Use unsafe PyList APIs for improved speed

In the case of the parse basecoro, we have full control over the
gen->path object, which is a list, so we can directly call a few of its
PyList_* unsafe functions instead of the safer, but more expensive
PySequence_* ones. In the of builder, we also can safely assume
builder->value_stack is a list, and when we access items we know we are
within boundaries.

One of the consequences of using PyList_GET_ITEM in particular in the
parse basecoro is that we now deal with borrowed references, and
therefore need to do less reference tracking. This in turned simplified
the CONCAT macro to the point where it became unnecessary (and it
already was a bit dirty to begin with).

Local benchmarks show a speed increase of ~4% in the parse method across
the different test cases.

Signed-off-by: Rodrigo Tobar <rtobar@icrar.org>

CHANGELOG.md

@@ -21,6 +21,7 @@
 * Restructured source code so all code lives under `src/`,
   and the `ijson.backends._yajl2` extension under `src/ijson/backends/ext/_yajl2`.
   This allows C backend tests to actually run on cibuildwheel.
+* Improved performance of `parse` routine in C backend by ~4%.
 * Fixed several potential stability issues in C backend
   around correct error handling.
 * Pointing to our own fork of yajl (for when we build it ourselves)

src/ijson/backends/ext/_yajl2/builder.h

@@ -112,7 +112,7 @@ int builder_reset(builder_t *builder)
 	Py_CLEAR(builder->value);
 	Py_CLEAR(builder->key);
 
-	Py_ssize_t nvals = PyList_Size(builder->value_stack);
+	Py_ssize_t nvals = PyList_GET_SIZE(builder->value_stack);
 	M1_M1(PyList_SetSlice(builder->value_stack, 0, nvals, NULL));
 
 	return 0;
@@ -121,14 +121,13 @@ int builder_reset(builder_t *builder)
 static inline
 int _builder_add(builder_t *builder, PyObject *value)
 {
-	Py_ssize_t nvals = PyList_Size(builder->value_stack);
+	Py_ssize_t nvals = PyList_GET_SIZE(builder->value_stack);
 	if (nvals == 0) {
 		Py_INCREF(value);
 		builder->value = value;
 	}
 	else {
-		PyObject *last;
-		M1_N(last = PyList_GetItem(builder->value_stack, nvals-1));
+		PyObject *last = PyList_GET_ITEM(builder->value_stack, nvals - 1);
 		assert(("stack element not list or dict-like",
 		        PyList_Check(last) || PyMapping_Check(last)));
 		if (PyList_Check(last)) {
@@ -182,7 +181,7 @@ int builder_event(builder_t *builder, enames_t enames, PyObject *ename, PyObject
 	}
 	else if (ename == enames.end_array_ename || ename == enames.end_map_ename) {
 		// pop
-		Py_ssize_t nvals = PyList_Size(builder->value_stack);
+		Py_ssize_t nvals = PyList_GET_SIZE(builder->value_stack);
 		M1_M1(PyList_SetSlice(builder->value_stack, nvals-1, nvals, NULL));
 	}
 	else {

src/ijson/backends/ext/_yajl2/parse_basecoro.c

@@ -39,17 +39,10 @@ static void parse_basecoro_dealloc(ParseBasecoro *self)
 	Py_TYPE(self)->tp_free((PyObject*)self);
 }
 
-#define CONCAT(tgt, first, second) \
-	do { \
-		tgt = PyUnicode_Concat(first, second); \
-		Py_DECREF(first); \
-		N_N(tgt); \
-	} while(0);
-
 PyObject* parse_basecoro_send_impl(PyObject *self, PyObject *event, PyObject *value)
 {
 	ParseBasecoro *gen = (ParseBasecoro *)self;
-	Py_ssize_t npaths = PyList_Size(gen->path);
+	Py_ssize_t npaths = PyList_GET_SIZE(gen->path);
 	enames_t enames = gen->module_state->enames;
 	PyObject *dot = gen->module_state->dot;
 	PyObject *dotitem = gen->module_state->dotitem;
@@ -61,48 +54,45 @@ PyObject* parse_basecoro_send_impl(PyObject *self, PyObject *event, PyObject *va
 		// pop
 		N_M1(PyList_SetSlice(gen->path, npaths - 1, npaths, NULL));
 		npaths--;
-		prefix = PySequence_GetItem(gen->path, npaths - 1);
+		prefix = PyList_GET_ITEM(gen->path, npaths - 1);
 	}
 	else if (event == enames.map_key_ename) {
 
 		// last_path = path_stack[-2]
 		// to_append = '.' + value if len(path_stack) > 1 else value
 		// new_path = path_stack[-2] + to_append
-		PyObject *last_path;
-		N_N(last_path = PySequence_GetItem(gen->path, npaths - 2));
+		PyObject *last_path = PyList_GET_ITEM(gen->path, npaths - 2);
+		PyObject *last_path_dot = NULL;
 		if (npaths > 2) {
-			PyObject *last_path_dot;
-			CONCAT(last_path_dot, last_path, dot);
+			last_path_dot = PyUnicode_Concat(last_path, dot);
+			N_N(last_path_dot);
 			last_path = last_path_dot;
 		}
-		PyObject *new_path;
-		CONCAT(new_path, last_path, value);
+		PyObject *new_path = PyUnicode_Concat(last_path, value);
+		N_N(new_path);
+		Py_XDECREF(last_path_dot);
 		PyList_SetItem(gen->path, npaths - 1, new_path);
 
-		prefix = PySequence_GetItem(gen->path, npaths - 2);
+		prefix = PyList_GET_ITEM(gen->path, npaths - 2);
 	}
 	else {
-		prefix = PySequence_GetItem(gen->path, npaths - 1);
+		prefix = PyList_GET_ITEM(gen->path, npaths - 1);
 	}
-	N_N(prefix);
 
 	// If entering a map/array, append name to path
 	if (event == enames.start_array_ename) {
 
 		// to_append = '.item' if path_stack[-1] else 'item'
 		// path_stack.append(path_stack[-1] + to_append)
-		PyObject *last_path;
-		N_N(last_path = PySequence_GetItem(gen->path, npaths - 1));
-
+		PyObject *last_path = PyList_GET_ITEM(gen->path, npaths - 1);
 		if (PyUnicode_GET_LENGTH(last_path) > 0) {
-			PyObject *new_path;
-			CONCAT(new_path, last_path, dotitem);
+			PyObject *new_path = PyUnicode_Concat(last_path, dotitem);
+			N_N(new_path);
 			N_M1(PyList_Append(gen->path, new_path));
 			Py_DECREF(new_path);
 		}
 		else {
 			N_M1(PyList_Append(gen->path, item));
-			Py_DECREF(last_path);
 		}
 	}
 	else if (event == enames.start_map_ename) {
@@ -121,7 +111,6 @@ PyObject* parse_basecoro_send_impl(PyObject *self, PyObject *event, PyObject *va
 		CORO_SEND(gen->target_send, res);
 		Py_DECREF(res);
 	}
-	Py_DECREF(prefix);
 	Py_RETURN_NONE;
 }