[PATCH v2 0/2] MR7895: Revert "kernel32/tests: Don't use _ReadWriteBarrier on ARM platforms."

[Jinoh Kang (＠iamahuman)]

This reverts commit 504a305a60849704f2d83b55e9aabb26d89edf11.

The choice of weak barrier was by design. The stronger barrier broke the
positive half of the litmus test for FlushProcessWriteBuffers():
> virtual.c:4568: Test failed: expected write-read reordering with compiler barrier
>  only (got 0 reorderings)

FlushProcessWriteBuffers() is used in tandem with a compiler-only
barrier to implement fast synchronization, where only one side is
executed frequently and the other side only occassionally (e.g., garbage
collection).  Prominent applications include .NET and HotSpot JVM.

Although _ReadWriteBarrier() is "marked deprecated," it is in fact used
by Microsoft's own STL library (with explicit suppression of warning) to
implement a compiler-only memory barrier[^1].  The deprecation notice
suggests C++11 atomics as the (only?) alternative.

[^1]: https://github.com/microsoft/STL/blob/b5df16a98934319e2e6864d6036cbe9cd9c74f...

--
  v2: kernel32/tests: Don't use _ReadWriteBarrier() on clang.

https://gitlab.winehq.org/wine/wine/-/merge_requests/7895

[PATCH v2 1/2] Revert "kernel32/tests: Don't use _ReadWriteBarrier on ARM platforms."

[Jinoh Kang]

From: Jinoh Kang

This reverts commit 504a305a60849704f2d83b55e9aabb26d89edf11.

The choice of weak barrier was by design. The stronger barrier broke the
positive half of the litmus test for FlushProcessWriteBuffers():
> virtual.c:4568: Test failed: expected write-read reordering with compiler barrier
>  only (got 0 reorderings)

FlushProcessWriteBuffers() is used in tandem with a compiler-only
barrier to implement fast synchronization, where only one side is
executed frequently and the other side only occassionally (e.g., garbage
collection).  Prominent applications include .NET and HotSpot JVM.

Although _ReadWriteBarrier() is "marked deprecated," it is in fact used
by Microsoft's own STL library (with explicit suppression of warning) to
implement a compiler-only memory barrier [1].  The deprecation notice
suggests C++11 atomics as the (only?) alternative.

[1]: https://github.com/microsoft/STL/blob/b5df16a98934319e2e6864d6036cbe9cd9c74f...
---
 dlls/kernel32/tests/virtual.c | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/dlls/kernel32/tests/virtual.c b/dlls/kernel32/tests/virtual.c
index b83b32dc88c..1c84acfc215 100644
--- a/dlls/kernel32/tests/virtual.c
+++ b/dlls/kernel32/tests/virtual.c
@@ -4469,16 +4469,13 @@ static DWORD CALLBACK sbtest_thread_proc( void *arg )

#ifdef _MSC_VER

+#pragma intrinsic(_ReadWriteBarrier)
+void _ReadWriteBarrier(void);
+
 static void WINAPI compiler_barrier(void)
 {
-#if defined(__i386__) || defined(__x86_64__)
 #pragma warning(suppress:4996)
     _ReadWriteBarrier();
-#elif defined(__arm__)
-    __dmb(_ARM_BARRIER_ISH);
-#elif defined(__aarch64__)
-    __dmb(_ARM64_BARRIER_ISH);
-#endif
 }

#else  /* _MSC_VER */

[PATCH v2 2/2] kernel32/tests: Don't use _ReadWriteBarrier() on clang.

[Jinoh Kang]

From: Jinoh Kang

Some clang versions do not support _ReadWriteBarrier() when targeting
armv7-windows (MSVC mode).
---
 dlls/kernel32/tests/virtual.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/dlls/kernel32/tests/virtual.c b/dlls/kernel32/tests/virtual.c
index 1c84acfc215..f35fbdee8dc 100644
--- a/dlls/kernel32/tests/virtual.c
+++ b/dlls/kernel32/tests/virtual.c
@@ -4467,7 +4467,7 @@ static DWORD CALLBACK sbtest_thread_proc( void *arg )
     return 0;
 }

-#ifdef _MSC_VER
+#if defined(_MSC_VER) && !defined(__clang__)

#pragma intrinsic(_ReadWriteBarrier)
 void _ReadWriteBarrier(void);
@@ -4478,14 +4478,14 @@ static void WINAPI compiler_barrier(void)
     _ReadWriteBarrier();
 }

-#else  /* _MSC_VER */
+#else  /* defined(_MSC_VER) && !defined(__clang__) */

static void WINAPI compiler_barrier(void)
 {
     __asm__ __volatile__("" ::: "memory");
 }

-#endif  /* _MSC_VER */
+#endif  /* defined(_MSC_VER) && !defined(__clang__) */

static LONG store_buffer_litmus_test( void (*WINAPI barrier0)(void), void (*WINAPI barrier1)(void) )
 {

[Jinoh Kang (＠iamahuman)]

v2: Fix build on clang MSVC mode for arm(v7)-windows.