RFR: 8370077: C2: make Compile::_major_progress a boolean

[Marc Chevalier]

On Tue, 21 Oct 2025 16:31:30 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

>> That makes sense. A suggestion? Maybe "Whether something big happened"?
>
> It is kind of scary that there is basically no documentation on this. But it is quite important actually. The current comment is really not very helpful.
> 
> My understanding is that the flag is set if the loop-opts data-structures are invalid (or at least there is no guarantee that they are valid). So we need to re-build the loop tree.
> 
> If we ever set the flag, we don't continue with more loop-opts, but spin back to IGVN, clean the graph, and maybe come back to a new loop-opts round.
> 
> There may be others who have a better understanding / definition though.

I don't think it's the right place for this kind of comment. It's quite hidden, far from where it's actually useful to know we need to set or check that. I'd say it should rather be on `PhaseIdealLoop` for instance, or `PhaseIdealLoop::optimize`, something like that, as a part of a more global overview of how things work.

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PR Review Comment: https://git.openjdk.org/jdk/pull/27912#discussion_r2449020728