diff --git a/llvm/lib/Target/X86/X86Instr64bit.td b/llvm/lib/Target/X86/X86Instr64bit.td
index d541bd4cd8d7..3f41ffd9944c 100644
--- a/llvm/lib/Target/X86/X86Instr64bit.td
+++ b/llvm/lib/Target/X86/X86Instr64bit.td
@@ -309,16 +309,22 @@ def BSR64rm  : RI<0xBD, MRMSrcMem, (outs GR64:$dst), (ins i64mem:$src),
 } // Defs = [EFLAGS]
 
 // Repeat string ops
-let Defs = [RCX,RDI,RSI], Uses = [RCX,RDI,RSI] in
+let Defs = [RCX,RDI,RSI], Uses = [RCX,RDI,RSI], isCodeGenOnly = 1 in
 def REP_MOVSQ : RI<0xA5, RawFrm, (outs), (ins), "{rep;movsq|rep movsq}",
                    [(X86rep_movs i64)]>, REP;
-let Defs = [RCX,RDI], Uses = [RAX,RCX,RDI] in
+let Defs = [RCX,RDI], Uses = [RAX,RCX,RDI], isCodeGenOnly = 1 in
 def REP_STOSQ : RI<0xAB, RawFrm, (outs), (ins), "{rep;stosq|rep stosq}",
                    [(X86rep_stos i64)]>, REP;
 
-def SCAS64 : RI<0xAF, RawFrm, (outs), (ins), "scas{q}", []>;
+let Defs = [EDI,ESI], Uses = [EDI,ESI,EFLAGS] in
+def MOVSQ : RI<0xA5, RawFrm, (outs), (ins), "movsq", []>;
 
-def CMPS64 : RI<0xA7, RawFrm, (outs), (ins), "cmps{q}", []>;
+let Defs = [RCX,RDI], Uses = [RAX,RCX,RDI,EFLAGS] in
+def STOSQ : RI<0xAB, RawFrm, (outs), (ins), "stosq", []>;
+
+def SCAS64 : RI<0xAF, RawFrm, (outs), (ins), "scasq", []>;
+
+def CMPS64 : RI<0xA7, RawFrm, (outs), (ins), "cmpsq", []>;
 
 // Fast system-call instructions
 def SYSEXIT64 : RI<0x35, RawFrm,
diff --git a/llvm/test/MC/AsmParser/X86/x86_64-new-encoder.s b/llvm/test/MC/AsmParser/X86/x86_64-new-encoder.s
index 4028beea7431..e2db48495bca 100644
--- a/llvm/test/MC/AsmParser/X86/x86_64-new-encoder.s
+++ b/llvm/test/MC/AsmParser/X86/x86_64-new-encoder.s
@@ -52,3 +52,20 @@ testq %rax, %rbx
 // CHECK: cmpq	%rbx, %r14
 // CHECK:   encoding: [0x49,0x39,0xde]
         cmpq %rbx, %r14
+
+// rdar://7947167
+
+movsq
+// CHECK: movsq
+// CHECK:   encoding: [0x48,0xa5]
+
+movsl
+// CHECK: movsl
+// CHECK:   encoding: [0xa5]
+
+stosq
+// CHECK: stosq
+// CHECK:   encoding: [0x48,0xab]
+stosl
+// CHECK: stosl
+// CHECK:   encoding: [0xab]