Index: llvm/trunk/lib/Transforms/Scalar/EarlyCSE.cpp
===================================================================
--- llvm/trunk/lib/Transforms/Scalar/EarlyCSE.cpp
+++ llvm/trunk/lib/Transforms/Scalar/EarlyCSE.cpp
@@ -562,13 +562,27 @@
   if (!MSSA)
     return false;
 
+  // If MemorySSA has determined that one of EarlierInst or LaterInst does not
+  // read/write memory, then we can safely return true here.
+  // FIXME: We could be more aggressive when checking doesNotAccessMemory(),
+  // onlyReadsMemory(), mayReadFromMemory(), and mayWriteToMemory() in this pass
+  // by also checking the MemorySSA MemoryAccess on the instruction.  Initial
+  // experiments suggest this isn't worthwhile, at least for C/C++ code compiled
+  // with the default optimization pipeline.
+  auto *EarlierMA = MSSA->getMemoryAccess(EarlierInst);
+  if (!EarlierMA)
+    return true;
+  auto *LaterMA = MSSA->getMemoryAccess(LaterInst);
+  if (!LaterMA)
+    return true;
+
   // Since we know LaterDef dominates LaterInst and EarlierInst dominates
   // LaterInst, if LaterDef dominates EarlierInst then it can't occur between
   // EarlierInst and LaterInst and neither can any other write that potentially
   // clobbers LaterInst.
   MemoryAccess *LaterDef =
       MSSA->getWalker()->getClobberingMemoryAccess(LaterInst);
-  return MSSA->dominates(LaterDef, MSSA->getMemoryAccess(EarlierInst));
+  return MSSA->dominates(LaterDef, EarlierMA);
 }
 
 bool EarlyCSE::processNode(DomTreeNode *Node) {
Index: llvm/trunk/test/Transforms/EarlyCSE/globalsaa-memoryssa.ll
===================================================================
--- llvm/trunk/test/Transforms/EarlyCSE/globalsaa-memoryssa.ll
+++ llvm/trunk/test/Transforms/EarlyCSE/globalsaa-memoryssa.ll
@@ -0,0 +1,25 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -S -globals-aa -early-cse-memssa | FileCheck %s
+
+define i16 @f1() readonly {
+  ret i16 0
+}
+
+declare void @f2()
+
+; Check that EarlyCSE correctly handles function calls that don't have
+; a MemoryAccess.  In this case the calls to @f1 have no
+; MemoryAccesses since globals-aa determines that @f1 doesn't
+; read/write memory at all.
+
+define void @f3() {
+; CHECK-LABEL: @f3(
+; CHECK-NEXT:    [[CALL1:%.*]] = call i16 @f1()
+; CHECK-NEXT:    call void @f2()
+; CHECK-NEXT:    ret void
+;
+  %call1 = call i16 @f1()
+  call void @f2()
+  %call2 = call i16 @f1()
+  ret void
+}