Index: include/llvm/Transforms/Utils/MemorySSA.h
===================================================================
--- include/llvm/Transforms/Utils/MemorySSA.h
+++ include/llvm/Transforms/Utils/MemorySSA.h
@@ -570,6 +570,15 @@
                                           MemoryAccess *Definition,
                                           MemoryAccess *InsertPt);
 
+  // \brief Splice \p What to just before \p Where.
+  //
+  // In order to be efficient, the following conditions must be met:
+  //   - \p Where  dominates \p What,
+  //   - All memory accesses in [\p Where, \p What) are no-alias with \p What.
+  //
+  // TODO: relax the MemoryDef requirement on Where.
+  void spliceMemoryAccessAbove(MemoryDef *Where, MemoryUseOrDef *What);
+
   /// \brief Remove a MemoryAccess from MemorySSA, including updating all
   /// definitions and uses.
   /// This should be called when a memory instruction that has a MemoryAccess
Index: lib/Transforms/Utils/MemorySSA.cpp
===================================================================
--- lib/Transforms/Utils/MemorySSA.cpp
+++ lib/Transforms/Utils/MemorySSA.cpp
@@ -1614,6 +1614,25 @@
   return NewAccess;
 }
 
+void MemorySSA::spliceMemoryAccessAbove(MemoryDef *Where,
+                                        MemoryUseOrDef *What) {
+  assert(What != getLiveOnEntryDef() &&
+         Where != getLiveOnEntryDef() && "Can't splice (above) LOE.");
+  assert(dominates(Where, What) && "Only upwards splices are permitted.");
+
+  if (Where == What)
+    return;
+  if (isa<MemoryDef>(What)) {
+    // TODO: possibly use removeMemoryAccess' more efficient RAUW
+    What->replaceAllUsesWith(What->getDefiningAccess());
+    What->setDefiningAccess(Where->getDefiningAccess());
+    Where->setDefiningAccess(What);
+  }
+  AccessList *Src = getWritableBlockAccesses(What->getBlock());
+  AccessList *Dest = getWritableBlockAccesses(Where->getBlock());
+  Dest->splice(AccessList::iterator(Where), *Src, What);
+}
+
 /// \brief Helper function to create new memory accesses
 MemoryUseOrDef *MemorySSA::createNewAccess(Instruction *I) {
   // The assume intrinsic has a control dependency which we model by claiming