invoke.texi (Optimize Options): Document that -fgcse may cause programs using…

invoke.texi (Optimize Options): Document that -fgcse may cause programs using computed gotos to run more slowly.

	* doc/invoke.texi (Optimize Options): Document that -fgcse may
	cause programs using computed gotos to run more slowly.

Co-Authored-By: Gerald Pfeifer <pfeifer@dbai.tuwien.ac.at>

From-SVN: r43786

gcc/ChangeLog

+2001-07-05  Brad Lucier <lucier@math.purdue.edu>
+	    Gerald Pfeifer  <pfeifer@dbai.tuwien.ac.at>
+
+	* doc/invoke.texi (Optimize Options): Document that -fgcse may
+	cause programs using computed gotos to run more slowly.
+
 2001-07-05  Rainer Orth  <ro@TechFak.Uni-Bielefeld.DE>
 
 	* doc/install.texi (Specific): Markup, spelling and typo fixes.

gcc/doc/invoke.texi

@@ -3189,6 +3189,9 @@ function inlining, and register renaming.  It also turns on the
 @option{-fforce-mem} option on all machines and frame pointer elimination
 on machines where doing so does not interfere with debugging.
 
+Please note the warning under @option{-fgcse} about
+invoking @option{-O2} on programs that use computed gotos.
+
 @item -O3
 @opindex O3
 Optimize yet more.  @option{-O3} turns on all optimizations specified by
@@ -3466,6 +3469,11 @@ Run the loop optimizer twice.
 Perform a global common subexpression elimination pass.
 This pass also performs global constant and copy propagation.
 
+@emph{Note:} When compiling a program using computed gotos, a GCC
+extension, you may get better runtime performance if you disable
+the global common subexpression elmination pass by adding
+@option{-fno-gcse} to the command line.
+
 @item -fgcse-lm
 @opindex fgcse-lm
 When @option{-fgcse-lm} is enabled, global common subexpression elimination will