Rollup merge of #126361 - celinval:issue-0079-intrinsic, r=oli-obk

Unify intrinsics body handling in StableMIR

rust-lang/rust#120675 introduced a new mechanism to declare intrinsics which will potentially replace the rust-intrinsic ABI.

The new mechanism introduces a placeholder body and mark the intrinsic with `#[rustc_intrinsic_must_be_overridden]`.
In practice, this means that a backend should not generate code for the placeholder, and shim the intrinsic.
The new annotation is an internal compiler implementation, and it doesn't need to be exposed to StableMIR users.

In this PR, we unify the interface for intrinsics marked with `rustc_intrinsic_must_be_overridden` and intrinsics that do not have a body.

Fixes https://github.com/rust-lang/project-stable-mir/issues/79

r? ``@oli-obk``

cc: ``@momvart``

5 files changed, 42 insertions, 25 deletions

diff --git a/compiler/rustc_smir/src/rustc_smir/context.rs b/compiler/rustc_smir/src/rustc_smir/context.rs
index 981231694bb..4348bc31bf9 100644
--- a/compiler/rustc_smir/src/rustc_smir/context.rs
+++ b/compiler/rustc_smir/src/rustc_smir/context.rs
@@ -64,9 +64,10 @@ impl<'tcx> Context for TablesWrapper<'tcx> {
     }
 
     fn has_body(&self, def: DefId) -> bool {
-        let tables = self.0.borrow();
-        let def_id = tables[def];
-        tables.tcx.is_mir_available(def_id)
+        let mut tables = self.0.borrow_mut();
+        let tcx = tables.tcx;
+        let def_id = def.internal(&mut *tables, tcx);
+        tables.item_has_body(def_id)
     }
 
     fn foreign_modules(&self, crate_num: CrateNum) -> Vec<stable_mir::ty::ForeignModuleDef> {
@@ -323,13 +324,6 @@ impl<'tcx> Context for TablesWrapper<'tcx> {
         tcx.intrinsic(def_id).unwrap().name.to_string()
     }
 
-    fn intrinsic_must_be_overridden(&self, def: IntrinsicDef) -> bool {
-        let mut tables = self.0.borrow_mut();
-        let tcx = tables.tcx;
-        let def_id = def.0.internal(&mut *tables, tcx);
-        tcx.intrinsic_raw(def_id).unwrap().must_be_overridden
-    }
-
     fn closure_sig(&self, args: &GenericArgs) -> PolyFnSig {
         let mut tables = self.0.borrow_mut();
         let tcx = tables.tcx;
@@ -516,7 +510,7 @@ impl<'tcx> Context for TablesWrapper<'tcx> {
         let mut tables = self.0.borrow_mut();
         let instance = tables.instances[def];
         tables
-            .has_body(instance)
+            .instance_has_body(instance)
             .then(|| BodyBuilder::new(tables.tcx, instance).build(&mut *tables))
     }
 
diff --git a/compiler/rustc_smir/src/rustc_smir/mod.rs b/compiler/rustc_smir/src/rustc_smir/mod.rs
index d13e7803326..89f9adfcfd6 100644
--- a/compiler/rustc_smir/src/rustc_smir/mod.rs
+++ b/compiler/rustc_smir/src/rustc_smir/mod.rs
@@ -51,9 +51,13 @@ impl<'tcx> Tables<'tcx> {
         self.mir_consts.create_or_fetch(constant)
     }
 
-    pub(crate) fn has_body(&self, instance: Instance<'tcx>) -> bool {
+    /// Return whether the instance as a body available.
+    ///
+    /// Items and intrinsics may have a body available from its definition.
+    /// Shims body may be generated depending on their type.
+    pub(crate) fn instance_has_body(&self, instance: Instance<'tcx>) -> bool {
         let def_id = instance.def_id();
-        self.tcx.is_mir_available(def_id)
+        self.item_has_body(def_id)
             || !matches!(
                 instance.def,
                 ty::InstanceDef::Virtual(..)
@@ -61,6 +65,19 @@ impl<'tcx> Tables<'tcx> {
                     | ty::InstanceDef::Item(..)
             )
     }
+
+    /// Return whether the item has a body defined by the user.
+    ///
+    /// Note that intrinsics may have a placeholder body that shouldn't be used in practice.
+    /// In StableMIR, we handle this case as if the body is not available.
+    pub(crate) fn item_has_body(&self, def_id: DefId) -> bool {
+        let must_override = if let Some(intrinsic) = self.tcx.intrinsic(def_id) {
+            intrinsic.must_be_overridden
+        } else {
+            false
+        };
+        !must_override && self.tcx.is_mir_available(def_id)
+    }
 }
 
