Implement P2401 which adds a `noexcept` specification to
`std::exchange`. Treated as a defect fix which is the motivation for
applying this change to all standards mode rather than just C++23 or
later as the paper suggests.

Reviewed By: Quuxplusone, Mordante, #libc

Differential Revision: https://reviews.llvm.org/D111481

C++98 and C++03 are effectively aliases as far as Clang is concerned.
As such, allowing both std=c++98 and std=c++03 as Lit parameters is
just slightly confusing, but provides no value. It's similar to allowing
both std=c++17 and std=c++1z, which we don't do.

This was discovered because we had an internal bot that ran the test
suite under both c++98 AND c++03 -- one of which is redundant.

Differential Revision: https://reviews.llvm.org/D80926

Summary:
Freestanding is *weird*. The standard allows it to differ in a bunch of odd
manners from regular C++, and the committee would like to improve that
situation. I'd like to make libc++ behave better with what freestanding should
be, so that it can be a tool we use in improving the standard. To do that we
need to try stuff out, both with "freestanding the language mode" and
"freestanding the library subset".

Let's start with the super basic: run the libc++ tests in freestanding, using
clang as the compiler, and see what works. The easiest hack to do this:

In utils/libcxx/test/config.py add:

  self.cxx.compile_flags += ['-ffreestanding']

Run the tests and they all fail.

Why? Because in freestanding `main` isn't special. This "not special" property
has two effects: main doesn't get mangled, and main isn't allowed to omit its
`return` statement. The first means main gets mangled and the linker can't
create a valid executable for us to test. The second means we spew out warnings
(ew) and the compiler doesn't insert the `return` we omitted, and main just
falls of the end and does whatever undefined behavior (if you're luck, ud2
leading to non-zero return code).

Let's start my work with the basics. This patch changes all libc++ tests to
declare `main` as `int main(int, char**` so it mangles consistently (enabling us
to declare another `extern "C"` main for freestanding which calls the mangled
one), and adds `return 0;` to all places where it was missing. This touches 6124
files, and I apologize.

The former was done with The Magic Of Sed.

The later was done with a (not quite correct but decent) clang tool:

  https://gist.github.com/jfbastien/793819ff360baa845483dde81170feed

This works for most tests, though I did have to adjust a few places when e.g.
the test runs with `-x c`, macros are used for main (such as for the filesystem
tests), etc.

Once this is in we can create a freestanding bot which will prevent further
regressions. After that, we can start the real work of supporting C++
freestanding fairly well in libc++.

<rdar://problem/47754795>

Reviewers: ldionne, mclow.lists, EricWF

Subscribers: christof, jkorous, dexonsmith, arphaman, miyuki, libcxx-commits

Differential Revision: https://reviews.llvm.org/D57624

llvm-svn: 353086

to reflect the new license. These used slightly different spellings that
defeated my regular expressions.

We understand that people may be surprised that we're moving the header
entirely to discuss the new license. We checked this carefully with the
Foundation's lawyer and we believe this is the correct approach.

Essentially, all code in the project is now made available by the LLVM
project under our new license, so you will see that the license headers
include that license only. Some of our contributors have contributed
code under our old license, and accordingly, we have retained a copy of
our old license notice in the top-level files in each project and
repository.

llvm-svn: 351648

llvm-svn: 324959

llvm-svn: 323159

[libcxx] [test] Fix MSVC warning C4244 "conversion from 'X' to 'Y', possible loss of data", part 7/7.

test/std/input.output/iostream.format/input.streams/istream.unformatted/get.pass.cpp
Add static_cast<char> because basic_istream::get() returns int_type (N4606 27.7.2.3 [istream.unformatted]/4).

test/std/input.output/iostream.format/output.streams/ostream.formatted/ostream.inserters.arithmetic/minus1.pass.cpp
Add static_cast<char> because toupper() returns int (C11 7.4.2.2/1).

test/std/iterators/stream.iterators/ostream.iterator/ostream.iterator.ops/assign_t.pass.cpp
This test is intentionally writing doubles to ostream_iterator<int>.
It's silencing -Wliteral-conversion for Clang, so I'm adding C4244 silencing for MSVC.

