JIT\Directed\tailcall fails at runtime with jitstress=2

[AndyAyersMS]

Stack overflow.
Return code: 1
BEGIN EXECUTION
 "C:\h\w\A59B0955\p\corerun.exe" tailcall.dll 
Test Start
Expected: 100
Actual: -1073741571

[AndyAyersMS]

See also dotnet/coreclr#27658

This looks like a stress mode imposed issue.

We have a method Recurse4 with an explicit tail call. But under STRESS_UNSAFE_BUFFER_CHECKS or STRESS_GENERIC_VARN this tail call is inhibited (via gs checks and gc checks, respectively). And this is likely what leads to stack overflow.

This test has passed jitstress in the past, eg it passes on my 3.0 snapshot, and the same inhibitions were in place there. But stress modes are a function of method hash, and it looks like the method hash has changed since then and new stress modes have been enabled for this method.

Timing of the first reported stress failure in dotnet/coreclr#27658 on Nov 3rd lines up nicely with dotnet/coreclr#27147 which went in on Oct 31 and altered method hash computations.

Suggest we mark this test as optimization sensitive and exclude it from jitstress.

[jakobbotsch]

Suggest we mark this test as optimization sensitive and exclude it from jitstress.

You can also explicitly disable this test for that stress mode, eg.
https://github.com/dotnet/runtime/blob/4f9ae42d861fcb4be2fcd5d3d55d5f227d30e723/src/coreclr/tests/src/JIT/Directed/tailcall/more_tailcalls.ilproj

However it would probably make more sense to disable this stress mode for functions containing explicit tail calls. By the way, #341 relaxes this and allows explicit tail calls out of functions with stack cookies.

[AndyAyersMS]

Thanks @jakobbotsch.

Looks like STRESS_UNSAFE_BUFFER_CHECKS could be handled internally (for now) by disabling it if there are explicit tail calls. But if that limitation is about to be relaxed, I will update the proj file insteaed.

STRESS_GENERIC_VARN sets compGcChecks early before we've imported anything, but it looks like we could selectively disable the check (added in impReturnInstruction) for explicit tail calls.