Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Jump to bottom

[experiment] rustc_mir: remove #![type_length_limit] checks. #76772

Closed
wants to merge 1 commit into from
Closed

[experiment] rustc_mir: remove #![type_length_limit] checks. #76772

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
54 changes: 1 addition & 53 deletions compiler/rustc_mir/src/monomorphize/collector.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -191,12 +191,11 @@ use rustc_middle::mir::mono::{InstantiationMode, MonoItem};
use rustc_middle::mir::visit::Visitor as MirVisitor;
use rustc_middle::mir::{self, Local, Location};
use rustc_middle::ty::adjustment::{CustomCoerceUnsized, PointerCast};
use rustc_middle::ty::subst::{GenericArgKind, InternalSubsts};
use rustc_middle::ty::subst::InternalSubsts;
use rustc_middle::ty::{self, GenericParamDefKind, Instance, Ty, TyCtxt, TypeFoldable};
use rustc_session::config::EntryFnType;
use rustc_span::source_map::{dummy_spanned, respan, Span, Spanned, DUMMY_SP};
use smallvec::SmallVec;
use std::iter;

#[derive(PartialEq)]
pub enum MonoItemCollectionMode {
Expand Down Expand Up @@ -375,7 +374,6 @@ fn collect_items_rec<'tcx>(
// Keep track of the monomorphization recursion depth
recursion_depth_reset =
Some(check_recursion_limit(tcx, instance, starting_point.span, recursion_depths));
check_type_length_limit(tcx, instance);

rustc_data_structures::stack::ensure_sufficient_stack(|| {
collect_neighbours(tcx, instance, &mut neighbors);
Expand Down Expand Up @@ -455,56 +453,6 @@ fn check_recursion_limit<'tcx>(
(def_id, recursion_depth)
}

fn check_type_length_limit<'tcx>(tcx: TyCtxt<'tcx>, instance: Instance<'tcx>) {
let type_length = instance
.substs
.iter()
.flat_map(|arg| arg.walk())
.filter(|arg| match arg.unpack() {
GenericArgKind::Type(_) | GenericArgKind::Const(_) => true,
GenericArgKind::Lifetime(_) => false,
})
.count();
debug!(" => type length={}", type_length);

// 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.sess.type_length_limit().value_within_limit(type_length) {
// The instance name is already known to be too long for rustc.
// Show only the first and last 32 characters to avoid blasting
// the user's terminal with thousands of lines of type-name.
let shrink = |s: String, before: usize, after: usize| {
// An iterator of all byte positions including the end of the string.
let positions = || s.char_indices().map(|(i, _)| i).chain(iter::once(s.len()));

let shrunk = format!(
"{before}...{after}",
before = &s[..positions().nth(before).unwrap_or(s.len())],
after = &s[positions().rev().nth(after).unwrap_or(0)..],
);

// Only use the shrunk version if it's really shorter.
// This also avoids the case where before and after slices overlap.
if shrunk.len() < s.len() { shrunk } else { s }
};
let msg = format!(
"reached the type-length limit while instantiating `{}`",
shrink(instance.to_string(), 32, 32)
);
let mut diag = tcx.sess.struct_span_fatal(tcx.def_span(instance.def_id()), &msg);
diag.note(&format!(
"consider adding a `#![type_length_limit=\"{}\"]` attribute to your crate",
type_length
));
diag.emit();
tcx.sess.abort_if_errors();
}
}

struct MirNeighborCollector<'a, 'tcx> {
tcx: TyCtxt<'tcx>,
body: &'a mir::Body<'tcx>,
Expand Down