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authorGravatar Abseil Team <absl-team@google.com>2020-08-13 14:05:00 -0700
committerGravatar Gennadiy Rozental <rogeeff@google.com>2020-08-14 03:35:22 -0400
commitc6b3f2cf583d8fec124f9d70a172b513363506fe (patch)
tree25125e2b94f758297a9919288cbd95eda1bbc9e1 /absl/container/internal/container_memory.h
parent1beb3191c20ea315186dc761540d25c4939f1892 (diff)
Export of internal Abseil changes
-- 0c8282d75798c77733eee6167870bcc6acc0bfc1 by Evan Brown <ezb@google.com>: Provide mutable access to the key in node handles using std::launder when compiled with C++17 or later. Also, document why we can't provide mutable access to the key without C++17. Note: we use Policy::mutable_key() because btree already uses Policy::key() internally to get const key access, and we want to avoid calling std::launder unless we need mutable access to the key. PiperOrigin-RevId: 326519000 -- 8018d0c3044400f0a731b0d2d00b606742c98818 by Xiaoyi Zhang <zhangxy@google.com>: Move `Status` internal symbols from the public header into an internal header file. PiperOrigin-RevId: 326471847 -- 87a7644864ba7c003b0611898aaba1b71c840376 by Abseil Team <absl-team@google.com>: Avoid a costly divide (the division accounts for 10% of the time spent in the function). When the division is signed, the compiler has to generate a div. When it is unsigned, it can generate a shift: https://godbolt.org/z/vGfTv4. As per the test above the div, we know that the value is unsigned. PiperOrigin-RevId: 326453275 GitOrigin-RevId: 0c8282d75798c77733eee6167870bcc6acc0bfc1 Change-Id: I0a953558358055ab3dc6a533d8930698509b1195
Diffstat (limited to 'absl/container/internal/container_memory.h')
-rw-r--r--absl/container/internal/container_memory.h15
1 files changed, 15 insertions, 0 deletions
diff --git a/absl/container/internal/container_memory.h b/absl/container/internal/container_memory.h
index c7777a93..d02c576d 100644
--- a/absl/container/internal/container_memory.h
+++ b/absl/container/internal/container_memory.h
@@ -18,6 +18,7 @@
#include <cassert>
#include <cstddef>
#include <memory>
+#include <new>
#include <tuple>
#include <type_traits>
#include <utility>
@@ -352,6 +353,20 @@ struct map_slot_policy {
return slot->value;
}
+ // When C++17 is available, we can use std::launder to provide mutable
+ // access to the key for use in node handle.
+#if defined(__cpp_lib_launder) && __cpp_lib_launder >= 201606
+ static K& mutable_key(slot_type* slot) {
+ // Still check for kMutableKeys so that we can avoid calling std::launder
+ // unless necessary because it can interfere with optimizations.
+ return kMutableKeys::value ? slot->key
+ : *std::launder(const_cast<K*>(
+ std::addressof(slot->value.first)));
+ }
+#else // !(defined(__cpp_lib_launder) && __cpp_lib_launder >= 201606)
+ static const K& mutable_key(slot_type* slot) { return key(slot); }
+#endif
+
static const K& key(const slot_type* slot) {
return kMutableKeys::value ? slot->key : slot->value.first;
}