[gc] initialize more stack-allocated ptrs

see GH #1067.
initialize more values on the C-stack to help the GC.
also change some mem_internal_* to mem_sys_*
mem_internal_* are only macros to mem_sys now.

testcase:
  valgrind --track-origins=yes ./parrot_old examples/benchmarks/dispatch.pir

There's still a remaining stack-object scanned,
int offset from runops(src/call/ops.c),
which can only be fixed with a precise GC.

src/gc/fixed_allocator.c

@@ -138,7 +138,6 @@ struct Fixed_Allocator*
 Parrot_gc_fixed_allocator_new(SHIM_INTERP)
 {
     ASSERT_ARGS(Parrot_gc_fixed_allocator_new)
-
     return mem_internal_allocate_zeroed_typed(Fixed_Allocator);
 }
 
@@ -311,7 +310,7 @@ Parrot_gc_pool_new(SHIM_INTERP, size_t object_size)
     newpool->newfree           = NULL;
     newpool->newlast           = NULL;
     newpool->num_arenas        = 0;
-    newpool->arena_bounds      = (void **)mem_sys_allocate(NEXT_ARENA_BOUNDS_SIZE(0));
+    newpool->arena_bounds      = (void **)mem_sys_allocate_zeroed(NEXT_ARENA_BOUNDS_SIZE(0));
 
     return newpool;
 }
@@ -323,16 +322,13 @@ Parrot_gc_pool_destroy(SHIM_INTERP, ARGMOD(Pool_Allocator *pool))
     ASSERT_ARGS(Parrot_gc_pool_destroy)
 
     Pool_Allocator_Arena *arena = pool->top_arena;
-
     while (arena) {
         Pool_Allocator_Arena * const next = arena->next;
-        mem_internal_free(arena);
+        mem_sys_free(arena);
         arena = next;
     }
-
     mem_sys_free(pool->arena_bounds);
-
-    mem_internal_free(pool);
+    mem_sys_free(pool);
 }
 
 PARROT_CANNOT_RETURN_NULL
@@ -544,7 +540,7 @@ allocate_new_pool_arena(PARROT_INTERP, ARGMOD(Pool_Allocator *pool))
     /* Run a GC if needed */
     Parrot_gc_maybe_mark_and_sweep(interp, GC_trace_stack_FLAG);
 
-    new_arena = (Pool_Allocator_Arena *)mem_internal_allocate_zeroed(total_size);
+    new_arena = (Pool_Allocator_Arena *)mem_sys_allocate_zeroed(total_size);
 
     interp->gc_sys->stats.memory_allocated += total_size;
 

src/gc/gc_gms.c

@@ -1477,7 +1477,7 @@ gc_gms_allocate_pmc_header(PARROT_INTERP, SHIM(UINTVAL flags))
     ASSERT_ARGS(gc_gms_allocate_pmc_header)
     MarkSweep_GC     * const self = (MarkSweep_GC *)interp->gc_sys->gc_private;
     Pool_Allocator   * const pool = self->pmc_allocator;
-    pmc_alloc_struct *item;
+    pmc_alloc_struct * item = NULL;
 
     gc_gms_maybe_mark_and_sweep(interp);
 

src/pmc.c

@@ -506,7 +506,7 @@ static PMC *
 get_new_pmc_header(PARROT_INTERP, INTVAL base_type, UINTVAL flags)
 {
     ASSERT_ARGS(get_new_pmc_header)
-    PMC    *newpmc;
+    PMC    *newpmc = NULL;
     VTABLE *vtable = interp->vtables[base_type];
     UINTVAL vtable_flags;
 

src/pmc/callcontext.pmc

@@ -465,10 +465,12 @@ mark_positionals(PARROT_INTERP, ARGIN(PMC *self))
     if (size) {
         Pcc_cell *cells;
         INTVAL i;
-        GETATTR_CallContext_positionals(interp, self, cells);
 
-        for (i = 0; i < size; ++i)
-            mark_cell(interp, &cells[i]);
+        GETATTR_CallContext_positionals(interp, self, cells);
+        if (cells) {
+            for (i = 0; i < size; ++i)
+                mark_cell(interp, &cells[i]);
+        }
     }
 }