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diff --git a/lib/Transforms/IPO/ConstantMerge.cpp b/lib/Transforms/IPO/ConstantMerge.cpp
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+++ b/lib/Transforms/IPO/ConstantMerge.cpp
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+//===- ConstantMerge.cpp - Merge duplicate global constants ---------------===//
+//
+//                     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.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file defines the interface to a pass that merges duplicate global
+// constants together into a single constant that is shared.  This is useful
+// because some passes (ie TraceValues) insert a lot of string constants into
+// the program, regardless of whether or not an existing string is available.
+//
+// Algorithm: ConstantMerge is designed to build up a map of available constants
+// and eliminate duplicates when it is initialized.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/IPO.h"
+#include "llvm/Module.h"
+#include "llvm/Pass.h"
+#include "llvm/ADT/Statistic.h"
+using namespace llvm;
+
+namespace {
+  Statistic<> NumMerged("constmerge", "Number of global constants merged");
+
+  struct ConstantMerge : public ModulePass {
+    // run - For this pass, process all of the globals in the module,
+    // eliminating duplicate constants.
+    //
+    bool runOnModule(Module &M);
+  };
+
+  RegisterOpt<ConstantMerge> X("constmerge","Merge Duplicate Global Constants");
+}
+
+ModulePass *llvm::createConstantMergePass() { return new ConstantMerge(); }
+
+bool ConstantMerge::runOnModule(Module &M) {
+  std::map<Constant*, GlobalVariable*> CMap;
+
+  // Replacements - This vector contains a list of replacements to perform.
+  std::vector<std::pair<GlobalVariable*, GlobalVariable*> > Replacements;
+
+  bool MadeChange = false;
+
+  // Iterate constant merging while we are still making progress.  Merging two
+  // constants together may allow us to merge other constants together if the
+  // second level constants have initializers which point to the globals that
+  // were just merged.
+  while (1) {
+    // First pass: identify all globals that can be merged together, filling in
+    // the Replacements vector.  We cannot do the replacement in this pass
+    // because doing so may cause initializers of other globals to be rewritten,
+    // invalidating the Constant* pointers in CMap.
+    //
+    for (Module::global_iterator GV = M.global_begin(), E = M.global_end(); GV != E; ++GV)
+      // Only process constants with initializers
+      if (GV->isConstant() && GV->hasInitializer()) {
+        Constant *Init = GV->getInitializer();
+
+        // Check to see if the initializer is already known...
+        std::map<Constant*, GlobalVariable*>::iterator I = CMap.find(Init);
+
+        if (I == CMap.end()) {    // Nope, add it to the map
+          CMap.insert(I, std::make_pair(Init, GV));
+        } else if (GV->hasInternalLinkage()) {    // Yup, this is a duplicate!
+          // Make all uses of the duplicate constant use the canonical version.
+          Replacements.push_back(std::make_pair(GV, I->second));
+        } else if (I->second->hasInternalLinkage()) {
+          // Make all uses of the duplicate constant use the canonical version.
+          Replacements.push_back(std::make_pair(I->second, GV));
+          I->second = GV;
+        }
+      }
+
+    if (Replacements.empty())
+      return MadeChange;
+    CMap.clear();
+
+    // Now that we have figured out which replacements must be made, do them all
+    // now.  This avoid invalidating the pointers in CMap, which are unneeded
+    // now.
+    for (unsigned i = 0, e = Replacements.size(); i != e; ++i) {
+      // Eliminate any uses of the dead global...
+      Replacements[i].first->replaceAllUsesWith(Replacements[i].second);
+
+      // Delete the global value from the module...
+      M.getGlobalList().erase(Replacements[i].first);
+    }
+
+    NumMerged += Replacements.size();
+    Replacements.clear();
+  }
+}