That function also takes care of converting a Scalar to a Pointer, should that be needed. Not all accesses need that though: if the access has size 0, None is returned.
Everyone accessing memory based on a Scalar should use this method to get the Pointer they need.
All operations on the Allocation work on Pointer inputs and expect all the checks to have happened (and will ICE if the bounds are violated).
The operations on Memory work on Scalar inputs and do the checks themselves.
The only other public method to check pointers is memory.ptr_may_be_null, which is needed in a few places.
With this, we can make all the other methods (tests for a pointer being in-bounds and checking alignment) private helper methods, used to implement the two public methods.
That maks the public API surface much easier to use and harder to mis-use.
While I am at it, this also removes the assumption that the vtable part of a `dyn Trait`-fat-pointer is a `Pointer` (as opposed to a pointer cast to an integer, stored as raw bits).
`ByRef` const values have no identity beyond their value, we should not treat them as having identity. The `AllocId` often differed between equal constants, because of the way that the miri-engine evaluates constants.
light refactoring of global AllocMap
* rename AllocKind -> GlobalAlloc. This stores the allocation itself, not just its kind.
* rename the methods that allocate stuff to have consistent names.
Cc @oli-obk
* rename AllocKind -> GlobalAlloc. This stores the allocation itself, not just its kind.
* rename the methods that allocate stuff to have consistent names.
rename Scalar::Bits to Scalar::Raw and bits field to data
Also use this opportunity to seal some abstraction leaks (other modules constructing `Scalar::Bits` directly instead of using a constructor).
r? @oli-obk
Multi-variant layouts for generators
This allows generators to overlap fields using variants, but doesn't do any such overlapping yet. It creates one variant for every state of the generator (unresumed, returned, panicked, plus one for every yield), and puts every stored local in each of the yield-point variants.
Required for optimizing generator layouts (#52924).
There was quite a lot of refactoring needed for this change. I've done my best in later commits to eliminate assumptions in the code that only certain kinds of types are multi-variant, and to centralize knowledge of the inner mechanics of generators in as few places as possible.
This change also emits debuginfo about the fields contained in each variant, as well as preserving debuginfo about stored locals while running in the generator.
Also, fixes#59972.
Future work:
- Use this change for an optimization pass that actually overlaps locals within the generator struct (#52924)
- In the type layout fields, don't include locals that are uninitialized for a particular variant, so miri and UB sanitizers can check our memory (see https://github.com/rust-lang/rust/issues/59972#issuecomment-483058172)
- Preserve debuginfo scopes across generator yield points
