On Wed, Mar 20, 2019 at 05:32:16PM -0400, Jason Merrill wrote:
> > Does this look reasonable, or do you have other proposals?
>
> IMO if you need to guard usage with
>
> + if (some_type_hash_table.size () == 0)
> + some_type_hash_table.create ();
>
> this isn't any better than
>
> /* Create the constexpr function table if necessary. */
> if (constexpr_fundef_table == NULL)
> constexpr_fundef_table
> = hash_table<constexpr_fundef_hasher>::create_ggc (101);
Well, this is surely more costly in that it allocates both the hash_table
structure and the memory pointed by it from GC.
> Better I think would be to make the member functions handle null m_entries
> sensibly.
The goal was not to slow down all current hash_{table,set,map} uses by
adding runtime checks if m_size is 0 or m_entries is NULL or similar
(and also grow code size that way).
I guess another option would be to make the decision whether
the hash_{table,set,map} is constructed with allocation right away (and no
runtime checks for it) or if it is lazy another template argument (bool
Lazy = false before the Allocator template argument), if !Lazy, it would
work exactly as it is now, if Lazy it would not allocate it in the ctor
and where needed would add m_entries checks.
Jakub
