From: Benjamin Kramer <benny.kra@googlemail.com>
Date: Sat, 14 Oct 2017 15:59:34 +0000 (+0000)
Subject: Re-land r315787, "[Sema] Warn about unused variables if we can constant evaluate... 
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=cb0b66133f560ff830c1ee82c117476a246f487d;p=clang

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.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@315811 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Sema/SemaDecl.cpp b/lib/Sema/SemaDecl.cpp
index 31abdfa3f6..e6f3aeae96 100644
--- a/lib/Sema/SemaDecl.cpp
+++ b/lib/Sema/SemaDecl.cpp
@@ -1723,7 +1723,8 @@ static bool ShouldDiagnoseUnusedDecl(const NamedDecl *D) {
             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;
           }
         }
diff --git a/test/SemaCXX/warn-unused-variables.cpp b/test/SemaCXX/warn-unused-variables.cpp
index d7be785b35..0974cf5a61 100644
--- a/test/SemaCXX/warn-unused-variables.cpp
+++ b/test/SemaCXX/warn-unused-variables.cpp
@@ -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