[LLVMdev] X86 disassembler & assembler mismatch

Jun Koi junkoi2004 at gmail.com
Thu Dec 25 20:22:43 PST 2014

On Fri, Dec 26, 2014 at 11:54 AM, Jun Koi <junkoi2004 at gmail.com> wrote:

> hi,
> some instructions mismatch between assembler & disassembler, like below.
> it seems this happens with all SSECC related instructions?
> thanks,
> Jun
> $ echo "cmpps xmm1, xmm2, 23" | ./Release+Asserts/bin/llvm-mc -assemble
> -triple=x86_64 --output-asm-variant=1 -x86-asm-syntax=intel -show-encoding
>     .text
>     cmpps    xmm1, xmm2, 23          # encoding: [0x0f,0xc2,0xca,0x17]
> $ echo "0x0f,0xc2,0xca,0x17"|./Release+Asserts/bin/llvm-mc -disassemble
> -triple=x86_64 --output-asm-variant=1
>     .text
> <stdin>:1:1: warning: invalid instruction encoding
> 0x0f,0xc2,0xca,0x17

i am trying to figure out why this bug happens. according to the code in
X86DisassemblerDecoder.cpp, the last operand of CMPSS is checked against
TYPE_IMM5 (to be in the range [0, 31]), but i cannot find this TYPE_IMM5
value anywhere in the definition of CMPSS, as below.
can somebody please enlighten me?


// sse12_cmp_packed - sse 1 & 2 compare packed instructions
multiclass sse12_cmp_packed<RegisterClass RC, X86MemOperand x86memop,
                            Operand CC, Intrinsic Int, string asm,
                            string asm_alt, Domain d,
                            OpndItins itins = SSE_ALU_F32P> {
  def rri : PIi8<0xC2, MRMSrcReg,
             (outs RC:$dst), (ins RC:$src1, RC:$src2, CC:$cc), asm,
             [(set RC:$dst, (Int RC:$src1, RC:$src2, imm:$cc))],
             itins.rr, d>,
  def rmi : PIi8<0xC2, MRMSrcMem,
             (outs RC:$dst), (ins RC:$src1, x86memop:$src2, CC:$cc), asm,
             [(set RC:$dst, (Int RC:$src1, (memop addr:$src2), imm:$cc))],
             itins.rm, d>,
            Sched<[WriteFAddLd, ReadAfterLd]>;

  // Accept explicit immediate argument form instead of comparison code.
  let isAsmParserOnly = 1, hasSideEffects = 0 in {
    def rri_alt : PIi8<0xC2, MRMSrcReg,
               (outs RC:$dst), (ins RC:$src1, RC:$src2, i8imm:$cc),
               asm_alt, [], itins.rr, d>, Sched<[WriteFAdd]>;
    def rmi_alt : PIi8<0xC2, MRMSrcMem,
               (outs RC:$dst), (ins RC:$src1, x86memop:$src2, i8imm:$cc),
               asm_alt, [], itins.rm, d>,
               Sched<[WriteFAddLd, ReadAfterLd]>;

let Constraints = "$src1 = $dst" in
  defm CMPPS : sse12_cmp_packed<VR128, f128mem, SSECC,
                 "cmp${cc}ps\t{$src2, $dst|$dst,
                 "cmpps\t{$cc, $src2, $dst|$dst, $src2,
                 SSEPackedSingle, SSE_ALU_F32P>,
  defm CMPPD : sse12_cmp_packed<VR128, f128mem, SSECC,
                 "cmp${cc}pd\t{$src2, $dst|$dst,
                 "cmppd\t{$cc, $src2, $dst|$dst, $src2,
                 SSEPackedDouble, SSE_ALU_F64P>,
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