RFR: 8332442: C2: refactor Mod cases in Compile::final_graph_reshaping_main_switch() [v2]

[Kangcheng Xu]

On Tue, 10 Sep 2024 14:59:40 GMT, Roland Westrelin <roland at openjdk.org> wrote:

>> I was under the impression aarch64 cannot calculate quotient and remainder with a single div instruction (unlike x86), and I assumed that's why existing tests on divmod doesn't include this arch. Looking at the source, only `src/hotspot/cpu/x86/x86_64.ad` and `s390.ad` seems to contain divmod related instructions.
>
> `UseDivMod` is true on all platforms but if there's no hardware support for `Op_DivModI` then this code:
> 
>         } else {
>           // replace a%b with a-((a/b)*b)
>           Node* mult = new MulINode(d, d->in(2));
>           Node* sub  = new SubINode(d->in(1), mult);
>           n->subsume_by(sub, this);
>         }
> 
> computes the `ModI` from the `DivI` result and removes the `DivI`. That's what you could match on aarch64.

I've added test configurations to reflect aarch64 with `+XX:+UseDivMod`

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PR Review Comment: https://git.openjdk.org/jdk/pull/20877#discussion_r1752241162