remove panic_str, inline into the only caller

Author: RalfJung

library/core/src/option.rs

@@ -554,7 +554,7 @@
 #![stable(feature = "rust1", since = "1.0.0")]
 
 use crate::iter::{self, FromIterator, FusedIterator, TrustedLen};
-use crate::panicking::{panic, panic_str};
+use crate::panicking::{panic, panic_display};
 use crate::pin::Pin;
 use crate::{
     cmp, convert, hint, mem,
@@ -1991,7 +1991,7 @@ const fn unwrap_failed() -> ! {
 #[track_caller]
 #[rustc_const_unstable(feature = "const_option", issue = "67441")]
 const fn expect_failed(msg: &str) -> ! {
-    panic_str(msg)
+    panic_display(&msg)
 }
 
 /////////////////////////////////////////////////////////////////////////////

library/core/src/panicking.rs

@@ -124,8 +124,8 @@ pub const fn panic_nounwind_fmt(fmt: fmt::Arguments<'_>, force_no_backtrace: boo
 // above.
 
 /// The underlying implementation of core's `panic!` macro when no formatting is used.
-// never inline unless panic_immediate_abort to avoid code
-// bloat at the call sites as much as possible
+// Never inline unless panic_immediate_abort to avoid code
+// bloat at the call sites as much as possible.
 #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never), cold)]
 #[cfg_attr(feature = "panic_immediate_abort", inline)]
 #[track_caller]
@@ -138,6 +138,11 @@ pub const fn panic(expr: &'static str) -> ! {
     // truncation and padding (even though none is used here). Using
     // Arguments::new_const may allow the compiler to omit Formatter::pad from the
     // output binary, saving up to a few kilobytes.
+    // However, this optimization only works for `'static` strings: `new_const` also makes this
+    // message return `Some` from `Arguments::as_str`, which means it can become part of the panic
+    // payload without any allocation or copying. Shorter-lived strings would become invalid as
+    // stack frames get popped during unwinding, and couldn't be directly referenced from the
+    // payload.
     panic_fmt(fmt::Arguments::new_const(&[expr]));
 }
 
@@ -160,14 +165,6 @@ pub fn panic_nounwind_nobacktrace(expr: &'static str) -> ! {
     panic_nounwind_fmt(fmt::Arguments::new_const(&[expr]), /* force_no_backtrace */ true);
 }
 
-#[inline]
-#[track_caller]
-#[rustc_diagnostic_item = "panic_str"]
-#[rustc_const_unstable(feature = "panic_internals", issue = "none")]
-pub const fn panic_str(expr: &str) -> ! {
-    panic_display(&expr);
-}
-
 #[track_caller]
 #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never), cold)]
 #[cfg_attr(feature = "panic_immediate_abort", inline)]