From 34bfc048bf24d74b2ade9382ec1b2addab45b844 Mon Sep 17 00:00:00 2001
From: Andy Ayers <andya@microsoft.com>
Date: Fri, 10 Jun 2022 12:56:36 -0700
Subject: [PATCH 1/2] JIT: relax fwd sub restriction on changing class handle

For HW SIMD types, at least.

Fixes #64879.
---
 src/coreclr/jit/forwardsub.cpp | 25 ++++++++++++++++---------
 1 file changed, 16 insertions(+), 9 deletions(-)

diff --git a/src/coreclr/jit/forwardsub.cpp b/src/coreclr/jit/forwardsub.cpp
index 4c3fae5f1d9f9..8fee053c5e19a 100644
--- a/src/coreclr/jit/forwardsub.cpp
+++ b/src/coreclr/jit/forwardsub.cpp
@@ -504,12 +504,6 @@ bool Compiler::fgForwardSubStatement(Statement* stmt)
         return false;
     }
 
-    if (gtGetStructHandleIfPresent(fwdSubNode) != gtGetStructHandleIfPresent(lhsNode))
-    {
-        JITDUMP(" would change struct handle (assignment)\n");
-        return false;
-    }
-
     // If lhs is mulit-reg, rhs must be too.
     //
     if (lhsNode->IsMultiRegNode() && !fwdSubNode->IsMultiRegNode())
@@ -667,10 +661,23 @@ bool Compiler::fgForwardSubStatement(Statement* stmt)
     //
     // We may sometimes lose or change a type handle. Avoid substituting if so.
     //
-    if (gtGetStructHandleIfPresent(fwdSubNode) != gtGetStructHandleIfPresent(fsv.GetNode()))
+    // However, we allow free substitution of hardware SIMD types.
+    //
+    CORINFO_CLASS_HANDLE fwdHnd = gtGetStructHandleIfPresent(fwdSubNode);
+    CORINFO_CLASS_HANDLE useHnd = gtGetStructHandleIfPresent(fsv.GetNode());
+    if (fwdHnd != useHnd)
     {
-        JITDUMP(" would change struct handle (substitution)\n");
-        return false;
+        if ((fwdHnd == NO_CLASS_HANDLE) || (useHnd == NO_CLASS_HANDLE))
+        {
+            JITDUMP(" would add/remove struct handle (substitution)\n");
+            return false;
+        }
+
+        if (!isHWSIMDClass(fwdHnd) || !isHWSIMDClass(useHnd))
+        {
+            JITDUMP(" would change struct handle (substitution)\n");
+            return false;
+        }
     }
 
 #ifdef FEATURE_SIMD

From 4826a7f5874d4f7c8067aaa965b99eddde02548a Mon Sep 17 00:00:00 2001
From: Andy Ayers <andya@microsoft.com>
Date: Fri, 10 Jun 2022 13:53:07 -0700
Subject: [PATCH 2/2] fix build issue

---
 src/coreclr/jit/forwardsub.cpp | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/src/coreclr/jit/forwardsub.cpp b/src/coreclr/jit/forwardsub.cpp
index 8fee053c5e19a..4da3c62323f23 100644
--- a/src/coreclr/jit/forwardsub.cpp
+++ b/src/coreclr/jit/forwardsub.cpp
@@ -673,7 +673,13 @@ bool Compiler::fgForwardSubStatement(Statement* stmt)
             return false;
         }
 
-        if (!isHWSIMDClass(fwdHnd) || !isHWSIMDClass(useHnd))
+#ifdef FEATURE_SIMD
+        const bool bothHWSIMD = isHWSIMDClass(fwdHnd) && isHWSIMDClass(useHnd);
+#else
+        const bool bothHWSIMD = false;
+#endif
+
+        if (!bothHWSIMD)
         {
             JITDUMP(" would change struct handle (substitution)\n");
             return false;