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Do not check for impossible predicates in const-prop lint.

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This commit is contained in:
Camille GILLOT 2023-10-01 13:48:29 +00:00
parent fd51cc6bc9
commit 7e1ecff56e
1 changed files with 0 additions and 37 deletions
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37
compiler/rustc_mir_transform/src/const_prop_lint.rs
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@ -22,7 +22,6 @@
};
use rustc_span::Span;
use rustc_target::abi::{HasDataLayout, Size, TargetDataLayout};
use rustc_trait_selection::traits;
use crate::const_prop::CanConstProp;
use crate::const_prop::ConstPropMachine;
@ -67,42 +66,6 @@ fn run_lint(&self, tcx: TyCtxt<'tcx>, body: &Body<'tcx>) {
return;
}
// Check if it's even possible to satisfy the 'where' clauses
// for this item.
// This branch will never be taken for any normal function.
// However, it's possible to `#!feature(trivial_bounds)]` to write
// a function with impossible to satisfy clauses, e.g.:
// `fn foo() where String: Copy {}`
//
// We don't usually need to worry about this kind of case,
// since we would get a compilation error if the user tried
// to call it. However, since we can do const propagation
// even without any calls to the function, we need to make
// sure that it even makes sense to try to evaluate the body.
// If there are unsatisfiable where clauses, then all bets are
// off, and we just give up.
//
// We manually filter the predicates, skipping anything that's not
// "global". We are in a potentially generic context
// (e.g. we are evaluating a function without substituting generic
// parameters, so this filtering serves two purposes:
//
// 1. We skip evaluating any predicates that we would
// never be able prove are unsatisfiable (e.g. `<T as Foo>`
// 2. We avoid trying to normalize predicates involving generic
// parameters (e.g. `<T as Foo>::MyItem`). This can confuse
// the normalization code (leading to cycle errors), since
// it's usually never invoked in this way.
let predicates = tcx
.predicates_of(def_id.to_def_id())
.predicates
.iter()
.filter_map(|(p, _)| if p.is_global() { Some(*p) } else { None });
if traits::impossible_predicates(tcx, traits::elaborate(tcx, predicates).collect()) {
trace!("ConstProp skipped for {:?}: found unsatisfiable predicates", def_id);
return;
}
trace!("ConstProp starting for {:?}", def_id);
// FIXME(oli-obk, eddyb) Optimize locals (or even local paths) to hold