make hasAddressTaken() constant time by storing a refcount in BB's subclass data.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@85625 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/BasicBlock.h

@@ -23,6 +23,7 @@ namespace llvm {
 
 class TerminatorInst;
 class LLVMContext;
+class BlockAddress;
 
 template<> struct ilist_traits<Instruction>
   : public SymbolTableListTraits<Instruction, BasicBlock> {
@@ -66,7 +67,7 @@ private:
 /// @brief LLVM Basic Block Representation
 class BasicBlock : public Value, // Basic blocks are data objects also
                    public ilist_node<BasicBlock> {
-
+  friend class BlockAddress;
 public:
   typedef iplist<Instruction> InstListType;
 private:
@@ -238,7 +239,15 @@ public:
 
   /// hasAddressTaken - returns true if there are any uses of this basic block
   /// other than direct branches, switches, etc. to it.
-  bool hasAddressTaken() const;
+  bool hasAddressTaken() const { return SubclassData != 0; }
+private:
+  /// AdjustBlockAddressRefCount - BasicBlock stores the number of BlockAddress
+  /// objects using it.  This is almost always 0, sometimes one, possibly but
+  /// almost never 2, and inconceivably 3 or more.
+  void AdjustBlockAddressRefCount(int Amt) {
+    SubclassData += Amt;
+    assert((int)(char)SubclassData >= 0 && "Refcount wrap-around");
+  }
 };
 
 } // End llvm namespace

lib/VMCore/BasicBlock.cpp

@@ -278,11 +278,3 @@ BasicBlock *BasicBlock::splitBasicBlock(iterator I, const Twine &BBName) {
   return New;
 }
 
-/// hasAddressTaken - returns true if there are any uses of this basic block
-/// other than direct branches, switches, etc. to it.
-bool BasicBlock::hasAddressTaken() const {
-  for (Value::use_const_iterator I = use_begin(), E = use_end(); I != E; ++I)
-    if (isa<BlockAddress>(*I))
-      return true;
-  return false;
-}

lib/VMCore/Constants.cpp

@@ -44,7 +44,7 @@ using namespace llvm;
 
 // Constructor to create a '0' constant of arbitrary type...
 static const uint64_t zero[2] = {0, 0};
-Constant* Constant::getNullValue(const Type* Ty) {
+Constant *Constant::getNullValue(const Type *Ty) {
   switch (Ty->getTypeID()) {
   case Type::IntegerTyID:
     return ConstantInt::get(Ty, 0);
@@ -72,7 +72,7 @@ Constant* Constant::getNullValue(const Type* Ty) {
   }
 }
 
-Constant* Constant::getIntegerValue(const Type* Ty, const APInt &V) {
+Constant* Constant::getIntegerValue(const Type *Ty, const APInt &V) {
   const Type *ScalarTy = Ty->getScalarType();
 
   // Create the base integer constant.
@@ -89,13 +89,13 @@ Constant* Constant::getIntegerValue(const Type* Ty, const APInt &V) {
   return C;
 }
 
-Constant* Constant::getAllOnesValue(const Type* Ty) {
-  if (const IntegerType* ITy = dyn_cast<IntegerType>(Ty))
+Constant* Constant::getAllOnesValue(const Type *Ty) {
+  if (const IntegerType *ITy = dyn_cast<IntegerType>(Ty))
     return ConstantInt::get(Ty->getContext(),
                             APInt::getAllOnesValue(ITy->getBitWidth()));
   
   std::vector<Constant*> Elts;
-  const VectorType* VTy = cast<VectorType>(Ty);
+  const VectorType *VTy = cast<VectorType>(Ty);
   Elts.resize(VTy->getNumElements(), getAllOnesValue(VTy->getElementType()));
   assert(Elts[0] && "Not a vector integer type!");
   return cast<ConstantVector>(ConstantVector::get(Elts));
@@ -1045,6 +1045,7 @@ BlockAddress::BlockAddress(Function *F, BasicBlock *BB)
            &Op<0>(), 2) {
   Op<0>() = F;
   Op<1>() = BB;
+  BB->AdjustBlockAddressRefCount(1);
 }
 
 
@@ -1053,6 +1054,7 @@ BlockAddress::BlockAddress(Function *F, BasicBlock *BB)
 void BlockAddress::destroyConstant() {
   getFunction()->getType()->getContext().pImpl
     ->BlockAddresses.erase(std::make_pair(getFunction(), getBasicBlock()));
+  getBasicBlock()->AdjustBlockAddressRefCount(-1);
   destroyConstantImpl();
 }