1 //! A solver for dataflow problems.
3 use std::borrow::BorrowMut;
4 use std::ffi::OsString;
5 use std::path::PathBuf;
8 use rustc_data_structures::work_queue::WorkQueue;
9 use rustc_graphviz as dot;
10 use rustc_hir::def_id::DefId;
11 use rustc_index::bit_set::BitSet;
12 use rustc_index::vec::{Idx, IndexVec};
13 use rustc_middle::mir::{self, traversal, BasicBlock};
14 use rustc_middle::mir::{create_dump_file, dump_enabled};
15 use rustc_middle::ty::TyCtxt;
16 use rustc_span::symbol::{sym, Symbol};
18 use super::fmt::DebugWithContext;
21 visit_results, Analysis, Direction, GenKill, GenKillAnalysis, GenKillSet, JoinSemiLattice,
22 ResultsCursor, ResultsVisitor,
25 /// A dataflow analysis that has converged to fixpoint.
26 pub struct Results<'tcx, A>
31 pub(super) entry_sets: IndexVec<BasicBlock, A::Domain>,
34 impl<A> Results<'tcx, A>
38 /// Creates a `ResultsCursor` that can inspect these `Results`.
39 pub fn into_results_cursor(self, body: &'mir mir::Body<'tcx>) -> ResultsCursor<'mir, 'tcx, A> {
40 ResultsCursor::new(body, self)
43 /// Gets the dataflow state for the given block.
44 pub fn entry_set_for_block(&self, block: BasicBlock) -> &A::Domain {
45 &self.entry_sets[block]
50 body: &'mir mir::Body<'tcx>,
51 blocks: impl IntoIterator<Item = BasicBlock>,
52 vis: &mut impl ResultsVisitor<'mir, 'tcx, FlowState = A::Domain>,
54 visit_results(body, blocks, self, vis)
57 pub fn visit_reachable_with(
59 body: &'mir mir::Body<'tcx>,
60 vis: &mut impl ResultsVisitor<'mir, 'tcx, FlowState = A::Domain>,
62 let blocks = mir::traversal::reachable(body);
63 visit_results(body, blocks.map(|(bb, _)| bb), self, vis)
67 /// A solver for dataflow problems.
68 pub struct Engine<'a, 'tcx, A>
73 body: &'a mir::Body<'tcx>,
74 dead_unwinds: Option<&'a BitSet<BasicBlock>>,
75 entry_sets: IndexVec<BasicBlock, A::Domain>,
76 pass_name: Option<&'static str>,
79 /// Cached, cumulative transfer functions for each block.
81 // FIXME(ecstaticmorse): This boxed `Fn` trait object is invoked inside a tight loop for
82 // gen/kill problems on cyclic CFGs. This is not ideal, but it doesn't seem to degrade
83 // performance in practice. I've tried a few ways to avoid this, but they have downsides. See
84 // the message for the commit that added this FIXME for more information.
85 apply_trans_for_block: Option<Box<dyn Fn(BasicBlock, &mut A::Domain)>>,
88 impl<A, D, T> Engine<'a, 'tcx, A>
90 A: GenKillAnalysis<'tcx, Idx = T, Domain = D>,
91 D: Clone + JoinSemiLattice + GenKill<T> + BorrowMut<BitSet<T>>,
94 /// Creates a new `Engine` to solve a gen-kill dataflow problem.
95 pub fn new_gen_kill(tcx: TyCtxt<'tcx>, body: &'a mir::Body<'tcx>, analysis: A) -> Self {
96 // If there are no back-edges in the control-flow graph, we only ever need to apply the
97 // transfer function for each block exactly once (assuming that we process blocks in RPO).
99 // In this case, there's no need to compute the block transfer functions ahead of time.
100 if !body.is_cfg_cyclic() {
101 return Self::new(tcx, body, analysis, None);
104 // Otherwise, compute and store the cumulative transfer function for each block.
