Document tbaa metadata in LangRef (documentation largely based on
comments at top of TypeBasedAliasAnalysis.cpp).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@143134 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/docs/GetElementPtr.html b/docs/GetElementPtr.html
index 2c32a9e..6297aa7 100644
--- a/docs/GetElementPtr.html
+++ b/docs/GetElementPtr.html
@@ -594,10 +594,10 @@
      because LLVM has no restrictions on mixing types in addressing, loads or
      stores.</p>
 
-  <p>It would be possible to add special annotations to the IR, probably using
-     metadata, to describe a different type system (such as the C type system),
-     and do type-based aliasing on top of that. This is a much bigger
-     undertaking though.</p>
+  <p>LLVM's type-based alias analysis pass uses metadata to describe a different
+     type system (such as the C type system), and performs type-based aliasing
+     on top of that.  Further details are in the
+     <a href="LangRef.html#tbaa">language reference</a>.</p>
 
 </div>