bpo-47053: Reduce deoptimization in BINARY_OP_INPLACE_ADD_UNICODE (GH-31318)

* Don't deopt if refcounts are too big

* Detect more at specialization time

4 files changed, 11 insertions, 7 deletions

diff --git a/Include/internal/pycore_code.h b/Include/internal/pycore_code.h
index 82dc9e4..0f6613b 100644
--- a/Include/internal/pycore_code.h
+++ b/Include/internal/pycore_code.h
@@ -263,7 +263,7 @@ extern int _Py_Specialize_Call(PyObject *callable, _Py_CODEUNIT *instr,
 extern int _Py_Specialize_Precall(PyObject *callable, _Py_CODEUNIT *instr,
                                   int nargs, PyObject *kwnames, int oparg);
 extern void _Py_Specialize_BinaryOp(PyObject *lhs, PyObject *rhs, _Py_CODEUNIT *instr,
-                                    int oparg);
+                                    int oparg, PyObject **locals);
 extern void _Py_Specialize_CompareOp(PyObject *lhs, PyObject *rhs,
                                      _Py_CODEUNIT *instr, int oparg);
 extern void _Py_Specialize_UnpackSequence(PyObject *seq, _Py_CODEUNIT *instr,
diff --git a/Misc/NEWS.d/next/Core and Builtins/2022-03-17-22-47-29.bpo-47053.QAXk8Q.rst b/Misc/NEWS.d/next/Core and Builtins/2022-03-17-22-47-29.bpo-47053.QAXk8Q.rst
new file mode 100644
index 0000000..097105b
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2022-03-17-22-47-29.bpo-47053.QAXk8Q.rst
@@ -0,0 +1 @@
+Reduce de-optimization in the specialized ``BINARY_OP_INPLACE_ADD_UNICODE`` opcode.
diff --git a/Python/ceval.c b/Python/ceval.c
index e1d961f..4824b19 100644
--- a/Python/ceval.c
+++ b/Python/ceval.c
@@ -2002,10 +2002,10 @@ handle_eval_breaker:
             PyObject *right = TOP();
             DEOPT_IF(!PyUnicode_CheckExact(left), BINARY_OP);
             DEOPT_IF(Py_TYPE(right) != Py_TYPE(left), BINARY_OP);
-            DEOPT_IF(Py_REFCNT(left) != 2, BINARY_OP);
             _Py_CODEUNIT true_next = next_instr[INLINE_CACHE_ENTRIES_BINARY_OP];
             int next_oparg = _Py_OPARG(true_next);
-            assert(_Py_OPCODE(true_next) == STORE_FAST);
+            assert(_Py_OPCODE(true_next) == STORE_FAST ||
+                   _Py_OPCODE(true_next) == STORE_FAST__LOAD_FAST);
             /* In the common case, there are 2 references to the value
             * stored in 'variable' when the v = v + ... is performed: one
             * on the value stack (in 'v') and one still stored in the
@@ -2016,7 +2016,8 @@ handle_eval_breaker:
             DEOPT_IF(var != left, BINARY_OP);
             STAT_INC(BINARY_OP, hit);
             GETLOCAL(next_oparg) = NULL;
-            Py_DECREF(left);
+            assert(Py_REFCNT(left) >= 2);
+            Py_DECREF(left); // XXX never need to dealloc
             STACK_SHRINK(1);
             PyUnicode_Append(&TOP(), right);
             Py_DECREF(right);
@@ -5378,7 +5379,7 @@ handle_eval_breaker:
                 PyObject *lhs = SECOND();
                 PyObject *rhs = TOP();
                 next_instr--;
-                _Py_Specialize_BinaryOp(lhs, rhs, next_instr, oparg);
+                _Py_Specialize_BinaryOp(lhs, rhs, next_instr, oparg, &GETLOCAL(0));
                 DISPATCH();
             }
             else {
diff --git a/Python/specialize.c b/Python/specialize.c
index ce091a2..720bc7f 100644
--- a/Python/specialize.c
+++ b/Python/specialize.c
@@ -1742,7 +1742,7 @@ binary_op_fail_kind(int oparg, PyObject *lhs, PyObject *rhs)
 
 void
 _Py_Specialize_BinaryOp(PyObject *lhs, PyObject *rhs, _Py_CODEUNIT *instr,
-                        int oparg)
+                        int oparg, PyObject **locals)
 {
     assert(_PyOpcode_Caches[BINARY_OP] == INLINE_CACHE_ENTRIES_BINARY_OP);
     _PyBinaryOpCache *cache = (_PyBinaryOpCache *)(instr + 1);
@@ -1754,7 +1754,9 @@ _Py_Specialize_BinaryOp(PyObject *lhs, PyObject *rhs, _Py_CODEUNIT *instr,
             }
             if (PyUnicode_CheckExact(lhs)) {
                 _Py_CODEUNIT next = instr[INLINE_CACHE_ENTRIES_BINARY_OP + 1];
-                if (_Py_OPCODE(next) == STORE_FAST && Py_REFCNT(lhs) == 2) {
+                bool to_store = (_Py_OPCODE(next) == STORE_FAST ||
+                                 _Py_OPCODE(next) == STORE_FAST__LOAD_FAST);
+                if (to_store && locals[_Py_OPARG(next)] == lhs) {
                     _Py_SET_OPCODE(*instr, BINARY_OP_INPLACE_ADD_UNICODE);
                     goto success;
                 }