The standard disallows narrowing conversions when constructing a variant.
This is checked by attempting to perform braced initialization of the
destination type from the argument type. However, braced initialization
can force the compiler (mostly clang) to eagerly instantiate the
constructors of the destintation type -- which can lead to errors in
a non-immediate context.
However, as variant is currently specified, the narrowing checks only
observably apply when the destination type is arithmetic. Meaning we can
skip the check for class types. Hense avoiding the hard errors.
In order to cause fewer build breakages, this patch avoids the narrowing
check except when the destination type is arithmetic.
git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@366022 91177308-0d34-0410-b5e6-96231b3b80d8
Previously we implemented all one trillion tuple-like constructors using
a single generic overload. This worked fairly well, except that it
differed in behavior from the standard version because it didn't
consider both T&& and T const&. This was observable for certain
types.
This patch addresses that issue by splitting the generic constructor
in two. We now provide both T&& and T const& versions of the
tuple-like constructors (sort of).
git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@365973 91177308-0d34-0410-b5e6-96231b3b80d8
The paper P0608R3 - "A sane variant converting constructor" disallows
narrowing conversions in variant. It was meant to address this
surprising problem:
std::variant<std::string, bool> v = "abc";
assert(v.index() == 1); // constructs a bool.
However, it also disables every potentially narrowing conversion. For
example:
variant<unsigned> v = 0; // ill-formed
variant<string, double> v2 = 42; // ill-formed (int -> double narrows)
These latter changes break code. A lot of code. Within Google it broke
on the order of a hundred thousand target with thousands of root causes
responsible for the breakages.
Of the breakages related to the narrowing restrictions, none of them
exposed outstanding bugs. However, the breakages caused by boolean
conversions (~13 root causes), all but one of them were bugs.
For this reasons, I am adding a flag to disable the narrowing conversion
changes but not the boolean conversions one.
One purpose of this flag is to allow users to opt-out of breaking changes
in variant until the offending code can be cleaned up. For non-trivial
variant usages the amount of cleanup may be significant.
This flag is also required to support automated tooling, such as
clang-tidy, that can automatically fix code broken by this change.
In order for clang-tidy to know the correct alternative to construct,
it must know what alternative was being constructed previously, which
means running it over the old version of std::variant.
Because this change breaks so much code, I will be implementing the
aforementioned clang-tidy check in the very near future.
Additionally I'm plan present this new information to the committee so they can
re-consider if this is a breaking change we want to make.
I think libc++ should very seriously consider pulling this change
before the 9.0 release branch is cut. But that's a separate discussion
that I will start on the lists.
For now this is the minimal first step.
git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@365960 91177308-0d34-0410-b5e6-96231b3b80d8
When assigning an initializer list into set/map, libc++ would
leak memory if the initializer list contained equivalent keys
because we failed to check if the insertion was successful.
git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@365840 91177308-0d34-0410-b5e6-96231b3b80d8
Currently std::mutex has a constexpr constructor, but a non-trivial
destruction.
The constexpr constructor is required to ensure the construction of a
mutex with static storage duration happens at compile time, during
constant initialization, and not during dynamic initialization.
This means that static mutex's are always initialized and can be used
safely during dynamic initialization without the "static initialization
order fiasco".
A trivial destructor is important for similar reasons. If a mutex is
used during dynamic initialization it might also be used during program
termination. If a static mutex has a non-trivial destructor it will be
invoked during termination. This can introduce the "static
deinitialization order fiasco".
Additionally, function-local statics emit a guard variable around
non-trivially destructible types. This results in horrible codegen and
adds a runtime cost to every call to that function. non-local static's
also result in slightly worse codegen but it's not as big of a problem.
Example codegen can be found here: https://goo.gl/3CSzbM
Note: This optimization is not safe with every pthread implementation.
Some implementations allocate on the first call to pthread_mutex_lock
and free the allocation in pthread_mutex_destroy.
Also, changing the triviality of the destructor is not an ABI break.
At least to the best of my knowledge :-)
git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@365273 91177308-0d34-0410-b5e6-96231b3b80d8
types.
It seems some people like to write types that can explicitly convert
to anything, but cannot be used to explicitly construct anything.
This patch makes tuple tolerate such types, as is required
by the standard.
git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@365074 91177308-0d34-0410-b5e6-96231b3b80d8
The new meta-programming primitives are lower cost than the old versions. This patch removes those old versions and switches libc++ to use the new ones.
git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@364160 91177308-0d34-0410-b5e6-96231b3b80d8
Clang provides __is_same that doesn't produce any instantiations
and just returns a bool. It's a lot faster than using std::is_same
I'll follow up with a patch to actually start using it.
git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@364148 91177308-0d34-0410-b5e6-96231b3b80d8
Using class templates instead of alias templates causes a lot of
instantiations. As part of the move away from C++03, we want to
improve the efficiency of our meta-programming.
This patch lays the groundwork by introducing new _If, _EnableIf,
_And, _Or, and _IsValidExpansion (detect member). Future patches
will replace the existing implementations after verifying there
compile time differences.
git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@364114 91177308-0d34-0410-b5e6-96231b3b80d8
These functions are key to allowing the use of rvalues and variadics
in C++03 mode. Everything works the same as in C++11, except for one
tangentially related case:
struct T {
T(T &&) = default;
};
In C++11, T has a deleted copy constructor. But in C++03 Clang gives
it both a move and a copy constructor. This seems reasonable enough
given the extensions it's using.
The other changes in this patch were the minimal set required
to keep the tests passing after the move/forward change. Most notably
the removal of the `__rv<unique_ptr>` hack that was present
in an attempt to make unique_ptr move only without language support.
git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@364063 91177308-0d34-0410-b5e6-96231b3b80d8
Summary:
AIX system headers need stdint.h and inttypes.h to be re-enterable when macro _STD_TYPES_T is defined so that limit macro definitions such as UINT32_MAX can be found. This patch attempts to allow that on AIX.
Reviewers: hubert.reinterpretcast, jasonliu, mclow.lists, EricWF
Reviewed by: hubert.reinterpretcast, mclow.lists
Subscribers: jfb, jsji, christof, cfe-commits, libcxx-commits, llvm-commits
Tags: #LLVM, #clang, #libc++
Differential Revision: https://reviews.llvm.org/D59253
git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@363939 91177308-0d34-0410-b5e6-96231b3b80d8
The change caused a large number of compiler failures in
Google's codebase. People need time to evaluate the impact.
git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@363764 91177308-0d34-0410-b5e6-96231b3b80d8
This was found to be broken on Clang trunk. This is a revert of the
following commits (the subsequent commits added XFAILs to the tests
that were missing from the original submission):
r362986: Implement deduction guides for map/multimap.
r363014: Add some XFAILs
r363097: Add more XFAILs
r363197: Add even more XFAILs
git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@363688 91177308-0d34-0410-b5e6-96231b3b80d8
