RFR: 8270886: Crash in PhaseIdealLoop::verify_strip_mined_scheduling

[Vladimir Kozlov]

On Tue, 27 Jul 2021 14:07:40 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.

Looks good. What testing you did?

src/hotspot/share/opto/compile.cpp line 2151:

> 2149:   remove_root_to_sfpts_edges(igvn);
> 2150: 
> 2151:     // Perform escape analysis

Indent is wrong for this line. Please, fix it.

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