[PATCH RFA] vec: Fix --enable-gather-detailed-mem-stats

[Jason Merrill]

On 10/5/21 07:27, Richard Biener wrote:
> On Mon, Oct 4, 2021 at 8:28 PM Jason Merrill via Gcc-patches
> <gcc-patches@gcc.gnu.org> wrote:
>>
>> When r12-4038 introduced the global auto_vec save_opt_decoded_options,
>> it broke compilers configured with --enable-gather-detailed-mem-stats,
>> due to the memory descriptors getting discarded before the auto_vec was
>> destroyed.  Attached below are two approaches to making this work,
>> either by using the init_priority attribute, or turning vec_mem_desc
>> into a singleton function.  I prefer the first one, primarily because it
>> doesn't require auto_vec variables to force immediate allocation.  It
>> relies on a G++ extension, but I figure that's OK for code that is only
>> exercised with a debugging configure flag.
>>
>> Thoughts?  Either one OK for trunk?
> 
> Hmm, isn't the way to fix this to turn the global auto_vec into
> vec<> *x and allocate it at runtime (thus explicitly mange its
> lifetime?).  We don't want global CTORs/DTORs in general
> because of startup cost and of course those pesky ordering issues...

That is the usual approach, yes.  I was giving up on that, but perhaps 
it's better to stick with it.  Martin, want to make that fix for 
save_opt_decoded_options?

> Oh, and maybe we can make
> 
>  static mem_alloc_description <vec_usage> vec_mem_desc;
> 
> statically initialized with some C++?  (constexpr? constinit? whatever?
It can't be statically initialized, because it needs to allocate 
multiple maps.

Jason