Investigate Condition21.Test5 failure in TailcallVerifyWithPrefix

[erozenfeld]

Condition21.Test5 in TailcallVerifyWithPrefix (in tests\src\JIT\opt\Tailcall) is currently failing and disabled. Here is the output of the test (checked x64):

   Executing Condition21.Test5 - Verifying helper frame location on the stack while using multiple threads.
    The following shows a list of stack addresses of a local on the stack.
    You should see the same address three times before it decreases and repeats again.
    This happens because the call chain looks like this E->E->E->E->O->O->O->E->E->E->E->O->O->O
    where E is a method where tailcalls are not allowed (it's synchronized) and O is a
    method that gets tailcall'ed.

    ------ Stack addresses for thread 1. ---------
    0xb23c57e054
    0xb23c57df84
    0xb23c57df84
    0xb23c57dcc4
    0xb23c57dbf4
    0xb23c57dbf4
    0xb23c57d934
    0xb23c57d864
    0xb23c57d864
    0xb23c57d5a4
    0xb23c57d4d4
    0xb23c57d4d4
    0xb23c57d214
    0xb23c57d144
    0xb23c57d144
    0xb23c57ce84
    0xb23c57cdb4
    0xb23c57cdb4
    0xb23c57caf4
    0xb23c57ca24
    0xb23c57ca24

    ------ Stack addresses for thread 2. ---------
    0xb23c6fe0e4
    0xb23c6fe014
    0xb23c6fe014
    0xb23c6fdd54
    0xb23c6fdc84
    0xb23c6fdc84
    0xb23c6fd9c4
    0xb23c6fd8f4
    0xb23c6fd8f4
    0xb23c6fd634
    0xb23c6fd564
    0xb23c6fd564
    0xb23c6fd2a4
    0xb23c6fd1d4
    0xb23c6fd1d4
    0xb23c6fcf14
    0xb23c6fce44
    0xb23c6fce44
    0xb23c6fcb84
    0xb23c6fcab4
    0xb23c6fcab4
    Execution finished - Test FAILED
    Executing Condition21.Test6  - Caller: Arguments: None - ReturnType: void; Callee: Arguments: None - ReturnType: void
    Execution finished - Test PASSED
    Executing Condition21.Test7  - Caller: Arguments: Int32 - ReturnType: Int32; Callee: Arguments: Int32 - ReturnType: Int32
    Execution finished - Test PASSED
    Executing Condition22.Test4  - Caller: Arguments: None - ReturnType: void; Callee(regular call instruction): Arguments: 0 - ReturnType: Int32
    Execution finished - Test PASSED
    Expected: 100
    Actual: 101
    END EXECUTION - FAILED

category:correctness
theme:testing
skill-level:intermediate
cost:small

[AndyAyersMS]

@jakobbotsch another something to look into someday...

[jakobbotsch]

A lot of the assumptions made by this test are invalid with portable tailcall helpers. That's because with portable tailcall helpers we don't try to implement the semantics that "a tailcall cleans up the stack frame before it transfers control", but rather the semantics that "for all n, any sequence of n tailcalls uses constant stack space". So with portable tailcall helpers we do see some number of stack frames that the test does not expect. The tests I introduced as part of the implementation test this latter semantics.

I believe dotnet/coreclr#26818 removed this particular test case so I'm not sure there's anything actionable here. Will close it.