https://github.com/python/cpython/commit/61532b4bc783c1570c0fd7fb2ff5f8157cf64e82
commit: 61532b4bc783c1570c0fd7fb2ff5f8157cf64e82
branch: main
author: Tomas R. <[email protected]>
committer: tomasr8 <[email protected]>
date: 2025-06-20T18:21:39+02:00
summary:
gh-131798: JIT: Optimize _CALL_LEN when the length is known (#135260)
* Add news entry
* Optimize _CALL_LEN
* Simplify tests
files:
A
Misc/NEWS.d/next/Core_and_Builtins/2025-06-08-14-24-29.gh-issue-131798.qfw91T.rst
M Lib/test/test_capi/test_opt.py
M Python/optimizer_bytecodes.c
M Python/optimizer_cases.c.h
diff --git a/Lib/test/test_capi/test_opt.py b/Lib/test/test_capi/test_opt.py
index 2b6934d747ebe0..84e864b44b9544 100644
--- a/Lib/test/test_capi/test_opt.py
+++ b/Lib/test/test_capi/test_opt.py
@@ -1968,6 +1968,49 @@ def testfunc(n):
self.assertNotIn("_GUARD_NOS_INT", uops)
self.assertNotIn("_GUARD_TOS_INT", uops)
+ def test_call_len_known_length_small_int(self):
+ def testfunc(n):
+ x = 0
+ for _ in range(n):
+ t = (1, 2, 3, 4, 5)
+ if len(t) == 5:
+ x += 1
+ return x
+
+ res, ex = self._run_with_optimizer(testfunc, TIER2_THRESHOLD)
+ self.assertEqual(res, TIER2_THRESHOLD)
+ self.assertIsNotNone(ex)
+ uops = get_opnames(ex)
+ # When the length is < _PY_NSMALLPOSINTS, the len() call is replaced
+ # with just an inline load.
+ self.assertNotIn("_CALL_LEN", uops)
+ self.assertNotIn("_POP_CALL_ONE_LOAD_CONST_INLINE_BORROW", uops)
+ self.assertNotIn("_POP_CALL_LOAD_CONST_INLINE_BORROW", uops)
+ self.assertNotIn("_POP_TOP_LOAD_CONST_INLINE_BORROW", uops)
+
+ def test_call_len_known_length(self):
+ def testfunc(n):
+ class C:
+ t = tuple(range(300))
+
+ x = 0
+ for _ in range(n):
+ if len(C.t) == 300: # comparison + guard removed
+ x += 1
+ return x
+
+ res, ex = self._run_with_optimizer(testfunc, TIER2_THRESHOLD)
+ self.assertEqual(res, TIER2_THRESHOLD)
+ self.assertIsNotNone(ex)
+ uops = get_opnames(ex)
+ # When the length is >= _PY_NSMALLPOSINTS, we cannot replace
+ # the len() call with an inline load, but knowing the exact
+ # length allows us to optimize more code, such as conditionals
+ # in this case
+ self.assertIn("_CALL_LEN", uops)
+ self.assertNotIn("_COMPARE_OP_INT", uops)
+ self.assertNotIn("_GUARD_IS_TRUE_POP", uops)
+
def test_get_len_with_const_tuple(self):
def testfunc(n):
x = 0.0
diff --git
a/Misc/NEWS.d/next/Core_and_Builtins/2025-06-08-14-24-29.gh-issue-131798.qfw91T.rst
b/Misc/NEWS.d/next/Core_and_Builtins/2025-06-08-14-24-29.gh-issue-131798.qfw91T.rst
new file mode 100644
index 00000000000000..7965169d46e820
--- /dev/null
+++
b/Misc/NEWS.d/next/Core_and_Builtins/2025-06-08-14-24-29.gh-issue-131798.qfw91T.rst
@@ -0,0 +1 @@
+Optimize _CALL_LEN in the JIT when the length is known. Patch by Tomas Roun
diff --git a/Python/optimizer_bytecodes.c b/Python/optimizer_bytecodes.c
index 2e240830013a46..3f2e2e0351e052 100644
--- a/Python/optimizer_bytecodes.c
+++ b/Python/optimizer_bytecodes.c
@@ -1203,8 +1203,21 @@ dummy_func(void) {
sym_set_const(callable, (PyObject *)&PyUnicode_Type);
}
- op(_CALL_LEN, (unused, unused, unused -- res)) {
+ op(_CALL_LEN, (callable, null, arg -- res)) {
res = sym_new_type(ctx, &PyLong_Type);
+ int tuple_length = sym_tuple_length(arg);
+ if (tuple_length >= 0) {
+ PyObject *temp = PyLong_FromLong(tuple_length);
+ if (temp == NULL) {
+ goto error;
+ }
+ if (_Py_IsImmortal(temp)) {
+ REPLACE_OP(this_instr, _POP_CALL_ONE_LOAD_CONST_INLINE_BORROW,
+ 0, (uintptr_t)temp);
+ }
+ res = sym_new_const(ctx, temp);
+ Py_DECREF(temp);
+ }
}
op(_GET_LEN, (obj -- obj, len)) {
diff --git a/Python/optimizer_cases.c.h b/Python/optimizer_cases.c.h
index 3cabf619fe81e7..91927180b3509d 100644
--- a/Python/optimizer_cases.c.h
+++ b/Python/optimizer_cases.c.h
@@ -2241,8 +2241,27 @@
}
case _CALL_LEN: {
+ JitOptRef arg;
JitOptRef res;
+ arg = stack_pointer[-1];
res = sym_new_type(ctx, &PyLong_Type);
+ int tuple_length = sym_tuple_length(arg);
+ if (tuple_length >= 0) {
+ PyObject *temp = PyLong_FromLong(tuple_length);
+ if (temp == NULL) {
+ goto error;
+ }
+ if (_Py_IsImmortal(temp)) {
+ REPLACE_OP(this_instr,
_POP_CALL_ONE_LOAD_CONST_INLINE_BORROW,
+ 0, (uintptr_t)temp);
+ }
+ res = sym_new_const(ctx, temp);
+ stack_pointer[-3] = res;
+ stack_pointer += -2;
+ assert(WITHIN_STACK_BOUNDS());
+ Py_DECREF(temp);
+ stack_pointer += 2;
+ }
stack_pointer[-3] = res;
stack_pointer += -2;
assert(WITHIN_STACK_BOUNDS());
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