8332369: C2: assert(false) failed: graph should be schedulable after JDK-8324517

[rwestrel]

The issue occurs when a Mod node is processed during final_graph_reshaping: if a Div node is found with the same inputs, the Mod is replaced either by a DivMod node or a subgraph that has the Div node as input. Finding the Div node is done find_similar() which ignores the precedence edges. What happens is that the Div node returned by find_similar() could have a precedence edge that pins it at a control that doesn't dominate the control of some of the uses of the Mod node.

The fix I propose is to simply not perfom the transformation if one of the nodes has precedence edges (which should be a rare corner case).

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Issue

• JDK-8332369: C2: assert(false) failed: graph should be schedulable after JDK-8324517 (Bug - P2)

Reviewers

• Christian Hagedorn (@chhagedorn - Reviewer)

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8332369: C2: assert(false) failed: graph should be schedulable after JDK-8324517

Reviewed-by: chagedorn, thartmann

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At the time when this comment was updated there had been 69 new commits pushed to the master branch:

• 90758f6735620776fcb60da9e0e2c91a4f53aaf1: 8332808: Always set java.io.tmpdir to a suitable value in the build
• e19a421c30534566ba0dea0fa84f812ebeecfc87: 8332720: ubsan: instanceKlass.cpp:3550:76: runtime error: member call on null pointer of type 'struct Array'
• 2581935b47afaf661a94c8a8e50ce08065d632f6: 8332528: Generate code in SwitchBootstraps.generateTypeSwitch that require fewer adaptations
• b890336e111ea8473ae49e9992bc2fd61e716792: 8328083: degrade virtual thread support for GetObjectMonitorUsage
• 4e6d851f3f061b4a9c2b5d2e3fba6a0277ac1f34: 8325324: Implement JEP 477: Implicitly Declared Classes and Instance Main Methods (Third Preview)
• 612ae9289a130b8701f74253fe5499358a2e2b5b: 8332735: [JVMCI] Add extra JVMCI events for exception translation
• 1ea76d338b99900089277b7a2da82c24382a6ce1: 8332675: test/hotspot/jtreg/gc/testlibrary/Helpers.java compileClass javadoc does not match after 8321812
• 94af3c23ea09ef2869cdc666d8170a655a0b3602: 8329203: Parallel: Investigate Mark-Compact for Full GC to decrease memory usage
• 1e5a2780d9cc8e73ce65bdccb98c1808aadd0784: 8332676: Remove unused BarrierSetAssembler::incr_allocated_bytes
• c2180d141ccca0e396ee9a0cd3044c4428b963d5: 8315767: InetAddress: constructing objects from BSD literal addresses
• ... and 59 more: https://git.openjdk.org/jdk/compare/ae999eae7e61072ad964a43f622fa930ce1179f7...master

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