Add PredicateSimplifier pass. Collapses equal variables into one form

and simplifies expressions. This implements the optimization described
in PR807.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@29947 91177308-0d34-0410-b5e6-96231b3b80d8

8 files changed, 977 insertions, 0 deletions

diff --git a/CREDITS.TXT b/CREDITS.TXT
index 7cc6e6fcf9..c3f15818a1 100644
--- a/CREDITS.TXT
+++ b/CREDITS.TXT
@@ -176,3 +176,7 @@ N: Bill Wendling
 E: isanbard@gmail.com
 W: http://web.mac.com/bwendling/
 D: The `Lower Setjmp/Longjmp' pass, improvements to the -lowerswitch pass.
+
+N: Nick Lewycky
+E: nicholas@mxc.ca
+D: PredicateSimplifier pass
diff --git a/include/llvm/LinkAllPasses.h b/include/llvm/LinkAllPasses.h
index b5ec20e6a6..0ef16ec896 100644
--- a/include/llvm/LinkAllPasses.h
+++ b/include/llvm/LinkAllPasses.h
@@ -120,6 +120,7 @@ namespace {
       (void) llvm::createDataStructureStatsPass();
       (void) llvm::createDataStructureGraphCheckerPass();
       (void) llvm::createInstCountPass();
+      (void) llvm::createPredicateSimplifierPass();
 
       (void)new llvm::LocalDataStructures();
       (void)new llvm::BUDataStructures();
diff --git a/include/llvm/Transforms/Scalar.h b/include/llvm/Transforms/Scalar.h
index d901972c9d..077972f681 100644
--- a/include/llvm/Transforms/Scalar.h
+++ b/include/llvm/Transforms/Scalar.h
@@ -308,6 +308,11 @@ FunctionPass *createBlockPlacementPass();
 FunctionPass *createLCSSAPass();
 extern const PassInfo *LCSSAID;
 
+//===----------------------------------------------------------------------===//
+// This pass collapses duplicate variables into one canonical form,
+// and tries to simplify expressions along the way.
+FunctionPass *createPredicateSimplifierPass();
+
 } // End llvm namespace
 
 #endif
diff --git a/lib/Transforms/Scalar/PredicateSimplifier.cpp b/lib/Transforms/Scalar/PredicateSimplifier.cpp
new file mode 100644
index 0000000000..4f11ca9525
--- /dev/null
+++ b/lib/Transforms/Scalar/PredicateSimplifier.cpp
@@ -0,0 +1,744 @@
+//===-- PredicateSimplifier.cpp - Path Sensitive Simplifier -----------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file was developed by Nick Lewycky and is distributed under the
+// University of Illinois Open Source License. See LICENSE.TXT for details.
+//
+//===------------------------------------------------------------------===//
+//
+// Path-sensitive optimizer. In a branch where x == y, replace uses of
+// x with y. Permits further optimization, such as the elimination of
+// the unreachable call:
+//
+// void test(int *p, int *q)
+// {
+//   if (p != q)
+//     return;
+// 
+//   if (*p != *q)
+//     foo(); // unreachable
+// }
+//
+//===------------------------------------------------------------------===//
+//
+// This optimization works by substituting %q for %p when protected by a
+// conditional that assures us of that fact. Equivalent variables are
+// called SynSets; sets of synonyms. We maintain a mapping from Value *
+// to the SynSet, and the SynSet maintains the best canonical form of the
+// Value.
+//
+// Properties are stored as relationships between two SynSets.
+//
+//===------------------------------------------------------------------===//
+
+// TODO:
+// * Handle SelectInst
+// * Switch to EquivalenceClasses ADT
+// * Check handling of NAN in floating point types
+// * Don't descend into false side of branches with ConstantBool condition.
+
+#define DEBUG_TYPE "predsimplify"
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/Constants.h"
+#include "llvm/Instructions.h"
+#include "llvm/Pass.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/Analysis/Dominators.h"
+#include "llvm/Support/CFG.h"
+#include "llvm/Support/Debug.h"
+#include <iostream>
+using namespace llvm;
+
+namespace {
+  Statistic<>
+  NumVarsReplaced("predsimplify", "Number of argument substitutions");
+  Statistic<>
+  NumResolved("predsimplify", "Number of instruction substitutions");
+  Statistic<>
+  NumSwitchCases("predsimplify", "Number of switch cases removed");
+
+  /// Used for choosing the canonical Value in a synonym set.
+  /// Leaves the better one in V1. Returns whether a swap took place.
+  static void order(Value *&V1, Value *&V2) {
+    if (isa<Constant>(V2)) {
+      if (!isa<Constant>(V1)) {
+        std::swap(V1, V2);
+        return;
+      }
+    } else if (isa<Argument>(V2)) {
+      if (!isa<Constant>(V1) && !isa<Argument>(V1)) {
+        std::swap(V1, V2);
+        return;
+      }
+    }
+    if (User *U1 = dyn_cast<User>(V1)) {
+      for (User::const_op_iterator I = U1->op_begin(), E = U1->op_end();
+           I != E; ++I) {
+        if (*I == V2) {
+          std::swap(V1, V2);
+          return;
+        }
+      }
+    }
+    return;
+  }
+
+  /// Represents the set of equivalent Value*s and provides insertion
+  /// and fast lookup. Also stores the set of inequality relationships.
