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Auto merge of #81453 - jumbatm:clashing-extern-decl-perf, r=nagisa 

clashing_extern_declarations: Use symbol interning to avoid string alloc.

Use symbol interning as a hack to avoid allocating a string for every symbol name we store in the seen set. This hopefully addresses the minor perf regression described in https://github.com/rust-lang/rust/pull/80009#issuecomment-763526902.

r? `@nagisa`
This commit is contained in:
bors 2021-01-30 16:41:05 +00:00
parent 7ce1b3b244 a1a7830465
commit fd20a8be0d
1 changed files with 4 additions and 4 deletions
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8
compiler/rustc_lint/src/builtin.rs
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@ -2607,7 +2607,7 @@ pub struct ClashingExternDeclarations {
/// the symbol should be reported as a clashing declaration.
// FIXME: Technically, we could just store a &'tcx str here without issue; however, the
// `impl_lint_pass` macro doesn't currently support lints parametric over a lifetime.
seen_decls: FxHashMap<String, HirId>,
seen_decls: FxHashMap<Symbol, HirId>,
}
/// Differentiate between whether the name for an extern decl came from the link_name attribute or
@ -2641,14 +2641,14 @@ impl ClashingExternDeclarations {
let local_did = tcx.hir().local_def_id(fi.hir_id);
let did = local_did.to_def_id();
let instance = Instance::new(did, ty::List::identity_for_item(tcx, did));
let name = tcx.symbol_name(instance).name;
if let Some(&hir_id) = self.seen_decls.get(name) {
let name = Symbol::intern(tcx.symbol_name(instance).name);
if let Some(&hir_id) = self.seen_decls.get(&name) {
// Avoid updating the map with the new entry when we do find a collision. We want to
// make sure we're always pointing to the first definition as the previous declaration.
// This lets us avoid emitting "knock-on" diagnostics.
Some(hir_id)
} else {
self.seen_decls.insert(name.to_owned(), hid)
self.seen_decls.insert(name, hid)
}
}