RFR: 8343148: C2: Refactor uses of "PhaseValue::*con*() + PhaseIdealLoop::set_ctrl()" into separate method [v4]

[Vladimir Kozlov]

On Mon, 11 Nov 2024 07:38:44 GMT, theoweidmannoracle <duke at openjdk.org> wrote:

>> src/hotspot/share/opto/loopnode.cpp line 3147:
>> 
>>> 3145:   ConINode* zero = igvn->intcon(0);
>>> 3146:   if (iloop != nullptr) {
>>> 3147:     iloop->set_root_as_ctrl(zero);
>> 
>> Please look on history of this code. This is suspicious - constant nodes should be always attached to Root.
>
> @TobiHartmann Pointed out that this method is also called from code outside of loop opts, for example, `PhaseMacroExpand::expand_macro_nodes`. Since there's no PhaseIdealLoop in this case, nullptr is passed instead and we cannot set control as we are not inside a loop opt. 
> 
> Maybe @rwestrel can also take a look as he originally introduced this code in [this PR](https://github.com/openjdk/jdk/pull/7364/files#diff-d49652d43244d52415873c37bf6990269b0d6e2f2111f4f971660470b6bca738R2860).

Got it. That is what `(iloop != nullptr)` check for.

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PR Review Comment: https://git.openjdk.org/jdk/pull/21836#discussion_r1868196480