src/librustc_mir/util/collect_writes.rs

use rustc::mir::{Local, Location};
use rustc::mir::ReadOnlyBodyCache;
use rustc::mir::visit::PlaceContext;
use rustc::mir::visit::Visitor;

crate trait FindAssignments {
    // Finds all statements that assign directly to local (i.e., X = ...)
    // and returns their locations.
    fn find_assignments(&self, local: Local) -> Vec<Location>;
}

impl<'a, 'tcx> FindAssignments for ReadOnlyBodyCache<'a, 'tcx>{
    fn find_assignments(&self, local: Local) -> Vec<Location>{
            let mut visitor = FindLocalAssignmentVisitor{ needle: local, locations: vec![]};
            visitor.visit_body(*self);
            visitor.locations
    }
}

// The Visitor walks the MIR to return the assignment statements corresponding
// to a Local.
struct FindLocalAssignmentVisitor {
    needle: Local,
    locations: Vec<Location>,
}

impl<'tcx> Visitor<'tcx> for FindLocalAssignmentVisitor {
    fn visit_local(&mut self,
                   local: &Local,
                   place_context: PlaceContext,
                   location: Location) {
        if self.needle != *local {
            return;
        }

        if place_context.is_place_assignment() {
            self.locations.push(location);
        }
    }
}