 /// Build a stable mir crate from a given crate number.
diff --git a/compiler/stable_mir/src/compiler_interface.rs b/compiler/stable_mir/src/compiler_interface.rs
index 085dfd9ea89..3e138e3c2e0 100644
--- a/compiler/stable_mir/src/compiler_interface.rs
+++ b/compiler/stable_mir/src/compiler_interface.rs
@@ -94,10 +94,6 @@ pub trait Context {
     /// Retrieve the plain function name of an intrinsic.
     fn intrinsic_name(&self, def: IntrinsicDef) -> Symbol;
 
-    /// Returns whether the intrinsic has no meaningful body and all backends
-    /// need to shim all calls to it.
-    fn intrinsic_must_be_overridden(&self, def: IntrinsicDef) -> bool;
-
     /// Retrieve the closure signature for the given generic arguments.
     fn closure_sig(&self, args: &GenericArgs) -> PolyFnSig;
 
diff --git a/compiler/stable_mir/src/ty.rs b/compiler/stable_mir/src/ty.rs
index 76f94e6beba..35927237281 100644
--- a/compiler/stable_mir/src/ty.rs
+++ b/compiler/stable_mir/src/ty.rs
@@ -668,6 +668,11 @@ impl FnDef {
         with(|ctx| ctx.has_body(self.0).then(|| ctx.mir_body(self.0)))
     }
 
+    // Check if the function body is available.
+    pub fn has_body(&self) -> bool {
+        with(|ctx| ctx.has_body(self.0))
+    }
+
     /// Get the information of the intrinsic if this function is a definition of one.
     pub fn as_intrinsic(&self) -> Option<IntrinsicDef> {
         with(|cx| cx.intrinsic(self.def_id()))
@@ -700,7 +705,7 @@ impl IntrinsicDef {
     /// Returns whether the intrinsic has no meaningful body and all backends
     /// need to shim all calls to it.
     pub fn must_be_overridden(&self) -> bool {
-        with(|cx| cx.intrinsic_must_be_overridden(*self))
+        with(|cx| !cx.has_body(self.0))
     }
 }
 
diff --git a/tests/ui-fulldeps/stable-mir/check_intrinsics.rs b/tests/ui-fulldeps/stable-mir/check_intrinsics.rs
index 7e247ce0c75..d7f37f36681 100644
--- a/tests/ui-fulldeps/stable-mir/check_intrinsics.rs
+++ b/tests/ui-fulldeps/stable-mir/check_intrinsics.rs
@@ -55,16 +55,19 @@ fn test_intrinsics() -> ControlFlow<()> {
 ///
 /// If by any chance this test breaks because you changed how an intrinsic is implemented, please
 /// update the test to invoke a different intrinsic.
+///
+/// In StableMIR, we only expose intrinsic body if they are not marked with
+/// `rustc_intrinsic_must_be_overridden`.
 fn check_instance(instance: &Instance) {
     assert_eq!(instance.kind, InstanceKind::Intrinsic);
     let name = instance.intrinsic_name().unwrap();
     if instance.has_body() {
         let Some(body) = instance.body() else { unreachable!("Expected a body") };
         assert!(!body.blocks.is_empty());
-        assert_matches!(name.as_str(), "likely" | "vtable_size");
+        assert_eq!(&name, "likely");
     } else {
         assert!(instance.body().is_none());
-        assert_eq!(&name, "size_of_val");
+        assert_matches!(name.as_str(), "size_of_val" | "vtable_size");
     }
 }
 
@@ -75,11 +78,13 @@ fn check_def(fn_def: FnDef) {
 
     let name = intrinsic.fn_name();
     match name.as_str() {
-        "likely" | "size_of_val" => {
+        "likely" => {
             assert!(!intrinsic.must_be_overridden());
+            assert!(fn_def.has_body());
         }
-        "vtable_size" => {
+        "vtable_size" | "size_of_val" => {
             assert!(intrinsic.must_be_overridden());
+            assert!(!fn_def.has_body());
         }
         _ => unreachable!("Unexpected intrinsic: {}", name),
     }
@@ -96,9 +101,9 @@ impl<'a> MirVisitor for CallsVisitor<'a> {
             TerminatorKind::Call { func, .. } => {
                 let TyKind::RigidTy(RigidTy::FnDef(def, args)) =
                     func.ty(self.locals).unwrap().kind()
-                else {
-                    return;
-                };
+                    else {
+                        return;
+                    };
                 self.calls.push((def, args.clone()));
             }
             _ => {}