invoke.texi (Optimize Options): Refine the description of asan-use-after-return.

	* doc/invoke.texi (Optimize Options): Refine the description
	of asan-use-after-return.

From-SVN: r245747

gcc/ChangeLog

+2017-02-26  Gerald Pfeifer  <gerald@pfeifer.com>
+
+	* doc/invoke.texi (Optimize Options): Refine the description
+	of asan-use-after-return.
+
 2017-02-25  Alan Modra  <amodra@gmail.com>
 
 	PR rtl-optimization/79584

gcc/doc/invoke.texi

@@ -10468,13 +10468,12 @@ To disable built-in functions protection use
 
 @item asan-use-after-return
 Enable detection of use-after-return.  This kind of protection
-is enabled by default when using @option{-fsanitize=address} option.
-To disable use-after-return detection use 
-@option{--param asan-use-after-return=0}.
+is enabled by default when using the @option{-fsanitize=address} option.
+To disable it use @option{--param asan-use-after-return=0}.
 
-Note: The check is disabled by default at runtime.  To enable the check,
-you should set environment variable @env{ASAN_OPTIONS} to
-@code{detect_stack_use_after_return=1}.
+Note: By default the check is disabled at run time.  To enable it,
+add @code{detect_stack_use_after_return=1} to the environment variable
+@env{ASAN_OPTIONS}.
 
 @item asan-instrumentation-with-call-threshold
 If number of memory accesses in function being instrumented