+  class PropertySet {
+    struct Property;
+  public:
+    typedef unsigned SynSet;
+    typedef std::map<Value*, unsigned>::iterator       SynonymIterator;
+    typedef std::map<Value*, unsigned>::const_iterator ConstSynonymIterator;
+    typedef std::vector<Property>::iterator       PropertyIterator;
+    typedef std::vector<Property>::const_iterator ConstPropertyIterator;
+
+    enum Ops {
+      EQ,
+      NE
+    };
+
+    Value *canonicalize(Value *V) const {
+      Value *C = lookup(V);
+      return C ? C : V;
+    }
+
+    Value *lookup(Value *V) const {
+      ConstSynonymIterator SI = SynonymMap.find(V);
+      if (SI == SynonymMap.end()) return NULL;
+
+      return Synonyms[SI->second];
+    }
+
+    Value *lookup(SynSet SS) const {
+      assert(SS < Synonyms.size());
+      return Synonyms[SS];
+    }
+
+    // Find a SynSet for a given Value.
+    //
+    // Given the Value *V sets SS to a valid SynSet. Returns true if it
+    // found it.
+    bool findSynSet(Value *V, SynSet &SS) const {
+      ConstSynonymIterator SI = SynonymMap.find(V);
+      if (SI != SynonymMap.end()) {
+        SS = SI->second;
+        return true;
+      }
+
+      std::vector<Value *>::const_iterator I =
+          std::find(Synonyms.begin(), Synonyms.end(), V);
+      if (I != Synonyms.end()) { 
+        SS = I-Synonyms.begin();
+        return true;
+      }
+
+      return false;
+    }
+
+    bool empty() const {
+      return Synonyms.empty();
+    }
+
+    void addEqual(Value *V1, Value *V2) {
+      order(V1, V2);
+      if (isa<Constant>(V2)) return; // refuse to set false == true.
+
+      V1 = canonicalize(V1);
+      V2 = canonicalize(V2);
+
+      if (V1 == V2) return; // already equivalent.
+
+      SynSet I1, I2;
+      bool F1 = findSynSet(V1, I1),
+           F2 = findSynSet(V2, I2);
+
+      DEBUG(std::cerr << "V1: " << *V1 << " I1: " << I1
+                      << " F1: " << F1 << "\n");
+      DEBUG(std::cerr << "V2: " << *V2 << " I2: " << I2
+                      << " F2: " << F2 << "\n");
+
+      if (!F1 && !F2) {
+        SynSet SS = addSynSet(V1);
+        SynonymMap[V1] = SS;
+        SynonymMap[V2] = SS;
+      }
+
+      else if (!F1 && F2) {
+        SynonymMap[V1] = I2;
+      }
+
+      else if (F1 && !F2) {
+        SynonymMap[V2] = I1;
+      }
+
+      else {
+        // This is the case where we have two sets, [%a1, %a2, %a3] and
+        // [%p1, %p2, %p3] and someone says that %a2 == %p3. We need to
+        // combine the two synsets.
+
+        // Collapse synonyms of V2 into V1.
+        for (SynonymIterator I = SynonymMap.begin(), E = SynonymMap.end();
+             I != E; ++I) {
+          if (I->second == I2) I->second = I1;
+          else if (I->second > I2) --I->second;
+        }
+
+        // Move Properties
+        for (PropertyIterator I = Properties.begin(), E = Properties.end();
+             I != E; ++I) {
+          if (I->S1 == I2) I->S1 = I1;
+          else if (I->S1 > I2) --I->S1;
+          if (I->S2 == I2) I->S2 = I1;
+          else if (I->S2 > I2) --I->S2;
+        }
+
+        // Remove the synonym
+        Synonyms.erase(Synonyms.begin() + I2);
+      }
+
+      addImpliedProperties(EQ, V1, V2);
+    }
+
+    void addNotEqual(Value *V1, Value *V2) {
+      DEBUG(std::cerr << "not equal: " << *V1 << " and " << *V2 << "\n");
+      bool skip_search = false;
+      V1 = canonicalize(V1);
+      V2 = canonicalize(V2);
+
+      SynSet S1, S2;
+      if (!findSynSet(V1, S1)) {
+        skip_search = true;
+        S1 = addSynSet(V1);
+      }
+      if (!findSynSet(V2, S2)) {
+        skip_search = true;
+        S2 = addSynSet(V2);
+      }
+
+      if (!skip_search) {
+        // Does the property already exist?
+        for (PropertyIterator I = Properties.begin(), E = Properties.end();
+             I != E; ++I) {
+          if (I->Opcode != NE) continue;
+
+          if ((I->S1 == S1 && I->S2 == S2) ||
+              (I->S1 == S2 && I->S2 == S1)) {
+            return; // Found.
