replace miri_start_panic intrinsic by 'extern fn'

Author: RalfJung

src/libcore/intrinsics.rs

@@ -1947,14 +1947,6 @@ extern "rust-intrinsic" {
     #[rustc_const_unstable(feature = "const_ptr_offset_from", issue = "41079")]
     pub fn ptr_offset_from<T>(ptr: *const T, base: *const T) -> isize;
 
-    /// Internal hook used by Miri to implement unwinding.
-    /// ICEs when encountered during non-Miri codegen.
-    ///
-    /// The `payload` ptr here will be exactly the one `do_catch` gets passed by `try`.
-    ///
-    /// Perma-unstable: do not use.
-    pub fn miri_start_panic(payload: *mut u8) -> !;
-
     /// Internal placeholder for injecting code coverage counters when the "instrument-coverage"
     /// option is enabled. The placeholder is replaced with `llvm.instrprof.increment` during code
     /// generation.

src/libpanic_unwind/miri.rs

@@ -6,11 +6,16 @@ use core::any::Any;
 // Must be pointer-sized.
 type Payload = Box<Box<dyn Any + Send>>;
 
+extern "Rust" {
+    /// Miri-provided extern function to begin unwinding.
+    fn miri_start_panic(payload: *mut u8) -> !;
+}
+
 pub unsafe fn panic(payload: Box<dyn Any + Send>) -> u32 {
     // The payload we pass to `miri_start_panic` will be exactly the argument we get
     // in `cleanup` below. So we just box it up once, to get something pointer-sized.
     let payload_box: Payload = Box::new(payload);
-    core::intrinsics::miri_start_panic(Box::into_raw(payload_box) as *mut u8)
+    miri_start_panic(Box::into_raw(payload_box) as *mut u8)
 }
 
 pub unsafe fn cleanup(payload_box: *mut u8) -> Box<dyn Any + Send> {

src/librustc_codegen_ssa/mir/block.rs

@@ -606,11 +606,6 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
             return;
         }
 
-        // For normal codegen, this Miri-specific intrinsic should never occur.
-        if intrinsic == Some(sym::miri_start_panic) {
-            bug!("`miri_start_panic` should never end up in compiled code");
-        }
-
         if self.codegen_panic_intrinsic(
             &helper,
             &mut bx,

src/librustc_span/symbol.rs

@@ -677,7 +677,6 @@ symbols! {
         minnumf32,
         minnumf64,
         mips_target_feature,
-        miri_start_panic,
         mmx_target_feature,
         module,
         module_path,

src/librustc_typeck/check/intrinsic.rs

@@ -379,12 +379,6 @@ pub fn check_intrinsic_type(tcx: TyCtxt<'_>, it: &hir::ForeignItem<'_>) {
 
             sym::nontemporal_store => (1, vec![tcx.mk_mut_ptr(param(0)), param(0)], tcx.mk_unit()),
 
-            sym::miri_start_panic => {
-                // FIXME - the relevant types aren't lang items,
-                // so it's not trivial to check this
-                return;
-            }
-
             sym::count_code_region => {
                 (0, vec![tcx.types.u64, tcx.types.u32, tcx.types.u32, tcx.types.u32], tcx.mk_unit())
             }