pipeline class for sequence of instructions

Alexeev, Alexander Alexander.Alexeev at caviumnetworks.com
Wed Jun 17 19:34:44 UTC 2015


Could somebody clarify how pipeline class is applied on sequence of instructions in architecture description file? For instance, class ialu_reg on countLeadingZerosL_bsr (snippet is below) or ialu_reg_mem on loadUB2L_immI (all from x86_64.ad).
Stages for arguments read/writes, decoder and execution unit are specified only once. Is it then applied on every instructions that uses that pipeline class arguments or for the whole ins_encode body?
BTW countLeadingZerosL_bsr isn't even a "single_instruction".

Class pipe_cmplt looks more reasonable, but and_cmpLTMask and cadd_cmpLTMask still don't have 4 instructions how it is defined. Why 4 cycles are allocated to decode?


// Integer ALU reg operation
pipe_class ialu_reg(rRegI dst)
    dst    : S4(write);
    dst    : S3(read);
    DECODE : S0;        // any decoder
    ALU    : S3;        // any alu

instruct countLeadingZerosL_bsr(rRegI dst, rRegL src, rFlagsReg cr) %{
  match(Set dst (CountLeadingZerosL src));
  effect(KILL cr);

  format %{ "bsrq    $dst, $src\t# count leading zeros (long)\n\t"
            "jnz     skip\n\t"
            "movl    $dst, -1\n"
            "negl    $dst\n\t"
            "addl    $dst, 63" %}
  ins_encode %{
    Register Rdst = $dst$$Register;
    Register Rsrc = $src$$Register;
    Label skip;
    __ bsrq(Rdst, Rsrc);
    __ jccb(Assembler::notZero, skip);
    __ movl(Rdst, -1);
    __ bind(skip);
    __ negl(Rdst);
    __ addl(Rdst, BitsPerLong - 1);

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