Document that attribute noreturn inhibits tail call optimization

	PR middle-end/81035
	* doc/extend.texi (Common Function Attributes): Mention that
	noreturn suppresses tail call optimization.

From-SVN: r264490

gcc/ChangeLog

+2018-09-21  Florian Weimer  <fweimer@redhat.com>
+
+	PR middle-end/81035
+	* doc/extend.texi (Common Function Attributes): Mention that
+	noreturn suppresses tail call optimization.
+
 2018-09-21  David Malcolm  <dmalcolm@redhat.com>
 
 	PR tree-optimization/87309

gcc/doc/extend.texi

@@ -3157,6 +3157,9 @@ The @code{noreturn} keyword does not affect the exceptional path when that
 applies: a @code{noreturn}-marked function may still return to the caller
 by throwing an exception or calling @code{longjmp}.
 
+In order to preserve backtraces, GCC will never turn calls to
+@code{noreturn} functions into tail calls.
+
 Do not assume that registers saved by the calling function are
 restored before calling the @code{noreturn} function.