JIT: Fix LowerHWIntrinsicGetElement for xarch (#104987)

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

Closes #89565.

Co-authored-by: Jakob Botsch Nielsen <[email protected]>

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>