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