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  1. JDK
  2. JDK-8257146

C2: extend the scope of StressGCM

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Details

    • Enhancement
    • Resolution: Duplicate
    • P4
    • tbd
    • 16
    • hotspot

    Description

      Currently, in PhaseCFG::hoist_to_cheaper_block(), StressGCM follows the GCM heuristic when the candidate block has strictly better frequency and only only randomizes tie-breaking among equally frequent blocks:

      if (LCA_freq < least_freq || // Better Frequency
          (StressGCM && C->randomized_select(cand_cnt)) || // Should be randomly accepted in stress mode
          ...

      The randomization scope can be significantly extended by allowing GCM to move instructions to blocks with worse frequency at random:

      if ((StressGCM && C->randomized_select(cand_cnt)) || // Should be randomly accepted in stress mode
          (!StressGCM && LCA_freq < least_freq) || // Better Frequency
          ...

      This would improve StressGCM's ability to expose bugs where C2 relies on GCM heuristics for correctness.

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        Issue Links

          duplicates

          Enhancement - null JDK-8271118 C2: StressGCM should have higher priority than frequency-based policy

          • P4 - Minor loss of function, or other problem where easy workaround is present.
          • Resolved
          is blocked by

          Bug - A problem which impairs or prevents the functions of the product. JDK-8258894 C2: Forbid GCM to move stores into loops

          • P3 - Major loss of function.
          • Resolved

          Bug - A problem which impairs or prevents the functions of the product. JDK-8263227 C2: inconsistent spilling due to dead nodes in exception block

          • P3 - Major loss of function.
          • Resolved

          Bug - A problem which impairs or prevents the functions of the product. JDK-8261236 C2: ClhsdbJstackXcompStress test fails when StressGCM is enabled

          • P4 - Minor loss of function, or other problem where easy workaround is present.
          • Resolved
          relates to

          Enhancement - null JDK-8258895 C2: Refine execution frequency estimation for irreducible CFGs

          • P4 - Minor loss of function, or other problem where easy workaround is present.
          • Open
          links to

          Review Review openjdk/jdk/1469

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              Unassigned Unassigned
              rcastanedalo Roberto Castaneda Lozano
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              Dates

                Created:
                Updated:
                Resolved: