Use erased regions in MIR

Author: matthewjasper

src/librustc_mir/interpret/intrinsics/caller_location.rs

@@ -39,7 +39,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         let loc_ty = self
             .tcx
             .type_of(self.tcx.require_lang_item(PanicLocationLangItem, None))
-            .subst(*self.tcx, self.tcx.mk_substs([self.tcx.lifetimes.re_static.into()].iter()));
+            .subst(*self.tcx, self.tcx.mk_substs([self.tcx.lifetimes.re_erased.into()].iter()));
         let loc_layout = self.layout_of(loc_ty).unwrap();
         let location = self.allocate(loc_layout, MemoryKind::CallerLocation);
 

src/librustc_mir/transform/cleanup_post_borrowck.rs

@@ -32,6 +32,7 @@ impl<'tcx> MirPass<'tcx> for CleanupNonCodegenStatements {
     fn run_pass(&self, tcx: TyCtxt<'tcx>, _source: MirSource<'tcx>, body: &mut BodyAndCache<'tcx>) {
         let mut delete = DeleteNonCodegenStatements { tcx };
         delete.visit_body(body);
+        body.user_type_annotations.raw.clear();
     }
 }
 

src/librustc_mir/transform/erase_regions.rs

@@ -357,18 +357,11 @@ impl MutVisitor<'tcx> for TransformVisitor<'tcx> {
     }
 }
 
-fn make_generator_state_argument_indirect<'tcx>(
-    tcx: TyCtxt<'tcx>,
-    def_id: DefId,
-    body: &mut BodyAndCache<'tcx>,
-) {
+fn make_generator_state_argument_indirect<'tcx>(tcx: TyCtxt<'tcx>, body: &mut BodyAndCache<'tcx>) {
     let gen_ty = body.local_decls.raw[1].ty;
 
-    let region = ty::ReFree(ty::FreeRegion { scope: def_id, bound_region: ty::BoundRegion::BrEnv });
-
-    let region = tcx.mk_region(region);
-
-    let ref_gen_ty = tcx.mk_ref(region, ty::TypeAndMut { ty: gen_ty, mutbl: hir::Mutability::Mut });
+    let ref_gen_ty =
+        tcx.mk_ref(tcx.lifetimes.re_erased, ty::TypeAndMut { ty: gen_ty, mutbl: Mutability::Mut });
 
     // Replace the by value generator argument
     body.local_decls.raw[1].ty = ref_gen_ty;
@@ -874,7 +867,6 @@ fn elaborate_generator_drops<'tcx>(
 fn create_generator_drop_shim<'tcx>(
     tcx: TyCtxt<'tcx>,
     transform: &TransformVisitor<'tcx>,
-    def_id: DefId,
     source: MirSource<'tcx>,
     gen_ty: Ty<'tcx>,
     body: &mut BodyAndCache<'tcx>,
@@ -912,7 +904,7 @@ fn create_generator_drop_shim<'tcx>(
         local_info: LocalInfo::Other,
     };
 
-    make_generator_state_argument_indirect(tcx, def_id, &mut body);
+    make_generator_state_argument_indirect(tcx, &mut body);
 
     // Change the generator argument from &mut to *mut
     body.local_decls[SELF_ARG] = LocalDecl {
@@ -1047,7 +1039,6 @@ fn can_unwind<'tcx>(tcx: TyCtxt<'tcx>, body: &Body<'tcx>) -> bool {
 fn create_generator_resume_function<'tcx>(
     tcx: TyCtxt<'tcx>,
     transform: TransformVisitor<'tcx>,
-    def_id: DefId,
     source: MirSource<'tcx>,
     body: &mut BodyAndCache<'tcx>,
     can_return: bool,
@@ -1112,7 +1103,7 @@ fn create_generator_resume_function<'tcx>(
 
     insert_switch(body, cases, &transform, TerminatorKind::Unreachable);
 
