FCS `ParseAndCheckProject` crash with stackoverflow on Mac OS

[enricosada]

FSharp.Compiler.Service ParseAndCheckProject crash with stackoverflow exception during typecheck on Mac OS

The minimized the repro point to """ usage

NOTE FCS v28.0.0 was integrated from visualfsharp master to Integrate visualfsharp master up to 8dfc02feb , but may happen in previous versions too, need to check, there where issues from users also in v27

Repro steps

An example is https://github.com/sjanahan/ionide-crash who crash on latest FSAC (FCS v28.0.0) in vscode+ionide on mac.

The issue is the usage of a big triple quoted """ string like this one

A repro using latest FSharp.Compiler.Service package v28.0.0 as library is in https://github.com/enricosada/fcs-crash/ , who just invoke ParseAndCheckProject on that project

The crash is shown on travis build matrix ( https://travis-ci.org/enricosada/fcs-crash/builds/524417824 ) where succeed on unix and fails on osx

NOTES

• seen the same crash with similar stacktrace running on .NET Framework, but failed to minimize the repro atm, codebase is private
• seen the same crash in Rider and VsCode+Ionide, both in Mac Osx. Win is not affected. Happen 100% of time with private codebase
• dotnet build is ok
• win/unix ok, mac osx fails

ref ionide/FsAutoComplete#356
ref ionide/ionide-vscode-fsharp#1039

Expected behavior

No crash

Actual behavior

Stackoverflow, with a stacktrace like backend-err.log

That stacktrace is from a .NET Version on Rider, who happen in a private codebase. The .NET Core version doesnt show the stacktrace for the SO

The minimal repro doesnt trigger in Rider but does in FSAC (FCS v28.0.0)

Stack overflow in unmanaged: IP: 0x10744b82b, fault addr: 0x7000076f5fb8
Stack overflow: IP: 0x10744b82b, fault addr: 0x7000076ecff8
Stacktrace:
  at <unknown> <0xffffffff>
  at string.CtorCharArrayStartLength (char[],int,int) [0x00061] in <53dca12e92aa4e3387f3b954838dd249>:0
  <...>
  at string.CreateString (char[],int,int) [0x00000] in <53dca12e92aa4e3387f3b954838dd249>:0
  at (wrapper managed-to-managed) string..ctor (char[],int,int) [0x00000] in <53dca12e92aa4e3387f3b954838dd249>:0
  at Internal.Utilities.Text.Lexing.LexBuffer`1<char>.LexemeString (Internal.Utilities.Text.Lexing.LexBuffer`1<char>) [0x00000] in <5b5b17b04d124a0ca7450383b0175b5b>:0
  at Microsoft.FSharp.Compiler.Lexer._fslex_tripleQuoteString (Microsoft.FSharp.Compiler.AbstractIL.Internal.ByteBuffer,Microsoft.FSharp.Core.FSharpFunc`2<Microsoft.FSharp.Compiler.Range/range, Microsoft.FSharp.Core.FSharpFunc`2<bool, Microsoft.FSharp.Core.FSharpFunc`2<byte[], Microsoft.FSharp.Compiler.Parser/token>>>,Microsoft.FSharp.Compiler.Range/range,Microsoft.FSharp.Compiler.Lexhelp/lexargs,bool,int,Internal.Utilities.Text.Lexing.LexBuffer`1<char>) [0x00193] in <5b5b17b04d124a0ca7450383b0175b5b>:0
  at Microsoft.FSharp.Compiler.Lexer.tripleQuoteString (Microsoft.FSharp.Compiler.AbstractIL.Internal.ByteBuffer,Microsoft.FSharp.Core.FSharpFunc`2<Microsoft.FSharp.Compiler.Range/range, Microsoft.FSharp.Core.FSharpFunc`2<bool, Microsoft.FSharp.Core.FSharpFunc`2<byte[], Microsoft.FSharp.Compiler.Parser/token>>>,Microsoft.FSharp.Compiler.Range/range,Microsoft.FSharp.Compiler.Lexhelp/lexargs,bool,Internal.Utilities.Text.Lexing.LexBuffer`1<char>) [0x00000] in <5b5b17b04d124a0ca7450383b0175b5b>:0
  at Microsoft.FSharp.Compiler.Lexer.tripleQuoteString (Microsoft.FSharp.Compiler.AbstractIL.Internal.ByteBuffer,Microsoft.FSharp.Core.FSharpFunc`2<Microsoft.FSharp.Compiler.Range/range, Microsoft.FSharp.Core.FSharpFunc`2<bool, Microsoft.FSharp.Core.FSharpFunc`2<byte[], Microsoft.FSharp.Compiler.Parser/token>>>,Microsoft.FSharp.Compiler.Range/range,Microsoft.FSharp.Compiler.Lexhelp/lexargs,bool,Internal.Utilities.Text.Lexing.LexBuffer`1<char>) [0x00000] in <5b5b17b04d124a0ca7450383b0175b5b>:0
  at Microsoft.FSharp.Compiler.Lexer.tripleQuoteString (Microsoft.FSharp.Compiler.AbstractIL.Internal.ByteBuffer,Microsoft.FSharp.Core.FSharpFunc`2<Microsoft.FSharp.Compiler.Range/range, Microsoft.FSharp.Core.FSharpFunc`2<bool, Microsoft.FSharp.Core.FSharpFunc`2<byte[], Microsoft.FSharp.Compiler.Parser/token>>>,Microsoft.FSharp.Compiler.Range/range,Microsoft.FSharp.Compiler.Lexhelp/lexargs,bool,Internal.Utilities.Text.Lexing.LexBuffer`1<char>) [0x00000] in <5b5b17b04d124a0ca7450383b0175b5b>:0
  at Microsoft.FSharp.Compiler.Lexer.tripleQuoteString (Microsoft.FSharp.Compiler.AbstractIL.Internal.ByteBuffer,Microsoft.FSharp.Core.FSharpFunc`2<Microsoft.FSharp.Compiler.Range/range, Microsoft.FSharp.Core.FSharpFunc`2<bool, Microsoft.FSharp.Core.FSharpFunc`2<byte[], Microsoft.FSharp.Compiler.Parser/token>>>,Microsoft.FSharp.Compiler.Range/range,Microsoft.FSharp.Compiler.Lexhelp/lexargs,bool,Internal.Utilities.Text.Lexing.LexBuffer`1<char>) [0x00000] in <5b5b17b04d124a0ca7450383b0175b5b>:0

