Use `(std::)f64::EPSILON` in the examples as suggested in the lints
`float_cmp(_const)` suggests using `{f32|f64}::EPSILON` and it'd be great if the docs mentioned it.
changelog: none
Revert libbacktrace -> gimli
This reverts 4cbd265c11028f8d7b8513db3cc1e8d7a36d8964 (and technically 79673d3009 but it's made empty by previous reverts).
The current plan is to land this PR as a temporary change, so that we can get a better handle on the regressions introduced by it. Trying to fix/examine them in master is difficult, and we want to be better able to evaluate them without impact to other PRs being landed in the mean time.
That said, it is currently *my* belief that gimli, in one form or another, will need to land sometime soon. I think it's quite likely that it may slip a week or two, but I would personally push for re-landing it then "regardless" of the regressions. We should try to focus efforts on understanding and removing as much of the performance impact as possible, as everyone pretty much agrees that it should be quite minimal (and entirely in the linker, basically).
r? @nnethercote
Rollup of 8 pull requests
Successful merges:
- #74141 (libstd/libcore: fix various typos)
- #74490 (add a Backtrace::disabled function)
- #74548 (one more Path::with_extension example, to demonstrate behavior)
- #74587 (Prefer constant over function)
- #74606 (Remove Linux workarounds for missing CLOEXEC support)
- #74637 (Make str point to primitive page)
- #74654 (require type defaults to be after const generic parameters)
- #74659 (Improve codegen for unchecked float casts on wasm)
Failed merges:
r? @ghost
Improve codegen for unchecked float casts on wasm
This commit improves codegen for unchecked casts on WebAssembly targets
to use the singluar `iNN.trunc_fMM_{u,s}` instructions. Previously rustc
would codegen a bare `fptosi` and `fptoui` for float casts but for
WebAssembly targets the codegen for these instructions is quite large.
This large codegen is due to the fact that LLVM can speculate these
instructions so the trapping behavior of WebAssembly needs to be
protected against in case they're speculated.
The change here is to update the codegen for the unchecked cast
intrinsics to have a wasm-specific case where they call the appropriate
LLVM intrinsic to generate the right wasm instruction. The intrinsic is
explicitly opting-in to undefined behavior so a trap here for
out-of-bounds inputs on wasm should be acceptable.
cc #73591
require type defaults to be after const generic parameters
From current discussions it seems like the goal here is for type and const parameters to be unordered and allow things like `struct Foo<const N: usize, T = u32>(T)` and `struct Foo<T, const N: usize = 7>` this way.
Note: This means that using `min_const_generics` it will not be possible for an adt to have both type defaults and const parameters.
closes#70471
r? @varkor @eddyb
Remove Linux workarounds for missing CLOEXEC support
Now that #74163 updated the minimum Linux kernel to 2.6.32, we can
assume the availability of APIs that open file descriptors that are
already set to close on exec, including the flags `O_CLOEXEC`,
`SOCK_CLOEXEC`, and `F_DUPFD_CLOEXEC`.
Closes#74519.
The check of the `exp` parameter seems useless if we execute the while-loop more than once.
The original implementation of `pow` function using one more comparison if the `exp==0` and may break the pipeline of the cpu, which may generate a slower code.
The performance gap between the old and the new implementation may be small, but IMO, at least the newer one looks more beautiful.
