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Rollup merge of #123089 - Philippe-Cholet:vecdeque_pop_assume_cap, r=Nilstrieb

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

Similar to #114370 for VecDeque instead of Vec.

I initially come from https://github.com/rust-itertools/itertools/pull/899 where we noticed that `pop_front;push_back;` was slower than expected so `@scottmcm` suggested I file an issue which lead to https://internals.rust-lang.org/t/vecdeque-pop-front-push-back/20483 where **kornel** mentionned #114334 (fixed by #114370).

This is my first time with codegen tests, I based the test on what was done for Vec.
This commit is contained in:
Matthias Krüger 2024-04-08 14:31:11 +02:00 • committed by GitHub
commit 17c94b5f12
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2 changed files with 75 additions and 2 deletions
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10
library/alloc/src/collections/vec_deque/mod.rs
View file

@ -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))
}
}
}
@ -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)))
}
}
}

67
tests/codegen/vecdeque_pop_push.rs Normal file
View file

@ -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>) {
// 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);
}