[llvm-commits] [llvm] r40100 - /llvm/trunk/include/llvm/ADT/DenseMap.h

[Chris Lattner]

Owen,

This looks like it always reduces the table size by half.  Is that  
intended?  What happened to "if it is 25% or less full, shrink to 2x  
the size it contained?"

-Chris

On Jul 20, 2007, at 9:15 AM, Owen Anderson wrote:

> Author: resistor
> Date: Fri Jul 20 11:15:24 2007
> New Revision: 40100
>
> URL: http://llvm.org/viewvc/llvm-project?rev=40100&view=rev
> Log:
> Have DenseMap auto-shrink itself on clear().  This improves the  
> time to optimize
> 403.gcc from 15.2s to 14.3s.
>
> 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=40100&r1=40099&r2=40100&view=diff
>
> ====================================================================== 
> ========
> --- llvm/trunk/include/llvm/ADT/DenseMap.h (original)
> +++ llvm/trunk/include/llvm/ADT/DenseMap.h Fri Jul 20 11:15:24 2007
> @@ -90,6 +90,11 @@
>    unsigned size() const { return NumEntries; }
>
>    void clear() {
> +    if (NumEntries * 4 < NumBuckets && NumBuckets > 64) {
> +      shrink_and_clear();
> +      return;
> +    }
> +
>      const KeyT EmptyKey = getEmptyKey(), TombstoneKey =  
> getTombstoneKey();
>      for (BucketT *P = Buckets, *E = Buckets+NumBuckets; P != E; + 
> +P) {
>        if (P->first != EmptyKey && P->first != TombstoneKey) {
> @@ -101,7 +106,7 @@
>      assert(NumEntries == 0 && "Node count imbalance!");
>      NumTombstones = 0;
>    }
> -
> +
>    /// count - Return true if the specified key is in the map.
>    bool count(const KeyT &Val) const {
>      BucketT *TheBucket;
> @@ -290,6 +295,36 @@
>      // Free the old table.
>      delete[] (char*)OldBuckets;
>    }
> +
> +  void shrink_and_clear() {
> +    unsigned OldNumBuckets = NumBuckets;
> +    BucketT *OldBuckets = Buckets;
> +
> +    // Halve the number of buckets.
> +    NumBuckets >>= 1;
> +    NumTombstones = 0;
> +    Buckets = (BucketT*)new char[sizeof(BucketT)*NumBuckets];
> +
> +    // Initialize all the keys to EmptyKey.
> +    const KeyT EmptyKey = getEmptyKey();
> +    for (unsigned i = 0, e = NumBuckets; i != e; ++i)
> +      new (&Buckets[i].first) KeyT(EmptyKey);
> +
> +    // Free the old buckets.
> +    const KeyT TombstoneKey = getTombstoneKey();
> +    for (BucketT *B = OldBuckets, *E = OldBuckets+OldNumBuckets;  
> B != E; ++B) {
> +      if (B->first != EmptyKey && B->first != TombstoneKey) {
> +        // Free the value.
> +        B->second.~ValueT();
> +      }
> +      B->first.~KeyT();
> +    }
> +
> +    // Free the old table.
> +    delete[] (char*)OldBuckets;
> +
> +    NumEntries = 0;
> +  }
>  };
>
>  template<typename KeyT, typename ValueT, typename KeyInfoT>
>
>
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