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
diff --git a/docs/LangRef.html b/docs/LangRef.html
index ab69b05..c1788ad 100644
--- a/docs/LangRef.html
+++ b/docs/LangRef.html
@@ -2318,6 +2318,15 @@
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