RFR: 8341293: Split field loads through Nested Phis [v7]

[Emanuel Peter]

On Wed, 5 Feb 2025 17:31:43 GMT, Dhamoder Nalla <dhanalla at openjdk.org> wrote:

>> @dhanalla Would you like this to be reviewed? We generally don't re-review until we get pinged again. The idea is that you are maybe still working on it, and so there is no point in reviewing half-processed code. So once you are happy, you can let us know ;)
>
>> @dhanalla Would you like this to be reviewed? We generally don't re-review until we get pinged again. The idea is that you are maybe still working on it, and so there is no point in reviewing half-processed code. So once you are happy, you can let us know ;)
> Thanks, @eme64 for checking with me. Yes, it's ready for review.

@dhanalla Testing failed for this test:
`compiler/c2/irTests/scalarReplacement/AllocationMergesNestedPhiTests.java`
With flags:
- `-server -Xcomp`
- `-ea -esa -XX:CompileThreshold=100 -XX:+UnlockExperimentalVMOptions -server -XX:-TieredCompilation`
- `-XX:-TieredCompilation -XX:+AlwaysIncrementalInline`
- `-XX:-TieredCompilation -XX:+StressReflectiveCode -XX:-ReduceInitialCardMarks -XX:-ReduceBulkZeroing -XX:-ReduceFieldZeroing`

We also have an internal test that is failing with the same assert:

`#  assert(jobj != nullptr && jobj != phantom_obj) failed: escaped allocation`

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PR Comment: https://git.openjdk.org/jdk/pull/21270#issuecomment-2643428408