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Auto merge of #125507 - compiler-errors:type-length-limit, r=lcnr

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Re-implement a type-size based limit

r? lcnr

This PR reintroduces the type length limit added in #37789, which was accidentally made practically useless by the caching changes to `Ty::walk` in #72412, which caused the `walk` function to no longer walk over identical elements.

Hitting this length limit is not fatal unless we are in codegen -- so it shouldn't affect passes like the mir inliner which creates potentially very large types (which we observed, for example, when the new trait solver compiles `itertools` in `--release` mode).

This also increases the type length limit from `1048576 == 2 ** 20` to `2 ** 24`, which covers all of the code that can be reached with craterbot-check. Individual crates can increase the length limit further if desired.

Perf regression is mild and I think we should accept it -- reinstating this limit is important for the new trait solver and to make sure we don't accidentally hit more type-size related regressions in the future.

Fixes #125460
This commit is contained in:
bors 2024-07-03 11:56:36 +00:00
commit c872a1418a
54 changed files with 360 additions and 268 deletions
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14
compiler/rustc_middle/src/error.rs
View file

@ -1,4 +1,5 @@
use std::fmt;
use std::path::PathBuf;
use rustc_errors::{codes::*, DiagArgName, DiagArgValue, DiagMessage};
use rustc_macros::{Diagnostic, Subdiagnostic};
@ -149,3 +150,16 @@ pub struct ErroneousConstant {
/// Used by `rustc_const_eval`
pub use crate::fluent_generated::middle_adjust_for_foreign_abi_error;
#[derive(Diagnostic)]
#[diag(middle_type_length_limit)]
#[help(middle_consider_type_length_limit)]
pub struct TypeLengthLimit {
#[primary_span]
pub span: Span,
pub shrunk: String,
#[note(middle_written_to_path)]
pub was_written: Option<()>,
pub path: PathBuf,
pub type_length: usize,
}

2
compiler/rustc_middle/src/middle/limits.rs
View file

@ -30,7 +30,7 @@ pub fn provide(providers: &mut Providers) {
tcx.hir().krate_attrs(),
tcx.sess,
sym::type_length_limit,
1048576,
2usize.pow(24),
),
}
}

4
compiler/rustc_middle/src/mir/interpret/queries.rs
View file

@ -73,7 +73,7 @@ impl<'tcx> TyCtxt<'tcx> {
bug!("did not expect inference variables here");
}
match ty::Instance::resolve(
match ty::Instance::try_resolve(
self, param_env,
// FIXME: maybe have a separate version for resolving mir::UnevaluatedConst?
ct.def, ct.args,
@ -106,7 +106,7 @@ impl<'tcx> TyCtxt<'tcx> {
bug!("did not expect inference variables here");
}
match ty::Instance::resolve(self, param_env, ct.def, ct.args) {
match ty::Instance::try_resolve(self, param_env, ct.def, ct.args) {
Ok(Some(instance)) => {
let cid = GlobalId { instance, promoted: None };
self.const_eval_global_id_for_typeck(param_env, cid, span).inspect(|_| {

4
compiler/rustc_middle/src/query/mod.rs
View file

@ -2197,8 +2197,8 @@ rustc_queries! {
/// * `Err(ErrorGuaranteed)` when the `Instance` resolution process
/// couldn't complete due to errors elsewhere - this is distinct
/// from `Ok(None)` to avoid misleading diagnostics when an error
/// has already been/will be emitted, for the original cause
query resolve_instance(
/// has already been/will be emitted, for the original cause.
query resolve_instance_raw(
key: ty::ParamEnvAnd<'tcx, (DefId, GenericArgsRef<'tcx>)>
) -> Result<Option<ty::Instance<'tcx>>, ErrorGuaranteed> {
desc { "resolving instance `{}`", ty::Instance::new(key.value.0, key.value.1) }

