1 files changed, 305 insertions, 0 deletions
diff --git a/lib/Transforms/Utils/LowerSwitch.cpp b/lib/Transforms/Utils/LowerSwitch.cpp
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+++ b/lib/Transforms/Utils/LowerSwitch.cpp
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+//===- LowerSwitch.cpp - Eliminate Switch instructions --------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// The LowerSwitch transformation rewrites switch instructions with a sequence
+// of branches, which allows targets to get away with not implementing the
+// switch instruction until it is convenient.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/Transforms/Utils/UnifyFunctionExitNodes.h"
+#include "llvm/Constants.h"
+#include "llvm/Function.h"
+#include "llvm/Instructions.h"
+#include "llvm/LLVMContext.h"
+#include "llvm/Pass.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/Support/Compiler.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
+#include <algorithm>
+using namespace llvm;
+
+namespace {
+  /// LowerSwitch Pass - Replace all SwitchInst instructions with chained branch
+  /// instructions.
+  class LowerSwitch : public FunctionPass {
+  public:
+    static char ID; // Pass identification, replacement for typeid
+    LowerSwitch() : FunctionPass(ID) {
+      initializeLowerSwitchPass(*PassRegistry::getPassRegistry());
+    } 
+
+    virtual bool runOnFunction(Function &F);
+    
+    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+      // This is a cluster of orthogonal Transforms
+      AU.addPreserved<UnifyFunctionExitNodes>();
+      AU.addPreserved("mem2reg");
+      AU.addPreservedID(LowerInvokePassID);
+    }
+
+    struct CaseRange {
+      Constant* Low;
+      Constant* High;
+      BasicBlock* BB;
+
+      CaseRange(Constant *low = 0, Constant *high = 0, BasicBlock *bb = 0) :
+        Low(low), High(high), BB(bb) { }
+    };
+
+    typedef std::vector<CaseRange>           CaseVector;
+    typedef std::vector<CaseRange>::iterator CaseItr;
+  private:
+    void processSwitchInst(SwitchInst *SI);
+
+    BasicBlock* switchConvert(CaseItr Begin, CaseItr End, Value* Val,
+                              BasicBlock* OrigBlock, BasicBlock* Default);
+    BasicBlock* newLeafBlock(CaseRange& Leaf, Value* Val,
+                             BasicBlock* OrigBlock, BasicBlock* Default);
+    unsigned Clusterify(CaseVector& Cases, SwitchInst *SI);
+  };
+}
+
+char LowerSwitch::ID = 0;
+INITIALIZE_PASS(LowerSwitch, "lowerswitch",
+                "Lower SwitchInst's to branches", false, false)
+
+// Publicly exposed interface to pass...
+char &llvm::LowerSwitchID = LowerSwitch::ID;
+// createLowerSwitchPass - Interface to this file...
+FunctionPass *llvm::createLowerSwitchPass() {
+  return new LowerSwitch();
+}
+
+bool LowerSwitch::runOnFunction(Function &F) {
+  bool Changed = false;
+
+  for (Function::iterator I = F.begin(), E = F.end(); I != E; ) {
+    BasicBlock *Cur = I++; // Advance over block so we don't traverse new blocks
+
+    if (SwitchInst *SI = dyn_cast<SwitchInst>(Cur->getTerminator())) {
+      Changed = true;
+      processSwitchInst(SI);
+    }
+  }
+
+  return Changed;
+}
+
+// operator<< - Used for debugging purposes.
+//
+static raw_ostream& operator<<(raw_ostream &O,
+                               const LowerSwitch::CaseVector &C)
+    LLVM_ATTRIBUTE_USED;
+static raw_ostream& operator<<(raw_ostream &O,
+                               const LowerSwitch::CaseVector &C) {
+  O << "[";
+
+  for (LowerSwitch::CaseVector::const_iterator B = C.begin(),
+         E = C.end(); B != E; ) {
+    O << *B->Low << " -" << *B->High;
+    if (++B != E) O << ", ";
+  }
+
+  return O << "]";
+}
+
+// switchConvert - Convert the switch statement into a binary lookup of
+// the case values. The function recursively builds this tree.
