Micro-optimization in FunctionCx::initialize_locals

[yotamofek]

This showed up in a profile I was looking at, hoping this might improve perf by a little bit.

[rustbot]

Some changes occurred in compiler/rustc_codegen_ssa

cc @WaffleLapkin

[rustbot]

r? @davidtwco

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[JonathanBrouwer]

@bors try @rust-timer queue

[rust-bors]

☀️ Try build successful (CI)
Build commit: 5b26667 (5b2666713c0320f62e357a7c134d7b62824b2daa, parent: 28d0a4a205f9e511ad2f51ee79a4aa19a704a455)

[rust-timer]

Finished benchmarking commit (5b26667): comparison URL.

Overall result: no relevant changes - 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

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

Max RSS (memory usage)

Results (primary -4.3%, secondary -3.0%)

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)	-4.3%	[-6.4%, -2.2%]	2
Improvements ✅ (secondary)	-3.0%	[-3.0%, -2.9%]	2
All ❌✅ (primary)	-4.3%	[-6.4%, -2.2%]	2

Cycles

Results (secondary 2.3%)

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)	2.3%	[2.3%, 2.3%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Binary size

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

Bootstrap: 474.854s -> 476.04s (0.25%)
Artifact size: 388.09 MiB -> 388.00 MiB (-0.02%)

[yotamofek]

Doesn't make a dent in instruction counts, but reduces max RSS in some cases - which makes sense. So I think it's still worth merging.

[JonathanBrouwer]

I'm not entirely convinced that the max RSS isn't just noise, but I think the new code is easier to read anyways, so lets merge this

@bors r+ rollup=iffy
Since this may have some effect on performance this maybe shouldn't be rolled up? It's probably fine tho since its so minimal

[bors]

📌 Commit 9361d64 has been approved by JonathanBrouwer

It is now in the queue for this repository.