239
compiler/rustc_middle/src/ty/instance.rs
View file

@ -1,23 +1,25 @@
use crate::error;
use crate::middle::codegen_fn_attrs::CodegenFnAttrFlags;
use crate::ty::print::{FmtPrinter, Printer};
use crate::ty::{self, Ty, TyCtxt, TypeFoldable, TypeSuperFoldable};
use crate::ty::{EarlyBinder, GenericArgs, GenericArgsRef, TypeVisitableExt};
use crate::ty::print::{shrunk_instance_name, FmtPrinter, Printer};
use crate::ty::{
self, EarlyBinder, GenericArgs, GenericArgsRef, Ty, TyCtxt, TypeFoldable, TypeSuperFoldable,
TypeSuperVisitable, TypeVisitable, TypeVisitableExt, TypeVisitor,
};
use rustc_errors::ErrorGuaranteed;
use rustc_hir as hir;
use rustc_hir::def::Namespace;
use rustc_hir::def_id::{CrateNum, DefId};
use rustc_hir::lang_items::LangItem;
use rustc_index::bit_set::FiniteBitSet;
use rustc_macros::{
Decodable, Encodable, HashStable, Lift, TyDecodable, TyEncodable, TypeVisitable,
};
use rustc_macros::{Decodable, Encodable, HashStable, Lift, TyDecodable, TyEncodable};
use rustc_middle::ty::normalize_erasing_regions::NormalizationError;
use rustc_span::def_id::LOCAL_CRATE;
use rustc_span::Symbol;
use rustc_span::{Span, Symbol, DUMMY_SP};
use tracing::{debug, instrument};
use std::assert_matches::assert_matches;
use std::fmt;
use std::path::PathBuf;
/// An `InstanceKind` along with the args that are needed to substitute the instance.
///
@ -385,7 +387,28 @@ impl<'tcx> InstanceKind<'tcx> {
}
}
fn fmt_instance(
fn type_length<'tcx>(item: impl TypeVisitable<TyCtxt<'tcx>>) -> usize {
struct Visitor {
type_length: usize,
}
impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for Visitor {
fn visit_ty(&mut self, t: Ty<'tcx>) {
self.type_length += 1;
t.super_visit_with(self);
}
fn visit_const(&mut self, ct: ty::Const<'tcx>) {
self.type_length += 1;
ct.super_visit_with(self);
}
}
let mut visitor = Visitor { type_length: 0 };
item.visit_with(&mut visitor);
visitor.type_length
}
pub fn fmt_instance(
f: &mut fmt::Formatter<'_>,
instance: Instance<'_>,
type_length: Option<rustc_session::Limit>,
@ -485,19 +508,30 @@ impl<'tcx> Instance<'tcx> {
///
/// Presuming that coherence and type-check have succeeded, if this method is invoked
/// in a monomorphic context (i.e., like during codegen), then it is guaranteed to return
/// `Ok(Some(instance))`.
/// `Ok(Some(instance))`, **except** for when the instance's inputs hit the type size limit,
/// in which case it may bail out and return `Ok(None)`.
///
/// Returns `Err(ErrorGuaranteed)` when the `Instance` resolution process
/// couldn't complete due to errors elsewhere - this is distinct
/// from `Ok(None)` to avoid misleading diagnostics when an error
/// has already been/will be emitted, for the original cause
#[instrument(level = "debug", skip(tcx), ret)]
pub fn resolve(
pub fn try_resolve(
tcx: TyCtxt<'tcx>,
param_env: ty::ParamEnv<'tcx>,
def_id: DefId,
args: GenericArgsRef<'tcx>,
) -> Result<Option<Instance<'tcx>>, ErrorGuaranteed> {
// Rust code can easily create exponentially-long types using only a
// polynomial recursion depth. Even with the default recursion
// depth, you can easily get cases that take >2^60 steps to run,
// which means that rustc basically hangs.
//
// Bail out in these cases to avoid that bad user experience.
if !tcx.type_length_limit().value_within_limit(type_length(args)) {
return Ok(None);
}
// All regions in the result of this query are erased, so it's
// fine to erase all of the input regions.
@ -505,7 +539,7 @@ impl<'tcx> Instance<'tcx> {
// below is more likely to ignore the bounds in scope (e.g. if the only
// generic parameters mentioned by `args` were lifetime ones).
let args = tcx.erase_regions(args);
tcx.resolve_instance(tcx.erase_regions(param_env.and((def_id, args))))
tcx.resolve_instance_raw(tcx.erase_regions(param_env.and((def_id, args))))
}
pub fn expect_resolve(
@ -513,10 +547,48 @@ impl<'tcx> Instance<'tcx> {
