Index: lib/Target/X86/AsmParser/X86AsmParser.cpp
===================================================================
--- lib/Target/X86/AsmParser/X86AsmParser.cpp
+++ lib/Target/X86/AsmParser/X86AsmParser.cpp
@@ -2376,6 +2376,13 @@
             .Cases("repne", "repnz", X86::IP_HAS_REPEAT_NE)
             .Default(X86::IP_NO_PREFIX); // Invalid prefix (impossible)
     Flags |= Prefix;
+    if (getLexer().is(AsmToken::EndOfStatement)) {
+      // We don't have real instr with the given prefix
+      //  let's use the prefix as the instr.
+      // TODO: there could be several prefixes one after another
+      Flags = X86::IP_NO_PREFIX;
+      break;
+    }
     Name = Parser.getTok().getString();
     Parser.Lex(); // eat the prefix
     // Hack: we could have something like "rep # some comment" or
Index: test/CodeGen/X86/inline-asm-A-constraint.ll
===================================================================
--- test/CodeGen/X86/inline-asm-A-constraint.ll
+++ test/CodeGen/X86/inline-asm-A-constraint.ll
@@ -19,7 +19,8 @@
   %.fca.1.insert = insertvalue { i64, i64 } %.fca.0.insert, i64 %retval.sroa.2.0.extract.trunc, 1
   ret { i64, i64 } %.fca.1.insert
 }
-; CHECK: lock cmpxchg16b
+; CHECK: lock
+; CHECK-NEXT: cmpxchg16b
 
 attributes #0 = { nounwind uwtable "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+fxsr,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
 attributes #1 = { nounwind }
Index: test/MC/X86/x86-64.s
===================================================================
--- test/MC/X86/x86-64.s
+++ test/MC/X86/x86-64.s
@@ -99,7 +99,8 @@
 // CHECK: shll $2, %eax
         sall $2, %eax
 
-// CHECK: rep movsb
+// CHECK: rep
+// CHECK-NEXT: movsb
 rep     # comment
 movsb
 
@@ -1557,3 +1558,38 @@
 // CHECK: ptwriteq %rax
 // CHECK:  encoding: [0xf3,0x48,0x0f,0xae,0xe0]
 ptwriteq %rax
+
+//  __asm __volatile(
+//    "pushf        \n\t"
+//    "popf       \n\t"
+//    "rep        \n\t"
+//    ".byte  0x0f, 0xa7, 0xd0"
+//  );
+// CHECK: pushfq
+// CHECK-NEXT: popfq
+// CHECK-NEXT: rep
+// CHECK-NEXT: .byte 15
+// CHECK-NEXT: .byte 167
+// CHECK-NEXT: .byte 208
+pushfq
+popfq
+rep
+.byte 15
+.byte 167
+.byte 208
+
+// CHECK: lock
+// CHECK: cmpxchgl
+        cmp $0, %edx
+        je 1f
+        lock
+1:      cmpxchgl %ecx,(%rdi)
+
+// CHECK: rep
+// CHECK-NEXT: byte
+rep
+.byte 0xa4      # movsb
+
+// CHECK: lock
+// This line has to be the last one in the file
+lock