From e23d61d12488dbf36c493c96c7607aaef176fab9 Mon Sep 17 00:00:00 2001
From: Wunk <wunkolo@gmail.com>
Date: Tue, 15 Nov 2022 12:22:47 -0800
Subject: [PATCH] backend/arm64: Add MSVC C++ ABI devirtualization (#718)

MSVC C++ uses a non-standard ABI definition that must be specially
handled:
https://rants.vastheman.com/2021/09/21/msvc
---
 src/dynarmic/backend/arm64/devirtualize.h | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/src/dynarmic/backend/arm64/devirtualize.h b/src/dynarmic/backend/arm64/devirtualize.h
index edddc954..14057db5 100644
--- a/src/dynarmic/backend/arm64/devirtualize.h
+++ b/src/dynarmic/backend/arm64/devirtualize.h
@@ -16,8 +16,16 @@ struct DevirtualizedCall {
     u64 this_ptr;
 };
 
+// https://rants.vastheman.com/2021/09/21/msvc/
 template<auto mfp>
-DevirtualizedCall Devirtualize(mcl::class_type<decltype(mfp)>* this_) {
+DevirtualizedCall DevirtualizeWindows(mcl::class_type<decltype(mfp)>* this_) {
+    static_assert(sizeof(mfp) == 8);
+    return DevirtualizedCall{mcl::bit_cast<u64>(mfp), reinterpret_cast<u64>(this_)};
+}
+
+// https://github.com/ARM-software/abi-aa/blob/main/cppabi64/cppabi64.rst#representation-of-pointer-to-member-function
+template<auto mfp>
+DevirtualizedCall DevirtualizeDefault(mcl::class_type<decltype(mfp)>* this_) {
     struct MemberFunctionPointer {
         // Address of non-virtual function or index into vtable.
         u64 ptr;
@@ -34,7 +42,16 @@ DevirtualizedCall Devirtualize(mcl::class_type<decltype(mfp)>* this_) {
         u64 vtable = mcl::bit_cast_pointee<u64>(this_ptr);
         fn_ptr = mcl::bit_cast_pointee<u64>(vtable + fn_ptr);
     }
-    return {fn_ptr, this_ptr};
+    return DevirtualizedCall{fn_ptr, this_ptr};
+}
+
+template<auto mfp>
+DevirtualizedCall Devirtualize(mcl::class_type<decltype(mfp)>* this_) {
+#if defined(_WIN32)
+    return DevirtualizeWindows<mfp>(this_);
+#else
+    return DevirtualizeDefault<mfp>(this_);
+#endif
 }
 
 }  // namespace Dynarmic::Backend::Arm64