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Make dyn*'s value backend type a pointer #107772

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merged 5 commits into from
Feb 19, 2023
Merged

Make dyn*'s value backend type a pointer #107772

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88e39ee
make first component of dyn* use pointer layout+type, and adjust DynS…
RalfJung Feb 6, 2023
df52e20
Use inttoptr to support usize as dyn* value, use pointercast to make …
compiler-errors Feb 7, 2023
1f11d84
Add codegen test
compiler-errors Feb 10, 2023
e82cc65
Make dyn* have the same scalar pair ABI as corresponding fat pointer
compiler-errors Feb 15, 2023
7f798c2
Emit the right types for vtable pointers when dropping dyn*
compiler-errors Feb 15, 2023
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7 changes: 6 additions & 1 deletion compiler/rustc_codegen_llvm/src/type_of.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -329,7 +329,7 @@ impl<'tcx> LayoutLlvmExt<'tcx> for TyAndLayout<'tcx> {
) -> &'a Type {
// HACK(eddyb) special-case fat pointers until LLVM removes
// pointee types, to avoid bitcasting every `OperandRef::deref`.
match self.ty.kind() {
match *self.ty.kind() {
ty::Ref(..) | ty::RawPtr(_) => {
return self.field(cx, index).llvm_type(cx);
}
Expand All @@ -339,6 +339,11 @@ impl<'tcx> LayoutLlvmExt<'tcx> for TyAndLayout<'tcx> {
let ptr_ty = cx.tcx.mk_mut_ptr(self.ty.boxed_ty());
return cx.layout_of(ptr_ty).scalar_pair_element_llvm_type(cx, index, immediate);
}
// `dyn* Trait` has the same ABI as `*mut dyn Trait`
ty::Dynamic(bounds, region, ty::DynStar) => {
let ptr_ty = cx.tcx.mk_mut_ptr(cx.tcx.mk_dynamic(bounds, region, ty::Dyn));
return cx.layout_of(ptr_ty).scalar_pair_element_llvm_type(cx, index, immediate);
}
_ => {}
}

Expand Down
15 changes: 8 additions & 7 deletions compiler/rustc_codegen_ssa/src/base.rs
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Expand Up @@ -39,7 +39,7 @@ use rustc_session::Session;
use rustc_span::symbol::sym;
use rustc_span::Symbol;
use rustc_span::{DebuggerVisualizerFile, DebuggerVisualizerType};
use rustc_target::abi::{Align, Size, VariantIdx};
use rustc_target::abi::{Align, VariantIdx};

use std::collections::BTreeSet;
use std::time::{Duration, Instant};
Expand Down Expand Up @@ -273,12 +273,13 @@ pub fn cast_to_dyn_star<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
matches!(dst_ty.kind(), ty::Dynamic(_, _, ty::DynStar)),
"destination type must be a dyn*"
);
// FIXME(dyn-star): this is probably not the best way to check if this is
// a pointer, and really we should ensure that the value is a suitable
// pointer earlier in the compilation process.
let src = match src_ty_and_layout.pointee_info_at(bx.cx(), Size::ZERO) {
Some(_) => bx.ptrtoint(src, bx.cx().type_isize()),
None => bx.bitcast(src, bx.type_isize()),
// FIXME(dyn-star): We can remove this when all supported LLVMs use opaque ptrs only.
let unit_ptr = bx.cx().type_ptr_to(bx.cx().type_struct(&[], false));
let src = match bx.cx().type_kind(bx.cx().backend_type(src_ty_and_layout)) {
TypeKind::Pointer => bx.pointercast(src, unit_ptr),
TypeKind::Integer => bx.inttoptr(src, unit_ptr),
// FIXME(dyn-star): We probably have to do a bitcast first, then inttoptr.
kind => bug!("unexpected TypeKind for left-hand side of `dyn*` cast: {kind:?}"),
Comment on lines +281 to +282
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This can probably be hit by using a type such as

#[repr(C)]
struct S(usize);

and then doing S(0) as dyn* Send or something like that.

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That's broken for another reason (#104694), which I plan on rebasing/reworking once your Miri support for dyn* PR lands.

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Yeah that's not surprising -- I assume so far this has only been tested with types that have Scalar layout.

(i32, i32) would also be an interesting testcase, that will have ScalarPair layout. Also better left for a future PR, probably.

