Optimize write with as_const_str for shorter code #122059

nyurik · 2024-03-06T03:49:50Z

Following up on #121001

Apparently this code generates significant code block for each call to write() with non-simple formatting string - approx 100 lines of assembly code, possibly due to dyn (?). See generated assembly code here:

Details

This is the inlining of write!(buffer, "Iteration {value} was written")

core::fmt::Write::write_fmt:
		// /home/nyurik/dev/rust/rust/library/core/src/fmt/mod.rs : 194
		fn write_fmt(&mut self, args: Arguments<'_>) -> Result {
	push r15
	push r14
	push r13
	push r12
	push rbx
	mov rdx, rsi
		// /home/nyurik/dev/rust/rust/library/core/src/fmt/mod.rs : 427
		match (self.pieces, self.args) {
	mov rcx, qword ptr [rsi + 8]
	mov rax, qword ptr [rsi + 24]
		// /home/nyurik/dev/rust/rust/library/core/src/fmt/mod.rs : 428
		([], []) => Some(""),
	cmp rcx, 1
	je .LBB0_8
	test rcx, rcx
	jne .LBB0_9
	test rax, rax
	jne .LBB0_9
		// /home/nyurik/dev/rust/rust/library/alloc/src/vec/mod.rs : 911
		self.buf.reserve(self.len, additional);
	lea r12, [rdi + 16]
	lea rsi, [rip + .L__unnamed_2]
	xor ebx, ebx
.LBB0_6:
	mov r14, qword ptr [r12]
	jmp .LBB0_7
.LBB0_8:
		// /home/nyurik/dev/rust/rust/library/core/src/fmt/mod.rs : 429
		([s], []) => Some(s),
	test rax, rax
	je .LBB0_4
.LBB0_9:
		// /home/nyurik/dev/rust/rust/library/core/src/fmt/mod.rs : 1108
		if let Some(s) = args.as_str() { output.write_str(s) } else { write_internal(output, args) }
	lea rsi, [rip + .L__unnamed_1]
	pop rbx
	pop r12
	pop r13
	pop r14
	pop r15
	jmp qword ptr [rip + core::fmt::write_internal@GOTPCREL]
.LBB0_4:
	mov rax, qword ptr [rdx]
		// /home/nyurik/dev/rust/rust/library/core/src/fmt/mod.rs : 429
		([s], []) => Some(s),
	mov rsi, qword ptr [rax]
	mov rbx, qword ptr [rax + 8]
		// /home/nyurik/dev/rust/rust/library/alloc/src/raw_vec.rs : 248
		if T::IS_ZST { usize::MAX } else { self.cap.0 }
	mov rax, qword ptr [rdi]
		// /home/nyurik/dev/rust/rust/library/alloc/src/vec/mod.rs : 911
		self.buf.reserve(self.len, additional);
	mov r14, qword ptr [rdi + 16]
		// /home/nyurik/dev/rust/rust/library/core/src/num/mod.rs : 1281
		uint_impl! {
	sub rax, r14
		// /home/nyurik/dev/rust/rust/library/alloc/src/raw_vec.rs : 392
		additional > self.capacity().wrapping_sub(len)
	cmp rax, rbx
		// /home/nyurik/dev/rust/rust/library/alloc/src/raw_vec.rs : 309
		if self.needs_to_grow(len, additional) {
	jb .LBB0_5
.LBB0_7:
	mov rax, qword ptr [rdi + 8]
		// /home/nyurik/dev/rust/rust/library/core/src/ptr/mut_ptr.rs : 1046
		unsafe { intrinsics::offset(self, count) }
	add rax, r14
	mov r15, rdi
		// /home/nyurik/dev/rust/rust/library/core/src/intrinsics.rs : 2922
		copy_nonoverlapping(src, dst, count)
	mov rdi, rax
	mov rdx, rbx
	call qword ptr [rip + memcpy@GOTPCREL]
		// /home/nyurik/dev/rust/rust/library/alloc/src/vec/mod.rs : 2040
		self.len += count;
	add r14, rbx
	mov qword ptr [r15 + 16], r14
		// /home/nyurik/dev/rust/rust/library/core/src/fmt/mod.rs : 216
		}
	xor eax, eax
	pop rbx
	pop r12
	pop r13
	pop r14
	pop r15
	ret
.LBB0_5:
		// /home/nyurik/dev/rust/rust/library/alloc/src/vec/mod.rs : 911
		self.buf.reserve(self.len, additional);
	lea r12, [rdi + 16]
	mov r15, rdi
	mov r13, rsi
		// /home/nyurik/dev/rust/rust/library/alloc/src/raw_vec.rs : 310
		do_reserve_and_handle(self, len, additional);
	mov rsi, r14
	mov rdx, rbx
	call alloc::raw_vec::RawVec<T,A>::reserve::do_reserve_and_handle
	mov rsi, r13
	mov rdi, r15
	jmp .LBB0_6