106 let identity = GenKillSet::identity(analysis.bottom_value(body).borrow().domain_size());
107 let mut trans_for_block = IndexVec::from_elem(identity, body.basic_blocks());
109 for (block, block_data) in body.basic_blocks().iter_enumerated() {
110 let trans = &mut trans_for_block[block];
111 A::Direction::gen_kill_effects_in_block(&analysis, trans, block, block_data);
114 let apply_trans = Box::new(move |bb: BasicBlock, state: &mut A::Domain| {
115 trans_for_block[bb].apply(state.borrow_mut());
118 Self::new(tcx, body, analysis, Some(apply_trans as Box<_>))
122 impl<A, D> Engine<'a, 'tcx, A>
124 A: Analysis<'tcx, Domain = D>,
125 D: Clone + JoinSemiLattice,
127 /// Creates a new `Engine` to solve a dataflow problem with an arbitrary transfer
130 /// Gen-kill problems should use `new_gen_kill`, which will coalesce transfer functions for
131 /// better performance.
132 pub fn new_generic(tcx: TyCtxt<'tcx>, body: &'a mir::Body<'tcx>, analysis: A) -> Self {
133 Self::new(tcx, body, analysis, None)
138 body: &'a mir::Body<'tcx>,
140 apply_trans_for_block: Option<Box<dyn Fn(BasicBlock, &mut A::Domain)>>,
142 let bottom_value = analysis.bottom_value(body);
143 let mut entry_sets = IndexVec::from_elem(bottom_value.clone(), body.basic_blocks());
144 analysis.initialize_start_block(body, &mut entry_sets[mir::START_BLOCK]);
146 if A::Direction::is_backward() && entry_sets[mir::START_BLOCK] != bottom_value {
147 bug!("`initialize_start_block` is not yet supported for backward dataflow analyses");
157 apply_trans_for_block,
161 /// Signals that we do not want dataflow state to propagate across unwind edges for these
164 /// You must take care that `dead_unwinds` does not contain a `BasicBlock` that *can* actually
165 /// unwind during execution. Otherwise, your dataflow results will not be correct.
166 pub fn dead_unwinds(mut self, dead_unwinds: &'a BitSet<BasicBlock>) -> Self {
167 self.dead_unwinds = Some(dead_unwinds);
171 /// Adds an identifier to the graphviz output for this particular run of a dataflow analysis.
173 /// Some analyses are run multiple times in the compilation pipeline. Give them a `pass_name`
174 /// to differentiate them. Otherwise, only the results for the latest run will be saved.
175 pub fn pass_name(mut self, name: &'static str) -> Self {
176 self.pass_name = Some(name);
180 /// Computes the fixpoint for this dataflow problem and returns it.
181 pub fn iterate_to_fixpoint(self) -> Results<'tcx, A>
183 A::Domain: DebugWithContext<A>,
191 apply_trans_for_block,
196 let mut dirty_queue: WorkQueue<BasicBlock> =
197 WorkQueue::with_none(body.basic_blocks().len());
199 if A::Direction::is_forward() {
200 for (bb, _) in traversal::reverse_postorder(body) {
201 dirty_queue.insert(bb);
204 // Reverse post-order on the reverse CFG may generate a better iteration order for
205 // backward dataflow analyses, but probably not enough to matter.
206 for (bb, _) in traversal::postorder(body) {
207 dirty_queue.insert(bb);
211 // `state` is not actually used between iterations;
212 // this is just an optimization to avoid reallocating
214 let mut state = analysis.bottom_value(body);
215 while let Some(bb) = dirty_queue.pop() {
216 let bb_data = &body[bb];
218 // Set the state to the entry state of the block.
219 // This is equivalent to `state = entry_sets[bb].clone()`,
220 // but it saves an allocation, thus improving compile times.
221 state.clone_from(&entry_sets[bb]);
223 // Apply the block transfer function, using the cached one if it exists.
224 match &apply_trans_for_block {
225 Some(apply) => apply(bb, &mut state),
226 None => A::Direction::apply_effects_in_block(&analysis, &mut state, bb, bb_data),
229 A::Direction::join_state_into_successors_of(
236 |target: BasicBlock, state: &A::Domain| {
237 let set_changed = entry_sets[target].join(state);
239 dirty_queue.insert(target);
245 let results = Results { analysis, entry_sets };
247 let res = write_graphviz_results(tcx, &body, &results, pass_name);
248 if let Err(e) = res {
249 error!("Failed to write graphviz dataflow results: {}", e);
258 /// Writes a DOT file containing the results of a dataflow analysis if the user requested it via
259 /// `rustc_mir` attributes.