+          }
+        }
+      }
+
+      // Add the property.
+      Properties.push_back(Property(NE, S1, S2));
+      addImpliedProperties(NE, V1, V2);
+    }
+
+    PropertyIterator findProperty(Ops Opcode, Value *V1, Value *V2) {
+      assert(Opcode != EQ && "Can't findProperty on EQ."
+             "Use the lookup method instead.");
+
+      SynSet S1, S2;
+      if (!findSynSet(V1, S1)) return Properties.end();
+      if (!findSynSet(V2, S2)) return Properties.end();
+
+      // Does the property already exist?
+      for (PropertyIterator I = Properties.begin(), E = Properties.end();
+           I != E; ++I) {
+        if (I->Opcode != Opcode) continue;
+
+        if ((I->S1 == S1 && I->S2 == S2) ||
+            (I->S1 == S2 && I->S2 == S1)) {
+          return I; // Found.
+        }
+      }
+      return Properties.end();
+    }
+
+    ConstPropertyIterator
+    findProperty(Ops Opcode, Value *V1, Value *V2) const {
+      assert(Opcode != EQ && "Can't findProperty on EQ."
+             "Use the lookup method instead.");
+
+      SynSet S1, S2;
+      if (!findSynSet(V1, S1)) return Properties.end();
+      if (!findSynSet(V2, S2)) return Properties.end();
+
+      // Does the property already exist?
+      for (ConstPropertyIterator I = Properties.begin(),
+           E = Properties.end(); I != E; ++I) {
+        if (I->Opcode != Opcode) continue;
+
+        if ((I->S1 == S1 && I->S2 == S2) ||
+            (I->S1 == S2 && I->S2 == S1)) {
+          return I; // Found.
+        }
+      }
+      return Properties.end();
+    }
+
+  private:
+    // Represents Head OP [Tail1, Tail2, ...]
+    // For example: %x != %a, %x != %b.
+    struct Property {
+      Property(Ops opcode, SynSet s1, SynSet s2)
+        : Opcode(opcode), S1(s1), S2(s2)
+      { assert(opcode != EQ && "Equality belongs in the synonym set,"
+               "not a property."); }
+
+      bool operator<(const Property &rhs) const {
+        if (Opcode != rhs.Opcode) return Opcode < rhs.Opcode;
+        if (S1 != rhs.S1) return S1 < rhs.S1;
+        return S2 < rhs.S2;
+      }
+
+      Ops Opcode;
+      SynSet S1, S2;
+    };
+
+    SynSet addSynSet(Value *V) {
+      Synonyms.push_back(V);
+      return Synonyms.size()-1;
+    }
+
+    void add(Ops Opcode, Value *V1, Value *V2, bool invert) {
+      switch (Opcode) {
+        case EQ:
+          if (invert) addNotEqual(V1, V2);
+          else        addEqual(V1, V2);
+          break;
+        case NE:
+          if (invert) addEqual(V1, V2);
+          else        addNotEqual(V1, V2);
+          break;
+        default:
+          assert(0 && "Unknown property opcode.");
+      }
+    }
+
+    // Finds the properties implied by a synonym and adds them too.
+    // Example: ("seteq %a, %b", true,  EQ) --> (%a, %b, EQ)
+    //          ("seteq %a, %b", false, EQ) --> (%a, %b, NE)
+    void addImpliedProperties(Ops Opcode, Value *V1, Value *V2) {
+      order(V1, V2);
+
+      if (BinaryOperator *BO = dyn_cast<BinaryOperator>(V2)) {
+        switch (BO->getOpcode()) {
+        case Instruction::SetEQ:
+          if (V1 == ConstantBool::True)
+            add(Opcode, BO->getOperand(0), BO->getOperand(1), false);
+          if (V1 == ConstantBool::False)
+            add(Opcode, BO->getOperand(0), BO->getOperand(1), true);
+          break;
+        case Instruction::SetNE:
+          if (V1 == ConstantBool::True)
+            add(Opcode, BO->getOperand(0), BO->getOperand(1), true);
+          if (V1 == ConstantBool::False)
+            add(Opcode, BO->getOperand(0), BO->getOperand(1), false);
+          break;
+        case Instruction::SetLT:
+        case Instruction::SetGT:
+          if (V1 == ConstantBool::True)
+            add(Opcode, BO->getOperand(0), BO->getOperand(1), true);
+          break;
+        case Instruction::SetLE:
+        case Instruction::SetGE:
+          if (V1 == ConstantBool::False)
+            add(Opcode, BO->getOperand(0), BO->getOperand(1), true);
+          break;
+        case Instruction::And:
+          if (V1 == ConstantBool::True) {
+            add(Opcode, ConstantBool::True, BO->getOperand(0), false);
+            add(Opcode, ConstantBool::True, BO->getOperand(1), false);
+          }
+          break;
+        case Instruction::Or:
+          if (V1 == ConstantBool::False) {
+            add(Opcode, ConstantBool::False, BO->getOperand(0), false);
+            add(Opcode, ConstantBool::False, BO->getOperand(1), false);
