add a highly efficient hash table that is specialized for mapping C strings

to some other type.

llvm-svn: 31286

llvm/include/llvm/ADT/CStringMap.h

@@ -0,0 +1,144 @@
+//===--- CStringMap.h - CString Hash table map interface --------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file was developed by Chris Lattner and is distributed under
+// the University of Illinois Open Source License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file defines the CStringMap class.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_ADT_CSTRINGMAP_H
+#define LLVM_ADT_CSTRINGMAP_H
+
+#include "llvm/Support/Allocator.h"
+#include <cstring>
+
+namespace llvm {
+  
+/// CStringMapVisitor - Subclasses of this class may be implemented to walk all
+/// of the items in a CStringMap.
+class CStringMapVisitor {
+public:
+  virtual ~CStringMapVisitor();
+  virtual void Visit(const char *Key, void *Value) const = 0;
+};
+  
+/// CStringMapImpl - This is the base class of CStringMap that is shared among
+/// all of its instantiations.
+class CStringMapImpl {
+protected:
+  /// ItemBucket - The hash table consists of an array of these.  If Item is
+  /// non-null, this is an extant entry, otherwise, it is a hole.
+  struct ItemBucket {
+    /// FullHashValue - This remembers the full hash value of the key for
+    /// easy scanning.
+    unsigned FullHashValue;
+    
+    /// Item - This is a pointer to the actual item object.
+    void *Item;
+  };
+  
+  ItemBucket *TheTable;
+  unsigned NumBuckets;
+  unsigned NumItems;
+  unsigned ItemSize;
+protected:
+  CStringMapImpl(unsigned InitSize, unsigned ItemSize);
+  void RehashTable();
+  
+  /// LookupBucketFor - Look up the bucket that the specified string should end
+  /// up in.  If it already exists as a key in the map, the Item pointer for the
+  /// specified bucket will be non-null.  Otherwise, it will be null.  In either
+  /// case, the FullHashValue field of the bucket will be set to the hash value
+  /// of the string.
+  unsigned LookupBucketFor(const char *KeyStart, const char *KeyEnd);
+  
+public:
+  unsigned getNumBuckets() const { return NumBuckets; }
+  unsigned getNumItems() const { return NumItems; }
+
+  void VisitEntries(const CStringMapVisitor &Visitor) const;
+};
+
+
+/// CStringMap - This is an unconventional map that is specialized for handling
+/// keys that are "C strings", that is, null-terminated strings.  This does some
+/// funky memory allocation and hashing things to make it extremely efficient,
+/// storing the string data *after* the value in the map.
+template<typename ValueTy, typename AllocatorTy = MallocAllocator>
+class CStringMap : public CStringMapImpl {
+  AllocatorTy Allocator;
+public:
+  CStringMap(unsigned InitialSize = 0)
+    : CStringMapImpl(InitialSize, sizeof(ValueTy)) {}
+  
+  AllocatorTy &getAllocator() { return Allocator; }
+  const AllocatorTy &getAllocator() const { return Allocator; }
+
+  /// FindValue - Look up the specified key in the map.  If it exists, return a
+  /// pointer to the element, otherwise return null.
+  ValueTy *FindValue(const char *KeyStart, const char *KeyEnd) {
+    unsigned BucketNo = LookupBucketFor(KeyStart, KeyEnd);
+    return static_cast<ValueTy*>(TheTable[BucketNo].Item);
+  }
+  
+  /// GetOrCreateValue - Look up the specified key in the table.  If a value
+  /// exists, return it.  Otherwise, default construct a value, insert it, and
+  /// return.
+  ValueTy &GetOrCreateValue(const char *KeyStart, const char *KeyEnd) {
+    unsigned BucketNo = LookupBucketFor(KeyStart, KeyEnd);
+    ItemBucket &Bucket = TheTable[BucketNo];
+    if (Bucket.Item)
+      return *static_cast<ValueTy*>(Bucket.Item);
+    
+    unsigned KeyLength = KeyEnd-KeyStart;
+    
+    // Okay, the item doesn't already exist, and Bucket is the bucket to fill
+    // in.  Allocate a new item with space for the null-terminated string at the
+    // end.
+    unsigned AllocSize = sizeof(ValueTy)+KeyLength+1;
+    
+#ifdef __GNUC__
+    unsigned Alignment = __alignof__(ValueTy);
+#else
+    // FIXME: ugly.
+    unsigned Alignment = 8;
+#endif
+    ValueTy *NewItem = (ValueTy*)Allocator.Allocate(AllocSize, Alignment);
+    new (NewItem) ValueTy();
+    ++NumItems;
+    
+    // Copy the string information.
+    char *StrBuffer = (char*)(NewItem+1);
+    memcpy(StrBuffer, KeyStart, KeyLength);
+    StrBuffer[KeyLength] = 0;  // Null terminate string.
+    
+    // Fill in the bucket for the hash table.  The FullHashValue was already
+    // filled in by LookupBucketFor.
+    Bucket.Item = NewItem;
+    
+    // If the hash table is now more than 3/4 full, rehash into a larger table.
+    if (NumItems > NumBuckets*3/4)
+      RehashTable();
+    return *NewItem;
+  }
+  
+  ~CStringMap() {
+    for (ItemBucket *I = TheTable, *E = TheTable+NumBuckets; I != E; ++I) {
+      if (ValueTy *Id = static_cast<ValueTy*>(I->Item)) {
+        // Free memory referenced by the item.
+        Id->~ValueTy();
+        Allocator.Deallocate(Id);
+      }
+    }
+    delete [] TheTable;
+  }
+};
+  
+}
+
+#endif

