8000 Remove const eval loop detector by ecstatic-morse · Pull Request #70087 · rust-lang/rust · GitHub
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Remove const eval loop detector #70087

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Merged
merged 4 commits into from
Mar 24, 2020
Merged

Remove const eval loop detector #70087

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5b66f27
Use `const_eval_limit` instead of infinite loop detector
ecstatic-morse Mar 17, 2020
e15c486
Remove infinite loop detector
ecstatic-morse Mar 17, 2020
044dc6e
Update const-eval tests
ecstatic-morse Mar 17, 2020
b5636b8
Rename `TimeLimitReached` -> `StepLimitReached`
ecstatic-morse Mar 22, 2020
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Update const-eval tests
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@ecstatic-morse
ecstatic-morse committed Mar 18, 2020
commit 044dc6e8dd435eb9c3b6f1dc0c85d0a6e70dae82
1 change: 0 additions & 1 deletion src/test/ui/consts/const-eval/infinite_loop.rs
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Expand Up @@ -2,7 +2,6 @@ fn main() {
// Tests the Collatz conjecture with an incorrect base case (0 instead of 1).
// The value of `n` will loop indefinitely (4 - 2 - 1 - 4).
let _ = [(); {
//~^ WARNING Constant evaluating a complex constant, this might take some time
let mut n = 113383; // #20 in https://oeis.org/A006884
while n != 0 {
//~^ ERROR `while` is not allowed in a `const`
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21 changes: 4 additions & 17 deletions src/test/ui/consts/const-eval/infinite_loop.stderr
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@@ -1,5 +1,5 @@
error[E0658]: `while` is not allowed in a `const`
--> $DIR/infinite_loop.rs:7:9
--> $DIR/infinite_loop.rs:6:9
|
LL | / while n != 0 {
LL | |
Expand All @@ -14,32 +14,19 @@ LL | | }
= help: add `#![feature(const_if_match)]` to the crate attributes to enable

error[E0658]: `if` is not allowed in a `const`
--> $DIR/infinite_loop.rs:9:17
--> $DIR/infinite_loop.rs:8:17
|
LL | n = if n % 2 == 0 { n/2 } else { 3*n + 1 };
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= note: see issue #49146 <https://github.com/rust-lang/rust/issues/49146> for more information
= help: add `#![feature(const_if_match)]` to the crate attributes to enable

warning: Constant evaluating a complex constant, this might take some time
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This may be useful to keep around.

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You mean at like 1% or 10% of the step limit? Not sure how to choose a good number for that, but anything above 10% of the step limit seems useless since you're hitting the step limit soon, and anything below 30s will likely be annoying more often than not. It's very hard to silence this warning (it may be getting emitted in a different crate from the one currently being evaluated).

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Anecdotally, the default step limit only takes a few seconds to trigger, so I don't think preserving the warning is helpful.

--> $DIR/infinite_loop.rs:4:18
|
LL | let _ = [(); {
| __________________^
LL | |
LL | | let mut n = 113383; // #20 in https://oeis.org/A006884
LL | | while n != 0 {
... |
LL | | n
LL | | }];
| |_____^

error[E0080]: evaluation of constant value failed
--> $DIR/infinite_loop.rs:9:20
--> $DIR/infinite_loop.rs:8:20
|
LL | n = if n % 2 == 0 { n/2 } else { 3*n + 1 };
| ^^^^^^^^^^ duplicate interpreter state observed here, const evaluation will never terminate
| ^^^^^^^^^^ exceeded interpreter time limit

