[X86] Missing rCX use/defs from LOOP instructions

[RKSimon]

// Loop instructions
let isBranch = 1, isTerminator = 1, SchedRW = [WriteJump] in {
def LOOP   : Ii8PCRel<0xE2, RawFrm, (outs), (ins brtarget8:$dst), "loop\t$dst", []>;
def LOOPE  : Ii8PCRel<0xE1, RawFrm, (outs), (ins brtarget8:$dst), "loope\t$dst", []>;
def LOOPNE : Ii8PCRel<0xE0, RawFrm, (outs), (ins brtarget8:$dst), "loopne\t$dst", []>;
}

LOOP instructions decrements the CX/ECX/RCX register (depending on encoding) and LOOPE/LOOPNE also reads (but doesn't write) the ZF flag.

Also, we're missing the LOOPNZ/LOOPZ aliases for LOOPNE/LOOPE

[llvmbot]

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