Auto merge of #122371 - oli-obk:visit_nested_body, r=<try>

Stop walking the bodies of statics for reachability, and evaluate them instead

cc `@saethlin` `@RalfJung`

cc #119214

This reuses the `DefIdVisitor` from `rustc_privacy`, because they basically try to do the same thing. It can probably be extended to constants, too, but let's tackle that separately, it's likely more involved.

Author: bors

Cargo.lock

@@ -4400,6 +4400,7 @@ dependencies = [
  "rustc_lexer",
  "rustc_macros",
  "rustc_middle",
+ "rustc_privacy",
  "rustc_session",
  "rustc_span",
  "rustc_target",

compiler/rustc_passes/Cargo.toml

@@ -18,6 +18,7 @@ rustc_index = { path = "../rustc_index" }
 rustc_lexer = { path = "../rustc_lexer" }
 rustc_macros = { path = "../rustc_macros" }
 rustc_middle = { path = "../rustc_middle" }
+rustc_privacy = { path = "../rustc_privacy" }
 rustc_session = { path = "../rustc_session" }
 rustc_span = { path = "../rustc_span" }
 rustc_target = { path = "../rustc_target" }

compiler/rustc_passes/src/reachable.rs

@@ -13,8 +13,10 @@ use rustc_hir::intravisit::{self, Visitor};
 use rustc_hir::Node;
 use rustc_middle::middle::codegen_fn_attrs::{CodegenFnAttrFlags, CodegenFnAttrs};
 use rustc_middle::middle::privacy::{self, Level};
+use rustc_middle::mir::interpret::{ConstAllocation, GlobalAlloc};
 use rustc_middle::query::Providers;
-use rustc_middle::ty::{self, TyCtxt};
+use rustc_middle::ty::{self, ExistentialTraitRef, TyCtxt};
+use rustc_privacy::DefIdVisitor;
 use rustc_session::config::CrateType;
 use rustc_target::spec::abi::Abi;
 
@@ -64,23 +66,8 @@ impl<'tcx> Visitor<'tcx> for ReachableContext<'tcx> {
             _ => None,
         };
 
-        if let Some(res) = res
-            && let Some(def_id) = res.opt_def_id().and_then(|el| el.as_local())
-        {
-            if self.def_id_represents_local_inlined_item(def_id.to_def_id()) {
-                self.worklist.push(def_id);
-            } else {
-                match res {
-                    // Reachable constants and reachable statics can have their contents inlined
-                    // into other crates. Mark them as reachable and recurse into their body.
-                    Res::Def(DefKind::Const | DefKind::AssocConst | DefKind::Static(_), _) => {
-                        self.worklist.push(def_id);
-                    }
-                    _ => {
-                        self.reachable_symbols.insert(def_id);
-                    }
-                }
-            }
+        if let Some(res) = res {
+            self.propagate_item(res);
         }
 
         intravisit::walk_expr(self, expr)
@@ -197,9 +184,14 @@ impl<'tcx> ReachableContext<'tcx> {
                     // Reachable constants will be inlined into other crates
                     // unconditionally, so we need to make sure that their
                     // contents are also reachable.
-                    hir::ItemKind::Const(_, _, init) | hir::ItemKind::Static(_, _, init) => {
+                    hir::ItemKind::Const(_, _, init) => {
                         self.visit_nested_body(init);
                     }
+                    hir::ItemKind::Static(..) => {
+                        if let Ok(alloc) = self.tcx.eval_static_initializer(item.owner_id.def_id) {
+                            self.propagate_from_alloc(item.owner_id.def_id, alloc);
+                        }
+                    }
 
