add an entry, add links to entries for demo page.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@20328 91177308-0d34-0410-b5e6-96231b3b80d8

docs/FAQ.html

@@ -72,12 +72,13 @@
 
   <li><a href="#cfe_code">Questions about code generated by the GCC front-end</a>
   <ol>
-     <li>What is this <tt>__main()</tt> call that gets inserted into
+     <li><a href="#__main">What is this <tt>__main()</tt> call that gets inserted into
-         <tt>main()</tt>?</li>
+         <tt>main()</tt>?</a></li>
-     <li>Where did all of my code go??</li>
+     <li><a href="#iosinit">What is this <tt>llvm.global_ctors</tt> and
-     <li>What is this <tt>llvm.global_ctors</tt> and
           <tt>_GLOBAL__I__tmp_webcompile...</tt> stuff that happens when I
-          #include &lt;iostream&gt;?</li>
+          #include &lt;iostream&gt;?</a></li>
+     <li><a href="#codedce">Where did all of my code go??</a></li>
+     <li><a href="#undef">What is this "<tt>undef</tt>" thing that shows up in my code?</a></li>
   </ol>
   </li>
 </ol>
@@ -448,6 +449,7 @@ correct this, do:</p>
 </div>
 
 <div class="question"><p>
+<a name="__main"></a>
 What is this <tt>__main()</tt> call that gets inserted into <tt>main()</tt>?
 </p></div>
 
@@ -469,29 +471,8 @@ linked in automatically when you link the program.
 
 <!--=========================================================================-->
 
-<div class="question"><p>
-Where did all of my code go??
-</p></div>
-
-<div class="answer">
-<p>
-If you are using the LLVM demo page, you may often wonder what happened to all
-of the code that you typed in.  Remember that the demo script is running the
-code through the LLVM optimizers, so if your code doesn't actually do anything
-useful, it might all be deleted.
-</p>
-
-<p>
-To prevent this, make sure that the code is actually needed.  For example, if
-you are computing some expression, return the value from the function instead of
-leaving it in a local variable.  If you really want to constrain the optimizer,
-you can read from and assign to <tt>volatile</tt> global variables.
-</p>
-</div>
-
-<!--=========================================================================-->
-
 <div class="question">
+<a name="iosinit"></a>
 <p> What is this <tt>llvm.global_ctors</tt> and
 <tt>_GLOBAL__I__tmp_webcompile...</tt> stuff that happens when I #include
 &lt;iostream&gt;?</p>
@@ -520,6 +501,51 @@ instead of <tt>iostream</tt>s to print values.</p>
 
 </div>
 
+<!--=========================================================================-->
+
+<div class="question"><p>
+<a name="codedce"></a>
+Where did all of my code go??
+</p></div>
+
+<div class="answer">
+<p>
+If you are using the LLVM demo page, you may often wonder what happened to all
+of the code that you typed in.  Remember that the demo script is running the
+code through the LLVM optimizers, so if your code doesn't actually do anything
+useful, it might all be deleted.
+</p>
+
+<p>
+To prevent this, make sure that the code is actually needed.  For example, if
+you are computing some expression, return the value from the function instead of
+leaving it in a local variable.  If you really want to constrain the optimizer,
+you can read from and assign to <tt>volatile</tt> global variables.
+</p>
+</div>
+
+<!--=========================================================================-->
+
+<div class="question"><p>
+<a name="undef"></a>
+<p>What is this "<tt>undef</tt>" thing that shows up in my code?
+</p></div>
+
+<div class="answer">
+<p>
+<a href="LangRef.html#undef"><tt>undef</tt></a> is the LLVM way of representing
+a value that is not defined.  You can get these if you do not initialize a 
+variable before you use it.  For example, the C function:</p>
+
+<div class="doc_code">
+  <tt>int X() { int i; return i; }</tt>
+</div>
+
+<p>Is compiled to "<tt>ret int undef</tt>" because "i" never has a value 
+specified for it.
+</p>
+</div>
+
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