add #[cold] attribute to abort intrinsic for optimization hints

[fereidani]

Hey,
as std::process::abort already has #[cold] attribute, and large part of rust core(no-std) is relying on intrinsics::abort instead, I believe marking it as cold will help the compiler generate more optimized code.

[rustbot]

Some changes occurred to the intrinsics. Make sure the CTFE / Miri interpreter
gets adapted for the changes, if necessary.

cc @rust-lang/miri, @RalfJung, @oli-obk, @lcnr

[rustbot]

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[RalfJung]

Does this attribute even work when applied to an intrinsic (which is not a regular function)?

[fereidani]

I have no idea, But even if that is the case couldn't we wrap it in another function and make it cold for optimization reason?

[saethlin]

This might cause branch weight metadata to be produced in more cases because of this logic:

rust/compiler/rustc_codegen_ssa/src/mir/block.rs

Line 483 in b7bcaa5

} else {

But also this intrinsic lowers to llvm.trap which already has the LLVM cold attribute, so I think it would be a missing optimization in LLVM if this PR actually improves optimization.

There is no reason to add a wrapper.

[Kobzol]

@bors try @rust-timer queue

[rust-bors]

☀️ Try build successful (CI)
Build commit: 5d0861d (5d0861d01ea52af610896e2430e49b5232d304ca, parent: b7bcaa5c715ed07af2d74dac7ddb8786abeb4299)

[rust-timer]

Finished benchmarking commit (5d0861d): comparison URL.

Overall result: ❌ regressions - no action needed

Benchmarking this pull request means it may be perf-sensitive – we'll automatically label it not fit for rolling up. You can override this, but we strongly advise not to, due to possible changes in compiler perf.

@bors rollup=never
@rustbot label: -S-waiting-on-perf -perf-regression

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	0.2%	[0.2%, 0.2%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.2%	[0.2%, 0.2%]	1

Max RSS (memory usage)

Results (secondary -0.2%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	2.9%	[2.6%, 3.2%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.2%	[-2.3%, -2.0%]	3
All ❌✅ (primary)	-	-	0

Cycles

Results (primary 2.5%, secondary 3.3%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	2.5%	[2.5%, 2.5%]	2
Regressions ❌ (secondary)	3.3%	[2.2%, 5.4%]	5
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	2.5%	[2.5%, 2.5%]	2

Binary size

Results (primary 0.0%, secondary 0.0%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	0.0%	[0.0%, 0.0%]	4
Regressions ❌ (secondary)	0.0%	[0.0%, 0.1%]	13
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.0%	[-0.0%, -0.0%]	1
All ❌✅ (primary)	0.0%	[0.0%, 0.0%]	4

Bootstrap: 474.563s -> 472.66s (-0.40%)
Artifact size: 390.70 MiB -> 390.85 MiB (0.04%)