Disable incr CGU merging

[saethlin]

For perf comparison in #145910

[saethlin]

@bors try @rust-timer queue

[rust-log-analyzer]

The job aarch64-gnu-llvm-19-1 failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

---- [codegen-units] tests/codegen-units/partitioning/incremental-merging.rs stdout ----

The following items were assigned to wrong codegen units:

fn aaa::foo
  expected: incremental_merging-aaa--incremental_merging-bbb[External] 
  actual:   incremental_merging-aaa[External] 

fn bbb::foo
  expected: incremental_merging-aaa--incremental_merging-bbb[External] 
  actual:   incremental_merging-bbb[External] 

FATAL: !(missing.is_empty() && unexpected.is_empty() && wrong_cgus.is_empty())

thread '[codegen-units] tests/codegen-units/partitioning/incremental-merging.rs' panicked at src/tools/compiletest/src/runtest/codegen_units.rs:103:13:
fatal error
stack backtrace:
   8: __rustc::rust_begin_unwind

[rust-bors]

☀️ Try build successful (CI)
Build commit: 7cb1a81 (7cb1a81145a739c4fd858abe3c624ce8e6e5f9cd, parent: 51ff895062ba60a7cba53f57af928c3fb7b0f2f4)

[rust-timer]

Finished benchmarking commit (7cb1a81): comparison URL.

Overall result: ❌✅ regressions and improvements - please read the text below

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.

Next Steps: If you can justify the regressions found in this try perf run, please do so in sufficient writing along with @rustbot label: +perf-regression-triaged. If not, please fix the regressions and do another perf run. If its results are neutral or positive, the label will be automatically removed.

@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)	1.3%	[0.4%, 4.0%]	16
Regressions ❌ (secondary)	19.0%	[0.1%, 59.8%]	8
Improvements ✅ (primary)	-13.3%	[-84.8%, -0.1%]	8
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-3.6%	[-84.8%, 4.0%]	24

Max RSS (memory usage)

Results (primary -2.9%, secondary 2.6%)

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

	mean	range	count
Regressions ❌ (primary)	7.0%	[7.0%, 7.0%]	1
Regressions ❌ (secondary)	2.6%	[2.1%, 3.1%]	5
Improvements ✅ (primary)	-12.8%	[-12.8%, -12.8%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-2.9%	[-12.8%, 7.0%]	2

Cycles

Results (primary -7.7%, secondary 16.3%)

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

	mean	range	count
Regressions ❌ (primary)	2.8%	[2.2%, 4.1%]	5
Regressions ❌ (secondary)	22.6%	[5.0%, 48.4%]	6
Improvements ✅ (primary)	-16.4%	[-84.4%, -1.8%]	6
Improvements ✅ (secondary)	-2.4%	[-2.8%, -2.0%]	2
All ❌✅ (primary)	-7.7%	[-84.4%, 4.1%]	11

Binary size

Results (primary 2.9%, secondary 3.8%)

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

	mean	range	count
Regressions ❌ (primary)	2.9%	[0.0%, 16.0%]	33
Regressions ❌ (secondary)	3.8%	[3.7%, 3.9%]	6
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	2.9%	[0.0%, 16.0%]	33

Bootstrap: 465.874s -> 465.493s (-0.08%)
Artifact size: 388.34 MiB -> 388.38 MiB (0.01%)