variable.c: reduce memory usage of instance variable table

This is a fundamentally simplified reimplementation of #5317
by @shuujii

Instead of having array of `struct iv_elem`, we have sequences of keys
and values packed in single chunk of malloc'ed memory. We don't have to
worry about gaps from alignment, especially on 64 bit architecture,
where `sizeof(struct iv_elem)` probably consumes 16 bytes, but
`sizeof(mrb_sym)+sizeof(mrb_value)` is 12 bytes.

In addition, this change could improve memory access locality.

close #5317

0 files changed, 0 insertions, 0 deletions