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 binary.

Author: Mark-Simulacrum

example/mini_core.rs

@@ -465,6 +465,36 @@ pub fn panic(_msg: &'static str) -> ! {
     }
 }
 
+macro_rules! panic_const {
+    ($($lang:ident = $message:expr,)+) => {
+        #[cfg(not(bootstrap))]
+        pub mod panic_const {
+            use super::*;
+
+            $(
+                #[track_caller]
+                #[lang = stringify!($lang)]
+                pub fn $lang() -> ! {
+                    panic($message);
+                }
+            )+
+        }
+    }
+}
+
+panic_const! {
+    panic_const_add_overflow = "attempt to add with overflow",
+    panic_const_sub_overflow = "attempt to subtract with overflow",
+    panic_const_mul_overflow = "attempt to multiply with overflow",
+    panic_const_div_overflow = "attempt to divide with overflow",
+    panic_const_rem_overflow = "attempt to calculate the remainder with overflow",
+    panic_const_neg_overflow = "attempt to negate with overflow",
+    panic_const_shr_overflow = "attempt to shift right with overflow",
+    panic_const_shl_overflow = "attempt to shift left with overflow",
+    panic_const_div_by_zero = "attempt to divide by zero",
+    panic_const_rem_by_zero = "attempt to calculate the remainder with a divisor of zero",
+}
+
 #[lang = "panic_bounds_check"]
 #[track_caller]
 fn panic_bounds_check(index: usize, len: usize) -> ! {

src/base.rs

@@ -369,8 +369,14 @@ fn codegen_fn_body(fx: &mut FunctionCx<'_, '_, '_>, start_block: Block) {
                         );
                     }
                     _ => {
-                        let msg_str = msg.description();
-                        codegen_panic(fx, msg_str, source_info);
+                        let location = fx.get_caller_location(source_info).load_scalar(fx);
+
+                        codegen_panic_inner(
+                            fx,
+                            msg.panic_function(),
+                            &[location],
+                            Some(source_info.span),
+                        );
                     }
                 }
             }
@@ -954,20 +960,6 @@ pub(crate) fn codegen_operand<'tcx>(
     }
 }
 
-pub(crate) fn codegen_panic<'tcx>(
-    fx: &mut FunctionCx<'_, '_, 'tcx>,
-    msg_str: &str,
-    source_info: mir::SourceInfo,
-) {
-    let location = fx.get_caller_location(source_info).load_scalar(fx);
-
-    let msg_ptr = fx.anonymous_str(msg_str);
-    let msg_len = fx.bcx.ins().iconst(fx.pointer_type, i64::try_from(msg_str.len()).unwrap());
-    let args = [msg_ptr, msg_len, location];
-
-    codegen_panic_inner(fx, rustc_hir::LangItem::Panic, &args, Some(source_info.span));
-}
-
 pub(crate) fn codegen_panic_nounwind<'tcx>(
     fx: &mut FunctionCx<'_, '_, 'tcx>,
     msg_str: &str,