fix bugs with effects fallback

Author: fee1-dead

compiler/rustc_monomorphize/src/collector.rs

@@ -815,12 +815,6 @@ impl<'a, 'tcx> MirVisitor<'tcx> for MirUsedCollector<'a, 'tcx> {
                     mir::AssertKind::BoundsCheck { .. } => LangItem::PanicBoundsCheck,
                     _ => LangItem::Panic,
                 };
-                let def_id = tcx.require_lang_item(lang_item, Some(source));
-                let instance = if has_host_effect {
-                    Instance::new(def_id, tcx.mk_args(&[tcx.consts.true_.into()]))
-                } else {
-                    Instance::mono(tcx, def_id)
-                };
                 push_mono_lang_item(self, lang_item);
             }
             mir::TerminatorKind::UnwindTerminate(reason) => {

compiler/rustc_passes/src/lang_items.rs

@@ -20,7 +20,8 @@ use rustc_hir::lang_items::{extract, GenericRequirement};
 use rustc_hir::{LangItem, LanguageItems, Target};
 use rustc_middle::ty::TyCtxt;
 use rustc_session::cstore::ExternCrate;
-use rustc_span::{symbol::kw::Empty, Span};
+use rustc_span::symbol::kw::Empty;
+use rustc_span::{sym, Span};
 
 use rustc_middle::query::Providers;
 
@@ -157,7 +158,14 @@ impl<'tcx> LanguageItemCollector<'tcx> {
             self.tcx.hir().get_by_def_id(item_def_id)
         {
             let (actual_num, generics_span) = match kind.generics() {
-                Some(generics) => (generics.params.len(), generics.span),
+                Some(generics) => (
+                    generics
+                        .params
+                        .iter()
+                        .filter(|p| !self.tcx.has_attr(p.def_id, sym::rustc_host))
+                        .count(),
+                    generics.span,
+                ),
                 None => (0, *item_span),
             };