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Auto merge of #107772 - compiler-errors:dyn-star-backend-is-ptr, r=eholk
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Make `dyn*`'s value backend type a pointer

One tweak on top of Ralf's commit should fix using `usize` as a `dyn*`-coercible type, and should fix when we're using various other pointer types when LLVM opaque pointers is disabled.

r? `@eholk` but feel free to reassign
cc #107728 (comment) `@RalfJung`
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@bors
bors committed Feb 19, 2023
2 parents fcdbd1c + 7f798c2 commit 73f4019
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Showing 8 changed files with 129 additions and 95 deletions.
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);
}
_ => {}
}

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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:?}"),
};
(src, unsized_info(bx, src_ty_and_layout.ty, dst_ty, old_info))
}
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158 changes: 78 additions & 80 deletions compiler/rustc_codegen_ssa/src/mir/block.rs
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Original file line number Diff line number Diff line change
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) =
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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Original file line number Diff line number Diff line change
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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Original file line number Diff line number Diff line change
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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Original file line number Diff line number Diff line change
@@ -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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Original file line number Diff line number Diff line change
@@ -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,)));
}

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