1 files changed, 222 insertions, 0 deletions
diff --git a/lib/Transforms/Utils/LowerSwitch.cpp b/lib/Transforms/Utils/LowerSwitch.cpp
new file mode 100644
index 0000000000..0ba37c275b
--- /dev/null
+++ b/lib/Transforms/Utils/LowerSwitch.cpp
@@ -0,0 +1,222 @@
+//===- LowerSwitch.cpp - Eliminate Switch instructions --------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file was developed by the LLVM research group and is distributed under
+// the University of Illinois Open Source License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// The LowerSwitch transformation rewrites switch statements with a sequence of
+// branches, which allows targets to get away with not implementing the switch
+// statement until it is convenient.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/Constants.h"
+#include "llvm/Function.h"
+#include "llvm/Instructions.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/ADT/Statistic.h"
+#include <algorithm>
+using namespace llvm;
+
+namespace {
+  Statistic<> NumLowered("lowerswitch", "Number of SwitchInst's replaced");
+
+  /// LowerSwitch Pass - Replace all SwitchInst instructions with chained branch
+  /// instructions.  Note that this cannot be a BasicBlock pass because it
+  /// modifies the CFG!
+  class LowerSwitch : public FunctionPass {
+  public:
+    bool runOnFunction(Function &F);
+    typedef std::pair<Constant*, BasicBlock*> Case;
+    typedef std::vector<Case>::iterator       CaseItr;
+  private:
+    void processSwitchInst(SwitchInst *SI);
+
+    BasicBlock* switchConvert(CaseItr Begin, CaseItr End, Value* Val,
+                              BasicBlock* OrigBlock, BasicBlock* Default);
+    BasicBlock* newLeafBlock(Case& Leaf, Value* Val,
+                             BasicBlock* OrigBlock, BasicBlock* Default);
+  };
+
+  /// The comparison function for sorting the switch case values in the vector.
+  struct CaseCmp {
+    bool operator () (const LowerSwitch::Case& C1,
+                      const LowerSwitch::Case& C2) {
+      if (const ConstantUInt* U1 = dyn_cast<const ConstantUInt>(C1.first))
+        return U1->getValue() < cast<const ConstantUInt>(C2.first)->getValue();
+
+      const ConstantSInt* S1 = dyn_cast<const ConstantSInt>(C1.first);
+      return S1->getValue() < cast<const ConstantSInt>(C2.first)->getValue();
+    }
+  };
+
+  RegisterOpt<LowerSwitch>
+  X("lowerswitch", "Lower SwitchInst's to branches");
+}
+
+// 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.
+//
+std::ostream& operator<<(std::ostream &O,
+                         const std::vector<LowerSwitch::Case> &C) {
+  O << "[";
+
+  for (std::vector<LowerSwitch::Case>::const_iterator B = C.begin(),
+         E = C.end(); B != E; ) {
+    O << *B->first;
+    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<Case> LHS(Begin, Begin + Mid);
+  DEBUG(std::cerr << "LHS: " << LHS << "\n");
+  std::vector<Case> RHS(Begin + Mid, End);
+  DEBUG(std::cerr << "RHS: " << RHS << "\n");
+
+  Case& Pivot = *(Begin + Mid);
+  DEBUG(std::cerr << "Pivot ==> "
+                  << (int64_t)cast<ConstantInt>(Pivot.first)->getRawValue()
+                  << "\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 = new BasicBlock("NodeBlock");
+  F->getBasicBlockList().insert(OrigBlock->getNext(), NewNode);
+
+  SetCondInst* Comp = new SetCondInst(Instruction::SetLT, Val, Pivot.first,
+                                      "Pivot");
+  NewNode->getInstList().push_back(Comp);
+  new BranchInst(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(Case& Leaf, Value* Val,
+                                      BasicBlock* OrigBlock,
+                                      BasicBlock* Default)
+{
+  Function* F = OrigBlock->getParent();
+  BasicBlock* NewLeaf = new BasicBlock("LeafBlock");
+  F->getBasicBlockList().insert(OrigBlock->getNext(), NewLeaf);
+
+  // Make the seteq instruction...
+  SetCondInst* Comp = new SetCondInst(Instruction::SetEQ, Val,
+                                      Leaf.first, "SwitchLeaf");
+  NewLeaf->getInstList().push_back(Comp);
+
+  // Make the conditional branch...
+  BasicBlock* Succ = Leaf.second;
+  new BranchInst(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);
+    int BlockIdx = PN->getBasicBlockIndex(OrigBlock);
+    assert(BlockIdx != -1 && "Switch didn't go to this successor??");
+    PN->setIncomingBlock((unsigned)BlockIdx, NewLeaf);
+  }
+
+  return NewLeaf;
+}
+
+// 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->getOperand(0);  // 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->getNumOperands() == 2) {
+    new BranchInst(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 = new BasicBlock("NewDefault");
+  F->getBasicBlockList().insert(Default, NewDefault);
+
+  new BranchInst(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);
+  }
+
+  std::vector<Case> Cases;
+
+  // Expand comparisons for all of the non-default cases...
+  for (unsigned i = 1; i < SI->getNumSuccessors(); ++i)
+    Cases.push_back(Case(SI->getSuccessorValue(i), SI->getSuccessor(i)));
+
+  std::sort(Cases.begin(), Cases.end(), CaseCmp());
+  DEBUG(std::cerr << "Cases: " << Cases << "\n");
+  BasicBlock* SwitchBlock = switchConvert(Cases.begin(), Cases.end(), Val,
+                                          OrigBlock, NewDefault);
+
+  // Branch to our shiny new if-then stuff...
+  new BranchInst(SwitchBlock, OrigBlock);
+
+  // We are now done with the switch instruction, delete it.
+  CurBlock->getInstList().erase(SI);
+}