Fix option detection.

Fixed a bug where the post-alloc fast path is not enabled if the plan is
not set from command line.  Now we read the actual value set in the MMTk
builder structure for the actually selected plan.

Also added a global variable so that mutators can test if write barrier
is needed before calling into the write barrier in mmtk-core.

Author: wks

gc.c

@@ -9195,7 +9195,7 @@ void
 rb_gc_writebarrier(VALUE a, VALUE b)
 {
 #if USE_MMTK
-    if (rb_mmtk_enabled_p()) {
+    if (rb_mmtk_enabled_p() && rb_mmtk_use_barrier) {
         mmtk_object_reference_write_post(GET_THREAD()->mutator, (MMTk_ObjectReference)a);
         return;
     }
@@ -9287,7 +9287,7 @@ void
 rb_gc_writebarrier_remember(VALUE obj)
 {
 #if USE_MMTK
-    if (rb_mmtk_enabled_p()) {
+    if (rb_mmtk_enabled_p() && rb_mmtk_use_barrier) {
         mmtk_object_reference_write_post(GET_THREAD()->mutator, (MMTk_ObjectReference)obj);
         return;
     }

internal/mmtk.h

@@ -114,6 +114,21 @@ void mmtk_builder_set_fixed_heap_size(MMTk_Builder *builder, size_t heap_size);
  */
 void mmtk_builder_set_plan(MMTk_Builder *builder, const char *plan_name);
 
+/**
+ * Query if the selected plan is MarkSweep.
+ */
+bool mmtk_builder_is_mark_sweep(MMTk_Builder *builder);
+
+/**
+ * Query if the selected plan is Immix.
+ */
+bool mmtk_builder_is_immix(MMTk_Builder *builder);
+
+/**
+ * Query if the selected plan is StickyImmix.
+ */
+bool mmtk_builder_is_sticky_immix(MMTk_Builder *builder);
+
 /**
  * Build an MMTk instance.
  *

internal/mmtk_support.h

@@ -32,6 +32,9 @@ typedef struct {
     VALUE ary[]; // The actual content.
 } rb_mmtk_objbuf_t;
 
+// Write barrier
+extern bool rb_mmtk_use_barrier;
+
 // Enabled?
 bool rb_mmtk_enabled_p(void);
 

mmtk_support.c

@@ -62,6 +62,7 @@ const char *mmtk_chosen_plan = NULL;
 bool mmtk_plan_is_immix = false;
 bool mmtk_plan_uses_bump_pointer = false;
 bool mmtk_plan_implicitly_pinning = false;
+bool rb_mmtk_use_barrier = false;
 
 size_t mmtk_pre_max_heap_size = 0;
 size_t mmtk_post_max_heap_size = 0;
@@ -269,16 +270,41 @@ apply_cmdline_options(MMTk_Builder *mmtk_builder)
 {
     if (mmtk_chosen_plan != NULL) {
         mmtk_builder_set_plan(mmtk_builder, mmtk_chosen_plan);
-        mmtk_plan_is_immix = strcmp(mmtk_chosen_plan, "Immix") == 0 || strcmp(mmtk_chosen_plan, "StickyImmix") == 0;
-        mmtk_plan_uses_bump_pointer = mmtk_plan_is_immix;
-        mmtk_plan_implicitly_pinning = strcmp(mmtk_chosen_plan, "MarkSweep") == 0;
     }
 
     if (mmtk_max_heap_size > 0) {
         mmtk_builder_set_fixed_heap_size(mmtk_builder, mmtk_max_heap_size);
     }
 }
 
+static void
+set_variables_from_options(MMTk_Builder *mmtk_builder)
+{
+    mmtk_plan_is_immix = mmtk_builder_is_immix(mmtk_builder) || mmtk_builder_is_sticky_immix(mmtk_builder);
+    RUBY_DEBUG_LOG("mmtk_plan_is_immix = %d\n", mmtk_plan_is_immix);
+
+    mmtk_plan_uses_bump_pointer = mmtk_plan_is_immix;
+    RUBY_DEBUG_LOG("mmtk_plan_uses_bump_pointer = %d\n", mmtk_plan_uses_bump_pointer);
+
+    mmtk_plan_implicitly_pinning = mmtk_builder_is_mark_sweep(mmtk_builder);
+    RUBY_DEBUG_LOG("mmtk_plan_implicitly_pinning = %d\n", mmtk_plan_implicitly_pinning);
+
+    // We sometimes for disabling or enabling barriers to measure the impact of barriers.
+    const char* barrier_env_var = getenv("RB_MMTK_FORCE_BARRIER");
+    if (barrier_env_var != NULL) {
+        if (strcmp(barrier_env_var, "1") == 0) {
+            rb_mmtk_use_barrier = true;
+            fprintf(stderr, "WARNING: Force enabling barrier!\n");
+        } else {
+            rb_mmtk_use_barrier = false;
+            fprintf(stderr, "WARNING: Force disabling barrier!\n");
+        }
+    } else {
+        rb_mmtk_use_barrier = mmtk_builder_is_sticky_immix(mmtk_builder);
+    }
+    RUBY_DEBUG_LOG("rb_mmtk_use_barrier = %d\n", rb_mmtk_use_barrier);
+}
+
 void
 rb_mmtk_main_thread_init(void)
 {
@@ -294,6 +320,9 @@ rb_mmtk_main_thread_init(void)
     // (4) Apply cmdline or RUBYOPT options if set.
     apply_cmdline_options(mmtk_builder);
 
+    // Set Ruby-level variables from the actually set options.
+    set_variables_from_options(mmtk_builder);
+
 #if RACTOR_CHECK_MODE
     ruby_binding_options.ractor_check_mode = true;
     // Ruby only needs a uint32_t for the ractor ID.