Don't use ThinVec for PendingObligations.

[nnethercote]

r? @ghost

[nnethercote]

@bors try @rust-timer queue

[rust-bors]

☀️ Try build successful (CI)
Build commit: a98c585 (a98c5859a5cc81e01f1ef5c746290fe9266668e2, parent: 451b7b6c775a2378fd18d2560bbfb31c3695d1cc)

[rust-timer]

Finished benchmarking commit (a98c585): 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)	-	-	0
Regressions ❌ (secondary)	0.6%	[0.1%, 2.0%]	6
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.6%	[-0.8%, -0.6%]	3
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (primary 2.7%)

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

	mean	range	count
Regressions ❌ (primary)	6.6%	[2.2%, 11.1%]	2
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-1.3%	[-1.8%, -0.8%]	2
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	2.7%	[-1.8%, 11.1%]	4

Cycles

Results (secondary -3.6%)

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)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-3.6%	[-3.6%, -3.6%]	1
All ❌✅ (primary)	-	-	0

Binary size

Results (primary 0.1%, secondary 0.1%)

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

	mean	range	count
Regressions ❌ (primary)	0.1%	[0.0%, 0.1%]	35
Regressions ❌ (secondary)	0.1%	[0.0%, 0.1%]	21
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.1%	[0.0%, 0.1%]	35

Bootstrap: 477.322s -> 474.639s (-0.56%)
Artifact size: 390.73 MiB -> 390.69 MiB (-0.01%)