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Rollup merge of #5248 - ThibsG:ConstValues, r=flip1995

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Add lint on large non scalar const

This PR adds the new lint `non_scalar_const` that aims to warn against `const` declaration of large arrays. For performance, because of inlining, large arrays should be preferably declared as `static`.

Note: i made this one to warn on all const arrays, whether they are in a body function or not. I don't know if this is really necessary, i could just reduce this lint to variables out of function scope.

Fixes: #400

changelog: add new lint for large non-scalar types declared as const
This commit is contained in:
Philipp Krones
2020-04-15 20:12:28 +02:00
committed by GitHub
parent 3481bf4102 629cc4ada3
commit ceea3c6a35
9 changed files with 253 additions and 5 deletions
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1
CHANGELOG.md
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@@ -1320,6 +1320,7 @@ Released 2018-09-13
[`iter_skip_next`]: https://rust-lang.github.io/rust-clippy/master/index.html#iter_skip_next
[`iterator_step_by_zero`]: https://rust-lang.github.io/rust-clippy/master/index.html#iterator_step_by_zero
[`just_underscores_and_digits`]: https://rust-lang.github.io/rust-clippy/master/index.html#just_underscores_and_digits
[`large_const_arrays`]: https://rust-lang.github.io/rust-clippy/master/index.html#large_const_arrays
[`large_digit_groups`]: https://rust-lang.github.io/rust-clippy/master/index.html#large_digit_groups
[`large_enum_variant`]: https://rust-lang.github.io/rust-clippy/master/index.html#large_enum_variant
[`large_stack_arrays`]: https://rust-lang.github.io/rust-clippy/master/index.html#large_stack_arrays

85
clippy_lints/src/large_const_arrays.rs Normal file
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@@ -0,0 +1,85 @@
use crate::rustc_target::abi::LayoutOf;
use crate::utils::span_lint_and_then;
use if_chain::if_chain;
use rustc_errors::Applicability;
use rustc_hir::{Item, ItemKind};
use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::mir::interpret::ConstValue;
use rustc_middle::ty::{self, ConstKind};
use rustc_session::{declare_tool_lint, impl_lint_pass};
use rustc_span::{BytePos, Pos, Span};
use rustc_typeck::hir_ty_to_ty;
declare_clippy_lint! {
/// **What it does:** Checks for large `const` arrays that should
/// be defined as `static` instead.
///
/// **Why is this bad?** Performance: const variables are inlined upon use.
/// Static items result in only one instance and has a fixed location in memory.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust,ignore
/// // Bad
/// pub const a = [0u32; 1_000_000];
///
/// // Good
/// pub static a = [0u32; 1_000_000];
/// ```
pub LARGE_CONST_ARRAYS,
perf,
"large non-scalar const array may cause performance overhead"
}
pub struct LargeConstArrays {
maximum_allowed_size: u64,
}
impl LargeConstArrays {
#[must_use]
pub fn new(maximum_allowed_size: u64) -> Self {
Self { maximum_allowed_size }
}
}
impl_lint_pass!(LargeConstArrays => [LARGE_CONST_ARRAYS]);
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for LargeConstArrays {
fn check_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx Item<'_>) {
if_chain! {
if !item.span.from_expansion();
if let ItemKind::Const(hir_ty, _) = &item.kind;
let ty = hir_ty_to_ty(cx.tcx, hir_ty);
if let ty::Array(element_type, cst) = ty.kind;
if let ConstKind::Value(val) = cst.val;
if let ConstValue::Scalar(element_count) = val;
if let Ok(element_count) = element_count.to_machine_usize(&cx.tcx);
if let Ok(element_size) = cx.layout_of(element_type).map(|l| l.size.bytes());
if self.maximum_allowed_size < element_count * element_size;
then {
let hi_pos = item.ident.span.lo() - BytePos::from_usize(1);
let sugg_span = Span::new(
hi_pos - BytePos::from_usize("const".len()),
hi_pos,
item.span.ctxt(),
);
span_lint_and_then(
cx,
LARGE_CONST_ARRAYS,
item.span,
"large array defined as const",
|db| {
db.span_suggestion(
sugg_span,
"make this a static item",
"static".to_string(),
Applicability::MachineApplicable,
);
}
);
}
}
}
}

