On Feb 4, 2012, at 12:04 PM, Eli Friedman wrote: > On Sat, Feb 4, 2012 at 8:53 AM, Howard Hinnant <[email protected]> wrote: >> On Feb 4, 2012, at 5:25 AM, Jean-Daniel Dupas wrote: >> >>> Hi, >>> >>> Am I the only one having trouble compiling libc++ with clang TOT. >>> For sometime now, clang refuse to compile (and use it) because of the >>> following issue: >>> >>> ../include/ratio:193:19: error: static_assert expression is not an integral >>> constant expression >>> static_assert(_Xp != nan && _Yp != nan && __a_x <= max / __a_y, >>> "overflow in __ll_mul"); >>> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ >>> ../include/ratio:308:13: note: in instantiation of template class >>> 'std::__1::__ll_mul<1, 1>' requested here >>> __ll_mul<_R1::num / __gcd_n1_n2, _R2::den / __gcd_d1_d2>::value, >>> ^ >>> ../include/ratio:315:33: note: in instantiation of template class >>> 'std::__1::__ratio_divide<std::__1::ratio<1, 1000000000>, >>> std::__1::ratio<1, 1000000000> >' requested >>> here >>> template <class _R1, class _R2> using ratio_divide >>> ^ >>> ../include/chrono:410:18: note: in instantiation of template type alias >>> 'ratio_divide' requested here >>> (ratio_divide<_Period2, period>::type::den == 1 && >>> ^ >>> ../include/chrono:406:9: note: while substituting deduced template >>> arguments into function template 'duration' [with _Rep2 = long long, >>> _Period2 = <no value>] >>> duration(const duration<_Rep2, _Period2>& __d, >>> ^ >>> ../include/ratio:193:26: note: initializer of 'nan' is not a constant >>> expression >>> static_assert(_Xp != nan && _Yp != nan && __a_x <= max / __a_y, >>> "overflow in __ll_mul"); >>> ^ >>> ../include/ratio:187:27: note: declared here >>> static const intmax_t nan = (1LL << (sizeof(intmax_t) * CHAR_BIT - 1)); >>> ^ >>> ../include/ratio:187:27: note: declared here >>> ../include/ratio:189:27: note: declared here >>> static const intmax_t max = -min; >> >> I haven't noticed because I'm not using TOT clang, and I've been distracted >> by libc++abi for the past couple of months. >> >> But I note the crux of this issue appears to be that this: >> >> static const intmax_t nan = (1LL << (sizeof(intmax_t) * CHAR_BIT - 1)); >> >> is no longer consider a compile time constant expression. >> >> This is one of two things: >> >> 1. A clang bug. >> 2. A standards defect. I.e. this will break a lot of C++03 code if the >> standard really says this. >> >> If it is 2) it would be good for me to know immediately. The next C++ >> standards meeting is next week (Feb. 6-10) and it would be good to give such >> a defect a high profile/priority at the meeting. >> >> Does anyone know if this is 1) or 2)? > > [expr.shift]p2: [...] if E1 has a signed type and non-negative value, > and E1×2E2 is representable in the result type, then that is the > resulting value; otherwise, the behavior is undefined. > > -Eli
I see, you're point is that I've walked into undefined territory because I set the sign bit on the long long? Does changing 1LL to 1ULL make the compiler happy? Howard _______________________________________________ cfe-commits mailing list [email protected] http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits
