silence a warning

llvm-svn: 25745
diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index 236179f..a2a7887 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -1293,6 +1293,7 @@
     // Get the X86 opcode to use.
     unsigned Opc;
     switch (MI->getOpcode()) {
+    default: assert(0 && "illegal opcode!");
     case X86::FP_TO_INT16_IN_MEM: Opc = X86::FpIST16m; break;
     case X86::FP_TO_INT32_IN_MEM: Opc = X86::FpIST32m; break;
     case X86::FP_TO_INT64_IN_MEM: Opc = X86::FpIST64m; break;