bpo-38249: Expand Py_UNREACHABLE() to __builtin_unreachable() in the release mode.

Include/pymacro.h

@@ -118,6 +118,10 @@
  "We've reached an unreachable state. Anything is possible.\n" \
  "The limits were in our heads all along. Follow your dreams.\n" \
  "https://xkcd.com/2200")
+#elif defined(__GNUC__) || defined(__clang__) || defined(__INTEL_COMPILER)
+#define Py_UNREACHABLE() __builtin_unreachable()
+#elif defined(_MSC_VER)
+#define Py_UNREACHABLE() __assume(0)
 #else
 #define Py_UNREACHABLE() \
  Py_FatalError("Unreachable C code path reached")

Modules/_tracemalloc.c

@@ -712,7 +712,7 @@ tracemalloc_realloc(void *ctx, void *ptr, size_t new_size)
 
  The GIL and the table lock ensures that only one thread is
  allocating memory. */
- Py_UNREACHABLE();
+ Py_FatalError("Memory allocation failed.");
  }
  TABLES_UNLOCK();
  }

Objects/abstract.c

@@ -1551,18 +1551,15 @@ PyNumber_Float(PyObject *o)
 PyObject *
 PyNumber_ToBase(PyObject *n, int base)
 {
- PyObject *res = NULL;
+ if (!(base == 2 || base == 8 || base == 10 || base == 16)) {
+ PyErr_SetString(PyExc_SystemError,
+ "PyNumber_ToBase: base must be 2, 8, 10 or 16");
+ return NULL;
+ }
  PyObject *index = PyNumber_Index(n);
-
  if (!index)
  return NULL;
- if (PyLong_Check(index))
- res = _PyLong_Format(index, base);
- else
- /* It should not be possible to get here, as
- PyNumber_Index already has a check for the same
- condition */
- PyErr_SetString(PyExc_ValueError, "PyNumber_ToBase: index not int");
+ PyObject *res = _PyLong_Format(index, base);
  Py_DECREF(index);
  return res;
 }

Objects/stringlib/eq.h

@@ -6,13 +6,14 @@
 Py_LOCAL_INLINE(int)
 unicode_eq(PyObject *aa, PyObject *bb)
 {
+ assert(PyUnicode_Check(aa));
+ assert(PyUnicode_Check(bb));
+ assert(PyUnicode_IS_READY(aa));
+ assert(PyUnicode_IS_READY(bb));
+
  PyUnicodeObject *a = (PyUnicodeObject *)aa;
  PyUnicodeObject *b = (PyUnicodeObject *)bb;
 
- if (PyUnicode_READY(a) == -1 || PyUnicode_READY(b) == -1) {
- Py_UNREACHABLE();
- }
-
  if (PyUnicode_GET_LENGTH(a) != PyUnicode_GET_LENGTH(b))
  return 0;
  if (PyUnicode_GET_LENGTH(a) == 0)

Python/formatter_unicode.c

@@ -574,7 +574,7 @@ calc_number_widths(NumberFieldWidths *spec, Py_ssize_t n_prefix,
  spec->n_lpadding = n_padding;
  break;
  default:
- /* Shouldn't get here, but treat it as '>' */
+ /* Shouldn't get here */
  Py_UNREACHABLE();
  }
  }

Python/peephole.c

@@ -511,8 +511,12 @@ PyCode_Optimize(PyObject *code, PyObject* consts, PyObject *names,
  if (instrsize(j) > ilen) {
  goto exitUnchanged;
  }
- assert(ilen <= INT_MAX);
  /* If instrsize(j) < ilen, we'll emit EXTENDED_ARG 0 */
+ if (ilen > 4) {
+ /* Can only happen when PyCode_Optimize() is called with
+ malformed bytecode. */
+ goto exitUnchanged;
+ }
  write_op_arg(codestr + h, opcode, j, (int)ilen);
  h += ilen;
  }

Python/pytime.c

@@ -746,7 +746,7 @@ _PyTime_GetSystemClock(void)
  _PyTime_t t;
  if (pygettimeofday(&t, NULL, 0) < 0) {
  /* should not happen, _PyTime_Init() checked the clock at startup */
- Py_UNREACHABLE();
+ Py_FatalError("pygettimeofday() failed.");
  }
  return t;
 }
@@ -775,8 +775,7 @@ pymonotonic(_PyTime_t *tp, _Py_clock_info_t *info, int raise)
  _PyTime_overflow();
  return -1;
  }
- /* Hello, time traveler! */
- Py_UNREACHABLE();
+ Py_FatalError("Hello, time traveler!");
  }
  *tp = t * MS_TO_NS;
 
@@ -918,7 +917,7 @@ _PyTime_GetMonotonicClock(void)
  if (pymonotonic(&t, NULL, 0) < 0) {
  /* should not happen, _PyTime_Init() checked that monotonic clock at
  startup */
- Py_UNREACHABLE();
+ Py_FatalError("pymonotonic() failed.");
  }
  return t;
 }
@@ -1019,7 +1018,7 @@ _PyTime_GetPerfCounter(void)
 {
  _PyTime_t t;
  if (_PyTime_GetPerfCounterWithInfo(&t, NULL)) {
- Py_UNREACHABLE();
+ Py_FatalError("_PyTime_GetPerfCounterWithInfo() failed.");
  }
  return t;
 }