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Sync the __builtin_expects for our 3 quadratically probed hash table implementations.

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This assumes that
  a) finding the bucket containing the value is LIKELY
  b) finding an empty bucket is LIKELY
  c) growing the table is UNLIKELY

I also switched the a) and b) cases for SmallPtrSet as we seem to use
the set mostly more for insertion than for checking existence.

In a simple benchmark consisting of 2^21 insertions of 2^20 unique
pointers into a DenseMap or SmallPtrSet a few percent speedup on average,
but nothing statistically significant.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@230232 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Benjamin Kramer
2015-02-23 16:41:36 +00:00
parent 01312dd0b4
commit 42f72e2c16
3 changed files with 18 additions and 15 deletions
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lib/Support/SmallPtrSet.cpp
+10 -9
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@@ -50,11 +50,12 @@ SmallPtrSetImplBase::insert_imp(const void *Ptr) {
}
// Otherwise, hit the big set case, which will call grow.
}
if (NumElements*4 >= CurArraySize*3) {
if (LLVM_UNLIKELY(NumElements * 4 >= CurArraySize * 3)) {
// If more than 3/4 of the array is full, grow.
Grow(CurArraySize < 64 ? 128 : CurArraySize*2);
} else if (CurArraySize-(NumElements+NumTombstones) < CurArraySize/8) {
} else if (LLVM_UNLIKELY(CurArraySize - (NumElements + NumTombstones) <
CurArraySize / 8)) {
// If fewer of 1/8 of the array is empty (meaning that many are filled with
// tombstones), rehash.
Grow(CurArraySize);
@@ -107,16 +108,16 @@ const void * const *SmallPtrSetImplBase::FindBucketFor(const void *Ptr) const {
const void *const *Array = CurArray;
const void *const *Tombstone = nullptr;
while (1) {
// Found Ptr's bucket?
if (Array[Bucket] == Ptr)
return Array+Bucket;
// If we found an empty bucket, the pointer doesn't exist in the set.
// Return a tombstone if we've seen one so far, or the empty bucket if
// not.
if (Array[Bucket] == getEmptyMarker())
if (LLVM_LIKELY(Array[Bucket] == getEmptyMarker()))
return Tombstone ? Tombstone : Array+Bucket;
// Found Ptr's bucket?
if (LLVM_LIKELY(Array[Bucket] == Ptr))
return Array+Bucket;
// If this is a tombstone, remember it. If Ptr ends up not in the set, we
// prefer to return it than something that would require more probing.
if (Array[Bucket] == getTombstoneMarker() && !Tombstone)