RFR: 8347499: C2: Make `PhaseIdealLoop` eliminate more redundant safepoints in loops [v3]

[Qizheng Xing]

On Fri, 24 Oct 2025 14:57:57 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

>> The first one (`loopConst`) is a counted loop. The second one (`loopVar`) is not, because it calls `empty` (not inlined) which may modify `loopCount`.
>> 
>> Both the two loops should have no safepoints, since the `empty` call always polls the safepoint.
>
> @MaxXSoft Can you please add some code comments in the test? Just if the rule ever fails, it would be nice to know why the rule was added ;)

@eme64 Added IR test comments in commit b42ffb46a590e2c1d8c2e8ad6cd765138a36f3cd to explain why such safepoints exist.

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/23057#discussion_r2464261417