-    make_generator_state_argument_indirect(tcx, def_id, body);
+    make_generator_state_argument_indirect(tcx, body);
     make_generator_state_argument_pinned(tcx, body);
 
     no_landing_pads(tcx, body);
@@ -1332,11 +1323,11 @@ impl<'tcx> MirPass<'tcx> for StateTransform {
 
         // Create a copy of our MIR and use it to create the drop shim for the generator
         let drop_shim =
-            create_generator_drop_shim(tcx, &transform, def_id, source, gen_ty, body, drop_clean);
+            create_generator_drop_shim(tcx, &transform, source, gen_ty, body, drop_clean);
 
         body.generator_drop = Some(box drop_shim);
 
         // Create the Generator::resume function
-        create_generator_resume_function(tcx, transform, def_id, source, body, can_return);
+        create_generator_resume_function(tcx, transform, source, body, can_return);
     }
 }

src/librustc_mir/transform/generator.rs

@@ -22,7 +22,6 @@ pub mod copy_prop;
 pub mod deaggregator;
 pub mod dump_mir;
 pub mod elaborate_drops;
-pub mod erase_regions;
 pub mod generator;
 pub mod inline;
 pub mod instcombine;
@@ -296,8 +295,6 @@ fn run_optimization_passes<'tcx>(
             &simplify::SimplifyCfg::new("elaborate-drops"),
             // No lifetime analysis based on borrowing can be done from here on out.
 
-            // From here on out, regions are gone.
-            &erase_regions::EraseRegions,
             // Optimizations begin.
             &unreachable_prop::UnreachablePropagation,
             &uninhabited_enum_branching::UninhabitedEnumBranching,
@@ -341,6 +338,9 @@ fn optimized_mir(tcx: TyCtxt<'_>, def_id: DefId) -> &BodyAndCache<'_> {
     let mut body = body.steal();
     run_optimization_passes(tcx, &mut body, def_id, None);
     body.ensure_predecessors();
+
+    debug_assert!(!body.has_free_regions(), "Free regions in optimized MIR");
+
     tcx.arena.alloc(body)
 }
 
@@ -358,5 +358,7 @@ fn promoted_mir(tcx: TyCtxt<'_>, def_id: DefId) -> &IndexVec<Promoted, BodyAndCa
         body.ensure_predecessors();
     }
 
+    debug_assert!(!promoted.has_free_regions(), "Free regions in promoted MIR");
+
     tcx.intern_promoted(promoted)
 }

src/librustc_mir/transform/mod.rs

@@ -913,7 +913,13 @@ impl<'a, 'tcx> Promoter<'a, 'tcx> {
                         ty,
                         val: ty::ConstKind::Unevaluated(
                             def_id,
-                            InternalSubsts::identity_for_item(tcx, def_id),
+                            InternalSubsts::for_item(tcx, def_id, |param, _| {
+                                if let ty::GenericParamDefKind::Lifetime = param.kind {
+                                    tcx.lifetimes.re_erased.into()
+                                } else {
+                                    tcx.mk_param_from_def(param)
+                                }
+                            }),
                             Some(promoted_id),
                         ),
                     }),

src/librustc_mir/transform/promote_consts.rs

@@ -6,7 +6,7 @@ use rustc::middle::lang_items;
 use rustc::middle::region;
 use rustc::mir::*;
 use rustc::ty::subst::Subst;
-use rustc::ty::{self, Ty, TyCtxt};
+use rustc::ty::{self, Ty, TyCtxt, TypeFoldable};
 use rustc_attr::{self as attr, UnwindAttr};
 use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
@@ -43,8 +43,7 @@ fn mir_build(tcx: TyCtxt<'_>, def_id: DefId) -> BodyAndCache<'_> {
             ..
         })
         | Node::TraitItem(hir::TraitItem {
-            kind:
-                hir::TraitItemKind::Fn(hir::FnSig { decl, .. }, hir::TraitFn::Provided(body_id)),
+            kind: hir::TraitItemKind::Fn(hir::FnSig { decl, .. }, hir::TraitFn::Provided(body_id)),
             ..
         }) => (*body_id, decl.output.span()),
         Node::Item(hir::Item { kind: hir::ItemKind::Static(ty, _, body_id), .. })
@@ -128,12 +127,8 @@ fn mir_build(tcx: TyCtxt<'_>, def_id: DefId) -> BodyAndCache<'_> {
                 let ty = if fn_sig.c_variadic && index == fn_sig.inputs().len() {
                     let va_list_did =
                         tcx.require_lang_item(lang_items::VaListTypeLangItem, Some(arg.span));
-                    let region = tcx.mk_region(ty::ReScope(region::Scope {
-                        id: body.value.hir_id.local_id,
-                        data: region::ScopeData::CallSite,
-                    }));
 