#[inline]
pub fn write(output: &mut dyn Write, args: Arguments<'_>) -> Result {
    if let Some(s) = args.as_str() { output.write_str(s) } else { write_internal(output, args) }
}

So, this brings back the older experiment - where I used if core::intrinsics::is_val_statically_known(s.is_some()) { s } else { None } helper function, and called it in multiple places that used write. This is not as optimal because now every user of write must do this logic, but at least it results in significantly smaller assembly code for the formatting case, and results in identical code as now for the "simple" (no formatting) case. See assembly comparison of what is now with what this change brings (focus only on fmt/intel-lib.txt and str/intel-lib.txt files).

if let Some(s) = args.as_const_str() {
    self.write_str(s)
} else {
    write(self, args)
}

rustbot · 2024-03-06T03:49:58Z

r? @scottmcm

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nyurik · 2024-03-06T03:52:11Z

@bors r? @cuviper

clubby789 · 2024-03-06T11:12:27Z

@bors try @rust-timer queue

bors · 2024-03-06T11:13:37Z

⌛ Trying commit 3d0d0ce with merge 61bc12c...

Optimize write with as_const_str for shorter code Following up on rust-lang#121001 Apparently this code generates significant code block for each call to `write()` with non-simple formatting string - approx 100 lines of assembly code, possibly due to `dyn` (?). See generated assembly code [here](https://github.com/nyurik/rust-optimize-format-str/compare/before-changes..with-my-change#diff-6b404e954c692d8cdc8c452d819a216aa5dcf40522b5944639e9ad947279a477): <details><summary>Details</summary> <p> This is the inlining of `write!(buffer, "Iteration {value} was written")` ```asm core::fmt::Write::write_fmt: // /home/nyurik/dev/rust/rust/library/core/src/fmt/mod.rs : 194 fn write_fmt(&mut self, args: Arguments<'_>) -> Result { push r15 push r14 push r13 push r12 push rbx mov rdx, rsi // /home/nyurik/dev/rust/rust/library/core/src/fmt/mod.rs : 427 match (self.pieces, self.args) { mov rcx, qword ptr [rsi + 8] mov rax, qword ptr [rsi + 24] // /home/nyurik/dev/rust/rust/library/core/src/fmt/mod.rs : 428 ([], []) => Some(""), cmp rcx, 1 je .LBB0_8 test rcx, rcx jne .LBB0_9 test rax, rax jne .LBB0_9 // /home/nyurik/dev/rust/rust/library/alloc/src/vec/mod.rs : 911 self.buf.reserve(self.len, additional); lea r12, [rdi + 16] lea rsi, [rip + .L__unnamed_2] xor ebx, ebx .LBB0_6: mov r14, qword ptr [r12] jmp .LBB0_7 .LBB0_8: // /home/nyurik/dev/rust/rust/library/core/src/fmt/mod.rs : 429 ([s], []) => Some(s), test rax, rax je .LBB0_4 .LBB0_9: // /home/nyurik/dev/rust/rust/library/core/src/fmt/mod.rs : 1108 if let Some(s) = args.as_str() { output.write_str(s) } else { write_internal(output, args) } lea rsi, [rip + .L__unnamed_1] pop rbx pop r12 pop r13 pop r14 pop r15 jmp qword ptr [rip + core::fmt::write_internal@GOTPCREL] .LBB0_4: mov rax, qword ptr [rdx] // /home/nyurik/dev/rust/rust/library/core/src/fmt/mod.rs : 429 ([s], []) => Some(s), mov rsi, qword ptr [rax] mov rbx, qword ptr [rax + 