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Auto merge of #120675 - oli-obk:intrinsics3.0, r=pnkfelix

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Add a scheme for moving away from `extern "rust-intrinsic"` entirely

All `rust-intrinsic`s can become free functions now, either with a fallback body, or with a dummy body and an attribute, requiring backends to actually implement the intrinsic.

This PR demonstrates the dummy-body scheme with the `vtable_size` intrinsic.

cc https://github.com/rust-lang/rust/issues/63585

follow-up to #120500

MCP at https://github.com/rust-lang/compiler-team/issues/720
This commit is contained in:
bors 2024-03-05 00:13:01 +00:00
commit 2eeff462b7
31 changed files with 207 additions and 51 deletions
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2
compiler/rustc_borrowck/src/type_check/mod.rs
View File

@ -1667,7 +1667,7 @@ fn check_call_inputs(
// (Eventually this should use const-generics, but those are not up for the task yet:
// https://github.com/rust-lang/rust/issues/85229.)
if let Some(name @ (sym::simd_shuffle | sym::simd_insert | sym::simd_extract)) =
self.tcx().intrinsic(def_id)
self.tcx().intrinsic(def_id).map(|i| i.name)
{
let idx = match name {
sym::simd_shuffle => 2,

12
compiler/rustc_codegen_cranelift/src/intrinsics/mod.rs
View File

@ -1255,7 +1255,17 @@ fn codegen_regular_intrinsic_call<'tcx>(
// Unimplemented intrinsics must have a fallback body. The fallback body is obtained
// by converting the `InstanceDef::Intrinsic` to an `InstanceDef::Item`.
_ => return Err(Instance::new(instance.def_id(), instance.args)),
_ => {
let intrinsic = fx.tcx.intrinsic(instance.def_id()).unwrap();
if intrinsic.must_be_overridden {
span_bug!(
source_info.span,
"intrinsic {} must be overridden by codegen_cranelift, but isn't",
intrinsic.name,
);
}
return Err(Instance::new(instance.def_id(), instance.args));
}
}
let ret_block = fx.get_block(destination.unwrap());

4
compiler/rustc_codegen_ssa/src/back/symbol_export.rs
View File

@ -81,6 +81,10 @@ fn reachable_non_generics_provider(tcx: TyCtxt<'_>, _: LocalCrate) -> DefIdMap<S
return library.kind.is_statically_included().then_some(def_id);
}
if tcx.intrinsic(def_id).is_some_and(|i| i.must_be_overridden) {
return None;
}
// Only consider nodes that actually have exported symbols.
match tcx.def_kind(def_id) {
DefKind::Fn | DefKind::Static(_) => {}

