| // This test case checks that LLVM is aware that computing the size of a slice cannot wrap. |
| // The possibility of wrapping results in an additional branch when dropping boxed slices |
| // in some situations, see https://github.com/rust-lang/rust/issues/96497#issuecomment-1112865218 |
| |
| //@ compile-flags: -Copt-level=3 |
| |
| #![crate_type = "lib"] |
| |
| // CHECK-LABEL: @simple_size_of_nowrap |
| #[no_mangle] |
| pub fn simple_size_of_nowrap(x: &[u32]) -> usize { |
| // Make sure the shift used to compute the size has a nowrap flag. |
| |
| // CHECK: [[A:%.*]] = shl nuw nsw {{.*}}, 2 |
| // CHECK-NEXT: ret {{.*}} [[A]] |
| core::mem::size_of_val(x) |
| } |
| |
| // CHECK-LABEL: @drop_write |
| #[no_mangle] |
| pub fn drop_write(mut x: Box<[u32]>) { |
| // Check that this write is optimized out. |
| // This depends on the size calculation not wrapping, |
| // since otherwise LLVM can't tell that the memory is always deallocated if the slice len > 0. |
| |
| // CHECK-NOT: store i32 42 |
| x[1] = 42; |
| } |
| |
| // CHECK-LABEL: @slice_size_plus_2 |
| #[no_mangle] |
| pub fn slice_size_plus_2(x: &[u16]) -> usize { |
| // Before #136575 this didn't get the `nuw` in the add. |
| |
| // CHECK: [[BYTES:%.+]] = shl nuw nsw {{i16|i32|i64}} %x.1, 1 |
| // CHECK: = add nuw {{i16|i32|i64}} [[BYTES]], 2 |
| core::mem::size_of_val(x) + 2 |
| } |
