8279886: C1: Turn off SelectivePhiFunctions in presence of irreducible loops

[veresov]

This change add irreducible loops detection to BlockListBuilder::mark_loops() - a loop marking routine necessary for the SSA conversion. Here is brief description of the algorithm (copy-pasted from the comments I left in the code).

The loop detection algorithm works as follows:

• We maintain the _loop_map, where for each block we have a bitmap indicating which loops contain this block.
• The CFG is recursively traversed (depth-first) and if we detect a loop, we assign the loop a unique number that is stored in the bitmap associated with the loop header block. Until we return back through that loop header the bitmap contains only a single bit corresponding to the loop number.
• The bit is then propagated for all the blocks in the loop after we exit them (post-order). There could be multiple bits of course in case of nested loops.
• When we exit the loop header we remove that single bit and assign the real loop state for it.
• Now, the tricky part here is how we detect irriducible loops. In the algorithm above the loop state bits are propagated to the predecessors. If we encounter an irreducible loop (a loop with multiple heads) we would see a node with some loop bit set that would then propagate back and be never cleared because we would never go back through the original loop header. Therefore if there are any irreducible loops the bits in the states for these loops are going to propagate back to the root.

Testing is clean: hs-tier{1-7}

---

Progress

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Issue

• JDK-8279886: C1: Turn off SelectivePhiFunctions in presence of irreducible loops

Reviewers

• Vladimir Kozlov (@vnkozlov - Reviewer)
• Dean Long (@dean-long - Reviewer)

Reviewing

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[mlbridge]

Webrevs

• 01: Full (8daaf312)
• 00: Full (803a83e5)

[vnkozlov]

Looks good.

[openjdk]

@veresov This change now passes all automated pre-integration checks.

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After integration, the commit message for the final commit will be:

8279886: C1: Turn off SelectivePhiFunctions in presence of irreducible loops

Reviewed-by: kvn, dlong

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At the time when this comment was updated there had been 31 new commits pushed to the master branch:

• fb6b929: 8277474: jarsigner does not check if algorithm parameters are disabled
• 1581e3f: 8282402: Create a regression test for JDK-4666101
• 268fa69: 8282511: Use fixed certificate validation date in SSLExampleCert template
• c777bb3: 8282619: G1: Fix indentation in G1CollectedHeap::mark_evac_failure_object
• 080baff: 8282483: Ensure that Utils.getAllInterfaces returns unique instances
• 57020fd: 8282582: Unused methods in Utils
• 5c187e3: 8282593: JDK-8281472 breaks 32-bit builds and gtests
• 7822cbc: 8276711: compiler/codecache/cli tests failing when SegmentedCodeCache used with -Xint
• 832729b: 6911375: mouseWheel has no effect without vertical scrollbar
• 0402a28: 8037965: NullPointerException in TextLayout.getBaselineFromGraphic() for JTextComponents
• ... and 21 more: https://git.openjdk.java.net/jdk/compare/76398c84007862bdf07cea6be792eca50eec9edd...master

As there are no conflicts, your changes will automatically be rebased on top of these commits when integrating. If you prefer to avoid this automatic rebasing, please check the documentation for the /integrate command for further details.

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[dean-long]

Very nice!

[veresov]

Thanks @vnkozlov and @dean-long for the reviews!
/integrate

[openjdk]

Going to push as commit b629782.
Since your change was applied there have been 33 commits pushed to the master branch:

• 7e1c67d: 8282608: RawNativeLibraryImpl can't be passed to NativeLibraries::findEntry0
• 8478173: 8282583: Update BCEL md to include the copyright notice
• fb6b929: 8277474: jarsigner does not check if algorithm parameters are disabled
• 1581e3f: 8282402: Create a regression test for JDK-4666101
• 268fa69: 8282511: Use fixed certificate validation date in SSLExampleCert template
• c777bb3: 8282619: G1: Fix indentation in G1CollectedHeap::mark_evac_failure_object
• 080baff: 8282483: Ensure that Utils.getAllInterfaces returns unique instances
• 57020fd: 8282582: Unused methods in Utils
• 5c187e3: 8282593: JDK-8281472 breaks 32-bit builds and gtests
• 7822cbc: 8276711: compiler/codecache/cli tests failing when SegmentedCodeCache used with -Xint
• ... and 23 more: https://git.openjdk.java.net/jdk/compare/76398c84007862bdf07cea6be792eca50eec9edd...master

Your commit was automatically rebased without conflicts.

[openjdk]

@veresov Pushed as commit b629782.

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