Use sparse bitsets instead of dense ones for NLL results #48245

spastorino · 2018-02-15T20:10:33Z

This is for #48170.

pnkfelix · 2018-02-16T11:45:13Z

Do we have data about how much this improves memory usage? And what its cost in execution time is, if any?

spastorino · 2018-02-16T14:41:34Z

@pnkfelix we should profile this 👍. I just started this as a wip thing and ended being a working solution quickly. I know the code is bad in some parts so I didn't bother until now to run benchs. I think I should do it now and then tidy up the code a bit 😃.

nikomatsakis

looks nice!

nikomatsakis · 2018-02-16T15:40:59Z

src/librustc_data_structures/bitvec.rs

@@ -260,7 +260,79 @@ impl BitMatrix {
    }
 }

-#[derive(Clone)]
+#[derive(Clone, Debug)]
+pub struct SparseBitMatrix<I: Idx> {


If we are going to use a type I, then I think this should be

SparseBitMatrix<R, C> where R: Idx, C: Idx { vector: IndexVec<R, SparseBitSet<C>> }

nikomatsakis · 2018-02-16T15:41:43Z

src/librustc_data_structures/bitvec.rs

+    /// Create a new `rows x columns` matrix, initially empty.
+    pub fn new(rows: usize, _columns: usize) -> SparseBitMatrix<I> {
+        SparseBitMatrix {
+            vector: vec![SparseBitSet::new(); rows],


and this would be IndexVec::from_elem_n(SparseBitSet::new(), rows)

nikomatsakis · 2018-02-16T15:41:55Z

src/librustc_data_structures/bitvec.rs

+    /// `column` to the bitset for `row`.
+    ///
+    /// Returns true if this changed the matrix, and false otherwise.
+    pub fn add(&mut self, row: usize, column: usize) -> bool {


and this would be row: R, column: C

nikomatsakis · 2018-02-16T15:42:54Z

src/librustc_mir/borrow_check/nll/region_infer/values.rs

 /// variable. The columns consist of either universal regions or
 /// points in the CFG.
 #[derive(Clone)]
 pub(super) struct RegionValues {
    elements: Rc<RegionValueElements>,
-    matrix: BitMatrix,
+    matrix: SparseBitMatrix<usize>,


then this would be SparseBitMatrix<RegionVid, RegionElementIndex> -- and some casting below would go away

spastorino · 2018-02-16T21:47:04Z

PR is now ready, I still need to run benchs, etc. Going to do that next.

spastorino · 2018-02-17T18:46:17Z

Using steps to reproduce here rust-lang/rust-memory-model#26 I see the following ...

master
    Finished dev [unoptimized + debuginfo] target(s) in 7.24 secs

sparse_bitsets
    Finished dev [unoptimized + debuginfo] target(s) in 7.14 secs

As you can see we have a little gain here, unsure if it's what @nikomatsakis expected or if he expected more :/.

I was algo trying to profile memory valgrind's massif, and I'm getting a segfault, unsure if you have made this run and how with rust ...

[santiago@archlinux syn ((0.12.0))]$ CARGO_INCREMENTAL=0 valgrind --tool=massif cargo +stage1 rustc -v
==7215== Massif, a heap profiler
==7215== Copyright (C) 2003-2017, and GNU GPL'd, by Nicholas Nethercote
==7215== Using Valgrind-3.13.0 and LibVEX; rerun with -h for copyright info
==7215== Command: cargo +stage1 rustc -v
==7215== 
thread 'main' panicked at 'internal error: entered unreachable code: not all instructions were compiled! found uncompiled instruction: Compiled(Bytes(InstBytes { goto: 12, start: 101, end: 101 }))', target/cargo-home/registry/src/github.com-1ecc6299db9ec823/regex-0.2.6/src/compile.rs:794:17
note: Run with `RUST_BACKTRACE=1` for a backtrace.
==7215== 
==7215== Process terminating with default action of signal 11 (SIGSEGV): dumping core
==7215==  Access not within mapped region at address 0x1000000823
==7215==    at 0x63573E: je_huge_dalloc (rtree.h:152)
==7215==    by 0x2D96C3: core::ptr::drop_in_place (in /home/santiago/.cargo/bin/cargo)
==7215==    by 0x2E409A: regex::compile::Compiler::fill (in /home/santiago/.cargo/bin/cargo)
==7215==    by 0x2E0B97: regex::compile::Compiler::c (in /home/santiago/.cargo/bin/cargo)
==7215==    by 0x2E2BEE: regex::compile::Compiler::c_alternate (in /home/santiago/.cargo/bin/cargo)
==7215==    by 0x2E0B3D: regex::compile::Compiler::c (in /home/santiago/.cargo/bin/cargo)
==7215==    by 0x2DEA2D: regex::compile::Compiler::compile (in /home/santiago/.cargo/bin/cargo)
==7215==    by 0x2E9ECB: regex::exec::ExecBuilder::build (in /home/santiago/.cargo/bin/cargo)
==7215==    by 0x30208C: regex::re_unicode::Regex::new (in /home/santiago/.cargo/bin/cargo)
==7215==    by 0x2837BE: rustup_dist::dist::PartialToolchainDesc::from_str (in /home/santiago/.cargo/bin/cargo)
==7215==    by 0x2537DC: rustup::config::Cfg::resolve_toolchain (in /home/santiago/.cargo/bin/cargo)
==7215==    by 0x2414B3: rustup::toolchain::Toolchain::from (in /home/santiago/.cargo/bin/cargo)
==7215==    by 0x252536: rustup::config::Cfg::create_command_for_toolchain (in /home/santiago/.cargo/bin/cargo)
==7215==    by 0x1B39F9: rustup_init::run_rustup (in /home/santiago/.cargo/bin/cargo)
==7215==    by 0x1B16AF: rustup_init::main (in /home/santiago/.cargo/bin/cargo)
==7215==    by 0x61078E: __rust_maybe_catch_panic (lib.rs:101)
==7215==    by 0x6082BB: std::rt::lang_start (panicking.rs:459)
==7215==    by 0x58A8F49: (below main) (in /usr/lib/libc-2.26.so)
==7215==  If you believe this happened as a result of a stack
==7215==  overflow in your program's main thread (unlikely but
==7215==  possible), you can try to increase the size of the
==7215==  main thread stack using the --main-stacksize= flag.
==7215==  The main thread stack size used in this run was 8388608.
==7215== 
Segmentation fault (core dumped)

