Check divergence value first before doing span operations in warn_if_unreachable

[compiler-errors]

It's more expensive to extract the span's desugaring first rather than check the value of the divergence enum. For some reason I inverted these checks, probably for readability, but as a consequence I regressed perf:

#128443 (comment)

r? fmease

[compiler-errors]

@bors try @rust-timer queue

[bors]

⌛ Trying commit f850e37 with merge 9643070...

[fmease]

I did wonder if the Always<->is_desugaring swap of ordering in the original PR had any perf implications ^^' Let's see :)

r=me if perf gud

[bors]

☀️ Try build successful - checks-actions
Build commit: 9643070 (9643070d2fd619f53c596be3a25561a82d48c68a)

[rust-timer]

Finished benchmarking commit (9643070): comparison URL.

Overall result: ✅ improvements - no action needed

Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up. While you can manually mark this PR as fit for rollup, we strongly recommend not doing so since this PR may lead to changes in compiler perf.

@bors rollup=never
@rustbot label: -S-waiting-on-perf -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
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.4%	[-0.8%, -0.2%]	22
Improvements ✅ (secondary)	-1.0%	[-2.1%, -0.2%]	33
All ❌✅ (primary)	-0.4%	[-0.8%, -0.2%]	22

Max RSS (memory usage)

Results (primary 1.4%)

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)	1.4%	[1.4%, 1.4%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	1.4%	[1.4%, 1.4%]	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: 759.288s -> 757.623s (-0.22%)
Artifact size: 336.86 MiB -> 336.64 MiB (-0.07%)

[compiler-errors]

@bors r=fmease

[bors]

📌 Commit f850e37 has been approved by fmease

It is now in the queue for this repository.

[bors]

⌛ Testing commit f850e37 with merge ab1527f...

[bors]

☀️ Test successful - checks-actions
Approved by: fmease
Pushing ab1527f to master...

[rust-timer]

Finished benchmarking commit (ab1527f): comparison URL.

Overall result: ✅ improvements - 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
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.3%	[-0.5%, -0.2%]	21
Improvements ✅ (secondary)	-1.0%	[-2.1%, -0.2%]	34
All ❌✅ (primary)	-0.3%	[-0.5%, -0.2%]	21

Max RSS (memory usage)

Results (primary 0.8%, secondary -1.8%)

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)	0.8%	[0.8%, 0.8%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-1.8%	[-1.8%, -1.8%]	1
All ❌✅ (primary)	0.8%	[0.8%, 0.8%]	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: 757.752s -> 757.91s (0.02%)
Artifact size: 336.82 MiB -> 336.82 MiB (0.00%)