1 use crate::rustc_target
::abi
::LayoutOf
;
2 use crate::utils
::span_lint_and_then
;
3 use if_chain
::if_chain
;
4 use rustc_errors
::Applicability
;
5 use rustc_hir
::{Item, ItemKind}
;
6 use rustc_lint
::{LateContext, LateLintPass}
;
7 use rustc_middle
::mir
::interpret
::ConstValue
;
8 use rustc_middle
::ty
::{self, ConstKind}
;
9 use rustc_session
::{declare_tool_lint, impl_lint_pass}
;
10 use rustc_span
::{BytePos, Pos, Span}
;
11 use rustc_typeck
::hir_ty_to_ty
;
13 declare_clippy_lint
! {
14 /// **What it does:** Checks for large `const` arrays that should
15 /// be defined as `static` instead.
17 /// **Why is this bad?** Performance: const variables are inlined upon use.
18 /// Static items result in only one instance and has a fixed location in memory.
20 /// **Known problems:** None.
25 /// pub const a = [0u32; 1_000_000];
28 /// pub static a = [0u32; 1_000_000];
30 pub LARGE_CONST_ARRAYS
,
32 "large non-scalar const array may cause performance overhead"
35 pub struct LargeConstArrays
{
36 maximum_allowed_size
: u64,
39 impl LargeConstArrays
{
41 pub fn new(maximum_allowed_size
: u64) -> Self {
42 Self { maximum_allowed_size }
46 impl_lint_pass
!(LargeConstArrays
=> [LARGE_CONST_ARRAYS
]);
48 impl<'tcx
> LateLintPass
<'tcx
> for LargeConstArrays
{
49 fn check_item(&mut self, cx
: &LateContext
<'tcx
>, item
: &'tcx Item
<'_
>) {
51 if !item
.span
.from_expansion();
52 if let ItemKind
::Const(hir_ty
, _
) = &item
.kind
;
53 let ty
= hir_ty_to_ty(cx
.tcx
, hir_ty
);
54 if let ty
::Array(element_type
, cst
) = ty
.kind();
55 if let ConstKind
::Value(ConstValue
::Scalar(element_count
)) = cst
.val
;
56 if let Ok(element_count
) = element_count
.to_machine_usize(&cx
.tcx
);
57 if let Ok(element_size
) = cx
.layout_of(element_type
).map(|l
| l
.size
.bytes());
58 if self.maximum_allowed_size
< element_count
* element_size
;
61 let hi_pos
= item
.ident
.span
.lo() - BytePos
::from_usize(1);
62 let sugg_span
= Span
::new(
63 hi_pos
- BytePos
::from_usize("const".len()),
71 "large array defined as const",
75 "make this a static item",
77 Applicability
::MachineApplicable
,