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bpo-43693: Eliminate unused "fast locals". #26587

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Merged
ericsnowcurrently merged 10 commits into from
Jun 15, 2021
Merged

bpo-43693: Eliminate unused "fast locals". #26587

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d63f73e
Merge cell locals with var locals for args.
ericsnowcurrently May 10, 2021
db2fd06
Eliminate co_cell2arg.
ericsnowcurrently May 10, 2021
6cae5e0
Add a NEWS entry.
ericsnowcurrently Jun 7, 2021
b5ef8e1
Bump the .pyc magic number.
ericsnowcurrently Jun 9, 2021
0e1cbc4
Drop an expensive check from super_init_without_args().
ericsnowcurrently Jun 15, 2021
2ec5ae4
Do not export _PyFrame_OpAlreadyRan().
ericsnowcurrently Jun 15, 2021
4b086e9
Check only the free vars in super_init_without_args().
ericsnowcurrently Jun 15, 2021
09c3cdd
Simplify a comment.
ericsnowcurrently Jun 15, 2021
8693744
Sort the MAKE_CELL ops by oparg.
ericsnowcurrently Jun 15, 2021
bdb12a7
Add a light-weight check to super_init_without_args().
ericsnowcurrently Jun 15, 2021
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Sort the MAKE_CELL ops by oparg.
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@ericsnowcurrently
ericsnowcurrently committed Jun 15, 2021
commit 8693744273632968987089a8a6b0cffa182d4b63
154 changes: 102 additions & 52 deletions Python/compile.c
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Original file line number Diff line number Diff line change
Expand Up @@ -21,6 +21,8 @@
* objects.
*/

#include <stdbool.h>

#include "Python.h"
#include "pycore_ast.h" // _PyAST_GetDocString()
#include "pycore_compile.h" // _PyFuture_FromAST()
Expand Down Expand Up @@ -7377,6 +7379,39 @@ optimize_cfg(struct compiler *c, struct assembler *a, PyObject *consts);
static int
ensure_exits_have_lineno(struct compiler *c);

static int *
build_cellfixedoffsets(struct compiler *c)
{
int nlocals = (int)PyDict_GET_SIZE(c->u->u_varnames);
int ncellvars = (int)PyDict_GET_SIZE(c->u->u_cellvars);
int nfreevars = (int)PyDict_GET_SIZE(c->u->u_freevars);

int noffsets = ncellvars + nfreevars;
int *fixed = PyMem_New(int, noffsets);
if (fixed == NULL) {
PyErr_NoMemory();
return NULL;
}
for (int i = 0; i < noffsets; i++) {
fixed[i] = nlocals + i;
}

PyObject *varname, *cellindex;
Py_ssize_t pos = 0;
while (PyDict_Next(c->u->u_cellvars, &pos, &varname, &cellindex)) {
PyObject *varindex = PyDict_GetItem(c->u->u_varnames, varname);
if (varindex != NULL) {
assert(PyLong_AS_LONG(cellindex) < INT_MAX);
assert(PyLong_AS_LONG(varindex) < INT_MAX);
int oldindex = (int)PyLong_AS_LONG(cellindex);
int argoffset = (int)PyLong_AS_LONG(varindex);
fixed[oldindex] = argoffset;
}
}

return fixed;
}

static inline int
insert_instruction(basicblock *block, int pos, struct instr *instr) {
if (compiler_next_instr(block) < 0) {
Expand All @@ -7390,29 +7425,48 @@ insert_instruction(basicblock *block, int pos, struct instr *instr) {
}

static int
insert_prefix_instructions(struct compiler *c, basicblock *entryblock) {
insert_prefix_instructions(struct compiler *c, basicblock *entryblock,
int *fixed)
{

int flags = compute_code_flags(c);
if (flags < 0) {
return -1;
}

/* Set up cells for any variable that escapes, to be put in a closure. */
PyObject *k, *v;
Py_ssize_t pos = 0;
while (PyDict_Next(c->u->u_cellvars, &pos, &k, &v)) {
assert(PyLong_AS_LONG(v) < INT_MAX);
int cellindex = (int)PyLong_AS_LONG(v);
struct instr make_cell = {
.i_opcode = MAKE_CELL,
// This will get fixed in offset_derefs().
.i_oparg = cellindex,
.i_lineno = -1,
.i_target = NULL,
};
if (insert_instruction(entryblock, (int)(pos - 1), &make_cell) < 0) {
const int ncellvars = (int)PyDict_GET_SIZE(c->u->u_cellvars);
if (ncellvars) {
// c->u->u_cellvars has the cells out of order so we sort them
// before adding the MAKE_CELL instructions. Note that we
// adjust for arg cells, which come first.
const int nvars = ncellvars + (int)PyDict_GET_SIZE(c->u->u_varnames);
int *sorted = PyMem_RawCalloc(nvars, sizeof(int));
if (sorted == NULL) {
PyErr_NoMemory();
return -1;
}
for (int i = 0; i < ncellvars; i++) {
sorted[fixed[i]] = i + 1;
}
for (int i = 0, ncellsused = 0; ncellsused < ncellvars; i++) {
int oldindex = sorted[i] - 1;
if (oldindex == -1) {
continue;
}
struct instr make_cell = {
.i_opcode = MAKE_CELL,
// This will get fixed in offset_derefs().
.i_oparg = oldindex,
.i_lineno = -1,
.i_target = NULL,
};
if (insert_instruction(entryblock, ncellsused, &make_cell) < 0) {
return -1;
}
ncellsused += 1;
}
PyMem_RawFree(sorted);
}

