[-Wunreachabe-code] Don't warn about unreachable destructors for temporaries.

This can possibly be refined later, but right now the experience
is so incomprehensible for a user to understand what is going on
this isn't a useful warning.

llvm-svn: 203336

clang/lib/Analysis/ReachableCode.cpp

@@ -397,10 +397,12 @@ const Stmt *DeadCodeScan::findDeadCode(const clang::CFGBlock *Block) {
     }
 
   if (CFGTerminator T = Block->getTerminator()) {
+    if (!T.isTemporaryDtorsBranch()) {
       const Stmt *S = T.getStmt();
       if (isValidDeadStmt(S))
         return S;
     }
+  }
 
   return 0;
 }

clang/test/SemaCXX/warn-unreachable.cpp

@@ -162,3 +162,16 @@ int test_global_as_conditionVariable() {
   return 0; // no-warning
 }
 
+// Handle unreachable temporary destructors.
+class A {
+public:
+  A();
+  ~A();
+};
+
+__attribute__((noreturn))
+void raze(const A& x);
+
+void test_with_unreachable_tmp_dtors(int x) {
+  raze(x ? A() : A()); // no-warning
+}