---
bench prog:
```
extern crate test;
($a:expr)=>{let time=std::time::Instant::now();{$a;}print!("{:?} ",time.elapsed())};
($a:expr,$b:literal)=>{let time=std::time::Instant::now();let mut a=0;for _ in 0..$b{a^=$a;}print!("{:?} {} ",time.elapsed(),a)}
}
pub fn pow_rust(x:i64, mut exp: u32) -> i64 {
let mut base = x;
let mut acc = 1;
while exp > 1 {
if (exp & 1) == 1 {
acc = acc * base;
}
exp /= 2;
base = base * base;
}
if exp == 1 {
acc = acc * base;
}
acc
}
pub fn pow_new(x:i64, mut exp: u32) -> i64 {
if exp==0{
1
}else{
let mut base = x;
let mut acc = 1;
while exp > 1 {
if (exp & 1) == 1 {
acc = acc * base;
}
exp >>= 1;
base = base * base;
}
acc * base
}
}
fn main(){
let a=2i64;
let b=1_u32;
println!();
timing!(test::black_box(a).pow(test::black_box(b)),100000000);
timing!(pow_new(test::black_box(a),test::black_box(b)),100000000);
timing!(pow_rust(test::black_box(a),test::black_box(b)),100000000);
println!();
timing!(test::black_box(a).pow(test::black_box(b)),100000000);
timing!(pow_new(test::black_box(a),test::black_box(b)),100000000);
timing!(pow_rust(test::black_box(a),test::black_box(b)),100000000);
println!();
timing!(test::black_box(a).pow(test::black_box(b)),100000000);
timing!(pow_new(test::black_box(a),test::black_box(b)),100000000);
timing!(pow_rust(test::black_box(a),test::black_box(b)),100000000);
println!();
timing!(test::black_box(a).pow(test::black_box(b)),100000000);
timing!(pow_new(test::black_box(a),test::black_box(b)),100000000);
timing!(pow_rust(test::black_box(a),test::black_box(b)),100000000);
println!();
timing!(test::black_box(a).pow(test::black_box(b)),100000000);
timing!(pow_new(test::black_box(a),test::black_box(b)),100000000);
timing!(pow_rust(test::black_box(a),test::black_box(b)),100000000);
println!();
timing!(test::black_box(a).pow(test::black_box(b)),100000000);
timing!(pow_new(test::black_box(a),test::black_box(b)),100000000);
timing!(pow_rust(test::black_box(a),test::black_box(b)),100000000);
println!();
timing!(test::black_box(a).pow(test::black_box(b)),100000000);
timing!(pow_new(test::black_box(a),test::black_box(b)),100000000);
timing!(pow_rust(test::black_box(a),test::black_box(b)),100000000);
println!();
timing!(test::black_box(a).pow(test::black_box(b)),100000000);
timing!(pow_new(test::black_box(a),test::black_box(b)),100000000);
timing!(pow_rust(test::black_box(a),test::black_box(b)),100000000);
println!();
}
```
bench in my laptop:
```
neutron@Neutron:/me/rust$ rc commit.rs
rustc commit.rs && ./commit
3.978419716s 0 4.079765171s 0 3.964630622s 0
3.997127013s 0 4.260304804s 0 3.997638211s 0
3.963195544s 0 4.11657718s 0 4.176054164s 0
3.830128579s 0 3.980396122s 0 3.937258567s 0
3.986055948s 0 4.127804162s 0 4.018943411s 0
4.185568857s 0 4.217512517s 0 3.98313603s 0
3.863018225s 0 4.030447988s 0 3.694878237s 0
4.206987927s 0 4.137608047s 0 4.115564664s 0
neutron@Neutron:/me/rust$ rc commit.rs -O
rustc commit.rs -O && ./commit
162.111993ms 0 165.107125ms 0 166.26924ms 0
175.20479ms 0 205.062565ms 0 176.278791ms 0
174.408975ms 0 166.526899ms 0 201.857604ms 0
146.190062ms 0 168.592821ms 0 154.61411ms 0
199.678912ms 0 168.411598ms 0 162.129996ms 0
147.420765ms 0 209.759326ms 0 154.807907ms 0
165.507134ms 0 188.476239ms 0 157.351524ms 0
121.320123ms 0 126.401229ms 0 114.86428ms 0
```
delete an unnecessary semicolon...
Sorry for the typo.
delete trailing whitespace
Sorry, too..
Sorry for the missing...
I checked all the implementations, and finally found that there is one function that does not check whether `exp == 0`
add extra tests
add extra tests.
finished adding the extra tests to prevent further typo
add pow(2) to negative exp
add whitespace.
add whitespace
add whitespace
delete extra line
