Index: include/llvm/CodeGen/GCStrategy.h
===================================================================
--- include/llvm/CodeGen/GCStrategy.h
+++ include/llvm/CodeGen/GCStrategy.h
@@ -70,6 +70,8 @@
     unsigned NeededSafePoints; ///< Bitmask of required safe points.
     bool CustomReadBarriers;   ///< Default is to insert loads.
     bool CustomWriteBarriers;  ///< Default is to insert stores.
+    bool CustomUndefRelocation;///< Default is to insert undef.
+    bool CustomNullRelocation; ///< Default is to insert null.
     bool CustomRoots;          ///< Default is to pass through to backend.
     bool CustomSafePoints;     ///< Default is to use NeededSafePoints
                                ///< to find safe points.
@@ -94,6 +96,14 @@
     /// them. 
     bool customReadBarrier() const { return CustomReadBarriers; }
 
+    /// By default, undef values are undef after relocation. If true, then
+    /// performCustomLowering must instead lower them.
+    bool customUndefRelocation() const { return CustomUndefRelocation; }
+
+    /// By default, null values are null after relocation. If true, then
+    /// performCustomLowering must instead lower them.
+    bool customNullRelocation() const { return CustomNullRelocation; }
+
     /** @name GCRoot Specific Properties
      * These properties and overrides only apply to collector strategies using
      * GCRoot. 
Index: lib/CodeGen/GCStrategy.cpp
===================================================================
--- lib/CodeGen/GCStrategy.cpp
+++ lib/CodeGen/GCStrategy.cpp
@@ -24,6 +24,7 @@
 #include "llvm/IR/Dominators.h"
 #include "llvm/IR/IntrinsicInst.h"
 #include "llvm/IR/Module.h"
+#include "llvm/IR/Statepoint.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/raw_ostream.h"
@@ -255,6 +256,8 @@
 bool LowerIntrinsics::PerformDefaultLowering(Function &F, GCStrategy &S) {
   bool LowerWr = !S.customWriteBarrier();
   bool LowerRd = !S.customReadBarrier();
+  bool LowerUndef = !S.customUndefRelocation();
+  bool LowerNull = !S.customNullRelocation();
   bool InitRoots = S.initializeRoots();
 
   SmallVector<AllocaInst*, 32> Roots;
@@ -290,6 +293,26 @@
             Roots.push_back(cast<AllocaInst>(
                               CI->getArgOperand(0)->stripPointerCasts()));
           }
+	  break;
+        case Intrinsic::experimental_gc_relocate:
+          if (LowerUndef) {
+            // Replace a relocation of an undef value with undef.
+	    GCRelocateOperands Operands(II);
+	    Value *DerivedPtr = Operands.derivedPtr();
+
+	    if (isa<UndefValue>(DerivedPtr))
+	      CI->replaceAllUsesWith(DerivedPtr);
+            CI->eraseFromParent();
+          }
+          if (LowerNull) {
+            // Replace a relocation of a null value with null.
+	    GCRelocateOperands Operands(II);
+	    Value *DerivedPtr = Operands.derivedPtr();
+
+	    if (isa<ConstantPointerNull>(DerivedPtr))
+	      CI->replaceAllUsesWith(DerivedPtr);
+            CI->eraseFromParent();
+          }
           break;
         default:
           continue;
Index: lib/Transforms/InstCombine/InstCombineCalls.cpp
===================================================================
--- lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -1132,19 +1132,6 @@
     if (II->use_empty())
       return EraseInstFromFunction(*II);
 
-    // Undef is undef, even after relocation.
-    // TODO: provide a hook for this in GCStrategy.  This is clearly legal for
-    // most practical collectors, but there was discussion in the review thread
-    // about whether it was legal for all possible collectors.
-    if (isa<UndefValue>(DerivedPtr))
-      return ReplaceInstUsesWith(*II, DerivedPtr);
-
-    // The relocation of null will be null for most any collector.
-    // TODO: provide a hook for this in GCStrategy.  There might be some weird
-    // collector this property does not hold for.
-    if (isa<ConstantPointerNull>(DerivedPtr))
-      return ReplaceInstUsesWith(*II, DerivedPtr);
-
     // isKnownNonNull -> nonnull attribute
     if (isKnownNonNull(DerivedPtr))
       II->addAttribute(AttributeSet::ReturnIndex, Attribute::NonNull);