more small tweaks to the layout optimization PR (#34177)

- fix GC/finalizer properties of CFunction definition
- fix jl_arrayunset implementation for hasptr
- fix missing GC metadata update step inside gc_mark_scan_array8

Author: vtjnash

base/c.jl

@@ -26,7 +26,7 @@ and will be converted automatically at the call site to the appropriate type.
 
 See [`@cfunction`](@ref).
 """
-struct CFunction <: Ref{Cvoid}
+mutable struct CFunction <: Ref{Cvoid}
     ptr::Ptr{Cvoid}
     f::Any
     _1::Ptr{Cvoid}

src/array.c

@@ -619,7 +619,7 @@ JL_DLLEXPORT void jl_arrayunset(jl_array_t *a, size_t i)
     else if (a->flags.hasptr) {
         size_t elsize = a->elsize;
         jl_assume(elsize >= sizeof(void*) && elsize % sizeof(void*) == 0);
-        memset(&((jl_value_t**)a->data)[i], 0, elsize);
+        memset((char*)a->data + elsize * i, 0, elsize);
     }
 }
 

src/gc.c

@@ -1794,6 +1794,7 @@ STATIC_INLINE int gc_mark_scan_array8(jl_ptls_t ptls, jl_gc_mark_sp_t *sp,
             if (elem_begin < elem_end) {
                 // Haven't done with this one yet. Update the content and push it back
                 ary8->elem.begin = elem_begin;
+                ary8->begin = begin;
                 gc_repush_markdata(sp, gc_mark_array8_t);
             }
             else {
@@ -1812,7 +1813,7 @@ STATIC_INLINE int gc_mark_scan_array8(jl_ptls_t ptls, jl_gc_mark_sp_t *sp,
             }
             return 1;
         }
-        ary8->elem.begin = elem_begin = ary8->rebegin;
+        elem_begin = ary8->rebegin;
     }
     gc_mark_push_remset(ptls, ary8->elem.parent, ary8->elem.nptr);
     return 0;