RFR: 8335708: C2: Compile::verify_graph_edges must start at root and safepoints, just like CCP traversal [v2]

[Marc Chevalier]

On Mon, 17 Mar 2025 06:47:30 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

>> src/hotspot/share/opto/compile.cpp line 4206:
>> 
>>> 4204:   uint stack_size = live_nodes() >> 4;
>>> 4205:   Node_List nstack(MAX2(stack_size, (uint) OptoNodeListSize));
>>> 4206:   if (root_and_safepoints != nullptr) {
>> 
>> Can you say in which cases we don't have `root_and_safepoints`? Why is it ok not to also start at SafePoint in those cases?
>
> I think you should also say that we start the traversal from Root and Safepoints, just like during CCP.

I've improved the comment on the declaration of `verify_graph_edges`: it is the only caller of `verify_bidirectional_edges`, which acts more like a helper, and `verify_graph_edges` is the one called a bit everywhere. Also, I think it's not an implementation detail, but a signature/contract thing: when writing a call to `verify_graph_edges`, I must know what I need to provide in `root_and_safepoints`, or when I can omit it. So now, I hope it's documented.

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PR Review Comment: https://git.openjdk.org/jdk/pull/23977#discussion_r2001122257