Add recommendation.

diff --git a/doc/doc.texi b/doc/doc.texi
index b2b3b5cb8b47a6d9e22ded0157eef5e39652fa56..a2b8b7a91f0d44dc87bd610ab30c1104b3d2b83e 100644 (file)
--- a/doc/doc.texi
+++ b/doc/doc.texi
@@ -112,6 +112,21 @@ should be in @file{pintos/src/threads/testcases}.
 
 @item
 Think about what may actually crash your code.
+
+@item
+Think about what the compiler might do to your code.  Suppose you write
+the following to test your virtual memory implementation's ability to
+expand the stack:
+@example
+int main (void) {
+  int array[4096];
+  array[123] = 234;
+  return 0;
+}
+@end example
+@noindent The compiler is quite likely to notice that the value that you
+write to the array is never used again and thereby decide not to write
+it at all.  The result is that your test does not test anything at all.
 @end itemize
 
 Your @file{TESTCASE} file is also where you can show us the