Initial checkin of Correlated Expression Elimination Pass

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@3599 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 974 insertions, 0 deletions

diff --git a/lib/Transforms/Scalar/CorrelatedExprs.cpp b/lib/Transforms/Scalar/CorrelatedExprs.cpp
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+++ b/lib/Transforms/Scalar/CorrelatedExprs.cpp
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+//===- CorrelatedExprs.cpp - Pass to detect and eliminated c.e.'s ---------===//
+//
+// Correlated Expression Elimination propogates information from conditional
+// branches to blocks dominated by destinations of the branch.  It propogates
+// information from the condition check itself into the body of the branch,
+// allowing transformations like these for example:
+//
+//  if (i == 7)
+//    ... 4*i;  // constant propogation
+//
+//  M = i+1; N = j+1;
+//  if (i == j)
+//    X = M-N;  // = M-M == 0;
+//
+// This is called Correlated Expression Elimination because we eliminate or
+// simplify expressions that are correlated with the direction of a branch.  In
+// this way we use static information to give us some information about the
+// dynamic value of a variable.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/Pass.h"
+#include "llvm/Function.h"
+#include "llvm/iTerminators.h"
+#include "llvm/iOperators.h"
+#include "llvm/ConstantHandling.h"
+#include "llvm/Assembly/Writer.h"
+#include "llvm/Analysis/Dominators.h"
+#include "llvm/Transforms/Utils/Local.h"
+#include "llvm/Support/ConstantRange.h"
+#include "llvm/Support/CFG.h"
+#include "Support/PostOrderIterator.h"
+#include "Support/StatisticReporter.h"
+#include <algorithm>
+
+namespace {
+  Statistic<>NumSetCCRemoved("cee\t\t- Number of setcc instruction eliminated");
+  Statistic<>NumOperandsCann("cee\t\t- Number of operands cannonicalized");
+  Statistic<>BranchRevectors("cee\t\t- Number of branches revectored");
+
+  class ValueInfo;
+  class Relation {
+    Value *Val;                 // Relation to what value?
+    Instruction::BinaryOps Rel; // SetCC relation, or Add if no information
+  public:
+    Relation(Value *V) : Val(V), Rel(Instruction::Add) {}
+    bool operator<(const Relation &R) const { return Val < R.Val; }
+    Value *getValue() const { return Val; }
+    Instruction::BinaryOps getRelation() const { return Rel; }
+
+    // contradicts - Return true if the relationship specified by the operand
+    // contradicts already known information.
+    //
+    bool contradicts(Instruction::BinaryOps Rel, const ValueInfo &VI) const;
+
+    // incorporate - Incorporate information in the argument into this relation
+    // entry.  This assumes that the information doesn't contradict itself.  If
+    // any new information is gained, true is returned, otherwise false is
+    // returned to indicate that nothing was updated.
+    //
+    bool incorporate(Instruction::BinaryOps Rel, ValueInfo &VI);
+
+    // KnownResult - Whether or not this condition determines the result of a
+    // setcc in the program.  False & True are intentionally 0 & 1 so we can
+    // convert to bool by casting after checking for unknown.
+    //
+    enum KnownResult { KnownFalse = 0, KnownTrue = 1, Unknown = 2 };
+
+    // getImpliedResult - If this relationship between two values implies that
+    // the specified relationship is true or false, return that.  If we cannot
+    // determine the result required, return Unknown.
+    //
+    KnownResult getImpliedResult(Instruction::BinaryOps Rel) const;
+
+    // print - Output this relation to the specified stream
+    void print(std::ostream &OS) const;
+    void dump() const;
+  };
+
+
+  // ValueInfo - One instance of this record exists for every value with
+  // relationships between other values.  It keeps track of all of the
+  // relationships to other values in the program (specified with Relation) that
+  // are known to be valid in a region.
+  //
+  class ValueInfo {
+    // RelationShips - this value is know to have the specified relationships to
+    // other values.  There can only be one entry per value, and this list is
+    // kept sorted by the Val field.
+    std::vector<Relation> Relationships;
+
+    // If information about this value is known or propogated from constant
+    // expressions, this range contains the possible values this value may hold.
+    ConstantRange Bounds;
+
+    // If we find that this value is equal to another value that has a lower
+    // rank, this value is used as it's replacement.
+    //
+    Value *Replacement;
+  public:
+    ValueInfo(const Type *Ty)
+      : Bounds(Ty->isIntegral() ? Ty : Type::IntTy), Replacement(0) {}
+
+    // getBounds() - Return the constant bounds of the value...
+    const ConstantRange &getBounds() const { return Bounds; }
+    ConstantRange &getBounds() { return Bounds; }
+
+    const std::vector<Relation> &getRelationships() { return Relationships; }
+
+    // getReplacement - Return the value this value is to be replaced with if it
+    // exists, otherwise return null.
+    //
+    Value *getReplacement() const { return Replacement; }
+
+    // setReplacement - Used by the replacement calculation pass to figure out
+    // what to replace this value with, if anything.
