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

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