+          }
+          break;
+        case Instruction::Xor:
+          if (V1 == ConstantBool::True) {
+            if (BO->getOperand(0) == ConstantBool::True)
+              add(Opcode, ConstantBool::False, BO->getOperand(1), false);
+            if (BO->getOperand(1) == ConstantBool::True)
+              add(Opcode, ConstantBool::False, BO->getOperand(0), false);
+          }
+          if (V1 == ConstantBool::False) {
+            if (BO->getOperand(0) == ConstantBool::True)
+              add(Opcode, ConstantBool::True, BO->getOperand(1), false);
+            if (BO->getOperand(1) == ConstantBool::True)
+              add(Opcode, ConstantBool::True, BO->getOperand(0), false);
+          }
+          break;
+        default:
+          break;
+        }
+      }
+    }
+
+    std::map<Value *, unsigned> SynonymMap;
+    std::vector<Value *> Synonyms;
+
+  public:
+    void debug(std::ostream &os) const {
+      os << Synonyms.size() << " synsets:\n";
+      for (unsigned I = 0, E = Synonyms.size(); I != E; ++I) {
+        os << I << ". " << *Synonyms[I] << "\n";
+      }
+      for (ConstSynonymIterator I = SynonymMap.begin(),E = SynonymMap.end();
+           I != E; ++I) {
+        os << *I->first << "-> #" << I->second << "\n";
+      }
+      os << Properties.size() << " properties:\n";
+      for (unsigned I = 0, E = Properties.size(); I != E; ++I) {
+        os << I << ". (" << Properties[I].Opcode << ","
+           << Properties[I].S1 << "," << Properties[I].S2 << ")\n";
+      }
+    }
+
+    std::vector<Property> Properties;
+  };
+
+  /// PredicateSimplifier - This class is a simplifier that replaces
+  /// one equivalent variable with another. It also tracks what
+  /// can't be equal and will solve setcc instructions when possible.
+  class PredicateSimplifier : public FunctionPass {
+  public:
+    bool runOnFunction(Function &F);
+    virtual void getAnalysisUsage(AnalysisUsage &AU) const;
+
+  private:
+    // Try to replace the Use of the instruction with something simpler.
+    Value *resolve(SetCondInst *SCI, const PropertySet &);
+    Value *resolve(BinaryOperator *BO, const PropertySet &);
+    Value *resolve(Value *V, const PropertySet &);
+
+    // Used by terminator instructions to proceed from the current basic
+    // block to the next. Verifies that "current" dominates "next",
+    // then calls visitBasicBlock.
+    void proceedToSuccessor(PropertySet &CurrentPS, PropertySet &NextPS,
+                  DominatorTree::Node *Current, DominatorTree::Node *Next);
+    void proceedToSuccessor(PropertySet &CurrentPS,
+                  DominatorTree::Node *Current, DominatorTree::Node *Next);
+
+    // Visits each instruction in the basic block.
+    void visitBasicBlock(DominatorTree::Node *DTNode,
+                         PropertySet &KnownProperties);
+
+    // For each instruction, add the properties to KnownProperties.
+    void visit(Instruction *I, DominatorTree::Node *, PropertySet &);
+    void visit(TerminatorInst *TI, DominatorTree::Node *, PropertySet &);
+    void visit(BranchInst *BI, DominatorTree::Node *, PropertySet &);
+    void visit(SwitchInst *SI, DominatorTree::Node *, PropertySet);
+    void visit(LoadInst *LI, DominatorTree::Node *, PropertySet &);
+    void visit(StoreInst *SI, DominatorTree::Node *, PropertySet &);
+    void visit(BinaryOperator *BO, DominatorTree::Node *, PropertySet &);
+
+    DominatorTree *DT;
+    bool modified;
+  };
+
+  RegisterPass<PredicateSimplifier> X("predsimplify",
+                                      "Predicate Simplifier");
+}
+
+FunctionPass *llvm::createPredicateSimplifierPass() {
+  return new PredicateSimplifier();
+}
+
+bool PredicateSimplifier::runOnFunction(Function &F) {
+  DT = &getAnalysis<DominatorTree>();
+
+  modified = false;
+  PropertySet KnownProperties;
+  visitBasicBlock(DT->getRootNode(), KnownProperties);
+  return modified;
+}
+
+void PredicateSimplifier::getAnalysisUsage(AnalysisUsage &AU) const {
+  AU.addRequired<DominatorTree>();
+}
+
+// resolve catches cases addProperty won't because it wasn't used as a
+// condition in the branch, and that visit won't, because the instruction
+// was defined outside of the range that the properties apply to.
+Value *PredicateSimplifier::resolve(SetCondInst *SCI,
+                                    const PropertySet &KP) {
+  // Attempt to resolve the SetCondInst to a boolean.
