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| author | Kwasi Mensah <kmensah@google.com> | 2016-07-08 15:34:28 +0000 |
|---|---|---|
| committer | Kwasi Mensah <kmensah@google.com> | 2016-07-08 15:34:28 +0000 |
| commit | 318d35a7bca6c4e54c75705245ee07277ac6e32c (patch) | |
| tree | 02f47357078e4aafaafaa0e775308296abd0ecd2 /libcxx | |
| parent | 3202f065b8d0ce93497760ed279372d108fc8506 (diff) | |
| download | bcm5719-llvm-318d35a7bca6c4e54c75705245ee07277ac6e32c.tar.gz bcm5719-llvm-318d35a7bca6c4e54c75705245ee07277ac6e32c.zip | |
[libc++] Check hash before calling __hash_table key_eq function
Summary: The current implementations of __hash_table::find used by std::unordered_set/unordered_map call key_eq on each key that lands in the same bucket as the key you're looking for. However, since equal objects mush hash to the same value, you can short-circuit the possibly expensive call to key_eq by checking the hashes first.
Reviewers: EricWF
Subscribers: kmensah, cfe-commits
Differential Revision: http://reviews.llvm.org/D21510
llvm-svn: 274857
Diffstat (limited to 'libcxx')
| -rw-r--r-- | libcxx/include/__hash_table | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/libcxx/include/__hash_table b/libcxx/include/__hash_table index 414019aa1fa..8b2565968cf 100644 --- a/libcxx/include/__hash_table +++ b/libcxx/include/__hash_table @@ -2205,7 +2205,7 @@ __hash_table<_Tp, _Hash, _Equal, _Alloc>::find(const _Key& __k) || __constrain_hash(__nd->__hash_, __bc) == __chash); __nd = __nd->__next_) { - if (key_eq()(__nd->__value_, __k)) + if ((__nd->__hash_ == __hash) && key_eq()(__nd->__value_, __k)) #if _LIBCPP_DEBUG_LEVEL >= 2 return iterator(__nd, this); #else @@ -2235,7 +2235,7 @@ __hash_table<_Tp, _Hash, _Equal, _Alloc>::find(const _Key& __k) const || __constrain_hash(__nd->__hash_, __bc) == __chash); __nd = __nd->__next_) { - if (key_eq()(__nd->__value_, __k)) + if ((__nd->__hash_ == __hash) && key_eq()(__nd->__value_, __k)) #if _LIBCPP_DEBUG_LEVEL >= 2 return const_iterator(__nd, this); #else |
