found via cppcheck:

remove code that will never run
make definition and declaration names for parameters match
change floats that were being set to bool values
remove pointer that is never used

core/os/dir_access.cpp

@@ -293,7 +293,7 @@ String DirAccess::get_full_path(const String &p_path, AccessType p_access) {
 	return full;
 }
 
-Error DirAccess::copy(String p_from, String p_to, int chmod_flags) {
+Error DirAccess::copy(String p_from, String p_to, int p_chmod_flags) {
 
 	//printf("copy %s -> %s\n",p_from.ascii().get_data(),p_to.ascii().get_data());
 	Error err;
@@ -330,9 +330,9 @@ Error DirAccess::copy(String p_from, String p_to, int chmod_flags) {
 		fdst->store_8(fsrc->get_8());
 	}
 
-	if (err == OK && chmod_flags != -1) {
+	if (err == OK && p_chmod_flags != -1) {
 		fdst->close();
-		err = fdst->_chmod(p_to, chmod_flags);
+		err = fdst->_chmod(p_to, p_chmod_flags);
 		// If running on a platform with no chmod support (i.e., Windows), don't fail
 		if (err == ERR_UNAVAILABLE)
 			err = OK;

core/os/dir_access.h

@@ -92,8 +92,8 @@ public:
 	static bool exists(String p_dir);
 	virtual size_t get_space_left() = 0;
 
-	Error copy_dir(String p_from, String p_to, int chmod_flags = -1);
-	virtual Error copy(String p_from, String p_to, int chmod_flags = -1);
+	Error copy_dir(String p_from, String p_to, int p_chmod_flags = -1);
+	virtual Error copy(String p_from, String p_to, int p_chmod_flags = -1);
 	virtual Error rename(String p_from, String p_to) = 0;
 	virtual Error remove(String p_name) = 0;
 

drivers/gles3/rasterizer_storage_gles3.h

@@ -1180,7 +1180,7 @@ public:
 
 			clear = true;
 			inactive = true;
-			inactive_time = false;
+			inactive_time = 0.0;
 
 			glGenBuffers(2, particle_buffers);
 			glGenVertexArrays(2, particle_vaos);

editor/plugins/baked_lightmap_editor_plugin.cpp

@@ -20,7 +20,6 @@ void BakedLightmapEditorPlugin::_bake() {
 			case BakedLightmap::BAKE_ERROR_CANT_CREATE_IMAGE:
 				EditorNode::get_singleton()->show_warning(TTR("Failed creating lightmap images, make sure path is writable."));
 				break;
-			defaut : {}
 		}
 	}
 }

scene/gui/tree.cpp

@@ -2352,8 +2352,6 @@ void Tree::_gui_input(Ref<InputEvent> p_event) {
 						last_keypress = 0;
 				}
 			} break;
-
-				last_keypress = 0;
 		}
 	}
 

scene/resources/environment.cpp

@@ -1218,7 +1218,7 @@ Environment::Environment() {
 	ssao_radius2 = 0;
 	ssao_intensity2 = 1;
 	ssao_bias = 0.01;
-	ssao_direct_light_affect = false;
+	ssao_direct_light_affect = 0.0;
 	ssao_blur = SSAO_BLUR_3x3;
 	set_ssao_edge_sharpness(4);
 	set_ssao_quality(SSAO_QUALITY_LOW);

servers/audio_server.cpp

@@ -122,7 +122,6 @@ int AudioDriverManager::get_driver_count() {
 }
 
 void AudioDriverManager::initialize(int p_driver) {
-	AudioDriver *driver;
 	int failed_driver = -1;
 
 	// Check if there is a selected driver