const limit for CTFE #67260

TheSamsa · 2019-12-12T16:35:06Z

I tried to tackle the first steps for this issue.
The active feature flag does link to the issue below, I think this has to change, because there should be a tracking issue?
https://github.com/TheSamsa/rust/blob/1679a7647da0de672bac26b716db82d16f3896a8/src/librustc_feature/active.rs#L530

Also, I only put up the storage of the limit like "recursion_limit" but created a seperate file in the same place. Since I guess the invocation happens seperately.
https://github.com/TheSamsa/rust/blob/const-limit/src/librustc/middle/const_limit.rs

If this does not hold up for the issue and since there is a time pressure, just reject it.

hopefully this does not put more load on you than I expected...

rust-highfive · 2019-12-12T16:35:11Z

r? @zackmdavis

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

Centril · 2019-12-12T16:48:47Z

src/librustc/middle/const_limit.rs

+}
+
+fn update_limit(krate: &ast::Crate, limit: &Once<usize>, name: Symbol, default: usize) {
+    for attr in &krate.attrs {


I think this would be cleaner as:

let value = krate .attrs .iter() .filter(|attr| attr.check_name(name)) .find(|attr| attr.value_str().as_str().parse().ok()) .unwrap_or(default); limit.set(value);

discussion regarding the possibility to merge const_limit.rs and the existing recursion_limit.rs is below.

Sure; If the identical logic exists in recursion_limit.rs I would rewrite that one as well, and try to unify the parsing.

src/librustc_session/session.rs

Centril · 2019-12-12T16:50:27Z

r? @oli-obk cc @ecstatic-morse @RalfJung

rust-highfive · 2019-12-12T16:52:57Z

The job x86_64-gnu-llvm-7 of your PR failed (pretty log, raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

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2019-12-12T16:35:49.4448577Z ##[command]git remote add origin https://github.com/rust-lang/rust
2019-12-12T16:35:49.4635588Z ##[command]git config gc.auto 0
2019-12-12T16:35:49.4704658Z ##[command]git config --get-all http.https://github.com/rust-lang/rust.extraheader
2019-12-12T16:35:49.4764391Z ##[command]git config --get-all http.proxy
2019-12-12T16:35:49.4917029Z ##[command]git -c http.extraheader="AUTHORIZATION: basic ***" fetch --force --tags --prune --progress --no-recurse-submodules --depth=2 origin +refs/heads/*:refs/remotes/origin/* +refs/pull/67260/merge:refs/remotes/pull/67260/merge
---
2019-12-12T16:41:02.2882385Z    Compiling serde_json v1.0.40
2019-12-12T16:41:03.8089940Z    Compiling tidy v0.1.0 (/checkout/src/tools/tidy)
2019-12-12T16:41:13.5348451Z     Finished release [optimized] target(s) in 1m 15s
2019-12-12T16:41:13.5450997Z tidy check
2019-12-12T16:41:14.1398020Z tidy error: /checkout/src/test/ui/consts/const_limit/const_limit_is_feature_gated.rs: missing trailing newline
2019-12-12T16:41:14.2706204Z tidy error: /checkout/src/librustc/middle/const_limit.rs: leading newline
2019-12-12T16:41:15.0916805Z tidy error: Found 1 features without a gate test.
2019-12-12T16:41:15.0918780Z Expected a gate test for the feature 'const_limit'.
2019-12-12T16:41:15.0919339Z Hint: create a failing test file named 'feature-gate-const_limit.rs'
2019-12-12T16:41:15.0920088Z       in the 'ui' test suite, with its failures due to
2019-12-12T16:41:15.0920203Z       missing usage of `#![feature(const_limit)]`.
2019-12-12T16:41:15.0920444Z Hint: If you already have such a test and don't want to rename it,
2019-12-12T16:41:15.0920695Z       you can also add a // gate-test-const_limit line to the test file.
2019-12-12T16:41:16.6984285Z some tidy checks failed
2019-12-12T16:41:16.6988282Z Found 485 error codes
2019-12-12T16:41:16.6988332Z Found 0 error codes with no tests
2019-12-12T16:41:16.6988370Z Done!
2019-12-12T16:41:16.6988370Z Done!
2019-12-12T16:41:16.6988395Z 
2019-12-12T16:41:16.6988418Z 
2019-12-12T16:41:16.6989628Z command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-tools-bin/tidy" "/checkout/src" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "--no-vendor"
2019-12-12T16:41:16.6989752Z 
2019-12-12T16:41:16.6989794Z 
2019-12-12T16:41:16.6989998Z failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test src/tools/tidy
2019-12-12T16:41:16.6990039Z Build completed unsuccessfully in 0:01:18
2019-12-12T16:41:16.6990039Z Build completed unsuccessfully in 0:01:18
2019-12-12T16:41:16.6990091Z == clock drift check ==
2019-12-12T16:41:16.6990127Z   local time: Thu Dec 12 16:41:15 UTC 2019
2019-12-12T16:41:16.6990165Z   network time: Thu, 12 Dec 2019 16:41:16 GMT
2019-12-12T16:41:16.6990217Z == end clock drift check ==
2019-12-12T16:41:17.4729565Z 
2019-12-12T16:41:17.4830950Z ##[error]Bash exited with code '1'.
2019-12-12T16:41:17.4855810Z ##[section]Starting: Checkout
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src/librustc/middle/const_limit.rs