...... tons more of at Microsoft.FSharp.Compiler.Lexer.tripleQuoteString

  at Microsoft.FSharp.Compiler.Lexer.tripleQuoteString (Microsoft.FSharp.Compiler.AbstractIL.Internal.ByteBuffer,Microsoft.FSharp.Core.FSharpFunc`2<Microsoft.FSharp.Compiler.Range/range, Microsoft.FSharp.Core.FSharpFunc`2<bool, Microsoft.FSharp.Core.FSharpFunc`2<byte[], Microsoft.FSharp.Compiler.Parser/token>>>,Microsoft.FSharp.Compiler.Range/range,Microsoft.FSharp.Compiler.Lexhelp/lexargs,bool,Internal.Utilities.Text.Lexing.LexBuffer`1<char>) [0x00000] in <5b5b17b04d124a0ca7450383b0175b5b>:0
  at Microsoft.FSharp.Compiler.Lexer.tripleQuoteString (Microsoft.FSharp.Compiler.AbstractIL.Internal.ByteBuffer,Microsoft.FSharp.Core.FSharpFunc`2<Microsoft.FSharp.Compiler.Range/range, Microsoft.FSharp.Core.FSharpFunc`2<bool, Microsoft.FSharp.Core.FSharpFunc`2<byte[], Microsoft.FSharp.Compiler.Parser/token>>>,Microsoft.FSharp.Compiler.Range/range,Microsoft.FSharp.Compiler.Lexhelp/lexargs,bool,Internal.Utilities.Text.Lexing.LexBuffer`1<char>) [0x00000] in <5b5b17b04d124a0ca7450383b0175b5b>:0
  at Microsoft.FSharp.Compiler.Lexer.tripleQuoteString (Microsoft.FSharp.Compiler.AbstractIL.Internal.ByteBuffer,Microsoft.FSharp.Core.FSharpFunc`2<Microsoft.FSharp.Compiler.Range/range, Microsoft.FSharp.Core.FSharpFunc`2<bool, Microsoft.FSharp.Core.FSharpFunc`2<byte[], Microsoft.FSharp.Compiler.Parser/token>>>,Microsoft.FSharp.Compiler.Range/range,Microsoft.FSharp.Compiler.Lexhelp/lexargs,bool,Internal.Utilities.Text.Lexing.LexBuffer`1<char>) [0x00000] in <5b5b17b04d124a0ca7450383b0175b5b>:0
  at Microsoft.FSharp.Compiler.Lexer.tripleQuoteString (Microsoft.FSharp.Compiler.AbstractIL.Internal.ByteBuffer,Microsoft.FSharp.Core.FSharpFunc`2<Microsoft.FSharp.Compiler.Range/range, Microsoft.FSharp.Core.FSharpFunc`2<bool, Microsoft.FSharp.Core.FSharpFunc`2<byte[], Microsoft.FSharp.Compiler.Parser/token>>>,Microsoft.FSharp.Compiler.Range/range,Microsoft.FSharp.Compiler.Lexhelp/lexargs,bool,Internal.Utilities.Text.Lexing.LexBuffer`1<char>) [0x00000] in <5b5b17b04d124a0ca7450383b0175b5b>:0
  at Microsoft.FSharp.Compiler.Lexer.tripleQuoteString (Microsoft.FSharp.Compiler.AbstractIL.Internal.ByteBuffer,Microsoft.FSharp.Core.FSharpFunc`2<Microsoft.FSharp.Compiler.Range/range, Microsoft.FSharp.Core.FSharpFunc`2<bool, Microsoft.FSharp.Core.FSharpFunc`2<byte[], Microsoft.FSharp.Compiler.Parser/token>>>,Microsoft.FSharp.Compiler.Range/range,Microsoft.FSharp.Compiler.Lexhelp/lexargs,bool,Internal.Utilities.Text.Lexing.LexBuffer`1<char>) [0x00000] in <5b5b17b04d124a0ca7450383b0175b5b>:0
  at Microsoft.FSharp.Compiler.LexFilter/LexFilterImpl.runWrappedLexerInConsistentLexbufState () [0x00031] in <5b5b17b04d124a0ca7450383b0175b5b>:0
