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rust/tests/codegen/option-as-slice.rs

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Move `Option::as_slice` to an always-sound implementation This approach depends on CSE to not have any branches or selects when the guessed offset is correct -- which it always will be right now -- but to also be *sound* (just less efficient) if the layout algorithms change such that the guess is incorrect.
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//@ compile-flags: -O -Z randomize-layout=no
Add `Option::as_slice`(`_mut`) This adds the following functions: * `Option<T>::as_slice(&self) -> &[T]` * `Option<T>::as_slice_mut(&mut self) -> &[T]` The `as_slice` and `as_slice_mut` functions benefit from an optimization that makes them completely branch-free. Note that the optimization's soundness hinges on the fact that either the niche optimization makes the offset of the `Some(_)` contents zero or the mempory layout of `Option<T>` is equal to that of `Option<MaybeUninit<T>>`.
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//@ only-x86_64
#![crate_type = "lib"]
extern crate core;
Use generic `NonZero` in tests.
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use core::num::NonZero;
Add `Option::as_slice`(`_mut`) This adds the following functions: * `Option<T>::as_slice(&self) -> &[T]` * `Option<T>::as_slice_mut(&mut self) -> &[T]` The `as_slice` and `as_slice_mut` functions benefit from an optimization that makes them completely branch-free. Note that the optimization's soundness hinges on the fact that either the niche optimization makes the offset of the `Some(_)` contents zero or the mempory layout of `Option<T>` is equal to that of `Option<MaybeUninit<T>>`.
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use core::option::Option;
// CHECK-LABEL: @u64_opt_as_slice
#[no_mangle]
pub fn u64_opt_as_slice(o: &Option<u64>) -> &[u64] {
// CHECK-NOT: select
Move `Option::as_slice` to an always-sound implementation This approach depends on CSE to not have any branches or selects when the guessed offset is correct -- which it always will be right now -- but to also be *sound* (just less efficient) if the layout algorithms change such that the guess is incorrect.
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// CHECK-NOT: br
// CHECK-NOT: switch
// CHECK-NOT: icmp
Add precondition checks to ptr::offset, ptr::add, ptr::sub
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// CHECK: %[[LEN:.+]] = load i64
// CHECK-SAME: !range ![[META_U64:[0-9]+]],
// CHECK-SAME: !noundef
Use Option's discriminant as its size hint
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// CHECK-NOT: select
// CHECK-NOT: br
// CHECK-NOT: switch
// CHECK-NOT: icmp
// CHECK: %[[T0:.+]] = insertvalue { ptr, i64 } poison, ptr %{{.+}}, 0
// CHECK-NEXT: %[[T1:.+]] = insertvalue { ptr, i64 } %[[T0]], i64 %[[LEN]], 1
// CHECK-NEXT: ret { ptr, i64 } %[[T1]]
Add `Option::as_slice`(`_mut`) This adds the following functions: * `Option<T>::as_slice(&self) -> &[T]` * `Option<T>::as_slice_mut(&mut self) -> &[T]` The `as_slice` and `as_slice_mut` functions benefit from an optimization that makes them completely branch-free. Note that the optimization's soundness hinges on the fact that either the niche optimization makes the offset of the `Some(_)` contents zero or the mempory layout of `Option<T>` is equal to that of `Option<MaybeUninit<T>>`.
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o.as_slice()
}
// CHECK-LABEL: @nonzero_u64_opt_as_slice
#[no_mangle]
Use generic `NonZero` in tests.
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pub fn nonzero_u64_opt_as_slice(o: &Option<NonZero<u64>>) -> &[NonZero<u64>] {
Add `Option::as_slice`(`_mut`) This adds the following functions: * `Option<T>::as_slice(&self) -> &[T]` * `Option<T>::as_slice_mut(&mut self) -> &[T]` The `as_slice` and `as_slice_mut` functions benefit from an optimization that makes them completely branch-free. Note that the optimization's soundness hinges on the fact that either the niche optimization makes the offset of the `Some(_)` contents zero or the mempory layout of `Option<T>` is equal to that of `Option<MaybeUninit<T>>`.
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// CHECK-NOT: select
Move `Option::as_slice` to an always-sound implementation This approach depends on CSE to not have any branches or selects when the guessed offset is correct -- which it always will be right now -- but to also be *sound* (just less efficient) if the layout algorithms change such that the guess is incorrect.
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// CHECK-NOT: br
// CHECK-NOT: switch
// CHECK-NOT: icmp
// CHECK: %[[NZ:.+]] = icmp ne i64 %{{.+}}, 0
Use Option's discriminant as its size hint
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// CHECK-NEXT: %[[LEN:.+]] = zext i1 %[[NZ]] to i64
Move `Option::as_slice` to an always-sound implementation This approach depends on CSE to not have any branches or selects when the guessed offset is correct -- which it always will be right now -- but to also be *sound* (just less efficient) if the layout algorithms change such that the guess is incorrect.
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// CHECK-NOT: select
// CHECK-NOT: br
// CHECK-NOT: switch
// CHECK-NOT: icmp
Use Option's discriminant as its size hint
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// CHECK: %[[T0:.+]] = insertvalue { ptr, i64 } poison, ptr %o, 0
// CHECK-NEXT: %[[T1:.+]] = insertvalue { ptr, i64 } %[[T0]], i64 %[[LEN]], 1
// CHECK-NEXT: ret { ptr, i64 } %[[T1]]
Add `Option::as_slice`(`_mut`) This adds the following functions: * `Option<T>::as_slice(&self) -> &[T]` * `Option<T>::as_slice_mut(&mut self) -> &[T]` The `as_slice` and `as_slice_mut` functions benefit from an optimization that makes them completely branch-free. Note that the optimization's soundness hinges on the fact that either the niche optimization makes the offset of the `Some(_)` contents zero or the mempory layout of `Option<T>` is equal to that of `Option<MaybeUninit<T>>`.
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o.as_slice()
}
Use Option's discriminant as its size hint
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// CHECK-LABEL: @u8_opt_as_slice
#[no_mangle]
pub fn u8_opt_as_slice(o: &Option<u8>) -> &[u8] {
// CHECK-NOT: select
// CHECK-NOT: br
// CHECK-NOT: switch
// CHECK-NOT: icmp
Add precondition checks to ptr::offset, ptr::add, ptr::sub
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// CHECK: %[[TAG:.+]] = load i8
// CHECK-SAME: !range ![[META_U8:[0-9]+]],
// CHECK-SAME: !noundef
Use Option's discriminant as its size hint
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// CHECK: %[[LEN:.+]] = zext{{.*}} i8 %[[TAG]] to i64
// CHECK-NOT: select
// CHECK-NOT: br
// CHECK-NOT: switch
// CHECK-NOT: icmp
// CHECK: %[[T0:.+]] = insertvalue { ptr, i64 } poison, ptr %{{.+}}, 0
// CHECK-NEXT: %[[T1:.+]] = insertvalue { ptr, i64 } %[[T0]], i64 %[[LEN]], 1
// CHECK-NEXT: ret { ptr, i64 } %[[T1]]
o.as_slice()
}
// CHECK: ![[META_U64]] = !{i64 0, i64 2}
// CHECK: ![[META_U8]] = !{i8 0, i8 2}
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