                     // These are normal, nothing reachable about these
                     // inherently and their children are already in the
@@ -266,6 +258,76 @@ impl<'tcx> ReachableContext<'tcx> {
             }
         }
     }
+
+    /// Finds things to add to `reachable_symbols` within allocations.
+    /// In contrast to visit_nested_body this ignores things that were only needed to evaluate
+    /// to the allocation.
+    fn propagate_from_alloc(&mut self, root: LocalDefId, alloc: ConstAllocation<'tcx>) {
+        if !self.any_library {
+            return;
+        }
+        for (_, prov) in alloc.0.provenance().ptrs().iter() {
+            match self.tcx.global_alloc(prov.alloc_id()) {
+                GlobalAlloc::Static(def_id) => {
+                    self.propagate_item(Res::Def(self.tcx.def_kind(def_id), def_id))
+                }
+                GlobalAlloc::Function(instance) => {
+                    // Manually visit to actually see the instance's `DefId`. Type visitors won't see it
+                    self.propagate_item(Res::Def(
+                        self.tcx.def_kind(instance.def_id()),
+                        instance.def_id(),
+                    ));
+                    self.visit(instance.args);
+                }
+                GlobalAlloc::VTable(ty, trait_ref) => {
+                    self.visit(ty);
+                    // Manually visit to actually see the trait's `DefId`. Type visitors won't see it
+                    if let Some(trait_ref) = trait_ref {
+                        let ExistentialTraitRef { def_id, args } = trait_ref.skip_binder();
+                        self.visit_def_id(def_id, "", &"");
+                        self.visit(args);
+                    }
+                }
+                GlobalAlloc::Memory(alloc) => self.propagate_from_alloc(root, alloc),
+            }
+        }
+    }
+
+    fn propagate_item(&mut self, res: Res) {
+        let Res::Def(kind, def_id) = res else { return };
+        let Some(def_id) = def_id.as_local() else { return };
+        if self.def_id_represents_local_inlined_item(def_id.to_def_id()) {
+            self.worklist.push(def_id);
+        } else {
+            match kind {
+                // Reachable constants and reachable statics can have their contents inlined
+                // into other crates. Mark them as reachable and recurse into their body.
+                DefKind::Const | DefKind::AssocConst | DefKind::Static(_) => {
+                    self.worklist.push(def_id);
+                }
+                _ => {
+                    self.reachable_symbols.insert(def_id);
+                }
+            }
+        }
+    }
+}
+
+impl<'tcx> DefIdVisitor<'tcx> for ReachableContext<'tcx> {
+    type Result = ();
+
+    fn tcx(&self) -> TyCtxt<'tcx> {
+        self.tcx
+    }
+
+    fn visit_def_id(
+        &mut self,
+        def_id: DefId,
+        _kind: &str,
+        _descr: &dyn std::fmt::Display,
+    ) -> Self::Result {
+        self.propagate_item(Res::Def(self.tcx.def_kind(def_id), def_id))
+    }
 }
 
 fn check_item<'tcx>(

compiler/rustc_privacy/src/lib.rs

@@ -67,7 +67,7 @@ impl<'tcx> fmt::Display for LazyDefPathStr<'tcx> {
 /// First, it doesn't have overridable `fn visit_trait_ref`, so we have to catch trait `DefId`s
 /// manually. Second, it doesn't visit some type components like signatures of fn types, or traits
 /// in `impl Trait`, see individual comments in `DefIdVisitorSkeleton::visit_ty`.
-trait DefIdVisitor<'tcx> {
+pub trait DefIdVisitor<'tcx> {
     type Result: VisitorResult = ();
     const SHALLOW: bool = false;
     const SKIP_ASSOC_TYS: bool = false;
@@ -98,7 +98,7 @@ trait DefIdVisitor<'tcx> {
     }
 }
 
-struct DefIdVisitorSkeleton<'v, 'tcx, V: ?Sized> {
+pub struct DefIdVisitorSkeleton<'v, 'tcx, V: ?Sized> {
     def_id_visitor: &'v mut V,
     visited_opaque_tys: FxHashSet<DefId>,
     dummy: PhantomData<TyCtxt<'tcx>>,

tests/ui/cross-crate/auxiliary/static_init_aux.rs

@@ -1,6 +1,8 @@
 pub static V: &u32 = &X;
 pub static F: fn() = f;
 pub static G: fn() = G0;
+pub static H: &(dyn Fn() + Sync) = &h;
+pub static I: fn() = Helper(j).mk();
 
 static X: u32 = 42;
 static G0: fn() = g;
@@ -12,3 +14,22 @@ pub fn v() -> *const u32 {
 fn f() {}
 
 fn g() {}
+
+fn h() {}
+
+#[derive(Copy, Clone)]
+struct Helper<T: Copy>(T);
+
+impl<T: Copy + FnOnce()> Helper<T> {
+    const fn mk(self) -> fn() {
+        i::<T>
+    }
+}
+
+fn i<T: FnOnce()>() {
+    assert_eq!(std::mem::size_of::<T>(), 0);
+    // unsafe to work around the lack of a `Default` impl for function items
+    unsafe { (std::mem::transmute_copy::<(), T>(&()))() }
+}
+
+fn j() {}

tests/ui/cross-crate/static-init.rs

@@ -6,6 +6,8 @@ extern crate static_init_aux as aux;
 static V: &u32 = aux::V;
 static F: fn() = aux::F;
 static G: fn() = aux::G;
+static H: &(dyn Fn() + Sync) = aux::H;
+static I: fn() = aux::I;
 
 fn v() -> *const u32 {
     V
@@ -15,4 +17,6 @@ fn main() {
     assert_eq!(aux::v(), crate::v());
     F();
     G();
+    H();
+    I();
 }