[mir-opt] Turn on the `ConstProp` pass by default #66074

wesleywiser · 2019-11-04T03:17:24Z

perf.rlo shows that running the ConstProp pass results in
across-the-board wins regardless of debug or opt complilation mode. As a
result, we're turning it on to get the compile time benefits.

wesleywiser · 2019-11-04T03:17:57Z

@bors try
@rust-timer queue

rust-timer · 2019-11-04T03:17:59Z

Awaiting bors try build completion

bors · 2019-11-04T03:18:07Z

⌛ Trying commit 09d7ce8 with merge 98da694...

@ghost

[experiment] Test ConstProp performance Experiment to see performance implications for turning on ConstProp for scalars. r? @ghost

bors · 2019-11-04T06:07:47Z

☀️ Try build successful - checks-azure
Build commit: 98da694 (98da694a4fda38435d86b0eb6f09d4f644ef83d4)

rust-timer · 2019-11-04T06:07:49Z

Queued 98da694 with parent 0d5264a, future comparison URL.

rust-timer · 2019-11-04T10:32:43Z

Finished benchmarking try commit 98da694, comparison URL.

oli-obk · 2019-11-06T11:47:36Z

@rfcbot poll I think we should turn on constant propagation unconditionally (so in release mode and additionally in debug mode) since it reduces the work that llvm has to do quite a bit. Right now there is no real degradation of the debugging experience, since the worst that happens to users is that 2 + 2 shows up as 4 in the assembly and the debug info is still completely available, since it is attached to the temporary holding the 4 (or the result of 2 + 2 before this PR).

In the future we may const prop function calls to const fns, if that is deemed overkill for debug mode, we can always add an additional check that prevents function calls from being propagated in debug mode.

Constant propagation does not propagate over user defined variables, only expressions (so MIR temporaries) are const propagated. This may change in the future, but we can reopen the debug info degradation question then.

rfcbot · 2019-11-06T11:47:36Z

eddyb · 2019-11-06T16:58:09Z

Note that post-#56231 you don't even need to care about debuginfo or "temp vs var", all you have to do is leave assignments around and run the pass to remove dead locals (which won't remove locals that have debuginfo attached).

nikomatsakis · 2019-11-07T15:07:37Z

@rfcbot reviewed

varkor · 2019-11-08T10:16:14Z

@rfcbot reviewed

michaelwoerister · 2019-11-08T10:56:45Z

I think we should turn on constant propagation unconditionally (so in release mode and additionally in debug mode)

Are the numbers above already with constant propagation turned on for debug builds too?

wesleywiser · 2019-11-08T11:19:32Z

I think we should turn on constant propagation unconditionally (so in release mode and additionally in debug mode)

Are the numbers above already with constant propagation turned on for debug builds too?

@michaelwoerister Yes, the results are with constant propagation turned on for both debug and release builds.

src/librustc_mir/transform/const_prop.rs

@oli-obk

…ovements, r=oli-obk [mir-opt] Handle return place in ConstProp and improve SimplifyLocals pass Temporarily rebased on top of rust-lang#66074. The top 2 commits are new. r? @oli-obk

perf.rlo shows that running the `ConstProp` pass results in across-the-board wins regardless of debug or opt complilation mode. As a result, we're turning it on to get the compile time benefits. `ConstProp` doesn't currently intern the memory used by its `Machine` so we can't yet propagate allocations which is why `ConstProp::should_const_prop()` checks if the value being propagated is a scalar or not.

wesleywiser · 2019-11-12T02:01:31Z

This is ready for a final review.

r? @oli-obk

oli-obk · 2019-11-12T14:43:39Z

@bors r+

bors · 2019-11-12T14:43:40Z

📌 Commit db5fc10 has been approved by oli-obk

…oli-obk [mir-opt] Turn on the `ConstProp` pass by default perf.rlo shows that running the `ConstProp` pass results in across-the-board wins regardless of debug or opt complilation mode. As a result, we're turning it on to get the compile time benefits.

@ghost

Rollup of 13 pull requests Successful merges: - #65932 (download .tar.xz if python3 is used) - #66074 ([mir-opt] Turn on the `ConstProp` pass by default) - #66094 (Fix documentation for `Iterator::count()`.) - #66166 (rename cfg(rustdoc) into cfg(doc)) - #66227 (docs: Fix link to BufWriter::flush) - #66292 (add Result::map_or) - #66297 (Add a callback that allows compiler consumers to override queries.) - #66317 (Use a relative bindir for rustdoc to find rustc) - #66330 (Improve non-exhaustiveness handling in usefulness checking) - #66331 (Add some tests for fixed ICEs) - #66334 (Move Session fields to CrateStore) - #66335 (Move self-profile infrastructure to data structures) - #66337 (Remove dead code for encoding/decoding lint IDs) Failed merges: r? @ghost

…oli-obk [mir-opt] Turn on the `ConstProp` pass by default perf.rlo shows that running the `ConstProp` pass results in across-the-board wins regardless of debug or opt complilation mode. As a result, we're turning it on to get the compile time benefits.