ecstatic-morse · 2019-12-12T19:45:54Z

src/doc/unstable-book/src/language-features/const-limit.md

@@ -0,0 +1,7 @@
+# `const_limit`


Bikeshed: I would prefer const_eval_limit. cc @Centril

I was leaning towards const_eval_limit too, since it is more expressive.
But decided against it, since it was a request to keep it more arbitrary

This is easily changeable based on community & language team discussion so go with whatever makes the PR easiest to land for now. ^^

I prefer const_limit since we don't have to care about e.g. "interpretation vs. evaluation vs. reduction vs. ..." and because it's shorter... but this is probably for an RFC to discuss & lay out the pros & cons of various alternatives.

ecstatic-morse · 2019-12-12T19:53:35Z

Good work so far @TheSamsa! In retrospect, I was overly concerned about this landing concurrently with #67216. No need to stress.

The next step would be to use the newly added const_limit field from tcx.sess in place of STEPS_UNTIL_DETECTOR_ENABLED.

rust/src/librustc_mir/const_eval.rs

Lines 30 to 32 in e9469a6

    
           /// Number of steps until the detector even starts doing anything. 
        
           /// Also, a warning is shown to the user when this number is reached. 
        
           const STEPS_UNTIL_DETECTOR_ENABLED: isize = 1_000_000;

Note that STEPS_UNTIL_DETECTOR_ENABLED is an isize, not a usize, so you probably want a saturating cast. Finally, I think you should use 0 as a sentinel value that disables the loop detector. You'll want to add an is_detector_enabled flag to CompileTimeInterpreter, and return early from the before_terminator callback if it is not set.

rust/src/librustc_mir/const_eval.rs

Lines 502 to 524 in e9469a6

    
           fn before_terminator(ecx: &mut InterpCx<'mir, 'tcx, Self>) -> InterpResult<'tcx> { 
        
               { 
        
                   let steps = &mut ecx.machine.steps_since_detector_enabled; 
        
                   *steps += 1; 
        
                   if *steps < 0 { 
        
                       return Ok(()); 
        
                   } 
        
                   *steps %= DETECTOR_SNAPSHOT_PERIOD; 
        
                   if *steps != 0 { 
        
                       return Ok(()); 
        
                   } 
        
               } 
        
               let span = ecx.frame().span; 
        
               ecx.machine.loop_detector.observe_and_analyze( 
        
                   *ecx.tcx, 
        
                   span, 
        
                   &ecx.memory, 
        
                   &ecx.stack[..], 
        
               ) 
        
           }

src/test/ui/consts/const_limit/const_limit_is_feature_gated.rs

Centril · 2019-12-12T21:22:40Z

Also a note re. merge commits:

Merge branch 'master' of github.com:rust-lang/rust

We would prefer to not have those in our history, so please try to remove them by squashing & rebasing as appropriate. :)

src/librustc/middle/limits.rs

src/librustc_mir/const_eval.rs

src/test/ui/consts/const_limit/feature-gate-const_limit.rs

src/test/ui/consts/const_limit/const_limit_not_reached.rs

bors · 2019-12-15T04:48:21Z

☔ The latest upstream changes (presumably #67216) made this pull request unmergeable. Please resolve the merge conflicts.

oli-obk · 2019-12-21T09:52:21Z

Oh, I didn't see your force push, sorry. Please rebase again.

