[libcxx-commits] [libcxx] ada2a8e - Remove the try/catch codepath if `swap` is `noexcept`.
Michael Park via libcxx-commits
libcxx-commits at lists.llvm.org
Tue Jun 16 14:51:34 PDT 2020
Author: Michael Park
Date: 2020-06-16T14:51:22-07:00
New Revision: ada2a8ea4a9c5b2141c30c77b80b85945e346999
URL: https://github.com/llvm/llvm-project/commit/ada2a8ea4a9c5b2141c30c77b80b85945e346999
DIFF: https://github.com/llvm/llvm-project/commit/ada2a8ea4a9c5b2141c30c77b80b85945e346999.diff
LOG: Remove the try/catch codepath if `swap` is `noexcept`.
Summary:
In the case where `swap` is `noexcept`, we should avoid the extension to provide strong-exception guarantee.
Fixes https://bugs.llvm.org/show_bug.cgi?id=46342
Reviewers: #libc, ldionne
Reviewed By: #libc, ldionne
Subscribers: dexonsmith, mclow.lists, miscco, ldionne, zoecarver, libcxx-commits
Tags: #libc
Differential Revision: https://reviews.llvm.org/D81954
Added:
Modified:
libcxx/include/variant
Removed:
################################################################################
diff --git a/libcxx/include/variant b/libcxx/include/variant
index 98a62c992fa1..897361fc3be3 100644
--- a/libcxx/include/variant
+++ b/libcxx/include/variant
@@ -1062,21 +1062,28 @@ public:
_VSTD::swap(__lhs, __rhs);
}
__impl __tmp(_VSTD::move(*__rhs));
-#ifndef _LIBCPP_NO_EXCEPTIONS
- // EXTENSION: When the move construction of `__lhs` into `__rhs` throws
- // and `__tmp` is nothrow move constructible then we move `__tmp` back
- // into `__rhs` and provide the strong exception safety guarantee.
- try {
+ static constexpr bool __is_noexcept =
+#ifdef _LIBCPP_NO_EXCEPTIONS
+ true;
+#else
+ __all<(is_nothrow_move_constructible_v<_Types> &&
+ is_nothrow_swappable_v<_Types>)...>::value;
+#endif
+ if constexpr (__is_noexcept) {
this->__generic_construct(*__rhs, _VSTD::move(*__lhs));
- } catch (...) {
- if (__tmp.__move_nothrow()) {
- this->__generic_construct(*__rhs, _VSTD::move(__tmp));
+ } else {
+ // EXTENSION: When the move construction of `__lhs` into `__rhs` throws
+ // and `__tmp` is nothrow move constructible then we move `__tmp` back
+ // into `__rhs` and provide the strong exception safety guarantee.
+ try {
+ this->__generic_construct(*__rhs, _VSTD::move(*__lhs));
+ } catch (...) {
+ if (__tmp.__move_nothrow()) {
+ this->__generic_construct(*__rhs, _VSTD::move(__tmp));
+ }
+ throw;
}
- throw;
}
-#else
- this->__generic_construct(*__rhs, _VSTD::move(*__lhs));
-#endif
this->__generic_construct(*__lhs, _VSTD::move(__tmp));
}
}
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