two-phase borrows: support multiple activations in one statement
The need for this has arisen since the introduction of two-phase borrows on
method autorefs in #49348. r'ing @pnkfelix to keep things off Niko's plate so he can make this redundant, and @pnkfelix is familiar with the code.
Fixes#49635Fixes#49662
r? @pnkfelix
Allow for re-using monomorphizations in upstream crates.
Followup to #48611. This implementation is pretty much finished modulo failing tests if there are any. Not quite ready for review yet though.
### DESCRIPTION
This PR introduces a `share-generics` mode for RLIBs and Rust dylibs. When a crate is compiled in this mode, two things will happen:
- before instantiating a monomorphization in the current crate, the compiler will look for that monomorphization in all upstream crates and link to it, if possible.
- monomorphizations are not internalized during partitioning. Instead they are added to the list of symbols exported from the crate.
This results in less code being translated and LLVMed. However, there are also downsides:
- it will impede optimization somewhat, since fewer functions can be internalized, and
- Rust dylibs will have bigger symbol tables since they'll also export monomorphizations.
Consequently, this PR only enables the `shared-generics` mode for opt-levels `No`, `Less`, `Size`, and `MinSize`, and for when incremental compilation is activated. `-O2` and `-O3` will still generate generic functions per-crate.
Another thing to note is that this has a somewhat similar effect as MIR-only RLIBs, in that monomorphizations are shared, but it is less effective because it cannot share monomorphizations between sibling crates:
```
A <--- defines `fn foo<T>() { .. }`
/ \
/ \
B C <--- both call `foo<u32>()`
\ /
\ /
D <--- calls `foo<u32>()` too
```
With `share-generics`, both `B` and `C` have to instantiate `foo<u32>` and only `D` can re-use it (from either `B` or `C`). With MIR-only RLIBs, `B` and `C` would not instantiate anything, and in `D` we would then only instantiate `foo<u32>` once.
On the other hand, when there are many leaf crates in the graph (e.g. when compiling many individual test binaries) then the `share-generics` approach will often be more effective.
### TODO
- [x] Add codegen test that makes sure monomorphizations can be internalized in non-Rust binaries.
- [x] Add codegen-units test that makes sure we share generics.
- [x] Add run-make test that makes sure we don't export any monomorphizations from non-Rust binaries.
- [x] Review for reproducible-builds implications.
avoid IdxSets containing garbage above the universe length
This makes sure that all bits in each IdxSet between the universe length
and the end of the word are all zero instead of being in an indeterminate state.
This fixes a crash with RUST_LOG=rustc_mir, and is probably a good idea
anyway.
r? @nikomatsakis - I think you are responsible for this code area now?
Add #[must_use] to a few standard library methods
Chosen to start a precedent of using it on ones that are potentially-expensive and where using it for side effects is particularly discouraged.
Discuss :)
```rust
warning: unused return value of `std::iter::Iterator::collect` which must be used: if you really need to exhaust the iterator, consider `.for_each(drop)` instead
--> $DIR/fn_must_use_stdlib.rs:19:5
|
LL | "1 2 3".split_whitespace().collect::<Vec<_>>();
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
warning: unused return value of `std::borrow::ToOwned::to_owned` which must be used: cloning is often expensive and is not expected to have side effects
--> $DIR/fn_must_use_stdlib.rs:21:5
|
LL | "hello".to_owned();
| ^^^^^^^^^^^^^^^^^^^
warning: unused return value of `std::clone::Clone::clone` which must be used: cloning is often expensive and is not expected to have side effects
--> $DIR/fn_must_use_stdlib.rs:23:5
|
LL | String::from("world").clone();
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
```
cc https://github.com/rust-lang/rust/issues/48926
Extend two-phase borrows to apply to method receiver autorefs
Fixes#48598 by permitting two-phase borrows on the autorefs created when functions and methods.
This makes sure that all bits in each IdxSet between the universe length
and the end of the word are all zero instead of being in an indeterminate state.
This fixes a crash with RUST_LOG=rustc_mir, and is probably a good idea
anyway.
Chosen to start a precedent of using it on ones that are potentially-expensive and where using it for side effects is particularly discouraged.
Discuss :)
optimize NLL constraint propagation a little
Removes a bone-headed hot spot in NLL constant propagation; we were re-allocating the stack vector and hashmap as we repeated the DFS. This change shares those resources across each call.
It also modifies the constraint list to be a linked list; arguably I should revert that, though, as this didn't turn out to be a perf hit and perhaps the old code was clearer? (Still, the new style appeals to me.)
r? @pnkfelix
