| //@ compile-flags: -Copt-level=3 |
| //@ only-x86_64 |
| //@ min-llvm-version: 20 |
| #![crate_type = "lib"] |
| |
| // This test verifies that LLVM 20 properly optimizes the bounds check |
| // when accessing the last few elements of a slice with proper conditions. |
| // Previously, this would generate an unreachable branch to |
| // slice_start_index_len_fail even when the bounds check was provably safe. |
| |
| // CHECK-LABEL: @last_four_initial( |
| #[no_mangle] |
| pub fn last_four_initial(s: &[u8]) -> &[u8] { |
| // Previously this would generate a branch to slice_start_index_len_fail |
| // that is unreachable. The LLVM 20 fix should eliminate this branch. |
| // CHECK-NOT: slice_start_index_len_fail |
| // CHECK-NOT: unreachable |
| let start = if s.len() <= 4 { 0 } else { s.len() - 4 }; |
| &s[start..] |
| } |
| |
| // CHECK-LABEL: @last_four_optimized( |
| #[no_mangle] |
| pub fn last_four_optimized(s: &[u8]) -> &[u8] { |
| // This version was already correctly optimized before the fix in LLVM 20. |
| // CHECK-NOT: slice_start_index_len_fail |
| // CHECK-NOT: unreachable |
| if s.len() <= 4 { &s[0..] } else { &s[s.len() - 4..] } |
| } |
| |
| // Just to verify we're correctly checking for the right thing |
| // CHECK-LABEL: @test_bounds_check_happens( |
| #[no_mangle] |
| pub fn test_bounds_check_happens(s: &[u8], i: usize) -> &[u8] { |
| // CHECK: slice_start_index_len_fail |
| &s[i..] |
| } |