260 fn write_graphviz_results<A>(
262 body: &mir::Body<'tcx>,
263 results: &Results<'tcx, A>,
264 pass_name: Option<&'static str>,
265 ) -> std::io::Result<()>
268 A::Domain: DebugWithContext<A>,
271 use std::io::{self, Write};
273 let def_id = body.source.def_id();
274 let attrs = match RustcMirAttrs::parse(tcx, def_id) {
277 // Invalid `rustc_mir` attrs are reported in `RustcMirAttrs::parse`
278 Err(()) => return Ok(()),
281 let mut file = match attrs.output_path(A::NAME) {
283 debug!("printing dataflow results for {:?} to {}", def_id, path.display());
284 if let Some(parent) = path.parent() {
285 fs::create_dir_all(parent)?;
287 io::BufWriter::new(fs::File::create(&path)?)
290 None if tcx.sess.opts.debugging_opts.dump_mir_dataflow
291 && dump_enabled(tcx, A::NAME, def_id) =>
298 &pass_name.unwrap_or("-----"),
306 let style = match attrs.formatter {
307 Some(sym::two_phase) => graphviz::OutputStyle::BeforeAndAfter,
308 _ => graphviz::OutputStyle::AfterOnly,
311 let mut buf = Vec::new();
313 let graphviz = graphviz::Formatter::new(body, results, style);
314 let mut render_opts =
315 vec![dot::RenderOption::Fontname(tcx.sess.opts.debugging_opts.graphviz_font.clone())];
316 if tcx.sess.opts.debugging_opts.graphviz_dark_mode {
317 render_opts.push(dot::RenderOption::DarkTheme);
319 dot::render_opts(&graphviz, &mut buf, &render_opts)?;
321 file.write_all(&buf)?;
327 struct RustcMirAttrs {
328 basename_and_suffix: Option<PathBuf>,
329 formatter: Option<Symbol>,
333 fn parse(tcx: TyCtxt<'tcx>, def_id: DefId) -> Result<Self, ()> {
334 let attrs = tcx.get_attrs(def_id);
336 let mut result = Ok(());
337 let mut ret = RustcMirAttrs::default();
339 let rustc_mir_attrs = attrs
341 .filter(|attr| attr.has_name(sym::rustc_mir))
342 .flat_map(|attr| attr.meta_item_list().into_iter().flat_map(|v| v.into_iter()));
344 for attr in rustc_mir_attrs {
345 let attr_result = if attr.has_name(sym::borrowck_graphviz_postflow) {
346 Self::set_field(&mut ret.basename_and_suffix, tcx, &attr, |s| {
347 let path = PathBuf::from(s.to_string());
348 match path.file_name() {
351 tcx.sess.span_err(attr.span(), "path must end in a filename");
356 } else if attr.has_name(sym::borrowck_graphviz_format) {
357 Self::set_field(&mut ret.formatter, tcx, &attr, |s| match s {
358 sym::gen_kill | sym::two_phase => Ok(s),
360 tcx.sess.span_err(attr.span(), "unknown formatter");
368 result = result.and(attr_result);
375 field: &mut Option<T>,
377 attr: &ast::NestedMetaItem,
378 mapper: impl FnOnce(Symbol) -> Result<T, ()>,
379 ) -> Result<(), ()> {
382 .span_err(attr.span(), &format!("duplicate values for `{}`", attr.name_or_empty()));
387 if let Some(s) = attr.value_str() {
388 *field = Some(mapper(s)?);
392 .span_err(attr.span(), &format!("`{}` requires an argument", attr.name_or_empty()));
397 /// Returns the path where dataflow results should be written, or `None`
398 /// `borrowck_graphviz_postflow` was not specified.
400 /// This performs the following transformation to the argument of `borrowck_graphviz_postflow`:
402 /// "path/suffix.dot" -> "path/analysis_name_suffix.dot"
403 fn output_path(&self, analysis_name: &str) -> Option<PathBuf> {
404 let mut ret = self.basename_and_suffix.as_ref().cloned()?;
405 let suffix = ret.file_name().unwrap(); // Checked when parsing attrs
407 let mut file_name: OsString = analysis_name.into();
409 file_name.push(suffix);
410 ret.set_file_name(file_name);