RFR: 8325064: C2 SuperWord: refactor construct_bb

[Vladimir Kozlov]

On Wed, 31 Jan 2024 16:53:59 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

> Subtask of https://github.com/openjdk/jdk/pull/16620
> 
> The goal is to further disentangle different "components" in Superword.
> 
> In this refactoring, I disentangle the `bb`, `reduction` and `memory_slice` "components" which were all intertwined in `construct_bb`.
> 
> 1. Move memory slice code -> `analyze_memory_slices`.
> 2. Remove reduction checking code -> simply use the `is_marked_reduction_loop` condition outside.
> 3. `_data_entry`: was used for non-CFG nodes in the loop that have no input node that is also inside the loop. But that actually never happens! I removed that array, and replaced the code with verification.

This looks reasonable.

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Marked as reviewed by kvn (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/17657#pullrequestreview-1857107701