1 //! A solver for dataflow problems.
3 use std::borrow::BorrowMut;
4 use std::ffi::OsString;
6 use std::path::PathBuf;
9 use rustc_data_structures::work_queue::WorkQueue;
10 use rustc_graphviz as dot;
11 use rustc_hir::def_id::DefId;
12 use rustc_index::bit_set::BitSet;
13 use rustc_index::vec::{Idx, IndexVec};
14 use rustc_middle::mir::{self, traversal, BasicBlock};
15 use rustc_middle::ty::{self, 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,
24 use crate::util::pretty::dump_enabled;
26 /// A dataflow analysis that has converged to fixpoint.
27 pub struct Results<'tcx, A>
32 pub(super) entry_sets: IndexVec<BasicBlock, A::Domain>,
35 impl<A> Results<'tcx, A>
39 /// Creates a `ResultsCursor` that can inspect these `Results`.
40 pub fn into_results_cursor(self, body: &'mir mir::Body<'tcx>) -> ResultsCursor<'mir, 'tcx, A> {
41 ResultsCursor::new(body, self)
44 /// Gets the dataflow state for the given block.
45 pub fn entry_set_for_block(&self, block: BasicBlock) -> &A::Domain {
46 &self.entry_sets[block]
51 body: &'mir mir::Body<'tcx>,
52 blocks: impl IntoIterator<Item = BasicBlock>,
53 vis: &mut impl ResultsVisitor<'mir, 'tcx, FlowState = A::Domain>,
55 visit_results(body, blocks, self, vis)
58 pub fn visit_reachable_with(
60 body: &'mir mir::Body<'tcx>,
61 vis: &mut impl ResultsVisitor<'mir, 'tcx, FlowState = A::Domain>,
63 let blocks = mir::traversal::reachable(body);
64 visit_results(body, blocks.map(|(bb, _)| bb), self, vis)
67 pub fn visit_in_rpo_with(
69 body: &'mir mir::Body<'tcx>,
70 vis: &mut impl ResultsVisitor<'mir, 'tcx, FlowState = A::Domain>,
72 let blocks = mir::traversal::reverse_postorder(body);
73 visit_results(body, blocks.map(|(bb, _)| bb), self, vis)
77 /// A solver for dataflow problems.
78 pub struct Engine<'a, 'tcx, A>
83 body: &'a mir::Body<'tcx>,
84 dead_unwinds: Option<&'a BitSet<BasicBlock>>,
85 entry_sets: IndexVec<BasicBlock, A::Domain>,
86 pass_name: Option<&'static str>,
89 /// Cached, cumulative transfer functions for each block.
91 // FIXME(ecstaticmorse): This boxed `Fn` trait object is invoked inside a tight loop for
92 // gen/kill problems on cyclic CFGs. This is not ideal, but it doesn't seem to degrade
93 // performance in practice. I've tried a few ways to avoid this, but they have downsides. See
94 // the message for the commit that added this FIXME for more information.
95 apply_trans_for_block: Option<Box<dyn Fn(BasicBlock, &mut A::Domain)>>,
98 impl<A, D, T> Engine<'a, 'tcx, A>
100 A: GenKillAnalysis<'tcx, Idx = T, Domain = D>,
101 D: Clone + JoinSemiLattice + GenKill<T> + BorrowMut<BitSet<T>>,
104 /// Creates a new `Engine` to solve a gen-kill dataflow problem.
105 pub fn new_gen_kill(tcx: TyCtxt<'tcx>, body: &'a mir::Body<'tcx>, analysis: A) -> Self {
106 // If there are no back-edges in the control-flow graph, we only ever need to apply the
107 // transfer function for each block exactly once (assuming that we process blocks in RPO).
109 // In this case, there's no need to compute the block transfer functions ahead of time.
110 if !body.is_cfg_cyclic() {
111 return Self::new(tcx, body, analysis, None);
114 // Otherwise, compute and store the cumulative transfer function for each block.
