1 files changed, 38 insertions, 0 deletions

diff --git a/tests/codegen-llvm/issues/issue-96497-slice-size-nowrap.rs b/tests/codegen-llvm/issues/issue-96497-slice-size-nowrap.rs
new file mode 100644
index 00000000000..7b3a20a295e
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+++ b/tests/codegen-llvm/issues/issue-96497-slice-size-nowrap.rs
@@ -0,0 +1,38 @@
+// 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
+}