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Auto merge of #31761 - Amanieu:volatile, r=alexcrichton
Tracking issue: #31756 RFC: rust-lang/rfcs#1467 I've made these unstable for now. Should they be stabilized straight away since we've had plenty of experience with people using the unstable intrinsics?
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a2fb48e9f7
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@ -161,6 +161,54 @@ pub unsafe fn write<T>(dst: *mut T, src: T) {
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intrinsics::move_val_init(&mut *dst, src)
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intrinsics::move_val_init(&mut *dst, src)
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}
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}
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/// Performs a volatile read of the value from `src` without moving it. This
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/// leaves the memory in `src` unchanged.
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///
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/// Volatile operations are intended to act on I/O memory, and are guaranteed
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/// to not be elided or reordered by the compiler across other volatile
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/// operations. See the LLVM documentation on [[volatile]].
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///
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/// [volatile]: http://llvm.org/docs/LangRef.html#volatile-memory-accesses
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///
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/// # Safety
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///
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/// Beyond accepting a raw pointer, this is unsafe because it semantically
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/// moves the value out of `src` without preventing further usage of `src`.
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/// If `T` is not `Copy`, then care must be taken to ensure that the value at
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/// `src` is not used before the data is overwritten again (e.g. with `write`,
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/// `zero_memory`, or `copy_memory`). Note that `*src = foo` counts as a use
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/// because it will attempt to drop the value previously at `*src`.
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#[inline]
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#[unstable(feature = "volatile", reason = "recently added", issue = "31756")]
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pub unsafe fn read_volatile<T>(src: *const T) -> T {
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intrinsics::volatile_load(src)
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}
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/// Performs a volatile write of a memory location with the given value without
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/// reading or dropping the old value.
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///
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/// Volatile operations are intended to act on I/O memory, and are guaranteed
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/// to not be elided or reordered by the compiler across other volatile
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/// operations. See the LLVM documentation on [[volatile]].
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///
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/// [volatile]: http://llvm.org/docs/LangRef.html#volatile-memory-accesses
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///
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/// # Safety
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///
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/// This operation is marked unsafe because it accepts a raw pointer.
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///
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/// It does not drop the contents of `dst`. This is safe, but it could leak
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/// allocations or resources, so care must be taken not to overwrite an object
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/// that should be dropped.
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///
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/// This is appropriate for initializing uninitialized memory, or overwriting
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/// memory that has previously been `read` from.
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#[inline]
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#[unstable(feature = "volatile", reason = "recently added", issue = "31756")]
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pub unsafe fn write_volatile<T>(dst: *mut T, src: T) {
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intrinsics::volatile_store(dst, src);
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}
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#[lang = "const_ptr"]
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#[lang = "const_ptr"]
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impl<T: ?Sized> *const T {
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impl<T: ?Sized> *const T {
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/// Returns true if the pointer is null.
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/// Returns true if the pointer is null.
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@ -8,9 +8,10 @@
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// option. This file may not be copied, modified, or distributed
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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// except according to those terms.
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#![feature(core_intrinsics)]
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#![feature(core_intrinsics, volatile)]
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use std::intrinsics::{volatile_load, volatile_store};
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use std::intrinsics::{volatile_load, volatile_store};
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use std::ptr::{read_volatile, write_volatile};
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pub fn main() {
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pub fn main() {
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unsafe {
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unsafe {
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@ -18,4 +19,9 @@ pub fn main() {
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volatile_store(&mut i, 2);
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volatile_store(&mut i, 2);
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assert_eq!(volatile_load(&i), 2);
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assert_eq!(volatile_load(&i), 2);
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}
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}
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unsafe {
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let mut i : isize = 1;
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write_volatile(&mut i, 2);
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assert_eq!(read_volatile(&i), 2);
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}
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}
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}
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