FYI, this found 3 separate cases of this in TableGen alone. My testing indicates many many instances elsewhere in LLVM and Clang. =/
I started digging into this because I wanted to add 'nsw' to the shl instruction when the standard guaranteed it... doing so made the world break, and i wondered why. =] now I know.... On Fri, Jun 3, 2011 at 12:50 AM, Chandler Carruth <[email protected]>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. > > Thanks! >
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