Index: lib/CodeGen/SelectionDAG/SelectionDAG.cpp
===================================================================
--- lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -4248,6 +4248,17 @@
   return DAG.getNode(ISD::TokenFactor, dl, MVT::Other, OutChains);
 }
 
+static void checkAddrSpaceIsValidForLibcall(const TargetLowering *TLI,
+                                            unsigned AS) {
+  // Lowering memcpy / memset / memmove intrinsics to calls is only valid if all
+  // pointer operands can be losslessly bitcasted to pointers of address space 0
+  if (AS != 0 && !TLI->isNoopAddrSpaceCast(AS, 0)) {
+    report_fatal_error("FIXME: lowering arbitrarily long memcpy / memset / "
+                       "memmove intrinsics for arbitrary address spaces is not "
+                       "yet implemented");
+  }
+}
+
 SDValue SelectionDAG::getMemcpy(SDValue Chain, SDLoc dl, SDValue Dst,
                                 SDValue Src, SDValue Size,
                                 unsigned Align, bool isVol, bool AlwaysInline,
@@ -4289,6 +4300,9 @@
                                    true, DstPtrInfo, SrcPtrInfo);
   }
 
+  checkAddrSpaceIsValidForLibcall(TLI, DstPtrInfo.getAddrSpace());
+  checkAddrSpaceIsValidForLibcall(TLI, SrcPtrInfo.getAddrSpace());
+
   // FIXME: If the memcpy is volatile (isVol), lowering it to a plain libc
   // memcpy is not guaranteed to be safe. libc memcpys aren't required to
   // respect volatile, so they may do things like read or write memory
@@ -4347,6 +4361,9 @@
       return Result;
   }
 
+  checkAddrSpaceIsValidForLibcall(TLI, DstPtrInfo.getAddrSpace());
+  checkAddrSpaceIsValidForLibcall(TLI, SrcPtrInfo.getAddrSpace());
+
   // FIXME: If the memmove is volatile, lowering it to plain libc memmove may
   // not be safe.  See memcpy above for more details.
 
@@ -4401,6 +4418,8 @@
       return Result;
   }
 
+  checkAddrSpaceIsValidForLibcall(TLI, DstPtrInfo.getAddrSpace());
+
   // Emit a library call.
   Type *IntPtrTy = TLI->getDataLayout()->getIntPtrType(*getContext());
   TargetLowering::ArgListTy Args;
Index: lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
===================================================================
--- lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -4775,14 +4775,6 @@
   case Intrinsic::longjmp:
     return &"_longjmp"[!TLI.usesUnderscoreLongJmp()];
   case Intrinsic::memcpy: {
-    // FIXME: this definition of "user defined address space" is x86-specific
-    // Assert for address < 256 since we support only user defined address
-    // spaces.
-    assert(cast<PointerType>(I.getArgOperand(0)->getType())->getAddressSpace()
-           < 256 &&
-           cast<PointerType>(I.getArgOperand(1)->getType())->getAddressSpace()
-           < 256 &&
-           "Unknown address space");
     SDValue Op1 = getValue(I.getArgOperand(0));
     SDValue Op2 = getValue(I.getArgOperand(1));
     SDValue Op3 = getValue(I.getArgOperand(2));
@@ -4796,12 +4788,6 @@
     return nullptr;
   }
   case Intrinsic::memset: {
-    // FIXME: this definition of "user defined address space" is x86-specific
-    // Assert for address < 256 since we support only user defined address
-    // spaces.
-    assert(cast<PointerType>(I.getArgOperand(0)->getType())->getAddressSpace()
-           < 256 &&
-           "Unknown address space");
     SDValue Op1 = getValue(I.getArgOperand(0));
     SDValue Op2 = getValue(I.getArgOperand(1));
     SDValue Op3 = getValue(I.getArgOperand(2));
@@ -4814,14 +4800,6 @@
     return nullptr;
   }
   case Intrinsic::memmove: {
-    // FIXME: this definition of "user defined address space" is x86-specific
-    // Assert for address < 256 since we support only user defined address
-    // spaces.
-    assert(cast<PointerType>(I.getArgOperand(0)->getType())->getAddressSpace()
-           < 256 &&
-           cast<PointerType>(I.getArgOperand(1)->getType())->getAddressSpace()
-           < 256 &&
-           "Unknown address space");
     SDValue Op1 = getValue(I.getArgOperand(0));
     SDValue Op2 = getValue(I.getArgOperand(1));
     SDValue Op3 = getValue(I.getArgOperand(2));