Address StackOverflowExceptions in typechecking #17654
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❗ Release notes required
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T-Gro
changed the title
…ting it in IL .filter is used
…/dotnet/fsharp into patch-netframework-stackoverflow
T-Gro
changed the title
edgarfgp
reviewed
Sep 5, 2024
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| | SynModuleDecl.Expr _ -> failwith "unreachable: SynModuleDecl.Expr - ElimSynModuleDeclExpr" | ||
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| | SynModuleDecl.NamespaceFragment _ as d -> error(Error(FSComp.SR.tcUnsupportedMutRecDecl(), d.Range))) |
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Is it possible to use errorR here too ?
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TBH this was just a code block moved, I did not touch it nor investigate it.
…er bug big being fixed in the meantime.
vzarytovskii
approved these changes
Sep 6, 2024
This was referenced Sep 11, 2024
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There have been two detected scenarios of System.StackoverFlowException crashing the IDE.
First was happening during typecheck, at TcModuleOrNamespaceElementNonMutRec (non recursive module/ns).
This is addressed by adding specific StackGuard calls integrated with the cancellable CE.
The second only happened in series of edits, which was eventually drilled down to be a consequence of System.OperationCanceledException triggered by the ID (new keystrokes invalidated previous requests for diagnostics).
It turned out that recursive calls into TcExpr were fitting into the stack (and they are wrapped in StackGuard as well), but when unrolling an exception, CLR has an overhead of roughly 10K for every catch+handler+rethrow.
The way the codegen for
try .. with | SomeActivePatternOnException -> ..works lead to always hitting the catch handler, and rethrowing in the scenario of the active pattern not matching.Which was happening every single frame with a catch handler, repeating this across 50-100 calls into TcExpr.
The change is to replace the IL generated
.try ... catchwith an.try ... filter ... catchin scenarios with either an active pattern or a when guard. With the filter IL block, the catch handler is invoked only if the filter passes.The reproducible StackOverflow was added as a test, and the same test is recompiled with different compiler switch to demonstrate it no longer stack overflows.