[llvm-commits] [llvm] r159648 - /llvm/trunk/include/llvm/ADT/DenseMap.h

[Chandler Carruth]

Author: chandlerc
Date: Tue Jul  3 02:16:13 2012
New Revision: 159648

URL: http://llvm.org/viewvc/llvm-project?rev=159648&view=rev
Log:
Micro-optimize this function a bit. This shrinks the generated code
some, and allows the routine to be inlined into common callers. The
various bits that hit this code in their hotpath seem slightly lower on
the profile, but I can't really measure a performance improvement as
everything seems to still be bottlenecked on likely cache misses. =/

Modified:
    llvm/trunk/include/llvm/ADT/DenseMap.h

Modified: llvm/trunk/include/llvm/ADT/DenseMap.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/ADT/DenseMap.h?rev=159648&r1=159647&r2=159648&view=diff
==============================================================================
--- llvm/trunk/include/llvm/ADT/DenseMap.h (original)
+++ llvm/trunk/include/llvm/ADT/DenseMap.h Tue Jul  3 02:16:13 2012
@@ -442,11 +442,10 @@
   template<typename LookupKeyT>
   bool LookupBucketFor(const LookupKeyT &Val,
                        const BucketT *&FoundBucket) const {
-    unsigned BucketNo = getHashValue(Val);
-    unsigned ProbeAmt = 1;
     const BucketT *BucketsPtr = getBuckets();
+    const unsigned NumBuckets = getNumBuckets();
 
-    if (getNumBuckets() == 0) {
+    if (NumBuckets == 0) {
       FoundBucket = 0;
       return false;
     }
@@ -459,8 +458,10 @@
            !KeyInfoT::isEqual(Val, TombstoneKey) &&
            "Empty/Tombstone value shouldn't be inserted into map!");
 
+    unsigned BucketNo = getHashValue(Val) & (NumBuckets-1);
+    unsigned ProbeAmt = 1;
     while (1) {
-      const BucketT *ThisBucket = BucketsPtr + (BucketNo & (getNumBuckets()-1));
+      const BucketT *ThisBucket = BucketsPtr + BucketNo;
       // Found Val's bucket?  If so, return it.
       if (KeyInfoT::isEqual(Val, ThisBucket->first)) {
         FoundBucket = ThisBucket;
@@ -485,6 +486,7 @@
       // Otherwise, it's a hash collision or a tombstone, continue quadratic
       // probing.
       BucketNo += ProbeAmt++;
+      BucketNo &= (NumBuckets-1);
     }
   }