[JIT] ARM64 - Temporary fix for ldp/stp optimizations - with test fix (…

…#90700)

* Added regression test 85765

* Mark M4 as NoInlining

* Check current and last ins format to determine whether to proceed with the optimized ldr/str pair

* Additional test

* Feedback

* Fix test

* Fixing test again...

src/coreclr/jit/emitarm64.cpp

@@ -16615,6 +16615,15 @@ emitter::RegisterOrder emitter::IsOptimizableLdrStrWithPair(
     emitAttr  prevSize   = emitLastIns->idOpSize();
     ssize_t   prevImm    = emitGetInsSC(emitLastIns);
 
+    // If we have this format, the 'imm' and/or 'prevImm' are not scaled(encoded),
+    // therefore we cannot proceed.
+    // TODO: In this context, 'imm' and 'prevImm' are assumed to be scaled(encoded).
+    //       They should never be scaled(encoded) until its about to be written to the buffer.
+    if (fmt == IF_LS_2C || lastInsFmt == IF_LS_2C)
+    {
+        return eRO_none;
+    }
+
     // Signed, *raw* immediate value fits in 7 bits, so for LDP/ STP the raw value is from -64 to +63.
     // For LDR/ STR, there are 9 bits, so we need to limit the range explicitly in software.
     if ((imm < -64) || (imm > 63) || (prevImm < -64) || (prevImm > 63))

src/tests/JIT/Regression/JitBlue/Runtime_85765/Runtime_85765.cs

@@ -0,0 +1,63 @@
+// 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;
+using Xunit;
+
+public class Runtime_85765
+{
+    public struct S0
+    {
+        public S0(bool f1): this()
+        {
+        }
+    }
+
+    public struct S1
+    {
+        public byte F0;
+        public bool F1;
+        public bool F2;
+    }
+
+    [Fact]
+    public static void Test()
+    {
+        S1 vr2 = M4();
+        vr2.F2 |= vr2.F1;
+        Assert.False(Consume(vr2.F2));
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    public static S1 M4()
+    {
+        S1 var1 = default(S1);
+        var vr0 = new S0(false);
+        return var1;
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private static bool Consume(bool value)
+    {
+        return value;
+    }
+
+    // ------
+
+    [Fact]
+    public unsafe static void Test2()
+    {
+        byte* bytes = stackalloc byte[1024];
+        bytes[0x1A] = 1;
+        bytes[0x1B] = 2;
+        int sum = Foo(bytes);
+        Assert.True(sum == 515);
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    public unsafe static int Foo(byte* b)
+    {
+        return Unsafe.ReadUnaligned<int>(ref b[0x1A]) + Unsafe.ReadUnaligned<int>(ref b[0x1B]);
+    }
+}

src/tests/JIT/Regression/JitBlue/Runtime_85765/Runtime_85765.csproj

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