Use BTreeMap to store attributes.

compiler/rustc_hir/src/hir.rs

@@ -2,7 +2,7 @@
 use crate::def::{CtorKind, DefKind, Namespace, Res};
 use crate::def_id::DefId;
 crate use crate::hir_id::HirId;
-use crate::{itemlikevisit, HirIdVec, LangItem};
+use crate::{itemlikevisit, LangItem};
 
 use rustc_ast::util::parser::ExprPrecedence;
 use rustc_ast::{self as ast, CrateSugar, LlvmAsmDialect};
@@ -675,7 +675,7 @@ pub struct Crate<'hir> {
     pub trait_map: BTreeMap<HirId, Vec<TraitCandidate>>,
 
     /// Collected attributes from HIR nodes.
-    pub attrs: HirIdVec<&'hir [Attribute]>,
+    pub attrs: BTreeMap<HirId, &'hir [Attribute]>,
 }
 
 impl Crate<'hir> {