gh-134584: Eliminate redundant refcounting from TO_BOOL_STR

Lib/test/test_capi/test_opt.py

@@ -2937,6 +2937,23 @@ def testfunc(n):
         self.assertLessEqual(count_ops(ex, "_POP_TOP"), 1)
         self.assertIn("_POP_TOP_NOP", uops)
 
+    def test_to_bool_str(self):
+        def f(n):
+            for i in range(n):
+                false = i == TIER2_THRESHOLD
+                empty = "X"[:false]
+                if empty:
+                    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_STR", uops)
+        self.assertLessEqual(count_ops(ex, "_POP_TOP"), 3)
+        self.assertIn("_POP_TOP_NOP", uops)
+
     def test_to_bool_always_true(self):
         def testfunc(n):
             class A:

Misc/NEWS.d/next/Core_and_Builtins/2026-01-04-23-53-42.gh-issue-134584.CNrxI_.rst

@@ -0,0 +1 @@
+Eliminate redundant refcounting from ``TO_BOOL_STR``.

Python/bytecodes.c

@@ -547,23 +547,16 @@ dummy_func(
             EXIT_IF(!PyUnicode_CheckExact(value_o));
         }
 
-        op(_TO_BOOL_STR, (value -- res)) {
+        op(_TO_BOOL_STR, (value -- res, v)) {
             STAT_INC(TO_BOOL, hit);
             PyObject *value_o = PyStackRef_AsPyObjectBorrow(value);
-            if (value_o == &_Py_STR(empty)) {
-                assert(_Py_IsImmortal(value_o));
-                DEAD(value);
-                res = PyStackRef_False;
-            }
-            else {
-                assert(Py_SIZE(value_o));
-                PyStackRef_CLOSE(value);
-                res = PyStackRef_True;
-            }
+            res = value_o == &_Py_STR(empty) ? PyStackRef_False : PyStackRef_True;
+            v = value;
+            DEAD(value);
         }
 
         macro(TO_BOOL_STR) =
-            _GUARD_TOS_UNICODE + unused/1 + unused/2 + _TO_BOOL_STR;
+            _GUARD_TOS_UNICODE + unused/1 + unused/2 + _TO_BOOL_STR + _POP_TOP_UNICODE;
 
         op(_REPLACE_WITH_TRUE, (value -- res, v)) {
             res = PyStackRef_True;

Python/optimizer_analysis.c

@@ -214,7 +214,8 @@ optimize_to_bool(
     _PyUOpInstruction *this_instr,
     JitOptContext *ctx,
     JitOptRef value,
-    JitOptRef *result_ptr)
+    JitOptRef *result_ptr,
+    bool insert_mode)
 {
     if (sym_matches_type(value, &PyBool_Type)) {
         REPLACE_OP(this_instr, _NOP, 0, 0);
@@ -224,7 +225,10 @@ optimize_to_bool(
     int truthiness = sym_truthiness(ctx, value);
     if (truthiness >= 0) {
         PyObject *load = truthiness ? Py_True : Py_False;
-        REPLACE_OP(this_instr, _POP_TOP_LOAD_CONST_INLINE_BORROW, 0, (uintptr_t)load);
+        int opcode = insert_mode ?
+            _INSERT_1_LOAD_CONST_INLINE_BORROW :
+            _POP_TOP_LOAD_CONST_INLINE_BORROW;
+        REPLACE_OP(this_instr, opcode, 0, (uintptr_t)load);
         *result_ptr = sym_new_const(ctx, load);
         return 1;
     }

Python/optimizer_bytecodes.c

@@ -44,7 +44,8 @@ optimize_to_bool(
     _PyUOpInstruction *this_instr,
     JitOptContext *ctx,
     JitOptSymbol *value,
-    JitOptSymbol **result_ptr);
+    JitOptSymbol **result_ptr,
+    bool insert_mode);
 
 extern void
 eliminate_pop_guard(_PyUOpInstruction *this_instr, bool exit);
@@ -377,36 +378,36 @@ dummy_func(void) {
     }
 
     op(_TO_BOOL, (value -- res)) {
-        int already_bool = optimize_to_bool(this_instr, ctx, value, &res);
+        int already_bool = optimize_to_bool(this_instr, ctx, value, &res, false);
         if (!already_bool) {
             res = sym_new_truthiness(ctx, value, true);
         }
     }
 
     op(_TO_BOOL_BOOL, (value -- value)) {
-        int already_bool = optimize_to_bool(this_instr, ctx, value, &value);
+        int already_bool = optimize_to_bool(this_instr, ctx, value, &value, false);
         if (!already_bool) {
             sym_set_type(value, &PyBool_Type);
         }
     }
 
     op(_TO_BOOL_INT, (value -- res)) {
-        int already_bool = optimize_to_bool(this_instr, ctx, value, &res);
+        int already_bool = optimize_to_bool(this_instr, ctx, value, &res, false);
         if (!already_bool) {
             sym_set_type(value, &PyLong_Type);
             res = sym_new_truthiness(ctx, value, true);
         }
     }
 
     op(_TO_BOOL_LIST, (value -- res)) {
-        int already_bool = optimize_to_bool(this_instr, ctx, value, &res);
+        int already_bool = optimize_to_bool(this_instr, ctx, value, &res, false);
         if (!already_bool) {
             res = sym_new_type(ctx, &PyBool_Type);
         }
     }
 
     op(_TO_BOOL_NONE, (value -- res)) {
-        int already_bool = optimize_to_bool(this_instr, ctx, value, &res);
+        int already_bool = optimize_to_bool(this_instr, ctx, value, &res, false);
         if (!already_bool) {
             sym_set_const(value, Py_None);
             res = sym_new_const(ctx, Py_False);
@@ -431,8 +432,9 @@ dummy_func(void) {
         sym_set_type(value, &PyUnicode_Type);
     }
 
-    op(_TO_BOOL_STR, (value -- res)) {
-        int already_bool = optimize_to_bool(this_instr, ctx, value, &res);
+    op(_TO_BOOL_STR, (value -- res, v)) {
+        int already_bool = optimize_to_bool(this_instr, ctx, value, &res, true);
+        v = value;
         if (!already_bool) {
             res = sym_new_truthiness(ctx, value, true);
         }