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8354383: C2: enable sinking of Type nodes out of loop #25396

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8354383: C2: enable sinking of Type nodes out of loop #25396

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rwestrel
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@rwestrel rwestrel commented May 22, 2025 •
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PhaseIdealLoop::try_sink_out_of_loop() excludes Type nodes because
we ran into some issues where a Type node is sunk and then becomes
top but the control path of its uses doesn't become unreachable.

8349479 should have fixed that so that exception no longer makes
sense.

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  • JDK-8354383: C2: enable sinking of Type nodes out of loop (Enhancement - P4)

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bridgekeeper bot commented May 22, 2025

👋 Welcome back roland! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

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@rwestrel This change is no longer ready for integration - check the PR body for details.

@openjdk openjdk bot added the rfr Pull request is ready for review label May 22, 2025
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@rwestrel The following label will be automatically applied to this pull request:

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When this pull request is ready to be reviewed, an "RFR" email will be sent to the corresponding mailing list. If you would like to change these labels, use the /label pull request command.

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TobiHartmann
TobiHartmann approved these changes May 23, 2025
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That looks good to me but given that we had quite a few bugs in that area in the past, I would suggest to only integrate into JDK 26 after the fork on June 05, 2025.

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chhagedorn
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Otherwise, looks reasonable to me, too.

src/hotspot/share/opto/loopopts.cpp
@@ -1685,7 +1689,8 @@ void PhaseIdealLoop::try_sink_out_of_loop(Node* n) {
!n->is_OpaqueNotNull() &&
!n->is_OpaqueInitializedAssertionPredicate() &&
!n->is_OpaqueTemplateAssertionPredicate() &&
!n->is_Type()) {
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I cannot remember exactly, how often was it a problem without JDK-8349479? If it was more common, we might want to only allow it when KillPathsReachableByDeadTypeNode is set.

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I made that change.
As far as I remember, the logic removed by JDK-8319372 played a key role in those failures. Not sure if any were still reproducible after than one.

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Yes, that matches what I remember. Maybe JDK-8319372 can now be reverted with JDK-8349479 in?

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That looks good to me but given that we had quite a few bugs in that area in the past, I would suggest to only integrate into JDK 26 after the fork on June 05, 2025.

Sounds reasonable to me.

@openjdk openjdk bot removed the ready Pull request is ready to be integrated label May 26, 2025
chhagedorn
chhagedorn approved these changes May 26, 2025
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src/hotspot/share/opto/loopopts.cpp
@@ -1685,7 +1689,8 @@ void PhaseIdealLoop::try_sink_out_of_loop(Node* n) {
!n->is_OpaqueNotNull() &&
!n->is_OpaqueInitializedAssertionPredicate() &&
!n->is_OpaqueTemplateAssertionPredicate() &&
!n->is_Type()) {
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Yes, that matches what I remember. Maybe JDK-8319372 can now be reverted with JDK-8349479 in?

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Maybe JDK-8319372 can now be reverted with JDK-8349479 in?

I think it would be safe but I'm unclear if it's worth doing or not.

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I'm not sure either, we would not to further investigate if we can find cases that benefit from it. Should we file an RFE either way?

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rwestrel commented Jun 3, 2025

I'm not sure either, we would not to further investigate if we can find cases that benefit from it. Should we file an RFE either way?

I filed: https://bugs.openjdk.org/browse/JDK-8358501

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@TobiHartmann TobiHartmann TobiHartmann approved these changes

@chhagedorn chhagedorn chhagedorn approved these changes

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