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[ADT] Add a much simpler loop to DenseMap::clear when the types are 

POD-like and we can just splat the empty key across memory.

Sadly we can't optimize the normal loop well enough because we can't
turn the conditional store into an unconditional store according to the
memory model.

This loop actually showed up in a profile of code that was calling clear
as a serious source of time. =[

llvm-svn: 310189
This commit is contained in:
Chandler Carruth 2017-08-05 22:48:37 +00:00
parent 7e84697e59
commit 6b78bac9fb
1 changed files with 14 additions and 8 deletions
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22
llvm/include/llvm/ADT/DenseMap.h
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@ -107,17 +107,23 @@ public:
}
const KeyT EmptyKey = getEmptyKey(), TombstoneKey = getTombstoneKey();
unsigned NumEntries = getNumEntries();
for (BucketT *P = getBuckets(), *E = getBucketsEnd(); P != E; ++P) {
if (!KeyInfoT::isEqual(P->getFirst(), EmptyKey)) {
if (!KeyInfoT::isEqual(P->getFirst(), TombstoneKey)) {
P->getSecond().~ValueT();
--NumEntries;
}
if (isPodLike<KeyT>::value && isPodLike<ValueT>::value) {
// Use a simpler loop when these are trivial types.
for (BucketT *P = getBuckets(), *E = getBucketsEnd(); P != E; ++P)
P->getFirst() = EmptyKey;
} else {
unsigned NumEntries = getNumEntries();
for (BucketT *P = getBuckets(), *E = getBucketsEnd(); P != E; ++P) {
if (!KeyInfoT::isEqual(P->getFirst(), EmptyKey)) {
if (!KeyInfoT::isEqual(P->getFirst(), TombstoneKey)) {
P->getSecond().~ValueT();
--NumEntries;
}
P->getFirst() = EmptyKey;
}
}
assert(NumEntries == 0 && "Node count imbalance!");
}
assert(NumEntries == 0 && "Node count imbalance!");
setNumEntries(0);
setNumTombstones(0);
}