a0215d8e46
Fundamentally, we have *three* disjoint categories of functions: 1. const-stable functions 2. private/unstable functions that are meant to be callable from const-stable functions 3. functions that can make use of unstable const features This PR implements the following system: - `#[rustc_const_stable]` puts functions in the first category. It may only be applied to `#[stable]` functions. - `#[rustc_const_unstable]` by default puts functions in the third category. The new attribute `#[rustc_const_stable_indirect]` can be added to such a function to move it into the second category. - `const fn` without a const stability marker are in the second category if they are still unstable. They automatically inherit the feature gate for regular calls, it can now also be used for const-calls. Also, several holes in recursive const stability checking are being closed. There's still one potential hole that is hard to avoid, which is when MIR building automatically inserts calls to a particular function in stable functions -- which happens in the panic machinery. Those need to *not* be `rustc_const_unstable` (or manually get a `rustc_const_stable_indirect`) to be sure they follow recursive const stability. But that's a fairly rare and special case so IMO it's fine. The net effect of this is that a `#[unstable]` or unmarked function can be constified simply by marking it as `const fn`, and it will then be const-callable from stable `const fn` and subject to recursive const stability requirements. If it is publicly reachable (which implies it cannot be unmarked), it will be const-unstable under the same feature gate. Only if the function ever becomes `#[stable]` does it need a `#[rustc_const_unstable]` or `#[rustc_const_stable]` marker to decide if this should also imply const-stability. Adding `#[rustc_const_unstable]` is only needed for (a) functions that need to use unstable const lang features (including intrinsics), or (b) `#[stable]` functions that are not yet intended to be const-stable. Adding `#[rustc_const_stable]` is only needed for functions that are actually meant to be directly callable from stable const code. `#[rustc_const_stable_indirect]` is used to mark intrinsics as const-callable and for `#[rustc_const_unstable]` functions that are actually called from other, exposed-on-stable `const fn`. No other attributes are required.
57 lines
2.1 KiB
Rust
57 lines
2.1 KiB
Rust
#![stable(feature = "dummy", since = "1.0.0")]
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// ignore-tidy-linelength
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#![feature(intrinsics, staged_api)]
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use std::mem;
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extern "rust-intrinsic" {
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#[stable(feature = "dummy", since = "1.0.0")]
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#[rustc_const_stable(feature = "const_intrinsic_copy", since = "1.63.0")]
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fn copy_nonoverlapping<T>(src: *const T, dst: *mut T, count: usize);
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#[stable(feature = "dummy", since = "1.0.0")]
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#[rustc_const_stable(feature = "const_intrinsic_copy", since = "1.63.0")]
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fn copy<T>(src: *const T, dst: *mut T, count: usize);
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}
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const COPY_ZERO: () = unsafe {
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// Since we are not copying anything, this should be allowed.
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let src = ();
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let mut dst = ();
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copy_nonoverlapping(&src as *const _ as *const u8, &mut dst as *mut _ as *mut u8, 0);
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};
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const COPY_OOB_1: () = unsafe {
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let mut x = 0i32;
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let dangle = (&mut x as *mut i32).wrapping_add(10);
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// Zero-sized copy is fine.
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copy_nonoverlapping(0x100 as *const i32, dangle, 0);
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// Non-zero-sized copy is not.
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copy_nonoverlapping(0x100 as *const i32, dangle, 1); //~ ERROR evaluation of constant value failed [E0080]
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//~| got 0x100[noalloc] which is a dangling pointer
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};
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const COPY_OOB_2: () = unsafe {
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let x = 0i32;
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let dangle = (&x as *const i32).wrapping_add(10);
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// Zero-sized copy is fine.
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copy_nonoverlapping(dangle, 0x100 as *mut i32, 0);
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// Non-zero-sized copy is not.
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copy_nonoverlapping(dangle, 0x100 as *mut i32, 1); //~ ERROR evaluation of constant value failed [E0080]
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//~| +0x28 which is at or beyond the end of the allocation
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};
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const COPY_SIZE_OVERFLOW: () = unsafe {
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let x = 0;
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let mut y = 0;
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copy(&x, &mut y, 1usize << (mem::size_of::<usize>() * 8 - 1)); //~ ERROR evaluation of constant value failed [E0080]
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//~| overflow computing total size of `copy`
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};
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const COPY_NONOVERLAPPING_SIZE_OVERFLOW: () = unsafe {
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let x = 0;
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let mut y = 0;
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copy_nonoverlapping(&x, &mut y, 1usize << (mem::size_of::<usize>() * 8 - 1)); //~ evaluation of constant value failed [E0080]
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//~| overflow computing total size of `copy_nonoverlapping`
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};
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fn main() {
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}
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