Use mimalloc as global_allocator for rustc_driver

[Zoxc]

This changes the Rust global allocator for rustc_driver to mimalloc, leaving LLVM unaffected.

Based on #122362.

[rustbot]

r? @lcnr

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[lqd]

Has anything changed since we last evaluated mimalloc and decided we wouldn't use it over jemalloc on linux?

[Zoxc]

I'd like to see the memory use of a mimalloc + jemalloc mix.

[lqd]

Ok then we can wait another hour for #122362's results in case there's an issue there, and then trigger a run for this PR. I'm not sure what code will get mimalloc vs jemalloc's symbol overrides (if any) but we'll see.

In the meantime:

@bors try

[bors]

⌛ Trying commit 3482094 with merge 7c1e667...

[bors]

☀️ Try build successful - checks-actions
Build commit: 7c1e667 (7c1e66778214e445126667614fe1d6a72eb7d2ea)

[lqd]

@rust-timer build 7c1e667

[rust-timer]

Finished benchmarking commit (7c1e667): 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)	0.5%	[0.3%, 0.6%]	3
Improvements ✅ (primary)	-2.7%	[-7.7%, -0.5%]	214
Improvements ✅ (secondary)	-2.8%	[-6.4%, -0.6%]	214
All ❌✅ (primary)	-2.7%	[-7.7%, -0.5%]	214

Max RSS (memory usage)

Results

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)	3.5%	[1.0%, 21.4%]	62
Regressions ❌ (secondary)	9.1%	[1.7%, 35.5%]	68
Improvements ✅ (primary)	-3.5%	[-5.7%, -1.6%]	9
Improvements ✅ (secondary)	-3.5%	[-4.6%, -3.2%]	4
All ❌✅ (primary)	2.6%	[-5.7%, 21.4%]	71

Cycles

Results

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
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-2.3%	[-4.9%, -0.9%]	73
Improvements ✅ (secondary)	-3.5%	[-9.6%, -2.0%]	96
All ❌✅ (primary)	-2.3%	[-4.9%, -0.9%]	73

Binary size

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

Bootstrap: 672.558s -> 667.981s (-0.68%)
Artifact size: 309.99 MiB -> 298.62 MiB (-3.67%)