mark rust_dealloc as captures(address)

Co-authored-by: Ralf Jung <post@ralfj.de>

Author: the8472

compiler/rustc_codegen_llvm/src/attributes.rs

@@ -517,7 +517,16 @@ pub(crate) fn llfn_attrs_from_instance<'ll, 'tcx>(
         to_add.push(llvm::CreateAllocKindAttr(cx.llcx, AllocKindFlags::Free));
         // applies to argument place instead of function place
         let allocated_pointer = AttributeKind::AllocatedPointer.create_attr(cx.llcx);
-        attributes::apply_to_llfn(llfn, AttributePlace::Argument(0), &[allocated_pointer]);
+        let attrs: &[_] = if llvm_util::get_version() >= (21, 0, 0) {
+            // "Does not capture provenance" means "if the function call stashes the pointer somewhere,
+            // accessing that pointer after the function returns is UB". That is definitely the case here since
+            // freeing will destroy the provenance.
+            let captures_addr = AttributeKind::CapturesAddress.create_attr(cx.llcx);
+            &[allocated_pointer, captures_addr]
+        } else {
+            &[allocated_pointer]
+        };
+        attributes::apply_to_llfn(llfn, AttributePlace::Argument(0), attrs);
     }
     if let Some(align) = codegen_fn_attrs.alignment {
         llvm::set_alignment(llfn, align);