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pythongh-106149: Simplify stack depth calculation. Replace asserts by…
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… exceptions. (python#107255)
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@iritkatriel @jtcave
iritkatriel authored and jtcave committed Jul 27, 2023
1 parent de6a352 commit cadc7a5
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Showing 4 changed files with 91 additions and 42 deletions.
4 changes: 2 additions & 2 deletions Include/internal/pycore_flowgraph.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -89,8 +89,8 @@ int _PyCfgBuilder_Init(_PyCfgBuilder *g);
void _PyCfgBuilder_Fini(_PyCfgBuilder *g);

int _PyCfg_OptimizeCodeUnit(_PyCfgBuilder *g, PyObject *consts, PyObject *const_cache,
int code_flags, int nlocals, int nparams, int firstlineno);
int _PyCfg_Stackdepth(_PyCfgBasicblock *entryblock, int code_flags);
int nlocals, int nparams, int firstlineno);
int _PyCfg_Stackdepth(_PyCfgBuilder *g);
void _PyCfg_ConvertPseudoOps(_PyCfgBasicblock *entryblock);
int _PyCfg_ResolveJumps(_PyCfgBuilder *g);

Expand Down
21 changes: 17 additions & 4 deletions Lib/test/test_peepholer.py
View file
Original file line number Diff line number Diff line change
Expand Up @@ -991,14 +991,15 @@ def test_conditional_jump_forward_non_const_condition(self):
('LOAD_NAME', 1, 11),
('POP_JUMP_IF_TRUE', lbl := self.Label(), 12),
('LOAD_CONST', 2, 13),
('RETURN_VALUE', 13),
lbl,
('LOAD_CONST', 3, 14),
('RETURN_VALUE', 14),
]
expected_insts = [
('LOAD_NAME', 1, 11),
('POP_JUMP_IF_TRUE', lbl := self.Label(), 12),
('LOAD_CONST', 1, 13),
('RETURN_CONST', 1, 13),
lbl,
('RETURN_CONST', 2, 14),
]
Expand Down Expand Up @@ -1072,6 +1073,7 @@ def test_no_unsafe_static_swap(self):
('STORE_FAST', 1, 4),
('STORE_FAST', 1, 4),
('POP_TOP', 0, 4),
('LOAD_CONST', 0, 5),
('RETURN_VALUE', 5)
]
expected_insts = [
Expand All @@ -1080,7 +1082,7 @@ def test_no_unsafe_static_swap(self):
('NOP', 0, 3),
('STORE_FAST', 1, 4),
('POP_TOP', 0, 4),
('RETURN_VALUE', 5)
('RETURN_CONST', 0)
]
self.cfg_optimization_test(insts, expected_insts, consts=list(range(3)), nlocals=1)

Expand All @@ -1092,6 +1094,7 @@ def test_dead_store_elimination_in_same_lineno(self):
('STORE_FAST', 1, 4),
('STORE_FAST', 1, 4),
('STORE_FAST', 1, 4),
('LOAD_CONST', 0, 5),
('RETURN_VALUE', 5)
]
expected_insts = [
Expand All @@ -1100,7 +1103,7 @@ def test_dead_store_elimination_in_same_lineno(self):
('NOP', 0, 3),
('POP_TOP', 0, 4),
('STORE_FAST', 1, 4),
('RETURN_VALUE', 5)
('RETURN_CONST', 0, 5)
]
self.cfg_optimization_test(insts, expected_insts, consts=list(range(3)), nlocals=1)

Expand All @@ -1112,9 +1115,19 @@ def test_no_dead_store_elimination_in_different_lineno(self):
('STORE_FAST', 1, 4),
('STORE_FAST', 1, 5),
('STORE_FAST', 1, 6),
('LOAD_CONST', 0, 5),
('RETURN_VALUE', 5)
]
self.cfg_optimization_test(insts, insts, consts=list(range(3)), nlocals=1)
expected_insts = [
('LOAD_CONST', 0, 1),
('LOAD_CONST', 1, 2),
('LOAD_CONST', 2, 3),
('STORE_FAST', 1, 4),
('STORE_FAST', 1, 5),
('STORE_FAST', 1, 6),
('RETURN_CONST', 0, 5)
]
self.cfg_optimization_test(insts, expected_insts, consts=list(range(3)), nlocals=1)


if __name__ == "__main__":
Expand Down
47 changes: 31 additions & 16 deletions Python/compile.c
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Original file line number Diff line number Diff line change
Expand Up @@ -7527,14 +7527,21 @@ build_cellfixedoffsets(_PyCompile_CodeUnitMetadata *umd)
return fixed;
}

#define IS_GENERATOR(CF) \
((CF) & (CO_GENERATOR | CO_COROUTINE | CO_ASYNC_GENERATOR))

static int
insert_prefix_instructions(_PyCompile_CodeUnitMetadata *umd, basicblock *entryblock,
int *fixed, int nfreevars, int code_flags)
{
assert(umd->u_firstlineno > 0);

