Miri provenance cleanup
Reviewing https://github.com/rust-lang/rust/pull/95826 by ``@carbotaniuman`` made me realize that we could clean things up a little here.
``@carbotaniuman`` please let me know if you're okay with landing this (it will create a lot of conflicts with your PR), or if you'd prefer incorporating the ideas from this PR into yours. I think we want to end up in a situation where the function you called `ptr_reify_alloc` returns just two things, a concrete tag and an offset. Getting an `AllocId` from a concrete tag should be infallible like now. However a concrete tag and `Tag` don't have to be the same type.
r? ``@oli-obk``
CTFE/Miri: detect out-of-bounds pointers in offset_from
Also I became uneasy with aggressively doing `try_to_int` here -- this will always succeed on Miri, leading to the wrong codepath being taken. We should rather try to convert them both to pointers, and use the integer path as a fallback, so that's what I implemented now.
Hiding whitespaces helps with the diff.
Fixes https://github.com/rust-lang/miri/issues/1950
r? ``@oli-obk``
Currently some `Allocation`s are interned, some are not, and it's very
hard to tell at a use point which is which.
This commit introduces `ConstAllocation` for the known-interned ones,
which makes the division much clearer. `ConstAllocation::inner()` is
used to get the underlying `Allocation`.
In some places it's natural to use an `Allocation`, in some it's natural
to use a `ConstAllocation`, and in some places there's no clear choice.
I've tried to make things look as nice as possible, while generally
favouring `ConstAllocation`, which is the type that embodies more
information. This does require quite a few calls to `inner()`.
The commit also tweaks how `PartialOrd` works for `Interned`. The
previous code was too clever by half, building on `T: Ord` to make the
code shorter. That caused problems with deriving `PartialOrd` and `Ord`
for `ConstAllocation`, so I changed it to build on `T: PartialOrd`,
which is slightly more verbose but much more standard and avoided the
problems.
