Index: lib/Transforms/Scalar/DeadStoreElimination.cpp
===================================================================
--- lib/Transforms/Scalar/DeadStoreElimination.cpp
+++ lib/Transforms/Scalar/DeadStoreElimination.cpp
@@ -768,6 +768,38 @@
       if (DeadStackObjects.empty())
         break;
 
+      // Check a corner case: when a tail call has a byval parameter,
+      // getModRefInfo report no mod ref for the call site. The reason
+      // is that a tail call cannot reference callers local memory nor
+      // can the caller own the byval of a tail call (which the caller
+      // by definiton of byval is supposed to do. But since the tail does not
+      // return getModRefInfo does not check that byval condition for tail
+      // calls).
+      // But DSE cannot remove a store to local memory when a byval argument of
+      // a tail call needs it.
+      if (const CallInst *CI = dyn_cast<CallInst>(CS.getInstruction()))
+        if (CI->isTailCall()) {
+          bool PassedAsArg = false;
+          unsigned OperandNo = 0;
+          for (auto Arg = CS.data_operands_begin(), CE = CS.data_operands_end();
+               Arg != CE; ++Arg, ++OperandNo) {
+            if ((*Arg)->getType()->isPointerTy() &&
+                CS.isByValArgument(OperandNo))
+              if (std::find_if(DeadStackObjects.begin(), DeadStackObjects.end(),
+                               [&](Value *I) {
+                    // Does the call site touch the value?
+                    AliasResult AR = AA->alias(
+                        MemoryLocation(*Arg),
+                        MemoryLocation(I, getPointerSize(I, DL, *TLI)));
+                    return AR != NoAlias;
+                    ;
+                  }))
+                PassedAsArg = true;
+          }
+          if (PassedAsArg)
+            break;
+        }
+
       continue;
     }
 
Index: test/Transforms/DeadStoreElimination/tail-call-with-byval-param.ll
===================================================================
--- /dev/null
+++ test/Transforms/DeadStoreElimination/tail-call-with-byval-param.ll
@@ -0,0 +1,35 @@
+; RUN: opt < %s -basicaa -dse -S | FileCheck %s
+target datalayout = "e-m:o-p:32:32-f64:32:64-f80:128-n8:16:32-S128"
+target triple = "i386-apple-macosx10.11.0"
+
+%class.IReproHeapDumb = type { i8 }
+%class.CReproHeapDumbObject = type { i32 (...)**, %class.IReproHeapDumb* }
+%class.IStreamDumb = type { i32 (...)** }
+%class.CByteStreamWrapperBase = type { %class.CReproHeapDumbObject, i64, i32, [4 x i8] }
+%class.CByteStreamToIStream = type { %class.CByteStreamWrapperBase.base, %class.IStreamDumb }
+%class.CByteStreamWrapperBase.base = type { %class.CReproHeapDumbObject, i64, i32 }
+%union._LARGE_INTEGER2 = type { %struct.anon }
+%struct.anon = type { i32, i32 }
+
+declare void @llvm.dbg.declare(metadata, metadata, metadata)
+declare void @llvm.dbg.value(metadata, i64)
+declare i32 @_ZN20CByteStreamToIStream4SeekE15_LARGE_INTEGER2jPS0_(%class.CByteStreamToIStream* %this, %union._LARGE_INTEGER2* align 4, i32 %dwOrigin, %union._LARGE_INTEGER2* %plibNewPosition)
+
+define i32
+@_ZThn20_N20CByteStreamToIStream4SeekE15_LARGE_INTEGER2jPS0_(%class.CByteStreamToIStream* %this, %union._LARGE_INTEGER2* byval align 4, i32 %dwOrigin, %union._LARGE_INTEGER2* %plibNewPosition)  {
+entry:
+  %dlibMove = alloca %union._LARGE_INTEGER2, align 8
+  %v1 = bitcast %union._LARGE_INTEGER2* %0 to i64*
+  %v2 = bitcast %union._LARGE_INTEGER2* %dlibMove to i64*
+  %v3 = load i64, i64* %v1, align 4
+; CHECK: store i64 %v3, i64* %v2
+  store i64 %v3, i64* %v2, align 8
+  call void @llvm.dbg.value(metadata %class.CByteStreamToIStream* %this, i64 0)
+  call void @llvm.dbg.value(metadata i32 %dwOrigin, i64 0)
+  call void @llvm.dbg.value(metadata %union._LARGE_INTEGER2* %plibNewPosition, i64 0)
+  %v4 = getelementptr inbounds %class.CByteStreamToIStream, %class.CByteStreamToIStream* %this, i32 -1, i32 0, i32 0, i32 1
+  %v5 = bitcast %class.IReproHeapDumb** %v4 to %class.CByteStreamToIStream*
+  call void @llvm.dbg.value(metadata %union._LARGE_INTEGER2* %dlibMove, i64 0)
+  %call = tail call i32 @_ZN20CByteStreamToIStream4SeekE15_LARGE_INTEGER2jPS0_(%class.CByteStreamToIStream* %v5, %union._LARGE_INTEGER2* nonnull byval  align 4 %dlibMove, i32 %dwOrigin, %union._LARGE_INTEGER2* %plibNewPosition) 
+  ret i32 %call
+}