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3b022d8cee
improve cold_path() #120370 added a new instrinsic `cold_path()` and used it to fix `likely` and `unlikely` However, in order to limit scope, the information about cold code paths is only used in 2-target switch instructions. This is sufficient for `likely` and `unlikely`, but limits usefulness of `cold_path` for idiomatic rust. For example, code like this: ``` if let Some(x) = y { ... } ``` may generate 3-target switch: ``` switch y.discriminator: 0 => true branch 1 = > false branch _ => unreachable ``` and therefore marking a branch as cold will have no effect. This PR improves `cold_path()` to work with arbitrary switch instructions. Note that for 2-target switches, we can use `llvm.expect`, but for multiple targets we need to manually emit branch weights. I checked Clang and it also emits weights in this situation. The Clang's weight calculation is more complex that this PR, which I believe is mainly because `switch` in `C/C++` can have multiple cases going to the same target. |
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| .. | ||
| aggregate-thin-pointer.rs | ||
| carrying_mul_add.rs | ||
| cold_path2.rs | ||
| cold_path3.rs | ||
| cold_path.rs | ||
| compare_bytes.rs | ||
| const_eval_select.rs | ||
| ctlz.rs | ||
| ctpop.rs | ||
| disjoint_bitor.rs | ||
| exact_div.rs | ||
| likely_assert.rs | ||
| likely.rs | ||
| mask.rs | ||
| nearby.rs | ||
| nontemporal.rs | ||
| offset_from.rs | ||
| offset.rs | ||
| prefetch.rs | ||
| ptr_metadata.rs | ||
| rotate_left.rs | ||
| rustc_intrinsic_must_be_overridden.rs | ||
| select_unpredictable.rs | ||
| three_way_compare.rs | ||
| transmute-niched.rs | ||
| transmute-x64.rs | ||
| transmute.rs | ||
| typed_swap.rs | ||
| unchecked_math.rs | ||
| unlikely.rs | ||
| volatile_order.rs | ||
| volatile.rs | ||