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  1. JDK
  2. JDK-8144582

AArch64 does not generate correct branch profile data

    Details

    • Type: Bug
    • Status: Resolved
    • Priority: P4
    • Resolution: Fixed
    • Affects Version/s: None
    • Fix Version/s: 9
    • Component/s: hotspot
    • Labels:
      None
    • Subcomponent:
    • Resolved In Build:
      b103
    • CPU:
      aarch64

      Description

      We're not generating enough profile data in the template interpreter for C2 to use. When we run with -Xbatch -XX:-TieredCompilation we get such low profile counts that they are of no use at all.

      final BitTests::testLongMaskBranch(JJ)J
        interpreter_invocation_count: 3301
        invocation_counter: 3301
        backedge_counter: 1
        mdo size: 496 bytes

      0 fast_aaccess_0
      1 fast_agetfield 4 <BitTests.r/LXorShift;>
      4 invokevirtual 11 <XorShift.nextLong()J>
        0 bci: 4 VirtualCallData count(0) entries(1)
                                          'XorShift'(2 1.00)
      7 lload_3
      8 land
      9 lconst_0
      10 lcmp
      11 ifeq 18
        48 bci: 11 BranchData taken(0) displacement(32)
                                          not taken(2)

      This should be something more like:

      final BitTests::testLongMaskBranch(JJ)J
        interpreter_invocation_count: 10000
        invocation_counter: 5000
        backedge_counter: 1
        mdo size: 496 bytes

      0 fast_aaccess_0
      1 fast_agetfield 4 <BitTests.r/LXorShift;>
      4 invokevirtual 11 <XorShift.nextLong()J>
        0 bci: 4 VirtualCallData count(0) entries(1)
                                          'XorShift'(6701 1.00)
      7 lload_3
      8 land
      9 lconst_0
      10 lcmp
      11 ifeq 18
        48 bci: 11 BranchData taken(3343) displacement(32)
                                          not taken(3358)

      ... which is what we see on x86. Note that the counter overflow is happening early: it should happen on 10000 invocations, but it is happening on only 3301.

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            • Assignee:
              aph Andrew Haley
              Reporter:
              aph Andrew Haley
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              • Created:
                Updated:
                Resolved: