imm: compiler bug: MSVC 19.12 with /permissive- flag doesn't support fold expressions

src/common/math_util.h

@@ -0,0 +1,28 @@
+/* This file is part of the dynarmic project.
+ * Copyright (c) 2018 MerryMage
+ * This software may be used and distributed according to the terms of the GNU
+ * General Public License version 2 or any later version.
+ */
+
+#pragma once
+
+#include <utility>
+
+namespace Dynarmic {
+namespace Common {
+
+/**
+ * This function is a workaround for a bug in MSVC 19.12 where fold expressions
+ * do not work when the /permissive- flag is enabled.
+ */
+template<typename T, typename... Ts>
+constexpr T Sum(T first, Ts ...rest) {
+    if constexpr (sizeof...(rest) == 0) {
+        return first;
+    } else {
+        return first + Sum(std::forward<Ts>(rest)...);
+    }
+}
+
+} // namespace Common
+} // namespace Dynarmic

src/frontend/A64/imm.h

@@ -9,6 +9,7 @@
 #include "common/assert.h"
 #include "common/bit_util.h"
 #include "common/common_types.h"
+#include "common/math_util.h"
 
 namespace Dynarmic {
 namespace A64 {
@@ -85,13 +86,13 @@ bool operator!=(const Imm<bit_size>& a, u32 b) {
  * This is equivalent to a:b:...:z in ASL.
  */
 template <size_t first_bit_size, size_t ...rest_bit_sizes>
-auto concatenate(Imm<first_bit_size> first, Imm<rest_bit_sizes> ...rest) -> Imm<(first_bit_size + ... + rest_bit_sizes)> {
+auto concatenate(Imm<first_bit_size> first, Imm<rest_bit_sizes> ...rest) {
     if constexpr (sizeof...(rest) == 0) {
         return first;
     } else {
         const auto concat_rest = concatenate(rest...);
         const u32 value = (first.ZeroExtend() << concat_rest.bit_size) | concat_rest.ZeroExtend();
-        return Imm<(first_bit_size + ... + rest_bit_sizes)>{value};
+        return Imm<Common::Sum(first_bit_size, rest_bit_sizes...)>{value};
     }
 }