The reference makes guarantees about "stack memory" that do not reflect our op.sem

https://doc.rust-lang.org/reference/variables.html says that "A local variable (or stack-local allocation) holds a value directly, allocated within the stack's memory." However, on the level of the Abstract Machine, there is no such thing as "the stack's memory". All allocated objects are placed at arbitrary locations in memory and there is no guarantee whatsoever that stack allocations are in "the stack" or Box allocations are on "the heap".

For instance, many local variables end up not having any actual memory allocated anywhere as they are entirely turned into registers.

The wording in the reference should be adjusted to avoid claims that cannot be held up by the Abstract Machine.

Thanks to @tautschnig for pointing this out.

Cc @rust-lang/opsem

Start with reference/variables.html and the quoted paragraph, then review the linked unsafe-code-guidelines discussion for the Abstract Machine concern. Done when the Reference no longer makes unsupported claims about physical stack or heap placement while still accurately describing local variables.