Em seg., 31 de ago. de 2020 às 17:05, Andres Freund <and...@anarazel.de> escreveu:
> Hi, > > On 2020-08-31 12:38:51 -0700, Peter Geoghegan wrote: > > On Mon, Aug 31, 2020 at 11:42 AM Andres Freund <and...@anarazel.de> > wrote: > > > Unsigned integer overflow is well defined in the standard. So I don't > understand what this is purporting to warn about. > > > > Presumably it's simply warning that the value -4294901760 (i.e. the > > result of 3 - 4294901763) cannot be faithfully represented as an > > unsigned int. This is true, of course. It's just not relevant. > > > > I'm pretty sure that UBSan does not actually state that this is > > undefined behavior. At least Ranier's sample output didn't seem to > > indicate it. > > Well, my point is that there's no point in discussing unsigned integer > overflow, since it's precisely specified. And hence I don't understand > what we're discussing in this sub-thread. > > https://clang.llvm.org/docs/UndefinedBehaviorSanitizer.html says: > > > -fsanitize=unsigned-integer-overflow: Unsigned integer overflow, where > > the result of an unsigned integer computation cannot be represented in > > its type. Unlike signed integer overflow, this is not undefined > > behavior, but it is often unintentional. This sanitizer does not check > > for lossy implicit conversions performed before such a computation > > (see -fsanitize=implicit-conversion). > > So it seems Rainier needs to turn this test off, because it actually is > intentional. > No problem. If intentional, the code at TransactionIdPrecedes, already knows that overflow can occur and trusts that the compiler will save it. Ranier Vilela