+    //
+    void setReplacement(Value *Repl) { Replacement = Repl; }
+
+    // getRelation - return the relationship entry for the specified value.
+    // This can invalidate references to other Relation's, so use it carefully.
+    //
+    Relation &getRelation(Value *V) {
+      // Binary search for V's entry...
+      std::vector<Relation>::iterator I =
+        std::lower_bound(Relationships.begin(), Relationships.end(), V);
+
+      // If we found the entry, return it...
+      if (I != Relationships.end() && I->getValue() == V)
+        return *I;
+
+      // Insert and return the new relationship...
+      return *Relationships.insert(I, V);
+    }
+
+    const Relation *requestRelation(Value *V) const {
+      // Binary search for V's entry...
+      std::vector<Relation>::const_iterator I =
+        std::lower_bound(Relationships.begin(), Relationships.end(), V);
+      if (I != Relationships.end() && I->getValue() == V)
+        return &*I;
+      return 0;
+    }
+
+    // print - Output information about this value relation...
+    void print(std::ostream &OS, Value *V) const;
+    void dump() const;
+  };
+
+  // RegionInfo - Keeps track of all of the value relationships for a region.  A
+  // region is the are dominated by a basic block.  RegionInfo's keep track of
+  // the RegionInfo for their dominator, because anything known in a dominator
+  // is known to be true in a dominated block as well.
+  //
+  class RegionInfo {
+    BasicBlock *BB;
+
+    // ValueMap - Tracks the ValueInformation known for this region
+    typedef std::map<Value*, ValueInfo> ValueMapTy;
+    ValueMapTy ValueMap;
+  public:
+    RegionInfo(BasicBlock *bb) : BB(bb) {}
+
+    // getEntryBlock - Return the block that dominates all of the members of
+    // this region.
+    BasicBlock *getEntryBlock() const { return BB; }
+
+    const RegionInfo &operator=(const RegionInfo &RI) {
+      ValueMap = RI.ValueMap;
+      return *this;
+    }
+
+    // print - Output information about this region...
+    void print(std::ostream &OS) const;
+
+    // Allow external access.
+    typedef ValueMapTy::iterator iterator;
+    iterator begin() { return ValueMap.begin(); }
+    iterator end() { return ValueMap.end(); }
+
+    ValueInfo &getValueInfo(Value *V) {
+      ValueMapTy::iterator I = ValueMap.lower_bound(V);
+      if (I != ValueMap.end() && I->first == V) return I->second;
+      return ValueMap.insert(I, std::make_pair(V, V->getType()))->second;
+    }
+
+    const ValueInfo *requestValueInfo(Value *V) const {
+      ValueMapTy::const_iterator I = ValueMap.find(V);
+      if (I != ValueMap.end()) return &I->second;
+      return 0;
+    }
+  };
+
+  /// CEE - Correlated Expression Elimination
+  class CEE : public FunctionPass {
+    std::map<Value*, unsigned> RankMap;
+    std::map<BasicBlock*, RegionInfo> RegionInfoMap;
+    DominatorSet *DS;
+    DominatorTree *DT;
+  public:
+    virtual bool runOnFunction(Function &F);
+
+    // We don't modify the program, so we preserve all analyses
+    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+      //AU.preservesCFG();
+      AU.addRequired<DominatorSet>();
+      AU.addRequired<DominatorTree>();
+    };
+
+    // print - Implement the standard print form to print out analysis
+    // information.
+    virtual void print(std::ostream &O, const Module *M) const;
+
+    virtual void releaseMemory() {
+      RegionInfoMap.clear();
+      RankMap.clear();
+    }
+
+  private:
+    RegionInfo &getRegionInfo(BasicBlock *BB) {
+      std::map<BasicBlock*, RegionInfo>::iterator I
+        = RegionInfoMap.lower_bound(BB);
+      if (I != RegionInfoMap.end() && I->first == BB) return I->second;
+      return RegionInfoMap.insert(I, std::make_pair(BB, BB))->second;
+    }
+
+    void BuildRankMap(Function &F);
+    unsigned getRank(Value *V) const {
+      if (isa<Constant>(V) || isa<GlobalValue>(V)) return 0;
+      std::map<Value*, unsigned>::const_iterator I = RankMap.find(V);
+      if (I != RankMap.end()) return I->second;
+      return 0; // Must be some other global thing
+    }
+
+    bool TransformRegion(BasicBlock *BB, std::set<BasicBlock*> &VisitedBlocks);
+
+    BasicBlock *isCorrelatedBranchBlock(BasicBlock *BB, RegionInfo &RI);
+    void PropogateBranchInfo(BranchInst *BI);
+    void PropogateEquality(Value *Op0, Value *Op1, RegionInfo &RI);
+    void PropogateRelation(Instruction::BinaryOps Opcode, Value *Op0,
+                           Value *Op1, RegionInfo &RI);
+    void UpdateUsersOfValue(Value *V, RegionInfo &RI);
+    void IncorporateInstruction(Instruction *Inst, RegionInfo &RI);
+    void ComputeReplacements(RegionInfo &RI);
+
+
+    // getSetCCResult - Given a setcc instruction, determine if the result is
+    // determined by facts we already know about the region under analysis.
