inlined_vector: relax the requirements on the move-construction fast path.
Don't require a trivial move constructor and trivial destructor. This excludes
types that have declared themselves trivially relocatable by another means, like
std::unique_ptr. Instead use "is trivially relocatable" directly, which includes
all previous types as well as those that have opted in.
PiperOrigin-RevId: 523557136
Change-Id: Icea2dbb8f36f99623308155f2e5b1edd8e5bd36b
diff --git a/absl/container/inlined_vector.h b/absl/container/inlined_vector.h
index 36327ad..9c3289a 100644
--- a/absl/container/inlined_vector.h
+++ b/absl/container/inlined_vector.h
@@ -217,20 +217,12 @@
absl::allocator_is_nothrow<allocator_type>::value ||
std::is_nothrow_move_constructible<value_type>::value)
: storage_(other.storage_.GetAllocator()) {
- // Fast path: if the value type can be trivally move constructed and
- // destroyed, and we know the allocator doesn't do anything fancy, then it's
- // safe for us to simply adopt the contents of the storage for `other` and
- // remove its own reference to them. It's as if we had individually
+ // Fast path: if the value type can be trivially relocated (i.e. moved from
+ // and destroyed), and we know the allocator doesn't do anything fancy, then
+ // it's safe for us to simply adopt the contents of the storage for `other`
+ // and remove its own reference to them. It's as if we had individually
// move-constructed each value and then destroyed the original.
- //
- // TODO(b/274984172): a move construction followed by destroying the source
- // is a "relocation" in the language of P1144R4. So actually the minimum
- // condition we need here (in addition to the allocator) is "trivially
- // relocatable". Relaxing this would allow using memcpy with types like
- // std::unique_ptr that opt in to declaring themselves trivially relocatable
- // despite not being trivially move-constructible and/oror destructible.
- if (absl::is_trivially_move_constructible<value_type>::value &&
- absl::is_trivially_destructible<value_type>::value &&
+ if (absl::is_trivially_relocatable<value_type>::value &&
std::is_same<A, std::allocator<value_type>>::value) {
storage_.MemcpyFrom(other.storage_);
other.storage_.SetInlinedSize(0);
@@ -271,20 +263,12 @@
const allocator_type&
allocator) noexcept(absl::allocator_is_nothrow<allocator_type>::value)
: storage_(allocator) {
- // Fast path: if the value type can be trivally move constructed and
- // destroyed and we know the allocator doesn't do anything fancy, then it's
- // safe for us to simply adopt the contents of the storage for `other` and
- // remove its own reference to them. It's as if we had individually
+ // Fast path: if the value type can be trivially relocated (i.e. moved from
+ // and destroyed), and we know the allocator doesn't do anything fancy, then
+ // it's safe for us to simply adopt the contents of the storage for `other`
+ // and remove its own reference to them. It's as if we had individually
// move-constructed each value and then destroyed the original.
- //
- // TODO(b/274984172): a move construction followed by destroying the source
- // is a "relocation" in the language of P1144R4. So actually the minimum
- // condition we need here (in addition to the allocator) is "trivially
- // relocatable". Relaxing this would allow using memcpy with types like
- // std::unique_ptr that opt in to declaring themselves trivially relocatable
- // despite not being trivially move-constructible and/oror destructible.
- if (absl::is_trivially_move_constructible<value_type>::value &&
- absl::is_trivially_destructible<value_type>::value &&
+ if (absl::is_trivially_relocatable<value_type>::value &&
std::is_same<A, std::allocator<value_type>>::value) {
storage_.MemcpyFrom(other.storage_);
other.storage_.SetInlinedSize(0);
diff --git a/absl/container/internal/inlined_vector.h b/absl/container/internal/inlined_vector.h
index 4e62842..e38cd8b 100644
--- a/absl/container/internal/inlined_vector.h
+++ b/absl/container/internal/inlined_vector.h
@@ -301,7 +301,7 @@
struct ElementwiseConstructPolicy {};
using MoveAssignmentPolicy = absl::conditional_t<
- // Fast path: if the value type can be trivally move assigned and
+ // Fast path: if the value type can be trivially move assigned and
// destroyed, and we know the allocator doesn't do anything fancy, then
// it's safe for us to simply adopt the contents of the storage for
// `other` and remove its own reference to them. It's as if we had
@@ -332,7 +332,7 @@
// The policy to be used specifically when swapping inlined elements.
using SwapInlinedElementsPolicy = absl::conditional_t<
- // Fast path: if the value type can be trivally move constructed/assigned
+ // Fast path: if the value type can be trivially move constructed/assigned
// and destroyed, and we know the allocator doesn't do anything fancy,
// then it's safe for us to simply swap the bytes in the inline storage.
// It's as if we had move-constructed a temporary vector, move-assigned
@@ -505,8 +505,10 @@
// we know the allocator doesn't do anything fancy, and one of the following
// holds:
//
- // * It's possible to trivially move construct/assign the elements and
- // then destroy the source.
+ // * The elements are trivially relocatable.
+ //
+ // * It's possible to trivially assign the elements and then destroy the
+ // source.
//
// * It's possible to trivially copy construct/assign the elements.
//
@@ -517,10 +519,11 @@
(std::is_same<A, std::allocator<V>>::value &&
(
// First case above
- ((absl::is_trivially_move_constructible<V>::value ||
- absl::is_trivially_move_assignable<V>::value) &&
- absl::is_trivially_destructible<V>::value) ||
+ absl::is_trivially_relocatable<V>::value ||
// Second case above
+ (absl::is_trivially_move_assignable<V>::value &&
+ absl::is_trivially_destructible<V>::value) ||
+ // Third case above
(absl::is_trivially_copy_constructible<V>::value ||
absl::is_trivially_copy_assignable<V>::value))));
}
