Auto merge of rust-lang#52612 - matthewjasper:remove-unnecessary-flow…

…, r=nikomatsakis

Don't keep the possibly initialized flow around longer than needed

The possibly initialized flow isn't used after liveness is computed, so don't keep it around. Locally this is about a 10% time win for tuple-stress (which is spending a lot of time calculating flows now that it's not spending so much on liveness).

r? @nikomatsakis

src/librustc_mir/borrow_check/flows.rs

@@ -26,15 +26,14 @@ use dataflow::move_paths::HasMoveData;
 use dataflow::Borrows;
 use dataflow::{EverInitializedPlaces, MovingOutStatements};
 use dataflow::{FlowAtLocation, FlowsAtLocation};
-use dataflow::{MaybeInitializedPlaces, MaybeUninitializedPlaces};
+use dataflow::MaybeUninitializedPlaces;
 use either::Either;
 use std::fmt;
 use std::rc::Rc;
 
 // (forced to be `pub` due to its use as an associated type below.)
 crate struct Flows<'b, 'gcx: 'tcx, 'tcx: 'b> {
     borrows: FlowAtLocation<Borrows<'b, 'gcx, 'tcx>>,
-    pub inits: FlowAtLocation<MaybeInitializedPlaces<'b, 'gcx, 'tcx>>,
     pub uninits: FlowAtLocation<MaybeUninitializedPlaces<'b, 'gcx, 'tcx>>,
     pub move_outs: FlowAtLocation<MovingOutStatements<'b, 'gcx, 'tcx>>,
     pub ever_inits: FlowAtLocation<EverInitializedPlaces<'b, 'gcx, 'tcx>>,
@@ -46,15 +45,13 @@ crate struct Flows<'b, 'gcx: 'tcx, 'tcx: 'b> {
 impl<'b, 'gcx, 'tcx> Flows<'b, 'gcx, 'tcx> {
     crate fn new(
         borrows: FlowAtLocation<Borrows<'b, 'gcx, 'tcx>>,
-        inits: FlowAtLocation<MaybeInitializedPlaces<'b, 'gcx, 'tcx>>,
         uninits: FlowAtLocation<MaybeUninitializedPlaces<'b, 'gcx, 'tcx>>,
         move_outs: FlowAtLocation<MovingOutStatements<'b, 'gcx, 'tcx>>,
         ever_inits: FlowAtLocation<EverInitializedPlaces<'b, 'gcx, 'tcx>>,
         polonius_output: Option<Rc<Output<RegionVid, BorrowIndex, LocationIndex>>>,
     ) -> Self {
         Flows {
             borrows,
-            inits,
             uninits,
             move_outs,
             ever_inits,
@@ -81,7 +78,6 @@ impl<'b, 'gcx, 'tcx> Flows<'b, 'gcx, 'tcx> {
 macro_rules! each_flow {
     ($this:ident, $meth:ident($arg:ident)) => {
         FlowAtLocation::$meth(&mut $this.borrows, $arg);
-        FlowAtLocation::$meth(&mut $this.inits, $arg);
         FlowAtLocation::$meth(&mut $this.uninits, $arg);
         FlowAtLocation::$meth(&mut $this.move_outs, $arg);
         FlowAtLocation::$meth(&mut $this.ever_inits, $arg);
@@ -134,18 +130,6 @@ impl<'b, 'gcx, 'tcx> fmt::Display for Flows<'b, 'gcx, 'tcx> {
         });
         s.push_str("] ");
 
-        s.push_str("inits: [");
-        let mut saw_one = false;
-        self.inits.each_state_bit(|mpi_init| {
-            if saw_one {
-                s.push_str(", ");
-            };
-            saw_one = true;
-            let move_path = &self.inits.operator().move_data().move_paths[mpi_init];
-            s.push_str(&format!("{}", move_path));
-        });
-        s.push_str("] ");
-
         s.push_str("uninits: [");
         let mut saw_one = false;
         self.uninits.each_state_bit(|mpi_uninit| {

src/librustc_mir/borrow_check/mod.rs

@@ -216,7 +216,6 @@ fn do_mir_borrowck<'a, 'gcx, 'tcx>(
         &borrow_set,
     );
     let regioncx = Rc::new(regioncx);
-    let flow_inits = flow_inits; // remove mut
 
     let flow_borrows = FlowAtLocation::new(do_dataflow(
         tcx,
@@ -262,7 +261,6 @@ fn do_mir_borrowck<'a, 'gcx, 'tcx>(
 
     let mut state = Flows::new(
         flow_borrows,
-        flow_inits,
         flow_uninits,
         flow_move_outs,
         flow_ever_inits,