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  1. JDK
  2. JDK-8292285

C2: remove unreachable block after NeverBranch-to-Goto conversion

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    Backports

      Description

        NeverBranch nodes introduce fake branches out of infinite loops to simplify intermediate optimizations that assume full reachability (see before.pdf). 'PhaseCFG::convert_NeverBranch_to_Goto()' transforms such nodes into simple Goto nodes, removing the fake branch and thus making its destination block unreachable (see after.pdf).

        This RFE proposes removing the unreachable destination block created by 'PhaseCFG::convert_NeverBranch_to_Goto()' from the list of basic blocks (see after-removal.pdf). Removing the unreachable block simplifies late control-flow analysis (for example, recomputing dominators during the output phase as required for late barrier analysis in Generational ZGC) and slightly reduces the size of the resulting nmethod.

        Attachments

          1. after.pdf
            6 kB
          2. after-removal.pdf
            5 kB
          3. before.pdf
            7 kB

          Issue Links

            backported by

            Backport - A issue that is required to port a Bug or Feature into another product release. This issue type is generally associated with the main Bug/Feature to represent each individual release of the port. JDK-8296379 C2: remove unreachable block after NeverBranch-to-Goto conversion

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

            Backport - A issue that is required to port a Bug or Feature into another product release. This issue type is generally associated with the main Bug/Feature to represent each individual release of the port. JDK-8299367 C2: remove unreachable block after NeverBranch-to-Goto conversion

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

            Bug - A problem which impairs or prevents the functions of the product. JDK-8292660 C2: blocks made unreachable by NeverBranch-to-Goto conversion are removed incorrectly

            • P3 - Major loss of function.
            • Resolved

            Bug - A problem which impairs or prevents the functions of the product. JDK-8292859 test/hotspot/jtreg/gc/shenandoah/compiler/BarrierInInfiniteLoop.java timeouts after JDK-8292285

            • P3 - Major loss of function.
            • Closed
            links to

            Commit Commit openjdk/jdk17u-dev/ade0edf8

            Commit Commit openjdk/jdk/a25e1dc5

            Review Review openjdk/jdk17u-dev/974

            Review Review openjdk/jdk/9853

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                rcastanedalo Roberto Castaneda Lozano
                rcastanedalo Roberto Castaneda Lozano
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                  Created:
                  Updated:
                  Resolved: