Auto merge of #44480 - Zoxc:gen-liveness, r=arielb1

Analyse storage liveness and preserve it during generator transformation

This uses a dataflow analysis on `StorageLive` and `StorageDead` statements to infer where the storage of locals are live. The result of this analysis is intersected with the regular liveness analysis such that a local is can only be live when its storage is. This fixes #44184. If the storage of a local is live across a suspension point, we'll insert a `StorageLive` statement for it after the suspension point so storage liveness is preserved. This fixes #44179.

r? @arielb1

Author: bors

src/librustc_data_structures/bitslice.rs

@@ -132,6 +132,11 @@ pub trait BitwiseOperator {
     fn join(&self, pred1: usize, pred2: usize) -> usize;
 }
 
+pub struct Intersect;
+impl BitwiseOperator for Intersect {
+    #[inline]
+    fn join(&self, a: usize, b: usize) -> usize { a & b }
+}
 pub struct Union;
 impl BitwiseOperator for Union {
     #[inline]

src/librustc_data_structures/indexed_set.rs

@@ -15,7 +15,7 @@ use std::mem;
 use std::ops::{Deref, DerefMut, Range};
 use std::slice;
 use bitslice::{BitSlice, Word};
-use bitslice::{bitwise, Union, Subtract};
+use bitslice::{bitwise, Union, Subtract, Intersect};
 use indexed_vec::Idx;
 
 /// Represents a set (or packed family of sets), of some element type
@@ -164,6 +164,10 @@ impl<T: Idx> IdxSet<T> {
         bitwise(self.words_mut(), other.words(), &Subtract)
     }
 
+    pub fn intersect(&mut self, other: &IdxSet<T>) -> bool {
+        bitwise(self.words_mut(), other.words(), &Intersect)
+    }
+
     pub fn iter(&self) -> Iter<T> {
         Iter {
             cur: None,

src/librustc_mir/dataflow/impls/mod.rs

@@ -27,6 +27,10 @@ use super::drop_flag_effects_for_function_entry;
 use super::drop_flag_effects_for_location;
 use super::on_lookup_result_bits;
 
+mod storage_liveness;
+
+pub use self::storage_liveness::*;
+
 #[allow(dead_code)]
 pub(super) mod borrows;
 

src/librustc_mir/dataflow/impls/storage_liveness.rs

@@ -0,0 +1,82 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+pub use super::*;
+
+use rustc::mir::*;
+use dataflow::BitDenotation;
+
+#[derive(Copy, Clone)]
+pub struct MaybeStorageLive<'a, 'tcx: 'a> {
+    mir: &'a Mir<'tcx>,
+}
+
+impl<'a, 'tcx: 'a> MaybeStorageLive<'a, 'tcx> {
+    pub fn new(mir: &'a Mir<'tcx>)
+               -> Self {
+        MaybeStorageLive { mir: mir }
+    }
+
+    pub fn mir(&self) -> &Mir<'tcx> {
+        self.mir
+    }
+}
+
+impl<'a, 'tcx> BitDenotation for MaybeStorageLive<'a, 'tcx> {
+    type Idx = Local;
+    fn name() -> &'static str { "maybe_storage_live" }
+    fn bits_per_block(&self) -> usize {
+        self.mir.local_decls.len()
+    }
+
+    fn start_block_effect(&self, _sets: &mut BlockSets<Local>) {
+        // Nothing is live on function entry
+    }
+
+    fn statement_effect(&self,
+                        sets: &mut BlockSets<Local>,
+                        loc: Location) {
+        let stmt = &self.mir[loc.block].statements[loc.statement_index];
+
+        match stmt.kind {
+            StatementKind::StorageLive(l) => sets.gen(&l),
+            StatementKind::StorageDead(l) => sets.kill(&l),
+            _ => (),
+        }
+    }
+
+    fn terminator_effect(&self,
+                         _sets: &mut BlockSets<Local>,
+                         _loc: Location) {
+        // Terminators have no effect
+    }
+
+    fn propagate_call_return(&self,
+                             _in_out: &mut IdxSet<Local>,
+                             _call_bb: mir::BasicBlock,
+                             _dest_bb: mir::BasicBlock,
+                             _dest_lval: &mir::Lvalue) {
+        // Nothing to do when a call returns successfully
+    }
+}
+
+impl<'a, 'tcx> BitwiseOperator for MaybeStorageLive<'a, 'tcx> {
+    #[inline]
+    fn join(&self, pred1: usize, pred2: usize) -> usize {
+        pred1 | pred2 // "maybe" means we union effects of both preds
+    }
+}
+
+impl<'a, 'tcx> DataflowOperator for MaybeStorageLive<'a, 'tcx> {
+    #[inline]
+    fn bottom_value() -> bool {
+        false // bottom = dead
+    }
+}

src/librustc_mir/dataflow/mod.rs

@@ -24,6 +24,7 @@ use std::mem;
 use std::path::PathBuf;
 use std::usize;
 
+pub use self::impls::{MaybeStorageLive};
 pub use self::impls::{MaybeInitializedLvals, MaybeUninitializedLvals};
 pub use self::impls::{DefinitelyInitializedLvals};
 pub use self::impls::borrows::{Borrows, BorrowData, BorrowIndex};
@@ -351,6 +352,29 @@ pub trait DataflowResultsConsumer<'a, 'tcx: 'a> {
                           flow_state: &mut Self::FlowState);
 }
 
+pub fn state_for_location<T: BitDenotation>(loc: Location,
+                                            analysis: &T,
+                                            result: &DataflowResults<T>)
+    -> IdxSetBuf<T::Idx> {
+    let mut entry = result.sets().on_entry_set_for(loc.block.index()).to_owned();
+
+    {
+        let mut sets = BlockSets {
+            on_entry: &mut entry.clone(),
+            kill_set: &mut entry.clone(),
+            gen_set: &mut entry,
+        };
+
+        for stmt in 0..loc.statement_index {
+            let mut stmt_loc = loc;
+            stmt_loc.statement_index = stmt;
+            analysis.statement_effect(&mut sets, stmt_loc);
+        }
+    }
+
+    entry
+}
+
 pub struct DataflowAnalysis<'a, 'tcx: 'a, O> where O: BitDenotation
 {
     flow_state: DataflowState<O>,