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Add invariant to VecDeque::pop_* that len < cap if pop successful #123089

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merged 1 commit into from
Apr 8, 2024
Merged

Add invariant to VecDeque::pop_* that len < cap if pop successful #123089

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10 changes: 8 additions & 2 deletions library/alloc/src/collections/vec_deque/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1614,7 +1614,10 @@ impl<T, A: Allocator> VecDeque<T, A> {
let old_head = self.head;
self.head = self.to_physical_idx(1);
self.len -= 1;
Some(unsafe { self.buffer_read(old_head) })
unsafe {
core::hint::assert_unchecked(self.len < self.capacity());
Some(self.buffer_read(old_head))
}
}
}

Expand All @@ -1638,7 +1641,10 @@ impl<T, A: Allocator> VecDeque<T, A> {
None
} else {
self.len -= 1;
Some(unsafe { self.buffer_read(self.to_physical_idx(self.len)) })
unsafe {
core::hint::assert_unchecked(self.len < self.capacity());
Some(self.buffer_read(self.to_physical_idx(self.len)))
}
}
}

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67 changes: 67 additions & 0 deletions tests/codegen/vecdeque_pop_push.rs
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@@ -0,0 +1,67 @@
//@ compile-flags: -O

#![crate_type = "lib"]

use std::collections::VecDeque;

#[no_mangle]
// CHECK-LABEL: @noop_back(
pub fn noop_back(v: &mut VecDeque<u8>) {
// CHECK-NOT: grow
// CHECK: tail call void @llvm.assume
// CHECK-NOT: grow
// CHECK: ret
if let Some(x) = v.pop_back() {
v.push_back(x);
}
}

#[no_mangle]
// CHECK-LABEL: @noop_front(
pub fn noop_front(v: &mut VecDeque<u8>) {
// CHECK-NOT: grow
// CHECK: tail call void @llvm.assume
// CHECK-NOT: grow
// CHECK: ret
if let Some(x) = v.pop_front() {
v.push_front(x);
}
}

#[no_mangle]
// CHECK-LABEL: @move_byte_front_to_back(
pub fn move_byte_front_to_back(v: &mut VecDeque<u8>) {
// CHECK-NOT: grow
// CHECK: tail call void @llvm.assume
// CHECK-NOT: grow
// CHECK: ret
if let Some(x) = v.pop_front() {
v.push_back(x);
}
}

#[no_mangle]
// CHECK-LABEL: @move_byte_back_to_front(
pub fn move_byte_back_to_front(v: &mut VecDeque<u8>) {
// CHECK-NOT: grow
// CHECK: tail call void @llvm.assume
// CHECK-NOT: grow
// CHECK: ret
if let Some(x) = v.pop_back() {
v.push_front(x);
}
}

#[no_mangle]
// CHECK-LABEL: @push_back_byte(
pub fn push_back_byte(v: &mut VecDeque<u8>) {
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thanks for including those tests btw, having the test to make sure the above tests are correct is super important!

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I merely mimicked the Vec version of this PR.
The 1st iteration was too much Vec-oriented.

// CHECK: call {{.*}}grow
v.push_back(3);
}

#[no_mangle]
// CHECK-LABEL: @push_front_byte(
pub fn push_front_byte(v: &mut VecDeque<u8>) {
// CHECK: call {{.*}}grow
v.push_front(3);
}
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