RFR: 8356453: C2: assert(!vbox->is_Phi()) during vector box expansion

[Vladimir Ivanov]

On Thu, 8 May 2025 09:14:00 GMT, SendaoYan <syan at openjdk.org> wrote:

>> Some Vector API tests fail with an assert during `PhaseVector::expand_vbox_node()`. The assert itself is the culprit, since it doesn't cover the case when VBox node is already expanded.
>> 
>> Proposed fix adjusts the assert.
>> 
>> Also, extended `PhaseVector::optimize_vector_boxes()` with `StressMacroExpansion` support.
>> 
>> Testing: hs-tier1 - hs-tier5
>
> test/hotspot/jtreg/compiler/vectorapi/VectorBoxExpandTest.java line 44:
> 
>> 42:     private static int[] iarr = new int[ARR_LEN];
>> 43:     private static IntVector g;
>> 44:     private static int acc = 0;
> 
> Maybe we should update the copyright year.

The file has non-Oracle legal notice, so I'm not eligible to change it.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25110#discussion_r2080189978