YJIT simplify gen_get_iver and gen_set_ivar

The `shape_id` now includes 3 bits for the `heap_id`.
It is always non-zero for `T_OBJECT` and always zero for all
other types.

Hence all these allocator checks are no longer necessary.

Author: byroot

yjit/src/codegen.rs

@@ -2848,24 +2848,12 @@ fn gen_get_ivar(
     recv: Opnd,
     recv_opnd: YARVOpnd,
 ) -> Option<CodegenStatus> {
-    let comptime_val_klass = comptime_receiver.class_of();
-
     // If recv isn't already a register, load it.
     let recv = match recv {
         Opnd::InsnOut { .. } => recv,
         _ => asm.load(recv),
     };
 
-    // Check if the comptime class uses a custom allocator
-    let custom_allocator = unsafe { rb_get_alloc_func(comptime_val_klass) };
-    let uses_custom_allocator = match custom_allocator {
-        Some(alloc_fun) => {
-            let allocate_instance = rb_class_allocate_instance as *const u8;
-            alloc_fun as *const u8 != allocate_instance
-        }
-        None => false,
-    };
-
     // Check if the comptime receiver is a T_OBJECT
     let receiver_t_object = unsafe { RB_TYPE_P(comptime_receiver, RUBY_T_OBJECT) };
     // Use a general C call at the last chain to avoid exits on megamorphic shapes
@@ -2874,12 +2862,9 @@ fn gen_get_ivar(
         gen_counter_incr(jit, asm, Counter::num_getivar_megamorphic);
     }
 
-    // If the class uses the default allocator, instances should all be T_OBJECT
-    // NOTE: This assumes nobody changes the allocator of the class after allocation.
-    //       Eventually, we can encode whether an object is T_OBJECT or not
-    //       inside object shapes.
+    // NOTE: This assumes T_OBJECT can't ever have the same shape_id as any other type.
     // too-complex shapes can't use index access, so we use rb_ivar_get for them too.
-    if !receiver_t_object || uses_custom_allocator || comptime_receiver.shape_too_complex() || megamorphic {
+    if !receiver_t_object || comptime_receiver.shape_too_complex() || megamorphic {
         // General case. Call rb_ivar_get().
         // VALUE rb_ivar_get(VALUE obj, ID id)
         asm_comment!(asm, "call rb_ivar_get()");
@@ -3073,8 +3058,6 @@ fn gen_set_ivar(
     recv_opnd: YARVOpnd,
     ic: Option<*const iseq_inline_iv_cache_entry>,
 ) -> Option<CodegenStatus> {
-    let comptime_val_klass = comptime_receiver.class_of();
-
     // If the comptime receiver is frozen, writing an IV will raise an exception
     // and we don't want to JIT code to deal with that situation.
     if comptime_receiver.is_frozen() {
@@ -3084,16 +3067,6 @@ fn gen_set_ivar(
 
     let stack_type = asm.ctx.get_opnd_type(StackOpnd(0));
 
-    // Check if the comptime class uses a custom allocator
-    let custom_allocator = unsafe { rb_get_alloc_func(comptime_val_klass) };
-    let uses_custom_allocator = match custom_allocator {
-        Some(alloc_fun) => {
-            let allocate_instance = rb_class_allocate_instance as *const u8;
-            alloc_fun as *const u8 != allocate_instance
-        }
-        None => false,
-    };
-
     // Check if the comptime receiver is a T_OBJECT
     let receiver_t_object = unsafe { RB_TYPE_P(comptime_receiver, RUBY_T_OBJECT) };
     // Use a general C call at the last chain to avoid exits on megamorphic shapes
@@ -3149,10 +3122,9 @@ fn gen_set_ivar(
         None
     };
 
-    // If the receiver isn't a T_OBJECT, or uses a custom allocator,
-    // then just write out the IV write as a function call.
+    // If the receiver isn't a T_OBJECT, then just write out the IV write as a function call.
     // too-complex shapes can't use index access, so we use rb_ivar_get for them too.
-    if !receiver_t_object || uses_custom_allocator || shape_too_complex || new_shape_too_complex || megamorphic {
+    if !receiver_t_object || shape_too_complex || new_shape_too_complex || megamorphic {
         // The function could raise FrozenError.
         // Note that this modifies REG_SP, which is why we do it first
         jit_prepare_non_leaf_call(jit, asm);