JIT: Update GTF_GLOB_REF after last-use copy omission

src/coreclr/jit/compiler.h

@@ -4534,6 +4534,7 @@ class Compiler
 
     bool fgRemoveRestOfBlock; // true if we know that we will throw
     bool fgStmtRemoved;       // true if we remove statements -> need new DFA
+    bool fgRemarkGlobalUses;  // true if morph should remark global uses after processing a statement
 
     enum FlowGraphOrder
     {
@@ -5818,6 +5819,7 @@ class Compiler
     GenTreeCall* fgMorphArgs(GenTreeCall* call);
 
     void fgMakeOutgoingStructArgCopy(GenTreeCall* call, CallArg* arg);
+    void fgMarkGlobalUses(Statement* stmt);
 
     GenTree* fgMorphLocal(GenTreeLclVarCommon* lclNode);
 #ifdef TARGET_X86

src/coreclr/jit/morph.cpp

@@ -3981,7 +3981,7 @@ void Compiler::fgMakeOutgoingStructArgCopy(GenTreeCall* call, CallArg* arg)
             //
             bool omitCopy = call->IsTailCall();
 
-            if (!omitCopy && fgDidEarlyLiveness)
+            if (!omitCopy && fgGlobalMorph)
             {
                 omitCopy = !varDsc->lvPromoted && ((lcl->gtFlags & GTF_VAR_DEATH) != 0);
             }
@@ -4016,6 +4016,17 @@ void Compiler::fgMakeOutgoingStructArgCopy(GenTreeCall* call, CallArg* arg)
 
                     // Copy prop could allow creating another later use of lcl if there are live assertions about it.
                     fgKillDependentAssertions(varNum DEBUGARG(lcl));
+
+                    // We may have seen previous uses of this local already,
+                    // and those uses should now be marked as GTF_GLOB_REF
+                    // since otherwise they could be reordered with the call.
+                    // The only known issues are under stress mode and happen
+                    // in the same statement, so we only handle this case currently.
+                    // TODO: A more complete fix will likely entail identifying
+                    // these candidates before morph and address exposing them
+                    // at that point, which first requires ABI determination to
+                    // be moved earlier.
+                    fgRemarkGlobalUses = true;
                 }
 
                 JITDUMP("did not need to make outgoing copy for last use of V%02d\n", varNum);
@@ -4096,6 +4107,51 @@ void Compiler::fgMakeOutgoingStructArgCopy(GenTreeCall* call, CallArg* arg)
     arg->SetEarlyNode(argNode);
 }
 
+//------------------------------------------------------------------------
+// fgMarkNewlyGlobalUses: Given a local that is newly address exposed, add
+// GTF_GLOB_REF whever necessary in the specified statement.
+//
+// Arguments:
+//    stmt   - The statement
+//    lclNum - The local that is newly address exposed
+//
+// Notes:
+//    See comment in fgMakeOutgoingStructArgCopy.
+//
+void Compiler::fgMarkGlobalUses(Statement* stmt)
+{
+    struct Visitor : GenTreeVisitor<Visitor>
+    {
+        enum
+        {
+            DoPostOrder = true,
+        };
+
+        Visitor(Compiler* comp) : GenTreeVisitor(comp)
+        {
+        }
+
+        fgWalkResult PostOrderVisit(GenTree** use, GenTree* user)
+        {
+            GenTree* node = *use;
+            if (node->OperIsLocal() && m_compiler->lvaGetDesc(node->AsLclVarCommon()->GetLclNum())->IsAddressExposed())
+            {
+                node->gtFlags |= GTF_GLOB_REF;
+            }
+
+            if (user != nullptr)
+            {
+                user->gtFlags |= node->gtFlags & GTF_GLOB_REF;
+            }
+
+            return WALK_CONTINUE;
+        }
+    };
+
+    Visitor visitor(this);
+    visitor.WalkTree(stmt->GetRootNodePointer(), nullptr);
+}
+
 /*****************************************************************************
  *
  *  A little helper used to rearrange nested commutative operations. The
@@ -13349,6 +13405,7 @@ bool Compiler::fgMorphBlockStmt(BasicBlock* block, Statement* stmt DEBUGARG(cons
 void Compiler::fgMorphStmts(BasicBlock* block)
 {
     fgRemoveRestOfBlock = false;
+    fgRemarkGlobalUses  = false;
 
     for (Statement* const stmt : block->Statements())
     {
@@ -13463,6 +13520,12 @@ void Compiler::fgMorphStmts(BasicBlock* block)
 
         stmt->SetRootNode(morphedTree);
 
+        if (fgRemarkGlobalUses)
+        {
+            fgMarkGlobalUses(stmt);
+            fgRemarkGlobalUses = false;
+        }
+
         if (fgRemoveRestOfBlock)
         {
             continue;