mv compiler to compiler/

compiler/rustc_mir/src/dataflow/framework/engine.rs

@@ -0,0 +1,411 @@
+//! A solver for dataflow problems.
+
+use std::ffi::OsString;
+use std::fs;
+use std::path::PathBuf;
+
+use rustc_ast as ast;
+use rustc_data_structures::work_queue::WorkQueue;
+use rustc_graphviz as dot;
+use rustc_hir::def_id::DefId;
+use rustc_index::bit_set::BitSet;
+use rustc_index::vec::IndexVec;
+use rustc_middle::mir::{self, traversal, BasicBlock};
+use rustc_middle::ty::{self, TyCtxt};
+use rustc_span::symbol::{sym, Symbol};
+
+use super::graphviz;
+use super::{
+    visit_results, Analysis, Direction, GenKillAnalysis, GenKillSet, ResultsCursor, ResultsVisitor,
+};
+use crate::util::pretty::dump_enabled;
+
+/// A dataflow analysis that has converged to fixpoint.
+pub struct Results<'tcx, A>
+where
+    A: Analysis<'tcx>,
+{
+    pub analysis: A,
+    pub(super) entry_sets: IndexVec<BasicBlock, BitSet<A::Idx>>,
+}
+
+impl<A> Results<'tcx, A>
+where
+    A: Analysis<'tcx>,
+{
+    /// Creates a `ResultsCursor` that can inspect these `Results`.
+    pub fn into_results_cursor(self, body: &'mir mir::Body<'tcx>) -> ResultsCursor<'mir, 'tcx, A> {
+        ResultsCursor::new(body, self)
+    }
+
+    /// Gets the dataflow state for the given block.
+    pub fn entry_set_for_block(&self, block: BasicBlock) -> &BitSet<A::Idx> {
+        &self.entry_sets[block]
+    }
+
+    pub fn visit_with(
+        &self,
+        body: &'mir mir::Body<'tcx>,
+        blocks: impl IntoIterator<Item = BasicBlock>,
+        vis: &mut impl ResultsVisitor<'mir, 'tcx, FlowState = BitSet<A::Idx>>,
+    ) {
+        visit_results(body, blocks, self, vis)
+    }
+
+    pub fn visit_reachable_with(
+        &self,
+        body: &'mir mir::Body<'tcx>,
+        vis: &mut impl ResultsVisitor<'mir, 'tcx, FlowState = BitSet<A::Idx>>,
+    ) {
+        let blocks = mir::traversal::reachable(body);
+        visit_results(body, blocks.map(|(bb, _)| bb), self, vis)
+    }
+
+    pub fn visit_in_rpo_with(
+        &self,
+        body: &'mir mir::Body<'tcx>,
+        vis: &mut impl ResultsVisitor<'mir, 'tcx, FlowState = BitSet<A::Idx>>,
+    ) {
+        let blocks = mir::traversal::reverse_postorder(body);
+        visit_results(body, blocks.map(|(bb, _)| bb), self, vis)
+    }
+}
+
+/// A solver for dataflow problems.
+pub struct Engine<'a, 'tcx, A>
+where
+    A: Analysis<'tcx>,
+{
+    bits_per_block: usize,
+    tcx: TyCtxt<'tcx>,
+    body: &'a mir::Body<'tcx>,
+    def_id: DefId,
+    dead_unwinds: Option<&'a BitSet<BasicBlock>>,
+    entry_sets: IndexVec<BasicBlock, BitSet<A::Idx>>,
+    analysis: A,
+
+    /// Cached, cumulative transfer functions for each block.
+    trans_for_block: Option<IndexVec<BasicBlock, GenKillSet<A::Idx>>>,
+}
+
+impl<A> Engine<'a, 'tcx, A>
+where
+    A: GenKillAnalysis<'tcx>,
+{
+    /// Creates a new `Engine` to solve a gen-kill dataflow problem.
+    pub fn new_gen_kill(
+        tcx: TyCtxt<'tcx>,
+        body: &'a mir::Body<'tcx>,
+        def_id: DefId,
+        analysis: A,
+    ) -> Self {
+        // If there are no back-edges in the control-flow graph, we only ever need to apply the
+        // transfer function for each block exactly once (assuming that we process blocks in RPO).
+        //
+        // In this case, there's no need to compute the block transfer functions ahead of time.
+        if !body.is_cfg_cyclic() {
+            return Self::new(tcx, body, def_id, analysis, None);
+        }
+
+        // Otherwise, compute and store the cumulative transfer function for each block.
+
+        let bits_per_block = analysis.bits_per_block(body);
+        let mut trans_for_block =
+            IndexVec::from_elem(GenKillSet::identity(bits_per_block), body.basic_blocks());
+
+        for (block, block_data) in body.basic_blocks().iter_enumerated() {
+            let trans = &mut trans_for_block[block];
+            A::Direction::gen_kill_effects_in_block(&analysis, trans, block, block_data);
+        }
+
+        Self::new(tcx, body, def_id, analysis, Some(trans_for_block))
+    }
+}
+
+impl<A> Engine<'a, 'tcx, A>
+where
+    A: Analysis<'tcx>,
+{
+    /// Creates a new `Engine` to solve a dataflow problem with an arbitrary transfer
+    /// function.
+    ///
+    /// Gen-kill problems should use `new_gen_kill`, which will coalesce transfer functions for
+    /// better performance.
