8265784: [C2] Hoisting of DecodeN leaves MachTemp inputs behind

[TheRealMDoerr]

PPC64 and s390 have DecodeN implementations which use a MachTemp input. When LCM hoists the DecodeN, the MachTemp nodes reside in the old block, but should get hoisted together with the DecodeN node.
Same is true for load Base input which exists on s390 for example. Unfortunately, that's just a platform specific MachNode which is not nicely recognizable in LCM.

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Issue

• JDK-8265784: [C2] Hoisting of DecodeN leaves MachTemp inputs behind

Reviewers

• Vladimir Kozlov (@vnkozlov - Reviewer) ⚠️ Review applies to 86a4a6a
• Goetz Lindenmaier (@GoeLin - Reviewer)

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[GoeLin]

Hi Martin,
I think the loop must go before the block->add_inst(val); .
Else you get a cycle within the block.
The MachTemp must be before the node that uses them in the list.
Best regards,
Goetz.

[mlbridge]

Webrevs

• 01: Full - Incremental (0c893cd4)
• 00: Full (86a4a6a8)

[vnkozlov]

Moving additional TEMP and CONST? input edges to the same block is correct.
Is base always constant (like CompressedOops::base())? Otherwise you may need add anti dependences for load.
Can you show where MachTemp edges are added for DecodeN?

[TheRealMDoerr]

Hi Vladimir, thanks for reviewing my PR.
Yes, base is an immediate constant (CompressedOops::base()). It's not a load from memory.
MachTemp nodes are added and connected by ADLC generated code (ArchDesc::defineExpand). PPC64 and s390 code contains "expand" and "postalloc_expand" rules. E.g. decodeN_Ex in ppc64.ad uses a register with TEMP effect.

[vnkozlov]

Good.

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@TheRealMDoerr 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:

8265784: [C2] Hoisting of DecodeN leaves MachTemp inputs behind

Reviewed-by: kvn, goetz

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At the time when this comment was updated there had been 187 new commits pushed to the master branch:

• 194bcec: 8265984: Concurrent GC: Some tests fail "assert(is_frame_safe(f)) failed: Frame must be safe"
• 1d9ea3a: 8266083: Shenandoah: Consolidate dedup/no dedup oop closures
• 80941f4: 8234446: Post-CMS workgroup hierarchy cleanup
• ac760c7: 8266295: Remove unused _concurrent_iteration_safe_limit
• b42d496: 8266388: C2: Improve constant ShiftCntV on x86
• 05cfac9: 8266412: Remove redundant TemplateInterpreter entries
• c5dc657: 8266056: runtime/stringtable/StringTableCleaningTest.java failed with "RuntimeException: Missing Callback in [10, 11]"
• 8fa50eb: 8263363: Minor cleanup of Lanai code - unused code removal and comments correction
• 7e30130: 8266401: mark hotspot compiler/intrinsics/sha/cli tests which ignore VM flags
• dedddd5: 8266248: Compilation failure in PLATFORM_API_MacOSX_MidiUtils.c with Xcode 12.5
• ... and 177 more: https://git.openjdk.java.net/jdk/compare/b930bb1a2cb56fc9642f07e9688b6f358bfd1532...master

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[GoeLin]

Hi,
I think temp must go into a block that dominates both, tempb and block.
Do you know block always dominates tempb (after the if?)
Then you could add assert(block->dominates(tempb), "find legal posittion")
Best regards,
Goetz.

[GoeLin]

LGTM

[TheRealMDoerr]

Hi Götz, thanks for reviewing!
Yes, block must always dominate tempb after the if. Otherwise, the placement would be illegal.
It's known that val (DecodeNNode) is movable to block at this place. So its inputs must be live along the same path.
I've added a sanity check.

[TheRealMDoerr]

Thanks for the reviews! I'll integrate it tomorrow if everything's fine.

[TheRealMDoerr]

/integrate

[openjdk]

@TheRealMDoerr Since your change was applied there have been 197 commits pushed to the master branch:

• ce1bc9d: 8266432: ZGC: GC allocation stalls can trigger deadlocks
• 30ccd80: 8264950: Set opaque for JTooltip in config file of NimbusLookAndFeel
• cfdf4a7: 8266449: cleanup jtreg tags in compiler/intrinsics/sha/cli tests
• 3544a9d: 8266391: Replace use of reflection in jdk.internal.platform.Metrics
• 020236c: 8264786: [macos] All Swing/AWT apps cause Allow Notifications prompt to appear when app is launched
• 45760d4: 8266320: (bf) ReadOnlyBufferException in heap buffer put(String,int,int) should not be conditional
• ff65920: 8265491: Math Signum optimization for x86
• 55cc0af: 8266185: Shenandoah: Fix incorrect comment/assertion messages
• 880c138: 8265349: vmTestbase/../stress/compiler/deoptimize/Test.java fails with OOME due to CodeCache exhaustion.
• 001c514: 8265322: C2: Simplify control inputs for BarrierSetC2::obj_allocate
• ... and 187 more: https://git.openjdk.java.net/jdk/compare/b930bb1a2cb56fc9642f07e9688b6f358bfd1532...master

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