[cfe-commits] libc++ and const expr.
Howard Hinnant
hhinnant at apple.com
Sat Feb 4 08:53:28 PST 2012
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)?
Howard
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