5
clippy_lints/src/lib.rs
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@@ -232,6 +232,7 @@ mod inline_fn_without_body;
mod int_plus_one;
mod integer_division;
mod items_after_statements;
mod large_const_arrays;
mod large_enum_variant;
mod large_stack_arrays;
mod len_zero;
@@ -582,6 +583,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
&int_plus_one::INT_PLUS_ONE,
&integer_division::INTEGER_DIVISION,
&items_after_statements::ITEMS_AFTER_STATEMENTS,
&large_const_arrays::LARGE_CONST_ARRAYS,
&large_enum_variant::LARGE_ENUM_VARIANT,
&large_stack_arrays::LARGE_STACK_ARRAYS,
&len_zero::LEN_WITHOUT_IS_EMPTY,
@@ -1026,6 +1028,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
store.register_late_pass(|| box to_digit_is_some::ToDigitIsSome);
let array_size_threshold = conf.array_size_threshold;
store.register_late_pass(move || box large_stack_arrays::LargeStackArrays::new(array_size_threshold));
store.register_late_pass(move || box large_const_arrays::LargeConstArrays::new(array_size_threshold));
store.register_late_pass(move || box floating_point_arithmetic::FloatingPointArithmetic);
store.register_early_pass(|| box as_conversions::AsConversions);
store.register_early_pass(|| box utils::internal_lints::ProduceIce);
@@ -1225,6 +1228,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
LintId::of(&inherent_to_string::INHERENT_TO_STRING_SHADOW_DISPLAY),
LintId::of(&inline_fn_without_body::INLINE_FN_WITHOUT_BODY),
LintId::of(&int_plus_one::INT_PLUS_ONE),
LintId::of(&large_const_arrays::LARGE_CONST_ARRAYS),
LintId::of(&large_enum_variant::LARGE_ENUM_VARIANT),
LintId::of(&len_zero::LEN_WITHOUT_IS_EMPTY),
LintId::of(&len_zero::LEN_ZERO),
@@ -1656,6 +1660,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
LintId::of(&bytecount::NAIVE_BYTECOUNT),
LintId::of(&entry::MAP_ENTRY),
LintId::of(&escape::BOXED_LOCAL),
LintId::of(&large_const_arrays::LARGE_CONST_ARRAYS),
LintId::of(&large_enum_variant::LARGE_ENUM_VARIANT),
LintId::of(&loops::MANUAL_MEMCPY),
LintId::of(&loops::NEEDLESS_COLLECT),

2
clippy_lints/src/utils/conf.rs
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@@ -150,7 +150,7 @@ define_Conf! {
(trivial_copy_size_limit, "trivial_copy_size_limit": Option<u64>, None),
/// Lint: TOO_MANY_LINES. The maximum number of lines a function or method can have
(too_many_lines_threshold, "too_many_lines_threshold": u64, 100),
/// Lint: LARGE_STACK_ARRAYS. The maximum allowed size for arrays on the stack
/// Lint: LARGE_STACK_ARRAYS, LARGE_CONST_ARRAYS. The maximum allowed size for arrays on the stack
(array_size_threshold, "array_size_threshold": u64, 512_000),
/// Lint: VEC_BOX. The size of the boxed type in bytes, where boxing in a `Vec` is allowed
(vec_box_size_threshold, "vec_box_size_threshold": u64, 4096),

7
src/lintlist/mod.rs
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@@ -948,6 +948,13 @@ pub static ref ALL_LINTS: Vec<Lint> = vec![
deprecation: None,
module: "non_expressive_names",
},
Lint {
name: "large_const_arrays",
group: "perf",
desc: "large non-scalar const array may cause performance overhead",
deprecation: None,
module: "large_const_arrays",
},
Lint {
name: "large_digit_groups",
group: "pedantic",