/* Add the generator prefix instructions. */
Expand Down Expand Up @@ -7471,42 +7525,16 @@ guarantee_lineno_for_exits(struct assembler *a, int firstlineno) {
}

static int
fix_cell_offsets(struct compiler *c, basicblock *entryblock)
fix_cell_offsets(struct compiler *c, basicblock *entryblock, int *fixedmap)
{
assert(PyDict_GET_SIZE(c->u->u_varnames) < INT_MAX);
assert(PyDict_GET_SIZE(c->u->u_cellvars) < INT_MAX);
assert(PyDict_GET_SIZE(c->u->u_freevars) < INT_MAX);
int nlocals = (int)PyDict_GET_SIZE(c->u->u_varnames);
int ncellvars = (int)PyDict_GET_SIZE(c->u->u_cellvars);
Comment thread
ericsnowcurrently marked this conversation as resolved.
int nfreevars = (int)PyDict_GET_SIZE(c->u->u_freevars);
assert(INT_MAX - nlocals - ncellvars - nfreevars > 0);
int nlocalsplus = nlocals + ncellvars + nfreevars;
int noffsets = ncellvars + nfreevars;

int maxoldoffset = ncellvars + nfreevars;
int *fixedmap = PyMem_New(int, maxoldoffset + 1);
if (fixedmap == NULL) {
PyErr_NoMemory();
return -1;
}
for (int i = 0; i < maxoldoffset; i++) {
fixedmap[i] = nlocals + i;
}

// First map cell vars to args.
PyObject *varname, *cellindex;
Py_ssize_t pos = 0;
while (PyDict_Next(c->u->u_cellvars, &pos, &varname, &cellindex)) {
PyObject *varindex = PyDict_GetItem(c->u->u_varnames, varname);
if (varindex != NULL) {
assert(PyLong_AS_LONG(cellindex) < INT_MAX);
assert(PyLong_AS_LONG(varindex) < INT_MAX);
int oldindex = (int)PyLong_AS_LONG(cellindex);
int argoffset = (int)PyLong_AS_LONG(varindex);
fixedmap[oldindex] = argoffset;
}
}
// First deal with duplicates (arg cells).
int numdropped = 0;
for (int i = 0; i < maxoldoffset; i++) {
for (int i = 0; i < noffsets ; i++) {
if (fixedmap[i] == i + nlocals) {
fixedmap[i] -= numdropped;
}
Expand All @@ -7516,7 +7544,7 @@ fix_cell_offsets(struct compiler *c, basicblock *entryblock)
}
}

// Then update offsets, either relative to locals or by cell2var.
// Then update offsets, either relative to locals or by cell2arg.
for (basicblock *b = entryblock; b != NULL; b = b->b_next) {
for (int i = 0; i < b->b_iused; i++) {
struct instr *inst = &b->b_instr[i];
Expand All @@ -7530,13 +7558,15 @@ fix_cell_offsets(struct compiler *c, basicblock *entryblock)
case STORE_DEREF:
case DELETE_DEREF:
case LOAD_CLASSDEREF:
assert(oldoffset >= 0);
assert(oldoffset < noffsets);
assert(fixedmap[oldoffset] >= 0);
inst->i_oparg = fixedmap[oldoffset];
}
}
}

PyMem_Free(fixedmap);
return nlocalsplus - numdropped;
return numdropped;
}

static PyCodeObject *
Expand Down Expand Up @@ -7577,8 +7607,22 @@ assemble(struct compiler *c, int addNone)
}
assert(entryblock != NULL);

assert(PyDict_GET_SIZE(c->u->u_varnames) < INT_MAX);
assert(PyDict_GET_SIZE(c->u->u_cellvars) < INT_MAX);
assert(PyDict_GET_SIZE(c->u->u_freevars) < INT_MAX);
int nlocals = (int)PyDict_GET_SIZE(c->u->u_varnames);
int ncellvars = (int)PyDict_GET_SIZE(c->u->u_cellvars);
int nfreevars = (int)PyDict_GET_SIZE(c->u->u_freevars);
assert(INT_MAX - nlocals - ncellvars > 0);
assert(INT_MAX - nlocals - ncellvars - nfreevars > 0);
int nlocalsplus = nlocals + ncellvars + nfreevars;
int *cellfixedoffsets = build_cellfixedoffsets(c);
if (cellfixedoffsets == NULL) {
goto error;
}

// This must be called before fix_cell_offsets().
if (insert_prefix_instructions(c, entryblock)) {
if (insert_prefix_instructions(c, entryblock, cellfixedoffsets)) {
goto error;
}

Expand All @@ -7595,10 +7639,13 @@ assemble(struct compiler *c, int addNone)
a.a_entry = entryblock;
a.a_nblocks = nblocks;

int nlocalsplus = fix_cell_offsets(c, entryblock);
if (nlocalsplus < 0) {
int numdropped = fix_cell_offsets(c, entryblock, cellfixedoffsets);
PyMem_Free(cellfixedoffsets); // At this point we're done with it.
cellfixedoffsets = NULL;
if (numdropped < 0) {
goto error;
}
nlocalsplus -= numdropped;

consts = consts_dict_keys_inorder(c->u->u_consts);
if (consts == NULL) {
Expand Down Expand Up @@ -7639,10 +7686,10 @@ assemble(struct compiler *c, int addNone)
}

if (!assemble_exception_table(&a)) {
return 0;
goto error;
}
if (!assemble_line_range(&a)) {
return 0;
goto error;
}

if (_PyBytes_Resize(&a.a_lnotab, a.a_lnotab_off) < 0) {
Expand All @@ -7667,6 +7714,9 @@ assemble(struct compiler *c, int addNone)
error:
Py_XDECREF(consts);
assemble_free(&a);
if (cellfixedoffsets != NULL) {
PyMem_Free(cellfixedoffsets);
}
return co;
}

Expand Down