59
compiler/rustc_codegen_ssa/src/mir/block.rs
View File

@ -12,12 +12,12 @@
use rustc_ast as ast;
use rustc_ast::{InlineAsmOptions, InlineAsmTemplatePiece};
use rustc_hir::lang_items::LangItem;
use rustc_middle::mir::{self, AssertKind, SwitchTargets, UnwindTerminateReason};
use rustc_middle::mir::{self, AssertKind, BasicBlock, SwitchTargets, UnwindTerminateReason};
use rustc_middle::ty::layout::{HasTyCtxt, LayoutOf, ValidityRequirement};
use rustc_middle::ty::print::{with_no_trimmed_paths, with_no_visible_paths};
use rustc_middle::ty::{self, Instance, Ty};
use rustc_session::config::OptLevel;
use rustc_span::{source_map::Spanned, sym, Span, Symbol};
use rustc_span::{source_map::Spanned, sym, Span};
use rustc_target::abi::call::{ArgAbi, FnAbi, PassMode, Reg};
use rustc_target::abi::{self, HasDataLayout, WrappingRange};
use rustc_target::spec::abi::Abi;
@ -680,7 +680,7 @@ fn codegen_panic_intrinsic(
&mut self,
helper: &TerminatorCodegenHelper<'tcx>,
bx: &mut Bx,
intrinsic: Option<Symbol>,
intrinsic: Option<ty::IntrinsicDef>,
instance: Option<Instance<'tcx>>,
source_info: mir::SourceInfo,
target: Option<mir::BasicBlock>,
@ -690,7 +690,7 @@ fn codegen_panic_intrinsic(
// Emit a panic or a no-op for `assert_*` intrinsics.
// These are intrinsics that compile to panics so that we can get a message
// which mentions the offending type, even from a const context.
let panic_intrinsic = intrinsic.and_then(|s| ValidityRequirement::from_intrinsic(s));
let panic_intrinsic = intrinsic.and_then(|i| ValidityRequirement::from_intrinsic(i.name));
if let Some(requirement) = panic_intrinsic {
let ty = instance.unwrap().args.type_at(0);
@ -826,14 +826,20 @@ fn codegen_call_terminator(
// The arguments we'll be passing. Plus one to account for outptr, if used.
let arg_count = fn_abi.args.len() + fn_abi.ret.is_indirect() as usize;
if intrinsic == Some(sym::caller_location) {
if matches!(intrinsic, Some(ty::IntrinsicDef { name: sym::caller_location, .. })) {
return if let Some(target) = target {
let location =
self.get_caller_location(bx, mir::SourceInfo { span: fn_span, ..source_info });
let mut llargs = Vec::with_capacity(arg_count);
let ret_dest =
self.make_return_dest(bx, destination, &fn_abi.ret, &mut llargs, true, true);
let ret_dest = self.make_return_dest(
bx,
destination,
&fn_abi.ret,
&mut llargs,
intrinsic,
Some(target),
);
assert_eq!(llargs, []);
if let ReturnDest::IndirectOperand(tmp, _) = ret_dest {
location.val.store(bx, tmp);
@ -846,7 +852,7 @@ fn codegen_call_terminator(
}
let instance = match intrinsic {
None | Some(sym::drop_in_place) => instance,
None | Some(ty::IntrinsicDef { name: sym::drop_in_place, .. }) => instance,
Some(intrinsic) => {
let mut llargs = Vec::with_capacity(1);
let ret_dest = self.make_return_dest(
@ -854,8 +860,8 @@ fn codegen_call_terminator(
destination,
&fn_abi.ret,
&mut llargs,
true,
target.is_some(),
Some(intrinsic),
target,
);
let dest = match ret_dest {
_ if fn_abi.ret.is_indirect() => llargs[0],
@ -873,7 +879,7 @@ fn codegen_call_terminator(
// The indices passed to simd_shuffle in the
// third argument must be constant. This is
// checked by the type-checker.
if i == 2 && intrinsic == sym::simd_shuffle {
if i == 2 && intrinsic.name == sym::simd_shuffle {
if let mir::Operand::Constant(constant) = &arg.node {
let (llval, ty) = self.simd_shuffle_indices(bx, constant);
return OperandRef {
@ -903,14 +909,33 @@ fn codegen_call_terminator(
MergingSucc::False
};
}
Err(instance) => Some(instance),
Err(instance) => {
if intrinsic.must_be_overridden {
span_bug!(
span,
"intrinsic {} must be overridden by codegen backend, but isn't",
intrinsic.name,
);
}
Some(instance)
}
}
}
};
let mut llargs = Vec::with_capacity(arg_count);
let destination = target.as_ref().map(|&target| {
(self.make_return_dest(bx, destination, &fn_abi.ret, &mut llargs, false, true), target)
(
self.make_return_dest(
bx,
destination,
&fn_abi.ret,
&mut llargs,
None,
Some(target),
),
target,
)
});
// Split the rust-call tupled arguments off.
@ -1643,10 +1668,10 @@ fn make_return_dest(
dest: mir::Place<'tcx>,
fn_ret: &ArgAbi<'tcx, Ty<'tcx>>,
llargs: &mut Vec<Bx::Value>,
is_intrinsic: bool,
has_target: bool,
intrinsic: Option<ty::IntrinsicDef>,
target: Option<BasicBlock>,
) -> ReturnDest<'tcx, Bx::Value> {
if !has_target {
if target.is_none() {
return ReturnDest::Nothing;
}
// If the return is ignored, we can just return a do-nothing `ReturnDest`.
@ -1667,7 +1692,7 @@ fn make_return_dest(
tmp.storage_live(bx);
llargs.push(tmp.llval);
ReturnDest::IndirectOperand(tmp, index)
} else if is_intrinsic {
} else if intrinsic.is_some() {
// Currently, intrinsics always need a location to store
// the result, so we create a temporary `alloca` for the
// result.

