JIT: block copy/zero assertion gen for structs with exposed promoted …

…fields

If a struct has an exposed field, we can't safely reason about is value in
local assertion prop.

Closes #75249.

src/coreclr/jit/assertionprop.cpp

@@ -1473,15 +1473,32 @@ AssertionIndex Compiler::optCreateAssertion(GenTree*         op1,
     //
     else if (op1->gtOper == GT_LCL_VAR)
     {
-        unsigned   lclNum = op1->AsLclVarCommon()->GetLclNum();
-        LclVarDsc* lclVar = lvaGetDesc(lclNum);
+        unsigned const   lclNum = op1->AsLclVarCommon()->GetLclNum();
+        LclVarDsc* const lclVar = lvaGetDesc(lclNum);
 
-        //  If the local variable has its address exposed then bail
+        // If the local variable has its address exposed then bail
+        //
         if (lclVar->IsAddressExposed())
         {
             goto DONE_ASSERTION; // Don't make an assertion
         }
 
+        // If the local is a promoted struct and has an exposed field then bail.
+        //
+        if (lclVar->lvPromoted)
+        {
+            for (unsigned childLclNum = lclVar->lvFieldLclStart;
+                 childLclNum < lclVar->lvFieldLclStart + lclVar->lvFieldCnt; ++childLclNum)
+            {
+                LclVarDsc* const childVar = lvaGetDesc(childLclNum);
+
+                if (childVar->IsAddressExposed())
+                {
+                    goto DONE_ASSERTION;
+                }
+            }
+        }
+
         if (helperCallArgs)
         {
             //
@@ -1701,6 +1718,22 @@ AssertionIndex Compiler::optCreateAssertion(GenTree*         op1,
                         goto DONE_ASSERTION; // Don't make an assertion
                     }
 
+                    // If the local is a promoted struct and has an exposed field then bail.
+                    //
+                    if (lclVar2->lvPromoted)
+                    {
+                        for (unsigned childLclNum = lclVar2->lvFieldLclStart;
+                             childLclNum < lclVar2->lvFieldLclStart + lclVar2->lvFieldCnt; ++childLclNum)
+                        {
+                            LclVarDsc* const childVar = lvaGetDesc(childLclNum);
+
+                            if (childVar->IsAddressExposed())
+                            {
+                                goto DONE_ASSERTION;
+                            }
+                        }
+                    }
+
                     assertion.op2.kind       = O2K_LCLVAR_COPY;
                     assertion.op2.vn         = optConservativeNormalVN(op2);
                     assertion.op2.lcl.lclNum = lclNum2;

src/tests/JIT/Regression/JitBlue/Runtime_75249/Runtime_75249.cs

@@ -0,0 +1,59 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+// Generated by Fuzzlyn v1.5 on 2022-09-04 15:54:25
+// Run on X86 Windows
+// Seed: 14105179845188319926
+// Reduced from 33.3 KiB to 0.8 KiB in 00:01:22
+// Debug: Outputs 0
+// Release: Outputs 1
+
+public struct S1
+{
+    public uint F0;
+    public S2 M18(ref int arg0, ulong arg1)
+    {
+        S1 var6;
+        try
+        {
+        }
+        finally
+        {
+            var6.F0 = Runtime_75249.s_13;
+            this = var6;
+        }
+
+        return new S2(0);
+    }
+}
+
+public struct S2
+{
+    public S1 F0;
+    public short F1;
+    public S2(short f1): this()
+    {
+        F1 = f1;
+    }
+}
+
+public class Runtime_75249
+{
+    public static byte s_4;
+    public static int s_10;
+    public static uint s_13 = 1;
+    public static int s_19;
+    public static int Main()
+    {
+        S2 vr1 = new S2(-1);
+        byte r = M17(vr1, M17(vr1.F0.M18(ref s_19, 0), s_4));
+        return r == 0 ? 100 : -1;
+    }
+
+    public static byte M17(S2 arg0, int arg4)
+    {
+        uint r = arg0.F0.F0;
+        System.Console.WriteLine(r);
+        return (byte) r;
+    }
+}

src/tests/JIT/Regression/JitBlue/Runtime_75249/Runtime_75249.csproj

@@ -0,0 +1,9 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <Optimize>True</Optimize>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="$(MSBuildProjectName).cs" />
+  </ItemGroup>
+</Project>