use slicing sugar
diff --git a/src/librustc_trans/trans/cabi.rs b/src/librustc_trans/trans/cabi.rs
index a901142..8a2a253 100644
--- a/src/librustc_trans/trans/cabi.rs
+++ b/src/librustc_trans/trans/cabi.rs
@@ -108,7 +108,7 @@
                         atys: &[Type],
                         rty: Type,
                         ret_def: bool) -> FnType {
-    match ccx.sess().target.target.arch.index(&FullRange) {
+    match &ccx.sess().target.target.arch[] {
         "x86" => cabi_x86::compute_abi_info(ccx, atys, rty, ret_def),
         "x86_64" => if ccx.sess().target.target.options.is_like_windows {
             cabi_x86_win64::compute_abi_info(ccx, atys, rty, ret_def)
@@ -118,7 +118,7 @@
         "arm" => cabi_arm::compute_abi_info(ccx, atys, rty, ret_def),
         "aarch64" => cabi_aarch64::compute_abi_info(ccx, atys, rty, ret_def),
         "mips" => cabi_mips::compute_abi_info(ccx, atys, rty, ret_def),
-        a => ccx.sess().fatal((format!("unrecognized arch \"{}\" in target specification", a))
-                              .index(&FullRange)),
+        a => ccx.sess().fatal(&format!("unrecognized arch \"{}\" in target specification", a)
+                              []),
     }
 }