+
+  Value *SCI0 = SCI->getOperand(0),
+        *SCI1 = SCI->getOperand(1);
+  PropertySet::ConstPropertyIterator NE =
+                   KP.findProperty(PropertySet::NE, SCI0, SCI1);
+
+  if (NE != KP.Properties.end()) {
+    switch (SCI->getOpcode()) {
+      case Instruction::SetEQ:
+        return ConstantBool::False;
+      case Instruction::SetNE:
+        return ConstantBool::True;
+      case Instruction::SetLE:
+      case Instruction::SetGE:
+      case Instruction::SetLT:
+      case Instruction::SetGT:
+        break;
+      default:
+        assert(0 && "Unknown opcode in SetCondInst.");
+        break;
+    }
+  }
+
+  SCI0 = KP.canonicalize(SCI0);
+  SCI1 = KP.canonicalize(SCI1);
+
+  ConstantIntegral *CI1 = dyn_cast<ConstantIntegral>(SCI0),
+                   *CI2 = dyn_cast<ConstantIntegral>(SCI1);
+
+  if (!CI1 || !CI2) return SCI;
+
+  switch(SCI->getOpcode()) {
+    case Instruction::SetLE:
+    case Instruction::SetGE:
+    case Instruction::SetEQ:
+      if (CI1->getRawValue() == CI2->getRawValue())
+        return ConstantBool::True;
+      else
+        return ConstantBool::False;
+    case Instruction::SetLT:
+    case Instruction::SetGT:
+    case Instruction::SetNE:
+      if (CI1->getRawValue() == CI2->getRawValue())
+        return ConstantBool::False;
+      else
+        return ConstantBool::True;
+    default:
+      assert(0 && "Unknown opcode in SetContInst.");
+      break;
+  }
+}
+
+Value *PredicateSimplifier::resolve(BinaryOperator *BO,
+                                    const PropertySet &KP) {
+  if (SetCondInst *SCI = dyn_cast<SetCondInst>(BO))
+    return resolve(SCI, KP);
+
+  DEBUG(std::cerr << "BO->getOperand(1) = " << *BO->getOperand(1) << "\n");
+
+  Value *lhs = resolve(BO->getOperand(0), KP),
+        *rhs = resolve(BO->getOperand(1), KP);
+  ConstantIntegral *CI1 = dyn_cast<ConstantIntegral>(lhs);
+  ConstantIntegral *CI2 = dyn_cast<ConstantIntegral>(rhs);
+
+  DEBUG(std::cerr << "resolveBO: lhs = " << *lhs
+                  << ", rhs = " << *rhs << "\n");
+  if (CI1) DEBUG(std::cerr << "CI1 = " << *CI1);
+  if (CI2) DEBUG(std::cerr << "CI2 = " << *CI2);
+
+  if (!CI1 || !CI2) return BO;
+
+  Value *V = ConstantExpr::get(BO->getOpcode(), CI1, CI2);
+  if (V) return V;
+  return BO;
+}
+
+Value *PredicateSimplifier::resolve(Value *V, const PropertySet &KP) {
+  if (isa<Constant>(V) || isa<BasicBlock>(V) || KP.empty()) return V;
+
+  V = KP.canonicalize(V);
+
+  if (BinaryOperator *BO = dyn_cast<BinaryOperator>(V))
+    return resolve(BO, KP);
+
+  return V;
+}
+
+void PredicateSimplifier::visitBasicBlock(DominatorTree::Node *DTNode,
+                                          PropertySet &KnownProperties) {
+  BasicBlock *BB = DTNode->getBlock();
+  for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
+    visit(I, DTNode, KnownProperties);
+  }
+}
+
+void PredicateSimplifier::visit(Instruction *I, DominatorTree::Node *DTNode,
+                                PropertySet &KnownProperties) {
+  DEBUG(std::cerr << "Considering instruction " << *I << "\n");
+  DEBUG(KnownProperties.debug(std::cerr));
+
+  // Substitute values known to be equal.
