[release/7.0-rc1] Don't track current field of state machines #74216
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MichalStrehovsky
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Aug 19, 2022
jeffschwMSFT
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Aug 19, 2022
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Backport of #74111 to release/7.0-rc1
/cc @MichalStrehovsky
Customer Impact
If customer code has many
yield returnstatements and the method also requires reflection dataflow analysis, the compiler would take a long time to analyze the method. This would look like a hang that is hard to troubleshoot (it can increase compilation times by tens of minutes). These hangs could be a support cost because they're not easy to root cause (no obvious crash with a printed stack trace that can be cheaply bucketed, etc.).Testing
We found this in one of the libraries tests. The test now compiles in a reasonable amount of time. The change also passes all NativeAOT testing and all IL Linker unit tests (this issue was in a shared codebase with IL Linker and we made the fix there first).
Risk
The issue is in analysis of compiler-generated state machine that is a new feature in .NET 7. We have unit tests for the core scenarios and they all pass.