py/obj.h: Make sequence grow more efficient and support overlapping.

The first memmove now copies less bytes in some cases (because len_adj <=
slice_len), and the memcpy is replaced with memmove to support the
possibility that dest and slice regions are overlapping.

py/obj.h

@@ -842,9 +842,10 @@ mp_obj_t mp_seq_extract_slice(size_t len, const mp_obj_t *seq, mp_bound_slice_t
     /*printf("memmove(%p, %p, %d)\n", dest + (beg + slice_len), dest + end, (dest_len - end) * (item_sz));*/ \
     memmove(((char*)dest) + (beg + slice_len) * (item_sz), ((char*)dest) + (end) * (item_sz), (dest_len - end) * (item_sz));
 
+// Note: dest and slice regions may overlap
 #define mp_seq_replace_slice_grow_inplace(dest, dest_len, beg, end, slice, slice_len, len_adj, item_sz) \
     /*printf("memmove(%p, %p, %d)\n", dest + beg + len_adj, dest + beg, (dest_len - beg) * (item_sz));*/ \
-    memmove(((char*)dest) + (beg + len_adj) * (item_sz), ((char*)dest) + (beg) * (item_sz), (dest_len - beg) * (item_sz)); \
+    memmove(((char*)dest) + (beg + slice_len) * (item_sz), ((char*)dest) + (end) * (item_sz), ((dest_len) + (len_adj) - ((beg) + (slice_len))) * (item_sz)); \
-    memcpy(((char*)dest) + (beg) * (item_sz), slice, slice_len * (item_sz));
+    memmove(((char*)dest) + (beg) * (item_sz), slice, slice_len * (item_sz));
 
 #endif // __MICROPY_INCLUDED_PY_OBJ_H__