Rollup merge of #65664 - anp:panic-location, r=eddyb

`std::panic::Location` is a lang_item, add `core::intrinsics::caller_location` (RFC 2091 3/N)

[Tracking issue](#47809)
[RFC text](https://github.com/rust-lang/rfcs/blob/master/text/2091-inline-semantic.md)

@eddyb suggested doing this intrinsic implementation ahead of actually implementing the `#[track_caller]` attribute so that there's an easily tested intermediate step between adding the shim and wiring up the attribute.

src/libcore/intrinsics.rs

@@ -696,6 +696,10 @@ extern "rust-intrinsic" {
     /// This will statically either panic, or do nothing.
     pub fn panic_if_uninhabited<T>();
 
+    /// Gets a reference to a static `Location` indicating where it was called.
+    #[cfg(not(bootstrap))]
+    pub fn caller_location() -> &'static crate::panic::Location<'static>;
+
     /// Creates a value initialized to zero.
     ///
     /// `init` is unsafe because it returns a zeroed-out datum,

src/libcore/macros.rs

@@ -1,8 +1,9 @@
 /// Panics the current thread.
 ///
 /// For details, see `std::macros`.
+#[cfg(bootstrap)]
 #[macro_export]
-#[allow_internal_unstable(core_panic)]
+#[allow_internal_unstable(core_panic, panic_internals)]
 #[stable(feature = "core", since = "1.6.0")]
 macro_rules! panic {
     () => (
@@ -20,6 +21,38 @@ macro_rules! panic {
     });
 }
 
+/// Panics the current thread.
+///
+/// For details, see `std::macros`.
+#[cfg(not(bootstrap))]
+#[macro_export]
+#[allow_internal_unstable(core_panic, panic_internals)]
+#[stable(feature = "core", since = "1.6.0")]
+macro_rules! panic {
+    () => (
+        $crate::panic!("explicit panic")
+    );
+    ($msg:expr) => ({
+        const LOC: &$crate::panic::Location<'_> = &$crate::panic::Location::internal_constructor(
+            $crate::file!(),
+            $crate::line!(),
+            $crate::column!(),
+        );
+        $crate::panicking::panic($msg, LOC)
+    });
+    ($msg:expr,) => (
+        $crate::panic!($msg)
+    );
+    ($fmt:expr, $($arg:tt)+) => ({
+        const LOC: &$crate::panic::Location<'_> = &$crate::panic::Location::internal_constructor(
+            $crate::file!(),
+            $crate::line!(),
+            $crate::column!(),
+        );
+        $crate::panicking::panic_fmt($crate::format_args!($fmt, $($arg)+), LOC)
+    });
+}
+
 /// 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/panic.rs

@@ -35,7 +35,7 @@ use crate::fmt;
 pub struct PanicInfo<'a> {
     payload: &'a (dyn Any + Send),
     message: Option<&'a fmt::Arguments<'a>>,
-    location: Location<'a>,
+    location: &'a Location<'a>,
 }
 
 impl<'a> PanicInfo<'a> {
@@ -45,11 +45,16 @@ impl<'a> PanicInfo<'a> {
                 issue = "0")]
     #[doc(hidden)]
     #[inline]
-    pub fn internal_constructor(message: Option<&'a fmt::Arguments<'a>>,
-                                location: Location<'a>)
-                                -> Self {
+    pub fn internal_constructor(
+        message: Option<&'a fmt::Arguments<'a>>,
+        location: &'a Location<'a>,
+    ) -> Self {
         struct NoPayload;
-        PanicInfo { payload: &NoPayload, location, message }
+        PanicInfo {
+            location,
+            message,
+            payload: &NoPayload,
+        }
     }
 
     #[doc(hidden)]
@@ -162,6 +167,7 @@ impl fmt::Display for PanicInfo<'_> {
 ///
 /// panic!("Normal panic");
 /// ```
+#[cfg_attr(not(bootstrap), lang = "panic_location")]
 #[derive(Debug)]
 #[stable(feature = "panic_hooks", since = "1.10.0")]
 pub struct Location<'a> {
@@ -176,7 +182,7 @@ impl<'a> Location<'a> {
                           and related macros",
                 issue = "0")]
     #[doc(hidden)]
-    pub fn internal_constructor(file: &'a str, line: u32, col: u32) -> Self {
+    pub const fn internal_constructor(file: &'a str, line: u32, col: u32) -> Self {
         Location { file, line, col }
     }
 

src/libcore/panicking.rs

@@ -29,6 +29,7 @@
 use crate::fmt;
 use crate::panic::{Location, PanicInfo};
 