-                    tcx.type_of(va_list_did).subst(tcx, &[region.into()])
+                    tcx.type_of(va_list_did).subst(tcx, &[tcx.lifetimes.re_erased.into()])
                 } else {
                     fn_sig.inputs()[index]
                 };
@@ -189,6 +184,20 @@ fn mir_build(tcx: TyCtxt<'_>, def_id: DefId) -> BodyAndCache<'_> {
 
         let mut body = BodyAndCache::new(body);
         body.ensure_predecessors();
+
+        // The borrow checker will replace all the regions here with its own
+        // inference variables. There's no point having non-erased regions here.
+        // The exception is `body.user_type_annotations`, which is used unmodified
+        // by borrow checking.
+        debug_assert!(
+            !(body.local_decls.has_free_regions()
+                || body.basic_blocks().has_free_regions()
+                || body.var_debug_info.has_free_regions()
+                || body.yield_ty.has_free_regions()),
+            "Unexpected free regions in MIR: {:?}",
+            body,
+        );
+
         body
     })
 }
@@ -209,7 +218,7 @@ fn liberated_closure_env_ty(
     };
 
     let closure_env_ty = tcx.closure_env_ty(closure_def_id, closure_substs).unwrap();
-    tcx.liberate_late_bound_regions(closure_def_id, &closure_env_ty)
+    tcx.erase_late_bound_regions(&closure_env_ty)
 }
 
 #[derive(Debug, PartialEq, Eq)]

src/librustc_mir_build/build/mod.rs

@@ -15,7 +15,7 @@ fn main() {
 }
 
 // END RUST SOURCE
-// START rustc.main.EraseRegions.after.mir
+// START rustc.main.SimplifyCfg-elaborate-drops.after.mir
 //     bb0: {
 //         ...
 //         _4 = &mut _2;
@@ -38,4 +38,4 @@ fn main() {
 //         ...
 //         return;
 //     }
-// END rustc.main.EraseRegions.after.mir
+// END rustc.main.SimplifyCfg-elaborate-drops.after.mir

src/test/mir-opt/array-index-is-temporary.rs

@@ -6,10 +6,10 @@ fn main() {
 }
 
 // END RUST SOURCE
-// START rustc.main.EraseRegions.after.mir
+// START rustc.main.SimplifyCfg-elaborate-drops.after.mir
 // ...
 // _1 = const b"foo";
 // ...
 // _2 = [const 5u8, const 120u8];
 // ...
-// END rustc.main.EraseRegions.after.mir
+// END rustc.main.SimplifyCfg-elaborate-drops.after.mir

src/test/mir-opt/byte_slice.rs

@@ -15,7 +15,7 @@ impl Drop for Droppy {
 }
 
 // END RUST SOURCE
-// START rustc.main.EraseRegions.before.mir
+// START rustc.main.SimplifyCfg-elaborate-drops.after.mir
 // fn main() -> () {
 //     let mut _0: ();
 //     let mut _1: Packed;
@@ -56,4 +56,4 @@ impl Drop for Droppy {
 //         drop(_1) -> [return: bb2, unwind: bb1];
 //     }
 // }
-// END rustc.main.EraseRegions.before.mir
+// END rustc.main.SimplifyCfg-elaborate-drops.after.mir