  at Microsoft.FSharp.Compiler.LexFilter/LexFilterImpl.popNextTokenTup () [0x0001a] in <5b5b17b04d124a0ca7450383b0175b5b>:0
  at Microsoft.FSharp.Compiler.LexFilter/LexFilterImpl.peekNextTokenTup () [0x00000] in <5b5b17b04d124a0ca7450383b0175b5b>:0
  at Microsoft.FSharp.Compiler.LexFilter/LexFilterImpl.pushCtxtSeqBlock (bool,Microsoft.FSharp.Compiler.LexFilter/AddBlockEnd) [0x00000] in <5b5b17b04d124a0ca7450383b0175b5b>:0
  at Microsoft.FSharp.Compiler.LexFilter/LexFilterImpl.hwTokenFetch (bool) [0x0466a] in <5b5b17b04d124a0ca7450383b0175b5b>:0
  at Microsoft.FSharp.Compiler.LexFilter/LexFilterImpl.Lexer<a_REF> (a_REF) [0x00021] in <5b5b17b04d124a0ca7450383b0175b5b>:0
  at Microsoft.FSharp.Compiler.LexFilter/LexFilter.popNextToken () [0x0001a] in <5b5b17b04d124a0ca7450383b0175b5b>:0
  at Microsoft.FSharp.Compiler.LexFilter.loop@2264-37 (Microsoft.FSharp.Compiler.LexFilter/LexFilter,Microsoft.FSharp.Core.Unit) [0x00000] in <5b5b17b04d124a0ca7450383b0175b5b>:0
  at Microsoft.FSharp.Compiler.LexFilter/LexFilter.Lexer<a_REF> (a_REF) [0x00002] in <5b5b17b04d124a0ca7450383b0175b5b>:0
  at Microsoft.FSharp.Compiler.SourceCodeServices.Parser/createLexerFunction@1534<a_REF>.Invoke (a_REF) [0x00000] in <5b5b17b04d124a0ca7450383b0175b5b>:0
  at Internal.Utilities.Text.Parsing.Implementation.interpret<tok_REF> (Internal.Utilities.Text.Parsing.Tables`1<tok_REF>,Microsoft.FSharp.Core.FSharpFunc`2<Internal.Utilities.Text.Lexing.LexBuffer`1<char>, tok_REF>,Internal.Utilities.Text.Lexing.LexBuffer`1<char>,int) [0x0013c] in <5b5b17b04d124a0ca7450383b0175b5b>:0
  at Internal.Utilities.Text.Parsing.Tables`1<tok_REF>.Interpret (Microsoft.FSharp.Core.FSharpFunc`2<Internal.Utilities.Text.Lexing.LexBuffer`1<char>, tok_REF>,Internal.Utilities.Text.Lexing.LexBuffer`1<char>,int) [0x00000] in <5b5b17b04d124a0ca7450383b0175b5b>:0
  at Microsoft.FSharp.Compiler.CompileOps.ParseInput (Microsoft.FSharp.Core.FSharpFunc`2<Internal.Utilities.Text.Lexing.LexBuffer`1<char>, Microsoft.FSharp.Compiler.Parser/token>,Microsoft.FSharp.Compiler.ErrorLogger/ErrorLogger,Internal.Utilities.Text.Lexing.LexBuffer`1<char>,Microsoft.FSharp.Core.FSharpOption`1<string>,string,System.Tuple`2<bool, bool>) [0x00070] in <5b5b17b04d124a0ca7450383b0175b5b>:0
  at Microsoft.FSharp.Compiler.SourceCodeServices.Parser/parseResult@1590.Invoke (Internal.Utilities.Text.Lexing.LexBuffer`1<char>) [0x0006b] in <5b5b17b04d124a0ca7450383b0175b5b>:0
  at Microsoft.FSharp.Compiler.Lexhelp/usingLexbufForParsing@92<a_REF>.Invoke (Microsoft.FSharp.Core.Unit) [0x00000] in <5b5b17b04d124a0ca7450383b0175b5b>:0
  at Microsoft.FSharp.Compiler.Lexhelp.reusingLexbufForParsing<a_REF> (Internal.Utilities.Text.Lexing.LexBuffer`1<char>,Microsoft.FSharp.Core.FSharpFunc`2<Microsoft.FSharp.Core.Unit, a_REF>) [0x00026] in <5b5b17b04d124a0ca7450383b0175b5b>:0
