From c30f6e1c89e5a046ab9a58b08248cbb3c796529c Mon Sep 17 00:00:00 2001
From: Dan Gohman <gohman@apple.com>
Date: Mon, 26 Apr 2010 20:54:53 +0000
Subject: [PATCH] Branching or switching on trap transfers imminent undefined
 behavior onto control-dependent instructions.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@102381 91177308-0d34-0410-b5e6-96231b3b80d8
---
 docs/LangRef.html | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/docs/LangRef.html b/docs/LangRef.html
index ab69b05bbf3..c1788ada2b9 100644
--- a/docs/LangRef.html
+++ b/docs/LangRef.html
@@ -2318,6 +2318,15 @@ has undefined behavior.</p>
    Any instruction with a trap operand which may have side effects emits
    those side effects as if it had an undef operand instead.</p>
 
+<p>If a <a href="#i_br"><tt>br</tt></a> or
+   <a href="#i_switch"><tt>switch</tt></a> instruction has a trap value
+   operand, all non-phi non-void instructions which control-depend on it
+   have trap as their result value. If any instruction which
+   control-depends on the <tt>br</tt> or <tt>switch</tt> invokes externally
+   visible side effects, the behavior of the program is undefined.</p>
+
+<!-- FIXME: What about exceptions thrown from control-dependent instrs? -->
+
 <p>For example, an <a href="#i_and"><tt>and</tt></a> of a trap value with
    zero still has a trap value result. Using that value as an index in a
    <a href="#i_getelementptr"><tt>getelementptr</tt></a> yields a trap