r315811 - Re-land r315787, "[Sema] Warn about unused variables if we can constant evaluate the initializer."

[Benjamin Kramer via cfe-commits]

Author: d0k
Date: Sat Oct 14 08:59:34 2017
New Revision: 315811

URL: http://llvm.org/viewvc/llvm-project?rev=315811&view=rev
Log:
Re-land r315787, "[Sema] Warn about unused variables if we can constant evaluate the initializer."

The warnings in libc++ tests were fixed in the meantime.

Modified:
    cfe/trunk/lib/Sema/SemaDecl.cpp
    cfe/trunk/test/SemaCXX/warn-unused-variables.cpp

Modified: cfe/trunk/lib/Sema/SemaDecl.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaDecl.cpp?rev=315811&r1=315810&r2=315811&view=diff
==============================================================================
--- cfe/trunk/lib/Sema/SemaDecl.cpp (original)
+++ cfe/trunk/lib/Sema/SemaDecl.cpp Sat Oct 14 08:59:34 2017
@@ -1723,7 +1723,8 @@ static bool ShouldDiagnoseUnusedDecl(con
             dyn_cast<CXXConstructExpr>(Init);
           if (Construct && !Construct->isElidable()) {
             CXXConstructorDecl *CD = Construct->getConstructor();
-            if (!CD->isTrivial() && !RD->hasAttr<WarnUnusedAttr>())
+            if (!CD->isTrivial() && !RD->hasAttr<WarnUnusedAttr>() &&
+                !VD->evaluateValue())
               return false;
           }
         }

Modified: cfe/trunk/test/SemaCXX/warn-unused-variables.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaCXX/warn-unused-variables.cpp?rev=315811&r1=315810&r2=315811&view=diff
==============================================================================
--- cfe/trunk/test/SemaCXX/warn-unused-variables.cpp (original)
+++ cfe/trunk/test/SemaCXX/warn-unused-variables.cpp Sat Oct 14 08:59:34 2017
@@ -1,4 +1,5 @@
 // RUN: %clang_cc1 -fsyntax-only -Wunused-variable -Wunused-label -Wno-c++1y-extensions -verify %s
+// RUN: %clang_cc1 -fsyntax-only -Wunused-variable -Wunused-label -Wno-c++1y-extensions -verify -std=c++11 %s
 template<typename T> void f() {
   T t;
   t = 17;
@@ -194,3 +195,35 @@ void test() {
 }
 
 }
+
+#if __cplusplus >= 201103L
+namespace with_constexpr {
+template <typename T>
+struct Literal {
+  T i;
+  Literal() = default;
+  constexpr Literal(T i) : i(i) {}
+};
+
+struct NoLiteral {
+  int i;
+  NoLiteral() = default;
+  constexpr NoLiteral(int i) : i(i) {}
+  ~NoLiteral() {}
+};
+
+static Literal<int> gl1;          // expected-warning {{unused variable 'gl1'}}
+static Literal<int> gl2(1);       // expected-warning {{unused variable 'gl2'}}
+static const Literal<int> gl3(0); // expected-warning {{unused variable 'gl3'}}
+
+template <typename T>
+void test(int i) {
+  Literal<int> l1;     // expected-warning {{unused variable 'l1'}}
+  Literal<int> l2(42); // expected-warning {{unused variable 'l2'}}
+  Literal<int> l3(i);  // no-warning
+  Literal<T> l4(0);    // no-warning
+  NoLiteral nl1;       // no-warning
+  NoLiteral nl2(42);   // no-warning
+}
+}
+#endif