Auto merge of #65672 - ecstatic-morse:unified-dataflow-proto, r=<try>

[WIP] A single framework for gen-kill and generic dataflow problems

This is the prototype implementation discussed in rust-lang/compiler-team#202. You can read a high-level description of it in [the proposal](https://hackmd.io/@39Qr_z9cQhasi25sGjmFnA/Skvd9rztS) for that design meeting. This would eventually supersede the existing `BitDenotation` interface.

r? @ghost

cc @rust-lang/compiler (esp. @eddyb and @pnkfelix)

src/librustc/mir/mod.rs

@@ -204,6 +204,31 @@ impl<'tcx> Body<'tcx> {
         }
     }
 
+    /// Returns a partially initialized MIR body containing only a list of basic blocks.
+    ///
+    /// The returned MIR contains no `LocalDecl`s (even for the return place) or source scopes. It
+    /// is only useful for testing but cannot be `#[cfg(test)]` because it is used in a different
+    /// crate.
+    pub fn new_cfg_only(basic_blocks: IndexVec<BasicBlock, BasicBlockData<'tcx>>) -> Self {
+        Body {
+            phase: MirPhase::Build,
+            basic_blocks,
+            source_scopes: IndexVec::new(),
+            source_scope_local_data: ClearCrossCrate::Clear,
+            yield_ty: None,
+            generator_drop: None,
+            generator_layout: None,
+            local_decls: IndexVec::new(),
+            user_type_annotations: IndexVec::new(),
+            arg_count: 0,
+            __upvar_debuginfo_codegen_only_do_not_use: Vec::new(),
+            spread_arg: None,
+            span: syntax_pos::DUMMY_SP,
+            cache: cache::Cache::new(),
+            control_flow_destroyed: Vec::new(),
+        }
+    }
+
     #[inline]
     pub fn basic_blocks(&self) -> &IndexVec<BasicBlock, BasicBlockData<'tcx>> {
         &self.basic_blocks

src/librustc_mir/borrow_check/mod.rs

@@ -37,7 +37,7 @@ use crate::dataflow::Borrows;
 use crate::dataflow::DataflowResultsConsumer;
 use crate::dataflow::FlowAtLocation;
 use crate::dataflow::MoveDataParamEnv;
-use crate::dataflow::{do_dataflow, DebugFormatted};
+use crate::dataflow::{self, do_dataflow, DebugFormatted};
 use crate::dataflow::EverInitializedPlaces;
 use crate::dataflow::{MaybeInitializedPlaces, MaybeUninitializedPlaces};
 
@@ -167,16 +167,10 @@ fn do_mir_borrowck<'a, 'tcx>(
         param_env,
     };
 
-    let dead_unwinds = BitSet::new_empty(body.basic_blocks().len());
-    let mut flow_inits = FlowAtLocation::new(do_dataflow(
-        tcx,
-        body,
-        def_id,
-        &attributes,
-        &dead_unwinds,
-        MaybeInitializedPlaces::new(tcx, body, &mdpe),
-        |bd, i| DebugFormatted::new(&bd.move_data().move_paths[i]),
-    ));
+    let flow_inits = MaybeInitializedPlaces::new(tcx, body, &mdpe);
+    let mut flow_inits = dataflow::generic::Engine::new_gen_kill(tcx, body, def_id, flow_inits)
+        .iterate_to_fixpoint()
+        .into_cursor(body);
 
     let locals_are_invalidated_at_exit = tcx.hir().body_owner_kind(id).is_fn_or_closure();
     let borrow_set = Rc::new(BorrowSet::build(
@@ -205,6 +199,7 @@ fn do_mir_borrowck<'a, 'tcx>(
 
     let regioncx = Rc::new(regioncx);
 
+    let dead_unwinds = BitSet::new_empty(body.basic_blocks().len());
     let flow_borrows = FlowAtLocation::new(do_dataflow(
         tcx,
         body,

