STINNER Victor <victor.stin...@gmail.com> added the comment:
Oh, I read again the patch. There are two different cases:
* The code is really unreachable. Ex: the loop of lookdict() does never stop,
return is used in the loop. Py_UNREACHABLE can be used in this case *to avoid a
compiler warning*. __builtin_unreachable() helps if you have GCC, but if you
don't have GCC, using return with a dummy value would be better than a
Py_FatalError(). I don't think that calling Py_FatalError() does make the
warning quiet.
* The code is reachable, but if it is reached, it's a bug. Ex: switch/case on
the Unicode kinde of a string. I like the current solution: assert(0) + return
a almost valid value, but Antoine and Benjamin don't like the "almost valid
value" (and so prefer a fatal error?). We may issue a warning instead of a
fatal error (e.g. write a message into stderr with fprintf ?) in release mode.
--
Using return, it gives something like:
+#ifdef NDEBUG
+#ifdef __GNUC__
+#define Py_UNREACHABLE(value) __builtin_unreachable()
+#else
+#define Py_UNREACHABLE(value) return (value);
+#endif
+#else
+#define Py_UNREACHABLE(value) do { assert(0); return (value); } while (0)
+#endif
It cannot be used if the function has no result value (void), but quite all
Python functions have a result.
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<http://bugs.python.org/issue14656>
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