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Relax a debug assertion in codegen

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This commit is contained in:
Michael Goulet 2024-09-28 14:16:05 -04:00
parent c3ce4e66a5
commit eb75d20a55
5 changed files with 49 additions and 20 deletions
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17
compiler/rustc_codegen_cranelift/src/unsize.rs
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@ -2,6 +2,7 @@
//!
//! [`PointerCoercion::Unsize`]: `rustc_middle::ty::adjustment::PointerCoercion::Unsize`
use rustc_codegen_ssa::base::validate_trivial_unsize;
use rustc_middle::ty::print::{with_no_trimmed_paths, with_no_visible_paths};
use crate::base::codegen_panic_nounwind;
@ -34,20 +35,8 @@ pub(crate) fn unsized_info<'tcx>(
let old_info =
old_info.expect("unsized_info: missing old info for trait upcasting coercion");
if data_a.principal_def_id() == data_b.principal_def_id() {
// 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 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(fx.tcx, data_a, data_b),
"NOP unsize vtable changed principal trait ref: {data_a} -> {data_b}"
);
return old_info;