[windows] Return x86 microsleep for Windows (#3563)

Microsleep removal may have regressed AOC in msvc

Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/3563
Reviewed-by: CamilleLaVey <camillelavey99@gmail.com>
Reviewed-by: Lizzie <lizzie@eden-emu.dev>
Co-authored-by: John <john@eden-emu.dev>
Co-committed-by: John <john@eden-emu.dev>

3 files changed, 87 insertions, 0 deletions

diff --git a/src/common/CMakeLists.txt b/src/common/CMakeLists.txt
index 58d2b2279e..7d299b708e 100644
--- a/src/common/CMakeLists.txt
+++ b/src/common/CMakeLists.txt
@@ -186,6 +186,8 @@ if(ARCHITECTURE_x86_64)
         common
         PRIVATE x64/cpu_detect.cpp
         x64/cpu_detect.h
+        x64/cpu_wait.cpp
+        x64/cpu_wait.h
         x64/native_clock.cpp
         x64/native_clock.h
         x64/rdtsc.cpp
diff --git a/src/common/x64/cpu_wait.cpp b/src/common/x64/cpu_wait.cpp
new file mode 100644
index 0000000000..85d27161ba
--- /dev/null
+++ b/src/common/x64/cpu_wait.cpp
@@ -0,0 +1,75 @@
+// SPDX-FileCopyrightText: Copyright 2026 Eden Emulator Project
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+#include <thread>
+
+#ifdef _MSC_VER
+#include <intrin.h>
+#endif
+
+#include "common/x64/cpu_detect.h"
+#include "common/x64/cpu_wait.h"
+#include "common/x64/rdtsc.h"
+
+namespace Common::X64 {
+
+namespace {
+
+// 100,000 cycles is a reasonable amount of time to wait to save on CPU resources.
+// For reference:
+// At 1 GHz, 100K cycles is 100us
+// At 2 GHz, 100K cycles is 50us
+// At 4 GHz, 100K cycles is 25us
+constexpr auto PauseCycles = 100'000U;
+
+} // Anonymous namespace
+
+#if defined(_MSC_VER) && !defined(__clang__)
+__forceinline static void TPAUSE() {
+    static constexpr auto RequestC02State = 0U;
+    _tpause(RequestC02State, FencedRDTSC() + PauseCycles);
+}
+
+__forceinline static void MWAITX() {
+    static constexpr auto EnableWaitTimeFlag = 1U << 1;
+    static constexpr auto RequestC1State = 0U;
+
+    // monitor_var should be aligned to a cache line.
+    alignas(64) u64 monitor_var{};
+    _mm_monitorx(&monitor_var, 0, 0);
+    _mm_mwaitx(EnableWaitTimeFlag, RequestC1State, PauseCycles);
+}
+#else
+static void TPAUSE() {
+    static constexpr auto RequestC02State = 0U;
+    const auto tsc = FencedRDTSC() + PauseCycles;
+    const auto eax = static_cast<u32>(tsc & 0xFFFFFFFF);
+    const auto edx = static_cast<u32>(tsc >> 32);
+    asm volatile("tpause %0" : : "r"(RequestC02State), "d"(edx), "a"(eax));
+}
+
+static void MWAITX() {
+    static constexpr auto EnableWaitTimeFlag = 1U << 1;
+    static constexpr auto RequestC1State = 0U;
+
+    // monitor_var should be aligned to a cache line.
+    alignas(64) u64 monitor_var{};
+    asm volatile("monitorx" : : "a"(&monitor_var), "c"(0), "d"(0));
+    asm volatile("mwaitx" : : "a"(RequestC1State), "b"(PauseCycles), "c"(EnableWaitTimeFlag));
+}
+#endif
+
+void MicroSleep() {
+    static const bool has_waitpkg = GetCPUCaps().waitpkg;
+    static const bool has_monitorx = GetCPUCaps().monitorx;
+
+    if (has_waitpkg) {
+        TPAUSE();
+    } else if (has_monitorx) {
+        MWAITX();
+    } else {
+        std::this_thread::yield();
+    }
+}
+
+} // namespace Common::X64
diff --git a/src/common/x64/cpu_wait.h b/src/common/x64/cpu_wait.h
new file mode 100644
index 0000000000..472ddca815
--- /dev/null
+++ b/src/common/x64/cpu_wait.h
@@ -0,0 +1,10 @@
+// SPDX-FileCopyrightText: Copyright 2026 Eden Emulator Project
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+#pragma once
+
+namespace Common::X64 {
+
+void MicroSleep();
+
+} // namespace Common::X64