You also have a not yet resolved review comment (#67260 (comment))

oli-obk · 2019-12-21T09:53:09Z

The reference submodule change was unintended I guess? please remove it

TheSamsa · 2020-03-03T12:56:48Z

I have a weird issue which i don't know how to resolve.
If I execute
x.py test src/test/ui/consts/const_limit
the stderr shows one WARNING

but if I executer
rustc +stage1 src/test/ui/consts/const_limit
it emmits two WARNINGS, like in the pipeline. So it either fails with my tests or the pipeline.

Do someone know how to fix this?

oli-obk · 2020-03-03T16:43:28Z

Stage 1 and stage 2 should not differ. I don't see how this is happening. I'll give it another review tomorrow

TheSamsa · 2020-03-04T15:09:04Z

Stage 1 and stage 2 should not differ. I don't see how this is happening. I'll give it another review tomorrow

I found the issue, on my machine it used "opt-level=2" and in the pipeline "opt-level=0" so I specified the test to use "opt-level=0" as in the pipeline. Now I have the correct stderr outputs even on my machine.

rust-highfive · 2020-03-04T15:32:56Z

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2020-03-04T15:09:45.7327329Z ========================== Starting Command Output ===========================
2020-03-04T15:09:45.7330326Z [command]/bin/bash --noprofile --norc /home/vsts/work/_temp/82e0e40f-17dd-4dbf-b84a-711c4c3c9b31.sh
2020-03-04T15:09:45.7330760Z 
2020-03-04T15:09:45.7335654Z ##[section]Finishing: Disable git automatic line ending conversion
2020-03-04T15:09:45.7350207Z ##[section]Starting: Checkout rust-lang/rust@refs/pull/67260/merge to s
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2020-03-04T15:09:45.7354053Z Version      : 1.0.0
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---
2020-03-04T15:09:46.7286628Z ##[command]git remote add origin https://github.com/rust-lang/rust
2020-03-04T15:09:46.7290945Z ##[command]git config gc.auto 0
2020-03-04T15:09:46.7293759Z ##[command]git config --get-all http.https://github.com/rust-lang/rust.extraheader
2020-03-04T15:09:46.7296381Z ##[command]git config --get-all http.proxy
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---
2020-03-04T15:16:00.8172914Z    Compiling serde_json v1.0.40
2020-03-04T15:16:02.3143678Z    Compiling tidy v0.1.0 (/checkout/src/tools/tidy)
2020-03-04T15:16:09.9443880Z     Finished release [optimized] target(s) in 1m 12s
2020-03-04T15:16:09.9559589Z tidy check
2020-03-04T15:16:10.1123568Z tidy error: /checkout/src/test/ui/consts/const_limit/const_eval_limit_reached.rs:16: line longer than 100 chars
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2020-03-04T15:16:12.0138017Z Found 489 error codes
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2020-03-04T15:16:12.0150608Z 
2020-03-04T15:16:12.0152957Z command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-tools-bin/tidy" "/checkout/src" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "--no-vendor"
2020-03-04T15:16:12.0154804Z 
2020-03-04T15:16:12.0155212Z 
2020-03-04T15:16:12.0156236Z failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test src/tools/tidy
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2020-03-04T15:16:12.0157124Z Build completed unsuccessfully in 0:01:20
2020-03-04T15:16:12.0189173Z == clock drift check ==
2020-03-04T15:16:12.0200355Z   local time: Wed Mar  4 15:16:12 UTC 2020
2020-03-04T15:16:12.3094208Z   network time: Wed, 04 Mar 2020 15:16:12 GMT
2020-03-04T15:16:12.3100644Z == end clock drift check ==
2020-03-04T15:16:13.0427944Z 
2020-03-04T15:16:13.0472385Z ##[error]Bash exited with code '1'.
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…, which defaults to 1_000_000