Centril · 2019-11-13T13:02:45Z

@bors rollup=never

wesleywiser · 2019-11-13T16:48:54Z

@bors r-

I'd like to resolve #66342 before this is merged.

joelpalmer · 2019-11-18T12:01:57Z

Ping from Triage: Hi @wesleywiser I see #66342 was closed yesterday. Please update this PR when you have a chance. Thanks!

wesleywiser · 2019-11-19T02:28:34Z

@bors r=oli-obk

bors · 2019-11-19T02:28:35Z

📌 Commit db5fc10 has been approved by oli-obk

bors · 2019-11-19T04:38:53Z

⌛ Testing commit db5fc10 with merge d1da802...

[mir-opt] Turn on the `ConstProp` pass by default perf.rlo shows that running the `ConstProp` pass results in across-the-board wins regardless of debug or opt complilation mode. As a result, we're turning it on to get the compile time benefits.

bors · 2019-11-19T07:49:47Z

☀️ Test successful - checks-azure
Approved by: oli-obk
Pushing d1da802 to master...

tesuji · 2019-11-20T09:56:20Z

Performance result: https://perf.rust-lang.org/compare.html?start=5c5a1209583d5ac0de67f57e0f1cd8ca28aa6c05&end=d1da8023dafd3e277b5a4c5475aa2cb199a176b9&stat=instructions%3Au

Rustup to rustc 1.41.0-nightly (35ef33a 2019-11-21) I don't have the right fix for the fmtstr tests, and I'm also hitting problems caused by messense/rustc-test#3 List of rustups: - rust-lang/rust#66271 (syntax: Keep string literals in ABIs and `asm!` more precisely) - rust-lang/rust#65355 (Stabilize `!` in Rust 1.41.0) - rust-lang/rust#66515 (Reduce size of `hir::Expr` by boxing more of `hir::InlineAsm`) - rust-lang/rust#66389 (Specific labels when referring to "expected" and "found" types) - rust-lang/rust#66074 ([mir-opt] Turn on the `ConstProp` pass by default) changelog: none

bors added a commit that referenced this pull request Nov 4, 2019

Auto merge of #66074 - wesleywiser:test_run_const_prop, r=<try>

98da694

[experiment] Test ConstProp performance Experiment to see performance implications for turning on ConstProp for scalars. r? @ghost

oli-obk added the T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. label Nov 6, 2019

wesleywiser force-pushed the test_run_const_prop branch from 09d7ce8 to db23021 Compare November 6, 2019 11:48

wesleywiser mentioned this pull request Nov 8, 2019

[mir-opt] Handle return place in ConstProp and improve SimplifyLocals pass #66216

Merged

bjorn3 reviewed Nov 8, 2019

View reviewed changes

src/librustc_mir/transform/const_prop.rs Show resolved Hide resolved

wesleywiser force-pushed the test_run_const_prop branch from db23021 to db5fc10 Compare November 12, 2019 01:58

wesleywiser changed the title ~~[experiment] Test ConstProp performance~~ [mir-opt] Turn on the ConstProp pass by default Nov 12, 2019

rust-highfive assigned oli-obk Nov 12, 2019

bors added the S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. label Nov 12, 2019

JohnTitor mentioned this pull request Nov 13, 2019

Rollup of 13 pull requests #66356

Closed

JohnTitor mentioned this pull request Nov 13, 2019

Rollup of 16 pull requests #66365

Closed

ecstatic-morse mentioned this pull request Nov 13, 2019

Spurious x86_64 Windows CI failures due to OOM #66342

Closed

bors added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Nov 13, 2019

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-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Nov 19, 2019

bors added the merged-by-bors This PR was explicitly merged by bors. label Nov 19, 2019

bors merged commit db5fc10 into rust-lang:master Nov 19, 2019

Manishearth mentioned this pull request Nov 22, 2019

Rustup to rustc 1.41.0-nightly (35ef33a8 2019-11-21) rust-lang/rust-clippy#4825

Merged

mbrubeck mentioned this pull request Nov 29, 2020

Modifying locals potentially broken with recent Rust rust-embedded/discovery#236

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[mir-opt] Turn on the `ConstProp` pass by default #66074

[mir-opt] Turn on the `ConstProp` pass by default #66074

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[mir-opt] Turn on the ConstProp pass by default #66074

[mir-opt] Turn on the ConstProp pass by default #66074

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[mir-opt] Turn on the `ConstProp` pass by default #66074

[mir-opt] Turn on the `ConstProp` pass by default #66074

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