nikomatsakis · 2018-02-17T21:01:46Z

As you can see we have a little gain here, unsure if it's what @nikomatsakis expected or if he expected more :/.

I did not expect a big impact here on this particular test case. But I think this will be more important on larger test cases. And the fact that we saw a small improvement means we're not paying a price for the improved memory usage.

nikomatsakis · 2018-02-19T15:27:56Z

src/librustc_data_structures/bitvec.rs

+    pub fn merge(&mut self, read: R, write: R) -> bool {
+        let mut changed = false;
+
+        let bit_set_read = self.vector[read].clone();


to avoid the clone, add a helper function like this one. Maybe we should add that somewhere else, if we don't have it already.

nikomatsakis · 2018-02-19T15:49:04Z

src/librustc_data_structures/bitvec.rs

+        let bit_set_a = &self.vector[a];
+        let bit_set_b = &self.vector[b];
+
+        for a_val in bit_set_a.iter().filter(|x| bit_set_b.contains(*x)) {


I bet this method can just be removed. But if not, it could be made faster by adding a method intersection on SparseBitset. I guess it would work something like this:

let mut result = SparseBitset::new(); for (key, value) in self.map { match other.map.get(key) { None => { /* other has no values with these key */ } Some(other_value) { if value & other_value != 0 { result.map.insert(key, value & other_value); } } } }

This of course generates a new sparse-bitset.

nikomatsakis · 2018-02-19T16:39:53Z

src/librustc_data_structures/slice_ext.rs

+impl<T> SliceExt<T> for [T] {
+    type Item = T;
+
+    fn pick2(&mut self, a: usize, b: usize) -> (&mut T, &mut T) {


Let's add a comment here?

Something like:

Return mutable references to two distinct elements, a and b. Panics if a == b.

Also, maybe we could call it get2_mut? (similar to get_mut?)

At least I think we should add a _mut suffix

Let's not call it get2 since it doesn't return an Option (as get does).

nikomatsakis · 2018-02-19T16:40:16Z

src/librustc_data_structures/slice_ext.rs

+pub trait SliceExt<T> {
+    type Item;
+
+    fn pick2(&mut self, a: usize, b: usize) -> (&mut T, &mut T);


Either:

This should be &mut Self::Item and there is no need for the T parameter

Or:

Remove the type Item

nikomatsakis · 2018-02-19T16:41:29Z

src/librustc_mir/borrow_check/nll/region_infer/values.rs

 /// variable. The columns consist of either universal regions or
 /// points in the CFG.
 #[derive(Clone)]
 pub(super) struct RegionValues {
    elements: Rc<RegionValueElements>,
-    matrix: BitMatrix,
+    matrix: SparseBitMatrix<RegionVid, RegionElementIndex>,


I have to say, pushing up the "index types" is nice.

nikomatsakis · 2018-02-19T19:17:32Z

@bors r+

bors · 2018-02-19T19:17:33Z

📌 Commit d5811f7 has been approved by nikomatsakis

eddyb · 2018-02-22T00:11:31Z

Could this use the chunked API from #47575 (comment)?

nikomatsakis · 2018-02-22T00:35:22Z

src/librustc_data_structures/bitvec.rs

+        if read != write {
+            let (bit_set_read, bit_set_write) = self.vector.pick2_mut(read, write);
+
+            for read_val in bit_set_read.iter() {


this could be made faster with chunks, right? (this is going a bit at a time, right, not a word at a time?)

