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  1. JDK
  2. JDK-8233033

C2 produces wrong result while unswitching a loop due to lost control dependencies

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    • b27
    • Fix failed

    Backports

      Description

        The attached test produces a wrong result for C2 due to lost control dependencies for loop predicates while unswitching a loop after it was partially peeled.

        The C2 compiled code produces a wrong result for 'iFld' in the attached test case. It is -8 instead of -7. The loop in the test case is partially peeled and then unswitched. The wrong result is produced because a wrong state is transferred to the interpreter when an uncommon trap is hit in the C2 compiled code in the fast version of the unswitched loop.

        The problem is when unswitching the loop, we clone the original loop predicates for the slow and fast version of the loop but we do not account for partially peeled statements that are control dependent on the loop predicates (i.e. need to be executed after the predicates). As a result, these are executed before the cloned loop predicates.

        Attachments

          1. fixed_dependencies.png
            fixed_dependencies.png
            30 kB
          2. FuzzerUtils.class
            8 kB
          3. FuzzerUtils.java
            13 kB
          4. FuzzerUtils$1.class
            0.8 kB
          5. Test.class
            6 kB
          6. Test.java
            9 kB
          7. wrong_dependencies.png
            wrong_dependencies.png
            33 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-8236303 C2 produces wrong result while unswitching a loop due to lost control dependencies

            • P2 - Crashes, loss of data, severe memory leak.
            • 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-8240674 C2 produces wrong result while unswitching a loop due to lost control dependencies

            • P2 - Crashes, loss of data, severe memory leak.
            • 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-8246418 C2 produces wrong result while unswitching a loop due to lost control dependencies

            • P2 - Crashes, loss of data, severe memory leak.
            • 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-8240608 C2 produces wrong result while unswitching a loop due to lost control dependencies

            • P2 - Crashes, loss of data, severe memory leak.
            • Closed
            relates to

            Enhancement - null JDK-8236722 Extend loop unswitching to handle loop predicates with a control dependency to partially peeled statements

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

            Bug - A problem which impairs or prevents the functions of the product. JDK-8235984 C2: assert(out->in(PhiNode::Region) == head || out->in(PhiNode::Region) == slow_head) failed: phi must be either part of the slow or the fast loop

            • P2 - Crashes, loss of data, severe memory leak.
            • Closed

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                chagedorn Christian Hagedorn
                lmesnik Leonid Mesnik
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                  Created:
                  Updated:
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