[turbofan] Unify referencing of stack slots

src/compiler/code-generator.cc

Index: src/compiler/code-generator.cc
diff --git a/src/compiler/code-generator.cc b/src/compiler/code-generator.cc
index 4f0b0390442d87dc8ba4f7a2446c502116ce68ed..fa07243760a9cf470d586d4eab5064881c0e7e21 100644
--- a/src/compiler/code-generator.cc
+++ b/src/compiler/code-generator.cc
@@ -216,10 +216,16 @@ void CodeGenerator::RecordSafepoint(ReferenceMap* references,
                                     Safepoint::DeoptMode deopt_mode) {
   Safepoint safepoint =
       safepoints()->DefineSafepoint(masm(), kind, arguments, deopt_mode);
+  int stackSlotToSpillSlotDelta =
+      frame()->GetTotalFrameSlotCount() - frame()->GetSpillSlotCount();
   for (auto& operand : references->reference_operands()) {
     if (operand.IsStackSlot()) {
-      safepoint.DefinePointerSlot(StackSlotOperand::cast(operand).index(),
-                                  zone());
+      int index = StackSlotOperand::cast(operand).index();
+      DCHECK(index >= 0);
+      // Safepoint table indices are 0-based from the beginning of the spill
+      // slot area, adjust appropriately.
+      index -= stackSlotToSpillSlotDelta;
+      safepoint.DefinePointerSlot(index, zone());
     } else if (operand.IsRegister() && (kind & Safepoint::kWithRegisters)) {
       Register reg =
           Register::FromAllocationIndex(RegisterOperand::cast(operand).index());