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Branching or switching on trap transfers imminent undefined behavior

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onto control-dependent instructions.

llvm-svn: 102381
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Dan Gohman 2010-04-26 20:54:53 +00:00
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@ -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