8] // /home/nyurik/dev/rust/rust/library/alloc/src/raw_vec.rs : 248 if T::IS_ZST { usize::MAX } else { self.cap.0 } mov rax, qword ptr [rdi] // /home/nyurik/dev/rust/rust/library/alloc/src/vec/mod.rs : 911 self.buf.reserve(self.len, additional); mov r14, qword ptr [rdi + 16] // /home/nyurik/dev/rust/rust/library/core/src/num/mod.rs : 1281 uint_impl! { sub rax, r14 // /home/nyurik/dev/rust/rust/library/alloc/src/raw_vec.rs : 392 additional > self.capacity().wrapping_sub(len) cmp rax, rbx // /home/nyurik/dev/rust/rust/library/alloc/src/raw_vec.rs : 309 if self.needs_to_grow(len, additional) { jb .LBB0_5 .LBB0_7: mov rax, qword ptr [rdi + 8] // /home/nyurik/dev/rust/rust/library/core/src/ptr/mut_ptr.rs : 1046 unsafe { intrinsics::offset(self, count) } add rax, r14 mov r15, rdi // /home/nyurik/dev/rust/rust/library/core/src/intrinsics.rs : 2922 copy_nonoverlapping(src, dst, count) mov rdi, rax mov rdx, rbx call qword ptr [rip + memcpy@GOTPCREL] // /home/nyurik/dev/rust/rust/library/alloc/src/vec/mod.rs : 2040 self.len += count; add r14, rbx mov qword ptr [r15 + 16], r14 // /home/nyurik/dev/rust/rust/library/core/src/fmt/mod.rs : 216 } xor eax, eax pop rbx pop r12 pop r13 pop r14 pop r15 ret .LBB0_5: // /home/nyurik/dev/rust/rust/library/alloc/src/vec/mod.rs : 911 self.buf.reserve(self.len, additional); lea r12, [rdi + 16] mov r15, rdi mov r13, rsi // /home/nyurik/dev/rust/rust/library/alloc/src/raw_vec.rs : 310 do_reserve_and_handle(self, len, additional); mov rsi, r14 mov rdx, rbx call alloc::raw_vec::RawVec<T,A>::reserve::do_reserve_and_handle mov rsi, r13 mov rdi, r15 jmp .LBB0_6 ``` </p> </details> ```rust #[inline] pub fn write(output: &mut dyn Write, args: Arguments<'_>) -> Result { if let Some(s) = args.as_str() { output.write_str(s) } else { write_internal(output, args) } } ``` So, this brings back the older experiment - where I used `if core::intrinsics::is_val_statically_known(s.is_some()) { s } else { None }` helper function, and called it in multiple places that used `write`. This is not as optimal because now every user of `write` must do this logic, but at least it results in significantly smaller assembly code for the formatting case, and results in identical code as now for the "simple" (no formatting) case. See [assembly comparison](https://github.com/nyurik/rust-optimize-format-str/compare/with-my-change..with-as-const-str#diff-6b404e954c692d8cdc8c452d819a216aa5dcf40522b5944639e9ad947279a477) of what is now with what this change brings (focus only on `fmt/intel-lib.txt` and `str/intel-lib.txt` files). ```rust if let Some(s) = args.as_const_str() { self.write_str(s) } else { write(self, args) } ```

bors · 2024-03-06T12:40:59Z

☀️ Try build successful - checks-actions
Build commit: 61bc12c (61bc12ca0210786789b3e8f6265106ba9701acde)

rust-timer · 2024-03-06T15:12:15Z

Finished benchmarking commit (61bc12c): 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
Improvements ✅ (primary)	-0.5%	[-1.2%, -0.2%]	4
Improvements ✅ (secondary)	-0.4%	[-1.9%, -0.2%]	9
All ❌✅ (primary)	-0.5%	[-1.2%, -0.2%]	4

