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Kevin Reid
f700fdc001
Adds internal `vec::IntoIter::forget_remaining_elements_and_dealloc()`, which is used by `fold()` and `spec_extend()`, when those operations complete, to forget the zero remaining elements and only deallocate the allocation, ensuring that there will never be a useless loop to drop zero remaining elements when the iterator is dropped.
68 lines
2.0 KiB
Rust
68 lines
2.0 KiB
Rust
//@ compile-flags: -Copt-level=3
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// Test that we can avoid generating an element dropping loop when `vec::IntoIter` is consumed.
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#![crate_type = "lib"]
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use std::vec;
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struct Bomb;
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impl Drop for Bomb {
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#[inline]
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fn drop(&mut self) {
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panic!("dropped")
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}
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}
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/// Test case originally from https://users.rust-lang.org/t/unnecessary-drop-in-place-emitted-for-a-fully-consumed-intoiter/135119
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///
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/// What we are looking for is that there should be no calls to `impl Drop for Bomb`
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/// because every element is unconditionally forgotten.
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//
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// CHECK-LABEL: @vec_for_each_doesnt_drop
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#[no_mangle]
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pub fn vec_for_each_doesnt_drop(v: vec::Vec<(usize, Option<Bomb>)>) -> usize {
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// CHECK-NOT: panic
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// CHECK-NOT: drop_in_place
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// CHECK-NOT: Bomb$u20$as$u20$core..ops..drop..Drop
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let mut last = 0;
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v.into_iter().for_each(|(x, bomb)| {
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last = x;
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std::mem::forget(bomb);
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});
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last
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}
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/// Test that does *not* get the above optimization we are expecting:
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/// it uses a normal `for` loop which calls `Iterator::next()` and then drops the iterator,
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/// and dropping the iterator drops remaining items.
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///
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/// This test exists to prove that the above CHECK-NOT is looking for the right things.
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/// However, it might start failing if LLVM figures out that there are no remaining items.
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//
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// CHECK-LABEL: @vec_for_loop
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#[no_mangle]
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pub fn vec_for_loop(v: vec::Vec<(usize, Option<Bomb>)>) -> usize {
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// CHECK: drop_in_place
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let mut last = 0;
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for (x, bomb) in v {
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last = x;
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std::mem::forget(bomb);
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}
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last
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}
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/// Test where there still should be drops because there are no forgets.
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///
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/// This test exists to prove that the above CHECK-NOT is looking for the right things
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/// and does not say anything interesting about codegen itself.
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//
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// CHECK-LABEL: @vec_for_each_does_drop
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#[no_mangle]
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pub fn vec_for_each_does_drop(v: vec::Vec<(usize, Option<Bomb>)>) -> usize {
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// CHECK: begin_panic
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let mut last = 0;
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v.into_iter().for_each(|(x, bomb)| {
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last = x;
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});
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last
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}
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