r186765 - add type attribute warn_unused, for -Wunused-variable warnings (pr#14253)

[Lubos Lunak]

Author: llunak
Date: Sat Jul 20 10:05:36 2013
New Revision: 186765

URL: http://llvm.org/viewvc/llvm-project?rev=186765&view=rev
Log:
add type attribute warn_unused, for -Wunused-variable warnings (pr#14253)

The functionality is equivalent to the GCC attribute. Variables of tagged
types will be warned about as unused if they are not used in any way
except for possible (even non-trivial) ctors/dtors called. Useful for tagging
classes like std::string (which is not part of this commit).


Added:
    cfe/trunk/test/SemaCXX/warn-unused-attribute.cpp
Modified:
    cfe/trunk/include/clang/Basic/Attr.td
    cfe/trunk/lib/Sema/SemaDecl.cpp
    cfe/trunk/lib/Sema/SemaDeclAttr.cpp

Modified: cfe/trunk/include/clang/Basic/Attr.td
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/Attr.td?rev=186765&r1=186764&r2=186765&view=diff
==============================================================================
--- cfe/trunk/include/clang/Basic/Attr.td (original)
+++ cfe/trunk/include/clang/Basic/Attr.td Sat Jul 20 10:05:36 2013
@@ -749,6 +749,11 @@ def VecReturn : InheritableAttr {
   let Subjects = [CXXRecord];
 }
 
+def WarnUnused : InheritableAttr {
+  let Spellings = [GNU<"warn_unused">, CXX11<"gnu", "warn_unused">];
+  let Subjects = [Record];
+}
+
 def WarnUnusedResult : InheritableAttr {
   let Spellings = [GNU<"warn_unused_result">,
                    CXX11<"clang", "warn_unused_result">,

Modified: cfe/trunk/lib/Sema/SemaDecl.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaDecl.cpp?rev=186765&r1=186764&r2=186765&view=diff
==============================================================================
--- cfe/trunk/lib/Sema/SemaDecl.cpp (original)
+++ cfe/trunk/lib/Sema/SemaDecl.cpp Sat Jul 20 10:05:36 2013
@@ -1320,7 +1320,7 @@ static bool ShouldDiagnoseUnusedDecl(con
         return false;
 
       if (const CXXRecordDecl *RD = dyn_cast<CXXRecordDecl>(Tag)) {
-        if (!RD->hasTrivialDestructor())
+        if (!RD->hasTrivialDestructor() && !RD->hasAttr<WarnUnusedAttr>())
           return false;
 
         if (const Expr *Init = VD->getInit()) {
@@ -1330,7 +1330,7 @@ static bool ShouldDiagnoseUnusedDecl(con
             dyn_cast<CXXConstructExpr>(Init);
           if (Construct && !Construct->isElidable()) {
             CXXConstructorDecl *CD = Construct->getConstructor();
-            if (!CD->isTrivial())
+            if (!CD->isTrivial() && !RD->hasAttr<WarnUnusedAttr>())
               return false;
           }
         }

Modified: cfe/trunk/lib/Sema/SemaDeclAttr.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaDeclAttr.cpp?rev=186765&r1=186764&r2=186765&view=diff
==============================================================================
--- cfe/trunk/lib/Sema/SemaDeclAttr.cpp (original)
+++ cfe/trunk/lib/Sema/SemaDeclAttr.cpp Sat Jul 20 10:05:36 2013
@@ -2668,6 +2668,17 @@ static void handleSentinelAttr(Sema &S,
                           Attr.getAttributeSpellingListIndex()));
 }
 
+static void handleWarnUnusedAttr(Sema &S, Decl *D, const AttributeList &Attr) {
+  // Check the attribute arguments.
+  if (!checkAttributeNumArgs(S, Attr, 0))
+    return;
+
+  if (RecordDecl *RD = dyn_cast<RecordDecl>(D))
+    RD->addAttr(::new (S.Context) WarnUnusedAttr(Attr.getRange(), S.Context));
+  else
+    S.Diag(Attr.getLoc(), diag::warn_attribute_ignored) << Attr.getName();
+}
+
 static void handleWarnUnusedResult(Sema &S, Decl *D, const AttributeList &Attr) {
   // check the attribute arguments.
   if (!checkAttributeNumArgs(S, Attr, 0))
@@ -4892,6 +4903,9 @@ static void ProcessInheritableDeclAttr(S
   case AttributeList::AT_TypeVisibility:
     handleVisibilityAttr(S, D, Attr, true);
     break;
+  case AttributeList::AT_WarnUnused:
+    handleWarnUnusedAttr(S, D, Attr);
+    break;
   case AttributeList::AT_WarnUnusedResult: handleWarnUnusedResult(S, D, Attr);
     break;
   case AttributeList::AT_Weak:        handleWeakAttr        (S, D, Attr); break;

Added: cfe/trunk/test/SemaCXX/warn-unused-attribute.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaCXX/warn-unused-attribute.cpp?rev=186765&view=auto
==============================================================================
--- cfe/trunk/test/SemaCXX/warn-unused-attribute.cpp (added)
+++ cfe/trunk/test/SemaCXX/warn-unused-attribute.cpp Sat Jul 20 10:05:36 2013
@@ -0,0 +1,20 @@
+// RUN: %clang_cc1 -fsyntax-only -Wunused-variable -verify %s
+struct __attribute__((warn_unused)) Test
+{
+    Test();
+    ~Test();
+    void use();
+};
+
+struct TestNormal
+{
+    TestNormal();
+};
+
+int main()
+{
+   Test unused;         // expected-warning {{unused variable 'unused'}}
+   Test used;
+   TestNormal normal;
+   used.use();
+}