[A64/Sequences] Centralize sequence registration

- Replace global table with a singleton accessor

- Switch registration to fold expressions with duplicate warnings

- Update SelectSequence signature and entrypoint lookup

src/xenia/cpu/backend/a64/a64_sequences.cc

@@ -1,4 +1,4 @@
-/**
+/**
  ******************************************************************************
  * Xenia : Xbox 360 Emulator Research Project                                 *
  ******************************************************************************
@@ -53,7 +53,7 @@ using namespace xe::cpu::hir;
 using xe::cpu::hir::Instr;
 
 typedef bool (*SequenceSelectFn)(A64Emitter&, const Instr*);
-std::unordered_map<uint32_t, SequenceSelectFn> sequence_table;
+// std::unordered_map<uint32_t, SequenceSelectFn> sequence_table; Removed
 
 // ============================================================================
 // OPCODE_COMMENT
@@ -2769,10 +2769,12 @@ static int anchor_memory_dest = anchor_memory;
 extern volatile int anchor_vector;
 static int anchor_vector_dest = anchor_vector;
 
-bool SelectSequence(A64Emitter* e, const Instr* i, const Instr** new_tail) {
+bool SelectSequence(A64Emitter* e, const hir::Instr* i,
+                    const hir::Instr** new_tail) {
   const InstrKey key(i);
-  auto it = sequence_table.find(key);
-  if (it != sequence_table.end()) {
+  auto& table = GetSequenceTable();  // Use the singleton accessor
+  auto it = table.find(key);
+  if (it != table.end()) {
     if (it->second(*e, i)) {
       *new_tail = i->next;
       return true;

src/xenia/cpu/backend/a64/a64_sequences.h

@@ -10,9 +10,10 @@
 #ifndef XENIA_CPU_BACKEND_A64_A64_SEQUENCES_H_
 #define XENIA_CPU_BACKEND_A64_A64_SEQUENCES_H_
 
-#include "xenia/cpu/hir/instr.h"
-
+#include <functional>
+#include <iostream>  // For logging
 #include <unordered_map>
+#include "xenia/cpu/hir/instr.h"
 
 namespace xe {
 namespace cpu {
@@ -22,24 +23,34 @@ namespace a64 {
 class A64Emitter;
 
 typedef bool (*SequenceSelectFn)(A64Emitter&, const hir::Instr*);
-extern std::unordered_map<uint32_t, SequenceSelectFn> sequence_table;
 
+// Singleton accessor for sequence_table
+inline std::unordered_map<uint32_t, SequenceSelectFn>& GetSequenceTable() {
+  static std::unordered_map<uint32_t, SequenceSelectFn> sequence_table;
+  return sequence_table;
+}
+
+// Registration Functions
 template <typename T>
-bool Register() {
-  sequence_table.insert({T::head_key(), T::Select});
-  return true;
+bool RegisterSingle() {
+  bool inserted = GetSequenceTable().emplace(T::head_key(), T::Select).second;
+  if (!inserted) {
+    std::cerr << "Warning: Duplicate head_key detected for key "
+              << T::head_key() << std::endl;
+  }
+  return inserted;
 }
 
-template <typename T, typename Tn, typename... Ts>
-static bool Register() {
-  bool b = true;
-  b = b && Register<T>();          // Call the above function
-  b = b && Register<Tn, Ts...>();  // Call ourself again (recursively)
-  return b;
+template <typename... Ts>
+bool RegisterAll() {
+  return (RegisterSingle<Ts>() && ...);  // Fold expression (C++17)
 }
+
+// Macro for Registration
 #define EMITTER_OPCODE_TABLE(name, ...) \
-  const auto A64_INSTR_##name = Register<__VA_ARGS__>();
+  static const bool A64_INSTR_##name = RegisterAll<__VA_ARGS__>();
 
+// Function to Select Sequence
 bool SelectSequence(A64Emitter* e, const hir::Instr* i,
                     const hir::Instr** new_tail);