/* Add the generator prefix instructions. */
if (code_flags & (CO_GENERATOR | CO_COROUTINE | CO_ASYNC_GENERATOR)) {
if (IS_GENERATOR(code_flags)) {
/* Note that RETURN_GENERATOR + POP_TOP have a net stack effect
* of 0. This is because RETURN_GENERATOR pushes an element
* with _PyFrame_StackPush before switching stacks.
*/
cfg_instr make_gen = {
.i_opcode = RETURN_GENERATOR,
.i_oparg = 0,
Expand Down Expand Up @@ -7715,19 +7722,27 @@ optimize_and_assemble_code_unit(struct compiler_unit *u, PyObject *const_cache,
int nparams = (int)PyList_GET_SIZE(u->u_ste->ste_varnames);
int nlocals = (int)PyDict_GET_SIZE(u->u_metadata.u_varnames);
assert(u->u_metadata.u_firstlineno);
if (_PyCfg_OptimizeCodeUnit(&g, consts, const_cache, code_flags, nlocals,
if (_PyCfg_OptimizeCodeUnit(&g, consts, const_cache, nlocals,
nparams, u->u_metadata.u_firstlineno) < 0) {
goto error;
}

/** Assembly **/
int nlocalsplus = prepare_localsplus(&u->u_metadata, &g, code_flags);
if (nlocalsplus < 0) {
int stackdepth = _PyCfg_Stackdepth(&g);
if (stackdepth < 0) {
goto error;
}

int maxdepth = _PyCfg_Stackdepth(g.g_entryblock, code_flags);
if (maxdepth < 0) {
/* prepare_localsplus adds instructions for generators that push
* and pop an item on the stack. This assertion makes sure there
* is space on the stack for that.
* It should always be true, because at least one expression is
* required to turn a function into a generator.
*/
assert(!(IS_GENERATOR(code_flags) && stackdepth == 0));

/** Assembly **/
int nlocalsplus = prepare_localsplus(&u->u_metadata, &g, code_flags);
if (nlocalsplus < 0) {
goto error;
}

Expand All @@ -7746,7 +7761,7 @@ optimize_and_assemble_code_unit(struct compiler_unit *u, PyObject *const_cache,
}

co = _PyAssemble_MakeCodeObject(&u->u_metadata, const_cache, consts,
maxdepth, &optimized_instrs, nlocalsplus,
stackdepth, &optimized_instrs, nlocalsplus,
code_flags, filename);

error:
Expand Down Expand Up @@ -8190,8 +8205,8 @@ _PyCompile_OptimizeCfg(PyObject *instructions, PyObject *consts, int nlocals)
if (instructions_to_cfg(instructions, &g) < 0) {
goto error;
}
int code_flags = 0, nparams = 0, firstlineno = 1;
if (_PyCfg_OptimizeCodeUnit(&g, consts, const_cache, code_flags, nlocals,
int nparams = 0, firstlineno = 1;
if (_PyCfg_OptimizeCodeUnit(&g, consts, const_cache, nlocals,
nparams, firstlineno) < 0) {
goto error;
}
Expand Down Expand Up @@ -8226,14 +8241,14 @@ _PyCompile_Assemble(_PyCompile_CodeUnitMetadata *umd, PyObject *filename,
goto error;
}

int code_flags = 0;
int nlocalsplus = prepare_localsplus(umd, &g, code_flags);
if (nlocalsplus < 0) {
int stackdepth = _PyCfg_Stackdepth(&g);
if (stackdepth < 0) {
goto error;
}

int maxdepth = _PyCfg_Stackdepth(g.g_entryblock, code_flags);
if (maxdepth < 0) {
int code_flags = 0;
int nlocalsplus = prepare_localsplus(umd, &g, code_flags);
if (nlocalsplus < 0) {
goto error;
}

Expand All @@ -8256,7 +8271,7 @@ _PyCompile_Assemble(_PyCompile_CodeUnitMetadata *umd, PyObject *filename,
goto error;
}
co = _PyAssemble_MakeCodeObject(umd, const_cache,
consts, maxdepth, &optimized_instrs,
consts, stackdepth, &optimized_instrs,
nlocalsplus, code_flags, filename);
Py_DECREF(consts);

Expand Down
61 changes: 41 additions & 20 deletions Python/flowgraph.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -615,23 +615,28 @@ make_cfg_traversal_stack(basicblock *entryblock) {
return stack;
}

Py_LOCAL_INLINE(void)
Py_LOCAL_INLINE(int)
stackdepth_push(basicblock ***sp, basicblock *b, int depth)
{
assert(b->b_startdepth < 0 || b->b_startdepth == depth);
if (!(b->b_startdepth < 0 || b->b_startdepth == depth)) {
PyErr_Format(PyExc_ValueError, "Invalid CFG, inconsistent stackdepth");
return ERROR;
}
if (b->b_startdepth < depth && b->b_startdepth < 100) {
assert(b->b_startdepth < 0);
b->b_startdepth = depth;
*(*sp)++ = b;
}
return SUCCESS;
}