src/librustc_mir/borrow_check/nll/mod.rs

@@ -3,9 +3,9 @@ use crate::borrow_check::location::{LocationIndex, LocationTable};
 use crate::borrow_check::nll::facts::AllFactsExt;
 use crate::borrow_check::nll::type_check::{MirTypeckResults, MirTypeckRegionConstraints};
 use crate::borrow_check::nll::region_infer::values::RegionValueElements;
+use crate::dataflow::generic::ResultsCursor;
 use crate::dataflow::indexes::BorrowIndex;
 use crate::dataflow::move_paths::{InitLocation, MoveData, MovePathIndex, InitKind};
-use crate::dataflow::FlowAtLocation;
 use crate::dataflow::MaybeInitializedPlaces;
 use crate::transform::MirSource;
 use crate::borrow_check::Upvar;
@@ -161,7 +161,7 @@ pub(in crate::borrow_check) fn compute_regions<'cx, 'tcx>(
     upvars: &[Upvar],
     location_table: &LocationTable,
     param_env: ty::ParamEnv<'tcx>,
-    flow_inits: &mut FlowAtLocation<'tcx, MaybeInitializedPlaces<'cx, 'tcx>>,
+    flow_inits: &mut ResultsCursor<'cx, 'tcx, MaybeInitializedPlaces<'cx, 'tcx>>,
     move_data: &MoveData<'tcx>,
     borrow_set: &BorrowSet<'tcx>,
     errors_buffer: &mut Vec<Diagnostic>,

src/librustc_mir/borrow_check/nll/type_check/liveness/mod.rs

@@ -4,8 +4,8 @@ use crate::borrow_check::nll::facts::{AllFacts, AllFactsExt};
 use crate::borrow_check::nll::region_infer::values::RegionValueElements;
 use crate::borrow_check::nll::universal_regions::UniversalRegions;
 use crate::borrow_check::nll::ToRegionVid;
+use crate::dataflow::generic::ResultsCursor;
 use crate::dataflow::move_paths::MoveData;
-use crate::dataflow::FlowAtLocation;
 use crate::dataflow::MaybeInitializedPlaces;
 use rustc::mir::{Body, Local};
 use rustc::ty::{RegionVid, TyCtxt};
@@ -26,11 +26,11 @@ mod trace;
 ///
 /// N.B., this computation requires normalization; therefore, it must be
 /// performed before
-pub(super) fn generate<'tcx>(
+pub(super) fn generate<'mir, 'tcx>(
     typeck: &mut TypeChecker<'_, 'tcx>,
     body: &Body<'tcx>,
     elements: &Rc<RegionValueElements>,
-    flow_inits: &mut FlowAtLocation<'tcx, MaybeInitializedPlaces<'_, 'tcx>>,
+    flow_inits: &mut ResultsCursor<'mir, 'tcx, MaybeInitializedPlaces<'mir, 'tcx>>,
     move_data: &MoveData<'tcx>,
     location_table: &LocationTable,
 ) {

src/librustc_mir/borrow_check/nll/type_check/liveness/trace.rs

@@ -3,9 +3,10 @@ use crate::borrow_check::nll::type_check::liveness::local_use_map::LocalUseMap;
 use crate::borrow_check::nll::type_check::liveness::polonius;
 use crate::borrow_check::nll::type_check::NormalizeLocation;
 use crate::borrow_check::nll::type_check::TypeChecker;
+use crate::dataflow::generic::ResultsCursor;
 use crate::dataflow::indexes::MovePathIndex;
-use crate::dataflow::move_paths::MoveData;
-use crate::dataflow::{FlowAtLocation, FlowsAtLocation, MaybeInitializedPlaces};
+use crate::dataflow::move_paths::{HasMoveData, MoveData};
+use crate::dataflow::MaybeInitializedPlaces;
 use rustc::infer::canonical::QueryRegionConstraints;
 use rustc::mir::{BasicBlock, Body, ConstraintCategory, Local, Location};
 use rustc::traits::query::dropck_outlives::DropckOutlivesResult;
@@ -34,7 +35,7 @@ pub(super) fn trace(
     typeck: &mut TypeChecker<'_, 'tcx>,
     body: &Body<'tcx>,
     elements: &Rc<RegionValueElements>,
-    flow_inits: &mut FlowAtLocation<'tcx, MaybeInitializedPlaces<'_, 'tcx>>,
+    flow_inits: &mut ResultsCursor<'mir, 'tcx, MaybeInitializedPlaces<'mir, 'tcx>>,
     move_data: &MoveData<'tcx>,
     live_locals: Vec<Local>,
     polonius_drop_used: Option<Vec<(Local, Location)>>,
@@ -81,7 +82,7 @@ struct LivenessContext<'me, 'typeck, 'flow, 'tcx> {
 
     /// Results of dataflow tracking which variables (and paths) have been
     /// initialized.
-    flow_inits: &'me mut FlowAtLocation<'tcx, MaybeInitializedPlaces<'flow, 'tcx>>,
+    flow_inits: &'me mut ResultsCursor<'flow, 'tcx, MaybeInitializedPlaces<'flow, 'tcx>>,
 
