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.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@230232 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/ADT/DenseMap.h

@@ -442,11 +442,12 @@ private:
     // causing infinite loops in lookup.
     unsigned NewNumEntries = getNumEntries() + 1;
     unsigned NumBuckets = getNumBuckets();
-    if (NewNumEntries*4 >= NumBuckets*3) {
+    if (LLVM_UNLIKELY(NewNumEntries * 4 >= NumBuckets * 3)) {
       this->grow(NumBuckets * 2);
       LookupBucketFor(Key, TheBucket);
       NumBuckets = getNumBuckets();
-    } else if (NumBuckets-(NewNumEntries+getNumTombstones()) <= NumBuckets/8) {
+    } else if (LLVM_UNLIKELY(NumBuckets-(NewNumEntries+getNumTombstones()) <=
+                             NumBuckets/8)) {
       this->grow(NumBuckets);
       LookupBucketFor(Key, TheBucket);
     }
@@ -492,14 +493,14 @@ private:
     while (1) {
       const BucketT *ThisBucket = BucketsPtr + BucketNo;
       // Found Val's bucket?  If so, return it.
-      if (KeyInfoT::isEqual(Val, ThisBucket->getFirst())) {
+      if (LLVM_LIKELY(KeyInfoT::isEqual(Val, ThisBucket->getFirst()))) {
         FoundBucket = ThisBucket;
         return true;
       }
 
       // If we found an empty bucket, the key doesn't exist in the set.
       // Insert it and return the default value.
-      if (KeyInfoT::isEqual(ThisBucket->getFirst(), EmptyKey)) {
+      if (LLVM_LIKELY(KeyInfoT::isEqual(ThisBucket->getFirst(), EmptyKey))) {
         // If we've already seen a tombstone while probing, fill it in instead
         // of the empty bucket we eventually probed to.
         FoundBucket = FoundTombstone ? FoundTombstone : ThisBucket;

lib/Support/SmallPtrSet.cpp

@@ -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)

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;