Assertion failed 'varDsc->lvExactSize == 12'

[BruceForstall]

Failure in libraries System.Numerics.Vectors.Tests: release libraries, checked coreclr with:

set COMPlus_JitStress=1

(note that TieredCompilation is the default 1)

Windows x64

E.g.,

build -s libs+libs.tests -runtimeConfiguration checked -c Release -arch x64 /p:ArchiveTests=true

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

C:\gh\runtime\artifacts\bin\System.Numerics.Vectors.Tests\net5.0-Release>call .\RunTests.cmd -r C:\gh\runtime\artifacts\bin\testhost\net5.0-Windows_NT-Release-x64

Assert failure(PID 42844 [0x0000a75c], Thread: 13268 [0x33d4]): Assertion failed 'varDsc->lvExactSize == 12' in 'System.Numerics.Tests.Matrix4x4Tests:Matrix4x4CreateFromAxisAngleTest():this' during 'Lowering nodeinfo' (IL size 357)

    File: C:\gh\runtime\src\coreclr\src\jit\compiler.h Line: 3498
    Image: C:\gh\runtime\artifacts\bin\testhost\net5.0-Windows_NT-Release-x64\dotnet.exe

@tannergooding @CarolEidt @echesakovMSFT

[tannergooding]

This is failing because optCSE is introducing a LCL_VAR but due to there being no known class handle, lvExactSize is never set and is therefore 0: https://github.com/dotnet/runtime/blob/master/src/coreclr/src/jit/optcse.cpp#L2640-L2651

[tannergooding]

@CarolEidt it looks like the relevant code was introduced back in dotnet/coreclr#22255, but the recent changes for implementing GT_SIMD as GT_HWINTRINSIC have exposed it: #35421.

It wasn't appearing for GT_SIMD because this particular case inserted the left/right shift in codegen (which was the one place I called out we were producing additional node in importation: #35421 (comment)).