rustc_codegen_ssa: use project_index, not project_field, for array literals.

[eddyb]

See #98615 (comment) for some context.

In short, we were using project_field even for array mir::Rvalue::Aggregates, which results in benchmarks like deep-vector.rs (and presumably also some real-world usecases?) being impacted by how we handle non-array aggregate fields.

(This is a separate PR so that we can measure the perf effects in isolation)

r? @nikic

[eddyb]

@bors try @rust-timer queue

[rust-timer]

Awaiting bors try build completion.

@rustbot label: +S-waiting-on-perf

[bors]

⌛ Trying commit 900309e with merge 3c75882df207e888735b29c93586041759b61c67...

[bors]

☀️ Try build successful - checks-actions
Build commit: 3c75882df207e888735b29c93586041759b61c67 (3c75882df207e888735b29c93586041759b61c67)

[rust-timer]

Queued 3c75882df207e888735b29c93586041759b61c67 with parent 66c83ff, future comparison URL.

[rust-timer]

Finished benchmarking commit (3c75882df207e888735b29c93586041759b61c67): comparison url.

Instruction count

• Primary benchmarks: no relevant changes found
• Secondary benchmarks: 🎉 relevant improvements found

	mean1	max	count2
Regressions 😿 (primary)	N/A	N/A	0
Regressions 😿 (secondary)	N/A	N/A	0
Improvements 🎉 (primary)	N/A	N/A	0
Improvements 🎉 (secondary)	-2.4%	-2.9%	4
All 😿🎉 (primary)	N/A	N/A	0

Max RSS (memory usage)

Results

• Primary benchmarks: mixed results
• Secondary benchmarks: mixed results

	mean1	max	count2
Regressions 😿 (primary)	2.8%	2.8%	1
Regressions 😿 (secondary)	2.2%	2.2%	1
Improvements 🎉 (primary)	-4.1%	-4.1%	1
Improvements 🎉 (secondary)	-2.3%	-2.3%	1
All 😿🎉 (primary)	-0.6%	-4.1%	2

Cycles

Results

• Primary benchmarks: no relevant changes found
• Secondary benchmarks: 🎉 relevant improvements found

	mean1	max	count2
Regressions 😿 (primary)	N/A	N/A	0
Regressions 😿 (secondary)	N/A	N/A	0
Improvements 🎉 (primary)	N/A	N/A	0
Improvements 🎉 (secondary)	-2.3%	-2.5%	4
All 😿🎉 (primary)	N/A	N/A	0

If you disagree with this performance assessment, please file an issue in rust-lang/rustc-perf.

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-review -S-waiting-on-perf -perf-regression

Footnotes

1. the arithmetic mean of the percent change ↩ ↩² ↩³

2. number of relevant changes ↩ ↩² ↩³

[eddyb]

cc @rust-lang/wg-llvm I don't know how well "struct GEP" on arrays works, or if other frontends even emit it, but it looks like moving from that to a normal array-oriented GEP is an improvement.

(And presumably even with opaque pointers we would always want to craft LLVM GEPs for array accesses such that they express a "stride" and an "index" instead of just being a raw offset, even if that "stride" isn't necessarily a typed array element - at least as long as LLVM cares about any of these things)

[nikic]

Sounds reasonable to me.

@bors r+

[bors]

📌 Commit 900309e has been approved by nikic

[bors]

⌛ Testing commit 900309e with merge 20dd693...

[bors]

☀️ Test successful - checks-actions
Approved by: nikic
Pushing 20dd693 to master...

[rust-timer]

Finished benchmarking commit (20dd693): comparison url.

Instruction count

• Primary benchmarks: no relevant changes found
• Secondary benchmarks: 🎉 relevant improvements found

	mean1	max	count2
Regressions 😿 (primary)	N/A	N/A	0
Regressions 😿 (secondary)	N/A	N/A	0
Improvements 🎉 (primary)	N/A	N/A	0
Improvements 🎉 (secondary)	-2.2%	-2.4%	4
All 😿🎉 (primary)	N/A	N/A	0

Max RSS (memory usage)

Results

• Primary benchmarks: 😿 relevant regressions found
• Secondary benchmarks: 😿 relevant regression found

	mean1	max	count2
Regressions 😿 (primary)	0.8%	1.5%	2
Regressions 😿 (secondary)	2.0%	2.0%	1
Improvements 🎉 (primary)	N/A	N/A	0
Improvements 🎉 (secondary)	N/A	N/A	0
All 😿🎉 (primary)	0.8%	1.5%	2

Cycles

Results

• Primary benchmarks: mixed results
• Secondary benchmarks: 🎉 relevant improvements found

	mean1	max	count2
Regressions 😿 (primary)	2.9%	2.9%	1
Regressions 😿 (secondary)	N/A	N/A	0
Improvements 🎉 (primary)	-2.4%	-2.4%	1
Improvements 🎉 (secondary)	-2.2%	-2.4%	2
All 😿🎉 (primary)	0.3%	2.9%	2

If you disagree with this performance assessment, please file an issue in rust-lang/rustc-perf.

@rustbot label: -perf-regression

Footnotes

1. the arithmetic mean of the percent change ↩ ↩² ↩³

2. number of relevant changes ↩ ↩² ↩³