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)	1.8%	[0.2%, 3.4%]	3
Regressions ❌ (secondary)	3.1%	[2.9%, 3.2%]	2
Improvements ✅ (primary)	-3.9%	[-4.8%, -2.3%]	3
Improvements ✅ (secondary)	-2.3%	[-2.3%, -2.3%]	1
All ❌✅ (primary)	-1.0%	[-4.8%, 3.4%]	6

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)	-1.0%	[-1.0%, -1.0%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-1.0%	[-1.0%, -1.0%]	1

Binary size

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)	0.1%	[0.0%, 1.2%]	33
Regressions ❌ (secondary)	0.6%	[0.6%, 0.6%]	3
Improvements ✅ (primary)	-0.1%	[-0.4%, -0.0%]	20
Improvements ✅ (secondary)	-0.9%	[-1.3%, -0.1%]	36
All ❌✅ (primary)	0.0%	[-0.4%, 1.2%]	53

Bootstrap: 647.585s -> 647.242s (-0.05%)
Artifact size: 175.07 MiB -> 175.02 MiB (-0.03%)

cuviper · 2024-03-06T20:04:24Z

@nnethercote are you happier with this than you were in #121001 (comment)?

It looks to me like binary size is swinging both good and bad, both here and in the previous PR.

nnethercote · 2024-03-06T21:15:28Z

I don't have strong opinions, but these new results seem good.

cuviper · 2024-03-07T20:19:39Z

@bors r+

bors · 2024-03-07T20:19:42Z

📌 Commit 3d0d0ce has been approved by cuviper

It is now in the queue for this repository.

bors · 2024-03-08T04:15:20Z

⌛ Testing commit 3d0d0ce with merge 9fb91aa...

bors · 2024-03-08T06:43:06Z

☀️ Test successful - checks-actions
Approved by: cuviper
Pushing 9fb91aa to master...

rust-timer · 2024-03-08T07:57:07Z

Finished benchmarking commit (9fb91aa): comparison URL.

Overall result: ❌✅ regressions and improvements - ACTION NEEDED

Next Steps: If you can justify the regressions found in this perf run, please indicate this with @rustbot label: +perf-regression-triaged along with sufficient written justification. If you cannot justify the regressions please open an issue or create a new PR that fixes the regressions, add a comment linking to the newly created issue or PR, and then add the perf-regression-triaged label to this PR.

@rustbot label: +perf-regression
cc @rust-lang/wg-compiler-performance

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)	1.1%	[0.3%, 1.9%]	2
Improvements ✅ (primary)	-0.8%	[-1.2%, -0.4%]	2
Improvements ✅ (secondary)	-0.3%	[-0.3%, -0.3%]	1
All ❌✅ (primary)	-0.8%	[-1.2%, -0.4%]	2

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%	[0.1%, 5.9%]	4
Regressions ❌ (secondary)	3.2%	[3.2%, 3.2%]	1
Improvements ✅ (primary)	-4.3%	[-4.3%, -4.3%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	2.0%	[-4.3%, 5.9%]	5

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)	2.2%	[2.0%, 2.5%]	3
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Binary size

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)	0.1%	[0.0%, 1.0%]	34
Regressions ❌ (secondary)	0.6%	[0.6%, 0.6%]	3
Improvements ✅ (primary)	-0.1%	[-0.4%, -0.1%]	20
Improvements ✅ (secondary)	-0.8%	[-1.3%, -0.1%]	42
All ❌✅ (primary)	0.0%	[-0.4%, 1.0%]	54

