Shrink `Statement`. #55346

nnethercote · 2018-10-25T11:23:54Z

This commit reduces the size of Statement from 80 bytes to 56 bytes on
64-bit platforms, by boxing the AscribeUserType variant of
StatementKind.

This change reduces instruction counts on most benchmarks by 1--3%.

rust-highfive · 2018-10-25T11:24:04Z

r? @pnkfelix

(rust_highfive has picked a reviewer for you, use r? to override)

nnethercote · 2018-10-25T11:26:24Z

Here are the instruction count improvements that exceed 1%.

style-servo-debug
	avg: -2.1%	min: -3.2%	max: 0.4%
webrender-debug
	avg: -1.4%	min: -2.9%	max: -0.1%
regression-31157-debug
	avg: -1.6%	min: -2.7%	max: -0.4%
issue-46449-debug
	avg: -2.4%	min: -2.7%	max: -1.2%
cargo-debug
	avg: -1.8%	min: -2.4%	max: -0.1%
piston-image-debug
	avg: -1.2%	min: -2.3%	max: -0.2%
regex-debug
	avg: -1.4%	min: -2.3%	max: -0.1%
crates.io-debug
	avg: -1.3%	min: -2.3%	max: -0.1%
syn-debug
	avg: -1.3%	min: -2.2%	max: -0.1%
clap-rs-debug
	avg: -1.4%	min: -2.2%	max: 0.2%
helloworld-check
	avg: -1.9%	min: -2.0%	max: -1.7%
encoding-debug
	avg: -1.1%	min: -1.9%	max: -0.2%
deeply-nested-debug
	avg: -1.7%	min: -1.9%	max: -1.3%
sentry-cli-debug
	avg: -1.0%	min: -1.9%	max: -0.0%
unify-linearly-check
	avg: -1.3%	min: -1.8%	max: -0.9%
deeply-nested-check
	avg: -1.2%	min: -1.8%	max: -0.8%
ctfe-stress-debug
	avg: 0.2%?	min: -1.3%?	max: 1.7%?
tokio-webpush-simple-debug
	avg: -1.2%	min: -1.6%	max: -0.1%
ctfe-stress-check
	avg: -0.5%?	min: -1.6%?	max: 0.7%?
ripgrep-debug
	avg: -0.7%	min: -1.4%	max: 0.1%
ctfe-stress-opt
	avg: -0.9%?	min: -1.4%?	max: -0.4%?
coercions-debug
	avg: -0.5%?	min: -1.3%?	max: -0.0%?
issue-46449-check
	avg: -1.1%	min: -1.3%	max: -0.8%
deeply-nested-opt
	avg: -1.1%	min: -1.3%	max: -0.9%
webrender-opt
	avg: -0.9%	min: -1.2%	max: -0.1%
issue-46449-opt
	avg: -0.9%	min: -1.1%	max: -0.7%
clap-rs-opt
	avg: -0.7%	min: -1.1%	max: -0.1%
tokio-webpush-simple-opt
	avg: -0.7%	min: -1.0%	max: -0.2%
style-servo-opt
	avg: -0.7%	min: -1.0%	max: 0.1%
coercions-check
	avg: -0.4%?	min: -1.0%?	max: 0.0%?

bjorn3 · 2018-10-25T12:46:15Z

src/librustc/mir/mod.rs

@@ -1674,6 +1674,10 @@ impl<'tcx> Statement<'tcx> {
    /// Changes a statement to a nop. This is both faster than deleting instructions and avoids
    /// invalidating statement indices in `Location`s.
    pub fn make_nop(&mut self) {
+        // `Statement` contributes significantly to peak memory usage. Make
+        // sure it doesn't get bigger.
+        debug_assert!(mem::size_of::<Statement<'_>>() <= 56usize);


Could you use a static assert instead:

#![feature(const_transmute, const_let)] use std::mem; #[allow(dead_code)] const ASSERT_STATMENT_IS_56_BYTES: () = { unsafe { mem::transmute::<_, [u8; 56]>(Statement::Nop); } () };

librustc also has a static_assert! macro for this kind of pattern.

Didn't know about that.

static_assert!(STATMENT_IS_AT_MOST_56_BYTES: std::mem::size_of::<Statement<'_>>() <= 56usize);

nagisa · 2018-10-25T18:53:50Z

This is another instance of #54526.

It is nice to see there is an effort to add a test for this :)

r=me when debug_assert! becomes a static_assert! or a #[test].

nnethercote · 2018-10-25T21:25:01Z

This is another instance of #54526.

Oh geez. I'd forgotten about that. Interestingly, that one didn't give an instruction count improvement, but this one does. Not sure why.

This commit reduces the size of `Statement` from 80 bytes to 56 bytes on 64-bit platforms, by boxing the `AscribeUserType` variant of `StatementKind`. This change reduces instruction counts on most benchmarks by 1--3%.

nnethercote · 2018-10-25T21:27:40Z

I've updated to use static_assert!.

