[cfe-commits] PATCH: Enhance -fcatch-undefined-behavior for the '<<' operator.

[Chandler Carruth]

This patch should catch more integer shift left undefined behavior according
to C and C++ standard semantics. Specifically it should catch the case where
a signed integer type when shifted is no longer representable in the result
type.

There are some general cleanups that can be made to the existing undefined
behavior check here given the this change, but I just wanted to add
functionality here. Let me know if I should just commit freely when adding
these types of checks (provided proper testing and certainty that the
behavior is in fact undefined). Also any guidance on other languages or
specs I should be checking prior to enabling such checks (Currently looking
at C99, C++98, C++03, and C++0x) would be welcome.

Finally, the testcase is a bit lame. I'd really like to test this by
creating sources that exhibit the undefined behavior being checked, compile
and run them verifying crash and non-crash inputs. Is that do-able in the
current test harness? Seems unlikely, but if folks have ideas I'm all ears.

Thanks!
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