+//
+BasicBlock* LowerSwitch::switchConvert(CaseItr Begin, CaseItr End,
+                                       Value* Val, BasicBlock* OrigBlock,
+                                       BasicBlock* Default)
+{
+  unsigned Size = End - Begin;
+
+  if (Size == 1)
+    return newLeafBlock(*Begin, Val, OrigBlock, Default);
+
+  unsigned Mid = Size / 2;
+  std::vector<CaseRange> LHS(Begin, Begin + Mid);
+  DEBUG(dbgs() << "LHS: " << LHS << "\n");
+  std::vector<CaseRange> RHS(Begin + Mid, End);
+  DEBUG(dbgs() << "RHS: " << RHS << "\n");
+
+  CaseRange& Pivot = *(Begin + Mid);
+  DEBUG(dbgs() << "Pivot ==> " 
+               << cast<ConstantInt>(Pivot.Low)->getValue() << " -"
+               << cast<ConstantInt>(Pivot.High)->getValue() << "\n");
+
+  BasicBlock* LBranch = switchConvert(LHS.begin(), LHS.end(), Val,
+                                      OrigBlock, Default);
+  BasicBlock* RBranch = switchConvert(RHS.begin(), RHS.end(), Val,
+                                      OrigBlock, Default);
+
+  // Create a new node that checks if the value is < pivot. Go to the
+  // left branch if it is and right branch if not.
+  Function* F = OrigBlock->getParent();
+  BasicBlock* NewNode = BasicBlock::Create(Val->getContext(), "NodeBlock");
+  Function::iterator FI = OrigBlock;
+  F->getBasicBlockList().insert(++FI, NewNode);
+
+  ICmpInst* Comp = new ICmpInst(ICmpInst::ICMP_ULT,
+                                Val, Pivot.Low, "Pivot");
+  NewNode->getInstList().push_back(Comp);
+  BranchInst::Create(LBranch, RBranch, Comp, NewNode);
+  return NewNode;
+}
+
+// newLeafBlock - Create a new leaf block for the binary lookup tree. It
+// checks if the switch's value == the case's value. If not, then it
+// jumps to the default branch. At this point in the tree, the value
+// can't be another valid case value, so the jump to the "default" branch
+// is warranted.
+//
+BasicBlock* LowerSwitch::newLeafBlock(CaseRange& Leaf, Value* Val,
+                                      BasicBlock* OrigBlock,
+                                      BasicBlock* Default)
+{
+  Function* F = OrigBlock->getParent();
+  BasicBlock* NewLeaf = BasicBlock::Create(Val->getContext(), "LeafBlock");
+  Function::iterator FI = OrigBlock;
+  F->getBasicBlockList().insert(++FI, NewLeaf);
+
+  // Emit comparison
+  ICmpInst* Comp = NULL;
+  if (Leaf.Low == Leaf.High) {
+    // Make the seteq instruction...
+    Comp = new ICmpInst(*NewLeaf, ICmpInst::ICMP_EQ, Val,
+                        Leaf.Low, "SwitchLeaf");
+  } else {
+    // Make range comparison
+    if (cast<ConstantInt>(Leaf.Low)->isMinValue(true /*isSigned*/)) {
+      // Val >= Min && Val <= Hi --> Val <= Hi
+      Comp = new ICmpInst(*NewLeaf, ICmpInst::ICMP_SLE, Val, Leaf.High,
+                          "SwitchLeaf");
+    } else if (cast<ConstantInt>(Leaf.Low)->isZero()) {
+      // Val >= 0 && Val <= Hi --> Val <=u Hi
+      Comp = new ICmpInst(*NewLeaf, ICmpInst::ICMP_ULE, Val, Leaf.High,
+                          "SwitchLeaf");      
+    } else {
+      // Emit V-Lo <=u Hi-Lo
+      Constant* NegLo = ConstantExpr::getNeg(Leaf.Low);
+      Instruction* Add = BinaryOperator::CreateAdd(Val, NegLo,
+                                                   Val->getName()+".off",
+                                                   NewLeaf);
+      Constant *UpperBound = ConstantExpr::getAdd(NegLo, Leaf.High);
+      Comp = new ICmpInst(*NewLeaf, ICmpInst::ICMP_ULE, Add, UpperBound,
+                          "SwitchLeaf");
+    }
+  }
+
+  // Make the conditional branch...
+  BasicBlock* Succ = Leaf.BB;
+  BranchInst::Create(Succ, Default, Comp, NewLeaf);
+
+  // If there were any PHI nodes in this successor, rewrite one entry
+  // from OrigBlock to come from NewLeaf.