116 let identity = GenKillSet::identity(analysis.bottom_value(body).borrow().domain_size());
117 let mut trans_for_block = IndexVec::from_elem(identity, body.basic_blocks());
119 for (block, block_data) in body.basic_blocks().iter_enumerated() {
120 let trans = &mut trans_for_block[block];
121 A::Direction::gen_kill_effects_in_block(&analysis, trans, block, block_data);
124 let apply_trans = Box::new(move |bb: BasicBlock, state: &mut A::Domain| {
125 trans_for_block[bb].apply(state.borrow_mut());
128 Self::new(tcx, body, analysis, Some(apply_trans as Box<_>))
132 impl<A, D> Engine<'a, 'tcx, A>
134 A: Analysis<'tcx, Domain = D>,
135 D: Clone + JoinSemiLattice,
137 /// Creates a new `Engine` to solve a dataflow problem with an arbitrary transfer
140 /// Gen-kill problems should use `new_gen_kill`, which will coalesce transfer functions for
141 /// better performance.
142 pub fn new_generic(tcx: TyCtxt<'tcx>, body: &'a mir::Body<'tcx>, analysis: A) -> Self {
143 Self::new(tcx, body, analysis, None)
148 body: &'a mir::Body<'tcx>,
150 apply_trans_for_block: Option<Box<dyn Fn(BasicBlock, &mut A::Domain)>>,
152 let bottom_value = analysis.bottom_value(body);
153 let mut entry_sets = IndexVec::from_elem(bottom_value.clone(), body.basic_blocks());
154 analysis.initialize_start_block(body, &mut entry_sets[mir::START_BLOCK]);
156 if A::Direction::is_backward() && entry_sets[mir::START_BLOCK] != bottom_value {
157 bug!("`initialize_start_block` is not yet supported for backward dataflow analyses");
167 apply_trans_for_block,
171 /// Signals that we do not want dataflow state to propagate across unwind edges for these
174 /// You must take care that `dead_unwinds` does not contain a `BasicBlock` that *can* actually
175 /// unwind during execution. Otherwise, your dataflow results will not be correct.
176 pub fn dead_unwinds(mut self, dead_unwinds: &'a BitSet<BasicBlock>) -> Self {
177 self.dead_unwinds = Some(dead_unwinds);
181 /// Adds an identifier to the graphviz output for this particular run of a dataflow analysis.
183 /// Some analyses are run multiple times in the compilation pipeline. Give them a `pass_name`
184 /// to differentiate them. Otherwise, only the results for the latest run will be saved.
185 pub fn pass_name(mut self, name: &'static str) -> Self {
186 self.pass_name = Some(name);
190 /// Computes the fixpoint for this dataflow problem and returns it.
191 pub fn iterate_to_fixpoint(self) -> Results<'tcx, A>
193 A::Domain: DebugWithContext<A>,
201 apply_trans_for_block,
206 let mut dirty_queue: WorkQueue<BasicBlock> =
207 WorkQueue::with_none(body.basic_blocks().len());
209 if A::Direction::is_forward() {
210 for (bb, _) in traversal::reverse_postorder(body) {
211 dirty_queue.insert(bb);
214 // Reverse post-order on the reverse CFG may generate a better iteration order for
215 // backward dataflow analyses, but probably not enough to matter.
216 for (bb, _) in traversal::postorder(body) {
217 dirty_queue.insert(bb);
221 let mut state = analysis.bottom_value(body);
222 while let Some(bb) = dirty_queue.pop() {
223 let bb_data = &body[bb];
225 // Apply the block transfer function, using the cached one if it exists.
226 state.clone_from(&entry_sets[bb]);
227 match &apply_trans_for_block {
228 Some(apply) => apply(bb, &mut state),
229 None => A::Direction::apply_effects_in_block(&analysis, &mut state, bb, bb_data),
232 A::Direction::join_state_into_successors_of(
239 |target: BasicBlock, state: &A::Domain| {
240 let set_changed = entry_sets[target].join(state);
242 dirty_queue.insert(target);
248 let results = Results { analysis, entry_sets };
250 let res = write_graphviz_results(tcx, &body, &results, pass_name);
251 if let Err(e) = res {
252 warn!("Failed to write graphviz dataflow results: {}", e);
261 /// Writes a DOT file containing the results of a dataflow analysis if the user requested it via
262 /// `rustc_mir` attributes.
