Rename MVM_cas => MVM_trycas.

The traditional cas definition is to return what was seen. We'll make
MVM_cas mean that in the future, so rename the bool-returning one to
MVM_trycas.

src/core/compunit.c

@@ -49,7 +49,7 @@ MVMCompUnit * MVM_cu_map_from_file(MVMThreadContext *tc, char *filename) {
     /* Add the compilation unit to the head of the unit linked lists. */
     do {
         MVM_ASSIGN_REF(tc, cu, cu->body.next_compunit, tc->instance->head_compunit);
-    } while (!MVM_cas(&tc->instance->head_compunit, cu->body.next_compunit, cu));
+    } while (!MVM_trycas(&tc->instance->head_compunit, cu->body.next_compunit, cu));
 
     return cu;
 }

src/core/frame.c

@@ -249,7 +249,7 @@ static MVMuint64 return_or_unwind(MVMThreadContext *tc, MVMuint8 unwind) {
      * set us as it. */
     do {
         prior = returner->static_info->body.prior_invocation;
-    } while (!MVM_cas(&returner->static_info->body.prior_invocation, prior, returner));
+    } while (!MVM_trycas(&returner->static_info->body.prior_invocation, prior, returner));
     if (prior)
         MVM_frame_dec_ref(tc, prior);
 

src/gc/orchestrate.c

@@ -249,7 +249,7 @@ static void signal_child(MVMThreadContext *tc) {
         /* this will never return nonzero, because the child's status
          * will always be UNABLE or STOLEN. */
         signal_one_thread(tc, child->body.tc);
-        while (!MVM_cas(&tc->thread_obj->body.new_child,
+        while (!MVM_trycas(&tc->thread_obj->body.new_child,
             tc->thread_obj->body.new_child, NULL));
     }
 }
@@ -305,7 +305,7 @@ void MVM_gc_enter_from_allocator(MVMThreadContext *tc) {
     GCORCH_LOG(tc, "Thread %d run %d : Entered from allocate\n");
 
     /* Try to start the GC run. */
-    if (MVM_cas(&tc->instance->gc_start, 0, 1)) {
+    if (MVM_trycas(&tc->instance->gc_start, 0, 1)) {
         MVMThread *last_starter = NULL;
         MVMuint32 num_threads = 0;
 
@@ -331,7 +331,7 @@ void MVM_gc_enter_from_allocator(MVMThreadContext *tc) {
             if (tc->instance->threads && tc->instance->threads != last_starter) {
                 MVMThread *head;
                 MVMuint32 add;
-                while (!MVM_cas(&tc->instance->threads, (head = tc->instance->threads), NULL));
+                while (!MVM_trycas(&tc->instance->threads, (head = tc->instance->threads), NULL));
 
                 add = signal_all_but(tc, head, last_starter);
                 last_starter = head;
@@ -343,7 +343,7 @@ void MVM_gc_enter_from_allocator(MVMThreadContext *tc) {
             }
         } while (tc->instance->gc_start > 1);
 
-        if (!MVM_cas(&tc->instance->threads, NULL, last_starter))
+        if (!MVM_trycas(&tc->instance->threads, NULL, last_starter))
             MVM_panic(MVM_exitcode_gcorch, "threads list corrupted\n");
 
         if (tc->instance->gc_finish != 0)
@@ -384,7 +384,7 @@ void MVM_gc_enter_from_interrupt(MVMThreadContext *tc) {
     GCORCH_LOG(tc, "Thread %d run %d : Entered from interrupt\n");
 
     while ((curr = tc->instance->gc_start) < 2
-            || !MVM_cas(&tc->instance->gc_start, curr, curr - 1)) {
+            || !MVM_trycas(&tc->instance->gc_start, curr, curr - 1)) {
     /*    apr_sleep(1);
         apr_thread_yield();*/
     }

src/moarvm.h

@@ -73,10 +73,13 @@ void MVM_vm_run_file(MVMInstance *instance, char *filename);
 void MVM_vm_dump_file(MVMInstance *instance, char *filename);
 void MVM_vm_destroy_instance(MVMInstance *instance);
 
-/* returns original. Use only on AO_t-sized values (including pointers). */
+/* Returns original. Use only on AO_t-sized values (including pointers). */
 #define MVM_atomic_incr(addr) AO_fetch_and_add1_full((volatile AO_t *)(addr))
 #define MVM_atomic_decr(addr) AO_fetch_and_sub1_full((volatile AO_t *)(addr))
 #define MVM_atomic_add(addr, add) AO_fetch_and_add_full((volatile AO_t *)(addr), (AO_t)(add))
-/* returns non-zero for success. Use for both AO_t numbers and pointers. */
-#define MVM_cas(addr, old, new) AO_compare_and_swap_full((volatile AO_t *)(addr), (AO_t)(old), (AO_t)(new))
+
+/* Returns non-zero for success. Use for both AO_t numbers and pointers. */
+#define MVM_trycas(addr, old, new) AO_compare_and_swap_full((volatile AO_t *)(addr), (AO_t)(old), (AO_t)(new))
+
+/* Full memory barrier. */
 #define MVM_barrier() AO_nop_full()