Remove exchange_malloc lang item.

Author: cjgillot

compiler/rustc_codegen_cranelift/example/mini_core.rs

@@ -619,11 +619,6 @@ impl<T: ?Sized> Deref for Box<T> {
     }
 }
 
-#[lang = "exchange_malloc"]
-unsafe fn allocate(size: usize, _align: usize) -> *mut u8 {
-    libc::malloc(size)
-}
-
 #[lang = "drop"]
 pub trait Drop {
     fn drop(&mut self);

compiler/rustc_codegen_gcc/example/mini_core.rs

@@ -628,11 +628,6 @@ impl<T: ?Sized, A: Allocator> Deref for Box<T, A> {
     }
 }
 
-#[lang = "exchange_malloc"]
-unsafe fn allocate(size: usize, _align: usize) -> *mut u8 {
-    libc::malloc(size)
-}
-
 #[lang = "drop"]
 pub trait Drop {
     fn drop(&mut self);

compiler/rustc_const_eval/src/check_consts/check.rs

@@ -852,9 +852,7 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
                 }
 
                 // This can be called on stable via the `vec!` macro.
-                if tcx.is_lang_item(callee, LangItem::ExchangeMalloc)
-                    || tcx.is_diagnostic_item(sym::box_new, callee)
-                {
+                if tcx.is_diagnostic_item(sym::box_new, callee) {
                     self.check_op(ops::HeapAllocation);
                     // Allow this call, skip all the checks below.
                     return;

compiler/rustc_hir/src/lang_items.rs

@@ -330,7 +330,6 @@ language_item_table! {
     FormatPlaceholder,       sym::format_placeholder,  format_placeholder,         Target::Struct,         GenericRequirement::None;
     FormatUnsafeArg,         sym::format_unsafe_arg,   format_unsafe_arg,          Target::Struct,         GenericRequirement::None;
 
-    ExchangeMalloc,          sym::exchange_malloc,     exchange_malloc_fn,         Target::Fn,             GenericRequirement::None;
     DropInPlace,             sym::drop_in_place,       drop_in_place_fn,           Target::Fn,             GenericRequirement::Minimum(1);
     AllocLayout,             sym::alloc_layout,        alloc_layout,               Target::Struct,         GenericRequirement::None;
 

compiler/rustc_span/src/symbol.rs

@@ -944,7 +944,6 @@ symbols! {
         exact_div,
         except,
         exception_handling: "exception-handling",
-        exchange_malloc,
         exclusive_range_pattern,
         exhaustive_integer_patterns,
         exhaustive_patterns,

library/alloc/src/alloc.rs

@@ -342,19 +342,6 @@ unsafe impl Allocator for Global {
     }
 }
 
-/// The allocator for `Box`.
-#[cfg(not(no_global_oom_handling))]
-#[lang = "exchange_malloc"]
-#[inline]
-#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
-unsafe fn exchange_malloc(size: usize, align: usize) -> *mut u8 {
-    let layout = unsafe { Layout::from_size_align_unchecked(size, align) };
-    match Global.allocate(layout) {
-        Ok(ptr) => ptr.as_mut_ptr(),
-        Err(_) => handle_alloc_error(layout),
-    }
-}
-
 // # Allocation error handler
 
 #[cfg(not(no_global_oom_handling))]

src/doc/rustc-dev-guide/src/lang-items.md

@@ -23,8 +23,8 @@ Features provided by lang items include:
   `core::marker`; lang item `phantom_data`.
 
 Lang items are loaded lazily by the compiler; e.g. if one never uses `Box`
-then there is no need to define functions for `exchange_malloc` and
-`box_free`. `rustc` will emit an error when an item is needed but not found
+then there is no need to define struct `global_alloc_ty`.
+`rustc` will emit an error when an item is needed but not found
 in the current crate or any that it depends on.
 
 Most lang items are defined by the `core` library, but if you're trying to build an