+#[cfg(bootstrap)]
 #[cold]
 // never inline unless panic_immediate_abort to avoid code
 // bloat at the call sites as much as possible
@@ -49,6 +50,27 @@ pub fn panic(expr_file_line_col: &(&'static str, &'static str, u32, u32)) -> ! {
     panic_fmt(fmt::Arguments::new_v1(&[expr], &[]), &(file, line, col))
 }
 
+#[cfg(not(bootstrap))]
+#[cold]
+// 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))]
+#[lang = "panic"]
+pub fn panic(expr: &str, location: &Location<'_>) -> ! {
+    if cfg!(feature = "panic_immediate_abort") {
+        unsafe { super::intrinsics::abort() }
+    }
+
+    // Use Arguments::new_v1 instead of format_args!("{}", expr) to potentially
+    // reduce size overhead. The format_args! macro uses str's Display trait to
+    // write expr, which calls Formatter::pad, which must accommodate string
+    // 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)
+}
+
+#[cfg(bootstrap)]
 #[cold]
 #[cfg_attr(not(feature="panic_immediate_abort"),inline(never))]
 #[lang = "panic_bounds_check"]
@@ -62,6 +84,22 @@ fn panic_bounds_check(file_line_col: &(&'static str, u32, u32),
                            len, index), file_line_col)
 }
 
+#[cfg(not(bootstrap))]
+#[cold]
+#[cfg_attr(not(feature="panic_immediate_abort"),inline(never))]
+#[lang = "panic_bounds_check"]
+fn panic_bounds_check(location: &Location<'_>, index: usize, len: usize) -> ! {
+    if cfg!(feature = "panic_immediate_abort") {
+        unsafe { super::intrinsics::abort() }
+    }
+
+    panic_fmt(
+        format_args!("index out of bounds: the len is {} but the index is {}", len, index),
+        location
+    )
+}
+
+#[cfg(bootstrap)]
 #[cold]
 #[cfg_attr(not(feature="panic_immediate_abort"),inline(never))]
 #[cfg_attr(    feature="panic_immediate_abort" ,inline)]
@@ -77,9 +115,26 @@ pub fn panic_fmt(fmt: fmt::Arguments<'_>, file_line_col: &(&'static str, u32, u3
     }
 
     let (file, line, col) = *file_line_col;
-    let pi = PanicInfo::internal_constructor(
-        Some(&fmt),
-        Location::internal_constructor(file, line, col),
-    );
+    let location = Location::internal_constructor(file, line, col);
+    let pi = PanicInfo::internal_constructor(Some(&fmt), &location);
+    unsafe { panic_impl(&pi) }
+}
+
+#[cfg(not(bootstrap))]
+#[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<'_>) -> ! {
+    if cfg!(feature = "panic_immediate_abort") {
+        unsafe { super::intrinsics::abort() }
+    }
+
+    // NOTE This function never crosses the FFI boundary; it's a Rust-to-Rust call
+    extern "Rust" {
+        #[lang = "panic_impl"]
+        fn panic_impl(pi: &PanicInfo<'_>) -> !;
+    }
+
+    let pi = PanicInfo::internal_constructor(Some(&fmt), location);
     unsafe { panic_impl(&pi) }
 }

src/librustc/middle/lang_items.rs

@@ -370,6 +370,7 @@ language_item_table! {
     PanicFnLangItem,             "panic",              panic_fn,                Target::Fn;
     PanicBoundsCheckFnLangItem,  "panic_bounds_check", panic_bounds_check_fn,   Target::Fn;
     PanicInfoLangItem,           "panic_info",         panic_info,              Target::Struct;
+    PanicLocationLangItem,       "panic_location",     panic_location,          Target::Struct;
     PanicImplLangItem,           "panic_impl",         panic_impl,              Target::Fn;
     // Libstd panic entry point. Necessary for const eval to be able to catch it
     BeginPanicFnLangItem,        "begin_panic",        begin_panic_fn,          Target::Fn;

src/librustc/query/mod.rs

@@ -466,6 +466,12 @@ rustc_queries! {
             no_force
             desc { "extract field of const" }
         }
+
+        query const_caller_location(key: (syntax_pos::Symbol, u32, u32)) -> &'tcx ty::Const<'tcx> {
+            eval_always
+            no_force
+            desc { "get a &core::panic::Location referring to a span" }
+        }
     }
 
