JIT: Fix LowerHWIntrinsicGetElement for xarch (#104987)

Ensure we don't reorder evaluation and change exceptional behavior.

Closes #89565.

Co-authored-by: Jakob Botsch Nielsen <Jakob.botsch.nielsen@gmail.com>

src/coreclr/jit/lowerxarch.cpp

@@ -5074,8 +5074,43 @@ GenTree* Lowering::LowerHWIntrinsicGetElement(GenTreeHWIntrinsic* node)
         uint32_t newScale;
         int32_t  newOffset;
 
-        GenTreeIndir* indir = op1->AsIndir();
-        GenTree*      addr  = indir->Addr();
+        // Normally we'd evaluate op1 (indir), then op2 (element index).
+        // We like to be able to reorder these to fold op2 into the indir.
+
+        GenTreeIndir* indir                = op1->AsIndir();
+        GenTree*      addr                 = indir->Addr();
+        bool const    canMoveTheIndirLater = IsInvariantInRange(indir, node);
+
+        // If we can't move the indir, force evaluation of its side effects.
+        //
+        if (!canMoveTheIndirLater)
+        {
+            // Force evaluation of the address, if it is complex
+            //
+            if (!(addr->IsInvariant() || addr->OperIsLocal()))
+            {
+                addr->ClearContained();
+                LIR::Use addrUse(BlockRange(), &indir->Addr(), indir);
+                addrUse.ReplaceWithLclVar(comp);
+                addr = indir->Addr();
+            }
+
+            // If the indir can fault, do a null check.
+            //
+            if (indir->OperMayThrow(comp))
+            {
+                GenTree* addrClone = comp->gtCloneExpr(addr);
+                GenTree* nullcheck = comp->gtNewNullCheck(addrClone, comp->compCurBB);
+                BlockRange().InsertBefore(indir, addrClone, nullcheck);
+                LowerNode(nullcheck);
+
+                indir->gtFlags |= GTF_IND_NONFAULTING;
+            }
+
+            // We should now be able to move the indir
+            //
+            indir->gtFlags &= ~GTF_EXCEPT;
+        }
 
         if (addr->OperIsAddrMode())
         {

src/tests/JIT/Regression/JitBlue/Runtime_89565/Runtime_89565.cs

@@ -0,0 +1,55 @@
+// 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 System.Runtime.Intrinsics;
+using Xunit;
+
+public class Runtime_89565
+{
+    [Fact]
+    public static unsafe int Test()
+    {
+        int result = 0;
+        try
+        {
+            Foo(null);
+        }
+        catch (NullReferenceException)
+        {
+            result += 50;
+        }
+        catch
+        {
+
+        }
+
+        try 
+        {
+            Bar(null, 0);
+        }
+        catch (DivideByZeroException)
+        {
+            result += 50;
+        }
+        catch
+        {
+
+        }
+
+        return result;
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private static unsafe float Foo(Vector256<float>* v)
+    {
+        return (*v)[8];
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private static unsafe float Bar(Vector256<float>* v, int x)
+    {
+        return (*v)[8/x];
+    }
+}

src/tests/JIT/Regression/JitBlue/Runtime_89565/Runtime_89565.csproj

@@ -0,0 +1,8 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="$(MSBuildProjectName).cs" />
+  </ItemGroup>
+</Project>