add llvm writable attribute conditionally

tests/codegen-llvm/llvm-writable.rs

@@ -0,0 +1,30 @@
+//! The tests here test that the `-Zllvm-writable` flag and
+//! the `#[rustc_no_writable]` attribute have the desired effect.
+//@ compile-flags: -Copt-level=3 -C no-prepopulate-passes -Zllvm-writable
+#![crate_type = "lib"]
+#![feature(rustc_attrs, unsafe_pinned)]
+
+// CHECK: @mutable_borrow(ptr noalias noundef writable align 4 dereferenceable(4) %_1)
+#[no_mangle]
+pub fn mutable_borrow(_: &mut i32) {}
+
+// CHECK: @mutable_unsafe_borrow(ptr noalias noundef writable align 2 dereferenceable(2) %_1)
+#[no_mangle]
+pub fn mutable_unsafe_borrow(_: &mut std::cell::UnsafeCell<i16>) {}
+
+// CHECK: @option_borrow_mut(ptr noalias noundef writable align 4 dereferenceable_or_null(4) %_1)
+#[no_mangle]
+pub fn option_borrow_mut(_: Option<&mut i32>) {}
+
+// CHECK: @box_moved(ptr noalias noundef nonnull align 4 %0)
+#[no_mangle]
+pub fn box_moved(_: Box<i32>) {}
+
+// CHECK: @unsafe_pinned_borrow_mut(ptr noundef nonnull align 4 %_1)
+#[no_mangle]
+pub fn unsafe_pinned_borrow_mut(_: &mut std::pin::UnsafePinned<i32>) {}
+
+// CHECK: @mutable_borrow_no_writable(ptr noalias noundef align 4 dereferenceable(4) %_1)
+#[no_mangle]
+#[rustc_no_writable]
+pub fn mutable_borrow_no_writable(_: &mut i32) {}