Assertion failed 'nonVarPtrRegs == RBM_NONE'

[BruceForstall]

Failure in libraries System.Threading.Tasks.Dataflow.Tests: release libraries, checked coreclr with:

COMPlus_TieredCompilation=0
COMPlus_JitStress=2
COMPlus_JitStressRegs=4

Windows arm32

E.g.,

build -s libs+libs.tests -runtimeConfiguration checked -c Release -arch arm /p:ArchiveTests=true

(the /p:ArchiveTests=true is required to build the RunTests.cmd wrapper scripts)

c:\bugs\System.Threading.Tasks.Dataflow.Tests\net5.0-Release>call .\RunTests.cmd -r C:\bugs\testhost\net5.0-Windows_NT-Release-arm
----- start Sun 05/31/2020 13:04:02.26 ===============  To repro directly: =====================================================
pushd c:\bugs\System.Threading.Tasks.Dataflow.Tests\net5.0-Release\
"C:\bugs\testhost\net5.0-Windows_NT-Release-arm\dotnet.exe" exec --runtimeconfig System.Threading.Tasks.Dataflow.Tests.runtimeconfig.json --depsfile System.Threading.Tasks.Dataflow.Tests.deps.json xunit.console.dll System.Threading.Tasks.Dataflow.Tests.dll -xml testResults.xml -nologo -nocolor -notrait category=IgnoreForCI -notrait category=OuterLoop -notrait category=failing
popd
===========================================================================================================

c:\bugs\System.Threading.Tasks.Dataflow.Tests\net5.0-Release>"C:\bugs\testhost\net5.0-Windows_NT-Release-arm\dotnet.exe" exec --runtimeconfig System.Threading.Tasks.Dataflow.Tests.runtimeconfig.json --depsfile System.Threading.Tasks.Dataflow.Tests.deps.json xunit.console.dll System.Threading.Tasks.Dataflow.Tests.dll -xml testResults.xml -nologo -nocolor -notrait category=IgnoreForCI -notrait category=OuterLoop -notrait category=failing
  Discovering: System.Threading.Tasks.Dataflow.Tests (method display = ClassAndMethod, method display options = None)
  Discovered:  System.Threading.Tasks.Dataflow.Tests (found 290 of 297 test cases)
  Starting:    System.Threading.Tasks.Dataflow.Tests (parallel test collections = on, max threads = 8)
Regset after BB27 gcr=0001 {r0}, byr=0000 {}, regVars=0004 {r2}

Assert failure(PID 12028 [0x00002efc], Thread: 6680 [0x1a18]): Assertion failed 'nonVarPtrRegs == RBM_NONE' in 'System.Collections.Generic.Dictionary`2[Int64,KeyValuePair`2][System.Int64,System.Collections.Generic.KeyValuePair`2[System.Boolean,System.__Canon]]:Remove(long):bool:this' during 'Generate code' (IL size 356)

    File: C:\gh\runtime\src\coreclr\src\jit\codegenlinear.cpp Line: 509
    Image: C:\bugs\testhost\net5.0-Windows_NT-Release-arm\dotnet.exe

----- end Sun 05/31/2020 13:04:13.92 ----- exit code -1073740286 ----------------------------------------------------------

category:correctness
theme:elt-hooks
skill-level:intermediate
cost:medium

[BruceForstall]

@CarolEidt