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

[Chris Lattner]

On Jun 3, 2011, at 12:50 AM, Chandler Carruth wrote:

> 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.

Hi Chandler,

Does this trap on:

int x = 1;  
x = x << 31;

While this is technically a signed overflow, I believe that we define it as valid. 

-Chris