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

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.

llvm-svn: 230232

1 files changed, 3 insertions, 2 deletions

diff --git a/llvm/lib/Support/StringMap.cpp b/llvm/lib/Support/StringMap.cpp
index ddb73494ff5..7be946642d9 100644
--- a/llvm/lib/Support/StringMap.cpp
+++ b/llvm/lib/Support/StringMap.cpp
@@ -188,9 +188,10 @@ unsigned StringMapImpl::RehashTable(unsigned BucketNo) {
   // If the hash table is now more than 3/4 full, or if fewer than 1/8 of
   // the buckets are empty (meaning that many are filled with tombstones),
   // grow/rehash the table.
-  if (NumItems*4 > NumBuckets*3) {
+  if (LLVM_UNLIKELY(NumItems * 4 > NumBuckets * 3)) {
     NewSize = NumBuckets*2;
-  } else if (NumBuckets-(NumItems+NumTombstones) <= NumBuckets/8) {
+  } else if (LLVM_UNLIKELY(NumBuckets - (NumItems + NumTombstones) <=
+                           NumBuckets / 8)) {
     NewSize = NumBuckets;
   } else {
     return BucketNo;