[jdk19] RFR: 8287851: C2 crash: assert(t->meet(t0) == t) failed: Not monotonic

[Christian Hagedorn]

On Sat, 2 Jul 2022 18:51:13 GMT, Jatin Bhateja <jbhateja at openjdk.org> wrote:

> Hi All,
> 
> Patch fixes the assertion failure seen during conditional constant propagation optimization on account of
> non-convergence, this happens when type values (lattice) associated with IR node seen during iterative data flow analysis are not-monotonic.
> 
> Problem was occurring due to incorrect result value range estimation by Value routines associated with Compress/ExpandBits IR nodes, non-constant mask lattice can take any value between _lo and _hi values,  special handling for +ve mask value range is using count_leading_zeros to estimate the maximum bit width needed to accommodate the result.  Since count_leading_zeros
> accepts a long argument there by sign-extending integer argument, hence for integer case we need to subtract 32 from the results to get correct value.
> 
> Patch also fixes a typo resulting into a dead code reported by [JDK-8287855](https://bugs.openjdk.org/browse/JDK-8287855): Problem in compress_expand_identity.
> 
> Failing unit test java/lang/CompressExpandTest.java has been removed from ProblemList.txt.
> 
> Kindly review and share your feedback.
> 
> Best Regards,
> Jatin

Looks good!

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Marked as reviewed by chagedorn (Reviewer).

PR: https://git.openjdk.org/jdk19/pull/104