rebase: use matcher to optimize manifestmerge
The old merge code would call manifestmerge and calculate the complete diff
between the source to the destination. In many cases, like rebase, the vast
majority of differences between the source and destination are irrelevant
because they are differences between the destination and the common ancestor
only, and therefore don't affect the merge. Since most actions are 'keep', all
the effort to compute them is wasted.
Instead, let's compute the difference between the source and the common ancestor
and only perform the diff of those files against the merge destination. When
using treemanifest, this lets us avoid loading almost the entire tree when
rebasing from a very old ancestor. This speeds up rebase of an old stack of 27
commits by 20x.
In mozilla-central, without treemanifest, when rebasing a commit from
default~100000 to default, this speeds up the manifestmerge step from 2.6s to
1.2s. However, the additional diff adds an overhead to all manifestmerge calls,
especially for flat manifests. When rebasing a commit from default~1 to default
it appears to add 100ms in mozilla-central. While we could put this optimization
behind a flag, I think the fact that it makes merge O(number of changes being
applied) instead of O(number of changes between X and Y) justifies it.
/*
* diffhelpers.c - helper routines for mpatch
*
* Copyright 2007 Chris Mason <chris.mason@oracle.com>
*
* This software may be used and distributed according to the terms
* of the GNU General Public License v2, incorporated herein by reference.
*/
#include <Python.h>
#include <stdlib.h>
#include <string.h>
#include "util.h"
static char diffhelpers_doc[] = "Efficient diff parsing";
static PyObject *diffhelpers_Error;
/* fixup the last lines of a and b when the patch has no newline at eof */
static void _fix_newline(PyObject *hunk, PyObject *a, PyObject *b)
{
Py_ssize_t hunksz = PyList_Size(hunk);
PyObject *s = PyList_GET_ITEM(hunk, hunksz-1);
char *l = PyBytes_AsString(s);
Py_ssize_t alen = PyList_Size(a);
Py_ssize_t blen = PyList_Size(b);
char c = l[0];
PyObject *hline;
Py_ssize_t sz = PyBytes_GET_SIZE(s);
if (sz > 1 && l[sz-2] == '\r')
/* tolerate CRLF in last line */
sz -= 1;
hline = PyBytes_FromStringAndSize(l, sz-1);
if (!hline) {
return;
}
if (c == ' ' || c == '+') {
PyObject *rline = PyBytes_FromStringAndSize(l + 1, sz - 2);
PyList_SetItem(b, blen-1, rline);
}
if (c == ' ' || c == '-') {
Py_INCREF(hline);
PyList_SetItem(a, alen-1, hline);
}
PyList_SetItem(hunk, hunksz-1, hline);
}
/* python callable form of _fix_newline */
static PyObject *
fix_newline(PyObject *self, PyObject *args)
{
PyObject *hunk, *a, *b;
if (!PyArg_ParseTuple(args, "OOO", &hunk, &a, &b))
return NULL;
_fix_newline(hunk, a, b);
return Py_BuildValue("l", 0);
}
#if (PY_VERSION_HEX < 0x02050000)
static const char *addlines_format = "OOiiOO";
#else
static const char *addlines_format = "OOnnOO";
#endif
/*
* read lines from fp into the hunk. The hunk is parsed into two arrays
* a and b. a gets the old state of the text, b gets the new state
* The control char from the hunk is saved when inserting into a, but not b
* (for performance while deleting files)
*/
static PyObject *
addlines(PyObject *self, PyObject *args)
{
PyObject *fp, *hunk, *a, *b, *x;
Py_ssize_t i;
Py_ssize_t lena, lenb;
Py_ssize_t num;
Py_ssize_t todoa, todob;
char *s, c;
PyObject *l;
if (!PyArg_ParseTuple(args, addlines_format,
&fp, &hunk, &lena, &lenb, &a, &b))
return NULL;
while (1) {
todoa = lena - PyList_Size(a);
todob = lenb - PyList_Size(b);
num = todoa > todob ? todoa : todob;
if (num == 0)
break;
for (i = 0; i < num; i++) {
x = PyFile_GetLine(fp, 0);
s = PyBytes_AsString(x);
c = *s;
if (strcmp(s, "\\ No newline at end of file\n") == 0) {
_fix_newline(hunk, a, b);
continue;
}
if (c == '\n') {
/* Some patches may be missing the control char
* on empty lines. Supply a leading space. */
Py_DECREF(x);
x = PyBytes_FromString(" \n");
}
PyList_Append(hunk, x);
if (c == '+') {
l = PyBytes_FromString(s + 1);
PyList_Append(b, l);
Py_DECREF(l);
} else if (c == '-') {
PyList_Append(a, x);
} else {
l = PyBytes_FromString(s + 1);
PyList_Append(b, l);
Py_DECREF(l);
PyList_Append(a, x);
}
Py_DECREF(x);
}
}
return Py_BuildValue("l", 0);
}
/*
* compare the lines in a with the lines in b. a is assumed to have
* a control char at the start of each line, this char is ignored in the
* compare
*/
static PyObject *
testhunk(PyObject *self, PyObject *args)
{
PyObject *a, *b;
long bstart;
Py_ssize_t alen, blen;
Py_ssize_t i;
char *sa, *sb;
if (!PyArg_ParseTuple(args, "OOl", &a, &b, &bstart))
return NULL;
alen = PyList_Size(a);
blen = PyList_Size(b);
if (alen > blen - bstart || bstart < 0) {
return Py_BuildValue("l", -1);
}
for (i = 0; i < alen; i++) {
sa = PyBytes_AsString(PyList_GET_ITEM(a, i));
sb = PyBytes_AsString(PyList_GET_ITEM(b, i + bstart));
if (strcmp(sa + 1, sb) != 0)
return Py_BuildValue("l", -1);
}
return Py_BuildValue("l", 0);
}
static PyMethodDef methods[] = {
{"addlines", addlines, METH_VARARGS, "add lines to a hunk\n"},
{"fix_newline", fix_newline, METH_VARARGS, "fixup newline counters\n"},
{"testhunk", testhunk, METH_VARARGS, "test lines in a hunk\n"},
{NULL, NULL}
};
#ifdef IS_PY3K
static struct PyModuleDef diffhelpers_module = {
PyModuleDef_HEAD_INIT,
"diffhelpers",
diffhelpers_doc,
-1,
methods
};
PyMODINIT_FUNC PyInit_diffhelpers(void)
{
PyObject *m;
m = PyModule_Create(&diffhelpers_module);
if (m == NULL)
return NULL;
diffhelpers_Error = PyErr_NewException("diffhelpers.diffhelpersError",
NULL, NULL);
Py_INCREF(diffhelpers_Error);
PyModule_AddObject(m, "diffhelpersError", diffhelpers_Error);
return m;
}
#else
PyMODINIT_FUNC
initdiffhelpers(void)
{
Py_InitModule3("diffhelpers", methods, diffhelpers_doc);
diffhelpers_Error = PyErr_NewException("diffhelpers.diffhelpersError",
NULL, NULL);
}
#endif