IROpt: Port get/set elimination pass to current IR

src/frontend/ir/ir.cpp

@@ -87,6 +87,18 @@ void Inst::Invalidate() {
     }
 }
 
+void Inst::ReplaceUsesWith(Value& replacement) {
+    Invalidate();
+
+    op = Opcode::Identity;
+
+    if (!replacement.IsImmediate()) {
+        Use(replacement);
+    }
+
+    args[0] = replacement;
+}
+
 void Inst::Use(Value& value) {
     value.GetInst()->use_count++;
 

src/frontend/ir/ir.h

@@ -148,6 +148,8 @@ public:
 
     void Invalidate();
 
+    void ReplaceUsesWith(Value& replacement);
+
     size_t use_count = 0;
     Inst* carry_inst = nullptr;
     Inst* overflow_inst = nullptr;

src/frontend/ir/opcodes.inc

@@ -1,5 +1,7 @@
 //     opcode name,             return type,    arg1 type,      arg2 type,      arg3 type,      ...
 
+OPCODE(Identity,                T::Opaque,      T::Opaque                                       )
+
 // ARM Context getters/setters
 OPCODE(GetRegister,             T::U32,         T::RegRef                                       )
 OPCODE(SetRegister,             T::Void,        T::RegRef,      T::U32                          )