Extra allocations are a significant cost of NLL, and the most common
ones come from within `Canonicalizer`. In particular, `canonical_var()`
contains this code:
indices
.entry(kind)
.or_insert_with(|| {
let cvar1 = variables.push(info);
let cvar2 = var_values.push(kind);
assert_eq!(cvar1, cvar2);
cvar1
})
.clone()
`variables` and `var_values` are `Vec`s. `indices` is a `HashMap` used
to track what elements have been inserted into `var_values`. If `kind`
hasn't been seen before, `indices`, `variables` and `var_values` all get
a new element. (The number of elements in each container is always the
same.) This results in lots of allocations.
In practice, most of the time these containers only end up holding a few
elements. This PR changes them to avoid heap allocations in the common
case, by changing the `Vec`s to `SmallVec`s and only using `indices`
once enough elements are present. (When the number of elements is small,
a direct linear search of `var_values` is as good or better than a
hashmap lookup.)
The changes to `variables` are straightforward and contained within
`Canonicalizer`. The changes to `indices` are more complex but also
contained within `Canonicalizer`. The changes to `var_values` are more
intrusive because they require defining a new type
`SmallCanonicalVarValues` -- which is to `CanonicalVarValues` as
`SmallVec` is to `Vec -- and passing stack-allocated values of that type
in from outside.
All this speeds up a number of NLL "check" builds, the best by 2%.
rustc: Stabilize the `proc_macro` feature
This commit stabilizes some of the `proc_macro` language feature as well as a
number of APIs in the `proc_macro` crate as [previously discussed][1]. This
means that on stable Rust you can now define custom procedural macros which
operate as attributes attached to items or `macro_rules!`-like bang-style
invocations. This extends the suite of currently stable procedural macros,
custom derives, with custom attributes and custom bang macros.
Note though that despite the stabilization in this commit procedural macros are
still not usable on stable Rust. To stabilize that we'll need to stabilize at
least part of the `use_extern_macros` feature. Currently you can define a
procedural macro attribute but you can't import it to call it!
A summary of the changes made in this PR (as well as the various consequences)
is:
* The `proc_macro` language and library features are now stable.
* Other APIs not stabilized in the `proc_macro` crate are now named under a
different feature, such as `proc_macro_diagnostic` or `proc_macro_span`.
* A few checks in resolution for `proc_macro` being enabled have switched over
to `use_extern_macros` being enabled. This means that code using
`#![feature(proc_macro)]` today will likely need to move to
`#![feature(use_extern_macros)]`.
It's intended that this PR, once landed, will be followed up with an attempt to
stabilize a small slice of `use_extern_macros` just for procedural macros to
make this feature 100% usable on stable.
[1]: https://internals.rust-lang.org/t/help-stabilize-a-subset-of-macros-2-0/7252
This commit transitions definitions of custom sections on the wasm target from
the unstable `#[wasm_custom_section]` attribute to the
already-stable-for-other-targets `#[link_section]` attribute. Mostly the same
restrictions apply as before, except that this now applies only to statics.
Closes#51088
Previously we'd only do so for stage 0 but with keep-stage
improvements it seems likely that we'll see more developers working in
the stage 1, so we should allow enabling incremental for them.
Ideally, the check we probably want is to only enable incremental for
the last compiler build scheduled, but there's no good way to do so
today. Just enabling incremental in all stages should be sufficient;
we may be doing extra work that's needles -- compiling incrementally
something that will never be recompiled in-place -- but that should be
sufficiently unlikely (i.e., users either don't care or won't be
compiling the compiler twice).
This commit stabilizes some of the `proc_macro` language feature as well as a
number of APIs in the `proc_macro` crate as [previously discussed][1]. This
means that on stable Rust you can now define custom procedural macros which
operate as attributes attached to items or `macro_rules!`-like bang-style
invocations. This extends the suite of currently stable procedural macros,
custom derives, with custom attributes and custom bang macros.
Note though that despite the stabilization in this commit procedural macros are
still not usable on stable Rust. To stabilize that we'll need to stabilize at
least part of the `use_extern_macros` feature. Currently you can define a
procedural macro attribute but you can't import it to call it!
A summary of the changes made in this PR (as well as the various consequences)
is:
* The `proc_macro` language and library features are now stable.
* Other APIs not stabilized in the `proc_macro` crate are now named under a
different feature, such as `proc_macro_diagnostic` or `proc_macro_span`.
* A few checks in resolution for `proc_macro` being enabled have switched over
to `use_extern_macros` being enabled. This means that code using
`#![feature(proc_macro)]` today will likely need to move to
`#![feature(use_extern_macros)]`.
It's intended that this PR, once landed, will be followed up with an attempt to
stabilize a small slice of `use_extern_macros` just for procedural macros to
make this feature 100% usable on stable.
[1]: https://internals.rust-lang.org/t/help-stabilize-a-subset-of-macros-2-0/7252
Clarify how the quote macro is loaded
@QuietMisdreavus needed to figure this out for writing a testcase, this should be better documented.
r? @jseyfried
