bjoernager/rust
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Auto merge of #101212 - eholk:dyn-star, r=compiler-errors

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Initial implementation of dyn*

This PR adds extremely basic and incomplete support for [dyn*](https://smallcultfollowing.com/babysteps//blog/2022/03/29/dyn-can-we-make-dyn-sized/). The goal is to get something in tree behind a flag to make collaboration easier, and also to make sure the implementation so far is not unreasonable. This PR does quite a few things:

* Introduce `dyn_star` feature flag
* Adds parsing for `dyn* Trait` types
* Defines `dyn* Trait` as a sized type
* Adds support for explicit casts, like `42usize as dyn* Debug`
  * Including const evaluation of such casts
* Adds codegen for drop glue so things are cleaned up properly when a `dyn* Trait` object goes out of scope
* Adds codegen for method calls, at least for methods that take `&self`

Quite a bit is still missing, but this gives us a starting point. Note that this is never intended to become stable surface syntax for Rust, but rather `dyn*` is planned to be used as an implementation detail for async functions in dyn traits.

Joint work with `@nikomatsakis` and `@compiler-errors.`

r? `@bjorn3`
This commit is contained in:
bors 2022-09-14 18:10:51 +00:00
commit 6153d3cbe6
69 changed files with 617 additions and 104 deletions
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5
compiler/rustc_codegen_ssa/src/meth.rs
View file

@ -69,7 +69,7 @@ impl<'a, 'tcx> VirtualIndex {
fn expect_dyn_trait_in_self<'tcx>(ty: Ty<'tcx>) -> ty::PolyExistentialTraitRef<'tcx> {
for arg in ty.peel_refs().walk() {
if let GenericArgKind::Type(ty) = arg.unpack() {
if let ty::Dynamic(data, _) = ty.kind() {
if let ty::Dynamic(data, _, _) = ty.kind() {
return data.principal().expect("expected principal trait object");
}
}
@ -86,6 +86,7 @@ fn expect_dyn_trait_in_self<'tcx>(ty: Ty<'tcx>) -> ty::PolyExistentialTraitRef<'
/// The `trait_ref` encodes the erased self type. Hence if we are
/// making an object `Foo<dyn Trait>` from a value of type `Foo<T>`, then
/// `trait_ref` would map `T: Trait`.
#[instrument(level = "debug", skip(cx))]
pub fn get_vtable<'tcx, Cx: CodegenMethods<'tcx>>(
cx: &Cx,
ty: Ty<'tcx>,
@ -93,8 +94,6 @@ pub fn get_vtable<'tcx, Cx: CodegenMethods<'tcx>>(
) -> Cx::Value {
let tcx = cx.tcx();
debug!("get_vtable(ty={:?}, trait_ref={:?})", ty, trait_ref);
// Check the cache.
if let Some(&val) = cx.vtables().borrow().get(&(ty, trait_ref)) {
return val;

