Get MMTK to use the newobj hook patchpoint for ZJIT's alloc fastpath

Previously only the default GC used this patchpoint. MMTK had to check if
newobj hooks were enabled in its fastpath, which it no longer does.

Author: luke-gruber

zjit/src/codegen/gc_fastpath.rs

@@ -63,17 +63,14 @@ pub(super) fn gc_fastpath_new_obj(
         return slow_path(asm);
     };
 
-    // The default GC's inline fast path bumps the ractor cache cursor in emitted
-    // code without calling rb_newobj, so it can't fire the NEWOBJ internal event.
-    // If such a hook is active, use the C path instead; otherwise assume none is
-    // active and install a patch point that discards this code if one is enabled
-    // later. (MMTk's fast path checks for the hook at run time, so it needs neither.)
-    if let PreparedNewObjFastpath::Default(_) = &fastpath {
-        if unsafe { rb_zjit_newobj_hook_enabled_p() } {
-            return slow_path(asm);
-        }
-        gen_patch_point(jit, asm, function, &Invariant::NoNewObjHook, state);
+    // Both inline fast paths bump an allocation cursor without calling rb_newobj,
+    // so neither fires the NEWOBJ internal event. If such a hook is active, use the
+    // C path; otherwise assume none is active and install a patch point that
+    // discards this code if one is enabled later.
+    if unsafe { rb_zjit_newobj_hook_enabled_p() } {
+        return slow_path(asm);
     }
+    gen_patch_point(jit, asm, function, &Invariant::NoNewObjHook, state);
 
     asm_comment!(asm, "GC inline allocation");
 
@@ -122,7 +119,6 @@ fn prepare_new_obj_fastpath(alloc_size: usize, flags: u64, klass: VALUE) -> Opti
             let fastpath = unsafe { fastpath.data.mmtk };
             if fastpath.objspace.is_null()
                 || fastpath.gc_stress_p_func == 0
-                || fastpath.newobj_tracing_p_func == 0
                 || fastpath.post_alloc_func == 0
                 || fastpath.min_obj_align == 0
                 || !fastpath.min_obj_align.is_power_of_two()
@@ -246,17 +242,11 @@ fn emit_mmtk_new_obj_fastpath(
         .try_into()
         .ok()?;
     let value_size_shift: u64 = fastpath.value_size_shift.try_into().ok()?;
-    let newobj_tracing_p_func = (fastpath.newobj_tracing_p_func != 0)
-        .then_some(fastpath.newobj_tracing_p_func as *const u8)?;
     let gc_stress_p_func = (fastpath.gc_stress_p_func != 0)
         .then_some(fastpath.gc_stress_p_func as *const u8)?;
     let post_alloc_func = (fastpath.post_alloc_func != 0)
         .then_some(fastpath.post_alloc_func as *const u8)?;
 
-    let event_hook = asm.ccall(newobj_tracing_p_func, vec![]);
-    asm.test(event_hook, event_hook);
-    asm.jnz(jit, miss.clone());
-
     let objspace_const = Opnd::const_ptr(fastpath.objspace);
     let gc_stress = asm.ccall(gc_stress_p_func, vec![objspace_const]);
     asm.test(gc_stress, gc_stress);