RFR: 8375010: C2 VectorAPI: assert(vbox->is_CheckCastPP()) failed: should be expanded

[Vladimir Ivanov]

On Tue, 13 Jan 2026 17:35:35 GMT, Kerem Kat <krk at openjdk.org> wrote:

> The check `vect->is_Vector() || vect->is_LoadVector()` doesn't handle `Proj` nodes that resolve to vector types, causing an assertion failure when such nodes flow through a `Phi` into `VectorBox`.

src/hotspot/share/opto/vector.cpp line 357:

> 355:   // any of the inputs to VectorBoxNode are value-numbered they can only
> 356:   // move up and are guaranteed to dominate.
> 357:   if (vbox->is_Phi() && vect->bottom_type()->isa_vect()) {

Does `vect->bottom_type()->isa_vect()` check become redundant? In other words, is it possible to observe a non-vector value here? It seems like the important bit is whether `vect` is a `Phi` or not. 

Another observation: `vbox->is_Phi() && vect->is_Phi()` and `vbox->is_Phi() && !vect->is_Phi()` cases can be commoned.

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PR Review Comment: https://git.openjdk.org/jdk/pull/29200#discussion_r2691294922