[release/6.0] Disable folding small-typed returned indirections (#82846)

* Normalize returns after optimizing returned indirs This ensures we normalize returned indirs of locals, even when we fold it into an access of a promoted local's field. This may change a signed indir into access of an unsigned field, which may need a sign-extending cast to be inserted. It is not ideal that fgMorphRetInd can 'lose' this information, but given that it is a specialized optimization it seems the simplest solution is to just rely on the follow-up normalization. Fix #61359 * Conservative fix * Remove spurious diff --------- Co-authored-by: Jakob Botsch Nielsen <[email protected]>
dotnet · Mar 10, 2023 · cbfaba5 · cbfaba5
1 parent 677c557
commit cbfaba5
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diff --git a/src/coreclr/jit/morph.cpp b/src/coreclr/jit/morph.cpp
@@ -14044,6 +14044,14 @@ GenTree* Compiler::fgMorphRetInd(GenTreeUnOp* ret)
             // long<->double` there.
             bool canFold = (indSize == lclVarSize) && (lclVarSize <= REGSIZE_BYTES);
 #endif
+
+            // Avoid folding primitives to a struct-typed local for cases where we would maybe need to insert normalization on top.
+            // The backend does not correctly handle this for some promoted locals.
+            if (varTypeIsSmall(info.compRetType) && lclVar->TypeIs(TYP_STRUCT))
+            {
+                canFold = false;
+            }
+
             // TODO: support `genReturnBB != nullptr`, it requires #11413 to avoid `Incompatible types for
             // gtNewTempAssign`.
             if (canFold && (genReturnBB == nullptr))

diff --git a/src/tests/JIT/Regression/JitBlue/Runtime_61359/Runtime_61359.cs b/src/tests/JIT/Regression/JitBlue/Runtime_61359/Runtime_61359.cs
@@ -0,0 +1,19 @@
+// 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;
+
+public unsafe class Runtime_61359
+{
+    public static int Main()
+    {
+        return HalfToInt16Bits((Half)(-1)) == -17408 ? 100 : -1;
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    static short HalfToInt16Bits(Half h)
+    {
+        return *(short*)&h;
+    }
+}  
diff --git a/src/tests/JIT/Regression/JitBlue/Runtime_61359/Runtime_61359.csproj b/src/tests/JIT/Regression/JitBlue/Runtime_61359/Runtime_61359.csproj
@@ -0,0 +1,13 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+  </PropertyGroup>
+  <PropertyGroup>
+    <DebugType>None</DebugType>
+    <Optimize>True</Optimize>
+    <AllowUnsafeBlocks>True</AllowUnsafeBlocks>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="$(MSBuildProjectName).cs" />
+  </ItemGroup>
+</Project>