Add a FIXME in SelectionDAGBuilder before an assert that is valid only on X86.

When lowering memcpy, memset or memmove, this assert checks whether the pointer
operands are in an address space < 256 which means "user defined address space"
on X86.  However, this notion of "user defined address space" does not exist
for other targets.

llvm-svn: 227191
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index df0c4ef..0074e14 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -4775,6 +4775,7 @@
   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()
@@ -4795,6 +4796,7 @@
     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()
@@ -4812,6 +4814,7 @@
     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()