diff --git a/include/llvm/Analysis/PHITransAddr.h b/include/llvm/Analysis/PHITransAddr.h
index 8257396a09f..d090dc38f1d 100644
--- a/include/llvm/Analysis/PHITransAddr.h
+++ b/include/llvm/Analysis/PHITransAddr.h
@@ -80,6 +80,13 @@ public:
   Value *PHITranslateWithInsertion(BasicBlock *CurBB, BasicBlock *PredBB,
                                    const DominatorTree &DT,
                                    SmallVectorImpl<Instruction*> &NewInsts);
+  
+  void dump() const;
+  
+  /// Verify - Check internal consistency of this data structure.  Though it
+  /// claims to return a bool, it actually aborts on error and always returns
+  /// true.
+  bool Verify() const;
 private:
   Value *PHITranslateSubExpr(Value *V, BasicBlock *CurBB, BasicBlock *PredBB);
   
@@ -103,6 +110,7 @@ private:
   /// array that are due to the specified instruction that is about to be
   /// removed from the address, and add any corresponding to V.  This returns V.
   Value *ReplaceInstWithValue(Instruction *I, Value *V);
+  
 };
 
 } // end namespace llvm
diff --git a/lib/Analysis/PHITransAddr.cpp b/lib/Analysis/PHITransAddr.cpp
index edb41f7f4cc..187924f45a8 100644
--- a/lib/Analysis/PHITransAddr.cpp
+++ b/lib/Analysis/PHITransAddr.cpp
@@ -14,6 +14,7 @@
 #include "llvm/Analysis/PHITransAddr.h"
 #include "llvm/Analysis/Dominators.h"
 #include "llvm/Analysis/InstructionSimplify.h"
+#include "llvm/Support/raw_ostream.h"
 using namespace llvm;
 
 static bool CanPHITrans(Instruction *Inst) {
@@ -32,6 +33,72 @@ static bool CanPHITrans(Instruction *Inst) {
   return false;
 }
 
+void PHITransAddr::dump() const {
+  if (Addr == 0) {
+    errs() << "PHITransAddr: null\n";
+    return;
+  }
+  errs() << "PHITransAddr: " << *Addr << "\n";
+  for (unsigned i = 0, e = InstInputs.size(); i != e; ++i)
+    errs() << "  Input #" << i << " is " << *InstInputs[i] << "\n";
+}
+
+
+static bool VerifySubExpr(Value *Expr,
+                          SmallVectorImpl<Instruction*> &InstInputs) {
+  // If this is a non-instruction value, there is nothing to do.
+  Instruction *I = dyn_cast<Instruction>(Expr);
+  if (I == 0) return true;
+  
+  // If it's an instruction, it is either in Tmp or its operands recursively
+  // are.
+  SmallVectorImpl<Instruction*>::iterator Entry =
+    std::find(InstInputs.begin(), InstInputs.end(), I);
+  if (Entry != InstInputs.end()) {
+    InstInputs.erase(Entry);
+    return true;
+  }
+  
+  // If it isn't in the InstInputs list it is a subexpr incorporated into the
+  // address.  Sanity check that it is phi translatable.
+  if (!CanPHITrans(I)) {
+    errs() << "Non phi translatable instruction found in PHITransAddr, either "
+              "something is missing from InstInputs or CanPHITrans is wrong:\n";
+    errs() << *I << '\n';
+    return false;
+  }
+  
+  // Validate the operands of the instruction.
+  for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
+    if (!VerifySubExpr(I->getOperand(i), InstInputs))
+      return false;
+
+  return true;
+}
+
+/// Verify - Check internal consistency of this data structure.  If the
+/// structure is valid, it returns true.  If invalid, it prints errors and
+/// returns false.
+bool PHITransAddr::Verify() const {
+  if (Addr == 0) return true;
+  
+  SmallVector<Instruction*, 8> Tmp(InstInputs.begin(), InstInputs.end());  
+  
+  if (!VerifySubExpr(Addr, Tmp))
+    return false;
+  
+  if (!Tmp.empty()) {
+    errs() << "PHITransAddr inconsistent, contains extra instructions:\n";
+    for (unsigned i = 0, e = InstInputs.size(); i != e; ++i)
+      errs() << "  InstInput #" << i << " is " << *InstInputs[i] << "\n";
+    return false;
+  }
+  
+  // a-ok.
+  return true;
+}
+
+
 /// IsPotentiallyPHITranslatable - If this needs PHI translation, return true
 /// if we have some hope of doing it.  This should be used as a filter to
 /// avoid calling PHITranslateValue in hopeless situations.
@@ -236,7 +303,9 @@ Value *PHITransAddr::PHITranslateSubExpr(Value *V, BasicBlock *CurBB,
 /// CurBB to Pred, updating our state the reflect any needed changes.  This
 /// returns true on failure and sets Addr to null.
 bool PHITransAddr::PHITranslateValue(BasicBlock *CurBB, BasicBlock *PredBB) {
+  assert(Verify() && "Invalid PHITransAddr!");
   Addr = PHITranslateSubExpr(Addr, CurBB, PredBB);
+  assert(Verify() && "Invalid PHITransAddr!");
   return Addr == 0;
 }