Auto merge of #50370 - nikomatsakis:nll-alias-analysis-flat, r=pnkfelix

introduce `-Znll-facts` to dump base-facts for the NLL analysis

r? @pnkfelix

Author: bors

src/librustc/mir/mod.rs

@@ -1978,6 +1978,11 @@ impl fmt::Debug for Location {
 }
 
 impl Location {
+    pub const START: Location = Location {
+        block: START_BLOCK,
+        statement_index: 0,
+    };
+
     /// Returns the location immediately after this one within the enclosing block.
     ///
     /// Note that if this location represents a terminator, then the

src/librustc/session/config.rs

@@ -1250,6 +1250,8 @@ options! {DebuggingOptions, DebuggingSetter, basic_debugging_options,
         "choose which RELRO level to use"),
     nll_subminimal_causes: bool = (false, parse_bool, [UNTRACKED],
         "when tracking region error causes, accept subminimal results for faster execution."),
+    nll_facts: bool = (false, parse_bool, [UNTRACKED],
+                       "dump facts from NLL analysis into side files"),
     disable_nll_user_type_assert: bool = (false, parse_bool, [UNTRACKED],
         "disable user provided type assertion in NLL"),
     trans_time_graph: bool = (false, parse_bool, [UNTRACKED],

src/librustc_mir/borrow_check/location.rs

@@ -0,0 +1,123 @@
+// 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.
+
+use rustc::mir::{BasicBlock, Location, Mir};
+use rustc_data_structures::indexed_vec::{Idx, IndexVec};
+
+/// Maps between a MIR Location, which identifies the a particular
+/// statement within a basic block, to a "rich location", which
+/// identifies at a finer granularity. In particular, we distinguish
+/// the *start* of a statement and the *mid-point*. The mid-point is
+/// the point *just* before the statement takes effect; in particular,
+/// for an assignment `A = B`, it is the point where B is about to be
+/// written into A. This mid-point is a kind of hack to work around
+/// our inability to track the position information at sufficient
+/// granularity through outlives relations; however, the rich location
+/// table serves another purpose: it compresses locations from
+/// multiple words into a single u32.
+crate struct LocationTable {
+    num_points: usize,
+    statements_before_block: IndexVec<BasicBlock, usize>,
+}
+
+newtype_index!(LocationIndex { DEBUG_FORMAT = "LocationIndex({})" });
+
+#[derive(Copy, Clone, Debug)]
+crate enum RichLocation {
+    Start(Location),
+    Mid(Location),
+}
+
+impl LocationTable {
+    crate fn new(mir: &Mir<'_>) -> Self {
+        let mut num_points = 0;
+        let statements_before_block = mir.basic_blocks()
+            .iter()
+            .map(|block_data| {
+                let v = num_points;
+                num_points += (block_data.statements.len() + 1) * 2;
+                v
+            })
+            .collect();
+
+        debug!(
+            "LocationTable(statements_before_block={:#?})",
+            statements_before_block
+        );
+        debug!("LocationTable: num_points={:#?}", num_points);
+
+        Self {
+            num_points,
+            statements_before_block,
+        }
+    }
+
+    crate fn all_points(&self) -> impl Iterator<Item = LocationIndex> {
+        (0..self.num_points).map(LocationIndex::new)
+    }
+
+    crate fn start_index(&self, location: Location) -> LocationIndex {
+        let Location {
+            block,
+            statement_index,
+        } = location;
+        let start_index = self.statements_before_block[block];
+        LocationIndex::new(start_index + statement_index * 2)
+    }
+
+    crate fn mid_index(&self, location: Location) -> LocationIndex {
+        let Location {
+            block,
+            statement_index,
+        } = location;
+        let start_index = self.statements_before_block[block];
+        LocationIndex::new(start_index + statement_index * 2 + 1)
+    }
+
+    crate fn to_location(&self, index: LocationIndex) -> RichLocation {
+        let point_index = index.index();
+
+        // Find the basic block. We have a vector with the
+        // starting index of the statement in each block. Imagine
+        // we have statement #22, and we have a vector like:
+        //
+        // [0, 10, 20]
+        //
+        // In that case, this represents point_index 2 of
+        // basic block BB2. We know this because BB0 accounts for
+        // 0..10, BB1 accounts for 11..20, and BB2 accounts for
+        // 20...
+        //
+        // To compute this, we could do a binary search, but
+        // because I am lazy we instead iterate through to find
+        // the last point where the "first index" (0, 10, or 20)
+        // was less than the statement index (22). In our case, this will
+        // be (BB2, 20).
+        let (block, &first_index) = self.statements_before_block
+            .iter_enumerated()
+            .filter(|(_, first_index)| **first_index <= point_index)
+            .last()
+            .unwrap();
+
+        let statement_index = (point_index - first_index) / 2;
+        if index.is_start() {
+            RichLocation::Start(Location { block, statement_index })
+        } else {
+            RichLocation::Mid(Location { block, statement_index })
+        }
+    }
+}
+
+impl LocationIndex {
+    fn is_start(&self) -> bool {
+        // even indices are start points; odd indices are mid points
+        (self.index() % 2) == 0
+    }
+}

src/librustc_mir/borrow_check/mod.rs

@@ -50,12 +50,14 @@ use std::iter;
 
 use self::borrow_set::{BorrowSet, BorrowData};
 use self::flows::Flows;
+use self::location::LocationTable;
 use self::prefixes::PrefixSet;
 use self::MutateMode::{JustWrite, WriteAndRead};
 
 crate mod borrow_set;
 mod error_reporting;
 mod flows;
+mod location;
 crate mod place_ext;
 mod prefixes;
 
@@ -110,6 +112,7 @@ fn do_mir_borrowck<'a, 'gcx, 'tcx>(
     let mut mir: Mir<'tcx> = input_mir.clone();
     let free_regions = nll::replace_regions_in_mir(infcx, def_id, param_env, &mut mir);
     let mir = &mir; // no further changes
+    let location_table = &LocationTable::new(mir);
 
     let move_data: MoveData<'tcx> = match MoveData::gather_moves(mir, tcx) {
         Ok(move_data) => move_data,
@@ -199,6 +202,7 @@ fn do_mir_borrowck<'a, 'gcx, 'tcx>(
         def_id,
         free_regions,
         mir,
+        location_table,
         param_env,
         &mut flow_inits,
         &mdpe.move_data,