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Commit 17c94b5

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Rollup merge of #123089 - Philippe-Cholet:vecdeque_pop_assume_cap, r=Nilstrieb
Add invariant to VecDeque::pop_* that len < cap if pop successful Similar to #114370 for VecDeque instead of Vec. I initially come from rust-itertools/itertools#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.
2 parents 98fbf86 + 7a2678d commit 17c94b5

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lines changed

2 files changed

+75
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lines changed

‎library/alloc/src/collections/vec_deque/mod.rs‎

Lines changed: 8 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -1614,7 +1614,10 @@ impl<T, A: Allocator> VecDeque<T, A> {
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let old_head = self.head;
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self.head = self.to_physical_idx(1);
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self.len -= 1;
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Some(unsafe { self.buffer_read(old_head) })
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unsafe {
1618+
core::hint::assert_unchecked(self.len < self.capacity());
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Some(self.buffer_read(old_head))
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}
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}
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}
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@@ -1638,7 +1641,10 @@ impl<T, A: Allocator> VecDeque<T, A> {
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None
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} else {
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self.len -= 1;
1641-
Some(unsafe { self.buffer_read(self.to_physical_idx(self.len)) })
1644+
unsafe {
1645+
core::hint::assert_unchecked(self.len < self.capacity());
1646+
Some(self.buffer_read(self.to_physical_idx(self.len)))
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}
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}
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}
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‎tests/codegen/vecdeque_pop_push.rs‎

Lines changed: 67 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,67 @@
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//@ compile-flags: -O
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#![crate_type = "lib"]
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use std::collections::VecDeque;
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#[no_mangle]
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// CHECK-LABEL: @noop_back(
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pub fn noop_back(v: &mut VecDeque<u8>) {
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// CHECK-NOT: grow
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// CHECK: tail call void @llvm.assume
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// CHECK-NOT: grow
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// CHECK: ret
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if let Some(x) = v.pop_back() {
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v.push_back(x);
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}
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}
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#[no_mangle]
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// CHECK-LABEL: @noop_front(
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pub fn noop_front(v: &mut VecDeque<u8>) {
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// CHECK-NOT: grow
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// CHECK: tail call void @llvm.assume
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// CHECK-NOT: grow
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// CHECK: ret
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if let Some(x) = v.pop_front() {
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v.push_front(x);
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}
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}
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#[no_mangle]
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// CHECK-LABEL: @move_byte_front_to_back(
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pub fn move_byte_front_to_back(v: &mut VecDeque<u8>) {
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// CHECK-NOT: grow
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// CHECK: tail call void @llvm.assume
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// CHECK-NOT: grow
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// CHECK: ret
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if let Some(x) = v.pop_front() {
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v.push_back(x);
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}
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}
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#[no_mangle]
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// CHECK-LABEL: @move_byte_back_to_front(
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pub fn move_byte_back_to_front(v: &mut VecDeque<u8>) {
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// CHECK-NOT: grow
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// CHECK: tail call void @llvm.assume
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// CHECK-NOT: grow
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// CHECK: ret
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if let Some(x) = v.pop_back() {
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v.push_front(x);
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}
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}
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#[no_mangle]
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// CHECK-LABEL: @push_back_byte(
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pub fn push_back_byte(v: &mut VecDeque<u8>) {
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// CHECK: call {{.*}}grow
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v.push_back(3);
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}
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#[no_mangle]
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// CHECK-LABEL: @push_front_byte(
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pub fn push_front_byte(v: &mut VecDeque<u8>) {
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// CHECK: call {{.*}}grow
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v.push_front(3);
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}

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