src/librustc_mir/borrow_check/nll/region_infer/dump_mir.rs

   1 // Copyright 2017 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 //! As part of generating the regions, if you enable `-Zdump-mir=nll`,
  12 //! we will generate an annotated copy of the MIR that includes the
  13 //! state of region inference. This code handles emitting the region
  14 //! context internal state.
  15
  16 use rustc::infer::NLLRegionVariableOrigin;
  17 use std::io::{self, Write};
  18 use super::{OutlivesConstraint, RegionInferenceContext};
  19
  20 // Room for "'_#NNNNr" before things get misaligned.
  21 // Easy enough to fix if this ever doesn't seem like
  22 // enough.
  23 const REGION_WIDTH: usize = 8;
  24
  25 impl<'tcx> RegionInferenceContext<'tcx> {
  26     /// Write out our state into the `.mir` files.
  27     pub(crate) fn dump_mir(&self, out: &mut dyn Write) -> io::Result<()> {
  28         writeln!(out, "| Free Region Mapping")?;
  29
  30         for region in self.regions() {
  31             if let NLLRegionVariableOrigin::FreeRegion = self.definitions[region].origin {
  32                 let classification = self
  33                     .universal_regions
  34                     .region_classification(region)
  35                     .unwrap();
  36                 let outlived_by = self.universal_region_relations.regions_outlived_by(region);
  37                 writeln!(
  38                     out,
  39                     "| {r:rw$?} | {c:cw$?} | {ob:?}",
  40                     r = region,
  41                     rw = REGION_WIDTH,
  42                     c = classification,
  43                     cw = 8, // "External" at most
  44                     ob = outlived_by
  45                 )?;
  46             }
  47         }
  48
  49         writeln!(out, "|")?;
  50         writeln!(out, "| Inferred Region Values")?;
  51         for region in self.regions() {
  52             writeln!(
  53                 out,
  54                 "| {r:rw$?} | {ui:4?} | {v}",
  55                 r = region,
  56                 rw = REGION_WIDTH,
  57                 ui = self.region_universe(region),
  58                 v = self.region_value_str(region),
  59             )?;
  60         }
  61
  62         writeln!(out, "|")?;
  63         writeln!(out, "| Inference Constraints")?;
  64         self.for_each_constraint(&mut |msg| writeln!(out, "| {}", msg))?;
  65
  66         Ok(())
  67     }
  68
  69     /// Debugging aid: Invokes the `with_msg` callback repeatedly with
  70     /// our internal region constraints.  These are dumped into the
  71     /// -Zdump-mir file so that we can figure out why the region
  72     /// inference resulted in the values that it did when debugging.
  73     fn for_each_constraint(
  74         &self,
  75         with_msg: &mut dyn FnMut(&str) -> io::Result<()>,
  76     ) -> io::Result<()> {
  77         for region in self.definitions.indices() {
  78             let value = self.liveness_constraints.region_value_str(region);
  79             if value != "{}" {
  80                 with_msg(&format!("{:?} live at {}", region, value))?;
  81             }
  82         }
  83
  84         let mut constraints: Vec<_> = self.constraints.iter().collect();
  85         constraints.sort();
  86         for constraint in &constraints {
  87             let OutlivesConstraint {
  88                 sup,
  89                 sub,
  90                 locations,
  91                 category,
  92             } = constraint;
  93             with_msg(&format!(
  94                 "{:?}: {:?} due to {:?} at {:?}",
  95                 sup,
  96                 sub,
  97                 category,
  98                 locations,
  99             ))?;
 100         }
 101
 102         Ok(())
 103     }
 104 }
 105