[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
diff --git a/libcxx/include/__hash_table b/libcxx/include/__hash_table
index 414019a..8b25659 100644
--- a/libcxx/include/__hash_table
+++ b/libcxx/include/__hash_table
@@ -2205,7 +2205,7 @@
|| __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 @@
|| __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