Author: kmensah Date: Fri Jul 8 10:34:28 2016 New Revision: 274857 URL: http://llvm.org/viewvc/llvm-project?rev=274857&view=rev Log: [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 Modified: libcxx/trunk/include/__hash_table Modified: libcxx/trunk/include/__hash_table URL: http://llvm.org/viewvc/llvm-project/libcxx/trunk/include/__hash_table?rev=274857&r1=274856&r2=274857&view=diff ============================================================================== --- libcxx/trunk/include/__hash_table (original) +++ libcxx/trunk/include/__hash_table Fri Jul 8 10:34:28 2016 @@ -2205,7 +2205,7 @@ __hash_table<_Tp, _Hash, _Equal, _Alloc> || __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> || __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 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
