contrib/fuzz/revlog.cc

stream-clone: disable gc for the initial section for the v3 format

The number of small container created turn Python in a gc-frenzy that seriously
impact performance.

This significantly boost performance. The following number comes from a large
private repository using perf::stream-locked-section:

base-line:   35.04 seconds
prev-change: 24.51 seconds (-30%)
prev-change: 20.88 seconds (-40%)
this-change: 14.22 seconds (-60% from baseline; -31% from prev)

#include <Python.h>
#include <assert.h>
#include <stdlib.h>
#include <unistd.h>

#include <string>

#include "pyutil.h"

extern "C" {

static PYCODETYPE *code;

extern "C" int LLVMFuzzerInitialize(int *argc, char ***argv)
{
	contrib::initpy(*argv[0]);
	code = (PYCODETYPE *)Py_CompileString(R"py(
for inline in (True, False):
    try:
        index, cache = parsers.parse_index2(data, inline)
        index.slicechunktodensity(list(range(len(index))), 0.5, 262144)
        index.stats()
        index.findsnapshots({}, 0, len(index) - 1)
        10 in index
        for rev in range(len(index)):
            index.reachableroots(0, [len(index)-1], [rev])
            node = index[rev][7]
            partial = index.shortest(node)
            index.partialmatch(node[:partial])
            index.deltachain(rev, None, True)
    except Exception as e:
        pass
        # uncomment this print if you're editing this Python code
        # to debug failures.
        # print e
)py",
	                                      "fuzzer", Py_file_input);
	return 0;
}

int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size)
{
	// Don't allow fuzzer inputs larger than 60k, since we'll just bog
	// down and not accomplish much.
	if (Size > 60000) {
		return 0;
	}
	PyObject *text =
	    PyBytes_FromStringAndSize((const char *)Data, (Py_ssize_t)Size);
	PyObject *locals = PyDict_New();
	PyDict_SetItemString(locals, "data", text);
	PyObject *res = PyEval_EvalCode(code, contrib::pyglobals(), locals);
	if (!res) {
		PyErr_Print();
	}
	Py_XDECREF(res);
	Py_DECREF(locals);
	Py_DECREF(text);
	return 0; // Non-zero return values are reserved for future use.
}
}