     TypeChecking {

src/librustc/ty/query/keys.rs

@@ -208,3 +208,13 @@ impl<'tcx, T> Key for Canonical<'tcx, T> {
         DUMMY_SP
     }
 }
+
+impl Key for (Symbol, u32, u32) {
+    fn query_crate(&self) -> CrateNum {
+        LOCAL_CRATE
+    }
+
+    fn default_span(&self, _tcx: TyCtxt<'_>) -> Span {
+        DUMMY_SP
+    }
+}

src/librustc_codegen_llvm/builder.rs

@@ -23,7 +23,6 @@ use std::ffi::CStr;
 use std::ops::{Deref, Range};
 use std::ptr;
 use std::iter::TrustedLen;
-use syntax::symbol::Symbol;
 
 // All Builders must have an llfn associated with them
 #[must_use]
@@ -1067,36 +1066,6 @@ impl StaticBuilderMethods for Builder<'a, 'll, 'tcx> {
         // Forward to the `get_static` method of `CodegenCx`
         self.cx().get_static(def_id)
     }
-
-    fn static_panic_msg(
-        &mut self,
-        msg: Option<Symbol>,
-        filename: Symbol,
-        line: Self::Value,
-        col: Self::Value,
-        kind: &str,
-    ) -> Self::Value {
-        let align = self.tcx.data_layout.aggregate_align.abi
-            .max(self.tcx.data_layout.i32_align.abi)
-            .max(self.tcx.data_layout.pointer_align.abi);
-
-        let filename = self.const_str_slice(filename);
-
-        let with_msg_components;
-        let without_msg_components;
-
-        let components = if let Some(msg) = msg {
-            let msg = self.const_str_slice(msg);
-            with_msg_components = [msg, filename, line, col];
-            &with_msg_components as &[_]
-        } else {
-            without_msg_components = [filename, line, col];
-            &without_msg_components as &[_]
-        };
-
-        let struct_ = self.const_struct(&components, false);
-        self.static_addr_of(struct_, align, Some(kind))
-    }
 }
 
 impl Builder<'a, 'll, 'tcx> {

src/librustc_codegen_llvm/common.rs

@@ -3,7 +3,6 @@
 //! Code that is useful in various codegen modules.
 
 use crate::llvm::{self, True, False, Bool, BasicBlock, OperandBundleDef, ConstantInt};
-use crate::abi;
 use crate::consts;
 use crate::type_::Type;
 use crate::type_of::LayoutLlvmExt;
@@ -96,16 +95,6 @@ impl BackendTypes for CodegenCx<'ll, 'tcx> {
 }
 
 impl CodegenCx<'ll, 'tcx> {
-    pub fn const_fat_ptr(
-        &self,
-        ptr: &'ll Value,
-        meta: &'ll Value
-    ) -> &'ll Value {
-        assert_eq!(abi::FAT_PTR_ADDR, 0);
-        assert_eq!(abi::FAT_PTR_EXTRA, 1);
-        self.const_struct(&[ptr, meta], false)
-    }
-
     pub fn const_array(&self, ty: &'ll Type, elts: &[&'ll Value]) -> &'ll Value {
         unsafe {
             return llvm::LLVMConstArray(ty, elts.as_ptr(), elts.len() as c_uint);
@@ -150,13 +139,6 @@ impl CodegenCx<'ll, 'tcx> {
         }
     }
 
-    pub fn const_str_slice(&self, s: Symbol) -> &'ll Value {
-        let len = s.as_str().len();
-        let cs = consts::ptrcast(self.const_cstr(s, false),
-            self.type_ptr_to(self.layout_of(self.tcx.mk_str()).llvm_type(self)));
-        self.const_fat_ptr(cs, self.const_usize(len as u64))
-    }
-
     pub fn const_get_elt(&self, v: &'ll Value, idx: u64) -> &'ll Value {
         unsafe {
             assert_eq!(idx as c_uint as u64, idx);
@@ -237,6 +219,13 @@ impl ConstMethods<'tcx> for CodegenCx<'ll, 'tcx> {
         unsafe { llvm::LLVMConstReal(t, val) }
     }
 
+    fn const_str(&self, s: Symbol) -> (&'ll Value, &'ll Value) {
+        let len = s.as_str().len();
+        let cs = consts::ptrcast(self.const_cstr(s, false),
+            self.type_ptr_to(self.layout_of(self.tcx.mk_str()).llvm_type(self)));
+        (cs, self.const_usize(len as u64))
+    }
+
     fn const_struct(
         &self,
         elts: &[&'ll Value],