Move unstatisfaction check earlier.
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0f857791ad
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0ee32fb3c7
@ -390,6 +390,50 @@ fn mir_drops_elaborated_and_const_checked(tcx: TyCtxt<'_>, def: LocalDefId) -> &
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body.tainted_by_errors = Some(error_reported);
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}
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// Check if it's even possible to satisfy the 'where' clauses
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// for this item.
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//
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// This branch will never be taken for any normal function.
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// However, it's possible to `#!feature(trivial_bounds)]` to write
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// a function with impossible to satisfy clauses, e.g.:
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// `fn foo() where String: Copy {}`
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//
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// We don't usually need to worry about this kind of case,
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// since we would get a compilation error if the user tried
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// to call it. However, since we optimize even without any
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// calls to the function, we need to make sure that it even
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// makes sense to try to evaluate the body.
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//
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// If there are unsatisfiable where clauses, then all bets are
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// off, and we just give up.
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//
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// We manually filter the predicates, skipping anything that's not
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// "global". We are in a potentially generic context
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// (e.g. we are evaluating a function without substituting generic
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// parameters, so this filtering serves two purposes:
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//
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// 1. We skip evaluating any predicates that we would
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// never be able prove are unsatisfiable (e.g. `<T as Foo>`
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// 2. We avoid trying to normalize predicates involving generic
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// parameters (e.g. `<T as Foo>::MyItem`). This can confuse
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// the normalization code (leading to cycle errors), since
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// it's usually never invoked in this way.
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let predicates = tcx
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.predicates_of(body.source.def_id())
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.predicates
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.iter()
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.filter_map(|(p, _)| if p.is_global() { Some(*p) } else { None });
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if traits::impossible_predicates(tcx, traits::elaborate(tcx, predicates).collect()) {
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trace!("found unsatisfiable predicates for {:?}", body.source);
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// Clear the body to only contain a single `unreachable` statement.
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let bbs = body.basic_blocks.as_mut();
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bbs.raw.truncate(1);
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bbs[START_BLOCK].statements.clear();
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bbs[START_BLOCK].terminator_mut().kind = TerminatorKind::Unreachable;
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body.var_debug_info.clear();
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body.local_decls.raw.truncate(body.arg_count + 1);
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}
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run_analysis_to_runtime_passes(tcx, &mut body);
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tcx.alloc_steal_mir(body)
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@ -482,56 +526,6 @@ fn run_optimization_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
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WithMinOptLevel(1, x)
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}
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// Check if it's even possible to satisfy the 'where' clauses
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// for this item.
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// This branch will never be taken for any normal function.
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// However, it's possible to `#!feature(trivial_bounds)]` to write
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// a function with impossible to satisfy clauses, e.g.:
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// `fn foo() where String: Copy {}`
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//
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// We don't usually need to worry about this kind of case,
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// since we would get a compilation error if the user tried
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// to call it. However, since we optimize even without any
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// calls to the function, we need to make sure that it even
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// makes sense to try to evaluate the body.
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//
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// If there are unsatisfiable where clauses, then all bets are
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// off, and we just give up.
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//
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// We manually filter the predicates, skipping anything that's not
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// "global". We are in a potentially generic context
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// (e.g. we are evaluating a function without substituting generic
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// parameters, so this filtering serves two purposes:
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//
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// 1. We skip evaluating any predicates that we would
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// never be able prove are unsatisfiable (e.g. `<T as Foo>`
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// 2. We avoid trying to normalize predicates involving generic
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// parameters (e.g. `<T as Foo>::MyItem`). This can confuse
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// the normalization code (leading to cycle errors), since
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// it's usually never invoked in this way.
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let predicates = tcx
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.predicates_of(body.source.def_id())
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.predicates
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.iter()
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.filter_map(|(p, _)| if p.is_global() { Some(*p) } else { None });
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if traits::impossible_predicates(tcx, traits::elaborate(tcx, predicates).collect()) {
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trace!("optimizations skipped for {:?}: found unsatisfiable predicates", body.source);
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// Clear the body to only contain a single `unreachable` statement.
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let bbs = body.basic_blocks.as_mut();
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bbs.raw.truncate(1);
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bbs[START_BLOCK].statements.clear();
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bbs[START_BLOCK].terminator_mut().kind = TerminatorKind::Unreachable;
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body.var_debug_info.clear();
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body.local_decls.raw.truncate(body.arg_count + 1);
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pm::run_passes(
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tcx,
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body,
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&[&reveal_all::RevealAll, &dump_mir::Marker("PreCodegen")],
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Some(MirPhase::Runtime(RuntimePhase::Optimized)),
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);
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return;
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}
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// The main optimizations that we do on MIR.
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pm::run_passes(
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tcx,
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