4
compiler/rustc_feature/src/builtin_attrs.rs
View File

@ -867,6 +867,10 @@ pub struct BuiltinAttribute {
rustc_no_mir_inline, Normal, template!(Word), WarnFollowing,
"#[rustc_no_mir_inline] prevents the MIR inliner from inlining a function while not affecting codegen"
),
rustc_attr!(
rustc_intrinsic_must_be_overridden, Normal, template!(Word), ErrorFollowing,
"the `#[rustc_intrinsic_must_be_overridden]` attribute is used to declare intrinsics without real bodies",
),
// ==========================================================================
// Internal attributes, Testing:

4
compiler/rustc_hir_analysis/src/check/check.rs
View File

@ -527,12 +527,12 @@ pub(crate) fn check_item_type(tcx: TyCtxt<'_>, def_id: LocalDefId) {
check_enum(tcx, def_id);
}
DefKind::Fn => {
if let Some(name) = tcx.intrinsic(def_id) {
if let Some(i) = tcx.intrinsic(def_id) {
intrinsic::check_intrinsic_type(
tcx,
def_id,
tcx.def_ident_span(def_id).unwrap(),
name,
i.name,
Abi::Rust,
)
}

2
compiler/rustc_hir_typeck/src/callee.rs
View File

@ -545,7 +545,7 @@ fn confirm_builtin_call(
if let Some(def_id) = def_id
&& self.tcx.def_kind(def_id) == hir::def::DefKind::Fn
&& matches!(self.tcx.intrinsic(def_id), Some(sym::const_eval_select))
&& self.tcx.is_intrinsic(def_id, sym::const_eval_select)
{
let fn_sig = self.resolve_vars_if_possible(fn_sig);
for idx in 0..=1 {

2
compiler/rustc_lint/src/builtin.rs
View File

@ -1231,7 +1231,7 @@ fn get_transmute_from_to<'tcx>(
}
fn def_id_is_transmute(cx: &LateContext<'_>, def_id: DefId) -> bool {
matches!(cx.tcx.intrinsic(def_id), Some(sym::transmute))
cx.tcx.is_intrinsic(def_id, sym::transmute)
}
}
}

2
compiler/rustc_metadata/src/rmeta/decoder.rs
View File

@ -1749,7 +1749,7 @@ fn get_attr_flags(self, index: DefIndex) -> AttrFlags {
self.root.tables.attr_flags.get(self, index)
}
fn get_intrinsic(self, index: DefIndex) -> Option<Symbol> {
fn get_intrinsic(self, index: DefIndex) -> Option<ty::IntrinsicDef> {
self.root.tables.intrinsic.get(self, index).map(|d| d.decode(self))
}

11
compiler/rustc_metadata/src/rmeta/encoder.rs
View File

@ -1053,11 +1053,14 @@ fn should_encode_mir(
// Full-fledged functions + closures
DefKind::AssocFn | DefKind::Fn | DefKind::Closure => {
let generics = tcx.generics_of(def_id);
let opt = tcx.sess.opts.unstable_opts.always_encode_mir
let mut opt = tcx.sess.opts.unstable_opts.always_encode_mir
|| (tcx.sess.opts.output_types.should_codegen()
&& reachable_set.contains(&def_id)
&& (generics.requires_monomorphization(tcx)
|| tcx.cross_crate_inlinable(def_id)));
if let Some(intrinsic) = tcx.intrinsic(def_id) {
opt &= !intrinsic.must_be_overridden;
}
// The function has a `const` modifier or is in a `#[const_trait]`.
let is_const_fn = tcx.is_const_fn_raw(def_id.to_def_id())
|| tcx.is_const_default_method(def_id.to_def_id());
@ -1409,9 +1412,9 @@ fn encode_def_ids(&mut self) {
if let DefKind::Fn | DefKind::AssocFn = def_kind {
self.tables.asyncness.set_some(def_id.index, tcx.asyncness(def_id));
record_array!(self.tables.fn_arg_names[def_id] <- tcx.fn_arg_names(def_id));
if let Some(name) = tcx.intrinsic(def_id) {
record!(self.tables.intrinsic[def_id] <- name);
}
}
if let Some(name) = tcx.intrinsic(def_id) {
record!(self.tables.intrinsic[def_id] <- name);
}
if let DefKind::TyParam = def_kind {
let default = self.tcx.object_lifetime_default(def_id);