  at Microsoft.FSharp.Compiler.Lexhelp.usingLexbufForParsing<a_REF> (Internal.Utilities.Text.Lexing.LexBuffer`1<char>,string,Microsoft.FSharp.Core.FSharpFunc`2<Internal.Utilities.Text.Lexing.LexBuffer`1<char>, a_REF>) [0x0001a] in <5b5b17b04d124a0ca7450383b0175b5b>:0
  at Microsoft.FSharp.Compiler.SourceCodeServices.Parser.parseFile (string,string,Microsoft.FSharp.Compiler.SourceCodeServices.FSharpParsingOptions,string) [0x00066] in <5b5b17b04d124a0ca7450383b0175b5b>:0
  at <StartupCode$FSharp-Compiler-Service>.$Service/ParseFile@2505.Invoke (Microsoft.FSharp.Core.Unit) [0x0006a] in <5b5b17b04d124a0ca7450383b0175b5b>:0
  at Microsoft.FSharp.Control.AsyncBuilderImpl/callA@522<b_REF, a_REF>.Invoke (Microsoft.FSharp.Control.AsyncParams`1<b_REF>) [0x00051] in <5a7d678a904cf4daa74503838a677d5a>:0
  at Microsoft.FSharp.Control.AsyncBuilderImpl/queueAsync@434<a_REF>.Invoke (Microsoft.FSharp.Core.Unit) [0x00033] in <5a7d678a904cf4daa74503838a677d5a>:0
  at <StartupCode$FSharp-Core>.$Control.loop@124-50 (Microsoft.FSharp.Control.Trampoline,Microsoft.FSharp.Core.FSharpFunc`2<Microsoft.FSharp.Core.Unit, Microsoft.FSharp.Control.FakeUnitValue>) [0x00000] in <5a7d678a904cf4daa74503838a677d5a>:0
  at Microsoft.FSharp.Control.Trampoline.ExecuteAction (Microsoft.FSharp.Core.FSharpFunc`2<Microsoft.FSharp.Core.Unit, Microsoft.FSharp.Control.FakeUnitValue>) [0x00017] in <5a7d678a904cf4daa74503838a677d5a>:0
  at Microsoft.FSharp.Control.TrampolineHolder.Protect (Microsoft.FSharp.Core.FSharpFunc`2<Microsoft.FSharp.Core.Unit, Microsoft.FSharp.Control.FakeUnitValue>) [0x00031] in <5a7d678a904cf4daa74503838a677d5a>:0
  at <StartupCode$FSharp-Core>.$Control/-ctor@200-1.Invoke (object) [0x00017] in <5a7d678a904cf4daa74503838a677d5a>:0
  at System.Threading.QueueUserWorkItemCallback.WaitCallback_Context (object) [0x00007] in <53dca12e92aa4e3387f3b954838dd249>:0
  at System.Threading.ExecutionContext.RunInternal (System.Threading.ExecutionContext,System.Threading.ContextCallback,object,bool) [0x00071] in <53dca12e92aa4e3387f3b954838dd249>:0
  at System.Threading.ExecutionContext.Run (System.Threading.ExecutionContext,System.Threading.ContextCallback,object,bool) [0x00000] in <53dca12e92aa4e3387f3b954838dd249>:0
  at System.Threading.QueueUserWorkItemCallback.System.Threading.IThreadPoolWorkItem.ExecuteWorkItem () [0x00021] in <53dca12e92aa4e3387f3b954838dd249>:0
  at System.Threading.ThreadPoolWorkQueue.Dispatch () [0x00074] in <53dca12e92aa4e3387f3b954838dd249>:0
  at System.Threading._ThreadPoolWaitCallback.PerformWaitCallback () [0x00000] in <53dca12e92aa4e3387f3b954838dd249>:0
  at (wrapper runtime-invoke) <Module>.runtime_invoke_bool (object,intptr,intptr,intptr) [0x0001e] in <53dca12e92aa4e3387f3b954838dd249>:0

