", 5)) return AT_alias;

clang/lib/Sema/SemaDeclAttr.cpp

@@ -431,6 +431,27 @@ static void HandleUnusedAttr(Decl *d, const AttributeList &Attr, Sema &S) {
   d->addAttr(new UnusedAttr());
 }
 
+static void HandleUsedAttr(Decl *d, const AttributeList &Attr, Sema &S) {
+  // check the attribute arguments.
+  if (Attr.getNumArgs() != 0) {
+    S.Diag(Attr.getLoc(), diag::err_attribute_wrong_number_arguments) << 0;
+    return;
+  }
+  
+  if (const VarDecl *VD = dyn_cast<VarDecl>(d)) {
+    if (VD->hasLocalStorage()) {
+      S.Diag(Attr.getLoc(), diag::warn_attribute_ignored) << "used";
+      return;
+    }
+  } else if (!isFunctionOrMethod(d)) {
+    S.Diag(Attr.getLoc(), diag::warn_attribute_wrong_decl_type)
+      << "used" << "variable and function";
+    return;
+  }
+  
+  d->addAttr(new UsedAttr());
+}
+
 static void HandleConstructorAttr(Decl *d, const AttributeList &Attr, Sema &S) {
   // check the attribute arguments.
   if (Attr.getNumArgs() != 0 && Attr.getNumArgs() != 1) {
@@ -1357,6 +1378,7 @@ static void ProcessDeclAttribute(Decl *D, const AttributeList &Attr, Sema &S) {
   case AttributeList::AT_stdcall:     HandleStdCallAttr   (D, Attr, S); break;
   case AttributeList::AT_unavailable: HandleUnavailableAttr(D, Attr, S); break;
   case AttributeList::AT_unused:      HandleUnusedAttr    (D, Attr, S); break;
+  case AttributeList::AT_used:        HandleUsedAttr      (D, Attr, S); break;
   case AttributeList::AT_vector_size: HandleVectorSizeAttr(D, Attr, S); break;
   case AttributeList::AT_visibility:  HandleVisibilityAttr(D, Attr, S); break;
   case AttributeList::AT_weak:        HandleWeakAttr      (D, Attr, S); break;

clang/test/Sema/attr-used.c

@@ -0,0 +1,17 @@
+// RUN: clang -verify -fsyntax-only %s
+
+struct __attribute__((used)) s { // expected-warning {{'used' attribute only applies to variable and function types}}
+  int x;
+};
+
+int a __attribute__((used));
+
+static void __attribute__((used)) f0(void) {
+}
+
+void f1() {
+  static int a __attribute__((used)); 
+  int b __attribute__((used)); // expected-warning {{used attribute ignored}}
+}
+
+