2
compiler/rustc_metadata/src/rmeta/mod.rs
View File

@ -375,7 +375,7 @@ fn encode(&self, buf: &mut FileEncoder) -> LazyTables {
define_tables! {
- defaulted:
intrinsic: Table<DefIndex, Option<LazyValue<Symbol>>>,
intrinsic: Table<DefIndex, Option<LazyValue<ty::IntrinsicDef>>>,
is_macro_rules: Table<DefIndex, bool>,
is_type_alias_impl_trait: Table<DefIndex, bool>,
type_alias_is_lazy: Table<DefIndex, bool>,

2
compiler/rustc_middle/src/query/erase.rs
View File

@ -241,7 +241,7 @@ impl EraseType for $ty {
Option<rustc_target::abi::FieldIdx>,
Option<rustc_target::spec::PanicStrategy>,
Option<usize>,
Option<rustc_span::Symbol>,
Option<rustc_middle::ty::IntrinsicDef>,
Result<(), rustc_errors::ErrorGuaranteed>,
Result<(), rustc_middle::traits::query::NoSolution>,
Result<rustc_middle::traits::EvaluationResult, rustc_middle::traits::OverflowError>,

2
compiler/rustc_middle/src/query/mod.rs
View File

@ -1760,7 +1760,7 @@
separate_provide_extern
}
/// Whether the function is an intrinsic
query intrinsic(def_id: DefId) -> Option<Symbol> {
query intrinsic(def_id: DefId) -> Option<rustc_middle::ty::IntrinsicDef> {
desc { |tcx| "fetch intrinsic name if `{}` is an intrinsic", tcx.def_path_str(def_id) }
separate_provide_extern
}

17
compiler/rustc_middle/src/ty/intrinsic.rs Normal file
View File

@ -0,0 +1,17 @@
use rustc_span::{def_id::DefId, Symbol};
use super::TyCtxt;
#[derive(Copy, Clone, Debug, Decodable, Encodable, HashStable)]
pub struct IntrinsicDef {
pub name: Symbol,
/// Whether the intrinsic has no meaningful body and all backends need to shim all calls to it.
pub must_be_overridden: bool,
}
impl TyCtxt<'_> {
pub fn is_intrinsic(self, def_id: DefId, name: Symbol) -> bool {
let Some(i) = self.intrinsic(def_id) else { return false };
i.name == name
}
}

2
compiler/rustc_middle/src/ty/mod.rs
View File

@ -30,6 +30,7 @@
pub use assoc::*;
pub use generic_args::*;
pub use generics::*;
pub use intrinsic::IntrinsicDef;
use rustc_ast as ast;
use rustc_ast::node_id::NodeMap;
pub use rustc_ast_ir::{Movability, Mutability};
@ -149,6 +150,7 @@
mod generics;
mod impls_ty;
mod instance;
mod intrinsic;
mod list;
mod opaque_types;
mod parameterized;

1
compiler/rustc_middle/src/ty/parameterized.rs
View File

@ -75,6 +75,7 @@ impl $crate::ty::ParameterizedOverTcx for $ty {
ty::Visibility<DefIndex>,
ty::adjustment::CoerceUnsizedInfo,
ty::fast_reject::SimplifiedType,
ty::IntrinsicDef,
rustc_ast::Attribute,
rustc_ast::DelimArgs,
rustc_ast::expand::StrippedCfgItem<rustc_hir::def_id::DefIndex>,