param_env: ty::ParamEnv<'tcx>,
def_id: DefId,
args: GenericArgsRef<'tcx>,
span: Span,
) -> Instance<'tcx> {
match ty::Instance::resolve(tcx, param_env, def_id, args) {
// We compute the span lazily, to avoid unnecessary query calls.
// If `span` is a DUMMY_SP, and the def id is local, then use the
// def span of the def id.
let span_or_local_def_span =
|| if span.is_dummy() && def_id.is_local() { tcx.def_span(def_id) } else { span };
match ty::Instance::try_resolve(tcx, param_env, def_id, args) {
Ok(Some(instance)) => instance,
instance => bug!(
Ok(None) => {
let type_length = type_length(args);
if !tcx.type_length_limit().value_within_limit(type_length) {
let (shrunk, written_to_path) =
shrunk_instance_name(tcx, Instance::new(def_id, args));
let mut path = PathBuf::new();
let was_written = if let Some(path2) = written_to_path {
path = path2;
Some(())
} else {
None
};
tcx.dcx().emit_fatal(error::TypeLengthLimit {
// We don't use `def_span(def_id)` so that diagnostics point
// to the crate root during mono instead of to foreign items.
// This is arguably better.
span: span_or_local_def_span(),
shrunk,
was_written,
path,
type_length,
});
} else {
span_bug!(
span_or_local_def_span(),
"failed to resolve instance for {}",
tcx.def_path_str_with_args(def_id, args)
)
}
}
instance => span_bug!(
span_or_local_def_span(),
"failed to resolve instance for {}: {instance:#?}",
tcx.def_path_str_with_args(def_id, args)
),
@ -533,7 +605,7 @@ impl<'tcx> Instance<'tcx> {
// Use either `resolve_closure` or `resolve_for_vtable`
assert!(!tcx.is_closure_like(def_id), "Called `resolve_for_fn_ptr` on closure: {def_id:?}");
let reason = tcx.sess.is_sanitizer_kcfi_enabled().then_some(ReifyReason::FnPtr);
Instance::resolve(tcx, param_env, def_id, args).ok().flatten().map(|mut resolved| {
Instance::try_resolve(tcx, param_env, def_id, args).ok().flatten().map(|mut resolved| {
match resolved.def {
InstanceKind::Item(def) if resolved.def.requires_caller_location(tcx) => {
debug!(" => fn pointer created for function with #[track_caller]");
@ -571,77 +643,82 @@ impl<'tcx> Instance<'tcx> {
})
}
pub fn resolve_for_vtable(
pub fn expect_resolve_for_vtable(
tcx: TyCtxt<'tcx>,
param_env: ty::ParamEnv<'tcx>,
def_id: DefId,
args: GenericArgsRef<'tcx>,
) -> Option<Instance<'tcx>> {
span: Span,
) -> Instance<'tcx> {
debug!("resolve_for_vtable(def_id={:?}, args={:?})", def_id, args);
let fn_sig = tcx.fn_sig(def_id).instantiate_identity();
let is_vtable_shim = !fn_sig.inputs().skip_binder().is_empty()
&& fn_sig.input(0).skip_binder().is_param(0)
&& tcx.generics_of(def_id).has_self;
if is_vtable_shim {
debug!(" => associated item with unsizeable self: Self");
Some(Instance { def: InstanceKind::VTableShim(def_id), args })
} else {
let reason = tcx.sess.is_sanitizer_kcfi_enabled().then_some(ReifyReason::Vtable);
Instance::resolve(tcx, param_env, def_id, args).ok().flatten().map(|mut resolved| {
match resolved.def {
InstanceKind::Item(def) => {
// We need to generate a shim when we cannot guarantee that
// the caller of a trait object method will be aware of
// `#[track_caller]` - this ensures that the caller
// and callee ABI will always match.
//
// The shim is generated when all of these conditions are met:
//
// 1) The underlying method expects a caller location parameter
// in the ABI
if resolved.def.requires_caller_location(tcx)
// 2) The caller location parameter comes from having `#[track_caller]`
// on the implementation, and *not* on the trait method.
&& !tcx.should_inherit_track_caller(def)
// If the method implementation comes from the trait definition itself
// (e.g. `trait Foo { #[track_caller] my_fn() { /* impl */ } }`),
// then we don't need to generate a shim. This check is needed because
// `should_inherit_track_caller` returns `false` if our method
// implementation comes from the trait block, and not an impl block
