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Rollup merge of #130863 - compiler-errors:relax-codegen-dyn-assert, r=lcnr

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Relax a debug assertion for dyn principal *equality* in codegen

Maybe this sucks and I should just bite the bullet and use `infcx.sub` here. Thoughts?

r? lcnr

Fixes #130855
This commit is contained in:
Matthias Krüger 2024-10-02 17:10:43 +02:00 • committed by GitHub
commit f9ba5529eb
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5 changed files with 66 additions and 20 deletions
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1
compiler/rustc_codegen_ssa/Cargo.toml
View file

@ -34,6 +34,7 @@ rustc_session = { path = "../rustc_session" }
rustc_span = { path = "../rustc_span" }
rustc_symbol_mangling = { path = "../rustc_symbol_mangling" }
rustc_target = { path = "../rustc_target" }
rustc_trait_selection = { path = "../rustc_trait_selection" }
rustc_type_ir = { path = "../rustc_type_ir" }
serde_json = "1.0.59"
smallvec = { version = "1.8.1", features = ["union", "may_dangle"] }

59
compiler/rustc_codegen_ssa/src/base.rs
View file

@ -27,6 +27,9 @@ use rustc_session::config::{self, CrateType, EntryFnType, OptLevel, OutputType};
use rustc_span::symbol::sym;
use rustc_span::{DUMMY_SP, Symbol};
use rustc_target::abi::FIRST_VARIANT;
use rustc_trait_selection::infer::at::ToTrace;
use rustc_trait_selection::infer::{BoundRegionConversionTime, TyCtxtInferExt};
use rustc_trait_selection::traits::{ObligationCause, ObligationCtxt};
use tracing::{debug, info};
use crate::assert_module_sources::CguReuse;
@ -101,6 +104,54 @@ pub fn compare_simd_types<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
bx.sext(cmp, ret_ty)
}
/// Codegen takes advantage of the additional assumption, where if the
/// principal trait def id of what's being casted doesn't change,
/// then we don't need to adjust the vtable at all. This
/// corresponds to the fact that `dyn Tr<A>: Unsize<dyn Tr<B>>`
/// requires that `A = B`; we don't allow *upcasting* objects
/// between the same trait with different args. If we, for
/// some reason, were to relax the `Unsize` trait, it could become
/// unsound, so let's validate here that the trait refs are subtypes.
pub fn validate_trivial_unsize<'tcx>(
tcx: TyCtxt<'tcx>,
source_data: &'tcx ty::List<ty::PolyExistentialPredicate<'tcx>>,
target_data: &'tcx ty::List<ty::PolyExistentialPredicate<'tcx>>,
) -> bool {
match (source_data.principal(), target_data.principal()) {
(Some(hr_source_principal), Some(hr_target_principal)) => {
let infcx = tcx.infer_ctxt().build();
let universe = infcx.universe();
let ocx = ObligationCtxt::new(&infcx);
infcx.enter_forall(hr_target_principal, |target_principal| {
let source_principal = infcx.instantiate_binder_with_fresh_vars(
DUMMY_SP,
BoundRegionConversionTime::HigherRankedType,
hr_source_principal,
);
let Ok(()) = ocx.eq_trace(
&ObligationCause::dummy(),
ty::ParamEnv::reveal_all(),
ToTrace::to_trace(
&ObligationCause::dummy(),
hr_target_principal,
hr_source_principal,
),
target_principal,
source_principal,
) else {
return false;
};
if !ocx.select_all_or_error().is_empty() {
return false;
}
infcx.leak_check(universe, None).is_ok()
})
}
(None, None) => true,
_ => false,
}
}
/// Retrieves the information we are losing (making dynamic) in an unsizing
/// adjustment.
///
@ -133,12 +184,8 @@ fn unsized_info<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
// between the same trait with different args. If we, for
// some reason, were to relax the `Unsize` trait, it could become
// unsound, so let's assert here that the trait refs are *equal*.
//
// We can use `assert_eq` because the binders should have been anonymized,
// and because higher-ranked equality now requires the binders are equal.
debug_assert_eq!(
data_a.principal(),
data_b.principal(),
debug_assert!(
validate_trivial_unsize(cx.tcx(), data_a, data_b),
"NOP unsize vtable changed principal trait ref: {data_a} -> {data_b}"
);