Implement some simple IR optimizations (get/set eliminiation and DCE)

src/ir_opt/dead_code_elimination_pass.cpp

@@ -0,0 +1,37 @@
+/* This file is part of the dynarmic project.
+ * Copyright (c) 2016 MerryMage
+ * This software may be used and distributed according to the terms of the GNU
+ * General Public License version 2 or any later version.
+ */
+
+#include "common/assert.h"
+#include "frontend/ir/ir.h"
+#include "ir_opt/passes.h"
+
+namespace Dynarmic {
+namespace Optimization {
+
+void DeadCodeElimination(IR::Block& block) {
+    const auto is_side_effect_free = [](IR::Opcode op) -> bool {
+        return IR::GetTypeOf(op) != IR::Type::Void;
+    };
+
+    // We iterate over the instructions in reverse order.
+    // This is because removing an instruction reduces the number of uses for earlier instructions.
+
+    if (block.instructions.empty()) {
+        return;
+    }
+
+    auto iter = block.instructions.end();
+    do {
+        --iter;
+        if (!(*iter)->HasUses() && is_side_effect_free((*iter)->GetOpcode())) {
+            (*iter)->Invalidate();
+            iter = block.instructions.erase(iter);
+        }
+    } while (iter != block.instructions.begin());
+}
+
+} // namespace Optimization
+} // namespace Dynarmic