+  for (unsigned i = 0, E = I->getNumOperands(); i != E; ++i) {
+    Value *Oper = I->getOperand(i);
+    Value *V = resolve(Oper, KnownProperties);
+    assert(V && "resolve not supposed to return NULL.");
+    if (V != Oper) {
+      modified = true;
+      ++NumVarsReplaced;
+      DEBUG(std::cerr << "resolving " << *I);
+      I->setOperand(i, V);
+      DEBUG(std::cerr << "into " << *I);
+    }
+  }
+
+  Value *V = resolve(I, KnownProperties);
+  assert(V && "resolve not supposed to return NULL.");
+  if (V != I) {
+    modified = true;
+    ++NumResolved;
+    I->replaceAllUsesWith(V);
+    I->eraseFromParent();
+  }
+
+  if (TerminatorInst *TI = dyn_cast<TerminatorInst>(I))
+    visit(TI, DTNode, KnownProperties);
+  else if (LoadInst *LI = dyn_cast<LoadInst>(I))
+    visit(LI, DTNode, KnownProperties);
+  else if (StoreInst *SI = dyn_cast<StoreInst>(I))
+    visit(SI, DTNode, KnownProperties);
+  else if (BinaryOperator *BO = dyn_cast<BinaryOperator>(I))
+    visit(BO, DTNode, KnownProperties);
+}
+
+void PredicateSimplifier::proceedToSuccessor(PropertySet &CurrentPS,
+    PropertySet &NextPS, DominatorTree::Node *Current,
+    DominatorTree::Node *Next) {
+  if (Next->getBlock()->getSinglePredecessor() == Current->getBlock())
+    proceedToSuccessor(NextPS, Current, Next);
+  else
+    proceedToSuccessor(CurrentPS, Current, Next);
+}
+
+void PredicateSimplifier::proceedToSuccessor(PropertySet &KP,
+    DominatorTree::Node *Current, DominatorTree::Node *Next) {
+  if (Current->properlyDominates(Next))
+    visitBasicBlock(Next, KP);
+}
+
+void PredicateSimplifier::visit(TerminatorInst *TI,
+                                DominatorTree::Node *Node, PropertySet &KP){
+  if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
+    visit(BI, Node, KP);
+    return;
+  }
+  if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
+    visit(SI, Node, KP);
+    return;
+  }
+
+  for (unsigned i = 0, E = TI->getNumSuccessors(); i != E; ++i) {
+    BasicBlock *BB = TI->getSuccessor(i);
+    PropertySet KPcopy(KP);
+    proceedToSuccessor(KPcopy, Node, DT->getNode(TI->getSuccessor(i)));
+  }
+}
+
+void PredicateSimplifier::visit(BranchInst *BI,
+                                DominatorTree::Node *Node, PropertySet &KP){
+  if (BI->isUnconditional()) {
+    proceedToSuccessor(KP, Node, DT->getNode(BI->getSuccessor(0)));
+    return;
+  }
+
+  Value *Condition = BI->getCondition();
+
+  PropertySet TrueProperties(KP), FalseProperties(KP);
+  DEBUG(std::cerr << "true set:\n");
+  TrueProperties.addEqual(ConstantBool::True,   Condition);
+  DEBUG(std::cerr << "false set:\n");
+  FalseProperties.addEqual(ConstantBool::False, Condition);
+
+  BasicBlock *TrueDest  = BI->getSuccessor(0),
+             *FalseDest = BI->getSuccessor(1);
+
+  PropertySet KPcopy(KP);
+  proceedToSuccessor(KP,     TrueProperties,  Node, DT->getNode(TrueDest));
+  proceedToSuccessor(KPcopy, FalseProperties, Node, DT->getNode(FalseDest));
+}
+
+void PredicateSimplifier::visit(SwitchInst *SI,
+                             DominatorTree::Node *DTNode, PropertySet KP) {
+  Value *Condition = SI->getCondition();
+
+  // If there's an NEProperty covering this SwitchInst, we may be able to
+  // eliminate one of the cases.
+  PropertySet::SynSet S;
+
+  if (KP.findSynSet(Condition, S)) {
+    for (PropertySet::ConstPropertyIterator I = KP.Properties.begin(),
+         E = KP.Properties.end(); I != E; ++I) {
+      if (I->Opcode != PropertySet::NE) continue;
+      if (I->S1 != S && I->S2 != S) continue;
+
+      // Is one side a number?
+      ConstantInt *CI = dyn_cast<ConstantInt>(KP.lookup(I->S1));
+      if (!CI)     CI = dyn_cast<ConstantInt>(KP.lookup(I->S2));
+
+      if (CI) {
+        unsigned i = SI->findCaseValue(CI);
+        if (i != 0) {
+          SI->getSuccessor(i)->removePredecessor(SI->getParent());
+          SI->removeCase(i);
+          modified = true;
+          ++NumSwitchCases;
+        }
+      }
+    }
+  }
+
+  // Set the EQProperty in each of the cases BBs,
+  // and the NEProperties in the default BB.