+    // Return KnownTrue, KnownFalse, or Unknown based on what we can determine.
+    //
+    Relation::KnownResult getSetCCResult(SetCondInst *SC, const RegionInfo &RI);
+
+
+    bool SimplifyBasicBlock(BasicBlock &BB, const RegionInfo &RI);
+    bool SimplifyInstruction(Instruction *Inst, const RegionInfo &RI);
+  }; 
+  RegisterOpt<CEE> X("cee", "Correlated Expression Elimination");
+}
+
+Pass *createCorrelatedExpressionEliminationPass() { return new CEE(); }
+
+
+bool CEE::runOnFunction(Function &F) {
+  // Build a rank map for the function...
+  BuildRankMap(F);
+
+  // Traverse the dominator tree, computing information for each node in the
+  // tree.  Note that our traversal will not even touch unreachable basic
+  // blocks.
+  DS = &getAnalysis<DominatorSet>();
+  DT = &getAnalysis<DominatorTree>();
+  
+  std::set<BasicBlock*> VisitedBlocks;
+  return TransformRegion(&F.getEntryNode(), VisitedBlocks);
+}
+
+// TransformRegion - Transform the region starting with BB according to the
+// calculated region information for the block.  Transforming the region
+// involves analyzing any information this block provides to successors,
+// propogating the information to successors, and finally transforming
+// successors.
+//
+// This method processes the function in depth first order, which guarantees
+// that we process the immediate dominator of a block before the block itself.
+// Because we are passing information from immediate dominators down to
+// dominatees, we obviously have to process the information source before the
+// information consumer.
+//
+bool CEE::TransformRegion(BasicBlock *BB, std::set<BasicBlock*> &VisitedBlocks){
+  // Prevent infinite recursion...
+  if (VisitedBlocks.count(BB)) return false;
+  VisitedBlocks.insert(BB);
+
+  // Get the computed region information for this block...
+  RegionInfo &RI = getRegionInfo(BB);
+
+  // Compute the replacement information for this block...
+  ComputeReplacements(RI);
+
+  // If debugging, print computed region information...
+  DEBUG(RI.print(std::cerr));
+
+  // Simplify the contents of this block...
+  bool Changed = SimplifyBasicBlock(*BB, RI);
+
+  // Get the terminator of this basic block...
+  TerminatorInst *TI = BB->getTerminator();
+
+  // If this is a conditional branch, make sure that there is a branch target
+  // for each successor that can hold any information gleaned from the branch,
+  // by breaking any critical edges that may be laying about.
+  //
+  if (TI->getNumSuccessors() > 1) {
+    // If any of the successors has multiple incoming branches, add a new dummy
+    // destination branch that only contains an unconditional branch to the real
+    // target.
+    for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) {
+      BasicBlock *Succ = TI->getSuccessor(i);
+      // If there is more than one predecessor of the destination block, break
+      // this critical edge by inserting a new block.  This updates dominatorset
+      // and dominatortree information.
+      //
+      if (isCriticalEdge(TI, i))
+        SplitCriticalEdge(TI, i, this);
+    }
+  }
+
+  // Loop over all of the blocks that this block is the immediate dominator for.
+  // Because all information known in this region is also known in all of the
+  // blocks that are dominated by this one, we can safely propogate the
+  // information down now.
+  //
+  DominatorTree::Node *BBN = (*DT)[BB];
+  for (unsigned i = 0, e = BBN->getChildren().size(); i != e; ++i) {
+    BasicBlock *Dominated = BBN->getChildren()[i]->getNode();
+    assert(RegionInfoMap.find(Dominated) == RegionInfoMap.end() &&
+           "RegionInfo should be calculated in dominanace order!");
+    getRegionInfo(Dominated) = RI;
+  }
+
+  // Now that all of our successors have information if they deserve it,
+  // propogate any information our terminator instruction finds to our
+  // successors.
+  if (BranchInst *BI = dyn_cast<BranchInst>(TI))
+    if (BI->isConditional())
+      PropogateBranchInfo(BI);
+
+  // If this is a branch to a block outside our region that simply performs
+  // another conditional branch, one whose outcome is known inside of this
+  // region, then vector this outgoing edge directly to the known destination.
+  //
+  for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) {
+    while (BasicBlock *Dest = isCorrelatedBranchBlock(TI->getSuccessor(i), RI)){
+      TI->setSuccessor(i, Dest);
+      ++BranchRevectors;
+    }
+  }
+
+  // Now that all of our successors have information, recursively process them.
+  for (unsigned i = 0, e = BBN->getChildren().size(); i != e; ++i)
+    Changed |= TransformRegion(BBN->getChildren()[i]->getNode(), VisitedBlocks);
+
+    //  for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
+    //Changed |= TransformRegion(TI->getSuccessor(i), VisitedBlocks);
+
+  return Changed;
+}
+
+// If this block is a simple block not in the current region, which contains
+// only a conditional branch, we determine if the outcome of the branch can be
+// determined from information inside of the region.  Instead of going to this
+// block, we can instead go to the destination we know is the right target.
