[release/11.0] Remove RCPC2 from the optimistic set on arm64 - #133701
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Testing on android (dotnet/android#12722) showed that older devices don't have rcpc2 instruction set available which leads to significant r2r code rejection. This is a simpler, cross platform fix for the issue, compared to exposing knobs to tweak the optimistic set (#133514) and have dotnet/android use them. --------- Co-authored-by: Jan Kotas <jkotas@microsoft.com>
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BrzVlad
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Backport of #133576 to release/11.0
/cc @BrzVlad
Customer Impact
When this instruction set is included in the optimistic set, a significant amount of methods from ready to run are rejected on older devices (just a few years old), which leads to startup slowdown by around 10% on android. On Android, CoreCLR is already slightly behind Mono on startup, so this can give us a much needed boost on a significant amount of devices.
Regression
The fix itself is not for a regression, but users can experience worse perf without this fix, compared to previous mono based .net android.
Testing
Impact of removing this instruction set from the optimistic set was tested on multiple devices, with more detailed information available in dotnet/android#12722
Risk
Low. This simply removes a fairly new instruction set from the optimistic set on r2r.