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Add attributes for #[global_allocator] functions #146766

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Merged
merged 1 commit into from
Sep 25, 2025
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Merged

Add attributes for #[global_allocator] functions #146766

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16 changes: 13 additions & 3 deletions compiler/rustc_builtin_macros/src/global_allocator.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -85,7 +85,7 @@ impl AllocFnFactory<'_, '_> {
body,
define_opaque: None,
}));
let item = self.cx.item(self.span, self.attrs(), kind);
let item = self.cx.item(self.span, self.attrs(method), kind);
self.cx.stmt_item(self.ty_span, item)
}

Expand All @@ -100,8 +100,18 @@ impl AllocFnFactory<'_, '_> {
self.cx.expr_call(self.ty_span, method, args)
}

fn attrs(&self) -> AttrVec {
thin_vec![self.cx.attr_word(sym::rustc_std_internal_symbol, self.span)]
fn attrs(&self, method: &AllocatorMethod) -> AttrVec {
let alloc_attr = match method.name {
sym::alloc => sym::rustc_allocator,
sym::dealloc => sym::rustc_deallocator,
sym::realloc => sym::rustc_reallocator,
sym::alloc_zeroed => sym::rustc_allocator_zeroed,
_ => unreachable!("Unknown allocator method!"),
};
thin_vec![
self.cx.attr_word(sym::rustc_std_internal_symbol, self.span),
self.cx.attr_word(alloc_attr, self.span)
]
}

fn arg_ty(&self, input: &AllocatorMethodInput, args: &mut ThinVec<Param>) -> Box<Expr> {
Expand Down
41 changes: 41 additions & 0 deletions tests/codegen-llvm/global-allocator-attributes.rs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,41 @@
//@ compile-flags: -C opt-level=3
#![crate_type = "lib"]

mod foobar {
use std::alloc::{GlobalAlloc, Layout};

struct Allocator;

unsafe impl GlobalAlloc for Allocator {
unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
// CHECK-LABEL: ; __rustc::__rust_alloc
// CHECK-NEXT: ; Function Attrs: {{.*}}allockind("alloc,uninitialized,aligned") allocsize(0){{.*}}
// CHECK-NEXT: define{{.*}} noalias{{.*}} ptr @{{.*}}__rust_alloc(i[[SIZE:[0-9]+]] {{.*}}%size, i[[SIZE]] allocalign{{.*}} %align)
panic!()
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How the the addition of the attribute change the behaviour here? I.e. what part of the checked stuff would have been missing?

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Basically all the attributes with alloc in the name (allockind, allocsize, allocalign, etc.) would be missing.

}

unsafe fn dealloc(&self, ptr: *mut u8, layout: Layout) {
// CHECK-LABEL: ; __rustc::__rust_dealloc
// CHECK-NEXT: ; Function Attrs: {{.*}}allockind("free"){{.*}}
// CHECK-NEXT: define{{.*}} void @{{.*}}__rust_dealloc(ptr allocptr{{.*}} %ptr, i[[SIZE]] {{.*}} %size, i[[SIZE]] {{.*}} %align)
panic!()
}

unsafe fn realloc(&self, ptr: *mut u8, layout: Layout, new_size: usize) -> *mut u8 {
// CHECK-LABEL: ; __rustc::__rust_realloc
// CHECK-NEXT: ; Function Attrs: {{.*}}allockind("realloc,aligned") allocsize(3){{.*}}
// CHECK-NEXT: define{{.*}} noalias{{.*}} ptr @{{.*}}__rust_realloc(ptr allocptr{{.*}} %ptr, i[[SIZE]] {{.*}} %size, i[[SIZE]] allocalign{{.*}} %align, i[[SIZE]] {{.*}} %new_size)
panic!()
}

unsafe fn alloc_zeroed(&self, layout: Layout) -> *mut u8 {
// CHECK-LABEL: ; __rustc::__rust_alloc_zeroed
// CHECK-NEXT: ; Function Attrs: {{.*}}allockind("alloc,zeroed,aligned") allocsize(0){{.*}}
// CHECK-NEXT: define{{.*}} noalias{{.*}} ptr @{{.*}}__rust_alloc_zeroed(i[[SIZE]] {{.*}} %size, i[[SIZE]] allocalign{{.*}} %align)
panic!()
}
}

#[global_allocator]
static GLOBAL: Allocator = Allocator;
}
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