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interpret: make identity upcasts a NOP again to avoid them generating a new random vtable

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This commit is contained in:
Ralf Jung 2024-08-09 18:08:34 +02:00
parent dec5b463fb
commit 9a233bb9dd
9 changed files with 173 additions and 92 deletions
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6
compiler/rustc_const_eval/src/interpret/cast.rs
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@ -400,6 +400,12 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
}
(ty::Dynamic(data_a, _, ty::Dyn), ty::Dynamic(data_b, _, ty::Dyn)) => {
let val = self.read_immediate(src)?;
// MIR building generates odd NOP casts, prevent them from causing unexpected trouble.
// See <https://github.com/rust-lang/rust/issues/128880>.
// FIXME: ideally we wouldn't have to do this.
if data_a == data_b {
return self.write_immediate(*val, dest);
}
// Take apart the old pointer, and find the dynamic type.
let (old_data, old_vptr) = val.to_scalar_pair();
let old_data = old_data.to_pointer(self)?;