15
compiler/rustc_middle/src/ty/util.rs
View File

@ -19,7 +19,7 @@
use rustc_index::bit_set::GrowableBitSet;
use rustc_macros::HashStable;
use rustc_session::Limit;
use rustc_span::{sym, Symbol};
use rustc_span::sym;
use rustc_target::abi::{Integer, IntegerType, Primitive, Size};
use rustc_target::spec::abi::Abi;
use smallvec::SmallVec;
@ -1641,12 +1641,19 @@ pub fn is_doc_notable_trait(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
.any(|items| items.iter().any(|item| item.has_name(sym::notable_trait)))
}
/// Determines whether an item is an intrinsic by Abi. or by whether it has a `rustc_intrinsic` attribute
pub fn intrinsic(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Option<Symbol> {
/// Determines whether an item is an intrinsic (which may be via Abi or via the `rustc_intrinsic` attribute)
pub fn intrinsic(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Option<ty::IntrinsicDef> {
match tcx.def_kind(def_id) {
DefKind::Fn | DefKind::AssocFn => {}
_ => return None,
}
if matches!(tcx.fn_sig(def_id).skip_binder().abi(), Abi::RustIntrinsic)
|| tcx.has_attr(def_id, sym::rustc_intrinsic)
{
Some(tcx.item_name(def_id.into()))
Some(ty::IntrinsicDef {
name: tcx.item_name(def_id.into()),
must_be_overridden: tcx.has_attr(def_id, sym::rustc_intrinsic_must_be_overridden),
})
} else {
None
}

2
compiler/rustc_mir_dataflow/src/rustc_peek.rs
View File

@ -202,7 +202,7 @@ fn from_terminator<'tcx>(
&terminator.kind
{
if let ty::FnDef(def_id, fn_args) = *func.const_.ty().kind() {
if tcx.intrinsic(def_id)? != sym::rustc_peek {
if tcx.intrinsic(def_id)?.name != sym::rustc_peek {
return None;
}

4
compiler/rustc_mir_transform/src/cross_crate_inline.rs
View File

@ -23,6 +23,10 @@ fn cross_crate_inlinable(tcx: TyCtxt<'_>, def_id: LocalDefId) -> bool {
return false;
}
if tcx.intrinsic(def_id).is_some_and(|i| i.must_be_overridden) {
return false;
}
// This just reproduces the logic from Instance::requires_inline.
match tcx.def_kind(def_id) {
DefKind::Ctor(..) | DefKind::Closure => return true,

4
compiler/rustc_mir_transform/src/instsimplify.rs
View File

@ -323,8 +323,8 @@ fn resolve_rust_intrinsic<'tcx>(
func_ty: Ty<'tcx>,
) -> Option<(Symbol, GenericArgsRef<'tcx>)> {
if let ty::FnDef(def_id, args) = *func_ty.kind() {
let name = tcx.intrinsic(def_id)?;
return Some((name, args));
let intrinsic = tcx.intrinsic(def_id)?;
return Some((intrinsic.name, args));
}
None
}

8
compiler/rustc_mir_transform/src/lib.rs
View File

@ -160,7 +160,7 @@ fn remap_mir_for_const_eval_select<'tcx>(
fn_span,
..
} if let ty::FnDef(def_id, _) = *const_.ty().kind()
&& matches!(tcx.intrinsic(def_id), Some(sym::const_eval_select)) =>
&& tcx.is_intrinsic(def_id, sym::const_eval_select) =>
{
let [tupled_args, called_in_const, called_at_rt]: [_; 3] =
std::mem::take(args).try_into().unwrap();
@ -632,6 +632,12 @@ fn optimized_mir(tcx: TyCtxt<'_>, did: LocalDefId) -> &Body<'_> {
}
fn inner_optimized_mir(tcx: TyCtxt<'_>, did: LocalDefId) -> Body<'_> {
if tcx.intrinsic(did).is_some_and(|i| i.must_be_overridden) {
span_bug!(
tcx.def_span(did),
"this intrinsic must be overridden by the codegen backend, it has no meaningful body",
)
}
if tcx.is_constructor(did.to_def_id()) {
// There's no reason to run all of the MIR passes on constructors when
// we can just output the MIR we want directly. This also saves const

