Rollup merge of rust-lang#69850 - RalfJung:panic-bounds-check, r=eddyb

panic_bounds_check: use caller_location, like PanicFnLangItem

The `PanicFnLangItem` got switched to using `#[caller_location]` at some point, but `PanicBoundsCheckFnLangItem` was kept in the old style. For consistency, switch that one over to use `#[caller_location]` as well.

This is also helpful for Miri as it means the `assert_panic` machine hook never needs to know the current `Span`.

Author: Centril

src/libcore/macros/mod.rs

@@ -1,3 +1,4 @@
+#[cfg(bootstrap)]
 #[doc(include = "panic.md")]
 #[macro_export]
 #[allow_internal_unstable(core_panic, track_caller)]
@@ -20,6 +21,26 @@ macro_rules! panic {
     );
 }
 
+#[cfg(not(bootstrap))]
+#[doc(include = "panic.md")]
+#[macro_export]
+#[allow_internal_unstable(core_panic, track_caller)]
+#[stable(feature = "core", since = "1.6.0")]
+macro_rules! panic {
+    () => (
+        $crate::panic!("explicit panic")
+    );
+    ($msg:expr) => (
+        $crate::panicking::panic($msg)
+    );
+    ($msg:expr,) => (
+        $crate::panic!($msg)
+    );
+    ($fmt:expr, $($arg:tt)+) => (
+        $crate::panicking::panic_fmt($crate::format_args!($fmt, $($arg)+))
+    );
+}
+
 /// Asserts that two expressions are equal to each other (using [`PartialEq`]).
 ///
 /// On panic, this macro will print the values of the expressions with their

src/libcore/panicking.rs

@@ -32,6 +32,7 @@
 use crate::fmt;
 use crate::panic::{Location, PanicInfo};
 
+/// The underlying implementation of libcore's `panic!` macro when no formatting is used.
 #[cold]
 // never inline unless panic_immediate_abort to avoid code
 // bloat at the call sites as much as possible
@@ -49,9 +50,28 @@ pub fn panic(expr: &str) -> ! {
     // truncation and padding (even though none is used here). Using
     // Arguments::new_v1 may allow the compiler to omit Formatter::pad from the
     // output binary, saving up to a few kilobytes.
-    panic_fmt(fmt::Arguments::new_v1(&[expr], &[]), Location::caller())
+    #[cfg(not(bootstrap))]
+    panic_fmt(fmt::Arguments::new_v1(&[expr], &[]));
+    #[cfg(bootstrap)]
+    panic_fmt(fmt::Arguments::new_v1(&[expr], &[]), Location::caller());
 }
 
+#[cfg(not(bootstrap))]
+#[cold]
+#[cfg_attr(not(feature = "panic_immediate_abort"), inline(never))]
+#[track_caller]
+#[lang = "panic_bounds_check"] // needed by codegen for panic on OOB array/slice access
+fn panic_bounds_check(index: usize, len: usize) -> ! {
+    if cfg!(feature = "panic_immediate_abort") {
+        unsafe { super::intrinsics::abort() }
+    }
+
+    panic!("index out of bounds: the len is {} but the index is {}", len, index)
+}
+
+// For bootstrap, we need a variant with the old argument order, and a corresponding
+// `panic_fmt`.
+#[cfg(bootstrap)]
 #[cold]
 #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never))]
 #[lang = "panic_bounds_check"] // needed by codegen for panic on OOB array/slice access
@@ -66,10 +86,12 @@ fn panic_bounds_check(location: &Location<'_>, index: usize, len: usize) -> ! {
     )
 }
 
+/// The underlying implementation of libcore's `panic!` macro when formatting is used.
 #[cold]
 #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never))]
 #[cfg_attr(feature = "panic_immediate_abort", inline)]
-pub fn panic_fmt(fmt: fmt::Arguments<'_>, location: &Location<'_>) -> ! {
+#[cfg_attr(not(bootstrap), track_caller)]
+pub fn panic_fmt(fmt: fmt::Arguments<'_>, #[cfg(bootstrap)] location: &Location<'_>) -> ! {
     if cfg!(feature = "panic_immediate_abort") {
         unsafe { super::intrinsics::abort() }
     }
@@ -81,6 +103,10 @@ pub fn panic_fmt(fmt: fmt::Arguments<'_>, location: &Location<'_>) -> ! {
         fn panic_impl(pi: &PanicInfo<'_>) -> !;
     }
 
+    #[cfg(bootstrap)]
     let pi = PanicInfo::internal_constructor(Some(&fmt), location);
+    #[cfg(not(bootstrap))]
+    let pi = PanicInfo::internal_constructor(Some(&fmt), Location::caller());
+
     unsafe { panic_impl(&pi) }
 }

src/librustc_codegen_ssa/mir/block.rs

@@ -415,11 +415,15 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
             AssertKind::BoundsCheck { ref len, ref index } => {
                 let len = self.codegen_operand(&mut bx, len).immediate();
                 let index = self.codegen_operand(&mut bx, index).immediate();
-                (lang_items::PanicBoundsCheckFnLangItem, vec![location, index, len])
+                // It's `fn panic_bounds_check(index: usize, len: usize)`,
+                // and `#[track_caller]` adds an implicit third argument.
+                (lang_items::PanicBoundsCheckFnLangItem, vec![index, len, location])
             }
             _ => {
                 let msg_str = Symbol::intern(msg.description());
                 let msg = bx.const_str(msg_str);
+                // It's `pub fn panic(expr: &str)`, with the wide reference being passed
+                // as two arguments, and `#[track_caller]` adds an implicit third argument.
                 (lang_items::PanicFnLangItem, vec![msg.0, msg.1, location])
             }
         };

src/librustc_mir/const_eval/machine.rs

@@ -280,7 +280,6 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir,
 
     fn assert_panic(
         ecx: &mut InterpCx<'mir, 'tcx, Self>,
-        _span: Span,
         msg: &AssertMessage<'tcx>,
         _unwind: Option<mir::BasicBlock>,
     ) -> InterpResult<'tcx> {

src/librustc_mir/interpret/machine.rs

@@ -165,7 +165,6 @@ pub trait Machine<'mir, 'tcx>: Sized {
     /// Called to evaluate `Assert` MIR terminators that trigger a panic.
     fn assert_panic(
         ecx: &mut InterpCx<'mir, 'tcx, Self>,
-        span: Span,
         msg: &mir::AssertMessage<'tcx>,
         unwind: Option<mir::BasicBlock>,
     ) -> InterpResult<'tcx>;

src/librustc_mir/interpret/terminator.rs

@@ -95,7 +95,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 if expected == cond_val {
                     self.go_to_block(target);
                 } else {
-                    M::assert_panic(self, terminator.source_info.span, msg, cleanup)?;
+                    M::assert_panic(self, msg, cleanup)?;
                 }
             }
 

src/librustc_mir/transform/const_prop.rs

@@ -197,7 +197,6 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for ConstPropMachine {
 
     fn assert_panic(
         _ecx: &mut InterpCx<'mir, 'tcx, Self>,
-        _span: Span,
         _msg: &rustc::mir::AssertMessage<'tcx>,
         _unwind: Option<rustc::mir::BasicBlock>,
     ) -> InterpResult<'tcx> {