Assertion failed 'stmt->GetTreeList()'

[BruceForstall]

COMPlus_JitStress=2, all platform

https://dev.azure.com/dnceng/public/_build/results?buildId=728106&view=ms.vss-test-web.build-test-results-tab&runId=22543846&resultId=101328&paneView=debug

C:\gh\runtime\artifacts\tests\coreclr\Windows_NT.x64.Release\baseservices\threading\monitor\tryenter\longtimeout>call longtimeout.cmd -coreroot C:\gh\runtime\artifacts\tests\coreclr\Windows_NT.x64.Checked\tests\Core_Root
BEGIN EXECUTION
 "C:\gh\runtime\artifacts\tests\coreclr\Windows_NT.x64.Checked\tests\Core_Root\corerun.exe" longtimeout.dll

Assert failure(PID 18744 [0x00004938], Thread: 13688 [0x3578]): Assertion failed 'stmt->GetTreeList()' in 'Repro:Thread2():this' during 'Determine first cold block' (IL size 243)                                                                                                                                                                                                                                                                                              File: C:\gh\runtime\src\coreclr\src\jit\flowgraph.cpp Line: 21972
    Image: C:\gh\runtime\artifacts\tests\coreclr\Windows_NT.x64.Checked\tests\Core_Root\CoreRun.exe                    

@dotnet/jit-contrib

[AndyAyersMS]

Would guess this is from #39111, that added a new phase just upstream of "determine first cold block."

[BruceForstall]

This also shows up in a number of libraries Windows x86 tailcallstress jobs:

https://dev.azure.com/dnceng/public/_build/results?buildId=728248&view=ms.vss-test-web.build-test-results-tab&runId=22547330&resultId=175084&paneView=dotnet-dnceng.dnceng-build-release-tasks.helix-test-information-tab

[erozenfeld]

I'll investigate.