Clean up some instances of -Wunreachable-code-aggressive (#27054)

See https://github.com/grpc/grpc/pull/26951 for why this is not enforced
at the moment.

src/core/ext/transport/cronet/transport/cronet_status.cc

@@ -304,7 +304,6 @@ const char* cronet_net_error_as_string(cronet_net_error_code net_error) {
       return "CRONET_NET_ERROR_ENCODING_CONVERSION_FAILED";
     case CRONET_NET_ERROR_UNRECOGNIZED_FTP_DIRECTORY_LISTING_FORMAT:
       return "CRONET_NET_ERROR_UNRECOGNIZED_FTP_DIRECTORY_LISTING_FORMAT";
-      return "CRONET_NET_ERROR_INVALID_SPDY_STREAM";
     case CRONET_NET_ERROR_NO_SUPPORTED_PROXIES:
       return "CRONET_NET_ERROR_NO_SUPPORTED_PROXIES";
     case CRONET_NET_ERROR_HTTP2_PROTOCOL_ERROR:
@@ -339,7 +338,6 @@ const char* cronet_net_error_as_string(cronet_net_error_code net_error) {
       return "CRONET_NET_ERROR_HTTP2_SERVER_REFUSED_STREAM";
     case CRONET_NET_ERROR_HTTP2_PING_FAILED:
       return "CRONET_NET_ERROR_HTTP2_PING_FAILED";
-      return "CRONET_NET_ERROR_PIPELINE_EVICTION";
     case CRONET_NET_ERROR_CONTENT_LENGTH_MISMATCH:
       return "CRONET_NET_ERROR_CONTENT_LENGTH_MISMATCH";
     case CRONET_NET_ERROR_INCOMPLETE_CHUNKED_ENCODING:
@@ -350,7 +348,6 @@ const char* cronet_net_error_as_string(cronet_net_error_code net_error) {
       return "CRONET_NET_ERROR_RESPONSE_HEADERS_TRUNCATED";
     case CRONET_NET_ERROR_QUIC_HANDSHAKE_FAILED:
       return "CRONET_NET_ERROR_QUIC_HANDSHAKE_FAILED";
-      return "CRONET_NET_ERROR_REQUEST_FOR_SECURE_RESOURCE_OVER_INSECURE_QUIC";
     case CRONET_NET_ERROR_HTTP2_INADEQUATE_TRANSPORT_SECURITY:
       return "CRONET_NET_ERROR_HTTP2_INADEQUATE_TRANSPORT_SECURITY";
     case CRONET_NET_ERROR_HTTP2_FLOW_CONTROL_ERROR:
@@ -367,7 +364,6 @@ const char* cronet_net_error_as_string(cronet_net_error_code net_error) {
       return "CRONET_NET_ERROR_PROXY_HTTP_1_1_REQUIRED";
     case CRONET_NET_ERROR_PAC_SCRIPT_TERMINATED:
       return "CRONET_NET_ERROR_PAC_SCRIPT_TERMINATED";
-      return "CRONET_NET_ERROR_TEMPORARY_BACKOFF";
     case CRONET_NET_ERROR_INVALID_HTTP_RESPONSE:
       return "CRONET_NET_ERROR_INVALID_HTTP_RESPONSE";
     case CRONET_NET_ERROR_CONTENT_DECODING_INIT_FAILED:
@@ -522,6 +518,4 @@ grpc_status_code cronet_net_error_to_grpc_error(
     default:
       return GRPC_STATUS_UNAVAILABLE;
   }
-
-  return GRPC_STATUS_UNAVAILABLE;
 }

test/core/compression/message_compress_test.cc

@@ -124,7 +124,6 @@ static compressability get_compressability(
       return SHOULD_COMPRESS;
     case TEST_VALUE_COUNT:
       abort();
-      break;
   }
   return MAYBE_COMPRESSES;
 }
@@ -139,7 +138,6 @@ static grpc_slice create_test_value(test_value id) {
       return repeated('a', 1024 * 1024);
     case TEST_VALUE_COUNT:
       abort();
-      break;
   }
   return grpc_slice_from_copied_string("bad value");
 }

test/core/end2end/cq_verifier.cc

@@ -209,7 +209,6 @@ std::string ExpectationString(const Expectation& e) {
     case GRPC_QUEUE_SHUTDOWN:
       gpr_log(GPR_ERROR, "not implemented");
       abort();
-      break;
   }
   return out;
 }
@@ -243,11 +242,9 @@ static void verify_matches(const Expectation& e, const grpc_event& ev) {
     case GRPC_QUEUE_SHUTDOWN:
       gpr_log(GPR_ERROR, "premature queue shutdown");
       abort();
-      break;
     case GRPC_QUEUE_TIMEOUT:
       gpr_log(GPR_ERROR, "not implemented");
       abort();
-      break;
   }
 }
 

test/core/util/subprocess_posix.cc

@@ -60,7 +60,6 @@ gpr_subprocess* gpr_subprocess_create(int argc, const char** argv) {
     /* if we reach here, an error has occurred */
     gpr_log(GPR_ERROR, "execv '%s' failed: %s", exec_args[0], strerror(errno));
     _exit(1);
-    return nullptr;
   } else {
     r = static_cast<gpr_subprocess*>(gpr_zalloc(sizeof(gpr_subprocess)));
     r->pid = pid;

test/cpp/end2end/server_crash_test_client.cc

@@ -68,6 +68,4 @@ int main(int argc, char** argv) {
             absl::GetFlag(FLAGS_mode).c_str());
     return 1;
   }
-
-  return 0;
 }

test/cpp/interop/xds_interop_client.cc

@@ -506,7 +506,7 @@ void RunTestLoop(std::chrono::duration<double> duration_per_query,
       }
     }
   }
-  thread.join();
+  GPR_UNREACHABLE_CODE(thread.join());
 }
 
 void RunServer(const int port, StatsWatchers* stats_watchers,

test/cpp/qps/client_async.cc

@@ -822,7 +822,6 @@ class ClientRpcContextGenericStreamingImpl : public ClientRpcContext {
           next_state_ = State::READ_DONE;
           stream_->Read(&response_, ClientRpcContext::tag(this));
           return true;
-          break;
         case State::READ_DONE:
           entry->set_value((UsageTimer::Now() - start_) * 1e9);
           callback_(status_, &response_);
@@ -841,7 +840,6 @@ class ClientRpcContextGenericStreamingImpl : public ClientRpcContext {
         case State::FINISH_DONE:
           next_state_ = State::INVALID;
           return false;
-          break;
         default:
           GPR_ASSERT(false);
           return false;

test/cpp/qps/qps_worker.cc

@@ -67,7 +67,6 @@ static std::unique_ptr<Client> CreateClient(const ClientConfig& config) {
     default:
       abort();
   }
-  abort();
 }
 
 static std::unique_ptr<Server> CreateServer(const ServerConfig& config) {
@@ -86,7 +85,6 @@ static std::unique_ptr<Server> CreateServer(const ServerConfig& config) {
     default:
       abort();
   }
-  abort();
 }
 
 class ScopedProfile final {