37
tests/ui/large_const_arrays.fixed Normal file
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@@ -0,0 +1,37 @@
// run-rustfix
#![warn(clippy::large_const_arrays)]
#![allow(dead_code)]
#[derive(Clone, Copy)]
pub struct S {
pub data: [u64; 32],
}
// Should lint
pub(crate) static FOO_PUB_CRATE: [u32; 1_000_000] = [0u32; 1_000_000];
pub static FOO_PUB: [u32; 1_000_000] = [0u32; 1_000_000];
static FOO: [u32; 1_000_000] = [0u32; 1_000_000];
// Good
pub(crate) const G_FOO_PUB_CRATE: [u32; 1_000] = [0u32; 1_000];
pub const G_FOO_PUB: [u32; 1_000] = [0u32; 1_000];
const G_FOO: [u32; 1_000] = [0u32; 1_000];
fn main() {
// Should lint
pub static BAR_PUB: [u32; 1_000_000] = [0u32; 1_000_000];
static BAR: [u32; 1_000_000] = [0u32; 1_000_000];
pub static BAR_STRUCT_PUB: [S; 5_000] = [S { data: [0; 32] }; 5_000];
static BAR_STRUCT: [S; 5_000] = [S { data: [0; 32] }; 5_000];
pub static BAR_S_PUB: [Option<&str>; 200_000] = [Some("str"); 200_000];
static BAR_S: [Option<&str>; 200_000] = [Some("str"); 200_000];
// Good
pub const G_BAR_PUB: [u32; 1_000] = [0u32; 1_000];
const G_BAR: [u32; 1_000] = [0u32; 1_000];
pub const G_BAR_STRUCT_PUB: [S; 500] = [S { data: [0; 32] }; 500];
const G_BAR_STRUCT: [S; 500] = [S { data: [0; 32] }; 500];
pub const G_BAR_S_PUB: [Option<&str>; 200] = [Some("str"); 200];
const G_BAR_S: [Option<&str>; 200] = [Some("str"); 200];
}

37
tests/ui/large_const_arrays.rs Normal file
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@@ -0,0 +1,37 @@
// run-rustfix
#![warn(clippy::large_const_arrays)]
#![allow(dead_code)]
#[derive(Clone, Copy)]
pub struct S {
pub data: [u64; 32],
}
// Should lint
pub(crate) const FOO_PUB_CRATE: [u32; 1_000_000] = [0u32; 1_000_000];
pub const FOO_PUB: [u32; 1_000_000] = [0u32; 1_000_000];
const FOO: [u32; 1_000_000] = [0u32; 1_000_000];
// Good
pub(crate) const G_FOO_PUB_CRATE: [u32; 1_000] = [0u32; 1_000];
pub const G_FOO_PUB: [u32; 1_000] = [0u32; 1_000];
const G_FOO: [u32; 1_000] = [0u32; 1_000];
fn main() {
// Should lint
pub const BAR_PUB: [u32; 1_000_000] = [0u32; 1_000_000];
const BAR: [u32; 1_000_000] = [0u32; 1_000_000];
pub const BAR_STRUCT_PUB: [S; 5_000] = [S { data: [0; 32] }; 5_000];
const BAR_STRUCT: [S; 5_000] = [S { data: [0; 32] }; 5_000];
pub const BAR_S_PUB: [Option<&str>; 200_000] = [Some("str"); 200_000];
const BAR_S: [Option<&str>; 200_000] = [Some("str"); 200_000];
// Good
pub const G_BAR_PUB: [u32; 1_000] = [0u32; 1_000];
const G_BAR: [u32; 1_000] = [0u32; 1_000];
pub const G_BAR_STRUCT_PUB: [S; 500] = [S { data: [0; 32] }; 500];
const G_BAR_STRUCT: [S; 500] = [S { data: [0; 32] }; 500];
pub const G_BAR_S_PUB: [Option<&str>; 200] = [Some("str"); 200];
const G_BAR_S: [Option<&str>; 200] = [Some("str"); 200];
}

