Assertion failed 'isCandidateVar(fieldVarDsc) == isMultiReg' during 'Linear scan register alloc'

[kunalspathak]

// Found by Antigen
using System;
using System.Collections.Generic;
using System.Runtime.CompilerServices;
public class TestClass
{
    public static void Main(string[] args)
    {
    }
}

/*
Environment:
set DOTNET_JitMaxLocalsToTrack=0
set DOTNET_ReadyToRun=0
set DOTNET_ZapDisable=1

Assert failure(PID 32228 [0x00007de4], Thread: 53992 [0xd2e8]): Assertion failed 'isCandidateVar(fieldVarDsc) == isMultiReg' in 'System.Text.Unicode.Utf8Utility:TranscodeToUtf8(uint,int,uint,int,byref,byref):int' during 'Linear scan register alloc' (IL size 1605; hash 0x6b1af0be; Tier1)
    File: E:\git\runtime\src\coreclr\jit\lsrabuild.cpp Line: 1270
    Image: e:\git\runtime\artifacts\tests\coreclr\windows.x86.checked\tests\Core_Root\CoreRun.exe
*/

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Issue Details

---

// Found by Antigen
using System;
using System.Collections.Generic;
using System.Runtime.CompilerServices;
public class TestClass
{
    public static void Main(string[] args)
    {
    }
}

/*
Environment:
set COMPlus_JitMaxLocalsToTrack=0
Assert failure(PID 32228 [0x00007de4], Thread: 53992 [0xd2e8]): Assertion failed 'isCandidateVar(fieldVarDsc) == isMultiReg' in 'System.Text.Unicode.Utf8Utility:TranscodeToUtf8(uint,int,uint,int,byref,byref):int' during 'Linear scan register alloc' (IL size 1605; hash 0x6b1af0be; Tier1)
    File: E:\git\runtime\src\coreclr\jit\lsrabuild.cpp Line: 1270
    Image: e:\git\runtime\artifacts\tests\coreclr\windows.x86.checked\tests\Core_Root\CoreRun.exe
*/

Author:	kunalspathak
Assignees:	kunalspathak
Labels:	arch-x86, os-windows, area-CodeGen-coreclr
Milestone:	-

[kunalspathak]

Most of the failing cases happen for multi-reg vars and for them, we check if compiler->lvaEnregMultiRegVars == true instead of check the lvLRACandidate. I will have to look deeper into what should be the right action - 1) Just update the asserts to include assert(!enregisterLocalVars || ...) or 2) need to make isCandidateMultiRegLclVar() also consider enregisterLocalVars.

Marking it for Future because this happens when COMPlus_JitMaxLocalsToTrack=0.