+  for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
+    PHINode* PN = cast<PHINode>(I);
+    // Remove all but one incoming entries from the cluster
+    uint64_t Range = cast<ConstantInt>(Leaf.High)->getSExtValue() -
+                     cast<ConstantInt>(Leaf.Low)->getSExtValue();    
+    for (uint64_t j = 0; j < Range; ++j) {
+      PN->removeIncomingValue(OrigBlock);
+    }
+    
+    int BlockIdx = PN->getBasicBlockIndex(OrigBlock);
+    assert(BlockIdx != -1 && "Switch didn't go to this successor??");
+    PN->setIncomingBlock((unsigned)BlockIdx, NewLeaf);
+  }
+
+  return NewLeaf;
+}
+
+// Clusterify - Transform simple list of Cases into list of CaseRange's
+unsigned LowerSwitch::Clusterify(CaseVector& Cases, SwitchInst *SI) {
+
+  IntegersSubsetToBB TheClusterifier;
+
+  // Start with "simple" cases
+  for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
+       i != e; ++i) {
+    BasicBlock *SuccBB = i.getCaseSuccessor();
+    IntegersSubset CaseRanges = i.getCaseValueEx();
+    TheClusterifier.add(CaseRanges, SuccBB);
+  }
+  
+  TheClusterifier.optimize();
+  
+  size_t numCmps = 0;
+  for (IntegersSubsetToBB::RangeIterator i = TheClusterifier.begin(),
+       e = TheClusterifier.end(); i != e; ++i, ++numCmps) {
+    IntegersSubsetToBB::Cluster &C = *i;
+    
+    // FIXME: Currently work with ConstantInt based numbers.
+    // Changing it to APInt based is a pretty heavy for this commit.
+    Cases.push_back(CaseRange(C.first.getLow().toConstantInt(),
+                              C.first.getHigh().toConstantInt(), C.second));
+    if (C.first.isSingleNumber())
+      // A range counts double, since it requires two compares.
+      ++numCmps;
+  }
+
+  return numCmps;  
+}
+
+// processSwitchInst - Replace the specified switch instruction with a sequence
+// of chained if-then insts in a balanced binary search.
+//
+void LowerSwitch::processSwitchInst(SwitchInst *SI) {
+  BasicBlock *CurBlock = SI->getParent();
+  BasicBlock *OrigBlock = CurBlock;
+  Function *F = CurBlock->getParent();
+  Value *Val = SI->getCondition();  // The value we are switching on...
+  BasicBlock* Default = SI->getDefaultDest();
+
+  // If there is only the default destination, don't bother with the code below.
+  if (!SI->getNumCases()) {
+    BranchInst::Create(SI->getDefaultDest(), CurBlock);
+    CurBlock->getInstList().erase(SI);
+    return;
+  }
+
+  // Create a new, empty default block so that the new hierarchy of
+  // if-then statements go to this and the PHI nodes are happy.
+  BasicBlock* NewDefault = BasicBlock::Create(SI->getContext(), "NewDefault");
+  F->getBasicBlockList().insert(Default, NewDefault);
+
+  BranchInst::Create(Default, NewDefault);
+
+  // If there is an entry in any PHI nodes for the default edge, make sure
+  // to update them as well.
+  for (BasicBlock::iterator I = Default->begin(); isa<PHINode>(I); ++I) {
+    PHINode *PN = cast<PHINode>(I);
+    int BlockIdx = PN->getBasicBlockIndex(OrigBlock);
+    assert(BlockIdx != -1 && "Switch didn't go to this successor??");
+    PN->setIncomingBlock((unsigned)BlockIdx, NewDefault);
+  }
+
+  // Prepare cases vector.
+  CaseVector Cases;
+  unsigned numCmps = Clusterify(Cases, SI);
+
+  DEBUG(dbgs() << "Clusterify finished. Total clusters: " << Cases.size()
+               << ". Total compares: " << numCmps << "\n");
+  DEBUG(dbgs() << "Cases: " << Cases << "\n");
+  (void)numCmps;
+  
+  BasicBlock* SwitchBlock = switchConvert(Cases.begin(), Cases.end(), Val,
+                                          OrigBlock, NewDefault);
+
+  // Branch to our shiny new if-then stuff...
+  BranchInst::Create(SwitchBlock, OrigBlock);
+
+  // We are now done with the switch instruction, delete it.
+  CurBlock->getInstList().erase(SI);
+}