error: aborting due to 3 previous errors

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1 change: 0 additions & 1 deletion src/test/ui/consts/const-eval/issue-52475.rs
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@@ -1,6 +1,5 @@
fn main() {
let _ = [(); {
//~^ WARNING Constant evaluating a complex constant, this might take some time
let mut x = &0;
let mut n = 0;
while n < 5 {
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19 changes: 3 additions & 16 deletions src/test/ui/consts/const-eval/issue-52475.stderr
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@@ -1,5 +1,5 @@
error[E0658]: `while` is not allowed in a `const`
--> $DIR/issue-52475.rs:6:9
--> $DIR/issue-52475.rs:5:9
|
LL | / while n < 5 {
LL | |
Expand All @@ -12,24 +12,11 @@ LL | | }
= help: add `#![feature(const_loop)]` to the crate attributes to enable
= help: add `#![feature(const_if_match)]` to the crate attributes to enable

warning: Constant evaluating a complex constant, this might take some time
--> $DIR/issue-52475.rs:2:18
|
LL | let _ = [(); {
| __________________^
LL | |
LL | | let mut x = &0;
LL | | let mut n = 0;
... |
LL | | 0
LL | | }];
| |_____^

error[E0080]: evaluation of constant value failed
--> $DIR/issue-52475.rs:8:17
--> $DIR/issue-52475.rs:7:17
|
LL | n = (n + 1) % 5;
| ^^^^^^^^^^^ duplicate interpreter state observed here, const evaluation will never terminate
| ^^^^^^^^^^^ exceeded interpreter time limit

error: aborting due to 2 previous errors

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22 changes: 14 additions & 8 deletions src/test/ui/consts/const_limit/const_eval_limit_not_reached.rs
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@@ -1,15 +1,21 @@
// check-pass

#![feature(const_eval_limit)]
#![const_eval_limit="1000"]
#![feature(const_loop, const_if_match)]

const CONSTANT: usize = limit();
// This needs to be higher than the number of loop iterations since each pass through the loop may
// hit more than one terminator.
#![const_eval_limit="4000"]

fn main() {
assert_eq!(CONSTANT, 1764);
}
const X: usize = {
let mut x = 0;
while x != 1000 {
x += 1;
10000 }

const fn limit() -> usize {
let x = 42;
x
};

x * 42
fn main() {
assert_eq!(X, 1000);
}
27 changes: 12 additions & 15 deletions src/test/ui/consts/const_limit/const_eval_limit_reached.rs
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@@ -1,21 +1,18 @@
// ignore-tidy-linelength
// only-x86_64
// check-pass
// NOTE: We always compile this test with -Copt-level=0 because higher opt-levels
// optimize away the const function
// compile-flags:-Copt-level=0
#![feature(const_eval_limit)]
#![const_eval_limit="2"]
#![feature(const_loop, const_if_match)]

const CONSTANT: usize = limit();
//~^ WARNING Constant evaluating a complex constant, this might take some time
#![const_eval_limit="500"]

fn main() {
assert_eq!(CONSTANT, 1764);
}
const X: usize = {
let mut x = 0;
while x != 1000 {
//~^ ERROR any use of this value will cause an error
x += 1;
}

const fn limit() -> usize { //~ WARNING Constant evaluating a complex constant, this might take some time
let x = 42;
x
};

x * 42
fn main() {
assert_eq!(X, 1000);
}
25 changes: 13 additions & 12 deletions src/test/ui/consts/const_limit/const_eval_limit_reached.stderr
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@@ -1,16 +1,17 @@
warning: Constant evaluating a complex constant, this might take some time
--> $DIR/const_eval_limit_reached.rs:17:1
error: any use of this value will cause an error
--> $DIR/const_eval_limit_reached.rs:8:11
|
LL | / const fn limit() -> usize {
LL | | let x = 42;
LL | / const X: usize = {
LL | | let mut x = 0;
LL | | while x != 1000 {
| | ^^^^^^^^^ exceeded interpreter time limit
LL | |
LL | | x * 42
LL | | }
| |_^

warning: Constant evaluating a complex constant, this might take some time
--> $DIR/const_eval_limit_reached.rs:10:1
... |
LL | | x
LL | | };
| |__-
|
LL | const CONSTANT: usize = limit();
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
= note: `#[deny(const_err)]` on by default

error: aborting due to previous error

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