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

2 files changed, 20 insertions, 33 deletions

diff --git a/absl/container/inlined_vector.h b/absl/container/inlined_vector.h
index 36327ad1..9c3289a7 100644
--- a/absl/container/inlined_vector.h
+++ b/absl/container/inlined_vector.h
@@ -217,20 +217,12 @@ class InlinedVector {
       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 @@ class InlinedVector {
       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 4e628424..e38cd8b1 100644
--- a/absl/container/internal/inlined_vector.h
+++ b/absl/container/internal/inlined_vector.h
@@ -301,7 +301,7 @@ class Storage {
   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 @@ class Storage {
 
   // 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 @@ class Storage {
     // 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 @@ class Storage {
           (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))));
     }