Auto merge of #120050 - scottmcm:vec-resize-memset, r= · rust-lang/rust@f5c3755 (original) (raw)
`@@ -145,6 +145,12 @@ use self::spec_extend::SpecExtend;
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`#[cfg(not(no_global_oom_handling))]
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`mod spec_extend;
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``
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#[cfg(not(no_global_oom_handling))]
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use self::spec_extend_elem::SpecExtendElem;
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#[cfg(not(no_global_oom_handling))]
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mod spec_extend_elem;
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`` /// A contiguous growable array type, written as Vec<T>, short for 'vector'.
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`///
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`/// # Examples
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`@@ -2871,7 +2877,7 @@ impl<T: Clone, A: Allocator> Vec<T, A> {
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`let len = self.len();
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`if new_len > len {
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self.extend_with(new_len - len, value)
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self.extend_elem(new_len - len, value)
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`} else {
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`self.truncate(new_len);
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`}
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`@@ -2985,32 +2991,38 @@ impl<T, A: Allocator, const N: usize> Vec<[T; N], A> {
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`impl<T: Clone, A: Allocator> Vec<T, A> {
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`#[cfg(not(no_global_oom_handling))]
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/// Extend the vector by n clones of value.
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fn extend_with(&mut self, n: usize, value: T) {
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#[inline]
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/// Extend the vector by n clones of value.
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///
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/// Uses specialization to dispatch to extend_elem_copy if possible.
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fn extend_elem(&mut self, n: usize, value: T) {
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self.spec_extend_elem(n, value);
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}
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#[cfg(not(no_global_oom_handling))]
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#[inline]
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/// Extend the vector by n copies of value.
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fn extend_elem_copy(&mut self, n: usize, value: T)
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where
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T: Copy,
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{
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`self.reserve(n);
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// SAFETY: We now have space for all the elements, so the pointer math
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// is all in-bounds. Because T: Copy, there's no user code being run
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// here (no clone nor any drop in the assignment).
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`unsafe {
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let mut ptr = self.as_mut_ptr().add(self.len());
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// Use SetLenOnDrop to work around bug where compiler
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// might not realize the store through ptr through self.set_len()
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// don't alias.
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let mut local_len = SetLenOnDrop::new(&mut self.len);
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// Write all elements except the last one
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for _ in 1..n {
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ptr::write(ptr, value.clone());
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ptr = ptr.add(1);
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// Increment the length in every step in case clone() panics
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local_len.increment_len(1);
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}
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if n > 0 {
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// We can write the last element directly without cloning needlessly
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ptr::write(ptr, value);
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local_len.increment_len(1);
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// Because there's no user code being run here, we can skip it for ZSTs.
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// That helps tests in debug mode that do things like vec![(); HUGE].
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// See https://github.com/rust-lang/rust/pull/118094
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if !T::IS_ZST {
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let ptr = self.as_mut_ptr().add(self.len);
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for i in 0..n {
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*ptr.add(i) = value;
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}
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`}
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`-
// len set by scope guard
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self.len += n;
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`}
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`}
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`}
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