RFR: 8342662: C2: Add new phase for backend-specific lowering [v2]

[Quan Anh Mai]

On Sun, 27 Oct 2024 01:22:13 GMT, Jatin Bhateja <jbhateja at openjdk.org> wrote:

>> I believe the matcher only needs the exact type of the node but not its inputs. E.g. it should not be an issue if we `AddVB` a `vector<int,8>` and a `vector<long,2>` into a `vector<byte,16>`.
>
> Generic vector operand resolution cocretizes generic operands based on type agnostic node size, its a post matcher pass,  and its job is to replace generic MachOper operand nodes with cocrete ones (vec[SDXYZ]) which holds precise register mask needed by register allocator.

@jaskarth I notice we have `process_late_inline_calls_no_inline` below, please put lowering after it because `process_late_inline_calls_no_inline` does do igvn.

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PR Review Comment: https://git.openjdk.org/jdk/pull/21599#discussion_r1819902884