[x64] Factor out a lot of the opcode handling code

src/xenia/cpu/backend/x64/x64_sequences.h

@@ -12,6 +12,8 @@
 
 #include "xenia/cpu/hir/instr.h"
 
+#include <unordered_map>
+
 namespace xe {
 namespace cpu {
 namespace backend {
@@ -19,6 +21,25 @@ namespace x64 {
 
 class X64Emitter;
 
+typedef bool (*SequenceSelectFn)(X64Emitter&, const hir::Instr*);
+extern std::unordered_map<uint32_t, SequenceSelectFn> sequence_table;
+
+template <typename T>
+bool Register() {
+  sequence_table.insert({T::head_key(), T::Select});
+  return true;
+}
+
+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;
+}
+#define EMITTER_OPCODE_TABLE(name, ...) \
+  const auto X64_INSTR_##name = Register<__VA_ARGS__>();
+
 void RegisterSequences();
 bool SelectSequence(X64Emitter* e, const hir::Instr* i,
                     const hir::Instr** new_tail);