+  PropertySet DefaultProperties(KP);
+
+  DominatorTree::Node *Node        = DT->getNode(SI->getParent()),
+                      *DefaultNode = DT->getNode(SI->getSuccessor(0));
+  if (!Node->dominates(DefaultNode)) DefaultNode = NULL;
+
+  for (unsigned I = 1, E = SI->getNumCases(); I < E; ++I) {
+    ConstantInt *CI = SI->getCaseValue(I);
+
+    BasicBlock *SuccBB = SI->getSuccessor(I);
+    PropertySet copy(KP);
+    if (SuccBB->getSinglePredecessor()) {
+      PropertySet NewProperties(KP);
+      NewProperties.addEqual(Condition, CI);
+      proceedToSuccessor(copy, NewProperties, DTNode, DT->getNode(SuccBB));
+    } else
+      proceedToSuccessor(copy, DTNode, DT->getNode(SuccBB));
+
+    if (DefaultNode)
+      DefaultProperties.addNotEqual(Condition, CI);
+  }
+
+  if (DefaultNode)
+    proceedToSuccessor(DefaultProperties, DTNode, DefaultNode);
+}
+
+void PredicateSimplifier::visit(LoadInst *LI,
+                                DominatorTree::Node *, PropertySet &KP) {
+  Value *Ptr = LI->getPointerOperand();
+  KP.addNotEqual(Constant::getNullValue(Ptr->getType()), Ptr);
+}
+
+void PredicateSimplifier::visit(StoreInst *SI,
+                                DominatorTree::Node *, PropertySet &KP) {
+  Value *Ptr = SI->getPointerOperand();
+  KP.addNotEqual(Constant::getNullValue(Ptr->getType()), Ptr);
+}
+
+void PredicateSimplifier::visit(BinaryOperator *BO,
+                                DominatorTree::Node *, PropertySet &KP) {
+  Instruction::BinaryOps ops = BO->getOpcode();
+  if (ops != Instruction::Div && ops != Instruction::Rem) return;
+
+  Value *Divisor = BO->getOperand(1);
+  const Type *Ty = cast<Type>(Divisor->getType());
+  KP.addNotEqual(Constant::getNullValue(Ty), Divisor);
+
+  // Some other things we could do:
+  // In f=x*y, if x != 1 && y != 1 then f != x && f != y.
+  // In f=x+y, if x != 0 then f != y and if y != 0 then f != x.
+}
diff --git a/test/Transforms/PredicateSimplifier/predsimplify.ll b/test/Transforms/PredicateSimplifier/predsimplify.ll
new file mode 100644
index 0000000000..056d8c97dc
--- /dev/null
+++ b/test/Transforms/PredicateSimplifier/predsimplify.ll
@@ -0,0 +1,130 @@
+; RUN: llvm-as < %s | opt -predsimplify -instcombine -simplifycfg | llvm-dis | grep -v declare | not grep fail
+
+void %test1(int %x) {
+entry:
+  %A = seteq int %x, 0
+  br bool %A, label %then.1, label %else.1
+then.1:
+  %B = seteq int %x, 1
+  br bool %B, label %then.2, label %else.1
+then.2:
+  call void (...)* %fail( )
+  ret void
+else.1:
+  ret void
+}
+
+void %test2(int %x) {
+entry:
+  %A = seteq int %x, 0
+  %B = seteq int %x, 1
+  br bool %A, label %then.1, label %else.1
+then.1:
+  br bool %B, label %then.2, label %else.1
+then.2:
+  call void (...)* %fail( )
+  ret void
+else.1:
+  ret void
+}
+
+void %test3(int %x) {
+entry:
+  %A = seteq int %x, 0
+  %B = seteq int %x, 1
+  br bool %A, label %then.1, label %else.1
+then.1:
+  br bool %B, label %then.2, label %else.1
+then.2:
+  call void (...)* %fail( )
+  ret void
+else.1:
+  ret void
+}
+
+void %test4(int %x, int %y) {
+entry:
+  %A = seteq int %x, 0
+  %B = seteq int %y, 0
+  %C = and bool %A, %B
+  br bool %C, label %then.1, label %else.1
+then.1:
+  %D = seteq int %x, 0
+  br bool %D, label %then.2, label %else.2
+then.2:
+  %E = seteq int %y, 0
+  br bool %E, label %else.1, label %else.2
+else.1:
+  ret void
+else.2:
+  call void (...)* %fail( )
+  ret void
+}
+
+void %test5(int %x) {
+entry:
+  %A = seteq int %x, 0
+  br bool %A, label %then.1, label %else.1
+then.1:
+  ret void
+then.2:
+  call void (...)* %fail( )
+  ret void
+else.1:
+  %B = seteq int %x, 0
+  br bool %B, label %then.2, label %then.1
+}
+
+void %test6(int %x, int %y) {
+entry:
+  %A = seteq int %x, 0
+  %B = seteq int %y, 0
+  %C = or bool %A, %B
+  br bool %C, label %then.1, label %else.1
+then.1:
+  ret void
+then.2:
+  call void (...)* %fail( )
+  ret void
+else.1:
+  %D = seteq int %x, 0
+  br bool %D, label %then.2, label %else.2
+else.2:
+  %E = setne int %y, 0
+  br bool %E, label %then.1, label %then.2
+}
+
+void %test7(int %x) {
+entry:
+  %A = setne int %x, 0
+  %B = xor bool %A, true
+  br bool %B, label %then.1, label %else.1
+then.1:
+  %C = seteq int %x, 1
+  br bool %C, label %then.2, label %else.1
+then.2:
+  call void (...)* %fail( )
+  ret void
+else.1:
+  ret void
+}
+
+void %test8(int %x) {
+entry:
+  %A = add int %x, 1
+  %B = seteq int %x, 0
+  br bool %B, label %then.1, label %then.2
+then.1:
+  %C = seteq int %A, 1
+  br bool %C, label %then.2, label %else.2
+then.2:
+  ret void
+else.2:
+  call void (...)* %fail( )
+  ret void
+}
+
+
+declare void %fail(...)