+//
+BasicBlock *CEE::isCorrelatedBranchBlock(BasicBlock *BB, RegionInfo &RI) {
+  // Check to see if we dominate the block. If so, this block will get the
+  // condition turned to a constant anyway.
+  //
+  //if (DS->dominates(RI.getEntryBlock(), BB))
+  // return 0;
+
+  // Check to see if this is a conditional branch...
+  if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator()))
+    if (BI->isConditional()) {
+      // Make sure that the block is either empty, or only contains a setcc.
+      if (BB->size() == 1 || 
+          (BB->size() == 2 && &BB->front() == BI->getCondition() &&
+           BI->getCondition()->use_size() == 1))
+        if (SetCondInst *SCI = dyn_cast<SetCondInst>(BI->getCondition())) {
+          Relation::KnownResult Result = getSetCCResult(SCI, RI);
+        
+          if (Result == Relation::KnownTrue)
+            return BI->getSuccessor(0);
+          else if (Result == Relation::KnownFalse)
+            return BI->getSuccessor(1);
+        }
+    }
+  return 0;
+}
+
+// BuildRankMap - This method builds the rank map data structure which gives
+// each instruction/value in the function a value based on how early it appears
+// in the function.  We give constants and globals rank 0, arguments are
+// numbered starting at one, and instructions are numbered in reverse post-order
+// from where the arguments leave off.  This gives instructions in loops higher
+// values than instructions not in loops.
+//
+void CEE::BuildRankMap(Function &F) {
+  unsigned Rank = 1;  // Skip rank zero.
+
+  // Number the arguments...
+  for (Function::aiterator I = F.abegin(), E = F.aend(); I != E; ++I)
+    RankMap[I] = Rank++;
+
+  // Number the instructions in reverse post order...
+  ReversePostOrderTraversal<Function*> RPOT(&F);
+  for (ReversePostOrderTraversal<Function*>::rpo_iterator I = RPOT.begin(),
+         E = RPOT.end(); I != E; ++I)
+    for (BasicBlock::iterator BBI = (*I)->begin(), E = (*I)->end();
+         BBI != E; ++BBI)
+      if (BBI->getType() != Type::VoidTy)
+        RankMap[BBI] = Rank++;
+}
+
+
+// PropogateBranchInfo - When this method is invoked, we need to propogate
+// information derived from the branch condition into the true and false
+// branches of BI.  Since we know that there aren't any critical edges in the
+// flow graph, this can proceed unconditionally.
+//
+void CEE::PropogateBranchInfo(BranchInst *BI) {
+  assert(BI->isConditional() && "Must be a conditional branch!");
+  BasicBlock *BB = BI->getParent();
+  BasicBlock *TrueBB  = BI->getSuccessor(0);
+  BasicBlock *FalseBB = BI->getSuccessor(1);
+
+  // Propogate information into the true block...
+  //
+  PropogateEquality(BI->getCondition(), ConstantBool::True,
+                    getRegionInfo(TrueBB));
+  
+  // Propogate information into the false block...
+  //
+  PropogateEquality(BI->getCondition(), ConstantBool::False,
+                    getRegionInfo(FalseBB));
+}
+
+
+// PropogateEquality - If we discover that two values are equal to each other in
+// a specified region, propogate this knowledge recursively.
+//
+void CEE::PropogateEquality(Value *Op0, Value *Op1, RegionInfo &RI) {
+  if (Op0 == Op1) return;  // Gee whiz. Are these really equal each other?
+
+  if (isa<Constant>(Op0))  // Make sure the constant is always Op1
+    std::swap(Op0, Op1);
+
+  // Make sure we don't already know these are equal, to avoid infinite loops...
+  ValueInfo &VI = RI.getValueInfo(Op0);
+
+  // Get information about the known relationship between Op0 & Op1
+  Relation &KnownRelation = VI.getRelation(Op1);
+
+  // If we already know they're equal, don't reprocess...
+  if (KnownRelation.getRelation() == Instruction::SetEQ)
+    return;
+
+  // If this is boolean, check to see if one of the operands is a constant.  If
+  // it's a constant, then see if the other one is one of a setcc instruction,
+  // an AND, OR, or XOR instruction.
+  //
+  if (ConstantBool *CB = dyn_cast<ConstantBool>(Op1)) {
+
+    if (Instruction *Inst = dyn_cast<Instruction>(Op0)) {
+      // If we know that this instruction is an AND instruction, and the result
+      // is true, this means that both operands to the OR are known to be true
+      // as well.
+      //
+      if (CB->getValue() && Inst->getOpcode() == Instruction::And) {
+        PropogateEquality(Inst->getOperand(0), CB, RI);
+        PropogateEquality(Inst->getOperand(1), CB, RI);
+      }
+      
+      // If we know that this instruction is an OR instruction, and the result
+      // is false, this means that both operands to the OR are know to be false
+      // as well.
