High-level picture: The old `Borrows` analysis is now called
`Reservations` (implemented as a newtype wrapper around `Borrows`);
this continues to compute whether a `Rvalue::Ref` can reach a
statement without an intervening `EndRegion`. In addition, we also
track what `Place` each such `Rvalue::Ref` was immediately assigned
to in a given borrow (yay for MIR-structural properties!).
The new `ActiveBorrows` analysis then tracks the initial use of any of
those assigned `Places` for a given borrow. I.e. a borrow becomes
"active" immediately after it starts being "used" in some way. (This
is conservative in the sense that we will treat a copy `x = y;` as a
use of `y`; in principle one might further delay activation in such
cases.)
The new `ActiveBorrows` analysis needs to take the `Reservations`
results as an initial input, because the reservation state influences
the gen/kill sets for `ActiveBorrows`. In particular, a use of `a`
activates a borrow `a = &b` if and only if there exists a path (in the
control flow graph) from the borrow to that use. So we need to know if
the borrow reaches a given use to know if it really gets a gen-bit or
not.
* Incorporating the output from one dataflow analysis into the input
of another required more changes to the infrastructure than I had
expected, and even after those changes, the resulting code is still
a bit subtle.
* In particular, Since we need to know the intrablock reservation
state, we need to dynamically update a bitvector for the
reservations as we are also trying to compute the gen/kills
bitvector for the active borrows.
* The way I ended up deciding to do this (after also toying with at
least two other designs) is to put both the reservation state and
the active borrow state into a single bitvector. That is why we now
have separate (but related) `BorrowIndex` and
`ReserveOrActivateIndex`: each borrow index maps to a pair of
neighboring reservation and activation indexes.
As noted above, these changes are solely adding the active borrows
dataflow analysis (and updating the existing code to cope with the
switch from `Borrows` to `Reservations`). The code to process the
bitvector in the borrow checker currently just skips over all of the
active borrow bits.
But atop this commit, one *can* observe the analysis results by
looking at the graphviz output, e.g. via
```rust
#[rustc_mir(borrowck_graphviz_preflow="pre_two_phase.dot",
borrowck_graphviz_postflow="post_two_phase.dot")]
```
Includes doc for `FindPlaceUses`, as well as `Reservations` and
`ActiveBorrows` structs, which are wrappers are the `Borrows` struct
that dictate which flow analysis should be performed.
This is meant to ease development of multi-stage dataflow analyses
where the output from one analysis is used to initialize the state
for the next; in such a context, you cannot start with `bottom_value`
for all the bits.
Having the HIR local id is useful for cases like understanding the
ReScope identifiers, which are now derived from the HIR local id, and
thus one can map an ReScope back to the HIR node, once one knows what
those local ids are.
Fix return value of `LLVMRustMetadataAsValue`
`LLVMRustMetadataAsValue` would previously return `void`, despite the
corresponding Rust function expecting to return a `ValueRef`.
Remove armv5te target from dist-various-1
Reverts https://github.com/rust-lang/rust/pull/46498
I must have made some mistake when I tested that commit and thought armv5te target worked. but testing it now the produced binaries segfaults (https://github.com/rust-lang/rust/pull/46498#issuecomment-350599233).
I tried using crosstool-ng and buildroot toolchain (for armv5te) but the produced binaries also segfaults. Maybe there is a issue with the target, but I cannot investigate it any further.
I think the best for now is not to distribute the armv5te target.
I'm sorry for what happened.
Mark ascii methods on primitive types stable in 1.23.0 not 1.21.0.
The ascii_methods_on_intrinsics feature stabilization
didn't land in time for 1.21.0. Update the annotation
so the documentation is correct about when these
methods became available.
move `resolve_lifetimes` into a proper query
Now that we made `resolve_lifetimes` into a query, elision errors no
longer abort compilation, which affects some tests.
Also, remove `dep_graph_crosscontaminate_tables` -- there is no a path in
the dep-graph, though red-green handles it. The same scenario
is (correctly) tested by issue-42602.rs in any case.
r? @michaelwoerister
Reverts https://github.com/rust-lang/rust/pull/46498
I must have made some mistake when I tested that commit and thought
armv5te target worked. but testing it now the produced binaries
segfaults
(https://github.com/rust-lang/rust/pull/46498#issuecomment-350599233).
I tried using crosstool-ng and buildroot toolchain (for armv5te) but
the produced binaries also segfaults. Maybe there is a issue with the
target, but I cannot investigate it any further.
I think the best for now is not to distribute the armv5te target.
I'm sorry for what happened.
Now that we made `resolve_lifetimes` into a query, elision errors no
longer abort compilation, which affects some tests.
Also, remove `dep_graph_crosscontaminate_tables` -- there is no a path in
the dep-graph, though red-green handles it. The same scenario
is (correctly) tested by issue-42602.rs in any case.
