+// Lock instruction prefix
+def LOCK_PREFIX : I<0xF0, RawFrm, (outs), (ins), "lock", []>;
+
+// Repeat string operation instruction prefixes
+// These uses the DF flag in the EFLAGS register to inc or dec ECX
+let Defs = [ECX], Uses = [ECX,EFLAGS] in {
+// Repeat (used with INS, OUTS, MOVS, LODS and STOS)
+def REP_PREFIX : I<0xF3, RawFrm, (outs), (ins), "rep", []>;
+// Repeat while not equal (used with CMPS and SCAS)
+def REPNE_PREFIX : I<0xF2, RawFrm, (outs), (ins), "repne", []>;
+}
+
+// Segment override instruction prefixes
+def CS_PREFIX : I<0x2E, RawFrm, (outs), (ins), "cs", []>;
+def SS_PREFIX : I<0x36, RawFrm, (outs), (ins), "ss", []>;
+def DS_PREFIX : I<0x3E, RawFrm, (outs), (ins), "ds", []>;
+def ES_PREFIX : I<0x26, RawFrm, (outs), (ins), "es", []>;
+def FS_PREFIX : I<0x64, RawFrm, (outs), (ins), "fs", []>;
+def GS_PREFIX : I<0x65, RawFrm, (outs), (ins), "gs", []>;
+