+
+declare void %pass(...)
diff --git a/test/Transforms/PredicateSimplifier/predsimplify.reg1.ll b/test/Transforms/PredicateSimplifier/predsimplify.reg1.ll
new file mode 100644
index 0000000000..a7fd4cabed
--- /dev/null
+++ b/test/Transforms/PredicateSimplifier/predsimplify.reg1.ll
@@ -0,0 +1,23 @@
+; RUN: llvm-as < %s | opt -predsimplify -verify
+
+void %dgefa() {
+entry:
+        br label %cond_true96
+
+cond_true:              ; preds = %cond_true96
+        %tmp19 = seteq int %tmp10, %k.0         ; <bool> [#uses=1]
+        br bool %tmp19, label %cond_next, label %cond_true20
+
+cond_true20:            ; preds = %cond_true
+        br label %cond_next
+
+cond_next:              ; preds = %cond_true20, %cond_true
+        %tmp84 = setgt int %tmp3, 1999          ; <bool> [#uses=0]
+        ret void
+
+cond_true96:            ; preds = %cond_true96, %entry
+        %k.0 = phi int [ 0, %entry ], [ 0, %cond_true96 ]               ; <int> [#uses=3]
+        %tmp3 = add int %k.0, 1         ; <int> [#uses=1]
+        %tmp10 = add int 0, %k.0                ; <int> [#uses=1]
+        br bool false, label %cond_true96, label %cond_true
+}
diff --git a/test/Transforms/PredicateSimplifier/predsimplify.reg2.ll b/test/Transforms/PredicateSimplifier/predsimplify.reg2.ll
new file mode 100644
index 0000000000..a5e77aa9e4
--- /dev/null
+++ b/test/Transforms/PredicateSimplifier/predsimplify.reg2.ll
@@ -0,0 +1,49 @@
+; RUN: llvm-as < %s | opt -predsimplify -verify
+
+; ModuleID = 'bugpoint-reduced-simplified.bc'
+target endian = little
+target pointersize = 32
+target triple = "i686-pc-linux-gnu"
+deplibs = [ "c", "crtend" ]
+	%struct.anon = type { %struct.set_family*, %struct.set_family*, %struct.set_family*, sbyte*, int, uint*, %struct.pair_struct*, sbyte**, %struct.symbolic_t*, %struct.symbolic_t* }
+	%struct.pair_struct = type { int, int*, int* }
+	%struct.set_family = type { int, int, int, int, int, uint*, %struct.set_family* }
+	%struct.symbolic_label_t = type { sbyte*, %struct.symbolic_label_t* }
+	%struct.symbolic_list_t = type { int, int, %struct.symbolic_list_t* }
+	%struct.symbolic_t = type { %struct.symbolic_list_t*, int, %struct.symbolic_label_t*, int, %struct.symbolic_t* }
+
+implementation   ; Functions:
+
+void %find_pairing_cost(int %strategy) {
+entry:
+	br bool false, label %cond_true299, label %bb314
+
+bb94:		; preds = %cond_true299
+	switch int %strategy, label %bb246 [
+		 int 0, label %bb196
+		 int 1, label %bb159
+	]
+
+cond_next113:		; preds = %cond_true299
+	switch int %strategy, label %bb246 [
+		 int 0, label %bb196
+		 int 1, label %bb159
+	]
+
+bb159:		; preds = %cond_next113, %bb94
+	ret void
+
+bb196:		; preds = %cond_next113, %bb94
+	%Rsave.0.3 = phi %struct.set_family* [ null, %bb94 ], [ null, %cond_next113 ]		; <%struct.set_family*> [#uses=0]
+	ret void
+
+bb246:		; preds = %cond_next113, %bb94
+	br label %bb314
+
+cond_true299:		; preds = %entry
+	%tmp55 = setgt int %strategy, 0		; <bool> [#uses=1]
+	br bool %tmp55, label %bb94, label %cond_next113
+
+bb314:		; preds = %bb246, %entry
+	ret void
+}
diff --git a/test/Transforms/PredicateSimplifier/predsimplify.reg3.ll b/test/Transforms/PredicateSimplifier/predsimplify.reg3.ll
new file mode 100644
index 0000000000..facf336fa1
--- /dev/null
+++ b/test/Transforms/PredicateSimplifier/predsimplify.reg3.ll
@@ -0,0 +1,21 @@
+; RUN: llvm-as < %s | opt -predsimplify -simplifycfg | llvm-dis | grep pass
+
+void %regtest(int %x) {
+entry:
+  %A = seteq int %x, 0
+  br bool %A, label %middle, label %after
+middle:
+  br label %after
+after:
+  %B = seteq int %x, 0
+  br bool %B, label %then, label %else
+then:
+  br label %end
+else:
+  call void (...)* %pass( )
+  br label %end
+end:
+  ret void
+}
+
+declare void %pass(...)