[-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.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@203336 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Analysis/ReachableCode.cpp

@@ -397,9 +397,11 @@ const Stmt *DeadCodeScan::findDeadCode(const clang::CFGBlock *Block) {
     }
 
   if (CFGTerminator T = Block->getTerminator()) {
-    const Stmt *S = T.getStmt();
-    if (isValidDeadStmt(S))
-      return S;
+    if (!T.isTemporaryDtorsBranch()) {
+      const Stmt *S = T.getStmt();
+      if (isValidDeadStmt(S))
+        return S;
+    }
   }
 
   return 0;

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
+}