+      //
+      if (!CB->getValue() && Inst->getOpcode() == Instruction::Or) {
+        PropogateEquality(Inst->getOperand(0), CB, RI);
+        PropogateEquality(Inst->getOperand(1), CB, RI);
+      }
+      
+      // If we know that this instruction is a NOT instruction, we know that the
+      // operand is known to be the inverse of whatever the current value is.
+      //
+      if (BinaryOperator *BOp = dyn_cast<BinaryOperator>(Inst))
+        if (BinaryOperator::isNot(BOp))
+          PropogateEquality(BinaryOperator::getNotArgument(BOp),
+                            ConstantBool::get(!CB->getValue()), RI);
+
+      // If we know the value of a SetCC instruction, propogate the information
+      // about the relation into this region as well.
+      //
+      if (SetCondInst *SCI = dyn_cast<SetCondInst>(Inst)) {
+        if (CB->getValue()) {  // If we know the condition is true...
+          // Propogate info about the LHS to the RHS & RHS to LHS
+          PropogateRelation(SCI->getOpcode(), SCI->getOperand(0),
+                            SCI->getOperand(1), RI);
+          PropogateRelation(SCI->getSwappedCondition(),
+                            SCI->getOperand(1), SCI->getOperand(0), RI);
+
+        } else {               // If we know the condition is false...
+          // We know the opposite of the condition is true...
+          Instruction::BinaryOps C = SCI->getInverseCondition();
+          
+          PropogateRelation(C, SCI->getOperand(0), SCI->getOperand(1), RI);
+          PropogateRelation(SetCondInst::getSwappedCondition(C),
+                            SCI->getOperand(1), SCI->getOperand(0), RI);
+        }
+      }
+    }
+  }
+
+  // Propogate information about Op0 to Op1 & visa versa
+  PropogateRelation(Instruction::SetEQ, Op0, Op1, RI);
+  PropogateRelation(Instruction::SetEQ, Op1, Op0, RI);
+}
+
+
+// PropogateRelation - We know that the specified relation is true in all of the
+// blocks in the specified region.  Propogate the information about Op0 and
+// anything derived from it into this region.
+//
+void CEE::PropogateRelation(Instruction::BinaryOps Opcode, Value *Op0,
+                            Value *Op1, RegionInfo &RI) {
+  assert(Op0->getType() == Op1->getType() && "Equal types expected!");
+
+  // Constants are already pretty well understood.  We will apply information
+  // about the constant to Op1 in another call to PropogateRelation.
+  //
+  if (isa<Constant>(Op0)) return;
+
+  // Get the region information for this block to update...
+  ValueInfo &VI = RI.getValueInfo(Op0);
+
+  // Get information about the known relationship between Op0 & Op1
+  Relation &Op1R = VI.getRelation(Op1);
+
+  // Quick bailout for common case if we are reprocessing an instruction...
+  if (Op1R.getRelation() == Opcode)
+    return;
+
+  // If we already have information that contradicts the current information we
+  // are propogating, ignore this info.  Something bad must have happened!
+  //
+  if (Op1R.contradicts(Opcode, VI)) {
+    Op1R.contradicts(Opcode, VI);
+    std::cerr << "Contradiction found for opcode: "
+              << Instruction::getOpcodeName(Opcode) << "\n";
+    Op1R.print(std::cerr);
+    return;
+  }
+
+  // If the information propogted is new, then we want process the uses of this
+  // instruction to propogate the information down to them.
+  //
+  if (Op1R.incorporate(Opcode, VI))
+    UpdateUsersOfValue(Op0, RI);
+}
+
+
+// UpdateUsersOfValue - The information about V in this region has been updated.
+// Propogate this to all consumers of the value.
+//
+void CEE::UpdateUsersOfValue(Value *V, RegionInfo &RI) {
+  for (Value::use_iterator I = V->use_begin(), E = V->use_end();
+       I != E; ++I)
+    if (Instruction *Inst = dyn_cast<Instruction>(*I)) {
+      // If this is an instruction using a value that we know something about,
+      // try to propogate information to the value produced by the
+      // instruction.  We can only do this if it is an instruction we can
+      // propogate information for (a setcc for example), and we only WANT to
+      // do this if the instruction dominates this region.
+      //
+      // If the instruction doesn't dominate this region, then it cannot be
+      // used in this region and we don't care about it.  If the instruction
+      // is IN this region, then we will simplify the instruction before we
+      // get to uses of it anyway, so there is no reason to bother with it
+      // here.  This check is also effectively checking to make sure that Inst
+      // is in the same function as our region (in case V is a global f.e.).
+      //
+      if (DS->properlyDominates(Inst->getParent(), RI.getEntryBlock()))
+        IncorporateInstruction(Inst, RI);
+    }
+}
+
+// IncorporateInstruction - We just updated the information about one of the
+// operands to the specified instruction.  Update the information about the
+// value produced by this instruction
+//
+void CEE::IncorporateInstruction(Instruction *Inst, RegionInfo &RI) {
+  if (SetCondInst *SCI = dyn_cast<SetCondInst>(Inst)) {
+    // See if we can figure out a result for this instruction...
