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List:       cfe-commits
Subject:    [PATCH] PR14253: 'warn_unused' attribute for unused warning for non-POD types
From:       Lubos Lunak <l.lunak () suse ! cz>
Date:       2013-07-16 6:55:06
Message-ID: 201307160855.06686.l.lunak () suse ! cz
[Download RAW message or body]

Hello,

 could somebody please review the attached patch for PR14253?

 The equivalent GCC patch has been accepted (GCC bug #55203) and libstdc++ 
should use the attribute whenever I or somebody write the patch for it. 
Presumably this Clang patch should be followed by a patch for libc++ (I do 
not intend to do that).

-- 
 Lubos Lunak
 l.lunak@suse.cz

["0001-add-type-attribute-warn_unused-allowing-to-warn-abou.patch" (text/x-diff)]

From 2b51f5ea6a84d6772d3006b86f75b7b574bae662 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Lubo=C5=A1=20Lu=C5=88=C3=A1k?= <l.lunak@suse.cz>
Date: Tue, 16 Jul 2013 08:42:24 +0200
Subject: [PATCH] add type attribute warn_unused , allowing to warn about
 non-POD unused variables

---
 include/clang/Basic/Attr.td            |  4 ++++
 lib/Sema/SemaDecl.cpp                  |  4 ++--
 lib/Sema/SemaDeclAttr.cpp              | 14 ++++++++++++++
 test/SemaCXX/warn-unused-attribute.cpp | 20 ++++++++++++++++++++
 4 files changed, 40 insertions(+), 2 deletions(-)
 create mode 100644 test/SemaCXX/warn-unused-attribute.cpp

diff --git a/include/clang/Basic/Attr.td b/include/clang/Basic/Attr.td
index cdb567d..b639c92 100644
--- a/include/clang/Basic/Attr.td
+++ b/include/clang/Basic/Attr.td
@@ -749,6 +749,10 @@ def VecReturn : InheritableAttr {
   let Subjects = [CXXRecord];
 }
 
+def WarnUnused : InheritableAttr {
+  let Spellings = [GNU<"warn_unused">, CXX11<"gnu", "warn_unused">];
+}
+
 def WarnUnusedResult : InheritableAttr {
   let Spellings = [GNU<"warn_unused_result">,
                    CXX11<"clang", "warn_unused_result">,
diff --git a/lib/Sema/SemaDecl.cpp b/lib/Sema/SemaDecl.cpp
index 38de4db..34c9404 100644
--- a/lib/Sema/SemaDecl.cpp
+++ b/lib/Sema/SemaDecl.cpp
@@ -1320,7 +1320,7 @@ static bool ShouldDiagnoseUnusedDecl(const NamedDecl *D) {
         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(const NamedDecl *D) {
             dyn_cast<CXXConstructExpr>(Init);
           if (Construct && !Construct->isElidable()) {
             CXXConstructorDecl *CD = Construct->getConstructor();
-            if (!CD->isTrivial())
+            if (!CD->isTrivial() && !RD->hasAttr<WarnUnusedAttr>())
               return false;
           }
         }
diff --git a/lib/Sema/SemaDeclAttr.cpp b/lib/Sema/SemaDeclAttr.cpp
index 4c18a33..76d8f2c 100644
--- a/lib/Sema/SemaDeclAttr.cpp
+++ b/lib/Sema/SemaDeclAttr.cpp
@@ -2669,6 +2669,17 @@ static void handleSentinelAttr(Sema &S, Decl *D, const AttributeList &Attr) {
                           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))
@@ -4895,6 +4906,9 @@ static void ProcessInheritableDeclAttr(Sema &S, Scope *scope, Decl *D,
   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;
diff --git a/test/SemaCXX/warn-unused-attribute.cpp b/test/SemaCXX/warn-unused-attribute.cpp
new file mode 100644
index 0000000..72f96ee
--- /dev/null
+++ b/test/SemaCXX/warn-unused-attribute.cpp
@@ -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();
+}
-- 
1.8.1.4



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