RFR: 8263227: C2: inconsistent spilling due to dead nodes in exception block [v2]

[Vladimir Kozlov]

On Mon, 12 Apr 2021 08:37:18 GMT, Roberto Castañeda Lozano <rcastanedalo at openjdk.org> wrote:

>> This change eliminates dead multi-nodes created by call-catch cleanup after GCM. Eliminating all dead code created by call-catch cleanup avoids potential issues when splitting the live range of call result values, see the analysis in the [bug report](https://bugs.openjdk.java.net/browse/JDK-8263227) for details. This solution is the least invasive of the three alternatives proposed in the bug report (the other two are constraining global code motion and extending live-range splitting).
>> 
>> The change also extends the control-flow graph verification pass to catch similar live-range splitting issues earlier (with `+VerifyRegisterAllocator`).
>> 
>> Tested on:
>> - original bug reproducer
>> - hs-tier1-5 (windows-x64, linux-x64, linux-aarch64, and macosx-x64) with `+VerifyRegisterAllocator`
>> - hs-tier1-3 (windows-x64, linux-x64, linux-aarch64, and macosx-x64) with `+VerifyRegisterAllocator` and `+StressGCM` (5 repetitions)
>
> Roberto Castañeda Lozano has updated the pull request incrementally with four additional commits since the last revision:
> 
>  - Complete projection assertions with basic checks
>  - Enforce code style in surrounding 'for' statements
>  - Simplify loop that removes dead projections, rename and comment for clarity
>  - Assert that projections are stuck to their parents

Marked as reviewed by kvn (Reviewer).

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PR: https://git.openjdk.java.net/jdk/pull/3303