2e365985be
`cold_path` has been around unstably for a while and is a rather useful
tool to have. It does what it is supposed to and there are no known
remaining issues, so stabilize it here (including const).
Newly stable API:
// in core::hint
pub const fn cold_path();
I have opted to exclude `likely` and `unlikely` for now since they have
had some concerns about ease of use that `cold_path` doesn't suffer
from. `cold_path` is also significantly more flexible; in addition to
working with boolean `if` conditions, it can be used in `match` arms,
`if let`, closures, and other control flow blocks. `likely` and
`unlikely` are also possible to implement in user code via `cold_path`,
if desired.
53 lines
956 B
Rust
53 lines
956 B
Rust
//@ compile-flags: -Copt-level=3
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#![crate_type = "lib"]
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use std::hint::cold_path;
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#[inline(never)]
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#[no_mangle]
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pub fn path_a() {
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println!("path a");
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}
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#[inline(never)]
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#[no_mangle]
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pub fn path_b() {
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println!("path b");
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}
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#[no_mangle]
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pub fn test1(x: bool) {
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if x {
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path_a();
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} else {
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cold_path();
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path_b();
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}
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// CHECK-LABEL: @test1(
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// CHECK: br i1 %x, label %bb1, label %bb2, !prof ![[NUM:[0-9]+]]
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// CHECK: bb2:
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// CHECK: path_b
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// CHECK: bb1:
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// CHECK: path_a
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}
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#[no_mangle]
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pub fn test2(x: i32) {
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match x > 0 {
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true => path_a(),
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false => {
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cold_path();
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path_b()
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}
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}
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// CHECK-LABEL: @test2(
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// CHECK: br i1 %_2, label %bb2, label %bb1, !prof ![[NUM]]
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// CHECK: bb1:
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// CHECK: path_b
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// CHECK: bb2:
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// CHECK: path_a
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}
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// CHECK: ![[NUM]] = !{!"branch_weights", {{(!"expected", )?}}i32 2000, i32 1}
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