mirror of
https://github.com/rust-lang/rust
synced 2024-10-02 14:54:35 +00:00
645c0fddd2
Previously, it was only put on scalars with range validity invariants like bool, was uninit was obviously invalid for those. Since then, we have normatively declared all uninit primitives to be undefined behavior and can therefore put `noundef` on them. The remaining concern was the `mem::uninitialized` function, which cause quite a lot of UB in the older parts of the ecosystem. This function now doesn't return uninit values anymore, making users of it safe from this change. The only real sources of UB where people could encounter uninit primitives are `MaybeUninit::uninit().assume_init()`, which has always be clear in the docs about being UB and from heap allocations (like reading from the spare capacity of a vec. This is hopefully rare enough to not break anything.
34 lines
1.2 KiB
Rust
34 lines
1.2 KiB
Rust
// compile-flags: -O
|
|
// min-llvm-version: 15.0
|
|
#![crate_type = "lib"]
|
|
|
|
use std::mem::MaybeUninit;
|
|
|
|
// Boxing a `MaybeUninit` value should not copy junk from the stack
|
|
#[no_mangle]
|
|
pub fn box_uninitialized() -> Box<MaybeUninit<usize>> {
|
|
// CHECK-LABEL: @box_uninitialized
|
|
// CHECK-NOT: store
|
|
// CHECK-NOT: alloca
|
|
// CHECK-NOT: memcpy
|
|
// CHECK-NOT: memset
|
|
Box::new(MaybeUninit::uninit())
|
|
}
|
|
|
|
// https://github.com/rust-lang/rust/issues/58201
|
|
#[no_mangle]
|
|
pub fn box_uninitialized2() -> Box<MaybeUninit<[usize; 1024 * 1024]>> {
|
|
// CHECK-LABEL: @box_uninitialized2
|
|
// CHECK-NOT: store
|
|
// CHECK-NOT: alloca
|
|
// CHECK-NOT: memcpy
|
|
// CHECK-NOT: memset
|
|
Box::new(MaybeUninit::uninit())
|
|
}
|
|
|
|
// Hide the `allocalign` attribute in the declaration of __rust_alloc
|
|
// from the CHECK-NOT above, and also verify the attributes got set reasonably.
|
|
// CHECK: declare noalias noundef ptr @__rust_alloc(i{{[0-9]+}} noundef, i{{[0-9]+}} allocalign noundef) unnamed_addr [[RUST_ALLOC_ATTRS:#[0-9]+]]
|
|
|
|
// CHECK-DAG: attributes [[RUST_ALLOC_ATTRS]] = { {{.*}} allockind("alloc,uninitialized,aligned") allocsize(0) uwtable "alloc-family"="__rust_alloc" {{.*}} }
|