8293996: C2: fix and simplify IdealLoopTree::do_remove_empty_loop

[GoeLin]

I backport this for parity with 17.0.7-oracle.

---

Progress

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Issue

• JDK-8293996: C2: fix and simplify IdealLoopTree::do_remove_empty_loop

Reviewing

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Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk17u-dev pull/998/head:pull/998
$ git checkout pull/998

Update a local copy of the PR:
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$ git pull https://git.openjdk.org/jdk17u-dev pull/998/head

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$ git pr checkout 998

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[bridgekeeper]

👋 Welcome back goetz! 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.

[openjdk]

This backport pull request has now been updated with issue from the original commit.

[openjdk]

@GoeLin 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:

8293996: C2: fix and simplify IdealLoopTree::do_remove_empty_loop

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[mlbridge]

Webrevs

• 00: Full (f34e0b97)

[GoeLin]

/integrate

[openjdk]

Going to push as commit 43668f9.
Since your change was applied there have been 14 commits pushed to the master branch:

• 330105c: 8292602: ZGC: C2 late barrier analysis uses invalid dominator information
• 4be52ee: 8292297: Fix up loading of override java.security properties file
• 475ca04: 8281122: [IR Framework] Cleanup IR matching code in preparation for JDK-8280378
• d667e32: 8280889: java/lang/instrument/GetObjectSizeIntrinsicsTest.java fails with -XX:-UseCompressedOops
• 587d5c5: 8280166: Extend java/lang/instrument/GetObjectSizeIntrinsicsTest.java test cases
• 410fa44: 8258512: serviceability/sa/TestJmapCore.java timed out on macOS 10.13.6
• eb76fa3: 8270156: Add "randomness" and "stress" keys to JTreg tests which use StressGCM, StressLCM and/or StressIGVN
• cfb3a3c: 8235297: sun/security/ssl/SSLSessionImpl/ResumptionUpdateBoundValues.java fails intermittent
• 5976752: 8298093: improve cleanup and error handling of awt_parseColorModel in awt_parseImage.c
• 82790b0: 8295724: VirtualMachineError: Out of space in CodeCache for method handle intrinsic
• ... and 4 more: https://git.openjdk.org/jdk17u-dev/compare/6042c6b9bbacbff1bd47f087f0f19646a20eef97...master

Your commit was automatically rebased without conflicts.

[openjdk]

@GoeLin Pushed as commit 43668f9.

💡 You may see a message that your pull request was closed with unmerged commits. This can be safely ignored.