};
(src, unsized_info(bx, src_ty_and_layout.ty, dst_ty, old_info))
}
Expand Down
158 changes: 78 additions & 80 deletions compiler/rustc_codegen_ssa/src/mir/block.rs
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Expand Up @@ -452,86 +452,84 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
args1 = [place.llval];
&args1[..]
};
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::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)
.get_fn(bx, vtable, ty, &fn_abi),
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(bx, vtable, ty, &fn_abi),
fn_abi,
)
}
_ => (bx.get_fn_addr(drop_fn), bx.fn_abi_of_instance(drop_fn, ty::List::empty())),
};
let (drop_fn, fn_abi) =
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match ty.kind() {
// FIXME(eddyb) perhaps move some of this logic into
// `Instance::resolve_drop_in_place`?
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)
.get_fn(bx, vtable, ty, &fn_abi),
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 meta_ptr = place.project_field(bx, 1);
let meta = bx.load_operand(meta_ptr);
// Truncate vtable off of args list
args = &args[..1];
debug!("args' = {:?}", args);
(
meth::VirtualIndex::from_index(ty::COMMON_VTABLE_ENTRIES_DROPINPLACE)
.get_fn(bx, meta.immediate(), ty, &fn_abi),
fn_abi,
)
}
_ => (bx.get_fn_addr(drop_fn), bx.fn_abi_of_instance(drop_fn, ty::List::empty())),
};
helper.do_call(
self,
bx,
Expand Down
2 changes: 1 addition & 1 deletion compiler/rustc_middle/src/ty/layout.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -770,7 +770,7 @@ where

ty::Dynamic(_, _, ty::DynStar) => {
if i == 0 {
TyMaybeWithLayout::Ty(tcx.types.usize)
TyMaybeWithLayout::Ty(tcx.mk_mut_ptr(tcx.types.unit))
} else if i == 1 {
// FIXME(dyn-star) same FIXME as above applies here too
TyMaybeWithLayout::Ty(
Expand Down
2 changes: 1 addition & 1 deletion compiler/rustc_ty_utils/src/layout.rs
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Expand Up @@ -193,7 +193,7 @@ fn layout_of_uncached<'tcx>(
}

ty::Dynamic(_, _, ty::DynStar) => {
let mut data = scalar_unit(Int(dl.ptr_sized_integer(), false));
let mut data = scalar_unit(Pointer(AddressSpace::DATA));
data.valid_range_mut().start = 0;
let mut vtable = scalar_unit(Pointer(AddressSpace::DATA));
vtable.valid_range_mut().start = 1;
Expand Down
8 changes: 3 additions & 5 deletions compiler/rustc_type_ir/src/sty.rs
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Expand Up @@ -26,11 +26,9 @@ pub enum DynKind {
Dyn,
/// A sized `dyn* Trait` object
///
/// These objects are represented as a `(data, vtable)` pair where `data` is a ptr-sized value
/// (often a pointer to the real object, but not necessarily) and `vtable` is a pointer to
/// the vtable for `dyn* Trait`. The representation is essentially the same as `&dyn Trait`
/// or similar, but the drop function included in the vtable is responsible for freeing the
/// underlying storage if needed. This allows a `dyn*` object to be treated agnostically with
/// These objects are represented as a `(data, vtable)` pair where `data` is a value of some
/// ptr-sized and ptr-aligned dynamically determined type `T` and `vtable` is a pointer to the
/// vtable of `impl T for Trait`. This allows a `dyn*` object to be treated agnostically with
/// respect to whether it points to a `Box<T>`, `Rc<T>`, etc.
DynStar,
}
Expand Down
9 changes: 9 additions & 0 deletions tests/codegen/function-arguments.rs
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@@ -1,6 +1,7 @@
// compile-flags: -O -C no-prepopulate-passes

#![crate_type = "lib"]
#![feature(dyn_star)]

use std::mem::MaybeUninit;
use std::num::NonZeroU64;
Expand Down Expand Up @@ -279,3 +280,11 @@ pub fn enum_id_1(x: Option<Result<u16, u16>>) -> Option<Result<u16, u16>> {
pub fn enum_id_2(x: Option<u8>) -> Option<u8> {
x
}

// CHECK: { {{\{\}\*|ptr}}, {{.+}} } @dyn_star({{\{\}\*|ptr}} noundef %x.0, {{.+}} noalias noundef readonly align {{.*}} dereferenceable({{.*}}) %x.1)
// Expect an ABI something like `{ {}*, [3 x i64]* }`, but that's hard to match on generically,
// so do like the `trait_box` test and just match on `{{.+}}` for the vtable.
#[no_mangle]
pub fn dyn_star(x: dyn* Drop) -> dyn* Drop {
x
}
23 changes: 23 additions & 0 deletions tests/ui/dyn-star/llvm-old-style-ptrs.rs
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@@ -0,0 +1,23 @@
// run-pass
// compile-flags: -Copt-level=0 -Cllvm-args=-opaque-pointers=0

// (opaque-pointers flag is called force-opaque-pointers in LLVM 13...)
// min-llvm-version: 14.0

// This test can be removed once non-opaque pointers are gone from LLVM, maybe.

#![feature(dyn_star, pointer_like_trait)]
#![allow(incomplete_features)]

use std::fmt::Debug;
use std::marker::PointerLike;

fn make_dyn_star<'a>(t: impl PointerLike + Debug + 'a) -> dyn* Debug + 'a {
t as _
}

fn main() {
println!("{:?}", make_dyn_star(Box::new(1i32)));
println!("{:?}", make_dyn_star(2usize));
println!("{:?}", make_dyn_star((3usize,)));
}