From f43c02236d5c5bcf7c2cad98070ca9164cebfe54 Mon Sep 17 00:00:00 2001 From: Giacomo Stevanato Date: Sun, 24 Jan 2021 21:04:18 +0100 Subject: [PATCH 1/2] Instruct LLVM that binary_search_by returns a valid index --- library/core/src/slice/mod.rs | 2 ++ 1 file changed, 2 insertions(+) diff --git a/library/core/src/slice/mod.rs b/library/core/src/slice/mod.rs index 5510bb0257e34..0aaccaed41667 100644 --- a/library/core/src/slice/mod.rs +++ b/library/core/src/slice/mod.rs @@ -2204,6 +2204,8 @@ impl [T] { } else if cmp == Greater { right = mid; } else { + // SAFETY: same as the `get_unchecked` above + unsafe { crate::intrinsics::assume(mid < self.len()) }; return Ok(mid); } From c9d04c2b238dc5ab51bd8a92c41ba17bb5b00ed7 Mon Sep 17 00:00:00 2001 From: Giacomo Stevanato Date: Sun, 24 Jan 2021 21:07:25 +0100 Subject: [PATCH 2/2] Add codegen test checking binary_search allows eliding bound checks --- .../binary-search-index-no-bound-check.rs | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) create mode 100644 src/test/codegen/binary-search-index-no-bound-check.rs diff --git a/src/test/codegen/binary-search-index-no-bound-check.rs b/src/test/codegen/binary-search-index-no-bound-check.rs new file mode 100644 index 0000000000000..110d1d55626f1 --- /dev/null +++ b/src/test/codegen/binary-search-index-no-bound-check.rs @@ -0,0 +1,19 @@ +// min-llvm-version: 11.0.0 +// compile-flags: -O +// ignore-debug: the debug assertions get in the way +#![crate_type = "lib"] + +// Make sure no bounds checks are emitted when slicing or indexing +// with an index from `binary_search`. + +// CHECK-LABEL: @binary_search_index_no_bounds_check +#[no_mangle] +pub fn binary_search_index_no_bounds_check(s: &[u8]) -> u8 { + // CHECK-NOT: panic + // CHECK-NOT: slice_index_len_fail + if let Ok(idx) = s.binary_search(&b'\\') { + s[idx] + } else { + 42 + } +}