Mark-Simulacrum · 2018-10-25T22:03:57Z

@bors r=nagisa

bors · 2018-10-25T22:03:58Z

📌 Commit 38d9277 has been approved by nagisa

…=nagisa Shrink `Statement`. This commit reduces the size of `Statement` from 80 bytes to 56 bytes on 64-bit platforms, by boxing the `AscribeUserType` variant of `StatementKind`. This change reduces instruction counts on most benchmarks by 1--3%.

Rollup of 21 pull requests Successful merges: - #54816 (Don't try to promote already promoted out temporaries) - #54824 (Cleanup rustdoc tests with `@!has` and `@!matches`) - #54921 (Add line numbers option to rustdoc) - #55167 (Add a "cheap" mode for `compute_missing_ctors`.) - #55258 (Fix Rustdoc ICE when checking blanket impls) - #55264 (Compile the libstd we distribute with -Ccodegen-unit=1) - #55271 (Unimplement ExactSizeIterator for MIR traversing iterators) - #55292 (Macro diagnostics tweaks) - #55298 (Point at macro definition when no rules expect token) - #55301 (List allowed tokens after macro fragments) - #55302 (Extend the impl_stable_hash_for! macro for miri.) - #55325 (Fix link to macros chapter) - #55343 (rustbuild: fix remap-debuginfo when building a release) - #55346 (Shrink `Statement`.) - #55358 (Remove redundant clone (2)) - #55370 (Update mailmap for estebank) - #55375 (Typo fixes in configure_cmake comments) - #55378 (rustbuild: use configured linker to build boostrap) - #55379 (validity: assert that unions are non-empty) - #55383 (Use `SmallVec` for the queue in `coerce_unsized`.) - #55391 (bootstrap: clean up a few clippy findings)

[beta]: Prepare the 1.31.0 beta release * Update to Cargo's branched 1.31.0 branch * Update the channel to `beta` Rolled up beta-accepted PRs: * #55362: Remove `cargo new --edition` from release notes. * #55325: Fix link to macros chapter * #55358: Remove redundant clone (2) * #55346: Shrink `Statement`. * #55274: Handle bindings in substructure of patterns with type ascriptions * #55297: Partial implementation of uniform paths 2.0 to land before beta * #55192: Fix ordering of nested modules in non-mod.rs mods * #55185: path suggestions in Rust 2018 should point out the change in semantics * #55423: back out bogus `Ok`-wrapping suggestion on `?` arm type mismatch Note that **this does not update the bootstrap compiler** due to #55404

RalfJung · 2018-11-01T08:49:58Z

src/librustc/mir/mod.rs

@@ -1674,6 +1674,10 @@ impl<'tcx> Statement<'tcx> {
    /// Changes a statement to a nop. This is both faster than deleting instructions and avoids
    /// invalidating statement indices in `Location`s.
    pub fn make_nop(&mut self) {
+        // `Statement` contributes significantly to peak memory usage. Make
+        // sure it doesn't get bigger.
+        static_assert!(STATEMENT_IS_AT_MOST_56_BYTES: mem::size_of::<Statement<'_>>() <= 56);


Why is this inside some random function, as opposed to, say, next to enum Statement?

I didn't realize static_assert! was valid at the top level. I'll fix it in another PR, thanks for the tip.

rust-highfive assigned pnkfelix Oct 25, 2018

rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Oct 25, 2018

bjorn3 requested changes Oct 25, 2018

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Shrink Statement.

38d9277

This commit reduces the size of `Statement` from 80 bytes to 56 bytes on 64-bit platforms, by boxing the `AscribeUserType` variant of `StatementKind`. This change reduces instruction counts on most benchmarks by 1--3%.

nnethercote force-pushed the shrink-StatementKind branch from 6cca15c to 38d9277 Compare October 25, 2018 21:26

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 Oct 25, 2018

kennytm mentioned this pull request Oct 26, 2018

Rollup of 15 pull requests #55371

Closed

kennytm mentioned this pull request Oct 26, 2018

Rollup of 21 pull requests #55382

Merged

bors merged commit 38d9277 into rust-lang:master Oct 26, 2018

nnethercote deleted the shrink-StatementKind branch October 28, 2018 21:42

pietroalbini mentioned this pull request Oct 29, 2018

[beta]: Prepare the 1.31.0 beta release #55405

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RalfJung reviewed Nov 1, 2018

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Shrink `Statement`. #55346

Shrink `Statement`. #55346

nnethercote commented Oct 25, 2018

rust-highfive commented Oct 25, 2018

nnethercote commented Oct 25, 2018

bjorn3 Oct 25, 2018

nikic Oct 25, 2018

bjorn3 Oct 25, 2018

nagisa commented Oct 25, 2018

nnethercote commented Oct 25, 2018

nnethercote commented Oct 25, 2018

Mark-Simulacrum commented Oct 25, 2018

bors commented Oct 25, 2018

RalfJung Nov 1, 2018

nnethercote Nov 4, 2018

Shrink Statement. #55346

Shrink Statement. #55346

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nnethercote commented Oct 25, 2018

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Shrink `Statement`. #55346

Shrink `Statement`. #55346