ZUntaggedIndex error during binary emit

[dsyme]

Occasionally when submitting PRs we get the error described here: #6415 (comment)

The FSC compiler from the .NET SDK using the bootstrap is hitting a bug on Linux and macOS as of commit #97d7a02:

    13>FSC : error FS2014: A problem occurred writing the binary '/Users/vsts/agent/2.149.2/work/1/s/fcs/../artifacts/obj/fcs/net461/FSharp.Compiler.Service.dll': EmitZUntaggedIndex: too big for small address or simple index [/Users/vsts/agent/2.149.2/work/1/s/fcs/FSharp.Compiler.Service/FSharp.Compiler.Service.fsproj]

This bug has cropped up now and then. The current compiler code has some extra instrumentation for this error to help us diagnose it, but compiling using the exact commit above might help us understand it too

[dsyme]

Note to self:

• looking at the failing CI, the F# compiler in the .NET SDK 2.2.1.05 (commit 5e9c7ca in this repository, built into visualfsharp2) appears to fail when used to compile commit 97d7a02 in this repository

• args.txt for this compile is https://gist.github.com/dsyme/749e4ccc05402f6f25b7f80b58432ffd

• confirmed this fails when using ..\..\..\visualfsharp2\release\net40\bin\fsc.exe @args.txt

• confirmed this fails when using ..\..\..\visualfsharp2\debug\net40\bin\fsc.exe @args.txt

• idx is 65536, big is false, hence the assert

• t is 17, RowElementTags.SimpleIndexMin is 7, so metadata table is Method

• sortedTables[6].Length is 65535. Why are we indexing outside this table?