Use the register of CAST for contained index operator

src/coreclr/jit/codegenarmarch.cpp

@@ -4458,12 +4458,26 @@ void CodeGen::genLeaInstruction(GenTreeAddrMode* lea)
         else
         {
 #ifdef TARGET_ARM64
-            // Handle LEA with "contained" BFIZ
-            if (index->isContained() && index->OperIs(GT_BFIZ))
+
+            if (index->isContained())
             {
-                assert(scale == 0);
-                scale = (DWORD)index->gtGetOp2()->AsIntConCommon()->IconValue();
-                index = index->gtGetOp1()->gtGetOp1();
+                if (index->OperIs(GT_BFIZ))
+                {
+                    // Handle LEA with "contained" BFIZ
+                    assert(scale == 0);
+                    scale = (DWORD)index->gtGetOp2()->AsIntConCommon()->IconValue();
+                    index = index->gtGetOp1()->gtGetOp1();
+                }
+                else if (index->OperIs(GT_CAST))
+                {
+                    index = index->AsCast()->gtGetOp1();
+                }
+                else
+                {
+                    // Only BFIZ/CAST nodes should be present for for contained index on ARM64.
+                    // If there are more, we need to handle them here.
+                    unreached();
+                }
             }
 #endif
 

src/coreclr/jit/lower.cpp

@@ -5362,29 +5362,43 @@ bool Lowering::TryCreateAddrMode(GenTree* addr, bool isContainable, GenTree* par
     }
 
 #ifdef TARGET_ARM64
-    if ((index != nullptr) && index->OperIs(GT_CAST) && (scale == 1) && (offset == 0) && varTypeIsByte(targetType))
-    {
-        index->AsCast()->CastOp()->ClearContained(); // Uncontain any memory operands.
-        MakeSrcContained(addrMode, index);
-    }
 
-    // Check if we can "contain" LEA(BFIZ) in order to extend 32bit index to 64bit as part of load/store.
-    if ((index != nullptr) && index->OperIs(GT_BFIZ) && index->gtGetOp1()->OperIs(GT_CAST) &&
-        index->gtGetOp2()->IsCnsIntOrI() && !varTypeIsStruct(targetType))
+    if (index != nullptr)
     {
-        // BFIZ node is a binary op where op1 is GT_CAST and op2 is GT_CNS_INT
-        GenTreeCast* cast = index->gtGetOp1()->AsCast();
-        assert(cast->isContained());
+        if (index->OperIs(GT_CAST) && (scale == 1) && (offset == 0) && varTypeIsByte(targetType))
+        {
+            if (IsSafeToContainMem(parent, index))
+            {
+                // Check containment safety against the parent node - this will ensure that LEA with the contained
+                // index will itself always be contained. We do not support uncontained LEAs with contained indices.
+                index->AsCast()->CastOp()->ClearContained(); // Uncontain any memory operands.
+                MakeSrcContained(addrMode, index);
+            }
+        }
+        else if (index->OperIs(GT_BFIZ) && index->gtGetOp1()->OperIs(GT_CAST) && index->gtGetOp2()->IsCnsIntOrI() &&
+                 !varTypeIsStruct(targetType))
+        {
+            // Check if we can "contain" LEA(BFIZ) in order to extend 32bit index to 64bit as part of load/store.
+            // BFIZ node is a binary op where op1 is GT_CAST and op2 is GT_CNS_INT
+            GenTreeCast* cast = index->gtGetOp1()->AsCast();
+            assert(cast->isContained());
 
-        const unsigned shiftBy = (unsigned)index->gtGetOp2()->AsIntCon()->IconValue();
+            const unsigned shiftBy = (unsigned)index->gtGetOp2()->AsIntCon()->IconValue();
 
-        // 'scale' and 'offset' have to be unset since we're going to use [base + index * SXTW/UXTW scale] form
-        // where there is no room for additional offsets/scales on ARM64. 'shiftBy' has to match target's width.
-        if (cast->CastOp()->TypeIs(TYP_INT) && cast->TypeIs(TYP_LONG) && (genTypeSize(targetType) == (1U << shiftBy)) &&
-            (scale == 1) && (offset == 0))
-        {
-            // TODO: Make sure that genCreateAddrMode marks such BFIZ candidates as GTF_DONT_CSE for better CQ.
-            MakeSrcContained(addrMode, index);
+            // 'scale' and 'offset' have to be unset since we're going to use [base + index * SXTW/UXTW scale] form
+            // where there is no room for additional offsets/scales on ARM64. 'shiftBy' has to match target's width.
+            if (cast->CastOp()->TypeIs(TYP_INT) && cast->TypeIs(TYP_LONG) &&
+                (genTypeSize(targetType) == (1U << shiftBy)) && (scale == 1) && (offset == 0))
+            {
+                if (IsSafeToContainMem(parent, index))
+                {
+                    // Check containment safety against the parent node - this will ensure that LEA with the contained
+                    // index will itself always be contained. We do not support uncontained LEAs with contained indices.
+
+                    // TODO: Make sure that genCreateAddrMode marks such BFIZ candidates as GTF_DONT_CSE for better CQ.
+                    MakeSrcContained(addrMode, index);
+                }
+            }
         }
     }
 #endif

src/tests/JIT/Regression/JitBlue/Runtime_74117/Runtime_74117.cs

@@ -0,0 +1,27 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Runtime.CompilerServices;
+
+unsafe class Runtime_74117
+{
+    public unsafe static int Main(string[] args)
+    {
+        byte a = 5;
+        Problem(ref a, 0);
+        return 100;
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    static byte GetByte() => 1;
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private static void Problem(ref byte x, int a)
+    {
+        JitUse(&a);
+        Unsafe.Add(ref x, a) = GetByte();
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    public static void JitUse<T>(T* arg) where T : unmanaged { }
+}

src/tests/JIT/Regression/JitBlue/Runtime_74373/Runtime_74373.csproj

@@ -0,0 +1,10 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <Optimize>True</Optimize>
+    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="$(MSBuildProjectName).cs" />
+  </ItemGroup>
+</Project>