ARM32: Assertion failed 'varDsc->lvType == TYP_STRUCT' in 'System.SpanHelpers:Fill(byref,int,System.__Canon)' during 'Generate code' in jitminopts runs

[jakobbotsch]

Pipeline run: https://dev.azure.com/dnceng/public/_build/results?buildId=1770681&view=results
Job: coreclr Linux arm Checked jitminopts

        Assert failure(PID 528 [0x00000210], Thread: 528 [0x0210]): Assertion failed 'varDsc->lvType == TYP_STRUCT' in 'System.SpanHelpers:Fill(byref,int,System.__Canon)' during 'Generate code' (IL size 911; hash 0xc319f39c; MinOpts)
        
            File: /__w/1/s/src/coreclr/jit/codegenarmarch.cpp Line: 1306
            Image: /root/helix/work/correlation/corerun

Introduced in range 72f9cb2d..6f15fdc8

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Issue Details

---

Pipeline run: https://dev.azure.com/dnceng/public/_build/results?buildId=1770681&view=results
Job: coreclr Linux arm Checked jitminopts

        Assert failure(PID 528 [0x00000210], Thread: 528 [0x0210]): Assertion failed 'varDsc->lvType == TYP_STRUCT' in 'System.SpanHelpers:Fill(byref,int,System.__Canon)' during 'Generate code' (IL size 911; hash 0xc319f39c; MinOpts)
        
            File: /__w/1/s/src/coreclr/jit/codegenarmarch.cpp Line: 1306
            Image: /root/helix/work/correlation/corerun

Introduced in range 72f9cb2..6f15fdc

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

[jakobbotsch]

Repros in arm32 altjit for

public static void Main()
{
    Span<object> foo = new object[1000];
    foo.Fill(null);
}

with COMPlus_JITMinOpts=1

[jakobbotsch]

Bisected this to #68739, cc @dotnet/jit-contrib @tannergooding

[tannergooding]

I wonder if this is handled by @SingleAccretion's PR: #69271

It might also be a different issue and in need of its own work item/fix.

[SingleAccretion]

I will investigate this; on first approximation the assert looks questionable because there is no requirement for the underlying local and the OBJ on top of it to match (there is a similarly questionable assert(!varDsc->lvIsHfa()) assert below).