Force results of rejected multi-reg-returning tail-call candidates to temp. (#22364)

* Force results of rejected multi-reg-returning tail-call candidates to temp.

Issue #20269 ran into an assert when trying to merge returns, one of which
is a call to a multi-reg-returning method. The repro in the bug is a pmi
of `System.Reflection.Metadata`. I added a simple repro test case.

Results of calls to multi-reg-returning methods are expected to
be saved to temps. Normally it's ensured by `impFixupCallStructReturn`;
however, it doesn't do that for tail-call candidates.

This change forces results of calls to multi-reg-returning methods
to temps if the tail call is rejected late in morph.

Fixes #20269.

1 files changed, 67 insertions, 0 deletions

diff --git a/tests/src/JIT/Regression/JitBlue/GitHub_20269/GitHub_20269.cs b/tests/src/JIT/Regression/JitBlue/GitHub_20269/GitHub_20269.cs
new file mode 100644
index 0000000000..39a6714ebe
--- /dev/null
+++ b/tests/src/JIT/Regression/JitBlue/GitHub_20269/GitHub_20269.cs
@@ -0,0 +1,67 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Runtime.CompilerServices;
+using System.Numerics;
+
+namespace GitHub_20269
+{
+    // This tests a case where 
+    // 1) We merge returns.
+    // 2) One of the returns has an operand that is a call to a multi-reg returning method.
+    // 3) The call is marked as a tail-call candidate in the importer.
+    // 3) The tail call is rejected late in morph.
+    // 
+
+    class Program
+    {
+        static int i;
+        static int Main(string[] args)
+        {
+            i = 1;
+            return (int)new Program().GetVector()[0] + 99;
+        }
+
+        public virtual Vector<float> GetVector()
+        {
+            // Address-taken local prevents tail-calling
+            // GetVectorHelper.
+            int x = 0;
+            DoNothing(ref x);
+
+            // 5 returns are needed to trigger merge of returns
+            switch(i)
+            {
+                case 1:
+                    // This call is a tail-call candidate rejected late.
+                    return GetVectorHelper();
+
+                case 2:
+                    return new Vector<float>(2.0f);
+
+                case 3:
+                    return new Vector<float>(3.0f);
+
+                case 4:
+                    return new Vector<float>(4.0f);
+
+                default:
+                    return new Vector<float>(100.0f);
+
+            }
+        }
+
+        // This is a multi-reg return method on ARM64
+        public virtual Vector<float> GetVectorHelper()
+        {
+            return new Vector<float>(1.0f);
+        }
+
+        [MethodImpl(MethodImplOptions.NoInlining)]
+        public static void DoNothing(ref int i)
+        {
+        }
+    }
+}