From 7779243281f82d6e73bd8b98cba84e934194509a Mon Sep 17 00:00:00 2001
From: Jakob Botsch Nielsen <jakob.botsch.nielsen@gmail.com>
Date: Thu, 12 Dec 2024 17:07:11 +0100
Subject: [PATCH] JIT: Avoid remorphing general `gtFoldExpr` return

---
 src/coreclr/jit/gentree.cpp | 24 +++++++++---------------
 src/coreclr/jit/morph.cpp   | 24 +-----------------------
 2 files changed, 10 insertions(+), 38 deletions(-)

diff --git a/src/coreclr/jit/gentree.cpp b/src/coreclr/jit/gentree.cpp
index d8d5752a5f6441..216b7a81785c63 100644
--- a/src/coreclr/jit/gentree.cpp
+++ b/src/coreclr/jit/gentree.cpp
@@ -16571,7 +16571,9 @@ GenTree* Compiler::gtFoldExprConst(GenTree* tree)
     // update args table. For this reason this optimization is enabled only
     // for global morphing phase.
     //
-    // TODO-CQ: Once fgMorphArgs() is fixed this restriction could be removed.
+    // TODO-CQ: Once fgMorphArgs() is fixed this restriction could be removed,
+    // but it would require to know whether or not we are after morph such that
+    // we know when the call created below needs to be in morphed form.
 
     if (!fgGlobalMorph)
     {
@@ -16581,10 +16583,10 @@ GenTree* Compiler::gtFoldExprConst(GenTree* tree)
 
     var_types type = genActualType(tree->TypeGet());
     op1            = type == TYP_LONG ? gtNewLconNode(0) : gtNewIconNode(0);
-    if (vnStore != nullptr)
-    {
-        op1->gtVNPair.SetBoth(vnStore->VNZeroForType(type));
-    }
+    INDEBUG(op1->gtDebugFlags |= GTF_DEBUG_NODE_MORPHED);
+
+    // Would need to set VNs if this wasn't in global morph only.
+    assert(vnStore == nullptr);
 
     JITDUMP("\nFolding binary operator with constant nodes into a comma throw:\n");
     DISPTREE(tree);
@@ -16598,18 +16600,10 @@ GenTree* Compiler::gtFoldExprConst(GenTree* tree)
 
     op2 = op1;
     op1 = gtNewHelperCallNode(CORINFO_HELP_OVERFLOW, TYP_VOID, gtNewIconNode(compCurBB->bbTryIndex));
-
-    // op1 is a call to the JIT helper that throws an Overflow exception.
-    // Attach the ExcSet for VNF_OverflowExc(Void) to this call.
-
-    if (vnStore != nullptr)
-    {
-        op1->gtVNPair = vnStore->VNPWithExc(ValueNumPair(ValueNumStore::VNForVoid(), ValueNumStore::VNForVoid()),
-                                            vnStore->VNPExcSetSingleton(vnStore->VNPairForFunc(TYP_REF, VNF_OverflowExc,
-                                                                                               vnStore->VNPForVoid())));
-    }
+    op1 = fgMorphTree(op1);
 
     tree = gtNewOperNode(GT_COMMA, tree->TypeGet(), op1, op2);
+    INDEBUG(tree->gtDebugFlags |= GTF_DEBUG_NODE_MORPHED);
 
     return tree;
 }
diff --git a/src/coreclr/jit/morph.cpp b/src/coreclr/jit/morph.cpp
index c0b7a6417b2980..e5237dd88b3fea 100644
--- a/src/coreclr/jit/morph.cpp
+++ b/src/coreclr/jit/morph.cpp
@@ -8307,29 +8307,7 @@ GenTree* Compiler::fgMorphSmpOp(GenTree* tree, MorphAddrContext* mac, bool* optA
     // Try to fold it, maybe we get lucky,
     tree = gtFoldExpr(tree);
 
-    if (oldTree != tree)
-    {
-        /* if gtFoldExpr returned op1 or op2 then we are done */
-        if ((tree == op1) || (tree == op2) || (tree == qmarkOp1) || (tree == qmarkOp2))
-        {
-            return tree;
-        }
-
-        /* If we created a comma-throw tree then we need to morph op1 */
-        if (fgIsCommaThrow(tree))
-        {
-            tree->AsOp()->gtOp1 = fgMorphTree(tree->AsOp()->gtOp1);
-            fgMorphTreeDone(tree);
-            return tree;
-        }
-
-        return tree;
-    }
-    else if (tree->OperIsConst())
-    {
-        return tree;
-    }
-    else if (tree->IsNothingNode())
+    if ((oldTree != tree) || tree->OperIsConst() || tree->IsNothingNode())
     {
         return tree;
     }