&& !matches!(
tcx.opt_associated_item(def),
Some(ty::AssocItem {
container: ty::AssocItemContainer::TraitContainer,
..
})
)
{
if tcx.is_closure_like(def) {
debug!(" => vtable fn pointer created for closure with #[track_caller]: {:?} for method {:?} {:?}",
def, def_id, args);
// Create a shim for the `FnOnce/FnMut/Fn` method we are calling
// - unlike functions, invoking a closure always goes through a
// trait.
resolved = Instance { def: InstanceKind::ReifyShim(def_id, reason), args };
} else {
debug!(
" => vtable fn pointer created for function with #[track_caller]: {:?}", def
);
resolved.def = InstanceKind::ReifyShim(def, reason);
}
}
}
InstanceKind::Virtual(def_id, _) => {
debug!(" => vtable fn pointer created for virtual call");
resolved.def = InstanceKind::ReifyShim(def_id, reason)
}
_ => {}
}
resolved
})
return Instance { def: InstanceKind::VTableShim(def_id), args };
}
let mut resolved = Instance::expect_resolve(tcx, param_env, def_id, args, span);
let reason = tcx.sess.is_sanitizer_kcfi_enabled().then_some(ReifyReason::Vtable);
match resolved.def {
InstanceKind::Item(def) => {
// We need to generate a shim when we cannot guarantee that
// the caller of a trait object method will be aware of
// `#[track_caller]` - this ensures that the caller
// and callee ABI will always match.
//
// The shim is generated when all of these conditions are met:
//
// 1) The underlying method expects a caller location parameter
// in the ABI
if resolved.def.requires_caller_location(tcx)
// 2) The caller location parameter comes from having `#[track_caller]`
// on the implementation, and *not* on the trait method.
&& !tcx.should_inherit_track_caller(def)
// If the method implementation comes from the trait definition itself
// (e.g. `trait Foo { #[track_caller] my_fn() { /* impl */ } }`),
// then we don't need to generate a shim. This check is needed because
// `should_inherit_track_caller` returns `false` if our method
// implementation comes from the trait block, and not an impl block
&& !matches!(
tcx.opt_associated_item(def),
Some(ty::AssocItem {
container: ty::AssocItemContainer::TraitContainer,
..
})
)
{
if tcx.is_closure_like(def) {
debug!(
" => vtable fn pointer created for closure with #[track_caller]: {:?} for method {:?} {:?}",
def, def_id, args
);
// Create a shim for the `FnOnce/FnMut/Fn` method we are calling
// - unlike functions, invoking a closure always goes through a
// trait.
resolved = Instance { def: InstanceKind::ReifyShim(def_id, reason), args };
} else {
debug!(
" => vtable fn pointer created for function with #[track_caller]: {:?}",
def
);
resolved.def = InstanceKind::ReifyShim(def, reason);
}
}
}
InstanceKind::Virtual(def_id, _) => {
debug!(" => vtable fn pointer created for virtual call");
resolved.def = InstanceKind::ReifyShim(def_id, reason)
}
_ => {}
}
resolved
}
pub fn resolve_closure(
@ -661,13 +738,25 @@ impl<'tcx> Instance<'tcx> {
pub fn resolve_drop_in_place(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> ty::Instance<'tcx> {
let def_id = tcx.require_lang_item(LangItem::DropInPlace, None);
let args = tcx.mk_args(&[ty.into()]);
Instance::expect_resolve(tcx, ty::ParamEnv::reveal_all(), def_id, args)
Instance::expect_resolve(
tcx,
ty::ParamEnv::reveal_all(),
def_id,
args,
ty.ty_adt_def().and_then(|adt| tcx.hir().span_if_local(adt.did())).unwrap_or(DUMMY_SP),
)
}
pub fn resolve_async_drop_in_place(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> ty::Instance<'tcx> {
let def_id = tcx.require_lang_item(LangItem::AsyncDropInPlace, None);
let args = tcx.mk_args(&[ty.into()]);
Instance::expect_resolve(tcx, ty::ParamEnv::reveal_all(), def_id, args)
Instance::expect_resolve(
tcx,
ty::ParamEnv::reveal_all(),
def_id,
args,
ty.ty_adt_def().and_then(|adt| tcx.hir().span_if_local(adt.did())).unwrap_or(DUMMY_SP),
)
}
#[instrument(level = "debug", skip(tcx), ret)]

