diff --git a/llvm/lib/Transforms/Scalar/EarlyCSE.cpp b/llvm/lib/Transforms/Scalar/EarlyCSE.cpp
--- a/llvm/lib/Transforms/Scalar/EarlyCSE.cpp
+++ b/llvm/lib/Transforms/Scalar/EarlyCSE.cpp
@@ -460,7 +460,8 @@
       return false;
 
     CallInst *CI = dyn_cast<CallInst>(Inst);
-    if (!CI || !CI->onlyReadsMemory())
+    // Handle readnone, readonly and writeonly.
+    if (!CI || !(CI->doesNotReadMemory() || CI->onlyReadsMemory()))
       return false;
     return true;
   }
@@ -1455,13 +1456,22 @@
         !(MemInst.isValid() && !MemInst.mayReadFromMemory()))
       LastStore = nullptr;
 
-    // If this is a read-only call, process it.
+    // If this is a read-only or write-ony call, process it.
     if (CallValue::canHandle(&Inst)) {
+      // Write-only calls can be CSE'd. Increment the generation to prevent
+      // replacement if there are intervening stores.
+      auto PreStoreGeneration = CurrentGeneration;
+      if (Inst.mayWriteToMemory()) {
+        assert(!Inst.mayReadFromMemory());
+        ++CurrentGeneration;
+        LastStore = nullptr;
+      }
+
       // If we have an available version of this call, and if it is the right
       // generation, replace this instruction.
       std::pair<Instruction *, unsigned> InVal = AvailableCalls.lookup(&Inst);
       if (InVal.first != nullptr &&
-          isSameMemGeneration(InVal.second, CurrentGeneration, InVal.first,
+          isSameMemGeneration(InVal.second, PreStoreGeneration, InVal.first,
                               &Inst)) {
         LLVM_DEBUG(dbgs() << "EarlyCSE CSE CALL: " << Inst
                           << "  to: " << *InVal.first << '\n');
@@ -1480,7 +1490,7 @@
       }
 
       // Otherwise, remember that we have this instruction.
-      AvailableCalls.insert(&Inst, std::make_pair(&Inst, CurrentGeneration));
+      AvailableCalls.insert(&Inst, std::make_pair(&Inst, PreStoreGeneration));
       continue;
     }
 
diff --git a/llvm/test/Transforms/EarlyCSE/memoryssa.ll b/llvm/test/Transforms/EarlyCSE/memoryssa.ll
--- a/llvm/test/Transforms/EarlyCSE/memoryssa.ll
+++ b/llvm/test/Transforms/EarlyCSE/memoryssa.ll
@@ -148,3 +148,33 @@
 
 declare void @llvm.lifetime.end.p0i8(i64, i32*)
 declare void @llvm.lifetime.start.p0i8(i64, i32*)
+
+;; Check that writeonly call gets CSE'd when using MSSA
+declare i32 @write_only() writeonly
+
+; CHECK-LABEL: @test_write_only
+; CHECK-NOMEMSSA-LABEL: @test_write_only
+define void @test_write_only(i1 %c, i32* %p) {
+; CHECK: call i32 @write_only()
+; CHECK-NOMEMSSA: call i32 @write_only()
+  %call = call i32 @write_only()
+; CHECK: %v1 = load i32, i32* @G1
+; CHECK-NOMEMSSA: %v1 = load i32, i32* @G1
+  %v1 = load i32, i32* @G1
+; CHECK-NOT: call i32 @write_only()
+; CHECK-NOMEMSSA: call i32 @write_only()
+  %call2 =  call i32 @write_only()
+; CHECK: store
+; CHECK-NOMEMSSA: store
+  store i32 %v1, i32* @G2
+; CHECK: call i32 @write_only()
+; CHECK-NOMEMSSA: call i32 @write_only()
+  %call3 = call i32 @write_only()
+; CHECK: store
+; CHECK-NOMEMSSA: store
+  store i32 %v1, i32* @G2
+; CHECK: call i32 @write_only()
+; CHECK-NOMEMSSA: call i32 @write_only()
+  %call4 = call i32 @write_only()
+  ret void
+}