The method seems ok to tail call

  .method assembly static class FSharp.Compiler.Parser/token 
    tripleQuoteString(
      class FSharp.Compiler.AbstractIL.Internal.ByteBuffer sargs_0, 
      class [FSharp.Core]Microsoft.FSharp.Core.FSharpFunc`2<valuetype FSharp.Compiler.Range/range, class [FSharp.Core]Microsoft.FSharp.Core.FSharpFunc`2<bool, class [FSharp.Core]Microsoft.FSharp.Core.FSharpFunc`2<unsigned int8[], class FSharp.Compiler.Parser/token>>> sargs_1, 
      valuetype FSharp.Compiler.Range/range sargs_2, 
      class FSharp.Compiler.Lexhelp/lexargs sargs_3, 
      bool skip, 
      class Internal.Utilities.Text.Lexing.LexBuffer`1<char> lexbuf
    ) cil managed 
  {
    .custom instance void [FSharp.Core]Microsoft.FSharp.Core.CompilationArgumentCountsAttribute::.ctor(int32[]) 
      = (
        01 00 03 00 00 00 04 00 00 00 01 00 00 00 01 00 // ................
        00 00 00 00                                     // ....
      )
      // int32[3]
        /*( int32(4) // 0x00000004
         int32(1) // 0x00000001
         int32(1) // 0x00000001
         )*/
    .maxstack 9

    // [1846 7 - 1846 100]
    IL_0000: ldarg.0      // sargs_0
    IL_0001: ldarg.1      // sargs_1
    IL_0002: ldarg.2      // sargs_2
    IL_0003: ldarg.3      // sargs_3
    IL_0004: ldarg.s      skip
    IL_0006: ldc.i4       178 // 0x000000b2
    IL_000b: ldarg.s      lexbuf
    IL_000d: tail.        
    IL_000f: call         class FSharp.Compiler.Parser/token FSharp.Compiler.Lexer::_fslex_tripleQuoteString(class FSharp.Compiler.AbstractIL.Internal.ByteBuffer, class [FSharp.Core]Microsoft.FSharp.Core.FSharpFunc`2<valuetype FSharp.Compiler.Range/range, class [FSharp.Core]Microsoft.FSharp.Core.FSharpFunc`2<bool, class [FSharp.Core]Microsoft.FSharp.Core.FSharpFunc`2<unsigned int8[], class FSharp.Compiler.Parser/token>>>, valuetype FSharp.Compiler.Range/range, class FSharp.Compiler.Lexhelp/lexargs, bool, int32, class Internal.Utilities.Text.Lexing.LexBuffer`1<char>)
    IL_0014: ret          

  } // end of method Lexer::tripleQuoteString

Known workarounds

None

Related information

Happen in mac osx only, in this repro does happen in .NET Core Runtime, but seen the same in .NET Framework Runtime too with private codebase

in the repro is using .NET Core v2.1.401 but newer version fails too.

