From 7e1ecff56eda38a7e5b2b68745aea91dd7c57bd7 Mon Sep 17 00:00:00 2001 From: Camille GILLOT Date: Sun, 1 Oct 2023 13:48:29 +0000 Subject: [PATCH] Do not check for impossible predicates in const-prop lint. --- .../src/const_prop_lint.rs | 37 ------------------- 1 file changed, 37 deletions(-) diff --git a/compiler/rustc_mir_transform/src/const_prop_lint.rs b/compiler/rustc_mir_transform/src/const_prop_lint.rs index 95d87c288da..66e63a7b156 100644 --- a/compiler/rustc_mir_transform/src/const_prop_lint.rs +++ b/compiler/rustc_mir_transform/src/const_prop_lint.rs @@ -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. `` - // 2. We avoid trying to normalize predicates involving generic - // parameters (e.g. `::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