Avoid needless creation of unique strings in fmt!()

Only the first portion has to be owned, as it acts as the buffer for the
constructed string. The remaining strings can be static.

Author: dotdash

src/libsyntax/ext/fmt.rs

@@ -273,15 +273,13 @@ fn pieces_to_expr(cx: @ext_ctxt, sp: span,
         match pc {
             /* Raw strings get appended via str::push_str */
             PieceString(s) => {
-                let portion = mk_uniq_str(cx, fmt_sp, s);
-
                 /* If this is the first portion, then initialize the local
                    buffer with it directly. If it's actually the only piece,
                    then there's no need for it to be mutable */
                 if i == 0 {
-                    stms.push(mk_local(cx, fmt_sp, npieces > 1, ident, portion));
+                    stms.push(mk_local(cx, fmt_sp, npieces > 1, ident, mk_uniq_str(cx, fmt_sp, s)));
                 } else {
-                    let args = ~[mk_mut_addr_of(cx, fmt_sp, buf()), portion];
+                    let args = ~[mk_mut_addr_of(cx, fmt_sp, buf()), mk_base_str(cx, fmt_sp, s)];
                     let call = mk_call_global(cx,
                                               fmt_sp,
                                               ~[str_ident, push_ident],