From 671d42c39cc85f3a4c33f4feff2c556415b19395 Mon Sep 17 00:00:00 2001
From: Jakob Botsch Nielsen <Jakob.botsch.nielsen@gmail.com>
Date: Sat, 9 Sep 2023 17:11:42 +0200
Subject: [PATCH] JIT: Fix invalid zero-init suppression for untracked
 variables (#91580)

optRemoveRedundantZeroInits has logic to remove unnecessary zero inits
if we can determine that the local will be zeroed in the prolog. In
addition, it also has logic to suppress the prolog zero init if there is
a dominating initialization already. The latter logic was trying to
reason about liveness for untracked locals, which does not make sense.

Fix #91576
---
 src/coreclr/jit/optimizer.cpp                 | 16 +++---
 .../JitBlue/Runtime_91576/Runtime_91576.cs    | 51 +++++++++++++++++++
 .../Runtime_91576/Runtime_91576.csproj        |  8 +++
 3 files changed, 67 insertions(+), 8 deletions(-)
 create mode 100644 src/tests/JIT/Regression/JitBlue/Runtime_91576/Runtime_91576.cs
 create mode 100644 src/tests/JIT/Regression/JitBlue/Runtime_91576/Runtime_91576.csproj

diff --git a/src/coreclr/jit/optimizer.cpp b/src/coreclr/jit/optimizer.cpp
index f36d1a730215f3..d5240152c26118 100644
--- a/src/coreclr/jit/optimizer.cpp
+++ b/src/coreclr/jit/optimizer.cpp
@@ -9044,9 +9044,9 @@ void Compiler::optRemoveRedundantZeroInits()
     CompAllocator   allocator(getAllocator(CMK_ZeroInit));
     LclVarRefCounts refCounts(allocator);
     BitVecTraits    bitVecTraits(lvaCount, this);
-    BitVec          zeroInitLocals = BitVecOps::MakeEmpty(&bitVecTraits);
-    bool            hasGCSafePoint = false;
-    bool            canThrow       = false;
+    BitVec          zeroInitLocals         = BitVecOps::MakeEmpty(&bitVecTraits);
+    bool            hasGCSafePoint         = false;
+    bool            hasImplicitControlFlow = false;
 
     assert(fgNodeThreading == NodeThreading::AllTrees);
 
@@ -9057,6 +9057,8 @@ void Compiler::optRemoveRedundantZeroInits()
         CompAllocator   allocator(getAllocator(CMK_ZeroInit));
         LclVarRefCounts defsInBlock(allocator);
         bool            removedTrackedDefs = false;
+        bool            hasEHSuccs         = block->HasPotentialEHSuccs(this);
+
         for (Statement* stmt = block->FirstNonPhiDef(); stmt != nullptr;)
         {
             Statement* next = stmt->GetNextStmt();
@@ -9067,10 +9069,7 @@ void Compiler::optRemoveRedundantZeroInits()
                     hasGCSafePoint = true;
                 }
 
-                if ((tree->gtFlags & GTF_EXCEPT) != 0)
-                {
-                    canThrow = true;
-                }
+                hasImplicitControlFlow |= hasEHSuccs && ((tree->gtFlags & GTF_EXCEPT) != 0);
 
                 switch (tree->gtOper)
                 {
@@ -9216,7 +9215,8 @@ void Compiler::optRemoveRedundantZeroInits()
                             }
                         }
 
-                        if (!removedExplicitZeroInit && isEntire && (!canThrow || !lclDsc->lvLiveInOutOfHndlr))
+                        if (!removedExplicitZeroInit && isEntire &&
+                            (!hasImplicitControlFlow || (lclDsc->lvTracked && !lclDsc->lvLiveInOutOfHndlr)))
                         {
                             // If compMethodRequiresPInvokeFrame() returns true, lower may later
                             // insert a call to CORINFO_HELP_INIT_PINVOKE_FRAME which is a gc-safe point.
diff --git a/src/tests/JIT/Regression/JitBlue/Runtime_91576/Runtime_91576.cs b/src/tests/JIT/Regression/JitBlue/Runtime_91576/Runtime_91576.cs
new file mode 100644
index 00000000000000..4df185d99ab241
--- /dev/null
+++ b/src/tests/JIT/Regression/JitBlue/Runtime_91576/Runtime_91576.cs
@@ -0,0 +1,51 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.aa
+
+// Generated by Fuzzlyn v1.6 on 2023-09-03 15:59:01
+// Run on X64 Windows
+// Seed: 11520325105937570553
+// Reduced from 294.5 KiB to 0.7 KiB in 00:04:32
+// Debug: Outputs False
+// Release: Outputs True
+using System;
+using System.Runtime.CompilerServices;
+using Xunit;
+
+public class Runtime_91576
+{
+    [Fact]
+    public static int TestEntryPoint()
+    {
+        Assert.Throws<NullReferenceException>(() =>
+        {
+            Run(new int[1]);
+            Run(null);
+        });
+
+        return s_result;
+    }
+
+    static int s_result;
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private static void Run(int[] l)
+    {
+        bool b = false;
+        try
+        {
+            int result = l[0];
+            b = true;
+        }
+        finally
+        {
+            Check(ref b);
+        }
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private static void Check(ref bool b)
+    {
+        s_result = b ? 101 : 100;
+    }
+}
+
diff --git a/src/tests/JIT/Regression/JitBlue/Runtime_91576/Runtime_91576.csproj b/src/tests/JIT/Regression/JitBlue/Runtime_91576/Runtime_91576.csproj
new file mode 100644
index 00000000000000..de6d5e08882e86
--- /dev/null
+++ b/src/tests/JIT/Regression/JitBlue/Runtime_91576/Runtime_91576.csproj
@@ -0,0 +1,8 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <Optimize>True</Optimize>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="$(MSBuildProjectName).cs" />
+  </ItemGroup>
+</Project>