Auto merge of #53109 - nikomatsakis:nll-escaping-into-return-revert, r=nikomatsakis

revert #52991

Reverts #52991 which is flawed. I have an idea how to fix it but might as well revert first since it is so wildly flawed. That's what I get for opening PRs while on PTO =)

r? @pnkfelix

Author: bors

src/librustc_mir/borrow_check/nll/escaping_locals.rs

@@ -16,10 +16,9 @@
 //! liveness code so that it only operates over variables with regions in their
 //! types, instead of all variables.
 
-use borrow_check::nll::escaping_locals::EscapingLocals;
-use rustc::mir::{Local, Mir};
 use rustc::ty::TypeFoldable;
 use rustc_data_structures::indexed_vec::IndexVec;
+use rustc::mir::{Mir, Local};
 use util::liveness::LiveVariableMap;
 
 use rustc_data_structures::indexed_vec::Idx;
@@ -30,13 +29,14 @@ use rustc_data_structures::indexed_vec::Idx;
 crate struct NllLivenessMap {
     /// For each local variable, contains either None (if the type has no regions)
     /// or Some(i) with a suitable index.
-    from_local: IndexVec<Local, Option<LocalWithRegion>>,
-
+    pub from_local: IndexVec<Local, Option<LocalWithRegion>>,
     /// For each LocalWithRegion, maps back to the original Local index.
-    to_local: IndexVec<LocalWithRegion, Local>,
+    pub to_local: IndexVec<LocalWithRegion, Local>,
+
 }
 
 impl LiveVariableMap for NllLivenessMap {
+
     fn from_local(&self, local: Local) -> Option<Self::LiveVar> {
         self.from_local[local]
     }
@@ -55,43 +55,21 @@ impl LiveVariableMap for NllLivenessMap {
 impl NllLivenessMap {
     /// Iterates over the variables in Mir and assigns each Local whose type contains
     /// regions a LocalWithRegion index. Returns a map for converting back and forth.
-    crate fn compute(mir: &Mir<'tcx>) -> Self {
-        let mut escaping_locals = EscapingLocals::compute(mir);
-
+    pub fn compute(mir: &Mir) -> Self {
         let mut to_local = IndexVec::default();
-        let mut escapes_into_return = 0;
-        let mut no_regions = 0;
-        let from_local: IndexVec<Local, Option<_>> = mir
+        let from_local: IndexVec<Local,Option<_>> = mir
             .local_decls
             .iter_enumerated()
             .map(|(local, local_decl)| {
-                if escaping_locals.escapes_into_return(local) {
-                    // If the local escapes into the return value,
-                    // then the return value will force all of the
-                    // regions in its type to outlive free regions
-                    // (e.g., `'static`) and hence liveness is not
-                    // needed. This is particularly important for big
-                    // statics.
-                    escapes_into_return += 1;
-                    None
-                } else if local_decl.ty.has_free_regions() {
-                    let l = to_local.push(local);
-                    debug!("liveness_map: {:?} = {:?}", local, l);
-                    Some(l)
-                } else {
-                    no_regions += 1;
-                    None
+                if local_decl.ty.has_free_regions() {
+                    Some(to_local.push(local))
                 }
+                    else {
+                        None
+                    }
             }).collect();
 
-        debug!("liveness_map: {} variables need liveness", to_local.len());
-        debug!("liveness_map: {} escapes into return", escapes_into_return);
-        debug!("liveness_map: {} no regions", no_regions);
-
-        Self {
-            from_local,
-            to_local,
-        }
+        Self { from_local, to_local }
     }
 }
 

src/librustc_mir/borrow_check/nll/liveness_map.rs

@@ -39,9 +39,7 @@ use polonius_engine::{Algorithm, Output};
 use util as mir_util;
 use util::pretty::{self, ALIGN};
 
-mod constraints;
 mod constraint_generation;
-mod escaping_locals;
 pub mod explain_borrow;
 mod facts;
 mod invalidation;
@@ -51,6 +49,8 @@ crate mod type_check;
 mod universal_regions;
 crate mod liveness_map;
 
+mod constraints;
+
 use self::facts::AllFacts;
 use self::region_infer::RegionInferenceContext;
 use self::universal_regions::UniversalRegions;
@@ -120,7 +120,6 @@ pub(in borrow_check) fn compute_regions<'cx, 'gcx, 'tcx>(
         location_table,
         borrow_set,
         &liveness,
-        &liveness_map,
         &mut all_facts,
         flow_inits,
         move_data,
@@ -206,7 +205,6 @@ pub(in borrow_check) fn compute_regions<'cx, 'gcx, 'tcx>(
     dump_mir_results(
         infcx,
         &liveness,
-        &liveness_map,
         MirSource::item(def_id),
         &mir,
         &regioncx,
@@ -223,7 +221,6 @@ pub(in borrow_check) fn compute_regions<'cx, 'gcx, 'tcx>(
 fn dump_mir_results<'a, 'gcx, 'tcx>(
     infcx: &InferCtxt<'a, 'gcx, 'tcx>,
     liveness: &LivenessResults<LocalWithRegion>,
-    liveness_map: &NllLivenessMap,
     source: MirSource,
     mir: &Mir<'tcx>,
     regioncx: &RegionInferenceContext,
@@ -233,14 +230,16 @@ fn dump_mir_results<'a, 'gcx, 'tcx>(
         return;
     }
 
+    let map = &NllLivenessMap::compute(mir);
+
     let regular_liveness_per_location: FxHashMap<_, _> = mir
         .basic_blocks()
         .indices()
         .flat_map(|bb| {
             let mut results = vec![];
             liveness
                 .regular
-                .simulate_block(&mir, bb, liveness_map, |location, local_set| {
+                .simulate_block(&mir, bb, map, |location, local_set| {
                     results.push((location, local_set.clone()));
                 });
             results
@@ -254,7 +253,7 @@ fn dump_mir_results<'a, 'gcx, 'tcx>(
             let mut results = vec![];
             liveness
                 .drop
-                .simulate_block(&mir, bb, liveness_map, |location, local_set| {
+                .simulate_block(&mir, bb, map, |location, local_set| {
                     results.push((location, local_set.clone()));
                 });
             results