Don't run optJumpThreading when fgCurBBEpochSize != (fgBBNumMax + 1)

src/coreclr/jit/redundantbranchopts.cpp

@@ -553,6 +553,12 @@ bool Compiler::optJumpThread(BasicBlock* const block, BasicBlock* const domBlock
     assert(block->bbJumpKind == BBJ_COND);
     assert(domBlock->bbJumpKind == BBJ_COND);
 
+    if (fgCurBBEpochSize != (fgBBNumMax + 1))
+    {
+        JITDUMP("Looks like we've added a new block (e.g. during optLoopHoist) since last renumber, so no threading\n");
+        return false;
+    }
+
     // If the dominating block is not the immediate dominator
     // we might need to duplicate a lot of code to thread
     // the jumps. See if that's the case.

src/tests/JIT/Regression/JitBlue/Runtime_71599/Runtime_71599.cs

@@ -0,0 +1,114 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+// Generated by Fuzzlyn v1.5 on 2022-07-03 16:41:26
+// Run on Arm64 MacOS
+// Seed: 15254214336696406464
+// Reduced from 47.2 KiB to 1.6 KiB in 00:00:23
+// Hits JIT assert in Release:
+// Assertion failed 'i < BitSetTraits::GetSize(env)' in 'Program:Main(Fuzzlyn.ExecutionServer.IRuntime)' during 'Redundant branch opts' (IL size 260; hash 0xade6b36b; FullOpts)
+// 
+//     File: /Users/runner/work/1/s/src/coreclr/jit/bitsetasshortlong.h Line: 261
+// 
+
+using System;
+
+public class C0
+{
+    public ushort F0;
+    public ulong F1;
+}
+
+public class C1
+{
+    public C0 F0;
+    public C0 F3;
+    public C0 F6;
+}
+
+public struct S0
+{
+    public bool F1;
+    public ushort F3;
+    public byte F6;
+}
+
+public struct S1
+{
+    public int F0;
+}
+
+public class Runtime_71599
+{
+    public static IRuntime s_rt;
+    public static C1[] s_1;
+    public static S0[] s_3;
+    public static S1 s_7;
+
+    public static int Main()
+    {
+        try
+        {
+            Test();
+        }
+        catch (NullReferenceException)
+        {
+            return 100;
+        }
+        return 101;
+    }
+
+
+    public static void Test()
+    {
+        ushort[] vr2 = default(ushort[]);
+        S0 vr3 = default(S0);
+        bool vr4 = vr3.F1;
+        byte vr5 = vr3.F6--;
+        if (vr4)
+        {
+            try
+            {
+                s_rt.WriteLine(1);
+            }
+            finally
+            {
+                C1 vr6 = s_1[0];
+                var vr7 = new long[] { 1 };
+                var vr8 = vr6.F3;
+                long[] vr10 = vr7;
+                C0 vr11 = vr8;
+                int vr13 = s_7.F0;
+                s_rt.WriteLine(vr6.F0.F0);
+                s_rt.WriteLine(vr6.F0.F1);
+                s_rt.WriteLine(vr6.F6.F0);
+            }
+
+            if (!vr4)
+            {
+                s_1[0].F3.F0 = vr3.F3;
+            }
+        }
+
+        for (int vr9 = 0; vr9 < 2; vr9++)
+        {
+            if (vr4)
+            {
+                s_3[0].F3 = vr2[0];
+            }
+
+            s_rt.WriteLine(vr9);
+        }
+
+    }
+}
+
+public interface IRuntime
+{
+    void WriteLine<T>(T value);
+}
+
+public class Runtime : IRuntime
+{
+    public void WriteLine<T>(T value) => System.Console.WriteLine(value);
+}

src/tests/JIT/Regression/JitBlue/Runtime_71599/Runtime_71599.csproj

@@ -0,0 +1,9 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <Optimize>True</Optimize>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="$(MSBuildProjectName).cs" />
+  </ItemGroup>
+</Project>