Auto merge of #111517 - lukas-code:addr-of-mutate, r=tmiasko

allow mutating function args through `&raw const`

Fixes https://github.com/rust-lang/rust/issues/111502 by "turning off the sketchy optimization while we figure out if this is ok", like `@JakobDegen` said.

The first commit in this PR removes some suspicious looking logic from the same method, but should have no functional changes, since it doesn't modify the `context` outside of the method. Best reviewed commit by commit.

r? opsem

1 files changed, 34 insertions, 0 deletions

diff --git a/tests/codegen/addr-of-mutate.rs b/tests/codegen/addr-of-mutate.rs
new file mode 100644
index 00000000000..bea1aad2352
--- /dev/null
+++ b/tests/codegen/addr-of-mutate.rs
@@ -0,0 +1,34 @@
+// compile-flags: -C opt-level=3 -C no-prepopulate-passes
+// min-llvm-version: 15.0 (for opaque pointers)
+
+#![crate_type = "lib"]
+
+// Test for the absence of `readonly` on the argument when it is mutated via `&raw const`.
+// See <https://github.com/rust-lang/rust/issues/111502>.
+
+// CHECK: i8 @foo(ptr noalias nocapture noundef dereferenceable(128) %x)
+#[no_mangle]
+pub fn foo(x: [u8; 128]) -> u8 {
+    let ptr = core::ptr::addr_of!(x).cast_mut();
+    unsafe {
+        (*ptr)[0] = 1;
+    }
+    x[0]
+}
+
+// CHECK: i1 @second(ptr noalias nocapture noundef dereferenceable({{[0-9]+}}) %a_ptr_and_b)
+#[no_mangle]
+pub unsafe fn second(a_ptr_and_b: (*mut (i32, bool), (i64, bool))) -> bool {
+    let b_bool_ptr = core::ptr::addr_of!(a_ptr_and_b.1.1).cast_mut();
+    (*b_bool_ptr) = true;
+    a_ptr_and_b.1.1
+}
+
+// If going through a deref (and there are no other mutating accesses), then `readonly` is fine.
+// CHECK: i1 @third(ptr noalias nocapture noundef readonly dereferenceable({{[0-9]+}}) %a_ptr_and_b)
+#[no_mangle]
+pub unsafe fn third(a_ptr_and_b: (*mut (i32, bool), (i64, bool))) -> bool {
+    let b_bool_ptr = core::ptr::addr_of!((*a_ptr_and_b.0).1).cast_mut();
+    (*b_bool_ptr) = true;
+    a_ptr_and_b.1.1
+}