[llvm-dev] Help lowering byte wise compare instruction

vivek pandya via llvm-dev llvm-dev at lists.llvm.org
Wed Feb 15 06:49:23 PST 2017

Hello LLVM Devs,

Hope you are doing well.
I am implementing LLVM back-end for an architecture which has instruction
that performs byte by byte comparison and stores result for each byte.

pcmpbf rD, rA, rB --> bytewise comparison returning position of first match
in rd

So with this regard I wanted to find similar instruction lowering for nay
other architecture which have similar instruction.
I found some thing similar on PPC. If I am wrong kindly suggest some

I am trying to understand following statement from PPCInstrInfo.td file:
  def CMPRB  : X_BF3_L1_RS5_RS5<31, 192, (outs crbitrc:$BF),
                                (ins u1imm:$L, g8rc:$rA, g8rc:$rB),
                                "cmprb $BF, $L, $rA, $rB", IIC_IntCompare,
Here I am not able to understand against which DAG pattern this gets
matched ? By doing grep I don't get any code which provide me the required

Basically I want to know which LLVM IR instruction or intrinsic has similar
semantics and then how I can lower it correctly.

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