Auto merge of #122671 - Mark-Simulacrum:const-panic-msg, r=Nilstrieb

Codegen const panic messages as function calls

This skips emitting extra arguments at every callsite (of which there
can be many). For a librustc_driver build with overflow checks enabled,
this cuts 0.7MB from the resulting shared library (see [perf]).

A sample improvement from nightly:

```
        leaq    str.0(%rip), %rdi
        leaq    .Lalloc_d6aeb8e2aa19de39a7f0e861c998af13(%rip), %rdx
        movl    $25, %esi
        callq   *_ZN4core9panicking5panic17h17cabb89c5bcc999E@GOTPCREL(%rip)
```

to this PR:

```
        leaq    .Lalloc_d6aeb8e2aa19de39a7f0e861c998af13(%rip), %rdi
        callq   *_RNvNtNtCsduqIKoij8JB_4core9panicking11panic_const23panic_const_div_by_zero@GOTPCREL(%rip)
```

[perf]: https://perf.rust-lang.org/compare.html?start=a7e4de13c1785819f4d61da41f6704ed69d5f203&end=64fbb4f0b2d621ff46d559d1e9f5ad89a8d7789b&stat=instructions:u

1 files changed, 2 insertions, 4 deletions

diff --git a/compiler/rustc_codegen_ssa/src/mir/block.rs b/compiler/rustc_codegen_ssa/src/mir/block.rs
index 8c668597a43..d4123329f44 100644
--- a/compiler/rustc_codegen_ssa/src/mir/block.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/block.rs
@@ -682,10 +682,8 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                 (LangItem::PanicMisalignedPointerDereference, vec![required, found, location])
             }
             _ => {
-                let msg = bx.const_str(msg.description());
-                // It's `pub fn panic(expr: &str)`, with the wide reference being passed
-                // as two arguments, and `#[track_caller]` adds an implicit third argument.
-                (LangItem::Panic, vec![msg.0, msg.1, location])
+                // It's `pub fn panic_...()` and `#[track_caller]` adds an implicit argument.
+                (msg.panic_function(), vec![location])
             }
         };