32
compiler/rustc_middle/src/ty/print/mod.rs
View file

@ -1,5 +1,7 @@
use std::path::PathBuf;
use crate::ty::GenericArg;
use crate::ty::{self, Ty, TyCtxt};
use crate::ty::{self, ShortInstance, Ty, TyCtxt};
use hir::def::Namespace;
use rustc_data_structures::fx::FxHashSet;
@ -356,3 +358,31 @@ where
with_no_trimmed_paths!(Self::print(t, fmt))
}
}
/// Format instance name that is already known to be too long for rustc.
/// Show only the first 2 types if it is longer than 32 characters to avoid blasting
/// the user's terminal with thousands of lines of type-name.
///
/// If the type name is longer than before+after, it will be written to a file.
pub fn shrunk_instance_name<'tcx>(
tcx: TyCtxt<'tcx>,
instance: ty::Instance<'tcx>,
) -> (String, Option<PathBuf>) {
let s = instance.to_string();
// Only use the shrunk version if it's really shorter.
// This also avoids the case where before and after slices overlap.
if s.chars().nth(33).is_some() {
let shrunk = format!("{}", ShortInstance(instance, 4));
if shrunk == s {
return (s, None);
}
let path = tcx.output_filenames(()).temp_path_ext("long-type.txt", None);
let written_to_path = std::fs::write(&path, s).ok().map(|_| path);
(shrunk, written_to_path)
} else {
(s, None)
}
}

2
compiler/rustc_middle/src/util/call_kind.rs
View file

@ -98,7 +98,7 @@ pub fn call_kind<'tcx>(
Some(CallKind::Operator { self_arg, trait_id, self_ty: method_args.type_at(0) })
} else if is_deref {
let deref_target = tcx.get_diagnostic_item(sym::deref_target).and_then(|deref_target| {
Instance::resolve(tcx, param_env, deref_target, method_args).transpose()
Instance::try_resolve(tcx, param_env, deref_target, method_args).transpose()
});
if let Some(Ok(instance)) = deref_target {
let deref_target_ty = instance.ty(tcx, param_env);