+    Relation::KnownResult Result = getSetCCResult(SCI, RI);
+    if (Result != Relation::Unknown) {
+      PropogateEquality(SCI, Result ? ConstantBool::True : ConstantBool::False,
+                        RI);
+    }
+  }
+}
+
+
+// ComputeReplacements - Some values are known to be equal to other values in a
+// region.  For example if there is a comparison of equality between a variable
+// X and a constant C, we can replace all uses of X with C in the region we are
+// interested in.  We generalize this replacement to replace variables with
+// other variables if they are equal and there is a variable with lower rank
+// than the current one.  This offers a cannonicalizing property that exposes
+// more redundancies for later transformations to take advantage of.
+//
+void CEE::ComputeReplacements(RegionInfo &RI) {
+  // Loop over all of the values in the region info map...
+  for (RegionInfo::iterator I = RI.begin(), E = RI.end(); I != E; ++I) {
+    ValueInfo &VI = I->second;
+
+    // If we know that this value is a particular constant, set Replacement to
+    // the constant...
+    Value *Replacement = VI.getBounds().getSingleElement();
+
+    // If this value is not known to be some constant, figure out the lowest
+    // rank value that it is known to be equal to (if anything).
+    //
+    if (Replacement == 0) {
+      // Find out if there are any equality relationships with values of lower
+      // rank than VI itself...
+      unsigned MinRank = getRank(I->first);
+
+      // Loop over the relationships known about Op0.
+      const std::vector<Relation> &Relationships = VI.getRelationships();
+      for (unsigned i = 0, e = Relationships.size(); i != e; ++i)
+        if (Relationships[i].getRelation() == Instruction::SetEQ) {
+          unsigned R = getRank(Relationships[i].getValue());
+          if (R < MinRank) {
+            MinRank = R;
+            Replacement = Relationships[i].getValue();
+          }
+        }
+    }
+
+    // If we found something to replace this value with, keep track of it.
+    if (Replacement)
+      VI.setReplacement(Replacement);
+  }
+}
+
+// SimplifyBasicBlock - Given information about values in region RI, simplify
+// the instructions in the specified basic block.
+//
+bool CEE::SimplifyBasicBlock(BasicBlock &BB, const RegionInfo &RI) {
+  bool Changed = false;
+  for (BasicBlock::iterator I = BB.begin(), E = BB.end(); I != E; ) {
+    Instruction *Inst = &*I++;
+
+    // Convert instruction arguments to canonical forms...
+    Changed |= SimplifyInstruction(Inst, RI);
+
+    if (SetCondInst *SCI = dyn_cast<SetCondInst>(Inst)) {
+      // Try to simplify a setcc instruction based on inherited information
+      Relation::KnownResult Result = getSetCCResult(SCI, RI);
+      if (Result != Relation::Unknown) {
+        DEBUG(std::cerr << "Replacing setcc with " << Result
+                        << " constant: " << SCI);
+
+        SCI->replaceAllUsesWith(ConstantBool::get((bool)Result));
+        // The instruction is now dead, remove it from the program.
+        SCI->getParent()->getInstList().erase(SCI);
+        ++NumSetCCRemoved;
+        Changed = true;
+      }
+    }
+  }
+
+  return Changed;
+}
+
+// SimplifyInstruction - Inspect the operands of the instruction, converting
+// them to their cannonical form if possible.  This takes care of, for example,
+// replacing a value 'X' with a constant 'C' if the instruction in question is
+// dominated by a true seteq 'X', 'C'.
+//
+bool CEE::SimplifyInstruction(Instruction *I, const RegionInfo &RI) {
+  bool Changed = false;
+
+  for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
+    if (const ValueInfo *VI = RI.requestValueInfo(I->getOperand(i)))
+      if (Value *Repl = VI->getReplacement()) {
+        // If we know if a replacement with lower rank than Op0, make the
+        // replacement now.
+        DEBUG(std::cerr << "In Inst: " << I << "  Replacing operand #" << i
+                        << " with " << Repl << "\n");
+        I->setOperand(i, Repl);
+        Changed = true;
+        ++NumOperandsCann;
+      }
+
+  return Changed;
+}
+
+
+// SimplifySetCC - Try to simplify a setcc instruction based on information
+// inherited from a dominating setcc instruction.  V is one of the operands to
+// the setcc instruction, and VI is the set of information known about it.  We
+// take two cases into consideration here.  If the comparison is against a
+// constant value, we can use the constant range to see if the comparison is
+// possible to succeed.  If it is not a comparison against a constant, we check
+// to see if there is a known relationship between the two values.  If so, we
+// may be able to eliminate the check.
+//
+Relation::KnownResult CEE::getSetCCResult(SetCondInst *SCI,
+                                          const RegionInfo &RI) {
+  Value *Op0 = SCI->getOperand(0), *Op1 = SCI->getOperand(1);
+  Instruction::BinaryOps Opcode = SCI->getOpcode();
+  
+  if (isa<Constant>(Op0)) {
+    if (isa<Constant>(Op1)) {
+      if (Constant *Result = ConstantFoldInstruction(SCI)) {
+        // Wow, this is easy, directly eliminate the SetCondInst.
