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Add a query for dereferencing constants of reference type
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@ -749,6 +749,14 @@ rustc_queries! {
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desc { "destructure constant" }
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}
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/// Dereference a constant reference or raw pointer and turn the result into a constant
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/// again.
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query deref_const(
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key: ty::ParamEnvAnd<'tcx, &'tcx ty::Const<'tcx>>
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) -> &'tcx ty::Const<'tcx> {
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desc { "deref constant" }
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}
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query const_caller_location(key: (rustc_span::Symbol, u32, u32)) -> ConstValue<'tcx> {
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desc { "get a &core::panic::Location referring to a span" }
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}
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@ -2,11 +2,14 @@
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use std::convert::TryFrom;
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use rustc_hir::Mutability;
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use rustc_middle::mir;
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use rustc_middle::ty::{self, TyCtxt};
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use rustc_span::{source_map::DUMMY_SP, symbol::Symbol};
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use crate::interpret::{intern_const_alloc_recursive, ConstValue, InternKind, InterpCx};
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use crate::interpret::{
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intern_const_alloc_recursive, ConstValue, InternKind, InterpCx, MemPlaceMeta, Scalar,
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};
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mod error;
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mod eval_queries;
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@ -67,3 +70,40 @@ pub(crate) fn destructure_const<'tcx>(
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mir::DestructuredConst { variant, fields }
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}
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pub(crate) fn deref_const<'tcx>(
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tcx: TyCtxt<'tcx>,
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param_env: ty::ParamEnv<'tcx>,
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val: &'tcx ty::Const<'tcx>,
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) -> &'tcx ty::Const<'tcx> {
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trace!("deref_const: {:?}", val);
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let ecx = mk_eval_cx(tcx, DUMMY_SP, param_env, false);
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let op = ecx.const_to_op(val, None).unwrap();
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let mplace = ecx.deref_operand(op).unwrap();
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if let Scalar::Ptr(ptr) = mplace.ptr {
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assert_eq!(
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ecx.memory.get_raw(ptr.alloc_id).unwrap().mutability,
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Mutability::Not,
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"deref_const cannot be used with mutable allocations as \
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that could allow pattern matching to observe mutable statics",
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);
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}
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let ty = match mplace.meta {
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MemPlaceMeta::None => mplace.layout.ty,
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MemPlaceMeta::Poison => bug!("poison metadata in `deref_const`: {:#?}", mplace),
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// In case of unsized types, figure out the real type behind.
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MemPlaceMeta::Meta(scalar) => match mplace.layout.ty.kind {
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ty::Dynamic(..) => ecx.read_drop_type_from_vtable(scalar).unwrap().1,
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ty::Str => bug!("there's no sized equivalent of a `str`"),
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ty::Slice(elem_ty) => tcx.mk_array(elem_ty, scalar.to_machine_usize(&tcx).unwrap()),
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_ => bug!(
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"type {} should not have metadata, but had {:?}",
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mplace.layout.ty,
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mplace.meta
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),
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},
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};
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tcx.mk_const(ty::Const { val: ty::ConstKind::Value(op_to_const(&ecx, mplace.into())), ty })
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}
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@ -60,4 +60,8 @@ pub fn provide(providers: &mut Providers) {
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let (param_env, value) = param_env_and_value.into_parts();
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const_eval::destructure_const(tcx, param_env, value)
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};
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providers.deref_const = |tcx, param_env_and_value| {
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let (param_env, value) = param_env_and_value.into_parts();
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const_eval::deref_const(tcx, param_env, value)
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};
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}
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