From eb83a264882a44ec08ee50eb9b2bff477c2812f1 Mon Sep 17 00:00:00 2001
From: Carl Meyer <carl@oddbird.net>
Date: Thu, 18 May 2023 17:10:18 -0700
Subject: [PATCH] [3.11] gh-104615: don't make unsafe swaps in
apply_static_swaps (GH-104620). (cherry picked from commit
0589c6a4d3d822cace42050198cb9a5e99c879ad)
Co-authored-by: Carl Meyer <carl@oddbird.net>
---
Lib/test/test_compile.py | 18 +++++++++++++++++
...-05-18-13-00-21.gh-issue-104615.h_rtw2.rst | 2 ++
Python/compile.c | 20 +++++++++++++++++++
3 files changed, 40 insertions(+)
create mode 100644 Misc/NEWS.d/next/Core and Builtins/2023-05-18-13-00-21.gh-issue-104615.h_rtw2.rst
diff --git a/Lib/test/test_compile.py b/Lib/test/test_compile.py
index c96ae4375df883..c756d43a3cf3b8 100644
--- a/Lib/test/test_compile.py
+++ b/Lib/test/test_compile.py
@@ -1064,6 +1064,24 @@ def test_compare_positions(self):
with self.subTest(source):
self.assertEqual(actual_positions, expected_positions)
+ def test_apply_static_swaps(self):
+ def f(x, y):
+ a, a = x, y
+ return a
+ self.assertEqual(f("x", "y"), "y")
+
+ def test_apply_static_swaps_2(self):
+ def f(x, y, z):
+ a, b, a = x, y, z
+ return a
+ self.assertEqual(f("x", "y", "z"), "z")
+
+ def test_apply_static_swaps_3(self):
+ def f(x, y, z):
+ a, a, b = x, y, z
+ return a
+ self.assertEqual(f("x", "y", "z"), "y")
+
@requires_debug_ranges()
class TestSourcePositions(unittest.TestCase):
diff --git a/Misc/NEWS.d/next/Core and Builtins/2023-05-18-13-00-21.gh-issue-104615.h_rtw2.rst b/Misc/NEWS.d/next/Core and Builtins/2023-05-18-13-00-21.gh-issue-104615.h_rtw2.rst
new file mode 100644
index 00000000000000..447291a619dd67
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2023-05-18-13-00-21.gh-issue-104615.h_rtw2.rst
@@ -0,0 +1,2 @@
+Fix wrong ordering of assignments in code like ``a, a = x, y``. Contributed by
+Carl Meyer.
diff --git a/Python/compile.c b/Python/compile.c
index f87a423acd1f02..1c712fba31573e 100644
--- a/Python/compile.c
+++ b/Python/compile.c
@@ -8690,6 +8690,9 @@ swaptimize(basicblock *block, int *ix)
#define SWAPPABLE(opcode) \
((opcode) == STORE_FAST || (opcode) == POP_TOP)
+#define STORES_TO(instr) \
+ (((instr).i_opcode == STORE_FAST) ? (instr).i_oparg : -1)
+
static int
next_swappable_instruction(basicblock *block, int i, int lineno)
{
@@ -8741,6 +8744,23 @@ apply_static_swaps(basicblock *block, int i)
return;
}
}
+ // The reordering is not safe if the two instructions to be swapped
+ // store to the same location, or if any intervening instruction stores
+ // to the same location as either of them.
+ int store_j = STORES_TO(block->b_instr[j]);
+ int store_k = STORES_TO(block->b_instr[k]);
+ if (store_j >= 0 || store_k >= 0) {
+ if (store_j == store_k) {
+ return;
+ }
+ for (int idx = j + 1; idx < k; idx++) {
+ int store_idx = STORES_TO(block->b_instr[idx]);
+ if (store_idx >= 0 && (store_idx == store_j || store_idx == store_k)) {
+ return;
+ }
+ }
+ }
+
// Success!
swap->i_opcode = NOP;
struct instr temp = block->b_instr[j];