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  1. JDK
  2. JDK-8169697

aarch64: vectorized MLA instruction not generated for some test cases

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    • 9
    • b21
    • aarch64
    • linux

    Description

      Reported by yang.zhang@linaro.org:

      > >> Currently, vector MLA/MLS instructions in aarch64 port have been enabled.
      > >> But when I investigate the status of NEON support, I find that vector
      > >> MLA instructions aren’t generated in a single multiply-add operation.
      > >>
      > >> Take the following function as an example:
      > >> public static int vectMulAdd(
      > >> int[] a,
      > >> int[] b,
      > >> int[] c,
      > >> int[] d) {
      > >> int total = 0;
      > >> for (int i = 0; i < LENGTH; i++) {
      > >> d[i] = (int)(a[i] * b[i] + c[i]);
      > >> total += d[i];
      > >> }
      > >> return total;
      > >> }
      > >>
      > >> The following code snippet is produced by C2:
      > >> 0x0000007f98af88fc: ldr q18, [x19,#32]
      > >> 0x0000007f98af8900: ldr q17, [x4,#32]
      > >> 0x0000007f98af8904: ldr q19, [x20,#32]
      > >> 0x0000007f98af8908: mul v17.4s, v17.4s, v18.4s
      > >> 0x0000007f98af890c: add v17.4s, v17.4s, v19.4s
      > >>
      > >> It can be further optimized into:
      > >> 0x0000007f843485e0: ldr q18, [x19,#16]
      > >> 0x0000007f843485e4: ldr q17, [x20,#16]
      > >> 0x0000007f843485e8: ldr q16, [x4,#16]
      > >> 0x0000007f843485ec: mla v18.4s, v16.4s, v17.4s

      Yang have a patch for this which is under JTreg test.

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            aph Andrew Haley
            fyang Fei Yang
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              Created:
              Updated:
              Resolved: