https://github.com/nyurik/rust-optimize-format-str
Rust optimization testcases for `write!` to handle simple non-formatting strings
https://github.com/nyurik/rust-optimize-format-str
Last synced: about 1 month ago
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Rust optimization testcases for `write!` to handle simple non-formatting strings
- Host: GitHub
- URL: https://github.com/nyurik/rust-optimize-format-str
- Owner: nyurik
- Created: 2024-02-15T05:14:37.000Z (about 1 year ago)
- Default Branch: main
- Last Pushed: 2024-03-06T03:36:01.000Z (about 1 year ago)
- Last Synced: 2025-03-07T16:09:56.053Z (about 2 months ago)
- Language: Shell
- Size: 178 KB
- Stars: 0
- Watchers: 2
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
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README
# Rust `format!` Optimization Tester
Test for `write!` to optimize the case of a non-formatting string:
```rust
write!(buf, "simple string");
```
There are two cases: `str` (no formatting args), and `fmt` (a regular formatting string with a param)
To setup compiler, from the Rust repo, run:
```sh
./x.py build --stage 1 library
rustup toolchain link stage1 build/host/stage1
```
Install `cargo asm` tool with `cargo install cargo-show-asm`
Compile compiler+lib in the rust dir with the above commands for the main branch,
then run this from this test repo to generate `./output/str/main/*` and `./output/fmt/main/*` output files.
```sh
./run.sh main
```
Repeat the process for any other core lib modifications. The checked in output is using 3 cases:
### main
Using ee9c7c940c0 branch
### as_const_str
New function was added:
```rust
impl<'a> Arguments<'a> {
/// Same as [`Arguments::as_str`], but will only return `Some(s)` if it can be determined at compile time.
#[must_use]
#[inline]
fn as_const_str(&self) -> Option<&'static str> {
let s = self.as_str();
// SAFETY: both cases are valid as the result
if unsafe { core::intrinsics::is_val_statically_known(s.is_some()) } { s } else { None }
}
}
```
All `library/core/src/fmt/mod.rs` usages of `write(self, args)` were updated like this:
```rust
fn write_fmt(self, args: Arguments<'_>) -> Result {
if let Some(s) = args.as_const_str() {
self.write_str(s)
} else {
write(self, args)
}
}
```
### as_str
A bad attempt to optimize, using the existing `Arguments::as_str` function. Nearly identical to the `as_const_str`, except that it used `as_str`