fix Issue 14747 - compiler insists on unnecessary return statement

src/statement.c

@@ -338,7 +338,9 @@ int Statement::blockExit(FuncDeclaration *func, bool mustNotThrow)
                 if (s)
                 {
                     int r = s->blockExit(func, mustNotThrow);
-                    result |= r & ~(BEbreak | BEcontinue);
+                    result |= r & ~(BEbreak | BEcontinue | BEfallthru);
+                    if ((r & (BEfallthru | BEcontinue | BEbreak)) == 0)
+                        result &= ~BEfallthru;
                 }
             }
         }

test/compilable/test14747.d

@@ -0,0 +1,31 @@
+// REQUIRED_ARGS: -o-
+// PERMUTE_ARGS: -w
+
+int foo(Args...)()
+{
+    int x;
+
+    foreach (arg; Args)
+    {
+        static if(is(arg == int))
+        {
+            return 0;
+        }
+        static if(is(arg == long))
+        {
+            // fallthrough
+            ++x;    // this statement might be unreachable, but
+                    // UnrollStatement does not warn that.
+        }
+    }
+    // no return
+}
+
+void main()
+{
+    auto r1 = foo!(int)();          // return
+    auto r2 = foo!(int, long)();    // return -> fallthrough (it's unreachable)
+    auto r3 = foo!(long, int)();    // fallthough -> return
+    static assert(!__traits(compiles, foo!(long)()));       // fallthough
+    static assert(!__traits(compiles, foo!(long, long)())); // fallthough -> fallthough
+}