Index: llvm/trunk/lib/Target/X86/X86AsmPrinter.cpp
===================================================================
--- llvm/trunk/lib/Target/X86/X86AsmPrinter.cpp
+++ llvm/trunk/lib/Target/X86/X86AsmPrinter.cpp
@@ -372,6 +372,12 @@
   unsigned Reg = MO.getReg();
   bool EmitPercent = true;
 
+  if (!X86::GR8RegClass.contains(Reg) &&
+      !X86::GR16RegClass.contains(Reg) &&
+      !X86::GR32RegClass.contains(Reg) &&
+      !X86::GR64RegClass.contains(Reg))
+    return true;
+
   switch (Mode) {
   default: return true;  // Unknown mode.
   case 'b': // Print QImode register
Index: llvm/trunk/test/CodeGen/X86/inline-asm-bad-modifier.ll
===================================================================
--- llvm/trunk/test/CodeGen/X86/inline-asm-bad-modifier.ll
+++ llvm/trunk/test/CodeGen/X86/inline-asm-bad-modifier.ll
@@ -0,0 +1,8 @@
+; RUN: not llc -mtriple=x86_64-- < %s 2>&1 | FileCheck %s
+
+;CHECK: error: invalid operand in inline asm: 'vmovd ${1:x}, $0'
+define i32 @foo() {
+entry:
+  %0 = tail call i32 asm sideeffect "vmovd ${1:x}, $0", "=r,x,~{dirflag},~{fpsr},~{flags}"(<2 x i64> <i64 240518168632, i64 240518168632>)
+  ret i32 %0
+}