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

[Jatin Bhateja]

On Mon, 28 Oct 2024 23:48:48 GMT, Quan Anh Mai <qamai at openjdk.org> wrote:

>> 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.

Invariants in the lowered graph will get scheduled out of the loop during GCM, but lowering may still impact the unrolling policy which is based on the [loop body size. ](https://github.com/openjdk/jdk/blob/master/src/hotspot/share/opto/loopTransform.cpp#L1024)

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PR Review Comment: https://git.openjdk.org/jdk/pull/21599#discussion_r1820624424