simple_v_extension/specification/mv.x.rst

   1 MV.X and MV.swizzle
   2 ===================
   3
   4 swizzle needs a MV.  see below for a potential way to use the funct7 to do a swizzle in rs2.
   5
   6 +---------------+-------------+-------+----------+----------+--------+----------+--------+--------+
   7 | Encoding      | 31:27       | 26:25 | 24:20    | 19:15    | 14:12  | 11:7     | 6:2    | 1:0    |
   8 +---------------+-------------+-------+----------+----------+--------+----------+--------+--------+
   9 | RV32-I-type   + imm[11:0]                      + rs1[4:0] + funct3 | rd[4:0]  + opcode + 0b11   |
  10 +---------------+-------------+-------+----------+----------+--------+----------+--------+--------+
  11 | RV32-I-type   + fn4[11:8] swizzle[7:0]         + rs1[4:0] + 0b000  | rd[4:0]  + OP-V   + 0b11   |
  12 +---------------+-------------+-------+----------+----------+--------+----------+--------+--------+
  13
  14 * funct3 = MV
  15 * OP-V = 0b1010111
  16 * fn4 = 4 bit function.
  17 * fn4 = 0b0000 - INT MV-SWIZZLE ?
  18 * fn4 = 0b0001 - FP MV-SWIZZLE ?
  19
  20 swizzle (only active on SV or P48/P64 when SUBVL!=0):
  21
  22 +-----+---+
  23 | 1:0 | x |
  24 +-----+---+
  25 | 3:2 | y |
  26 +-----+---+
  27 | 5:4 | z |
  28 +-----+---+
  29 | 7:6 | w |
  30 +-----+---+
  31
  32 ----
  33
  34 potential MV.X?  register-version of MV-swizzle?
  35
  36 +---------------+-------------+-------+----------+----------+--------+----------+--------+--------+
  37 | Encoding      | 31:27       | 26:25 | 24:20    | 19:15    | 14:12  | 11:7     | 6:2    | 1:0    |
  38 +---------------+-------------+-------+----------+----------+--------+----------+--------+--------+
  39 | RV32-R-type   +    funct7           + rs2[4:0] + rs1[4:0] + funct3 | rd[4:0]  + opcode + 0b11   |
  40 +---------------+-------------+-------+----------+----------+--------+----------+--------+--------+
  41 | RV32-R-type   +    0b0000000        + rs2[4:0] + rs1[4:0] + 0b001  | rd[4:0]  + OP-V   + 0b11   |
  42 +---------------+-------------+-------+----------+----------+--------+----------+--------+--------+
  43
  44 * funct3 = MV.X
  45 * OP-V = 0b1010111
  46 * funct7 = 0b0000000 - INT MV.X
  47 * funct7 = 0b0000001 - FP MV.X
  48 * funct7 = 0b0000010 - INT MV.swizzle to say that rs2 is a swizzle argument?
  49 * funct7 = 0b0000011 - FP MV.swizzle to say that rs2 is a swizzle argument?
  50
  51 question: do we need a swizzle MV.X as well?
  52
  53 macro-op fusion
  54 ===============
  55
  56 there is the potential for macro-op fusion of mv-swizzle with the following instruction.
  57 <http://lists.libre-riscv.org/pipermail/libre-riscv-dev/2019-August/002486.html>