core library: Disable fpmath tests for i586 ...

[liushuyu]

This patch disables the floating-point epsilon test for i586 since x87 registers are too imprecise and can't produce the expected results.

[rustbot]

r? @m-ou-se

(rustbot has picked a reviewer for you, use r? to override)

[workingjubilee]

What is the actual result from the test?

[liushuyu]

fn main() {
    let angle = std::f32::consts::PI;
    let abs_difference = (angle.to_degrees() - 180.0).abs();
    println!("diff = {}, epsilon = {}", abs_difference, f32::EPSILON);
}

When compiling with rustc --target i586-unknown-linux-gnu -Copt-level=0 (using any optimization level higher than 0 will have LLVM constant evaluate the expression), I got:

diff = 0.0000071100612, epsilon = 0.00000011920929

Compiler Explorer link: https://godbolt.org/z/K1eajMY5K

[workingjubilee]

oh dear.

[liushuyu]

Looks like someone else also started to track this issue in #114479

[workingjubilee]

Oh, good. I think my main concern slowing me down from signing off on this was losing track of the problem.

@bors r+ rollup

[bors]

📌 Commit 40a52cf has been approved by workingjubilee

It is now in the queue for this repository.

[bors]

⌛ Testing commit 40a52cf with merge cf9fd95...

[bors]

☀️ Test successful - checks-actions
Approved by: workingjubilee
Pushing cf9fd95 to master...

[rust-timer]

Finished benchmarking commit (cf9fd95): comparison URL.

Overall result: ❌ regressions - ACTION NEEDED

Next Steps: If you can justify the regressions found in this perf run, please indicate this with @rustbot label: +perf-regression-triaged along with sufficient written justification. If you cannot justify the regressions please open an issue or create a new PR that fixes the regressions, add a comment linking to the newly created issue or PR, and then add the perf-regression-triaged label to this PR.

@rustbot label: +perf-regression
cc @rust-lang/wg-compiler-performance

Instruction count

This is a highly reliable metric that was used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	0.8%	[0.7%, 0.9%]	4
Regressions ❌ (secondary)	0.7%	[0.6%, 0.8%]	3
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.8%	[0.7%, 0.9%]	4

Max RSS (memory usage)

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	2.2%	[2.2%, 2.2%]	1
Regressions ❌ (secondary)	3.8%	[2.7%, 5.0%]	4
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	2.2%	[2.2%, 2.2%]	1

Cycles

This benchmark run did not return any relevant results for this metric.

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 621.055s -> 623.65s (0.42%)
Artifact size: 271.92 MiB -> 271.98 MiB (0.02%)

[lqd]

This is a doctest change and I'm pretty sure helloworld, unify-linearly, issue-46449 and await-call-tree are currently being noisy (at a very small magnitude, but still), and that noise is on check builds, not rustdoc benchmarks.

@rustbot label: +perf-regression-triaged