test/std/language.support/support.limits/limits/numeric.limits.members/infinity.pass.cpp
Given `extern float zero;`, the expression `1./zero` has type double, which emits a truncation warning
when being passed to test<float>() taking float. The fix is to say `1.f/zero` which has type float.

test/std/numerics/complex.number/cmplx.over/arg.pass.cpp
test/std/numerics/complex.number/cmplx.over/norm.pass.cpp
These tests were constructing std::complex<double>(x, 0), emitting truncation warnings when x is long long.
Saying static_cast<double>(x) avoids this.

test/std/numerics/rand/rand.eng/rand.eng.lcong/seed_result_type.pass.cpp
This was using `int s` to construct and seed a linear_congruential_engine<T, stuff>, where T is
unsigned short/unsigned int/unsigned long/unsigned long long. That emits a truncation warning in the
unsigned short case. Because the range [0, 20) is tiny and we aren't doing anything else with the index,
we can just iterate with `T s`.

test/std/re/re.traits/value.pass.cpp
regex_traits<wchar_t>::value()'s first parameter is wchar_t (N4606 28.7 [re.traits]/13). This loop is
using int to iterate through ['g', 0xFFFF), emitting a truncation warning from int to wchar_t
(which is 16-bit for some of us). Because the bound is exclusive, we can just iterate with wchar_t.

test/std/strings/basic.string/string.cons/size_char_alloc.pass.cpp
This test is a little strange. It's trying to verify that basic_string's (InIt, InIt) range constructor
isn't confused by "N copies of C" when N and C have the same integral type. To do this, it was
testing (100, 65), but that eventually emits truncation warnings from int to char. There's a simple way
to avoid this - passing (static_cast<char>(100), static_cast<char>(65)) also exercises the disambiguation.
(And 100 is representable even when char has a signed range.)

test/std/strings/string.view/string.view.hash/string_view.pass.cpp
Add static_cast<char_type> because `'0' + i` has type int.

test/std/utilities/function.objects/bind/func.bind/func.bind.bind/nested.pass.cpp
What's more horrible than nested bind()? pow() overloads! This operator()(T a, T b) was assuming that
std::pow(a, b) can be returned as T. (In this case, T is int.) However, N4606 26.9.1 [cmath.syn]/2
says that pow(int, int) returns double, so this was truncating double to int.
Adding static_cast<T> silences this.

test/std/utilities/function.objects/unord.hash/integral.pass.cpp
This was iterating `for (int i = 0; i <= 5; ++i)` and constructing `T t(i);` but that's truncating
when T is short. (And super truncating when T is bool.) Adding static_cast<T> silences this.

test/std/utilities/utility/exchange/exchange.pass.cpp
First, this was exchanging 67.2 into an int, but that's inherently truncating.
Changing this to static_cast<short>(67) avoids the truncation while preserving the
"what if T and U are different" test coverage.
Second, this was exchanging {} with the explicit type float into an int, and that's also
inherently truncating. Specifying short is just as good.

test/std/utilities/utility/pairs/pairs.spec/make_pair.pass.cpp
Add static_cast<short>. Note that this affects template argument deduction for make_pair(),
better fulfilling the test's intent. For example, this was saying
`typedef std::pair<int, short> P1; P1 p1 = std::make_pair(3, 4);` but that was asking
make_pair() to return pair<int, int>, which was then being converted to pair<int, short>.
(pair's converting constructors are tested elsewhere.)
Now, std::make_pair(3, static_cast<short>(4)) actually returns pair<int, short>.
(There's still a conversion from pair<nullptr_t, short> to pair<unique_ptr<int>, short>.)

Fixes D27544.

llvm-svn: 289111

llvm-svn: 271435

Quite a few libcxx tests seem to follow the format:
 #if _LIBCPP_STD_VER > X
   // Do test.
 #else
   // Empty test.
 #endif
We should instead use the UNSUPPORTED lit directive to exclude the test on
earlier C++ standards. This gives us a more accurate number of test passes
for those standards and avoids unnecessary conflicts with other lit
directives on the same tests.

Reviewers: bcraig, ericwf, mclow.lists

Differential revision: http://reviews.llvm.org/D20730

llvm-svn: 271108

llvm-svn: 224658

llvm-svn: 186022

llvm-svn: 185865

llvm-svn: 185863