Avoid some unnecessary symbol interning.

- `Ident::from_str_and_span` -> `Ident::new` when the string is
  pre-interned.
- `Ident::from_str` -> `Ident::with_dummy_span` when the string is
  pre-interned.
- `_d` and `_e` are unused.

compiler/rustc_builtin_macros/src/alloc_error_handler.rs

@@ -62,8 +62,8 @@ pub(crate) fn expand(
 fn generate_handler(cx: &ExtCtxt<'_>, handler: Ident, span: Span, sig_span: Span) -> Stmt {
     let usize = cx.path_ident(span, Ident::new(sym::usize, span));
     let ty_usize = cx.ty_path(usize);
-    let size = Ident::from_str_and_span("size", span);
-    let align = Ident::from_str_and_span("align", span);
+    let size = Ident::new(sym::size, span);
+    let align = Ident::new(sym::align, span);
 
     let layout_new = cx.std_path(&[sym::alloc, sym::Layout, sym::from_size_align_unchecked]);
     let layout_new = cx.expr_path(cx.path(span, layout_new));

compiler/rustc_builtin_macros/src/autodiff.rs

@@ -652,8 +652,10 @@ mod llvm_enzyme {
                 exprs = ecx.expr_call(new_decl_span, bb_call_expr, thin_vec![exprs]);
             } else {
                 let q = QSelf { ty: d_ret_ty, path_span: span, position: 0 };
-                let y =
-                    ExprKind::Path(Some(P(q)), ecx.path_ident(span, Ident::from_str("default")));
+                let y = ExprKind::Path(
+                    Some(P(q)),
+                    ecx.path_ident(span, Ident::with_dummy_span(kw::Default)),
+                );
                 let default_call_expr = ecx.expr(span, y);
                 let default_call_expr =
                     ecx.expr_call(new_decl_span, default_call_expr, thin_vec![]);

compiler/rustc_hir_pretty/src/lib.rs

@@ -22,7 +22,7 @@ use rustc_hir::{
     TyPatKind,
 };
 use rustc_span::source_map::SourceMap;
-use rustc_span::{FileName, Ident, Span, Symbol, kw};
+use rustc_span::{FileName, Ident, Span, Symbol, kw, sym};
 use {rustc_ast as ast, rustc_hir as hir};
 
 pub fn id_to_string(cx: &dyn rustc_hir::intravisit::HirTyCtxt<'_>, hir_id: HirId) -> String {
@@ -1517,7 +1517,7 @@ impl<'a> State<'a> {
                 self.bopen(ib);
 
                 // Print `let _t = $init;`:
-                let temp = Ident::from_str("_t");
+                let temp = Ident::with_dummy_span(sym::_t);
                 self.print_local(false, Some(init), None, |this| this.print_ident(temp));
                 self.word(";");
 

compiler/rustc_span/src/symbol.rs

@@ -396,8 +396,7 @@ symbols! {
         __S,
         __awaitee,
         __try_var,
-        _d,
-        _e,
+        _t,
         _task_context,
         a32,
         aarch64_target_feature,

src/tools/clippy/clippy_lints/src/bool_assert_comparison.rs

@@ -56,7 +56,7 @@ fn is_impl_not_trait_with_bool_out<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -
         .and_then(|trait_id| {
             cx.tcx.associated_items(trait_id).find_by_ident_and_kind(
                 cx.tcx,
-                Ident::from_str("Output"),
+                Ident::with_dummy_span(sym::Output),
                 ty::AssocTag::Type,
                 trait_id,
             )