[enricosada]

/cc @sjanahan @Krzysztof-Cieslak @baronfel @alfonsogarciacaro

@auduchinok happen in latest Rider too, but not yet minimized private codebase, do you have seen something similar?

@dustinmoris maybe is similar to your issue, can you repro with that project?

[alfonsogarciacaro]

SO exceptions are a party with FCS on mac since the first netcore versions. There's obviously a problem with tail calls in netcore runtime on macos. That's what should be fixed instead of pinpointing all the issues as they appear :/

[enricosada]

@alfonsogarciacaro i got the same error on Rider who afaik use mono, so it not just on .NET Core, maybe there is more visibile (stack deep smaller?)

Maybe that code shouldnt use recursion+tail at all? to fix the root issue F# side.

Meanwhile i'll open an issue in https://github.com/dotnet/coreclr to ask for guidance about that, if it's expected or can be mitigated somehow or is a bug who need to be fixed.

[auduchinok]

@enricosada in Rider we currently use Mono on Mac and Linux and .NET Framework on Windows.

@auduchinok happen in latest Rider too, but not yet minimized private codebase, do you have seen something similar?

We've seen it on a particular bigger file with a similar stacktrace, issues are: mono/mono#11933 and JetBrains/resharper-fsharp#23, but this particular exception seems to be fixed.

[enricosada]

added https://github.com/dotnet/coreclr/issues/24249 in coreclr to ask about tail calls.

Closed as duplicated of https://github.com/dotnet/coreclr/issues/2556 but https://github.com/dotnet/coreclr/issues/24249#issuecomment-486722733 contains useful info

[cartermp]

Another thing worth considering is that the processing of very large literals has been a source of stack overflows and has recently been fixed: #6258

The actual fix isn't released in anything other than a VS preview right now, but eventually FCS can update and it's worth seeing if the problem still persists. Just want to rule out anything we know here before we dive into CoreCLR issues.

[baronfel]

@cartermp the fslex and large-expression updates are in FCS 28, which is merged up to commit 8dfc02f in this repository (ie 28 days ago).

[baronfel]

@enricosada COMPlus_DefaultStackSize=180000 could be a reasonable quick-fix for ionide, if we added a set of settings for environment-variables to use when spawning FSAC. I tried it with my stack-overflowing work project and things work great.

my steps (macos):

• export COMPlus_DefaultStackSize=180000 in a shell, so that child processes will inherit that value
• navigated to my work project
• code . to spawn vscode
• changed FSharp.fsacRuntime from net to netcore
• reloaded
• and it's been ~10m now with no stackoverflows, where before it would happen within 30s.

[cartermp]

@baronfel Is this one as well? #6294

[baronfel]

Yes. Everything from March 28th and back is in FCS 28.

[enricosada]

@baronfel good workaround, but it depends on stacktrace deep anyway.

As a note, this https://github.com/sjanahan/rider-crash-reproducer/ is a repro with Rider on mono, we cannot apply same workaround of .net core, and will crash anyway on fsac .net

[sjanahan]

@enricosada I've opened a ticket with JetBrains about the crash in Rider

Please let me know how if there's anything else I can do to help get this resolved. Thanks!

[dustinmoris]

I will try this repo a little bit later as I'm on a train right now, but I just want to add that the StackOverflowException which I am getting on macOS with .NET Core in Ionide is/must be a regression, because it only started happening after upgrading to Ionide 3.34.0 and above. When I revert Ionide back to 3.33.0 then everything works. So it might be worth checking what has changed in the dependencies which Ionide relies on between those two versions.

[enricosada]

@dsyme @KevinRansom usually how these kind of issues are fixed?
rewriting the code without recursion?

Dunno if feasible, but adding a new warning if recursion doesnt satify @jkotas rules on the comment https://github.com/dotnet/coreclr/issues/2556#issuecomment-169755535 may make FCS/fsc safer

The simple rule that should hold across platforms over time is that the fast tailcall will be used if both of the following are true:

• Return value and call target arguments are all either primitive types, reference types, or valuetypes with a single primitive type or reference type fields
• The aligned size of call target arguments is less or equal to aligned size of caller arguments