use if let instead of single match arm expressions
use if let instead of single match arm expressions to compact code and reduce nesting (clippy::single_match)
Use const-checking to forbid use of unstable features in const-stable functions
First step towards #76618.
Currently this code isn't ever hit because `qualify_min_const_fn` runs first and catches pretty much everything. One exception is `const_precise_live_drops`, which does not use the newly added code since it runs as part of a separate pass.
Also contains some unrelated refactoring, which is split into separate commits.
r? @oli-obk
Don't use `zip` to compare iterators during pretty-print hack
If the right-hand iterator has exactly one more element than the
left-hand iterator, then both iterators will be fully consumed, but
the extra element will never be compared.
Split out from https://github.com/rust-lang/rust/pull/76130
If the right-hand iterator has exactly one more element than the
left-hand iterator, then both iterators will be fully consumed, but
the extra element will never be compared.
Make `ensure_sufficient_stack()` non-generic, using cargo-llvm-lines
Inspired by [this blog post](https://blog.mozilla.org/nnethercote/2020/08/05/how-to-speed-up-the-rust-compiler-some-more-in-2020/) from `@nnethercote,` I used [cargo-llvm-lines](https://github.com/dtolnay/cargo-llvm-lines/) on the rust compiler itself, to improve it's compile time. This PR contains only one low-hanging fruit, but I also want to share some measurements.
The function `ensure_sufficient_stack()` was monomorphized 1500 times, and with it the `stacker` and `psm` crates, for a total of 1.5% of all llvm IR lines. With some trickery I convert the generic closure into a dynamic one, and thus all that code is only monomorphized once.
# Measurements
Getting these numbers took some fiddling with CLI flags and I [modified](https://github.com/Julian-Wollersberger/cargo-llvm-lines/blob/master/src/main.rs#L115) cargo-llvm-lines to read from a folder instead of invoking cargo. Commands I used:
```
./x.py clean
RUSTFLAGS="--emit=llvm-ir -C link-args=-fuse-ld=lld -Z self-profile=profile" CARGOFLAGS_BOOTSTRAP="-Ztimings" RUSTC_BOOTSTRAP=1 ./x.py build -i --stage 1 library/std
# Then manually copy all .ll files into a folder I hardcoded in cargo-llvm-lines in main.rs#L115
cd ../cargo-llvm-lines
cargo run llvm-lines
```
The result is this list (see [first 500 lines](https://github.com/Julian-Wollersberger/cargo-llvm-lines/blob/master/llvm-lines-rustc-before.txt) ), before the change:
```
Lines Copies Function name
----- ------ -------------
16894211 (100%) 58417 (100%) (TOTAL)
2223855 (13.2%) 502 (0.9%) rustc_query_system::query::plumbing::get_query_impl::{{closure}}
1331918 (7.9%) 1287 (2.2%) hashbrown::raw::RawTable<T>::reserve_rehash
774434 (4.6%) 12043 (20.6%) core::ptr::drop_in_place
294170 (1.7%) 499 (0.9%) rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
245410 (1.5%) 1552 (2.7%) psm::on_stack::with_on_stack
210311 (1.2%) 1 (0.0%) rustc_target::spec::load_specific
200962 (1.2%) 513 (0.9%) rustc_query_system::query::plumbing::get_query_impl
190704 (1.1%) 1 (0.0%) rustc_middle::ty::query::<impl rustc_middle::ty::context::TyCtxt>::alloc_self_profile_query_strings
180272 (1.1%) 468 (0.8%) rustc_query_system::query::plumbing::load_from_disk_and_cache_in_memory
177396 (1.1%) 114 (0.2%) rustc_query_system::query::plumbing::force_query_impl
161134 (1.0%) 445 (0.8%) rustc_query_system::dep_graph::graph::DepGraph<K>::with_anon_task
141551 (0.8%) 186 (0.3%) rustc_query_system::query::plumbing::incremental_verify_ich
110191 (0.7%) 7 (0.0%) rustc_middle::ty::context::_DERIVE_rustc_serialize_Decodable_D_FOR_TypeckResults::<impl rustc_serialize::serialize::Decodable<__D> for rustc_middle::ty::context::TypeckResults>::decode::{{closure}}
108590 (0.6%) 420 (0.7%) core::ops::function::FnOnce::call_once
88488 (0.5%) 21 (0.0%) rustc_query_system::dep_graph::graph::DepGraph<K>::try_mark_previous_green
86368 (0.5%) 1 (0.0%) rustc_middle::ty::query::stats::query_stats
85654 (0.5%) 3973 (6.8%) <&T as core::fmt::Debug>::fmt
84475 (0.5%) 1 (0.0%) rustc_middle::ty::query::Queries::try_collect_active_jobs
81220 (0.5%) 862 (1.5%) <hashbrown::raw::RawIterHash<T> as core::iter::traits::iterator::Iterator>::next
77636 (0.5%) 54 (0.1%) core::slice::sort::recurse
66484 (0.4%) 461 (0.8%) <hashbrown::raw::RawIter<T> as core::iter::traits::iterator::Iterator>::next
```
All `.ll` files together had 4.4GB. After my change they had 4.2GB. So a few percent less code LLVM has to process. Hurray!
Sadly, I couldn't measure an actual wall-time improvement. Watching YouTube while compiling added to much noise...
Here is the top of the list after the change:
```
16460866 (100%) 58341 (100%) (TOTAL)
1903085 (11.6%) 504 (0.9%) rustc_query_system::query::plumbing::get_query_impl::{{closure}}
1331918 (8.1%) 1287 (2.2%) hashbrown::raw::RawTable<T>::reserve_rehash
777796 (4.7%) 12031 (20.6%) core::ptr::drop_in_place
551462 (3.4%) 1519 (2.6%) rustc_data_structures::stack::ensure_sufficient_stack::{{closure}}
```
Note that the total was reduced by 430 000 lines and `psm::on_stack::with_on_stack` has disappeared. Instead `rustc_data_structures::stack::ensure_sufficient_stack::{{closure}}` appeared. I'm confused about that one, but it seems to consist of inlined calls to `rustc_query_system::*` stuff.
Further note the other two big culprits in this list: `rustc_query_system` and `hashbrown`. These two are monomorphized many times, the query system summing to more than 20% of all lines, not even counting code that's probably inlined elsewhere.
Assuming compile times scale linearly with llvm-lines, that means a possible 20% compile time reduction.
Reducing eg. `get_query_impl` would probably need a major refactoring of the qery system though. _Everything_ in there is generic over multiple types, has associated types and passes generic Self arguments by value. Which means you can't simply make things `dyn`.
---------------------------------------
This PR is a small step to make rustc compile faster and thus make contributing to rustc less painful. Nonetheless I love Rust and I find the work around rustc fascinating :)
Remove DeclareMethods
Most of the `DeclareMethods` API was only used internally by rustc_codegen_llvm. As such, it makes no sense to require other backends to implement them.
(`get_declared_value` and `declare_cfn` were used, in one place, specific to the `main` symbol, which I've replaced with a more specialized function to allow more flexibility in implementation - the intent is that `declare_c_main` can go away once we do something more clever, e.g. @eddyb has ideas around having a MIR shim or somesuch we can explore in a follow-up PR)
Let user see the full type of type-length limit error
Seeing the full type of the error is sometimes essential to diagnosing the problem, but the type itself is too long to be displayed in the terminal in a useful fashion. This change solves this dilemma by writing the full offending type name to a file, and displays this filename as a note.
> note: the full type name been written to '$TEST_BUILD_DIR/issues/issue-22638/issue-22638.long-type.txt'
Closes#76777
