Change `Rc::inc_{weak,strong}` to better hint optimization to LLVM
As discussed in #13018, `Rc::inc_strong` and `Rc::inc_weak` are changed to allow compositions of `clone` and `drop` to be better optimized. Almost entirely as in [this comment](https://github.com/rust-lang/rust/issues/13018#issuecomment-408642184), except that `abort` on zero is added so that a `drop(t.clone())` does not produce a zero check followed by conditional deallocation.
This is different from #21418 in that it doesn't rely on `assume`, avoiding the prohibitive compilation slowdown.
[Before and after IR](https://gist.github.com/hermord/266e55451b7fe0bb8caa6e35d17c86e1).
`fn resolve_legacy_scope` can now resolve only to `macro_rules!` items,
`fn resolve_lexical_macro_path_segment` is for everything else - modularized macros, preludes
Currently in the `wasm-bindgen` project we have a very very large crate that's
procedurally generated, `web-sys`. To generate this crate we parse all of a
browser's WebIDL and we then generate bindings for all of the APIs contained
within.
The resulting Rust file is 18MB large (wow!) and currently takes a very long
time to compile in debug mode. On the nightly compiler a *debug* build takes 90s
for the crate to finish. I was curious what was taking so long and upon
investigating a *massive* portion of the time was spent in the `lit_token`
method of the compiler, primarily formatting strings via `format!`.
Upon some more investigation it looks like the `byte_str_lit` was allocating an
error message once per byte, causing a very large number of allocations to
happen for large literals, of which wasm-bindgen generates quite a few (some are
MB large).
This commit fixes the issue by lazily allocating the error message, only doing
so if the error message is actually needed (which should be never). As a result,
the debug mode compilation time for our `web-sys` crate decreased from 90s to
20s, a very nice improvement! (although we've still got some work to do).
The Great Generics Generalisation: HIR Followup
Addresses the final comments in #48149.
r? @eddyb, but there are a few things I have yet to clean up. Making the PR now to more easily see when things break.
cc @yodaldevoid
Options:
-h, --help Display this message
--cfg SPEC Configure the compilation environment
-L [KIND=]PATH Add a directory to the library search path. The
optional KIND can be one of dependency, crate, native,
framework or all (the default).
-l [KIND=]NAME Link the generated crate(s) to the specified native
library NAME. The optional KIND can be one of static,
dylib, or framework. If omitted, dylib is assumed.
--crate-type [bin|lib|rlib|dylib|cdylib|staticlib|proc-macro]
Comma separated list of types of crates for the
compiler to emit
--crate-name NAME
Specify the name of the crate being built
--emit [asm|llvm-bc|llvm-ir|obj|metadata|link|dep-info|mir]
Comma separated list of types of output for the
compiler to emit
--print [crate-name|file-names|sysroot|cfg|target-list|target-cpus|target-features|relocation-models|code-models|tls-models|target-spec-json|native-static-libs]
Comma separated list of compiler information to print
on stdout
-g Equivalent to -C debuginfo=2
-O Equivalent to -C opt-level=2
-o FILENAME Write output to <filename>
--out-dir DIR Write output to compiler-chosen filename in <dir>
--explain OPT Provide a detailed explanation of an error message
--test Build a test harness
--target TARGET Target triple for which the code is compiled
-W, --warn OPT Set lint warnings
-A, --allow OPT Set lint allowed
-D, --deny OPT Set lint denied
-F, --forbid OPT Set lint forbidden
--cap-lints LEVEL
Set the most restrictive lint level. More restrictive
lints are capped at this level
-C, --codegen OPT[=VALUE]
Set a codegen option
-V, --version Print version info and exit
-v, --verbose Use verbose output
Additional help:
-C help Print codegen options
-W help Print 'lint' options and default settings
--help -v Print the full set of options rustc accepts command.
Add the identity function as core::convert::identity
## New notes
This implements rust-lang/rfcs#2306 (see https://github.com/rust-lang/rust/issues/53500).
## Old notes (ignore this in new reviews)
Adds the identity function `fn id<T>(x: T) -> T { x }` to core::convert and the prelude.
Some motivations for why this is useful are explained in the doc tests.
Another is that using the identity function instead of `{ x }` or `|x| x` makes it clear that you intended to use an identity conversion on purpose.
The reasoning:
+ behind adding this to `convert` and not `mem` is that this is an identity *conversion*.
+ for adding this to the prelude is that it should be easy enough to use that the ease of writing your own identity function or using a closure `|x| x` doesn't overtake that.
I've separated this out into two feature gates so that the addition to the prelude can be considered and stabilized separately.
cc @bluss
In some profiling on OSX I saw the `write` syscall as quite high up on
the profiling graph, which is definitely not good! It looks like we're
setting the output stream of an object file as directly to a file
descriptor which means that we run the risk of doing lots of little
writes rather than a few large writes.
This commit fixes this issue by adding a buffered stream on the output,
causing the `write` syscall to disappear from the profiles on OSX.
