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Auto merge of #128250 - Amanieu:select_unpredictable, r=nikic

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Add `select_unpredictable` to force LLVM to use CMOV

Since https://reviews.llvm.org/D118118, LLVM will no longer turn CMOVs into branches if it comes from a `select` marked with an `unpredictable` metadata attribute.

This PR introduces `core::intrinsics::select_unpredictable` which emits such a `select` and uses it in the implementation of `binary_search_by`.
This commit is contained in:
bors 2024-07-30 03:22:27 +00:00
commit 710ce90fbe
7 changed files with 107 additions and 1 deletions
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2
compiler/rustc_hir_analysis/src/check/intrinsic.rs
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@ -120,6 +120,7 @@ pub fn intrinsic_operation_unsafety(tcx: TyCtxt<'_>, intrinsic_id: LocalDefId) -
| sym::type_id
| sym::likely
| sym::unlikely
| sym::select_unpredictable
| sym::ptr_guaranteed_cmp
| sym::minnumf16
| sym::minnumf32
@ -488,6 +489,7 @@ pub fn check_intrinsic_type(
sym::assume => (0, 0, vec![tcx.types.bool], tcx.types.unit),
sym::likely => (0, 0, vec![tcx.types.bool], tcx.types.bool),
sym::unlikely => (0, 0, vec![tcx.types.bool], tcx.types.bool),
sym::select_unpredictable => (1, 0, vec![tcx.types.bool, param(0), param(0)], param(0)),
sym::read_via_copy => (1, 0, vec![Ty::new_imm_ptr(tcx, param(0))], param(0)),
sym::write_via_move => {