8376421: C2: Missing branch on SubTypeCheck node

[iwanowww]

SubTypeCheck relies on custom logic to detect when the operation is redundant during GVN while subsequent CheckCastPP on instanceof success branch (introduced by JDK-8372634) uses C2 type system.

It turns out the latter is superior and the bug demonstrates one case when C2 proves that receiver type after the check is empty while Compile::static_subtype_check() doesn't report corresponding SubTypeCheck as redundant. It leaves the branch im corrupted state with a single control projection.

Proposed fix piggybacks on control pruning for dead type nodes introduced by JDK-8349479. It keeps the redundant runtime check, but places a Halt node on pruned branch thus preserving CFG correctness.

I filed an RFE (JDK-8381646) to improve the analysis performed by SubTypeCheck node during GVN.

Testing: hs-tier1 - hs-tier5

Thanks!

---

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Issue

• JDK-8376421: C2: Missing branch on SubTypeCheck node (Bug - P3)

Reviewers

• Vladimir Kozlov (@vnkozlov - Reviewer)

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

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8376421: C2: Missing branch on SubTypeCheck node

Reviewed-by: kvn

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At the time when this comment was updated there had been 29 new commits pushed to the master branch:

• f21e47d: 8381549: GenShen: Global collections skip coalesce and fill when the collection set is empty
• a333111: 8380291: AOT cache should store only unregistered classes with file: code source
• e254526: 8380958: GenShen: Regulator thread may observe inconsistent old generation state
• ... and 26 more: https://git.openjdk.org/jdk/compare/d2c1907349afcbc40b2626060960511e2dca01d4...master

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[vnkozlov]

Looks reasonable.