Bootstrap: 647.024s -> 646.506s (-0.08%)
Artifact size: 172.57 MiB -> 172.55 MiB (-0.01%)

pnkfelix · 2024-03-12T16:49:36Z

(secondary) regressions are to deep-vector debug-full (which may be spurious based on the graph) and wg-grammar debug-incr-unchanged
since @nnethercote was already involved in related efforts here (e.g. PR #121001) and this resulting refinement, I'm going to mark this as triaged.

@rustbot label: +perf-regression-triaged

Relevant upstream changes: rust-lang/rust#120675: An intrinsic `Symbol` is now wrapped in a `IntrinsicDef` struct, so the relevant part of the code needed to be updated. rust-lang/rust#121464: The second argument of the `create_wrapper_file` function changed from a vector to a string. rust-lang/rust#121662: `NullOp::DebugAssertions` was renamed to `NullOp::UbCheck` and it now has data (currently unused by Kani) rust-lang/rust#121728: Introduces `F16` and `F128`, so needed to add stubs for them rust-lang/rust#121969: `parse_sess` was renamed to `psess`, so updated the relevant code. rust-lang/rust#122059: The `is_val_statically_known` intrinsic is now used in some `core::fmt` code, so had to handle it in (codegen'ed to false). rust-lang/rust#122233: This added a new `retag_box_to_raw` intrinsic. This is an operation that is primarily relevant for stacked borrows. For Kani, we just return the pointer. Resolves #3057

RalfJung · 2024-03-23T20:34:30Z

library/core/src/fmt/mod.rs

+    /// Same as [`Arguments::as_str`], but will only return `Some(s)` if it can be determined at compile time.
+    #[must_use]
+    #[inline]
+    fn as_const_str(&self) -> Option<&'static str> {


"const_str" is a very confusing name since const has a meaning in Rust and it's not this. We have very deliberately called the intrinsic is_val_statically_known, not is_val_const or anything like that. Would be nice if the functions using that intrinsic would follow the same pattern. :)

So... as_statically_known_str?

Yes, that would be better IMO. (I'm also open to suggestions for a shorter term that captures this, but "constant" is too misleading IMO. In Rust, whether something is a "constant" is a language guarantee, and we have things like const fn that relate to that. In contrast, "statically known" is a very unstable notion depending on tons of factors that impact how good the compiler is able to analyze some piece of code. Also, const fn is not the same meaning of "const" as in "constant propagation" -- a common misconception that the standard library should not perpetuate. :)

Optimize write with as_const_str for shorter code

3d0d0ce

rustbot assigned scottmcm Mar 6, 2024

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Mar 6, 2024

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nyurik mentioned this pull request Mar 6, 2024

perf: improve write_fmt to handle simple strings #121001

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bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Mar 7, 2024

bors added the merged-by-bors This PR was explicitly merged by bors. label Mar 8, 2024

bors merged commit 9fb91aa into rust-lang:master Mar 8, 2024
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rustbot added this to the 1.78.0 milestone Mar 8, 2024

bors mentioned this pull request Mar 8, 2024

Implementation of fmt::FormattingOptions #118159

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rustbot added the perf-regression Performance regression. label Mar 8, 2024

nyurik deleted the with-as-const-str branch March 8, 2024 17:05

zhassan-aws mentioned this pull request Mar 11, 2024

Upgrade toolchain to 2024-03-11 model-checking/kani#3071

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Optimize write with as_const_str for shorter code #122059

Optimize write with as_const_str for shorter code #122059

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Optimize write with as_const_str for shorter code #122059

Optimize write with as_const_str for shorter code #122059

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Overall result: ✅ improvements - no action needed

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rust-timer commented Mar 8, 2024

Overall result: ❌✅ regressions and improvements - ACTION NEEDED

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