10
compiler/rustc_mir_transform/src/lower_intrinsics.rs
View File

@ -14,9 +14,9 @@ fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
if let TerminatorKind::Call { func, args, destination, target, .. } =
&mut terminator.kind
&& let ty::FnDef(def_id, generic_args) = *func.ty(local_decls, tcx).kind()
&& let Some(intrinsic_name) = tcx.intrinsic(def_id)
&& let Some(intrinsic) = tcx.intrinsic(def_id)
{
match intrinsic_name {
match intrinsic.name {
sym::unreachable => {
terminator.kind = TerminatorKind::Unreachable;
}
@ -105,7 +105,7 @@ fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
lhs = args.next().unwrap();
rhs = args.next().unwrap();
}
let bin_op = match intrinsic_name {
let bin_op = match intrinsic.name {
sym::wrapping_add => BinOp::Add,
sym::wrapping_sub => BinOp::Sub,
sym::wrapping_mul => BinOp::Mul,
@ -136,7 +136,7 @@ fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
lhs = args.next().unwrap();
rhs = args.next().unwrap();
}
let bin_op = match intrinsic_name {
let bin_op = match intrinsic.name {
sym::add_with_overflow => BinOp::Add,
sym::sub_with_overflow => BinOp::Sub,
sym::mul_with_overflow => BinOp::Mul,
@ -155,7 +155,7 @@ fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
sym::size_of | sym::min_align_of => {
if let Some(target) = *target {
let tp_ty = generic_args.type_at(0);
let null_op = match intrinsic_name {
let null_op = match intrinsic.name {
sym::size_of => NullOp::SizeOf,
sym::min_align_of => NullOp::AlignOf,
_ => bug!("unexpected intrinsic"),

5
compiler/rustc_monomorphize/src/collector.rs
View File

@ -1019,6 +1019,11 @@ fn should_codegen_locally<'tcx>(tcx: TyCtxt<'tcx>, instance: &Instance<'tcx>) ->
return false;
}
if tcx.intrinsic(def_id).is_some_and(|i| i.must_be_overridden) {
// These are implemented by backends directly and have no meaningful body.
return false;
}
if def_id.is_local() {
// Local items cannot be referred to locally without monomorphizing them locally.
return true;

1
compiler/rustc_span/src/symbol.rs
View File

@ -1525,6 +1525,7 @@
rustc_inherit_overflow_checks,
rustc_insignificant_dtor,
rustc_intrinsic,
rustc_intrinsic_must_be_overridden,
rustc_layout,
rustc_layout_scalar_valid_range_end,
rustc_layout_scalar_valid_range_start,

4
compiler/rustc_ty_utils/src/instance.rs
View File

@ -1,5 +1,4 @@
use rustc_errors::ErrorGuaranteed;
use rustc_hir::def::DefKind;
use rustc_hir::def_id::DefId;
use rustc_infer::infer::TyCtxtInferExt;
use rustc_middle::query::Providers;
@ -28,8 +27,7 @@ fn resolve_instance<'tcx>(
tcx.normalize_erasing_regions(param_env, args),
)
} else {
let def = if matches!(tcx.def_kind(def_id), DefKind::Fn) && tcx.intrinsic(def_id).is_some()
{
let def = if tcx.intrinsic(def_id).is_some() {
debug!(" => intrinsic");
ty::InstanceDef::Intrinsic(def_id)
} else if Some(def_id) == tcx.lang_items().drop_in_place_fn() {

14
library/core/src/intrinsics.rs
View File

@ -2499,9 +2499,8 @@ pub const fn unlikely(b: bool) -> bool {
#[rustc_nounwind]
pub fn black_box<T>(dummy: T) -> T;
/// `ptr` must point to a vtable.
/// The intrinsic will return the size stored in that vtable.
#[rustc_nounwind]
#[cfg(bootstrap)]
pub fn vtable_size(ptr: *const ()) -> usize;
/// `ptr` must point to a vtable.
@ -2681,6 +2680,17 @@ pub(crate) const fn debug_assertions() -> bool {
#[cfg_attr(bootstrap, inline)]
pub const unsafe fn const_deallocate(_ptr: *mut u8, _size: usize, _align: usize) {}
/// `ptr` must point to a vtable.
/// The intrinsic will return the size stored in that vtable.
#[rustc_nounwind]
#[unstable(feature = "core_intrinsics", issue = "none")]
#[cfg_attr(not(bootstrap), rustc_intrinsic)]
#[cfg_attr(not(bootstrap), rustc_intrinsic_must_be_overridden)]
#[cfg(not(bootstrap))]
pub unsafe fn vtable_size(_ptr: *const ()) -> usize {
unreachable!()
}
// Some functions are defined here because they accidentally got made
// available in this module on stable. See <https://github.com/rust-lang/rust/issues/15702>.
// (`transmute` also falls into this category, but it cannot be wrapped due to the