     /// Index indicating where each variable is assigned, used, or
     /// dropped.
@@ -389,23 +390,26 @@ impl LivenessResults<'me, 'typeck, 'flow, 'tcx> {
 }
 
 impl LivenessContext<'_, '_, '_, 'tcx> {
+    /// Returns `true` if the local variable (or some part of it) is initialized at the current
+    /// cursor position. Callers should call one of the `seek` methods immediately before to point
+    /// the cursor to the desired location.
+    fn initialized_at_curr_loc(&self, mpi: MovePathIndex) -> bool {
+        let state = self.flow_inits.get();
+        if state.contains(mpi) {
+            return true;
+        }
+
+        let move_paths = &self.flow_inits.analysis().move_data().move_paths;
+        move_paths[mpi].find_child(&move_paths, |mpi| state.contains(mpi)).is_some()
+    }
+
     /// Returns `true` if the local variable (or some part of it) is initialized in
     /// the terminator of `block`. We need to check this to determine if a
     /// DROP of some local variable will have an effect -- note that
     /// drops, as they may unwind, are always terminators.
     fn initialized_at_terminator(&mut self, block: BasicBlock, mpi: MovePathIndex) -> bool {
-        // Compute the set of initialized paths at terminator of block
-        // by resetting to the start of the block and then applying
-        // the effects of all statements. This is the only way to get
-        // "just ahead" of a terminator.
-        self.flow_inits.reset_to_entry_of(block);
-        for statement_index in 0..self.body[block].statements.len() {
-            let location = Location { block, statement_index };
-            self.flow_inits.reconstruct_statement_effect(location);
-            self.flow_inits.apply_local_effect(location);
-        }
-
-        self.flow_inits.has_any_child_of(mpi).is_some()
+        self.flow_inits.seek_before(self.body.terminator_loc(block));
+        self.initialized_at_curr_loc(mpi)
     }
 
     /// Returns `true` if the path `mpi` (or some part of it) is initialized at
@@ -414,8 +418,8 @@ impl LivenessContext<'_, '_, '_, 'tcx> {
     /// **Warning:** Does not account for the result of `Call`
     /// instructions.
     fn initialized_at_exit(&mut self, block: BasicBlock, mpi: MovePathIndex) -> bool {
-        self.flow_inits.reset_to_exit_of(block);
-        self.flow_inits.has_any_child_of(mpi).is_some()
+        self.flow_inits.seek_after(self.body.terminator_loc(block));
+        self.initialized_at_curr_loc(mpi)
     }
 
     /// Stores the result that all regions in `value` are live for the

src/librustc_mir/borrow_check/nll/type_check/mod.rs

@@ -17,8 +17,8 @@ use crate::borrow_check::nll::type_check::free_region_relations::{
 use crate::borrow_check::nll::universal_regions::{DefiningTy, UniversalRegions};
 use crate::borrow_check::nll::ToRegionVid;
 use crate::transform::promote_consts::should_suggest_const_in_array_repeat_expressions_attribute;
+use crate::dataflow::generic::ResultsCursor;
 use crate::dataflow::move_paths::MoveData;
-use crate::dataflow::FlowAtLocation;
 use crate::dataflow::MaybeInitializedPlaces;
 use either::Either;
 use rustc::hir;
@@ -112,7 +112,7 @@ mod relate_tys;
 ///   constraints for the regions in the types of variables
 /// - `flow_inits` -- results of a maybe-init dataflow analysis
 /// - `move_data` -- move-data constructed when performing the maybe-init dataflow analysis
-pub(crate) fn type_check<'tcx>(
+pub(crate) fn type_check<'mir, 'tcx>(
     infcx: &InferCtxt<'_, 'tcx>,
     param_env: ty::ParamEnv<'tcx>,
     body: &Body<'tcx>,
@@ -122,7 +122,7 @@ pub(crate) fn type_check<'tcx>(
     location_table: &LocationTable,
     borrow_set: &BorrowSet<'tcx>,
     all_facts: &mut Option<AllFacts>,
-    flow_inits: &mut FlowAtLocation<'tcx, MaybeInitializedPlaces<'_, 'tcx>>,
+    flow_inits: &mut ResultsCursor<'mir, 'tcx, MaybeInitializedPlaces<'mir, 'tcx>>,
     move_data: &MoveData<'tcx>,
     elements: &Rc<RegionValueElements>,
 ) -> MirTypeckResults<'tcx> {