Rollup merge of #135748 - compiler-errors:len-2, r=RalfJung,oli-obk

Lower index bounds checking to `PtrMetadata`, this time with the right fake borrow semantics 😸

Change `Rvalue::RawRef` to take a `RawRefKind` instead of just a `Mutability`. Then introduce `RawRefKind::FakeForPtrMetadata` and use that for lowering index bounds checking to a `PtrMetadata`. This new `RawRefKind::FakeForPtrMetadata` acts like a shallow fake borrow in borrowck, which mimics the semantics of the old `Rvalue::Len` operation we're replacing.

We can then use this `RawRefKind` instead of using a span desugaring hack in CTFE.

cc ``@scottmcm`` ``@RalfJung``

compiler/rustc_mir_transform/src/gvn.rs

@@ -192,7 +192,7 @@ enum AggregateTy<'tcx> {
 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
 enum AddressKind {
     Ref(BorrowKind),
-    Address(Mutability),
+    Address(RawPtrKind),
 }
 
 #[derive(Debug, PartialEq, Eq, Hash)]
@@ -504,7 +504,9 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
                         mplace.layout.ty,
                         bk.to_mutbl_lossy(),
                     ),
-                    AddressKind::Address(mutbl) => Ty::new_ptr(self.tcx, mplace.layout.ty, mutbl),
+                    AddressKind::Address(mutbl) => {
+                        Ty::new_ptr(self.tcx, mplace.layout.ty, mutbl.to_mutbl_lossy())
+                    }
                 };
                 let layout = self.ecx.layout_of(ty).ok()?;
                 ImmTy::from_immediate(pointer, layout).into()

compiler/rustc_mir_transform/src/instsimplify.rs

@@ -46,7 +46,6 @@ impl<'tcx> crate::MirPass<'tcx> for InstSimplify {
                         }
                         ctx.simplify_bool_cmp(rvalue);
                         ctx.simplify_ref_deref(rvalue);
-                        ctx.simplify_len(rvalue);
                         ctx.simplify_ptr_aggregate(rvalue);
                         ctx.simplify_cast(rvalue);
                         ctx.simplify_repeated_aggregate(rvalue);
@@ -166,18 +165,6 @@ impl<'tcx> InstSimplifyContext<'_, 'tcx> {
         }
     }
 
-    /// Transform `Len([_; N])` ==> `N`.
-    fn simplify_len(&self, rvalue: &mut Rvalue<'tcx>) {
-        if let Rvalue::Len(ref place) = *rvalue {
-            let place_ty = place.ty(self.local_decls, self.tcx).ty;
-            if let ty::Array(_, len) = *place_ty.kind() {
-                let const_ = Const::Ty(self.tcx.types.usize, len);
-                let constant = ConstOperand { span: DUMMY_SP, const_, user_ty: None };
-                *rvalue = Rvalue::Use(Operand::Constant(Box::new(constant)));
-            }
-        }
-    }
-
     /// Transform `Aggregate(RawPtr, [p, ()])` ==> `Cast(PtrToPtr, p)`.
     fn simplify_ptr_aggregate(&self, rvalue: &mut Rvalue<'tcx>) {
         if let Rvalue::Aggregate(box AggregateKind::RawPtr(pointee_ty, mutability), fields) = rvalue

compiler/rustc_mir_transform/src/large_enums.rs

@@ -125,7 +125,7 @@ impl<'tcx> crate::MirPass<'tcx> for EnumSizeOpt {
                     source_info,
                     kind: StatementKind::Assign(Box::new((
                         dst,
-                        Rvalue::RawPtr(Mutability::Mut, *lhs),
+                        Rvalue::RawPtr(RawPtrKind::Mut, *lhs),
                     ))),
                 };
 
@@ -146,7 +146,7 @@ impl<'tcx> crate::MirPass<'tcx> for EnumSizeOpt {
                     source_info,
                     kind: StatementKind::Assign(Box::new((
                         src,
-                        Rvalue::RawPtr(Mutability::Not, *rhs),
+                        Rvalue::RawPtr(RawPtrKind::Const, *rhs),
                     ))),
                 };
 

compiler/rustc_mir_transform/src/shim/async_destructor_ctor.rs

@@ -2,17 +2,11 @@ use std::iter;
 
 use itertools::Itertools;
 use rustc_abi::{FieldIdx, VariantIdx};
-use rustc_ast::Mutability;
 use rustc_const_eval::interpret;
 use rustc_hir::def_id::DefId;
 use rustc_hir::lang_items::LangItem;
 use rustc_index::{Idx, IndexVec};
-use rustc_middle::mir::{
-    BasicBlock, BasicBlockData, Body, CallSource, CastKind, CoercionSource, Const, ConstOperand,
-    ConstValue, Local, LocalDecl, MirSource, Operand, Place, PlaceElem, RETURN_PLACE, Rvalue,
-    SourceInfo, Statement, StatementKind, Terminator, TerminatorKind, UnwindAction,
-    UnwindTerminateReason,
-};
+use rustc_middle::mir::*;
 use rustc_middle::ty::adjustment::PointerCoercion;
 use rustc_middle::ty::util::{AsyncDropGlueMorphology, Discr};
 use rustc_middle::ty::{self, Ty, TyCtxt};
@@ -345,7 +339,7 @@ impl<'tcx> AsyncDestructorCtorShimBuilder<'tcx> {
                 .tcx
                 .mk_place_elems(&[PlaceElem::Deref, PlaceElem::Field(field, field_ty)]),
         };
-        self.put_temp_rvalue(Rvalue::RawPtr(Mutability::Mut, place))
+        self.put_temp_rvalue(Rvalue::RawPtr(RawPtrKind::Mut, place))
     }
 
     /// If given Self is an enum puts `to_drop: *mut FieldTy` on top of
@@ -365,7 +359,7 @@ impl<'tcx> AsyncDestructorCtorShimBuilder<'tcx> {
                 PlaceElem::Field(field, field_ty),
             ]),
         };
-        self.put_temp_rvalue(Rvalue::RawPtr(Mutability::Mut, place))
+        self.put_temp_rvalue(Rvalue::RawPtr(RawPtrKind::Mut, place))
     }
 
     /// If given Self is an enum puts `to_drop: *mut FieldTy` on top of

compiler/rustc_mir_transform/src/validate.rs

@@ -1128,14 +1128,6 @@ impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> {
                         );
                     }
                     UnOp::PtrMetadata => {
-                        if !matches!(self.body.phase, MirPhase::Runtime(_)) {
-                            // It would probably be fine to support this in earlier phases, but at
-                            // the time of writing it's only ever introduced from intrinsic
-                            // lowering or other runtime-phase optimization passes, so earlier
-                            // things can just `bug!` on it.
-                            self.fail(location, "PtrMetadata should be in runtime MIR only");
-                        }
-
                         check_kinds!(
                             a,
                             "Cannot PtrMetadata non-pointer non-reference type {:?}",