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Reexport likely/unlikely in std::hint
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5 files changed

+225
-2
lines changed

5 files changed

+225
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lines changed

‎library/core/src/hint.rs

+62
Original file line numberDiff line numberDiff line change
@@ -511,3 +511,65 @@ pub const fn black_box<T>(dummy: T) -> T {
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pub const fn must_use<T>(value: T) -> T {
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value
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}
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/// Hints to the compiler that branch condition is likely to be true.
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/// Returns the value passed to it.
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///
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/// It can be used with `if` or boolean `match` expressions.
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///
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/// # Examples
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///
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/// ```
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/// #![feature(likely_unlikely)]
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/// use core::hint::likely;
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///
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/// fn foo(x: i32) {
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/// if likely(x > 0) {
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/// println!("this branch is likely to be taken");
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/// } else {
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/// println!("this branch is unlikely to be taken");
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/// }
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///
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/// match likely(x > 0) {
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/// true => println!("this branch is likely to be taken"),
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/// false => println!("this branch is unlikely to be taken"),
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/// }
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/// }
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/// ```
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#[unstable(feature = "likely_unlikely", issue = "26179")]
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#[rustc_nounwind]
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#[inline(always)]
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pub const fn likely(b: bool) -> bool {
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crate::intrinsics::likely(b)
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}
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/// Hints to the compiler that the branch condition is unlikely to be true.
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/// Returns the value passed to it.
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///
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/// It can be used with `if` or boolean `match` expressions.
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///
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/// # Examples
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///
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/// ```
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/// #![feature(likely_unlikely)]
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/// use core::hint::unlikely;
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///
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/// fn foo(x: i32) {
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/// if unlikely(x > 0) {
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/// println!("this branch is unlikely to be taken");
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/// } else {
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/// println!("this branch is likely to be taken");
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/// }
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///
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/// match unlikely(x > 0) {
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/// true => println!("this branch is unlikely to be taken"),
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/// false => println!("this branch is likely to be taken"),
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/// }
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/// }
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/// ```
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#[unstable(feature = "likely_unlikely", issue = "26179")]
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#[rustc_nounwind]
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#[inline(always)]
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pub const fn unlikely(b: bool) -> bool {
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crate::intrinsics::unlikely(b)
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}

‎tests/codegen/hint/likely.rs

+81
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,81 @@
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//@ compile-flags: -O
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#![crate_type = "lib"]
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#![feature(likely_unlikely)]
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use std::hint::likely;
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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 likely(x) {
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path_a();
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} else {
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path_b();
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}
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}
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#[no_mangle]
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pub fn test2(x: i32) {
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match likely(x > 0) {
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true => path_a(),
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false => path_b(),
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}
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}
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#[no_mangle]
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pub fn test3(x: i8) {
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match likely(x < 7) {
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true => path_a(),
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_ => path_b(),
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}
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}
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#[no_mangle]
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pub fn test4(x: u64) {
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match likely(x != 33) {
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false => path_a(),
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_ => path_b(),
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}
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}
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// CHECK-LABEL: @test1(
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// CHECK: br i1 %x, label %bb2, label %bb3, !prof ![[NUM:[0-9]+]]
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// CHECK: bb3:
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// CHECK: path_b
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// CHECK: bb2:
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// CHECK: path_a
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// CHECK-LABEL: @test2(
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// CHECK: br i1 %_2, label %bb2, label %bb3, !prof ![[NUM]]
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// CHECK: bb3:
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// CHECK: path_b
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// CHECK: bb2:
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// CHECK: path_a
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// CHECK-LABEL: @test3(
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// CHECK: br i1 %_2, label %bb2, label %bb3, !prof ![[NUM]]
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// CHECK: bb3:
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// CHECK: path_b
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// CHECK: bb2:
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// CHECK: path_a
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// CHECK-LABEL: @test4(
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// CHECK: br i1 %0, label %bb3, label %bb2, !prof ![[NUM2:[0-9]+]]
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// CHECK: bb3:
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// CHECK: path_a
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// CHECK: bb2:
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// CHECK: path_b
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// CHECK: ![[NUM]] = !{!"branch_weights", {{(!"expected", )?}}i32 2000, i32 1}
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// CHECK: ![[NUM2]] = !{!"branch_weights", {{(!"expected", )?}}i32 1, i32 2000}

‎tests/codegen/hint/unlikely.rs

+80
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,80 @@
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//@ compile-flags: -O
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#![crate_type = "lib"]
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#![feature(likely_unlikely)]
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use std::hint::unlikely;
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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 unlikely(x) {
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path_a();
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} else {
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path_b();
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}
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}
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#[no_mangle]
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pub fn test2(x: i32) {
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match unlikely(x > 0) {
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true => path_a(),
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false => path_b(),
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}
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}
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#[no_mangle]
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pub fn test3(x: i8) {
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match unlikely(x < 7) {
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true => path_a(),
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_ => path_b(),
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}
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}
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#[no_mangle]
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pub fn test4(x: u64) {
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match unlikely(x != 33) {
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false => path_a(),
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_ => path_b(),
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}
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}
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// CHECK-LABEL: @test1(
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// CHECK: br i1 %x, label %bb2, label %bb4, !prof ![[NUM:[0-9]+]]
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// CHECK: bb4:
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// CHECK: path_b
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// CHECK: bb2:
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// CHECK: path_a
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// CHECK-LABEL: @test2(
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// CHECK: br i1 %_2, label %bb2, label %bb4, !prof ![[NUM]]
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// CHECK: bb4:
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// CHECK: path_b
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// CHECK: bb2:
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// CHECK: path_a
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// CHECK-LABEL: @test3(
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// CHECK: br i1 %_2, label %bb2, label %bb4, !prof ![[NUM]]
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// CHECK: bb4:
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// CHECK: path_b
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// CHECK: bb2:
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// CHECK: path_a
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// CHECK-LABEL: @test4(
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// CHECK: br i1 %0, label %bb4, label %bb2, !prof ![[NUM2:[0-9]+]]
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// CHECK: bb4:
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// CHECK: path_a
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// CHECK: bb2:
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// CHECK: path_b
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// CHECK: ![[NUM]] = !{!"branch_weights", {{(!"expected", )?}}i32 1, i32 2000}

‎tests/mir-opt/pre-codegen/checked_ops.step_forward.PreCodegen.after.panic-abort.mir

+1-1
Original file line numberDiff line numberDiff line change
@@ -13,7 +13,7 @@ fn step_forward(_1: u16, _2: usize) -> u16 {
1313
scope 6 (inlined core::num::<impl u16>::checked_add) {
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let mut _5: (u16, bool);
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let mut _6: bool;
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scope 7 (inlined unlikely) {
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scope 7 (inlined std::intrinsics::unlikely) {
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let _7: ();
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}
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}

‎tests/mir-opt/pre-codegen/checked_ops.step_forward.PreCodegen.after.panic-unwind.mir

+1-1
Original file line numberDiff line numberDiff line change
@@ -13,7 +13,7 @@ fn step_forward(_1: u16, _2: usize) -> u16 {
1313
scope 6 (inlined core::num::<impl u16>::checked_add) {
1414
let mut _5: (u16, bool);
1515
let mut _6: bool;
16-
scope 7 (inlined unlikely) {
16+
scope 7 (inlined std::intrinsics::unlikely) {
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let _7: ();
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}
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}

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