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<'a, 'tcx> LateLintPass<'a, 'tcx> for LargeConstArrays {
49 fn check_item(&mut self, cx: &LateContext<'a, '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(val) = cst.val;
56 if let ConstValue::Scalar(element_count) = val;
57 if let Ok(element_count) = element_count.to_machine_usize(&cx.tcx);
58 if let Ok(element_size) = cx.layout_of(element_type).map(|l| l.size.bytes());
59 if self.maximum_allowed_size < element_count * element_size;
62 let hi_pos = item.ident.span.lo() - BytePos::from_usize(1);
63 let sugg_span = Span::new(
64 hi_pos - BytePos::from_usize("const".len()),
72 "large array defined as const",
76 "make this a static item",
78 Applicability::MachineApplicable,