(I think @spastorino and I talked about that already at some point...)

nikomatsakis · 2018-02-22T00:36:40Z

src/librustc_mir/borrow_check/nll/region_infer/values.rs

        // it does not always merge an entire row. That would
        // complicate causal tracking though.
        debug!(
            "add_universal_regions_outlived_by(from_region={:?}, to_region={:?})",
-            from_region,
-            to_region
+            from_region, to_region
        );
        let mut changed = false;
        for elem in self.elements.all_universal_region_indices() {


this could probably use chunks

nikomatsakis · 2018-02-22T00:37:16Z

src/librustc_mir/borrow_check/nll/region_infer/values.rs

@@ -238,7 +238,7 @@ impl RegionValues {
    where
        F: FnOnce(&CauseMap) -> Cause,
    {
-        if self.matrix.add(r.index(), i.index()) {
+        if self.matrix.add(r, i) {


we'd have to look at the callers of these add methods...

eddyb · 2018-02-22T17:47:03Z

(from IRC) SparseBitMatrix could also have a chunked API, e.g. row_chunks(row).

nikomatsakis · 2018-02-23T00:24:30Z

@eddyb I'm inclined to land some variant of these changes, but otherwise let you revise and merge this with your own API when that is making progress. Seem reasonable?

Fixes rust-lang#48170

nikomatsakis · 2018-02-23T15:09:14Z

@bors r+

bors · 2018-02-23T15:09:15Z

📌 Commit 6a74615 has been approved by nikomatsakis

eddyb · 2018-02-23T15:19:34Z

@nikomatsakis Yeah. Context is @spastorino explicitly asked for me to leave a comment on GitHub.

whoisj · 2018-02-23T15:55:37Z

As an aside, @spastorino if you format your pull request description with a line that says "Resolves #48170" instead of "this is for", GitHub will automagically link the PR and issue, and resolve the issue if/when the PR merges. Just a helpful usage hint. 😄

spastorino · 2018-02-23T16:29:23Z

@whoisj yeah, I added that in the commit message ff9eb56 for exactly that reason. Anyway, good to know that's possible (and maybe better) to do it on the PR.

@nikomatsakis

…tsakis Use sparse bitsets instead of dense ones for NLL results This is for rust-lang#48170. r? @nikomatsakis

Rollup of 12 pull requests - Successful merges: #47933, #48072, #48083, #48123, #48157, #48219, #48221, #48245, #48429, #48436, #48438, #48472 - Failed merges:

rust-highfive assigned nikomatsakis Feb 15, 2018

rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Feb 15, 2018

spastorino force-pushed the sparse_bitsets branch 2 times, most recently from d1d264a to de71da1 Compare February 15, 2018 22:22

spastorino changed the title ~~[WIP] use sparse bitsets instead of dense ones for NLL results~~ Use sparse bitsets instead of dense ones for NLL results Feb 15, 2018

spastorino force-pushed the sparse_bitsets branch from ee64b73 to 21aa4d8 Compare February 15, 2018 22:37

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spastorino force-pushed the sparse_bitsets branch from 21aa4d8 to ffc357d Compare February 16, 2018 21:43

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spastorino force-pushed the sparse_bitsets branch from 9305336 to edc764e Compare February 19, 2018 16:35

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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 Feb 19, 2018

nikomatsakis reviewed Feb 22, 2018

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Move word type and word size usage to constants & make it of 128 bits

e5d79c4

spastorino added 3 commits February 22, 2018 21:27

Use Sparse bitsets instead of dense ones for NLL results

ff9eb56

Fixes rust-lang#48170

Fix typo otherwies -> otherwise

aa3409c

Run rustfmt over bitvec.rs and region_infer/values.rs

6a74615

spastorino force-pushed the sparse_bitsets branch from d5811f7 to 6a74615 Compare February 23, 2018 00:29

spastorino mentioned this pull request Feb 23, 2018

Use BTreeMap with u128 values for sparse bit sets/"vectors" (in dataflow etc.). #47575

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Manishearth added a commit to Manishearth/rust that referenced this pull request Feb 23, 2018

Rollup merge of rust-lang#48245 - spastorino:sparse_bitsets, r=nikoma…

74f6794

…tsakis Use sparse bitsets instead of dense ones for NLL results This is for rust-lang#48170. r? @nikomatsakis

Manishearth mentioned this pull request Feb 23, 2018

Rollup of 12 pull requests #48476

Merged

bors added a commit that referenced this pull request Feb 23, 2018

Auto merge of #48476 - Manishearth:rollup, r=Manishearth

2fbb63a

Rollup of 12 pull requests - Successful merges: #47933, #48072, #48083, #48123, #48157, #48219, #48221, #48245, #48429, #48436, #48438, #48472 - Failed merges:

bors added a commit that referenced this pull request Feb 24, 2018

Auto merge of #48476 - Manishearth:rollup, r=Manishearth

6070d3e

Rollup of 12 pull requests - Successful merges: #47933, #48072, #48083, #48123, #48157, #48219, #48221, #48245, #48429, #48436, #48438, #48472 - Failed merges:

bors merged commit 6a74615 into rust-lang:master Feb 24, 2018

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