gh-126835: Fix _PY_IS_SMALL_INT() macro (#146631)

Include/internal/pycore_long.h

@@ -64,7 +64,8 @@ PyAPI_FUNC(void) _PyLong_ExactDealloc(PyObject *self);
 #  error "_PY_NSMALLPOSINTS must be greater than or equal to 257"
 #endif
 
-#define _PY_IS_SMALL_INT(val) ((val) >= 0 && (val) < 256 && (val) < _PY_NSMALLPOSINTS)
+#define _PY_IS_SMALL_INT(val) \
+    (-_PY_NSMALLNEGINTS <= (val) && (val) < _PY_NSMALLPOSINTS)
 
 // Return a reference to the immortal zero singleton.
 // The function cannot return NULL.

Objects/longobject.c

@@ -26,7 +26,7 @@ class int "PyObject *" "&PyLong_Type"
 
 #define medium_value(x) ((stwodigits)_PyLong_CompactValue(x))
 
-#define IS_SMALL_INT(ival) (-_PY_NSMALLNEGINTS <= (ival) && (ival) < _PY_NSMALLPOSINTS)
+#define IS_SMALL_INT(ival) _PY_IS_SMALL_INT(ival)
 #define IS_SMALL_UINT(ival) ((ival) < _PY_NSMALLPOSINTS)
 
 #define _MAX_STR_DIGITS_ERROR_FMT_TO_INT "Exceeds the limit (%d digits) for integer string conversion: value has %zd digits; use sys.set_int_max_str_digits() to increase the limit"

Python/flowgraph.c

@@ -1411,7 +1411,7 @@ maybe_instr_make_load_smallint(cfg_instr *instr, PyObject *newconst,
         if (val == -1 && PyErr_Occurred()) {
             return -1;
         }
-        if (!overflow && _PY_IS_SMALL_INT(val)) {
+        if (!overflow && _PY_IS_SMALL_INT(val) && 0 <= val && val <= 255) {
             assert(_Py_IsImmortal(newconst));
             INSTR_SET_OP1(instr, LOAD_SMALL_INT, (int)val);
             return 1;