llvm/lib/Support/CStringMap.cpp

@@ -0,0 +1,134 @@
+//===--- CStringMap.cpp - CString Hash table map implementation -----------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file was developed by Chris Lattner and is distributed under
+// the University of Illinois Open Source License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements the CStringMap class.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/ADT/CStringMap.h"
+#include <cassert>
+using namespace llvm;
+
+CStringMapVisitor::~CStringMapVisitor() {
+}
+
+CStringMapImpl::CStringMapImpl(unsigned InitSize, unsigned itemSize) {
+  assert((InitSize & (InitSize-1)) == 0 &&
+         "Init Size must be a power of 2 or zero!");
+  NumBuckets = InitSize ? InitSize : 512;
+  ItemSize = itemSize;
+  NumItems = 0;
+  
+  TheTable = new ItemBucket[NumBuckets]();
+  memset(TheTable, 0, NumBuckets*sizeof(ItemBucket));
+}
+
+
+/// HashString - Compute a hash code for the specified string.
+///
+static unsigned HashString(const char *Start, const char *End) {
+  unsigned int Result = 0;
+  // Perl hash function.
+  while (Start != End)
+    Result = Result * 33 + *Start++;
+  Result = Result + (Result >> 5);
+  return Result;
+}
+
+/// LookupBucketFor - Look up the bucket that the specified string should end
+/// up in.  If it already exists as a key in the map, the Item pointer for the
+/// specified bucket will be non-null.  Otherwise, it will be null.  In either
+/// case, the FullHashValue field of the bucket will be set to the hash value
+/// of the string.
+unsigned CStringMapImpl::LookupBucketFor(const char *NameStart,
+                                         const char *NameEnd) {
+  unsigned HTSize = NumBuckets;
+  unsigned FullHashValue = HashString(NameStart, NameEnd);
+  unsigned BucketNo = FullHashValue & (HTSize-1);
+  
+  unsigned ProbeAmt = 1;
+  while (1) {
+    ItemBucket &Bucket = TheTable[BucketNo];
+    void *BucketItem = Bucket.Item;
+    // If we found an empty bucket, this key isn't in the table yet, return it.
+    if (BucketItem == 0) {
+      Bucket.FullHashValue = FullHashValue;
+      return BucketNo;
+    }
+    
+    // If the full hash value matches, check deeply for a match.  The common
+    // case here is that we are only looking at the buckets (for item info
+    // being non-null and for the full hash value) not at the items.  This
+    // is important for cache locality.
+    if (Bucket.FullHashValue == FullHashValue) {
+      // Do the comparison like this because NameStart isn't necessarily
+      // null-terminated!
+      char *ItemStr = (char*)BucketItem+ItemSize;
+      if (strlen(ItemStr) == unsigned(NameEnd-NameStart) &&
+          memcmp(ItemStr, NameStart, (NameEnd-NameStart)) == 0) {
+        // We found a match!
+        return BucketNo;
+      }
+    }
+    
+    // Okay, we didn't find the item.  Probe to the next bucket.
+    BucketNo = (BucketNo+ProbeAmt) & (HTSize-1);
+    
+    // Use quadratic probing, it has fewer clumping artifacts than linear
+    // probing and has good cache behavior in the common case.
+    ++ProbeAmt;
+  }
+}
+
+/// RehashTable - Grow the table, redistributing values into the buckets with
+/// the appropriate mod-of-hashtable-size.
+void CStringMapImpl::RehashTable() {
+  unsigned NewSize = NumBuckets*2;
+  ItemBucket *NewTableArray = new ItemBucket[NewSize]();
+  memset(NewTableArray, 0, NewSize*sizeof(ItemBucket));
+  
+  // Rehash all the items into their new buckets.  Luckily :) we already have
+  // the hash values available, so we don't have to rehash any strings.
+  for (ItemBucket *IB = TheTable, *E = TheTable+NumBuckets; IB != E; ++IB) {
+    if (IB->Item) {
+      // Fast case, bucket available.
+      unsigned FullHash = IB->FullHashValue;
+      unsigned NewBucket = FullHash & (NewSize-1);
+      if (NewTableArray[NewBucket].Item == 0) {
+        NewTableArray[FullHash & (NewSize-1)].Item = IB->Item;
+        NewTableArray[FullHash & (NewSize-1)].FullHashValue = FullHash;
+        continue;
+      }
+      
+      unsigned ProbeSize = 1;
+      do {
+        NewBucket = (NewBucket + ProbeSize++) & (NewSize-1);
+      } while (NewTableArray[NewBucket].Item);
+      
+      // Finally found a slot.  Fill it in.
+      NewTableArray[NewBucket].Item = IB->Item;
+      NewTableArray[NewBucket].FullHashValue = FullHash;
+    }
+  }
+  
+  delete[] TheTable;
+  
+  TheTable = NewTableArray;
+  NumBuckets = NewSize;
+}
+
+
+/// VisitEntries - This method walks through all of the items,
+/// invoking Visitor.Visit for each of them.
+void CStringMapImpl::VisitEntries(const CStringMapVisitor &Visitor) const {
+  for (ItemBucket *IB = TheTable, *E = TheTable+NumBuckets; IB != E; ++IB) {
+    if (void *Id = IB->Item)
+      Visitor.Visit((char*)Id + ItemSize, Id);
+  }
+}