On Thu, Jan 17, 2013 at 08:44:20AM -0800, Linus Torvalds wrote: > On Thu, Jan 17, 2013 at 3:00 AM, John Keeping <j...@keeping.me.uk> wrote: >> >> There's also a warning that triggers with clang 3.2 but not clang trunk, >> which >> I think is a legitimate warning - perhaps someone who understands integer >> type >> promotion better than me can explain why the code is OK (patch->score is >> declared as 'int'): >> >> builtin/apply.c:1044:47: warning: comparison of constant 18446744073709551615 >> with expression of type 'int' is always false >> [-Wtautological-constant-out-of-range-compare] >> if ((patch->score = strtoul(line, NULL, 10)) == ULONG_MAX) >> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^ ~~~~~~~~~ > > The warning seems to be very very wrong, and implies that clang has > some nasty bug in it. > > Since patch->score is 'int', and UNLONG_MAX is 'unsigned long', the > conversion rules for the comparison is that the int result from the > assignment is cast to unsigned long. And if you cast (int)-1 to > unsigned long, you *do* get ULONG_MAX. That's true regardless of > whether "long" has the same number of bits as "int" or is bigger. The > implicit cast will be done as a sign-extension (unsigned long is not > signed, but the source type of 'int' *is* signed, and that is what > determines the sign extension on casting). > > So the "is always false" is pure and utter crap. clang is wrong, and > it is wrong in a way that implies that it actually generates incorrect > code. It may well be worth making a clang bug report about this.
The warning doesn't occur with a build from their trunk so it looks like it's already fixed - it just won't make into into a release for about 5 months going by their timeline. Thanks for the clear explanation. -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
