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Add invariant to Vec::pop that len < cap if pop successful #114370

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merged 1 commit into from
Oct 16, 2023
Merged

Add invariant to Vec::pop that len < cap if pop successful #114370

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1 change: 1 addition & 0 deletions library/alloc/src/vec/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1956,6 +1956,7 @@ impl<T, A: Allocator> Vec<T, A> {
} else {
unsafe {
self.len -= 1;
core::intrinsics::assume(self.len < self.capacity());
Some(ptr::read(self.as_ptr().add(self.len())))
}
}
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24 changes: 24 additions & 0 deletions tests/codegen/vec_pop_push_noop.rs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,24 @@
// compile-flags: -O

#![crate_type = "lib"]

#[no_mangle]
// CHECK-LABEL: @noop(
pub fn noop(v: &mut Vec<u8>) {
// CHECK-NOT: reserve_for_push
// CHECK-NOT: call
// CHECK: tail call void @llvm.assume
// CHECK-NOT: reserve_for_push
// CHECK-NOT: call
// CHECK: ret
if let Some(x) = v.pop() {
v.push(x)
}
}

#[no_mangle]
// CHECK-LABEL: @push_byte(
pub fn push_byte(v: &mut Vec<u8>) {
// CHECK: call {{.*}}reserve_for_push
v.push(3);
}
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