3 files changed, 98 insertions, 2 deletions

diff --git a/crates/hir_def/src/item_tree/lower.rs b/crates/hir_def/src/item_tree/lower.rs
index 3328639cf..1a29081c5 100644
--- a/crates/hir_def/src/item_tree/lower.rs
+++ b/crates/hir_def/src/item_tree/lower.rs
@@ -3,7 +3,7 @@
 use std::{collections::hash_map::Entry, mem, sync::Arc};
 
 use arena::map::ArenaMap;
-use hir_expand::{ast_id_map::AstIdMap, hygiene::Hygiene, HirFileId};
+use hir_expand::{ast_id_map::AstIdMap, hygiene::Hygiene, name::known, HirFileId};
 use smallvec::SmallVec;
 use syntax::{
     ast::{self, ModuleItemOwner},
@@ -42,6 +42,45 @@ pub(super) struct Ctx {
     forced_visibility: Option<RawVisibilityId>,
 }
 
+/// Returns `true` if the given intrinsic is unsafe to call or not.
+pub fn is_intrinsic_fn_unsafe(name: &Name) -> bool {
+    // Should be kept in sync with https://github.com/rust-lang/rust/blob/c6e4db620a7d2f569f11dcab627430921ea8aacf/compiler/rustc_typeck/src/check/intrinsic.rs#L68
+    *name != known::abort
+        && *name != known::min_align_of
+        && *name != known::needs_drop
+        && *name != known::caller_location
+        && *name != known::size_of_val
+        && *name != known::min_align_of_val
+        && *name != known::add_with_overflow
+        && *name != known::sub_with_overflow
+        && *name != known::mul_with_overflow
+        && *name != known::wrapping_add
+        && *name != known::wrapping_sub
+        && *name != known::wrapping_mul
+        && *name != known::saturating_add
+        && *name != known::saturating_sub
+        && *name != known::rotate_left
+        && *name != known::rotate_right
+        && *name != known::ctpop
+        && *name != known::ctlz
+        && *name != known::cttz
+        && *name != known::bswap
+        && *name != known::bitreverse
+        && *name != known::discriminant_value
+        && *name != known::type_id
+        && *name != known::likely
+        && *name != known::unlikely
+        && *name != known::ptr_guaranteed_eq
+        && *name != known::ptr_guaranteed_ne
+        && *name != known::minnumf32
+        && *name != known::minnumf64
+        && *name != known::maxnumf32
+        && *name != known::rustc_peek
+        && *name != known::maxnumf64
+        && *name != known::type_name
+        && *name != known::variant_count
+}
+
 impl Ctx {
     pub(super) fn new(db: &dyn DefDatabase, hygiene: Hygiene, file: HirFileId) -> Self {
         Self {
@@ -555,7 +594,8 @@ impl Ctx {
                     let id: ModItem = match item {
                         ast::ExternItem::Fn(ast) => {
                             let func = self.lower_function(&ast)?;
-                            self.data().functions[func.index].is_unsafe = true;
+                            self.data().functions[func.index].is_unsafe =
+                                is_intrinsic_fn_unsafe(&self.data().functions[func.index].name);
                             func.into()
                         }
                         ast::ExternItem::Static(ast) => {
diff --git a/crates/hir_def/src/item_tree/tests.rs b/crates/hir_def/src/item_tree/tests.rs
index 4b354c4c1..495c5a7e9 100644
--- a/crates/hir_def/src/item_tree/tests.rs
+++ b/crates/hir_def/src/item_tree/tests.rs
@@ -437,3 +437,23 @@ fn assoc_item_macros() {
         "#]],
     );
 }
+
+#[test]
+fn safe_intrinsic() {
+    check(
+        r"
+        #![feature(core_intrinsics)]
+
+        fn reverse(input: u32) -> u32 {
+            std::intrinsics::bitreverse(input)
+        }
+    ",
+        expect![[r#"
+            inner attrs: Attrs { entries: Some([Attr { path: ModPath { kind: Plain, segments: [Name(Text("feature"))] }, input: Some(TokenTree(SUBTREE () 0
+              IDENT   core_intrinsics 1)) }]) }
+
+            top-level items:
+            Function { name: Name(Text("reverse")), visibility: RawVisibilityId("pub(self)"), generic_params: GenericParamsId(4294967295), has_self_param: false, has_body: true, is_unsafe: false, params: [Path(Path { type_anchor: None, mod_path: ModPath { kind: Plain, segments: [Name(Text("u32"))] }, generic_args: [None] })], is_varargs: false, ret_type: Path(Path { type_anchor: None, mod_path: ModPath { kind: Plain, segments: [Name(Text("u32"))] }, generic_args: [None] }), ast_id: FileAstId::<syntax::ast::generated::nodes::Fn>(0) }
+        "#]],
+    );
+}
diff --git a/crates/hir_expand/src/name.rs b/crates/hir_expand/src/name.rs
index 63f828707..0d5b56681 100644
--- a/crates/hir_expand/src/name.rs
+++ b/crates/hir_expand/src/name.rs
@@ -208,6 +208,42 @@ pub mod known {
         PartialOrd,
         Eq,
         PartialEq,
+        // Safe primitives
+        abort,
+        size_of,
+        min_align_of,
+        needs_drop,
+        caller_location,
+        size_of_val,
+        min_align_of_val,
+        add_with_overflow,
+        sub_with_overflow,
+        mul_with_overflow,
+        wrapping_add,
+        wrapping_sub,
+        wrapping_mul,
+        saturating_add,
+        saturating_sub,
+        rotate_left,
+        rotate_right,
+        ctpop,
+        ctlz,
+        cttz,
+        bswap,
+        bitreverse,
+        discriminant_value,
+        type_id,
+        likely,
+        unlikely,
+        ptr_guaranteed_eq,
+        ptr_guaranteed_ne,
+        minnumf32,
+        minnumf64,
+        maxnumf32,
+        rustc_peek,
+        maxnumf64,
+        type_name,
+        variant_count,
     );
 
     // self/Self cannot be used as an identifier