ZJIT: Use rb_zjit_writebarrier_check_immediate() instead of rb_gc_writebarrier() in gen_write_barrier()

* To avoid calling rb_gc_writebarrier() with an immediate value in gen_write_barrier(),
  and avoid the LIR jump issue.

Author: eregon

zjit.c

@@ -302,6 +302,14 @@ rb_zjit_class_has_default_allocator(VALUE klass)
 
 VALUE rb_vm_get_untagged_block_handler(rb_control_frame_t *reg_cfp);
 
+void
+rb_zjit_writebarrier_check_immediate(VALUE recv, VALUE val)
+{
+    if (!RB_SPECIAL_CONST_P(val)) {
+        rb_gc_writebarrier(recv, val);
+    }
+}
+
 // Primitives used by zjit.rb. Don't put other functions below, which wouldn't use them.
 VALUE rb_zjit_enable(rb_execution_context_t *ec, VALUE self);
 VALUE rb_zjit_assert_compiles(rb_execution_context_t *ec, VALUE self);

zjit/bindgen/src/main.rs

@@ -144,6 +144,7 @@ fn main() {
         .allowlist_function("rb_gc_location")
         .allowlist_function("rb_gc_writebarrier")
         .allowlist_function("rb_gc_writebarrier_remember")
+        .allowlist_function("rb_zjit_writebarrier_check_immediate")
 
         // VALUE variables for Ruby class objects
         .allowlist_var("rb_cBasicObject")

zjit/src/codegen.rs

@@ -1130,11 +1130,12 @@ fn gen_store_field(asm: &mut Assembler, recv: Opnd, id: ID, offset: i32, val: Op
 }
 
 fn gen_write_barrier(asm: &mut Assembler, recv: Opnd, val: Opnd, val_type: Type) {
-    // See RB_OBJ_WRITE/rb_obj_write: it's just assignment and rb_obj_written()->rb_gc_writebarrier()
+    // See RB_OBJ_WRITE/rb_obj_write: it's just assignment and rb_obj_written().
+    // rb_obj_written() does: if (!RB_SPECIAL_CONST_P(val)) { rb_gc_writebarrier(recv, val); }
     if !val_type.is_immediate() {
         asm_comment!(asm, "Write barrier");
         let recv = asm.load(recv);
-        asm_ccall!(asm, rb_gc_writebarrier, recv, val);
+        asm_ccall!(asm, rb_zjit_writebarrier_check_immediate, recv, val);
     }
 }