invoke.texi (Optimize Options): Add cross-reference to -Q --help=optimizers examples.

2009-04-09  Sandra Loosemore  <sandra@codesourcery.com>

	gcc/
	* doc/invoke.texi (Optimize Options): Add cross-reference to
	-Q --help=optimizers examples.

From-SVN: r145864

gcc/ChangeLog

+2009-04-09  Sandra Loosemore  <sandra@codesourcery.com>
+
+	* doc/invoke.texi (Optimize Options): Add cross-reference to
+	-Q --help=optimizers examples.
+
 2009-04-10  Ben Elliston  <bje@au.ibm.com>
 
 	PR target/36800

gcc/doc/invoke.texi

@@ -5372,7 +5372,13 @@ the compiler to use information gained from all of the files when compiling
 each of them.
 
 Not all optimizations are controlled directly by a flag.  Only
-optimizations that have a flag are listed.
+optimizations that have a flag are listed in this section.
+
+Depending on the target and how GCC was configured, a slightly different 
+set of optimizations may be enabled at each @option{-O} level than 
+those listed here.  You can invoke GCC with @samp{-Q --help=optimizers} 
+to find out the exact set of optimizations that are enabled at each level.
+@xref{Overall Options}, for examples.
 
 @table @gcctabopt
 @item -O