From f3bf27c816ba43266e339c8dfc558d0222f0e275 Mon Sep 17 00:00:00 2001
From: Merry <git@mary.rs>
Date: Sun, 24 Jul 2022 11:50:04 +0100
Subject: [PATCH] backend/arm64: Implement Devirtualize

---
 src/dynarmic/CMakeLists.txt               |  1 +
 src/dynarmic/backend/arm64/devirtualize.h | 40 +++++++++++++++++++++++
 2 files changed, 41 insertions(+)
 create mode 100644 src/dynarmic/backend/arm64/devirtualize.h

diff --git a/src/dynarmic/CMakeLists.txt b/src/dynarmic/CMakeLists.txt
index de5167fc..b033e7c1 100644
--- a/src/dynarmic/CMakeLists.txt
+++ b/src/dynarmic/CMakeLists.txt
@@ -373,6 +373,7 @@ elseif(ARCHITECTURE STREQUAL "arm64")
         backend/arm64/a32_jitstate.h
         backend/arm64/abi.cpp
         backend/arm64/abi.h
+        backend/arm64/devirtualize.h
         backend/arm64/emit_arm64.cpp
         backend/arm64/emit_arm64.h
         backend/arm64/emit_arm64_a32.cpp
diff --git a/src/dynarmic/backend/arm64/devirtualize.h b/src/dynarmic/backend/arm64/devirtualize.h
new file mode 100644
index 00000000..edddc954
--- /dev/null
+++ b/src/dynarmic/backend/arm64/devirtualize.h
@@ -0,0 +1,40 @@
+/* This file is part of the dynarmic project.
+ * Copyright (c) 2022 MerryMage
+ * SPDX-License-Identifier: 0BSD
+ */
+
+#pragma once
+
+#include <mcl/bit_cast.hpp>
+#include <mcl/stdint.hpp>
+#include <mcl/type_traits/function_info.hpp>
+
+namespace Dynarmic::Backend::Arm64 {
+
+struct DevirtualizedCall {
+    u64 fn_ptr;
+    u64 this_ptr;
+};
+
+template<auto mfp>
+DevirtualizedCall Devirtualize(mcl::class_type<decltype(mfp)>* this_) {
+    struct MemberFunctionPointer {
+        // Address of non-virtual function or index into vtable.
+        u64 ptr;
+        // LSB is discriminator for if function is virtual. Other bits are this adjustment.
+        u64 adj;
+    } mfp_struct = mcl::bit_cast<MemberFunctionPointer>(mfp);
+
+    static_assert(sizeof(MemberFunctionPointer) == 16);
+    static_assert(sizeof(MemberFunctionPointer) == sizeof(mfp));
+
+    u64 fn_ptr = mfp_struct.ptr;
+    u64 this_ptr = mcl::bit_cast<u64>(this_) + (mfp_struct.adj >> 1);
+    if (mfp_struct.adj & 1) {
+        u64 vtable = mcl::bit_cast_pointee<u64>(this_ptr);
+        fn_ptr = mcl::bit_cast_pointee<u64>(vtable + fn_ptr);
+    }
+    return {fn_ptr, this_ptr};
+}
+
+}  // namespace Dynarmic::Backend::Arm64