13
src/doc/unstable-book/src/language-features/intrinsics.md
View File

@ -52,12 +52,23 @@ with any regular function.
Various intrinsics have native MIR operations that they correspond to. Instead of requiring
backends to implement both the intrinsic and the MIR operation, the `lower_intrinsics` pass
will convert the calls to the MIR operation. Backends do not need to know about these intrinsics
at all.
at all. These intrinsics only make sense without a body, and can either be declared as a "rust-intrinsic"
or as a `#[rustc_intrinsic]`. The body is never used, as calls to the intrinsic do not exist
anymore after MIR analyses.
## Intrinsics without fallback logic
These must be implemented by all backends.
### `#[rustc_intrinsic]` declarations
These are written like intrinsics with fallback bodies, but the body is irrelevant.
Use `loop {}` for the body or call the intrinsic recursively and add
`#[rustc_intrinsic_must_be_overridden]` to the function to ensure that backends don't
invoke the body.
### Legacy extern ABI based intrinsics
These are imported as if they were FFI functions, with the special
`rust-intrinsic` ABI. For example, if one was in a freestanding
context, but wished to be able to `transmute` between types, and

2
src/tools/clippy/clippy_utils/src/qualify_min_const_fn.rs
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@ -334,7 +334,7 @@ fn check_terminator<'tcx>(
// within const fns. `transmute` is allowed in all other const contexts.
// This won't really scale to more intrinsics or functions. Let's allow const
// transmutes in const fn before we add more hacks to this.
if matches!(tcx.intrinsic(fn_def_id), Some(sym::transmute)) {
if tcx.is_intrinsic(fn_def_id, sym::transmute) {
return Err((
span,
"can only call `transmute` from const items, not `const fn`".into(),

20
tests/ui/intrinsics/always-gets-overridden.rs Normal file
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@ -0,0 +1,20 @@
//! Check that `vtable_size` gets overridden by llvm backend even if there is no
//! `rustc_intrinsic_must_be_overridden` attribute on this usage.
#![feature(rustc_attrs)]
//@run-pass
#[rustc_intrinsic]
pub unsafe fn vtable_size(_ptr: *const ()) -> usize {
panic!();
}
trait Trait {}
impl Trait for () {}
fn main() {
let x: &dyn Trait = &();
unsafe {
let (_data, vtable): (*const (), *const ()) = core::mem::transmute(x);
assert_eq!(vtable_size(vtable), 0);
}
}

18
tests/ui/intrinsics/not-overridden.rs Normal file
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@ -0,0 +1,18 @@
//! Check that intrinsics that do not get overridden, but are marked as such,
//! cause an error instead of silently invoking the body.
#![feature(rustc_attrs, effects)]
//@ build-fail
//@ failure-status:101
//@ normalize-stderr-test ".*note: .*\n\n" -> ""
//@ normalize-stderr-test "thread 'rustc' panicked.*:\n.*\n" -> ""
//@ normalize-stderr-test "internal compiler error:.*: intrinsic const_deallocate " -> ""
//@ rustc-env:RUST_BACKTRACE=0
#[rustc_intrinsic]
#[rustc_intrinsic_must_be_overridden]
pub const unsafe fn const_deallocate(_ptr: *mut u8, _size: usize, _align: usize) {}
fn main() {
unsafe { const_deallocate(std::ptr::null_mut(), 0, 0) }
//~^ ERROR: must be overridden
}

10
tests/ui/intrinsics/not-overridden.stderr Normal file
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@ -0,0 +1,10 @@
error: must be overridden by codegen backend, but isn't
--> $DIR/not-overridden.rs:16:14
|
LL | unsafe { const_deallocate(std::ptr::null_mut(), 0, 0) }
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
query stack during panic:
end of query stack
error: aborting due to 1 previous error