JIT: clear lvMustInit from dependent locals (#64877)

Their initialization is handled by the parent local.

Closes #64808.

Author: AndyAyersMS

src/coreclr/jit/codegencommon.cpp

@@ -4631,6 +4631,7 @@ void CodeGen::genCheckUseBlockInit()
         if (!varDsc->lvIsInReg() && !varDsc->lvOnFrame)
         {
             noway_assert(varDsc->lvRefCnt() == 0);
+            varDsc->lvMustInit = 0;
             continue;
         }
 
@@ -4643,6 +4644,7 @@ void CodeGen::genCheckUseBlockInit()
 
         if (compiler->fgVarIsNeverZeroInitializedInProlog(varNum))
         {
+            varDsc->lvMustInit = 0;
             continue;
         }
 
@@ -4651,6 +4653,7 @@ void CodeGen::genCheckUseBlockInit()
             // For Compiler::PROMOTION_TYPE_DEPENDENT type of promotion, the whole struct should have been
             // initialized by the parent struct. No need to set the lvMustInit bit in the
             // field locals.
+            varDsc->lvMustInit = 0;
             continue;
         }
 

src/tests/JIT/Regression/JitBlue/Runtime_64808/Runtime_64808.cs

@@ -0,0 +1,81 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Runtime.CompilerServices;
+
+// Generated by Fuzzlyn v1.5 on 2022-02-03 20:05:52
+// Run on X64 Linux
+// Seed: 17645686525285880576
+// Reduced from 66.2 KiB to 1.0 KiB in 00:04:27
+// Hits JIT assert in Release:
+// Assertion failed 'compiler->opts.IsOSR() || ((genInitStkLclCnt > 0) == hasUntrLcl)' in 'Program:M8():S0' during 'Generate code' (IL size 110)
+// 
+//     File: /__w/1/s/src/coreclr/jit/codegencommon.cpp Line: 7256
+// 
+
+public class C0
+{
+    public int F0;
+    public ulong F1;
+    public sbyte F2;
+}
+
+public struct S0
+{
+    public int F0;
+    public S0(int f0): this()
+    {
+    }
+}
+
+public class Runtime_64808
+{
+    private static IRT s_rt;
+    public static long[] s_16;
+    public static bool s_23;
+    public static int s_result;
+    public static int Main()
+    {
+        s_16 = new long[1];
+        s_rt = new C();
+        s_result = -1;
+        M8();
+        return s_result;
+    }
+
+    public static S0 M8()
+    {
+        try
+        {
+            var vr0 = new ushort[]{0};
+            C0[] vr3 = default(C0[]);
+            return M15(vr0, ref s_23, vr3);
+        }
+        finally
+        {
+            var vr2 = new S0[]{new S0(0), new S0(0), new S0(0), new S0(0), new S0(0), new S0(0)};
+        }
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    public static S0 M15(ushort[] arg0, ref bool arg1, C0[] arg2)
+    {
+        s_result = 100;
+        S0 vr5 = default(S0);
+        return vr5;
+    }
+}
+
+public interface IRT
+{
+    void WriteLine<T>(string a, T value);
+}
+
+public class C : IRT
+{
+    public void WriteLine<T>(string a, T value)
+    {
+        System.Console.WriteLine(value);
+    }
+}

src/tests/JIT/Regression/JitBlue/Runtime_64808/Runtime_64808.csproj

@@ -0,0 +1,11 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <Optimize>True</Optimize>
+    <AllowUnsafeBlocks>True</AllowUnsafeBlocks>
+  </PropertyGroup>
+  <ItemGroup>
+    <ProjectReference Include="$(TestSourceDir)Common/CoreCLRTestLibrary/CoreCLRTestLibrary.csproj" />
+    <Compile Include="$(MSBuildProjectName).cs" />
+  </ItemGroup>
+</Project>