8264958: C2 compilation fails with assert "n is later than its clone"

[rwestrel]

JDK-8229483 added logic to hoist a load that would wrongly end up in
an outer strip mined loop. That logic checks that it's legal to do so
with:

is_dominator(n_ctrl, x_head)

but that test passes for n_ctrl == x_head when it's not legal to hoist
the load i.e. the test we want is for strict domination. The fix I
propose is to add an explicit check for that case.

---

Progress

• Change must not contain extraneous whitespace
• Commit message must refer to an issue
• Change must be properly reviewed

Issue

• JDK-8264958: C2 compilation fails with assert "n is later than its clone"

Reviewers

• Nils Eliasson (@neliasso - Reviewer)
• Tobias Hartmann (@TobiHartmann - Reviewer)

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.java.net/jdk pull/3539/head:pull/3539
$ git checkout pull/3539

Update a local copy of the PR:
$ git checkout pull/3539
$ git pull https://git.openjdk.java.net/jdk pull/3539/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 3539

View PR using the GUI difftool:
$ git pr show -t 3539

Using diff file

Download this PR as a diff file:
https://git.openjdk.java.net/jdk/pull/3539.diff

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[mlbridge]

Webrevs

• 00: Full (0532d32b)

[neliasso]

Looks good!

[openjdk]

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

ℹ️ This project also has non-automated pre-integration requirements. Please see the file CONTRIBUTING.md for details.

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

8264958: C2 compilation fails with assert "n is later than its clone"

Reviewed-by: neliasso, thartmann

You can use pull request commands such as /summary, /contributor and /issue to adjust it as needed.

At the time when this comment was updated there had been 13 new commits pushed to the master branch:

• 1d66a15: 8265330: G1: Fix comment in G1FullGCPrepareTask::G1CalculatePointersClosure
• b4ba74e: 8264987: G1: Fill BOTs for Survivor-turned-to-Old regions in full gc
• fc89fe6: 8265119: G1: update_remset_before_rebuild mixes liveness in words with liveness in bytes
• 50f3da8: 8264480: Unreachable code in nmethod.cpp inside #ifdef DEBUG
• e0151a6: 8264104: Eliminate unnecessary vector mask conversion during VectorUnbox for floating point VectorMask
• 64e2130: 8262108: SimpleDateFormat formatting broken for sq_MK Locale
• 3423f3e: 8265180: JvmtiCompiledMethodLoadEvent should include the stub section of nmethods
• f6e54f2: 8258794: Support for CLDR version 39
• e89fd15: 8261301: StringWriter.flush() is NOOP but documentation does not indicate it
• 0b1b5c8: 8264373: javac hangs when annotation is declared with sealed public modifier
• ... and 3 more: https://git.openjdk.java.net/jdk/compare/e43aee58e176d43dbec90271c6249c0771de0ef5...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.

➡️ To integrate this PR with the above commit message to the master branch, type /integrate in a new comment.

[TobiHartmann]

Looks good to me.

[rwestrel]

@neliasso @TobiHartmann thanks for the reviews

[rwestrel]

/integrate

[openjdk]

@rwestrel Since your change was applied there have been 13 commits pushed to the master branch:

• 1d66a15: 8265330: G1: Fix comment in G1FullGCPrepareTask::G1CalculatePointersClosure
• b4ba74e: 8264987: G1: Fill BOTs for Survivor-turned-to-Old regions in full gc
• fc89fe6: 8265119: G1: update_remset_before_rebuild mixes liveness in words with liveness in bytes
• 50f3da8: 8264480: Unreachable code in nmethod.cpp inside #ifdef DEBUG
• e0151a6: 8264104: Eliminate unnecessary vector mask conversion during VectorUnbox for floating point VectorMask
• 64e2130: 8262108: SimpleDateFormat formatting broken for sq_MK Locale
• 3423f3e: 8265180: JvmtiCompiledMethodLoadEvent should include the stub section of nmethods
• f6e54f2: 8258794: Support for CLDR version 39
• e89fd15: 8261301: StringWriter.flush() is NOOP but documentation does not indicate it
• 0b1b5c8: 8264373: javac hangs when annotation is declared with sealed public modifier
• ... and 3 more: https://git.openjdk.java.net/jdk/compare/e43aee58e176d43dbec90271c6249c0771de0ef5...master

Your commit was automatically rebased without conflicts.

Pushed as commit 7137328.

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