Merge pull request #8505 from pgavlin/VSO297215

Use a left-leaning comma tree when morphing a stelem.ref helper.

1 files changed, 15 insertions, 18 deletions

diff --git a/src/jit/morph.cpp b/src/jit/morph.cpp
index f0312c0571..aef6029b16 100644
--- a/src/jit/morph.cpp
+++ b/src/jit/morph.cpp
@@ -8141,8 +8141,7 @@ NO_TAIL_CALL:
 
             // Either or both of the array and index arguments may have been spilled to temps by `fgMorphArgs`. Copy
             // the spill trees as well if necessary.
-            GenTree*   argSetup       = nullptr;
-            GenTreeOp* argSetupCursor = nullptr;
+            GenTreeOp* argSetup = nullptr;
             for (GenTreeArgList* earlyArgs = call->gtCallArgs; earlyArgs != nullptr; earlyArgs = earlyArgs->Rest())
             {
                 GenTree* const arg = earlyArgs->Current();
@@ -8154,24 +8153,21 @@ NO_TAIL_CALL:
                 assert(arg != arr);
                 assert(arg != index);
 
-                // NOTE: we pass `arg` as both op1 and op2 of the comma becuase the constructor insists that we provide
-                // a non-null op2. The value of op2 will later be replaced with either the comma node for the next arg
-                // setup node or with the eventual assignment node that replaces the call.
-                GenTreeOp* commaNode = new (this, GT_COMMA) GenTreeOp(GT_COMMA, TYP_VOID, arg, arg);
-                if (argSetup == nullptr)
-                {
-                    argSetup = commaNode;
-                }
-                else
+                arg->gtFlags &= ~GTF_LATE_ARG;
+
+                GenTree* op1 = argSetup;
+                if (op1 == nullptr)
                 {
-                    assert(argSetupCursor != nullptr);
-                    argSetupCursor->gtOp2 = commaNode;
+                    op1 = gtNewNothingNode();
+#if DEBUG
+                    op1->gtDebugFlags |= GTF_DEBUG_NODE_MORPHED;
+#endif // DEBUG
                 }
 
-                argSetupCursor = commaNode;
+                argSetup = new (this, GT_COMMA) GenTreeOp(GT_COMMA, TYP_VOID, op1, arg);
 
 #if DEBUG
-                commaNode->gtDebugFlags |= GTF_DEBUG_NODE_MORPHED;
+                argSetup->gtDebugFlags |= GTF_DEBUG_NODE_MORPHED;
 #endif // DEBUG
             }
 
@@ -8194,9 +8190,10 @@ NO_TAIL_CALL:
             GenTree* result = fgMorphTree(arrStore);
             if (argSetup != nullptr)
             {
-                assert(argSetupCursor != nullptr);
-                argSetupCursor->gtOp2 = result;
-                result                = argSetup;
+                result = new (this, GT_COMMA) GenTreeOp(GT_COMMA, TYP_VOID, argSetup, result);
+#if DEBUG
+                result->gtDebugFlags |= GTF_DEBUG_NODE_MORPHED;
+#endif // DEBUG
             }
 
             return result;