Port backtrace's line-tables-only test over to rustc

[jieyouxu]

Part of #122899.

[rustbot]

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[jieyouxu]

Where line numbers :(

[workingjubilee]

it is starting to seem like "reusing the existing c file" isn't going to work if it requires reusing the existing gcc which might be trash (at least, at generating debuginfo).

[jieyouxu]

It was because ui test mode by default has -C strip=debuginfo which... strips debuginfo. If I override it with -C strip=none, then we have debuginfo :)

[workingjubilee]

oh nice.

[jieyouxu]

So the helper does have line-tables, bar and baz:

{ file: "C:\a\rust\rust\tests\ui\debuginfo\auxiliary\line-tables-only-helper.rs", line: 5 },
{ file: "C:\a\rust\rust\tests\ui\debuginfo\auxiliary\line-tables-only-helper.rs", line: 10 },

backtrace does not contain expected name foo

but where did my foo go :ferrisAware:? @workingjubilee do you have any clue why i686-msvc would yeet foo's line table entry?

(the helper is this:)

//@ compile-flags: -Cstrip=none -Cdebuginfo=line-tables-only

#[no_mangle]
pub fn baz<F>(mut cb: F, data: u32) where F: FnMut(u32) {
    cb(data);
}

#[no_mangle]
pub fn bar<F>(cb: F, data: u32) where F: FnMut(u32) {
    baz(cb, data);
}

#[no_mangle]
pub fn foo<F>(cb: F, data: u32) where F: FnMut(u32) {
    bar(cb, data);
}

pub fn capture_backtrace() -> std::backtrace::Backtrace {
    let mut bt = None;
    foo(|_| bt = Some(std::backtrace::Backtrace::capture()), 42);
    bt.unwrap()
}

[workingjubilee]

terrifying.

[jieyouxu]

Somehow made it even worse on i686-msvc. I'll fix this tmrw 😆

[jieyouxu]

[jieyouxu]

@rustbot ready

[workingjubilee]

Looks good to me, but in practice we're playing roulette.

@bors r+

[bors]

📌 Commit d4aeff7 has been approved by workingjubilee

It is now in the queue for this repository.

[jieyouxu]

I'm going to mark this as iffy because... I kinda expect this to bounce in full build CI
@bors rollup=iffy

[bors]

⌛ Testing commit d4aeff7 with merge 493ef5d...

[pietroalbini]

@bors retry

Yielding priority to the stable release.

[rust-log-analyzer]

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[bors]

⌛ Testing commit d4aeff7 with merge 93c131e...

[bors]

☀️ Test successful - checks-actions
Approved by: workingjubilee
Pushing 93c131e to master...

[rust-timer]

Finished benchmarking commit (93c131e): comparison URL.

Overall result: ❌ regressions - no action needed

@rustbot label: -perf-regression

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)	0.2%	[0.2%, 0.2%]	1
Regressions ❌ (secondary)	2.0%	[0.2%, 3.7%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.2%	[0.2%, 0.2%]	1

Max RSS (memory usage)

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

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: 673.348s -> 674.369s (0.15%)
Artifact size: 318.36 MiB -> 318.42 MiB (0.02%)