Rollup merge of #110930 - b-naber:normalize-elaborate-drops, r=cjgillot

Don't expect normalization to succeed in elaborate_drops

Fixes #110682

This was exposed through the changes in #109247, which causes more things to be inlined. Inlining can happen before monomorphization, so we can't expect normalization to succeed. In the elaborate_drops analysis we currently have [this call](https://github.com/rust-lang/rust/blob/033aa092ab23ba14cdad27073c5e37ba0eddb428/compiler/rustc_mir_dataflow/src/elaborate_drops.rs#L278) to `normalize_erasing_regions`, which ICEs when normalization fails. The types are used to infer [whether the type needs a drop](https://github.com/rust-lang/rust/blob/033aa092ab23ba14cdad27073c5e37ba0eddb428/compiler/rustc_mir_dataflow/src/elaborate_drops.rs#L374), where `needs_drop` itself [uses `try_normalize_erasing_regions`](https://github.com/rust-lang/rust/blob/033aa092ab23ba14cdad27073c5e37ba0eddb428/compiler/rustc_middle/src/ty/util.rs#L1121).

~[`instance_mir`](https://doc.rust-lang.org/stable/nightly-rustc/rustc_middle/ty/context/struct.TyCtxt.html#method.instance_mir) isn't explicit about whether it expects the instances corresponding to the `InstanceDef`s to be monomorphized (though I think in all other contexts the function is used post-monomorphization), so the use of `instance_mir` in inlining doesn't necessarily seem wrong to me.~

Author: Dylan-DPC

compiler/rustc_mir_dataflow/src/elaborate_drops.rs

@@ -276,6 +276,7 @@ where
                 assert_eq!(self.elaborator.param_env().reveal(), Reveal::All);
                 let field_ty =
                     tcx.normalize_erasing_regions(self.elaborator.param_env(), f.ty(tcx, substs));
+
                 (tcx.mk_place_field(base_place, field, field_ty), subpath)
             })
             .collect()

compiler/rustc_mir_transform/src/inline.rs

@@ -7,6 +7,7 @@ use rustc_index::Idx;
 use rustc_middle::middle::codegen_fn_attrs::{CodegenFnAttrFlags, CodegenFnAttrs};
 use rustc_middle::mir::visit::*;
 use rustc_middle::mir::*;
+use rustc_middle::ty::TypeVisitableExt;
 use rustc_middle::ty::{self, Instance, InstanceDef, ParamEnv, Ty, TyCtxt};
 use rustc_session::config::OptLevel;
 use rustc_span::{hygiene::ExpnKind, ExpnData, LocalExpnId, Span};
@@ -168,7 +169,7 @@ impl<'tcx> Inliner<'tcx> {
         let callee_attrs = self.tcx.codegen_fn_attrs(callsite.callee.def_id());
         self.check_codegen_attributes(callsite, callee_attrs)?;
         self.check_mir_is_available(caller_body, &callsite.callee)?;
-        let callee_body = self.tcx.instance_mir(callsite.callee.def);
+        let callee_body = try_instance_mir(self.tcx, callsite.callee.def)?;
         self.check_mir_body(callsite, callee_body, callee_attrs)?;
 
         if !self.tcx.consider_optimizing(|| {
@@ -1128,3 +1129,27 @@ impl<'tcx> MutVisitor<'tcx> for Integrator<'_, 'tcx> {
         }
     }
 }
+
+#[instrument(skip(tcx), level = "debug")]
+fn try_instance_mir<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    instance: InstanceDef<'tcx>,
+) -> Result<&'tcx Body<'tcx>, &'static str> {
+    match instance {
+        ty::InstanceDef::DropGlue(_, Some(ty)) => match ty.kind() {
+            ty::Adt(def, substs) => {
+                let fields = def.all_fields();
+                for field in fields {
+                    let field_ty = field.ty(tcx, substs);
+                    if field_ty.has_param() && field_ty.has_projections() {
+                        return Err("cannot build drop shim for polymorphic type");
+                    }
+                }
+
+                Ok(tcx.instance_mir(instance))
+            }
+            _ => Ok(tcx.instance_mir(instance)),
+        },
+        _ => Ok(tcx.instance_mir(instance)),
+    }
+}

tests/ui/drop/issue-110682.rs

@@ -0,0 +1,92 @@
+// build-pass
+// compile-flags: -Zmir-opt-level=3
+
+use std::fmt::Debug;
+use std::mem::ManuallyDrop;
+use std::ptr;
+
+pub trait BitRegister {}
+
+macro_rules! register {
+    ($($t:ty),+ $(,)?) => { $(
+        impl BitRegister for $t {
+        }
+    )* };
+}
+
+register!(u8, u16, u32);
+
+pub trait BitStore: Sized + Debug {
+    /// The register type that the implementor describes.
+    type Mem: BitRegister + Into<Self>;
+}
+
+macro_rules! store {
+    ($($t:ty),+ $(,)?) => { $(
+        impl BitStore for $t {
+            type Mem = Self;
+        }
+    )+ };
+}
+
+store!(u8, u16, u32,);
+
+#[repr(C)]
+pub struct BitVec<T>
+where
+    T: BitStore,
+{
+    /// Region pointer describing the live portion of the owned buffer.
+    pointer: ptr::NonNull<T>,
+    /// Allocated capacity, in elements `T`, of the owned buffer.
+    capacity: usize,
+}
+
+impl<T> BitVec<T>
+where
+    T: BitStore,
+{
+    pub fn new() -> Self {
+        let pointer = ptr::NonNull::<T>::new(ptr::null_mut()).unwrap();
+
+        BitVec { pointer, capacity: 10 }
+    }
+
+    pub fn clear(&mut self) {
+        unsafe {
+            self.set_len(0);
+        }
+    }
+
+    #[inline]
+    pub unsafe fn set_len(&mut self, new_len: usize) {}
+
+    fn with_vec<F, R>(&mut self, func: F) -> R
+    where
+        F: FnOnce(&mut ManuallyDrop<Vec<T::Mem>>) -> R,
+    {
+        let cap = self.capacity;
+        let elts = 10;
+        let mut vec = ManuallyDrop::new(unsafe { Vec::from_raw_parts(ptr::null_mut(), elts, cap) });
+        let out = func(&mut vec);
+
+        out
+    }
+}
+
+impl<T> Drop for BitVec<T>
+where
+    T: BitStore,
+{
+    #[inline]
+    fn drop(&mut self) {
+        //  The buffer elements do not have destructors.
+        self.clear();
+        //  Run the `Vec` destructor to deällocate the buffer.
+        self.with_vec(|vec| unsafe { ManuallyDrop::drop(vec) });
+    }
+}
+
+fn main() {
+    let bitvec = BitVec::<u32>::new();
+}