…INGs yet rename feature to const_eval_limit

and renamed 'recursion_limit' in limits.rs to simple 'limit' because it does handle other limits too.

oli-obk · 2020-03-05T11:45:05Z

@bors r+

bors · 2020-03-05T11:45:07Z

📌 Commit 527456e has been approved by oli-obk

bors · 2020-03-05T17:47:03Z

⌛ Testing commit 527456e with merge 96bb8b3...

bors · 2020-03-05T21:38:54Z

☀️ Test successful - checks-azure
Approved by: oli-obk
Pushing 96bb8b3 to master...

RalfJung · 2020-03-09T12:23:55Z

Now that this landed, is the intention to kill the snapshot / loop detector infrastructure? Is there an issue for that or is there someone working on it?

@oli-obk

…op-detector, r=RalfJung Remove const eval loop detector Now that there is a configurable instruction limit for CTFE (see rust-lang#67260), we can replace the loop detector with something much simpler. See rust-lang#66946 for more discussion about this. Although the instruction limit is nightly-only, the only practical way to reach the default limit uses nightly-only features as well (although CTFE will still execute code using such features inside an array initializer on stable). This will at the very least require a crater run, since it will result in an error wherever the "long running const eval" warning appeared before. We may need to increase the default for `const_eval_limit` to work around this. Resolves rust-lang#54384 cc rust-lang#49980 r? @oli-obk cc @RalfJung

@oli-obk

…op-detector, r=RalfJung Remove const eval loop detector Now that there is a configurable instruction limit for CTFE (see rust-lang#67260), we can replace the loop detector with something much simpler. See rust-lang#66946 for more discussion about this. Although the instruction limit is nightly-only, the only practical way to reach the default limit uses nightly-only features as well (although CTFE will still execute code using such features inside an array initializer on stable). This will at the very least require a crater run, since it will result in an error wherever the "long running const eval" warning appeared before. We may need to increase the default for `const_eval_limit` to work around this. Resolves rust-lang#54384 cc rust-lang#49980 r? @oli-obk cc @RalfJung

rust-highfive assigned zackmdavis Dec 12, 2019

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TheSamsa force-pushed the const-limit branch from 93a97f1 to 73425ca Compare December 12, 2019 22:23

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TheSamsa force-pushed the const-limit branch 2 times, most recently from 0605ff2 to 7f00a07 Compare December 16, 2019 16:39

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oli-obk mentioned this pull request Dec 21, 2019

Use a DFS to compare CTFE snapshots #66946

Closed

TheSamsa force-pushed the const-limit branch from 7f00a07 to d654c22 Compare December 26, 2019 10:10

bors added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Mar 2, 2020

TheSamsa force-pushed the const-limit branch 2 times, most recently from 3492b49 to ad670e1 Compare March 4, 2020 15:07

TheSamsa added 5 commits March 5, 2020 08:09

Prepare const_limit feature gate and attribute

337af5e

Disable CTFE if const_limit was set to 0, otherwise use the value set…

ff38bab

…, which defaults to 1_000_000

Add a new test to reach const_limit setting, although with wrong WARN…

288e142

…INGs yet rename feature to const_eval_limit

Opt out of CTFE if the 'const_eval_limit' is set to 0

c94c74e

Bumped version number for const_eval_limit in active.rs

527456e

and renamed 'recursion_limit' in limits.rs to simple 'limit' because it does handle other limits too.

TheSamsa force-pushed the const-limit branch from ad670e1 to 527456e Compare March 5, 2020 07:10

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bors added the merged-by-bors This PR was explicitly merged by bors. label Mar 5, 2020

bors merged commit 96bb8b3 into rust-lang:master Mar 5, 2020

bors mentioned this pull request Mar 5, 2020

Enable AVR as a Tier 3 target upstream #69478

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remove CTFE loop detector #54384

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Remove const eval loop detector #70087

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const limit for CTFE #67260

const limit for CTFE #67260

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const limit for CTFE #67260

const limit for CTFE #67260

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