89
compiler/rustc_codegen_ssa/src/mir/block.rs
View file

@ -367,6 +367,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
bx.ret(llval);
}
#[tracing::instrument(level = "trace", skip(self, helper, bx))]
fn codegen_drop_terminator(
&mut self,
helper: TerminatorCodegenHelper<'tcx>,
@ -397,13 +398,29 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
let (drop_fn, fn_abi) = match ty.kind() {
// FIXME(eddyb) perhaps move some of this logic into
// `Instance::resolve_drop_in_place`?
ty::Dynamic(..) => {
ty::Dynamic(_, _, ty::Dyn) => {
// IN THIS ARM, WE HAVE:
// ty = *mut (dyn Trait)
// which is: exists<T> ( *mut T, Vtable<T: Trait> )
// args[0] args[1]
//
// args = ( Data, Vtable )
// |
// v
// /-------\
// | ... |
// \-------/
//
let virtual_drop = Instance {
def: ty::InstanceDef::Virtual(drop_fn.def_id(), 0),
substs: drop_fn.substs,
};
debug!("ty = {:?}", ty);
debug!("drop_fn = {:?}", drop_fn);
debug!("args = {:?}", args);
let fn_abi = bx.fn_abi_of_instance(virtual_drop, ty::List::empty());
let vtable = args[1];
// Truncate vtable off of args list
args = &args[..1];
(
meth::VirtualIndex::from_index(ty::COMMON_VTABLE_ENTRIES_DROPINPLACE)
@ -411,6 +428,51 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
fn_abi,
)
}
ty::Dynamic(_, _, ty::DynStar) => {
// IN THIS ARM, WE HAVE:
// ty = *mut (dyn* Trait)
// which is: *mut exists<T: sizeof(T) == sizeof(usize)> (T, Vtable<T: Trait>)
//
// args = [ * ]
// |
// v
// ( Data, Vtable )
// |
// v
// /-------\
// | ... |
// \-------/
//
//
// WE CAN CONVERT THIS INTO THE ABOVE LOGIC BY DOING
//
// data = &(*args[0]).0 // gives a pointer to Data above (really the same pointer)
// vtable = (*args[0]).1 // loads the vtable out
// (data, vtable) // an equivalent Rust `*mut dyn Trait`
//
// SO THEN WE CAN USE THE ABOVE CODE.
let virtual_drop = Instance {
def: ty::InstanceDef::Virtual(drop_fn.def_id(), 0),
substs: drop_fn.substs,
};
debug!("ty = {:?}", ty);
debug!("drop_fn = {:?}", drop_fn);
debug!("args = {:?}", args);
let fn_abi = bx.fn_abi_of_instance(virtual_drop, ty::List::empty());
let data = args[0];
let data_ty = bx.cx().backend_type(place.layout);
let vtable_ptr =
bx.gep(data_ty, data, &[bx.cx().const_i32(0), bx.cx().const_i32(1)]);
let vtable = bx.load(bx.type_i8p(), vtable_ptr, abi::Align::ONE);
// Truncate vtable off of args list
args = &args[..1];
debug!("args' = {:?}", args);
(
meth::VirtualIndex::from_index(ty::COMMON_VTABLE_ENTRIES_DROPINPLACE)
.get_fn(&mut bx, vtable, ty, &fn_abi),
fn_abi,
)
}
_ => (bx.get_fn_addr(drop_fn), bx.fn_abi_of_instance(drop_fn, ty::List::empty())),
};
helper.do_call(
@ -845,7 +907,30 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
llargs.push(data_ptr);
continue;
}
_ => span_bug!(span, "can't codegen a virtual call on {:?}", op),
Immediate(_) => {
let ty::Ref(_, ty, _) = op.layout.ty.kind() else {
span_bug!(span, "can't codegen a virtual call on {:#?}", op);
};
if !ty.is_dyn_star() {
span_bug!(span, "can't codegen a virtual call on {:#?}", op);
}
// FIXME(dyn-star): Make sure this is done on a &dyn* receiver
let place = op.deref(bx.cx());
let data_ptr = place.project_field(&mut bx, 0);
let meta_ptr = place.project_field(&mut bx, 1);
let meta = bx.load_operand(meta_ptr);
llfn = Some(meth::VirtualIndex::from_index(idx).get_fn(
&mut bx,
meta.immediate(),
op.layout.ty,
&fn_abi,
));
llargs.push(data_ptr.llval);
continue;
}
_ => {
span_bug!(span, "can't codegen a virtual call on {:#?}", op);
}
}
}

16
compiler/rustc_codegen_ssa/src/mir/rvalue.rs
View file

@ -4,6 +4,7 @@ use super::{FunctionCx, LocalRef};
use crate::base;
use crate::common::{self, IntPredicate};
use crate::meth::get_vtable;
use crate::traits::*;
use crate::MemFlags;
@ -271,6 +272,21 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
bug!("unexpected non-pair operand");
}
}
mir::CastKind::DynStar => {
let data = match operand.val {
OperandValue::Ref(_, _, _) => todo!(),
OperandValue::Immediate(v) => v,
OperandValue::Pair(_, _) => todo!(),
};
let trait_ref =
if let ty::Dynamic(data, _, ty::DynStar) = cast.ty.kind() {
data.principal()
} else {
bug!("Only valid to do a DynStar cast into a DynStar type")
};
let vtable = get_vtable(bx.cx(), source.ty(self.mir, bx.tcx()), trait_ref);
OperandValue::Pair(data, vtable)
}
mir::CastKind::Pointer(
PointerCast::MutToConstPointer | PointerCast::ArrayToPointer,
)