JIT: Give up on the tail call if there are unexpected blocks after it

src/coreclr/jit/morph.cpp

@@ -7733,7 +7733,31 @@ GenTree* Compiler::fgMorphPotentialTailCall(GenTreeCall* call)
             //
             if (nextBlock->bbJumpKind != BBJ_RETURN)
             {
-                BasicBlock* const nextNextBlock = nextBlock->GetUniqueSucc();
+                BasicBlock* nextNextBlock = nextBlock->GetUniqueSucc();
+
+                // Check if we have a sequence of GT_ASG blocks where the same variable is assigned to temps over
+                // and over (can happen after multiple GDVs of potential tall calls).
+                // TODO-CQ: Don't introduce new temps when we replace GT_RET_EXPR which is already assigned to a
+                // local.
+                if (nextNextBlock->bbJumpKind != BBJ_RETURN)
+                {
+                    assert(nextBlock->firstStmt() == nextBlock->lastStmt());
+                    GenTree* asgNode = nextBlock->firstStmt()->GetRootNode();
+                    assert(asgNode->OperIs(GT_ASG));
+
+                    unsigned lcl = asgNode->gtGetOp1()->AsLclVarCommon()->GetLclNum();
+
+                    while (nextNextBlock->bbJumpKind != BBJ_RETURN)
+                    {
+                        assert(nextNextBlock->firstStmt() == nextNextBlock->lastStmt());
+                        asgNode = nextNextBlock->firstStmt()->GetRootNode();
+                        assert(asgNode->OperIs(GT_ASG));
+                        assert(lcl == asgNode->gtGetOp2()->AsLclVarCommon()->GetLclNum());
+                        lcl = asgNode->gtGetOp1()->AsLclVarCommon()->GetLclNum();
+                        nextNextBlock = nextNextBlock->GetUniqueSucc();
+                    }
+                }
+
                 assert(nextNextBlock->bbJumpKind == BBJ_RETURN);
 
                 if (nextNextBlock->hasProfileWeight())

src/tests/JIT/opt/Devirtualization/GitHub_50492.cs

@@ -0,0 +1,42 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Runtime.CompilerServices;
+using System.Threading;
+
+class Base
+{
+    public virtual int Test(Base b1, Base b2, bool p) => 0;
+
+    public virtual int Foo() => 1;
+}
+
+class ClassA : Base
+{
+    public override int Test(Base b1, Base b2, bool p) => p ? b2.Foo() : 42;
+}
+
+class ClassB : ClassA
+{
+    public override int Test(Base b1, Base b2, bool p) => b1.Test(b1, b2, p);
+}
+
+class Program
+{
+    public static int Main()
+    {
+        for (int i = 0; i < 100; i++)
+        {
+            // Make sure it doesn't assert, see https://github.com/dotnet/runtime/issues/50492
+            Test(new ClassB(), new ClassA(), new Base(), true);
+            Thread.Sleep(15);
+        }
+        return 100;
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    static int Test(Base b0, Base b1, Base b2, bool p)
+    {
+        return b0.Test(b1, b2, p);
+    }
+}

src/tests/JIT/opt/Devirtualization/GitHub_50492.csproj

@@ -0,0 +1,9 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <Optimize>True</Optimize>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="GitHub_50492.cs" />
+  </ItemGroup>
+</Project>