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

[SendaoYan]

On Thu, 8 May 2025 01:48:17 GMT, Vladimir Ivanov <vlivanov 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

Changes requested by syan (Committer).

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.

-------------

PR Review: https://git.openjdk.org/jdk/pull/25110#pullrequestreview-2824388298
PR Review Comment: https://git.openjdk.org/jdk/pull/25110#discussion_r2079251986