Index: lib/CodeGen/CGCall.cpp
===================================================================
--- lib/CodeGen/CGCall.cpp	(revision 176249)
+++ lib/CodeGen/CGCall.cpp	(working copy)
@@ -2072,17 +2072,23 @@
         checkArgMatches(AI, IRArgNo, IRFuncTy);
       } else {
         // We want to avoid creating an unnecessary temporary+copy here;
-        // however, we need one in two cases:
+        // however, we need one in three cases:
         // 1. If the argument is not byval, and we are required to copy the
         //    source.  (This case doesn't occur on any common architecture.)
         // 2. If the argument is byval, RV is not sufficiently aligned, and
         //    we cannot force it to be sufficiently aligned.
+        // 3. If the argument is byval, but RV is located in an address space
+        //    different than that of the argument (0).
         llvm::Value *Addr = RV.getAggregateAddr();
         unsigned Align = ArgInfo.getIndirectAlign();
         const llvm::DataLayout *TD = &CGM.getDataLayout();
+        const unsigned RVAddrSpace = Addr->getType()->getPointerAddressSpace();
+        const unsigned ArgAddrSpace = (IRArgNo < IRFuncTy->getNumParams() ?
+          IRFuncTy->getParamType(IRArgNo)->getPointerAddressSpace() : 0);
         if ((!ArgInfo.getIndirectByVal() && I->NeedsCopy) ||
             (ArgInfo.getIndirectByVal() && TypeAlign < Align &&
-             llvm::getOrEnforceKnownAlignment(Addr, Align, TD) < Align)) {
+             llvm::getOrEnforceKnownAlignment(Addr, Align, TD) < Align) ||
+             (ArgInfo.getIndirectByVal() && (RVAddrSpace != ArgAddrSpace))) {
           // Create an aligned temporary, and copy to it.
           llvm::AllocaInst *AI = CreateMemTemp(I->Ty);
           if (Align > AI->getAlignment())
Index: test/CodeGenOpenCL/addr-space-struct-arg.cl
===================================================================
--- test/CodeGenOpenCL/addr-space-struct-arg.cl	(revision 0)
+++ test/CodeGenOpenCL/addr-space-struct-arg.cl	(revision 0)
@@ -0,0 +1,23 @@
+// RUN: %clang_cc1 %s -emit-llvm -o - -O0 -ffake-address-space-map -triple i686-pc-darwin | FileCheck %s
+
+typedef struct {
+  int cells[9];
+} Mat3X3;
+
+typedef struct {
+  int cells[16];
+} Mat4X4;
+
+Mat4X4 __attribute__((noinline)) foo(Mat3X3 in) {
+  Mat4X4 out;
+  return out;
+}
+
+kernel void ker(global Mat3X3 *in, global Mat4X4 *out) {
+  out[0] = foo(in[1]);
+}
+
+// Expect two mem copies: one for the argument "in", and one for
+// the return value.
+// CHECK: call void @llvm.memcpy.p0i8.p1i8.i32(i8*
+// CHECK: call void @llvm.memcpy.p1i8.p0i8.i32(i8 addrspace(1)*