JIT: Assertion failed 'arg->OperIsStore() || arg->OperIsCopyBlkOp()' in PGO testing

[AndyAyersMS]

x64 windows. seems to be a recent regression

5 different legs hit this error. https://dev.azure.com/dnceng/public/_build/results?buildId=1735161&view=ms.vss-test-web.build-test-results-tab

This one is probably the simplest to repro:

set COMPlus_TieredCompilation=1
set COMPlus_ReadyToRun=0
set COMPlus_TC_QuickJitForLoops=1
set COMPlus_TieredPGO=1

C:\h\w\ACB30978\w\B2480937\e>dotnet C:\h\w\ACB30978\p\xunit\xunit.console.dll JIT\Regression\JIT.Regression.XUnitWrapper.dll -parallel collections -nocolor -noshadow -xml testResults.xml -trait TestGroup=JIT.Regression 
Microsoft.DotNet.XUnitConsoleRunner v2.5.0 (64-bit .NET 6.0.0-rtm.21522.10)
  Discovering: JIT.Regression.XUnitWrapper (method display = ClassAndMethod, method display options = None)
  Discovered:  JIT.Regression.XUnitWrapper (found 611 of 1595 test cases)
  Starting:    JIT.Regression.XUnitWrapper (parallel test collections = on, max threads = 4)
    JIT\Regression\JitBlue\Runtime_56953\Runtime_56953\Runtime_56953.cmd [FAIL]
      
      Assert failure(PID 84 [0x00000054], Thread: 3936 [0x0f60]): Assertion failed 'arg->OperIsStore() || arg->OperIsCopyBlkOp()' in 'System.String:SplitInternal(System.ReadOnlySpan`1[Char],int,int):System.String[]:this' during 'Lowering nodeinfo' (IL size 224; hash 0x1e680f85; Tier0-FullOpts)
      
          File: D:\a\_work\1\s\src\coreclr\jit\lower.cpp Line: 6428
          Image: C:\h\w\ACB30978\p\corerun.exe

cc @dotnet/jit-contrib

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Issue Details

---

x64 windows. seems to be a recent regression

5 different legs hit this error. https://dev.azure.com/dnceng/public/_build/results?buildId=1735161&view=ms.vss-test-web.build-test-results-tab

This one is probably the simplest to repro:

set COMPlus_TieredCompilation=1
set COMPlus_ReadyToRun=0
set COMPlus_TC_QuickJitForLoops=1
set COMPlus_TieredPGO=1

C:\h\w\ACB30978\w\B2480937\e>dotnet C:\h\w\ACB30978\p\xunit\xunit.console.dll JIT\Regression\JIT.Regression.XUnitWrapper.dll -parallel collections -nocolor -noshadow -xml testResults.xml -trait TestGroup=JIT.Regression 
Microsoft.DotNet.XUnitConsoleRunner v2.5.0 (64-bit .NET 6.0.0-rtm.21522.10)
  Discovering: JIT.Regression.XUnitWrapper (method display = ClassAndMethod, method display options = None)
  Discovered:  JIT.Regression.XUnitWrapper (found 611 of 1595 test cases)
  Starting:    JIT.Regression.XUnitWrapper (parallel test collections = on, max threads = 4)
    JIT\Regression\JitBlue\Runtime_56953\Runtime_56953\Runtime_56953.cmd [FAIL]
      
      Assert failure(PID 84 [0x00000054], Thread: 3936 [0x0f60]): Assertion failed 'arg->OperIsStore() || arg->OperIsCopyBlkOp()' in 'System.String:SplitInternal(System.ReadOnlySpan`1[Char],int,int):System.String[]:this' during 'Lowering nodeinfo' (IL size 224; hash 0x1e680f85; Tier0-FullOpts)
      
          File: D:\a\_work\1\s\src\coreclr\jit\lower.cpp Line: 6428
          Image: C:\h\w\ACB30978\p\corerun.exe

cc @dotnet/jit-contrib

Author:	AndyAyersMS
Assignees:	-
Labels:	area-CodeGen-coreclr, untriaged
Milestone:	-

[jakobbotsch]

I'm guessing it's from #68140, I removed an IsNothingNode() check from that assert. I must have missed changing this place to make it null instead of GT_NOP.