panic_nounwind in Arguments::new* instead of recursing

Author: saethlin

library/core/src/fmt/mod.rs

@@ -340,7 +340,9 @@ impl<'a> Arguments<'a> {
     #[rustc_const_unstable(feature = "const_fmt_arguments_new", issue = "none")]
     pub const fn new_const(pieces: &'a [&'static str]) -> Self {
         if pieces.len() > 1 {
-            panic!("invalid args");
+            // Since panic!() expands to panic_fmt(format_args!()), using panic! here is both a
+            // bit silly and also significantly increases the amount of MIR generated by panics.
+            crate::panicking::panic_nounwind("invalid args");
         }
         Arguments { pieces, fmt: None, args: &[] }
     }
@@ -350,7 +352,8 @@ impl<'a> Arguments<'a> {
     #[inline]
     pub fn new_v1(pieces: &'a [&'static str], args: &'a [rt::Argument<'a>]) -> Arguments<'a> {
         if pieces.len() < args.len() || pieces.len() > args.len() + 1 {
-            panic!("invalid args");
+            // See Arguments::new_const for why we don't use panic!.
+            crate::panicking::panic_nounwind("invalid args");
         }
         Arguments { pieces, fmt: None, args }
     }