Re-enable automatic gc safe transitions in threaded wasm mode (#71229)

Gc safe transitions and memory barriers were disabled for wasm, now they are enabled if the wasm_gc_safepoints AOT compiler option is set or the DISABLE_THREADS define is not active

src/mono/mono/metadata/marshal-lightweight.c

@@ -45,6 +45,7 @@
 #include <mono/utils/mono-threads.h>
 #include <mono/utils/mono-threads-coop.h>
 #include <mono/utils/mono-error-internals.h>
+#include <mono/utils/options.h>
 #include <string.h>
 #include <errno.h>
 #include "icall-decl.h"
@@ -662,7 +663,12 @@ gc_safe_transition_builder_init (GCSafeTransitionBuilder *builder, MonoMethodBui
 	builder->coop_cominterop_fnptr = -1;
 #endif
 #if defined (TARGET_WASM)
-	return FALSE;
+	#ifndef DISABLE_THREADS
+		return TRUE;
+	#else
+		/* if we're in the AOT compiler, obey the --wasm-gc-safepoints option even if the AOT compiler doesn't have threads enabled */
+		return mono_opt_wasm_gc_safepoints;
+	#endif
 #else
 	return TRUE;
 #endif
@@ -2289,7 +2295,12 @@ emit_thunk_invoke_wrapper_ilgen (MonoMethodBuilder *mb, MonoMethod *method, Mono
 	MonoExceptionClause *clause;
 	MonoType *object_type = mono_get_object_type ();
 #if defined (TARGET_WASM)
-	const gboolean do_blocking_transition = FALSE;
+	/* in the AOT compiler emit blocking transitions if --wasm-gc-safepoints was used */
+	#ifndef DISABLE_THREADS
+		const gboolean do_blocking_transition = TRUE;
+	#else
+		const gboolean do_blocking_transition = mono_opt_wasm_gc_safepoints;
+	#endif
 #else
 	const gboolean do_blocking_transition = TRUE;
 #endif

src/mono/mono/mini/interp/transform.c

@@ -3724,9 +3724,7 @@ save_seq_points (TransformData *td, MonoJitInfo *jinfo)
 static void
 interp_emit_memory_barrier (TransformData *td, int kind)
 {
-#if defined(TARGET_WASM)
-	// mono_memory_barrier is dummy on wasm
-#elif defined(TARGET_X86) || defined(TARGET_AMD64)
+#if defined(TARGET_X86) || defined(TARGET_AMD64)
 	if (kind == MONO_MEMORY_BARRIER_SEQ)
 		interp_add_ins (td, MINT_MONO_MEMORY_BARRIER);
 #else

src/mono/mono/mini/mini.h

@@ -2932,7 +2932,11 @@ static inline gboolean
 mini_safepoints_enabled (void)
 {
 #if defined (TARGET_WASM)
-	return mono_opt_wasm_gc_safepoints;
+	#ifndef DISABLE_THREADS
+		return TRUE;
+	#else
+		return mono_opt_wasm_gc_safepoints;
+	#endif
 #else
 	return TRUE;
 #endif

src/mono/mono/utils/mono-membar.h

@@ -21,23 +21,7 @@
  */
 //#define mono_compiler_barrier() asm volatile("": : :"memory")
 
-#ifdef HOST_WASM
-
-static inline void mono_memory_barrier (void)
-{
-}
-
-static inline void mono_memory_read_barrier (void)
-{
-}
-
-static inline void mono_memory_write_barrier (void)
-{
-}
-
-#define mono_compiler_barrier() asm volatile("": : :"memory")
-
-#elif _MSC_VER
+#if _MSC_VER
 #ifndef WIN32_LEAN_AND_MEAN
 #define WIN32_LEAN_AND_MEAN
 #endif
@@ -71,7 +55,7 @@ static inline void mono_memory_write_barrier (void)
 
 #define mono_compiler_barrier() _ReadWriteBarrier ()
 
-#elif defined(USE_GCC_ATOMIC_OPS)
+#elif defined(USE_GCC_ATOMIC_OPS) || defined(HOST_WASM)
 
 static inline void mono_memory_barrier (void)
 {