Index: lib/Transforms/Scalar/EarlyCSE.cpp
===================================================================
--- lib/Transforms/Scalar/EarlyCSE.cpp
+++ lib/Transforms/Scalar/EarlyCSE.cpp
@@ -271,8 +271,11 @@
       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;
   }
 };
@@ -996,7 +999,7 @@
         !(MemInst.isValid() && !MemInst.mayReadFromMemory()))
       LastStore = nullptr;
 
-    // If this is a read-only call, process it.
+    // If this is a read-only or writeonly call, process it.
     if (CallValue::canHandle(Inst)) {
       // If we have an available version of this call, and if it is the right
       // generation, replace this instruction.
@@ -1010,6 +1013,13 @@
           LLVM_DEBUG(dbgs() << "Skipping due to debug counter\n");
           continue;
         }
+      // When handling writeonly function calls we need to update lastStore
+      // and currentGen.
+        if (dyn_cast<CallInst>(Inst)->doesNotReadMemory() &&
+            !dyn_cast<CallInst>(Inst)->doesNotAccessMemory()) {
+          ++CurrentGeneration;
+          LastStore = nullptr;
+        }
         if (!Inst->use_empty())
           Inst->replaceAllUsesWith(InVal.first);
         removeMSSA(Inst);
@@ -1018,10 +1028,18 @@
         ++NumCSECall;
         continue;
       }
-
       // Otherwise, remember that we have this instruction.
       AvailableCalls.insert(
           Inst, std::pair<Instruction *, unsigned>(Inst, CurrentGeneration));
+
+      // When handling writeonly function calls we need to update lastStore
+      // and currentGen.
+      if (dyn_cast<CallInst>(Inst)->doesNotReadMemory() &&
+          !dyn_cast<CallInst>(Inst)->doesNotAccessMemory()) {
+        ++CurrentGeneration;
+        LastStore = nullptr;
+      }
+
       continue;
     }