diff --git a/llvm/include/llvm/LinkAllPasses.h b/llvm/include/llvm/LinkAllPasses.h
index aabebf766a36..9e82e67507b1 100644
--- a/llvm/include/llvm/LinkAllPasses.h
+++ b/llvm/include/llvm/LinkAllPasses.h
@@ -85,6 +85,7 @@ namespace {
       (void) llvm::createLowerInvokePass();
       (void) llvm::createLowerSetJmpPass();
       (void) llvm::createLowerSwitchPass();
+      (void) llvm::createMarkModRefPass();
       (void) llvm::createNoAAPass();
       (void) llvm::createNoProfileInfoPass();
       (void) llvm::createProfileLoaderPass();
diff --git a/llvm/include/llvm/Transforms/Scalar.h b/llvm/include/llvm/Transforms/Scalar.h
index 8799a6f10931..3cd4a5c49951 100644
--- a/llvm/include/llvm/Transforms/Scalar.h
+++ b/llvm/include/llvm/Transforms/Scalar.h
@@ -137,6 +137,11 @@ LoopPass *createLoopRotatePass();
 //
 LoopPass *createLoopIndexSplitPass();
 
+//===----------------------------------------------------------------------===//
+//
+// MarkModRef - This pass marks functions readnone/readonly.
+//
+FunctionPass *createMarkModRefPass();
 
 //===----------------------------------------------------------------------===//
 //
diff --git a/llvm/lib/Transforms/Scalar/MarkModRef.cpp b/llvm/lib/Transforms/Scalar/MarkModRef.cpp
new file mode 100644
index 000000000000..e20278aed3ee
--- /dev/null
+++ b/llvm/lib/Transforms/Scalar/MarkModRef.cpp
@@ -0,0 +1,69 @@
+//===--------- MarkModRef.cpp - Mark functions readnone/readonly ----------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass marks functions readnone/readonly based on the results of alias
+// analysis.  This requires a sufficiently powerful alias analysis, such as
+// GlobalsModRef (invoke as "opt ... -globalsmodref-aa -markmodref ...").
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "markmodref"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/Analysis/AliasAnalysis.h"
+#include "llvm/Support/Compiler.h"
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/Function.h"
+#include "llvm/Pass.h"
+using namespace llvm;
+
+STATISTIC(NumReadNone, "Number of functions marked readnone");
+STATISTIC(NumReadOnly, "Number of functions marked readonly");
+
+namespace {
+  struct VISIBILITY_HIDDEN MarkModRef : public FunctionPass {
+    static char ID; // Pass identification, replacement for typeid
+    MarkModRef() : FunctionPass((intptr_t)&ID) {}
+
+    bool runOnFunction(Function &F);
+
+    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+      AU.setPreservesCFG();
+      AU.addRequired<AliasAnalysis>();
+      AU.addPreserved<AliasAnalysis>();
+    }
+  };
+}
+
+char MarkModRef::ID = 0;
+static RegisterPass<MarkModRef>
+X("markmodref", "Mark functions readnone/readonly");
+
+bool MarkModRef::runOnFunction(Function &F) {
+  // FIXME: Wrong for functions with weak linkage.
+  if (F.doesNotAccessMemory())
+    // Cannot do better.
+    return false;
+
+  AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
+  AliasAnalysis::ModRefBehavior ModRef = AA.getModRefBehavior(&F);
+  if (ModRef == AliasAnalysis::DoesNotAccessMemory) {
+    F.setDoesNotAccessMemory();
+    NumReadNone++;
+    return true;
+  } else if (ModRef == AliasAnalysis::OnlyReadsMemory && !F.onlyReadsMemory()) {
+    F.setOnlyReadsMemory();
+    NumReadOnly++;
+    return true;
+  }
+  return false;
+}
+
+FunctionPass *llvm::createMarkModRefPass() {
+  return new MarkModRef();
+}