diff --git a/src/llvm/lib/Target/W65816/W65816StackSlotMerge.cpp b/src/llvm/lib/Target/W65816/W65816StackSlotMerge.cpp
index 908a52e..216404f 100644
--- a/src/llvm/lib/Target/W65816/W65816StackSlotMerge.cpp
+++ b/src/llvm/lib/Target/W65816/W65816StackSlotMerge.cpp
@@ -549,12 +549,16 @@ bool W65816StackSlotMerge::runOnMachineFunction(MachineFunction &MF) {
   // a DBG_VALUE that still points at slot-X reads stale data.
   //
   // For DBG_VALUEs whose DIExpression has a leading constant offset that
-  // matches a renamed slot, we mark them as undef.  This loses debug
-  // info at the affected PC range but never reports a wrong variable
-  // value.  A future enhancement could rewrite the offset to point at
-  // the merged slot Y (the merge proves they hold equivalent values
-  // function-wide), but that requires DIExpression rewriting and
-  // re-uniquing which is non-trivial in this position.
+  // matches a renamed slot X, relocate them to the merged slot Y by
+  // rewriting that leading offset (the merge proved X and Y hold
+  // equivalent values function-wide, so Y's memory is a correct location
+  // for the variable).  The trailing ops are preserved verbatim and the
+  // offset is re-encoded with the canonical appendOffset form, which is
+  // exactly what extractLeadingOffset decodes -- so this is faithful.
+  // This keeps the variable's location live across the rename; previously
+  // we dropped it (setDebugValueUndef), losing debug info at those PCs.
+  // Falls back to undef only if re-encoding somehow fails.
+  LLVMContext &Ctx = MF.getFunction().getContext();
   bool Changed = false;
   for (MachineBasicBlock &MBB : MF) {
     for (MachineInstr &MI : MBB) {
@@ -565,14 +569,21 @@ bool W65816StackSlotMerge::runOnMachineFunction(MachineFunction &MF) {
       SmallVector<uint64_t, 4> Remaining;
       if (!Expr->extractLeadingOffset(LeadingOff, Remaining))
         continue;
-      if (!Renames.count(LeadingOff)) continue;
-      // Match: this DBG_VALUE points at slot X (now renamed).  Undef
-      // every register debug operand to drop the location at this PC.
-      for (MachineOperand &Op : MI.debug_operands()) {
-        if (Op.isReg()) {
-          Op.setReg(0);
-          Op.setSubReg(0);
-        }
+      auto RIt = Renames.find(LeadingOff);
+      if (RIt == Renames.end()) continue;
+      // Match: this DBG_VALUE points at slot X (now renamed to Y).
+      SmallVector<uint64_t, 8> NewOps;
+      DIExpression::appendOffset(NewOps, RIt->second);
+      NewOps.append(Remaining.begin(), Remaining.end());
+      if (const DIExpression *NewExpr = DIExpression::get(Ctx, NewOps)) {
+        MI.getDebugExpressionOp().setMetadata(NewExpr);
+      } else {
+        // Should not happen; keep the old fail-safe behavior.
+        for (MachineOperand &Op : MI.debug_operands())
+          if (Op.isReg()) {
+            Op.setReg(0);
+            Op.setSubReg(0);
+          }
       }
       Changed = true;
     }