Specialization for StepBy<ops::Range<T>>

[dhulke]

Evidence

I remember seeing this commit that specialized StepBy for ops::Range and today when looking back at the library's source code I saw that the specialization is gone.
Here's the specialization commit merged: 95979dc
Here's the current code for StepBy::next(): https://github.com/rust-lang/rust/blob/master/library/core/src/iter/adapters/step_by.rs#L34

Why was this specialization removed and can we add it back?

[Noratrieb]

The PR was immediately reverted in #56049 because it was broken. It may be able to be readded if someone finds a way to fix it.

[jyn514]

I don't think this should be treated as a regression.

[dhulke]

@Nilstrieb Thank you, I missed that revert. I might pick this up in the next couple of weeks then. Should we close the issue and I open a new discussion with a PR pointing to this issue in the future?

[Noratrieb]

Keeping it open is fine, it's a suggestion for an improvement to the standard library

[the8472]

This would be a welcome improvement, e.g. in #103779 I had to handroll loops because range + step_by wasn't up to snuff.

rust/library/core/src/str/pattern.rs

Lines 1832 to 1838 in f77bfb7

	while i + last_byte_offset + Block::LANES < haystack.len() && !result {
	let mask = test_chunk(i);
	if mask != 0 {
	result |= check_mask(i, mask, result);
	}
	i += Block::LANES;
	}

[the8472]

Closing as duplicate of #51557