RFR: 8270886: Crash in PhaseIdealLoop::verify_strip_mined_scheduling [v2]

[Tobias Hartmann]

On Wed, 28 Jul 2021 08:35:02 GMT, Roland Westrelin <roland at openjdk.org> wrote:

>> The crash occurs because an OuterStripMinedLoopEnd has only a single
>> projection. The root cause is that an IfNode has a single
>> projection. When the condition of that If constant folds, the IfNode
>> ends up with no use which causes it to be removed. The
>> OuterStripMinedLoopEnd projection is removed as a consequence.
>> 
>> When the If is constructed, it does have 2 projections. One of the
>> projections lead to an infinite loop. That infinite loop has a
>> safepoint node that's input to the Root node. When
>> remove_root_to_sfpts_edges() executes in Compile::Optimize(), that
>> edge is removed. But because PhaseRenumberLive runs next (a subclass
>> of PhaseRemoveUseless), the infinite loop is removed.
>> 
>> The fix is to simply move the call to remove_root_to_sfpts_edges()
>> after PhaseRemoveUseless.
>
> Roland Westrelin has updated the pull request incrementally with one additional commit since the last revision:
> 
>   review

Looks good to me.

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Marked as reviewed by thartmann (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/4911