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[release/11.0-rc1] Fix transition from monomorphic to polymorphic VSD - #132622
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akoeplinger merged 1 commit intoAug 21, 2026
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An interface call site initially uses a dispatch stub specialized for one receiver type. After enough misses, the site should be backpatched to a resolve stub to handle polymorphic receivers. On ARM, ARM64, LoongArch64, and RISC-V64, the expired-counter path set `SDF_ResolveBackPatch` but then probed the inline resolve cache. A cache hit there branched directly to the target without processing the flag, leaving the site monomorphic and causing subsequent receiver-type misses to continue through the dispatch stub. Enter the slow resolve path after setting `SDF_ResolveBackPatch` so the call site is backpatched as intended. Also correct the inverted miss-counter handling on LoongArch64 and RISC-V64. This matches the existing x64 behavior. --------- Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> Copilot-Session: 6bd43e03-841f-47ee-80f4-4da985b32a67
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Tagging subscribers to this area: @agocke |
AndyAyersMS
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Aug 21, 2026
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@jkotas PTAL |
jkotas
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Aug 21, 2026
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Backport of #132544 to release/11.0-rc1
/cc @AndyAyersMS
Customer Impact
Perf issue on arm64 on many core machines.
Regression
Arm64 VSD implementation has diverged from x64 for a long time, and was able to get trapped in a continually mispredicting mode. The shared misprediction counter writes were causing a high amount of cache coherence overhead, seriously limiting scaling.
Testing
Verified with user app on 32 core Arm64 HW.
Risk
Low. Arm64 (and other arches) now use exact same logic as x64.