+        DEBUG(std::cerr << "Replacing setcc with constant fold: " << SCI);
+        return cast<ConstantBool>(Result)->getValue()
+          ? Relation::KnownTrue : Relation::KnownFalse;
+      }
+    } else {
+      // We want to swap this instruction so that operand #0 is the constant.
+      std::swap(Op0, Op1);
+      Opcode = SCI->getSwappedCondition();
+    }
+  }
+
+  // Try to figure out what the result of this comparison will be...
+  Relation::KnownResult Result = Relation::Unknown;
+
+  // We have to know something about the relationship to prove anything...
+  if (const ValueInfo *Op0VI = RI.requestValueInfo(Op0)) {
+
+    // At this point, we know that if we have a constant argument that it is in
+    // Op1.  Check to see if we know anything about comparing value with a
+    // constant, and if we can use this info to fold the setcc.
+    //
+    if (ConstantIntegral *C = dyn_cast<ConstantIntegral>(Op1)) {
+      // Check to see if we already know the result of this comparison...
+      ConstantRange R = ConstantRange(Opcode, C);
+      ConstantRange Int = R.intersectWith(Op0VI->getBounds());
+
+      // If the intersection of the two ranges is empty, then the condition
+      // could never be true!
+      // 
+      if (Int.isEmptySet()) {
+        Result = Relation::KnownFalse;
+
+      // Otherwise, if VI.getBounds() (the possible values) is a subset of R
+      // (the allowed values) then we know that the condition must always be
+      // true!
+      //
+      } else if (Int == Op0VI->getBounds()) {
+        Result = Relation::KnownTrue;
+      }
+    } else {
+      // If we are here, we know that the second argument is not a constant
+      // integral.  See if we know anything about Op0 & Op1 that allows us to
+      // fold this anyway.
+      //
+      // Do we have value information about Op0 and a relation to Op1?
+      if (const Relation *Op2R = Op0VI->requestRelation(Op1))
+        Result = Op2R->getImpliedResult(Opcode);
+    }
+  }
+  return Result;
+}
+
+//===----------------------------------------------------------------------===//
+//  Relation Implementation
+//===----------------------------------------------------------------------===//
+
+// CheckCondition - Return true if the specified condition is false.  Bound may
+// be null.
+static bool CheckCondition(Constant *Bound, Constant *C,
+                           Instruction::BinaryOps BO) {
+  assert(C != 0 && "C is not specified!");
+  if (Bound == 0) return false;
+
+  ConstantBool *Val;
+  switch (BO) {
+  default: assert(0 && "Unknown Condition code!");
+  case Instruction::SetEQ: Val = *Bound == *C; break;
+  case Instruction::SetNE: Val = *Bound != *C; break;
+  case Instruction::SetLT: Val = *Bound <  *C; break;
+  case Instruction::SetGT: Val = *Bound >  *C; break;
+  case Instruction::SetLE: Val = *Bound <= *C; break;
+  case Instruction::SetGE: Val = *Bound >= *C; break;
+  }
+
+  // ConstantHandling code may not succeed in the comparison...
+  if (Val == 0) return false;
+  return !Val->getValue();  // Return true if the condition is false...
+}
+
+// contradicts - Return true if the relationship specified by the operand
+// contradicts already known information.
+//
+bool Relation::contradicts(Instruction::BinaryOps Op,
+                           const ValueInfo &VI) const {
+  assert (Op != Instruction::Add && "Invalid relation argument!");
+
+  // If this is a relationship with a constant, make sure that this relationship
+  // does not contradict properties known about the bounds of the constant.
+  //
+  if (ConstantIntegral *C = dyn_cast<ConstantIntegral>(Val))
+    if (ConstantRange(Op, C).intersectWith(VI.getBounds()).isEmptySet())
+      return true;
+
+  switch (Rel) {
+  default: assert(0 && "Unknown Relationship code!");
+  case Instruction::Add: return false;  // Nothing known, nothing contradicts
+  case Instruction::SetEQ:
+    return Op == Instruction::SetLT || Op == Instruction::SetGT ||
+           Op == Instruction::SetNE;
+  case Instruction::SetNE: return Op == Instruction::SetEQ;
+  case Instruction::SetLE: return Op == Instruction::SetGT;
+  case Instruction::SetGE: return Op == Instruction::SetLT;
+  case Instruction::SetLT:
+    return Op == Instruction::SetEQ || Op == Instruction::SetGT ||
+           Op == Instruction::SetGE;
+  case Instruction::SetGT:
+    return Op == Instruction::SetEQ || Op == Instruction::SetLT ||
+           Op == Instruction::SetLE;
+  }
+}
+
+// incorporate - Incorporate information in the argument into this relation
+// entry.  This assumes that the information doesn't contradict itself.  If any
+// new information is gained, true is returned, otherwise false is returned to
+// indicate that nothing was updated.
+//
+bool Relation::incorporate(Instruction::BinaryOps Op, ValueInfo &VI) {
+  assert(!contradicts(Op, VI) &&
+         "Cannot incorporate contradictory information!");
+
+  // If this is a relationship with a constant, make sure that we update the
+  // range that is possible for the value to have...
