src/librustc_mir/borrow_check/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 super::{OutlivesConstraint, RegionInferenceContext};
   7 use rustc_infer::infer::NLLRegionVariableOrigin;
   8 use std::io::{self, Write};
   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.universal_regions.region_classification(region).unwrap();
  23                 let outlived_by = self.universal_region_relations.regions_outlived_by(region);
  24                 writeln!(
  25                     out,
  26                     "| {r:rw$?} | {c:cw$?} | {ob:?}",
  27                     r = region,
  28                     rw = REGION_WIDTH,
  29                     c = classification,
  30                     cw = 8, // "External" at most
  31                     ob = outlived_by
  32                 )?;
  33             }
  34         }
  35
  36         writeln!(out, "|")?;
  37         writeln!(out, "| Inferred Region Values")?;
  38         for region in self.regions() {
  39             writeln!(
  40                 out,
  41                 "| {r:rw$?} | {ui:4?} | {v}",
  42                 r = region,
  43                 rw = REGION_WIDTH,
  44                 ui = self.region_universe(region),
  45                 v = self.region_value_str(region),
  46             )?;
  47         }
  48
  49         writeln!(out, "|")?;
  50         writeln!(out, "| Inference Constraints")?;
  51         self.for_each_constraint(&mut |msg| writeln!(out, "| {}", msg))?;
  52
  53         Ok(())
  54     }
  55
  56     /// Debugging aid: Invokes the `with_msg` callback repeatedly with
  57     /// our internal region constraints. These are dumped into the
  58     /// -Zdump-mir file so that we can figure out why the region
  59     /// inference resulted in the values that it did when debugging.
  60     fn for_each_constraint(
  61         &self,
  62         with_msg: &mut dyn FnMut(&str) -> io::Result<()>,
  63     ) -> io::Result<()> {
  64         for region in self.definitions.indices() {
  65             let value = self.liveness_constraints.region_value_str(region);
  66             if value != "{}" {
  67                 with_msg(&format!("{:?} live at {}", region, value))?;
  68             }
  69         }
  70
  71         let mut constraints: Vec<_> = self.constraints.outlives().iter().collect();
  72         constraints.sort();
  73         for constraint in &constraints {
  74             let OutlivesConstraint { sup, sub, locations, category } = constraint;
  75             with_msg(&format!("{:?}: {:?} due to {:?} at {:?}", sup, sub, category, locations,))?;
  76         }
  77
  78         Ok(())
  79     }
  80 }