/* Find the flow path that needs the largest stack. We assume that
* cycles in the flow graph have no net effect on the stack depth.
*/
int
_PyCfg_Stackdepth(basicblock *entryblock, int code_flags)
_PyCfg_Stackdepth(cfg_builder *g)
{
basicblock *entryblock = g->g_entryblock;
for (basicblock *b = entryblock; b != NULL; b = b->b_next) {
b->b_startdepth = INT_MIN;
}
Expand All @@ -640,42 +645,54 @@ _PyCfg_Stackdepth(basicblock *entryblock, int code_flags)
return ERROR;
}


int stackdepth = -1;
int maxdepth = 0;
basicblock **sp = stack;
if (code_flags & (CO_GENERATOR | CO_COROUTINE | CO_ASYNC_GENERATOR)) {
stackdepth_push(&sp, entryblock, 1);
} else {
stackdepth_push(&sp, entryblock, 0);
if (stackdepth_push(&sp, entryblock, 0) < 0) {
goto error;
}

while (sp != stack) {
basicblock *b = *--sp;
int depth = b->b_startdepth;
assert(depth >= 0);
basicblock *next = b->b_next;
for (int i = 0; i < b->b_iused; i++) {
cfg_instr *instr = &b->b_instr[i];
int effect = PyCompile_OpcodeStackEffectWithJump(instr->i_opcode, instr->i_oparg, 0);
int effect = PyCompile_OpcodeStackEffectWithJump(
instr->i_opcode, instr->i_oparg, 0);
if (effect == PY_INVALID_STACK_EFFECT) {
PyErr_Format(PyExc_SystemError,
"compiler PyCompile_OpcodeStackEffectWithJump(opcode=%d, arg=%i) failed",
"Invalid stack effect for opcode=%d, arg=%i",
instr->i_opcode, instr->i_oparg);
return ERROR;
goto error;
}
int new_depth = depth + effect;
assert(new_depth >= 0); /* invalid code or bug in stackdepth() */
if (new_depth < 0) {
PyErr_Format(PyExc_ValueError,
"Invalid CFG, stack underflow");
goto error;
}
if (new_depth > maxdepth) {
maxdepth = new_depth;
}
if (HAS_TARGET(instr->i_opcode)) {
effect = PyCompile_OpcodeStackEffectWithJump(instr->i_opcode, instr->i_oparg, 1);
assert(effect != PY_INVALID_STACK_EFFECT);
effect = PyCompile_OpcodeStackEffectWithJump(
instr->i_opcode, instr->i_oparg, 1);
if (effect == PY_INVALID_STACK_EFFECT) {
PyErr_Format(PyExc_SystemError,
"Invalid stack effect for opcode=%d, arg=%i",
instr->i_opcode, instr->i_oparg);
goto error;
}
int target_depth = depth + effect;
assert(target_depth >= 0); /* invalid code or bug in stackdepth() */
if (target_depth > maxdepth) {
maxdepth = target_depth;
}
stackdepth_push(&sp, instr->i_target, target_depth);
if (stackdepth_push(&sp, instr->i_target, target_depth) < 0) {
goto error;
}
}
depth = new_depth;
assert(!IS_ASSEMBLER_OPCODE(instr->i_opcode));
Expand All @@ -689,11 +706,15 @@ _PyCfg_Stackdepth(basicblock *entryblock, int code_flags)
}
if (next != NULL) {
assert(BB_HAS_FALLTHROUGH(b));
stackdepth_push(&sp, next, depth);
if (stackdepth_push(&sp, next, depth) < 0) {
goto error;
}
}
}
stackdepth = maxdepth;
error:
PyMem_Free(stack);
return maxdepth;
return stackdepth;
}

static int
Expand Down Expand Up @@ -2009,7 +2030,7 @@ mark_cold(basicblock *entryblock) {


static int
push_cold_blocks_to_end(cfg_builder *g, int code_flags) {
push_cold_blocks_to_end(cfg_builder *g) {
basicblock *entryblock = g->g_entryblock;
if (entryblock->b_next == NULL) {
/* single basicblock, no need to reorder */
Expand Down Expand Up @@ -2251,7 +2272,7 @@ resolve_line_numbers(cfg_builder *g, int firstlineno)

int
_PyCfg_OptimizeCodeUnit(cfg_builder *g, PyObject *consts, PyObject *const_cache,
int code_flags, int nlocals, int nparams, int firstlineno)
int nlocals, int nparams, int firstlineno)
{
assert(cfg_builder_check(g));
/** Preprocessing **/
Expand All @@ -2268,7 +2289,7 @@ _PyCfg_OptimizeCodeUnit(cfg_builder *g, PyObject *consts, PyObject *const_cache,
g->g_entryblock, nlocals, nparams));
insert_superinstructions(g);

RETURN_IF_ERROR(push_cold_blocks_to_end(g, code_flags));
RETURN_IF_ERROR(push_cold_blocks_to_end(g));
RETURN_IF_ERROR(resolve_line_numbers(g, firstlineno));
return SUCCESS;
}

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