Bug with GCC's handling of lifetimes of implicit-lifetime types

[Gavin Ray <ray.gavin97@gmail.com>]

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This came up when I was asking around about what the proper way was to:

- Allocate aligned storage for a buffer pool/page cache
- Then create pointers to "Page" structs inside of the storage memory area

I thought something like this might do:

struct buffer_pool
{
  alignas(PAGE_SIZE) std::byte storage[NUM_PAGES * PAGE_SIZE];
  page* pages = new (storage) page[NUM_PAGES];
}

Someone told me that this was a valid solution but not to do it, because it
wouldn't function properly on GCC
They gave this as a reproduction:

https://godbolt.org/z/EhzM37Gzh

I'm not experienced enough with C++ to grok the connection between this
repro and my code, but I figured
I'd post it on the mailing list in case it was useful for others/might get
fixed in the future =)

They said it had to do with "handling of lifetimes of implicit-lifetime
types"