PGO work planned for .NET 8

[jakobbotsch]

This issue captures the planned work for .NET 8. This list is expected to change throughout the release cycle according to ongoing planning and discussions, with possible additions and subtractions to the scope. Note that we have not finished .NET 8 planning so most items are only under consideration.

Completed in .NET 8

• PGO: Add new tiers #70941
• JIT: build pred lists early, persist them throughout compilation #80193
  • JIT: maintain pred lists during loop unrolling #80625
  • JIT: fix remaining phases that were rebuilding pred edges #80769
  • JIT: update bbNums before inverting loops #80827
  • JIT: build pred lists before the eh opt phases #80856
  • JIT: build pred lists before object allocation phase #80891
  • JIT: have inliner use fgSplitBlockAfterStatement #80928
  • JIT: reset max bbnum after failed inline attempt #80958
  • JIT: build pred lists before inlining #81000
  • JIT: build pred lists before patchpoint expansion #81196
  • JIT: update fgReplaceJumpTarget to maintain pred lists #81246
  • JIT: build pred lists before instrumentation #81288
  • JIT: build pred lists first #81448
  • JIT: build pred lists when we first build the flow graph #81524
  • JIT: remove cheap preds #81562
  • JIT: fix issue with partial comp pred list maintenance #81605
• JIT: initial implementation of profile synthesis #82926
• JIT: add concept of edge likelihood #81738
• Look into tradeoffs in profile accuracy -- run TE benchmarks with the new Interlocked profiling mode and see if it helps steady state perf.
• JIT: resolve issues with OSR and PGO #47942
• Fix interaction of PGO and partial compilation #66101
• Enhance delegate GDV: Loop cloning support
• Reduce performance overhead of Tier0 instrumentation
• JIT: rename flowList to FlowEdge and encapsulate all fields #81621

Opportunistic for .NET 8

• Enhance delegate GDV
  • Instance methods on value types (delegates pointing to unboxing stubs)
  • Static methods (delegates pointing to shuffle thunks)
  • R2R support
• Profile Synthesis Work Items #82964
• JIT: refactor edge weight representation #46885
• JIT: use normalized counts throughout #46883
• Profile Maintenance. See below for more on the overall approach and because of the larger than expected amount of inconsistencies in profile data, the revised plan.
  • JIT: PGO: fgOptimizeUncondBranchToSimpleCond corrupts profile data #50419
  • [JIT][PGO] Incorrect weights produced by expand-casts optimizations #50030
  • optOptimizeLayout introducing edge profile inconsistencies #48476
  • JIT: fgReorderBlocks does nonsensical things #53636
• JIT: use normalized counts throughout #46883
• Array interface method devirtualization #62457 (too many missing pieces)
• PGO considerations for finally cloning #48925
• Enhance GDV-like capability for indirect calls (optimization of indirect calls #44610)
• JIT: optimize redundant type tests created by PGO #46887 (needs SSA update)
• JIT: optimize redundant type tests created by PGO #46887
• RyuJIT: Allow developers to provide Branch Prediction Information #6225

Deferred

• JIT: annotate pseudo-edges in pgo schema and/or internal model #81638

category:planning
theme:profile-feedback
skill-level:expert
cost:large
impact:large

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Issue Details

---

This issue captures the planned work for .NET 8. This list is expected to change throughout the release cycle according to ongoing planning and discussions, with possible additions and subtractions to the scope. Note that we have not finished .NET 8 planning so most items are only under consideration.

Planned for .NET 8

• (EgorBo in PR) PGO: Add new tiers #70941

Under Consideration

• Array interface method devirtualization #62457 (too many missing pieces)
• Fix issues in profile maintenance: JIT: PGO: fgOptimizeUncondBranchToSimpleCond corrupts profile data #50419, [JIT][PGO] Incorrect weights produced by expand-casts optimizations #50030, optOptimizeLayout introducing edge profile inconsistencies #48476
• PGO considerations for finally cloning #48925
• JIT: refactor edge weight representation #46885
• JIT: use normalized counts throughout #46883
• Reduce performance overhead of Tier0 instrumentation
• Enhance GDV-like capability for indirect calls (optimization of indirect calls #44610)
• JIT: optimize redundant type tests created by PGO #46887 (needs SSA update)
• Enhance delegate GDV
  • Instance methods on value types (delegates pointing to unboxing stubs)
  • Static methods (delegates pointing to shuffle thunks)
  • R2R support
  • Loop cloning support

Author:	jakobbotsch
Assignees:	-
Labels:	area-CodeGen-coreclr, untriaged
Milestone:	-

[jakobbotsch]

cc @dotnet/jit-contrib

[EgorBo]

I'd add context-sensitive instrumentation, I do think it should be beneficial

[jakobbotsch]

@EgorBo feel free to edit the issue with anything you can think of 🙂