263 fn write_graphviz_results<A>(
265 body: &mir::Body<'tcx>,
266 results: &Results<'tcx, A>,
267 pass_name: Option<&'static str>,
268 ) -> std::io::Result<()>
271 A::Domain: DebugWithContext<A>,
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 path = match attrs.output_path(A::NAME) {
284 None if tcx.sess.opts.debugging_opts.dump_mir_dataflow
285 && dump_enabled(tcx, A::NAME, def_id) =>
287 // FIXME: Use some variant of `pretty::dump_path` for this
288 let mut path = PathBuf::from(&tcx.sess.opts.debugging_opts.dump_mir_dir);
290 let crate_name = tcx.crate_name(def_id.krate);
291 let item_name = ty::print::with_forced_impl_filename_line(|| {
292 tcx.def_path(def_id).to_filename_friendly_no_crate()
295 let pass_name = pass_name.map(|s| format!(".{}", s)).unwrap_or_default();
297 path.push(format!("{}.{}.{}{}.dot", crate_name, item_name, A::NAME, pass_name));
301 None => return Ok(()),
304 let style = match attrs.formatter {
305 Some(sym::two_phase) => graphviz::OutputStyle::BeforeAndAfter,
306 _ => graphviz::OutputStyle::AfterOnly,
309 debug!("printing dataflow results for {:?} to {}", def_id, path.display());
310 let mut buf = Vec::new();
312 let graphviz = graphviz::Formatter::new(body, results, style);
313 let mut render_opts =
314 vec![dot::RenderOption::Fontname(tcx.sess.opts.debugging_opts.graphviz_font.clone())];
315 if tcx.sess.opts.debugging_opts.graphviz_dark_mode {
316 render_opts.push(dot::RenderOption::DarkTheme);
318 dot::render_opts(&graphviz, &mut buf, &render_opts)?;
320 if let Some(parent) = path.parent() {
321 fs::create_dir_all(parent)?;
323 fs::write(&path, buf)?;
329 struct RustcMirAttrs {
330 basename_and_suffix: Option<PathBuf>,
331 formatter: Option<Symbol>,
335 fn parse(tcx: TyCtxt<'tcx>, def_id: DefId) -> Result<Self, ()> {
336 let attrs = tcx.get_attrs(def_id);
338 let mut result = Ok(());
339 let mut ret = RustcMirAttrs::default();
341 let rustc_mir_attrs = attrs
343 .filter(|attr| tcx.sess.check_name(attr, sym::rustc_mir))
344 .flat_map(|attr| attr.meta_item_list().into_iter().flat_map(|v| v.into_iter()));
346 for attr in rustc_mir_attrs {
347 let attr_result = if attr.has_name(sym::borrowck_graphviz_postflow) {
348 Self::set_field(&mut ret.basename_and_suffix, tcx, &attr, |s| {
349 let path = PathBuf::from(s.to_string());
350 match path.file_name() {
353 tcx.sess.span_err(attr.span(), "path must end in a filename");
358 } else if attr.has_name(sym::borrowck_graphviz_format) {
359 Self::set_field(&mut ret.formatter, tcx, &attr, |s| match s {
360 sym::gen_kill | sym::two_phase => Ok(s),
362 tcx.sess.span_err(attr.span(), "unknown formatter");
370 result = result.and(attr_result);
377 field: &mut Option<T>,
379 attr: &ast::NestedMetaItem,
380 mapper: impl FnOnce(Symbol) -> Result<T, ()>,
381 ) -> Result<(), ()> {
384 .span_err(attr.span(), &format!("duplicate values for `{}`", attr.name_or_empty()));
389 if let Some(s) = attr.value_str() {
390 *field = Some(mapper(s)?);
394 .span_err(attr.span(), &format!("`{}` requires an argument", attr.name_or_empty()));
399 /// Returns the path where dataflow results should be written, or `None`
400 /// `borrowck_graphviz_postflow` was not specified.
402 /// This performs the following transformation to the argument of `borrowck_graphviz_postflow`:
404 /// "path/suffix.dot" -> "path/analysis_name_suffix.dot"
405 fn output_path(&self, analysis_name: &str) -> Option<PathBuf> {
406 let mut ret = self.basename_and_suffix.as_ref().cloned()?;
407 let suffix = ret.file_name().unwrap(); // Checked when parsing attrs
409 let mut file_name: OsString = analysis_name.into();
411 file_name.push(suffix);
412 ret.set_file_name(file_name);