76
tests/ui/large_const_arrays.stderr Normal file
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@@ -0,0 +1,76 @@
error: large array defined as const
--> $DIR/large_const_arrays.rs:12:1
|
LL | pub(crate) const FOO_PUB_CRATE: [u32; 1_000_000] = [0u32; 1_000_000];
| ^^^^^^^^^^^-----^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
| |
| help: make this a static item: `static`
|
= note: `-D clippy::large-const-arrays` implied by `-D warnings`
error: large array defined as const
--> $DIR/large_const_arrays.rs:13:1
|
LL | pub const FOO_PUB: [u32; 1_000_000] = [0u32; 1_000_000];
| ^^^^-----^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
| |
| help: make this a static item: `static`
error: large array defined as const
--> $DIR/large_const_arrays.rs:14:1
|
LL | const FOO: [u32; 1_000_000] = [0u32; 1_000_000];
| -----^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
| |
| help: make this a static item: `static`
error: large array defined as const
--> $DIR/large_const_arrays.rs:23:5
|
LL | pub const BAR_PUB: [u32; 1_000_000] = [0u32; 1_000_000];
| ^^^^-----^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
| |
| help: make this a static item: `static`
error: large array defined as const
--> $DIR/large_const_arrays.rs:24:5
|
LL | const BAR: [u32; 1_000_000] = [0u32; 1_000_000];
| -----^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
| |
| help: make this a static item: `static`
error: large array defined as const
--> $DIR/large_const_arrays.rs:25:5
|
LL | pub const BAR_STRUCT_PUB: [S; 5_000] = [S { data: [0; 32] }; 5_000];
| ^^^^-----^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
| |
| help: make this a static item: `static`
error: large array defined as const
--> $DIR/large_const_arrays.rs:26:5
|
LL | const BAR_STRUCT: [S; 5_000] = [S { data: [0; 32] }; 5_000];
| -----^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
| |
| help: make this a static item: `static`
error: large array defined as const
--> $DIR/large_const_arrays.rs:27:5
|
LL | pub const BAR_S_PUB: [Option<&str>; 200_000] = [Some("str"); 200_000];
| ^^^^-----^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
| |
| help: make this a static item: `static`
error: large array defined as const
--> $DIR/large_const_arrays.rs:28:5
|
LL | const BAR_S: [Option<&str>; 200_000] = [Some("str"); 200_000];
| -----^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
| |
| help: make this a static item: `static`
error: aborting due to 9 previous errors

8
util/lintlib.py
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@@ -14,7 +14,7 @@ lintname_re = re.compile(r'''pub\s+([A-Z_][A-Z_0-9]*)''')
group_re = re.compile(r'''\s*([a-z_][a-z_0-9]+)''')
conf_re = re.compile(r'''define_Conf! {\n([^}]*)\n}''', re.MULTILINE)
confvar_re = re.compile(
r'''/// Lint: (\w+)\. (.*)\n\s*\([^,]+,\s+"([^"]+)":\s+([^,]+),\s+([^\.\)]+).*\),''', re.MULTILINE)
r'''/// Lint: ([\w,\s]+)\. (.*)\n\s*\([^,]+,\s+"([^"]+)":\s+([^,]+),\s+([^\.\)]+).*\),''', re.MULTILINE)
comment_re = re.compile(r'''\s*/// ?(.*)''')
lint_levels = {
@@ -93,9 +93,9 @@ def parse_configs(path):
match = re.search(conf_re, contents)
confvars = re.findall(confvar_re, match.group(1))
for (lint, doc, name, ty, default) in confvars:
configs[lint.lower()] = Config(name.replace("_", "-"), ty, doc, default)
for (lints, doc, name, ty, default) in confvars:
for lint in lints.split(','):
configs[lint.strip().lower()] = Config(name.replace("_", "-"), ty, doc, default)
return configs