https://github.com/python/cpython/commit/8fdbbf8b18f1405abe677d0e04874c1c86ccdb4a
commit: 8fdbbf8b18f1405abe677d0e04874c1c86ccdb4a
branch: main
author: Amit Lavon <[email protected]>
committer: brandtbucher <[email protected]>
date: 2025-06-07T14:08:44-07:00
summary:
GH-131798: Type-propagate string/list/tuple slices (GH-134671)
files:
A
Misc/NEWS.d/next/Core_and_Builtins/2025-05-25-19-32-15.gh-issue-131798.f5h8aI.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 ee8d261685d463..8a3819dabe44ce 100644
--- a/Lib/test/test_capi/test_opt.py
+++ b/Lib/test/test_capi/test_opt.py
@@ -1666,13 +1666,11 @@ def testfunc(n):
self.assertIn("_CONTAINS_OP_DICT", uops)
self.assertNotIn("_TO_BOOL_BOOL", uops)
-
def test_remove_guard_for_known_type_str(self):
def f(n):
for i in range(n):
false = i == TIER2_THRESHOLD
empty = "X"[:false]
- empty += "" # Make JIT realize this is a string.
if empty:
return 1
return 0
@@ -2249,6 +2247,34 @@ def f(n):
self.assertNotIn("_LOAD_ATTR_METHOD_NO_DICT", uops)
self.assertNotIn("_LOAD_ATTR_METHOD_LAZY_DICT", uops)
+ def test_remove_guard_for_slice_list(self):
+ def f(n):
+ for i in range(n):
+ false = i == TIER2_THRESHOLD
+ sliced = [1, 2, 3][:false]
+ if sliced:
+ return 1
+ return 0
+
+ res, ex = self._run_with_optimizer(f, TIER2_THRESHOLD)
+ self.assertEqual(res, 0)
+ self.assertIsNotNone(ex)
+ uops = get_opnames(ex)
+ self.assertIn("_TO_BOOL_LIST", uops)
+ self.assertNotIn("_GUARD_TOS_LIST", uops)
+
+ def test_remove_guard_for_slice_tuple(self):
+ def f(n):
+ for i in range(n):
+ false = i == TIER2_THRESHOLD
+ a, b = (1, 2, 3)[: false + 2]
+
+ _, ex = self._run_with_optimizer(f, TIER2_THRESHOLD)
+ self.assertIsNotNone(ex)
+ uops = get_opnames(ex)
+ self.assertIn("_UNPACK_SEQUENCE_TWO_TUPLE", uops)
+ self.assertNotIn("_GUARD_TOS_TUPLE", uops)
+
def global_identity(x):
return x
diff --git
a/Misc/NEWS.d/next/Core_and_Builtins/2025-05-25-19-32-15.gh-issue-131798.f5h8aI.rst
b/Misc/NEWS.d/next/Core_and_Builtins/2025-05-25-19-32-15.gh-issue-131798.f5h8aI.rst
new file mode 100644
index 00000000000000..6ecbfb8d9cf7df
--- /dev/null
+++
b/Misc/NEWS.d/next/Core_and_Builtins/2025-05-25-19-32-15.gh-issue-131798.f5h8aI.rst
@@ -0,0 +1 @@
+Make the JIT optimizer understand that slicing a string/list/tuple returns the
same type.
diff --git a/Python/optimizer_bytecodes.c b/Python/optimizer_bytecodes.c
index 12efaacd8f0dfc..fbf4dfd3db629c 100644
--- a/Python/optimizer_bytecodes.c
+++ b/Python/optimizer_bytecodes.c
@@ -1237,6 +1237,20 @@ dummy_func(void) {
sym_set_const(callable, list_append);
}
+ op(_BINARY_SLICE, (container, start, stop -- res)) {
+ // Slicing a string/list/tuple always returns the same type.
+ PyTypeObject *type = sym_get_type(container);
+ if (type == &PyUnicode_Type ||
+ type == &PyList_Type ||
+ type == &PyTuple_Type)
+ {
+ res = sym_new_type(ctx, type);
+ }
+ else {
+ res = sym_new_not_null(ctx);
+ }
+ }
+
// END BYTECODES //
}
diff --git a/Python/optimizer_cases.c.h b/Python/optimizer_cases.c.h
index 1a2d49973ee916..b42f47c75eaf50 100644
--- a/Python/optimizer_cases.c.h
+++ b/Python/optimizer_cases.c.h
@@ -568,8 +568,19 @@
}
case _BINARY_SLICE: {
+ JitOptSymbol *container;
JitOptSymbol *res;
- res = sym_new_not_null(ctx);
+ container = stack_pointer[-3];
+ PyTypeObject *type = sym_get_type(container);
+ if (type == &PyUnicode_Type ||
+ type == &PyList_Type ||
+ type == &PyTuple_Type)
+ {
+ res = sym_new_type(ctx, type);
+ }
+ else {
+ res = sym_new_not_null(ctx);
+ }
stack_pointer[-3] = res;
stack_pointer += -2;
assert(WITHIN_STACK_BOUNDS());
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