+  //
+  if (ConstantIntegral *C = dyn_cast<ConstantIntegral>(Val))
+    VI.getBounds() = ConstantRange(Op, C).intersectWith(VI.getBounds());
+
+  switch (Rel) {
+  default: assert(0 && "Unknown prior value!");
+  case Instruction::Add:   Rel = Op; return true;
+  case Instruction::SetEQ: return false;  // Nothing is more precise
+  case Instruction::SetNE: return false;  // Nothing is more precise
+  case Instruction::SetLT: return false;  // Nothing is more precise
+  case Instruction::SetGT: return false;  // Nothing is more precise
+  case Instruction::SetLE:
+    if (Op == Instruction::SetEQ || Op == Instruction::SetLT) {
+      Rel = Op;
+      return true;
+    } else if (Op == Instruction::SetNE) {
+      Rel = Instruction::SetLT;
+      return true;
+    }
+    return false;
+  case Instruction::SetGE: return Op == Instruction::SetLT;
+    if (Op == Instruction::SetEQ || Op == Instruction::SetGT) {
+      Rel = Op;
+      return true;
+    } else if (Op == Instruction::SetNE) {
+      Rel = Instruction::SetGT;
+      return true;
+    }
+    return false;
+  }
+}
+
+// getImpliedResult - If this relationship between two values implies that
+// the specified relationship is true or false, return that.  If we cannot
+// determine the result required, return Unknown.
+//
+Relation::KnownResult
+Relation::getImpliedResult(Instruction::BinaryOps Op) const {
+  if (Rel == Op) return KnownTrue;
+  if (Rel == SetCondInst::getInverseCondition(Op)) return KnownFalse;
+
+  switch (Rel) {
+  default: assert(0 && "Unknown prior value!");
+  case Instruction::SetEQ:
+    if (Op == Instruction::SetLE || Op == Instruction::SetGE) return KnownTrue;
+    if (Op == Instruction::SetLT || Op == Instruction::SetGT) return KnownFalse;
+    break;
+  case Instruction::SetLT:
+    if (Op == Instruction::SetNE || Op == Instruction::SetLE) return KnownTrue;
+    if (Op == Instruction::SetEQ) return KnownFalse;
+    break;
+  case Instruction::SetGT:
+    if (Op == Instruction::SetNE || Op == Instruction::SetGE) return KnownTrue;
+    if (Op == Instruction::SetEQ) return KnownFalse;
+    break;
+  case Instruction::SetNE:
+  case Instruction::SetLE:
+  case Instruction::SetGE:
+  case Instruction::Add:
+    break;
+  }
+  return Unknown;
+}
+
+
+//===----------------------------------------------------------------------===//
+// Printing Support...
+//===----------------------------------------------------------------------===//
+
+// print - Implement the standard print form to print out analysis information.
+void CEE::print(std::ostream &O, const Module *M) const {
+  O << "\nPrinting Correlated Expression Info:\n";
+  for (std::map<BasicBlock*, RegionInfo>::const_iterator I = 
+         RegionInfoMap.begin(), E = RegionInfoMap.end(); I != E; ++I)
+    I->second.print(O);
+}
+
+// print - Output information about this region...
+void RegionInfo::print(std::ostream &OS) const {
+  if (ValueMap.empty()) return;
+
+  OS << " RegionInfo for basic block: " << BB->getName() << "\n";
+  for (std::map<Value*, ValueInfo>::const_iterator
+         I = ValueMap.begin(), E = ValueMap.end(); I != E; ++I)
+    I->second.print(OS, I->first);
+  OS << "\n";
+}
+
+// print - Output information about this value relation...
+void ValueInfo::print(std::ostream &OS, Value *V) const {
+  if (Relationships.empty()) return;
+
+  if (V) {
+    OS << "  ValueInfo for: ";
+    WriteAsOperand(OS, V);
+  }
+  OS << "\n    Bounds = " << Bounds << "\n";
+  if (Replacement) {
+    OS << "    Replacement = ";
+    WriteAsOperand(OS, Replacement);
+    OS << "\n";
+  }
+  for (unsigned i = 0, e = Relationships.size(); i != e; ++i)
+    Relationships[i].print(OS);
+}
+
+// print - Output this relation to the specified stream
+void Relation::print(std::ostream &OS) const {
+  OS << "    is ";
+  switch (Rel) {
+  default:           OS << "*UNKNOWN*"; break;
+  case Instruction::SetEQ: OS << "== "; break;
+  case Instruction::SetNE: OS << "!= "; break;
+  case Instruction::SetLT: OS << "< "; break;
+  case Instruction::SetGT: OS << "> "; break;
+  case Instruction::SetLE: OS << "<= "; break;
+  case Instruction::SetGE: OS << ">= "; break;
+  }
+
+  WriteAsOperand(OS, Val);
+  OS << "\n";
+}
+
+void Relation::dump() const { print(std::cerr); }
+void ValueInfo::dump() const { print(std::cerr, 0); }