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Auto merge of #75346 - davidtwco:issue-69925-polymorphic-instancedef-fnptrshim, r=nikomatsakis

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shim: monomorphic `FnPtrShim`s during construction

Fixes #69925.

This PR adjusts MIR shim construction so that substitutions are applied to function pointer shims during construction, rather than during codegen (as determined by `substs_for_mir_body`).

r? `@eddyb`
This commit is contained in:
bors 2020-09-20 04:15:43 +00:00
commit a3bc0e752f
3 changed files with 57 additions and 58 deletions
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53
compiler/rustc_middle/src/ty/instance.rs
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@ -62,10 +62,6 @@ pub enum InstanceDef<'tcx> {
/// `<fn() as FnTrait>::call_*` (generated `FnTrait` implementation for `fn()` pointers).
///
/// `DefId` is `FnTrait::call_*`.
///
/// NB: the (`fn` pointer) type must currently be monomorphic to avoid double substitution
/// problems with the MIR shim bodies. `Instance::resolve` enforces this.
// FIXME(#69925) support polymorphic MIR shim bodies properly instead.
FnPtrShim(DefId, Ty<'tcx>),
/// Dynamic dispatch to `<dyn Trait as Trait>::fn`.
@ -87,10 +83,6 @@ pub enum InstanceDef<'tcx> {
/// The `DefId` is for `core::ptr::drop_in_place`.
/// The `Option<Ty<'tcx>>` is either `Some(T)`, or `None` for empty drop
/// glue.
///
/// NB: the type must currently be monomorphic to avoid double substitution
/// problems with the MIR shim bodies. `Instance::resolve` enforces this.
// FIXME(#69925) support polymorphic MIR shim bodies properly instead.
DropGlue(DefId, Option<Ty<'tcx>>),
/// Compiler-generated `<T as Clone>::clone` implementation.
@ -99,10 +91,6 @@ pub enum InstanceDef<'tcx> {
/// Additionally, arrays, tuples, and closures get a `Clone` shim even if they aren't `Copy`.
///
/// The `DefId` is for `Clone::clone`, the `Ty` is the type `T` with the builtin `Clone` impl.
///
/// NB: the type must currently be monomorphic to avoid double substitution
/// problems with the MIR shim bodies. `Instance::resolve` enforces this.
// FIXME(#69925) support polymorphic MIR shim bodies properly instead.
CloneShim(DefId, Ty<'tcx>),
}
@ -243,6 +231,27 @@ impl<'tcx> InstanceDef<'tcx> {
_ => false,
}
}
/// Returns `true` when the MIR body associated with this instance should be monomorphized
/// by its users (e.g. codegen or miri) by substituting the `substs` from `Instance` (see
/// `Instance::substs_for_mir_body`).
///
/// Otherwise, returns `false` only for some kinds of shims where the construction of the MIR
/// body should perform necessary substitutions.
pub fn has_polymorphic_mir_body(&self) -> bool {
match *self {
InstanceDef::CloneShim(..)
| InstanceDef::FnPtrShim(..)
| InstanceDef::DropGlue(_, Some(_)) => false,
InstanceDef::ClosureOnceShim { .. }
| InstanceDef::DropGlue(..)
| InstanceDef::Item(_)
| InstanceDef::Intrinsic(..)
| InstanceDef::ReifyShim(..)
| InstanceDef::Virtual(..)
| InstanceDef::VtableShim(..) => true,
}
}
}
impl<'tcx> fmt::Display for Instance<'tcx> {
@ -440,30 +449,18 @@ impl<'tcx> Instance<'tcx> {
Instance { def, substs }
}
/// FIXME(#69925) Depending on the kind of `InstanceDef`, the MIR body associated with an
/// Depending on the kind of `InstanceDef`, the MIR body associated with an
/// instance is expressed in terms of the generic parameters of `self.def_id()`, and in other
/// cases the MIR body is expressed in terms of the types found in the substitution array.
/// In the former case, we want to substitute those generic types and replace them with the
/// values from the substs when monomorphizing the function body. But in the latter case, we
/// don't want to do that substitution, since it has already been done effectively.
///
/// This function returns `Some(substs)` in the former case and None otherwise -- i.e., if
/// This function returns `Some(substs)` in the former case and `None` otherwise -- i.e., if
/// this function returns `None`, then the MIR body does not require substitution during
/// monomorphization.
/// codegen.
pub fn substs_for_mir_body(&self) -> Option<SubstsRef<'tcx>> {
match self.def {
InstanceDef::CloneShim(..)
| InstanceDef::DropGlue(_, Some(_)) => None,
InstanceDef::ClosureOnceShim { .. }
| InstanceDef::DropGlue(..)
// FIXME(#69925): `FnPtrShim` should be in the other branch.
| InstanceDef::FnPtrShim(..)
| InstanceDef::Item(_)
| InstanceDef::Intrinsic(..)
| InstanceDef::ReifyShim(..)
| InstanceDef::Virtual(..)
| InstanceDef::VtableShim(..) => Some(self.substs),
}
if self.def.has_polymorphic_mir_body() { Some(self.substs) } else { None }
}
/// Returns a new `Instance` where generic parameters in `instance.substs` are replaced by