Evaluate std::fmt::Arguments::new_const() during Compile Time

[veera-sivarajan]

Fixes #128709

This PR aims to optimize calls to string formating macros without any arguments by evaluating std::fmt::Arguments::new_const() in a const context.

Currently,
println!("hola") compiles to std::io::_print(std::fmt::Arguments::new_const(&["hola\n"])).

With this PR,
println!("hola") compiles to std::io::_print(const { std::fmt::Arguments::new_const(&["hola\n"]) }).

This is accomplished by wrapping calls to std::fmt::Arguments::new_const() in an inline const block when lowering the AST to HIR.

This reduces the generated code to a memcpy instead of multiple getelementptr and store instructions even with -C no-prepopulate-passes -C opt-level=0. Godbolt for code comparison: https://rust.godbolt.org/z/P7Px7de6c

This is a safe and sound transformation because std::fmt::Arguments::new_const() is a trivial constructor function taking a slice containing a 'static string literal as input.

CC #99012

[rustbot]

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[Kobzol]

@bors try @rust-timer queue

[bors]

⌛ Trying commit 7638733 with merge ed038de...

[rustbot]

Some changes occurred in coverage tests.

cc @Zalathar

[rustbot]

This PR modifies tests/run-make/. If this PR is trying to port a Makefile
run-make test to use rmake.rs, please update the
run-make port tracking issue
so we can track our progress. You can either modify the tracking issue
directly, or you can comment on the tracking issue and link this PR.

cc @jieyouxu

[lqd]

@bors try @rust-timer queue

[bors]

⌛ Trying commit 95b1d81 with merge 814ddfe...

[bors]

☀️ Try build successful - checks-actions
Build commit: 814ddfe (814ddfee7d50cf02df6549a9aec46528285bdf12)

[rust-timer]

Finished benchmarking commit (814ddfe): comparison URL.

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

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.

Next Steps: If you can justify the regressions found in this try perf run, please indicate this with @rustbot label: +perf-regression-triaged along with sufficient written justification. If you cannot justify the regressions please fix the regressions and do another perf run. If the next run shows neutral or positive results, the label will be automatically removed.

@bors rollup=never
@rustbot label: -S-waiting-on-perf +perf-regression

Instruction count

This is the most reliable metric that we have; it was used to determine the overall result at the top of this comment. However, even this metric can sometimes exhibit noise.

	mean	range	count
Regressions ❌ (primary)	0.8%	[0.2%, 2.7%]	56
Regressions ❌ (secondary)	1.2%	[1.1%, 1.4%]	9
Improvements ✅ (primary)	-0.7%	[-2.9%, -0.1%]	14
Improvements ✅ (secondary)	-0.3%	[-1.1%, -0.1%]	25
All ❌✅ (primary)	0.5%	[-2.9%, 2.7%]	70

Max RSS (memory usage)

Results (primary 2.3%, secondary 1.9%)

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)	2.5%	[0.8%, 10.4%]	34
Regressions ❌ (secondary)	2.6%	[1.6%, 3.3%]	7
Improvements ✅ (primary)	-4.1%	[-4.1%, -4.1%]	1
Improvements ✅ (secondary)	-2.7%	[-2.7%, -2.7%]	1
All ❌✅ (primary)	2.3%	[-4.1%, 10.4%]	35

Cycles

Results (primary 1.8%, secondary -0.6%)

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)	1.8%	[0.9%, 4.1%]	15
Regressions ❌ (secondary)	1.0%	[1.0%, 1.0%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.1%	[-2.1%, -2.1%]	1
All ❌✅ (primary)	1.8%	[0.9%, 4.1%]	15

Binary size

Results (primary 0.1%, secondary 0.1%)

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)	0.6%	[0.0%, 1.4%]	47
Regressions ❌ (secondary)	0.4%	[0.0%, 2.4%]	47
Improvements ✅ (primary)	-0.3%	[-0.6%, -0.0%]	56
Improvements ✅ (secondary)	-0.6%	[-1.3%, -0.1%]	14
All ❌✅ (primary)	0.1%	[-0.6%, 1.4%]	103

Bootstrap: 782.597s -> 784.903s (0.29%)
Artifact size: 332.70 MiB -> 333.44 MiB (0.22%)

[bors]

☔ The latest upstream changes (presumably #132020) made this pull request unmergeable. Please resolve the merge conflicts.

[veera-sivarajan]

I don't know what's causing the large number of regressions.

Please let me know if it's better to close this.

[chenyukang]

@bors try @rust-timer queue

[bors]

⌛ Trying commit e20cc8e with merge 1e4519d...

[bors]

☀️ Try build successful - checks-actions
Build commit: 1e4519d (1e4519d5900fc165d4cffd1a82ce0aeca8bab9fd)

[rust-timer]

Finished benchmarking commit (1e4519d): comparison URL.

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

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.

Next Steps: If you can justify the regressions found in this try perf run, please indicate this with @rustbot label: +perf-regression-triaged along with sufficient written justification. If you cannot justify the regressions please fix the regressions and do another perf run. If the next run shows neutral or positive results, the label will be automatically removed.

@bors rollup=never
@rustbot label: -S-waiting-on-perf +perf-regression

Instruction count

This is the most reliable metric that we have; it was used to determine the overall result at the top of this comment. However, even this metric can sometimes exhibit noise.

	mean	range	count
Regressions ❌ (primary)	0.8%	[0.2%, 3.0%]	59
Regressions ❌ (secondary)	1.5%	[1.1%, 2.7%]	13
Improvements ✅ (primary)	-0.5%	[-2.6%, -0.2%]	16
Improvements ✅ (secondary)	-0.3%	[-0.5%, -0.0%]	16
All ❌✅ (primary)	0.5%	[-2.6%, 3.0%]	75

Max RSS (memory usage)

Results (primary 1.9%, secondary 2.7%)

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)	2.1%	[0.7%, 6.5%]	17
Regressions ❌ (secondary)	2.7%	[1.7%, 4.3%]	3
Improvements ✅ (primary)	-1.8%	[-1.8%, -1.8%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	1.9%	[-1.8%, 6.5%]	18

Cycles

Results (primary 2.6%, secondary -0.9%)

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)	2.6%	[1.9%, 3.7%]	6
Regressions ❌ (secondary)	5.1%	[5.0%, 5.2%]	3
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-3.1%	[-4.4%, -2.3%]	8
All ❌✅ (primary)	2.6%	[1.9%, 3.7%]	6

Binary size

Results (primary 0.2%, secondary 0.1%)

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)	0.6%	[0.0%, 1.5%]	49
Regressions ❌ (secondary)	0.4%	[0.0%, 2.5%]	49
Improvements ✅ (primary)	-0.3%	[-0.6%, -0.0%]	57
Improvements ✅ (secondary)	-0.6%	[-1.3%, -0.1%]	16
All ❌✅ (primary)	0.2%	[-0.6%, 1.5%]	106

Bootstrap: 783.63s -> 779.85s (-0.48%)
Artifact size: 333.67 MiB -> 333.71 MiB (0.01%)

[chenyukang]

@veera-sivarajan do you want to continue to resolve the performance issue?
if not we can close this PR now.

[veera-sivarajan]

Ah no, I don't have anything to add. Will close this now.