diff --git a/lib/Transforms/Utils/SimplifyCFG.cpp b/lib/Transforms/Utils/SimplifyCFG.cpp
index a63d31d5af5..a5c5c22aa5a 100644
--- a/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -3944,11 +3944,13 @@ static bool passingValueIsAlwaysUndefined(Value *V, Instruction *I) {
 
     // Load from null is undefined.
     if (LoadInst *LI = dyn_cast<LoadInst>(Use))
-      return LI->getPointerAddressSpace() == 0;
+      if (!LI->isVolatile())
+        return LI->getPointerAddressSpace() == 0;
 
     // Store to null is undefined.
     if (StoreInst *SI = dyn_cast<StoreInst>(Use))
-      return SI->getPointerAddressSpace() == 0 && SI->getPointerOperand() == I;
+      if (!SI->isVolatile())
+        return SI->getPointerAddressSpace() == 0 && SI->getPointerOperand() == I;
   }
   return false;
 }
diff --git a/test/Transforms/SimplifyCFG/volatile-phioper.ll b/test/Transforms/SimplifyCFG/volatile-phioper.ll
new file mode 100644
index 00000000000..164898897ef
--- /dev/null
+++ b/test/Transforms/SimplifyCFG/volatile-phioper.ll
@@ -0,0 +1,48 @@
+; RUN: opt < %s -simplifycfg -S | FileCheck %s
+;
+; rdar:13349374
+;
+; SimplifyCFG should not eliminate blocks with volatile stores.
+; Essentially, volatile needs to be backdoor that tells the optimizer
+; it can no longer use language standard as an excuse. The compiler
+; needs to expose the volatile access to the platform.
+;
+; CHECK: @test
+; CHECK: entry:
+; CHECK: @Trace
+; CHECK: while.body:
+; CHECK: store volatile
+; CHECK: end:
+target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
+
+define void @test(i8** nocapture %PeiServices) #0 {
+entry:
+  %call = tail call i32 (...)* @Trace() #2
+  %tobool = icmp eq i32 %call, 0
+  br i1 %tobool, label %while.body, label %if.then
+
+if.then:                                          ; preds = %entry
+  %call1 = tail call i32 (...)* @Trace() #2
+  br label %while.body
+
+while.body:                                       ; preds = %entry, %if.then, %while.body
+  %Addr.017 = phi i8* [ %incdec.ptr, %while.body ], [ null, %if.then ], [ null, %entry ]
+  %x.016 = phi i8 [ %inc, %while.body ], [ 0, %if.then ], [ 0, %entry ]
+  %inc = add i8 %x.016, 1
+  %incdec.ptr = getelementptr inbounds i8* %Addr.017, i64 1
+  store volatile i8 %x.016, i8* %Addr.017, align 1
+  %0 = ptrtoint i8* %incdec.ptr to i64
+  %1 = trunc i64 %0 to i32
+  %cmp = icmp ult i32 %1, 4096
+  br i1 %cmp, label %while.body, label %end
+
+end:
+  ret void
+}
+declare i32 @Trace(...) #1
+
+attributes #0 = { nounwind ssp uwtable "fp-contract-model"="standard" "no-frame-pointer-elim" "no-frame-pointer-elim-non-leaf" "realign-stack" "relocation-model"="pic" "ssp-buffers-size"="8" }
+attributes #1 = { "fp-contract-model"="standard" "no-frame-pointer-elim" "no-frame-pointer-elim-non-leaf" "realign-stack" "relocation-model"="pic" "ssp-buffers-size"="8" }
+attributes #2 = { nounwind }
+
+!0 = metadata !{i32 1039}