+    pub fn new_generic(
+        tcx: TyCtxt<'tcx>,
+        body: &'a mir::Body<'tcx>,
+        def_id: DefId,
+        analysis: A,
+    ) -> Self {
+        Self::new(tcx, body, def_id, analysis, None)
+    }
+
+    fn new(
+        tcx: TyCtxt<'tcx>,
+        body: &'a mir::Body<'tcx>,
+        def_id: DefId,
+        analysis: A,
+        trans_for_block: Option<IndexVec<BasicBlock, GenKillSet<A::Idx>>>,
+    ) -> Self {
+        let bits_per_block = analysis.bits_per_block(body);
+
+        let bottom_value_set = if A::BOTTOM_VALUE {
+            BitSet::new_filled(bits_per_block)
+        } else {
+            BitSet::new_empty(bits_per_block)
+        };
+
+        let mut entry_sets = IndexVec::from_elem(bottom_value_set.clone(), body.basic_blocks());
+        analysis.initialize_start_block(body, &mut entry_sets[mir::START_BLOCK]);
+
+        if A::Direction::is_backward() && entry_sets[mir::START_BLOCK] != bottom_value_set {
+            bug!("`initialize_start_block` is not yet supported for backward dataflow analyses");
+        }
+
+        Engine {
+            analysis,
+            bits_per_block,
+            tcx,
+            body,
+            def_id,
+            dead_unwinds: None,
+            entry_sets,
+            trans_for_block,
+        }
+    }
+
+    /// Signals that we do not want dataflow state to propagate across unwind edges for these
+    /// `BasicBlock`s.
+    ///
+    /// You must take care that `dead_unwinds` does not contain a `BasicBlock` that *can* actually
+    /// unwind during execution. Otherwise, your dataflow results will not be correct.
+    pub fn dead_unwinds(mut self, dead_unwinds: &'a BitSet<BasicBlock>) -> Self {
+        self.dead_unwinds = Some(dead_unwinds);
+        self
+    }
+
+    /// Computes the fixpoint for this dataflow problem and returns it.
+    pub fn iterate_to_fixpoint(self) -> Results<'tcx, A> {
+        let Engine {
+            analysis,
+            bits_per_block,
+            body,
+            dead_unwinds,
+            def_id,
+            mut entry_sets,
+            tcx,
+            trans_for_block,
+            ..
+        } = self;
+
+        let mut dirty_queue: WorkQueue<BasicBlock> =
+            WorkQueue::with_none(body.basic_blocks().len());
+
+        if A::Direction::is_forward() {
+            for (bb, _) in traversal::reverse_postorder(body) {
+                dirty_queue.insert(bb);
+            }
+        } else {
+            // Reverse post-order on the reverse CFG may generate a better iteration order for
+            // backward dataflow analyses, but probably not enough to matter.
+            for (bb, _) in traversal::postorder(body) {
+                dirty_queue.insert(bb);
+            }
+        }
+
+        let mut state = BitSet::new_empty(bits_per_block);
+        while let Some(bb) = dirty_queue.pop() {
+            let bb_data = &body[bb];
+
+            // Apply the block transfer function, using the cached one if it exists.
+            state.overwrite(&entry_sets[bb]);
+            match &trans_for_block {
+                Some(trans_for_block) => trans_for_block[bb].apply(&mut state),
+                None => A::Direction::apply_effects_in_block(&analysis, &mut state, bb, bb_data),
+            }
+
+            A::Direction::join_state_into_successors_of(
+                &analysis,
+                tcx,
+                body,
+                dead_unwinds,
+                &mut state,
+                (bb, bb_data),
+                |target: BasicBlock, state: &BitSet<A::Idx>| {
+                    let set_changed = analysis.join(&mut entry_sets[target], state);
+                    if set_changed {
+                        dirty_queue.insert(target);
+                    }
+                },
+            );
+        }
+
+        let results = Results { analysis, entry_sets };
+
+        let res = write_graphviz_results(tcx, def_id, &body, &results, trans_for_block);
+        if let Err(e) = res {
+            warn!("Failed to write graphviz dataflow results: {}", e);
+        }
+
+        results
+    }
+}
+
+// Graphviz
+
+/// Writes a DOT file containing the results of a dataflow analysis if the user requested it via
+/// `rustc_mir` attributes.
+fn write_graphviz_results<A>(
+    tcx: TyCtxt<'tcx>,
+    def_id: DefId,
+    body: &mir::Body<'tcx>,
+    results: &Results<'tcx, A>,
+    block_transfer_functions: Option<IndexVec<BasicBlock, GenKillSet<A::Idx>>>,
+) -> std::io::Result<()>
+where
+    A: Analysis<'tcx>,
+{
+    let attrs = match RustcMirAttrs::parse(tcx, def_id) {
+        Ok(attrs) => attrs,
+
+        // Invalid `rustc_mir` attrs are reported in `RustcMirAttrs::parse`
+        Err(()) => return Ok(()),
+    };
+
+    let path = match attrs.output_path(A::NAME) {
+        Some(path) => path,
+
+        None if tcx.sess.opts.debugging_opts.dump_mir_dataflow
+            && dump_enabled(tcx, A::NAME, def_id) =>
+        {
+            let mut path = PathBuf::from(&tcx.sess.opts.debugging_opts.dump_mir_dir);
+
+            let item_name = ty::print::with_forced_impl_filename_line(|| {
+                tcx.def_path(def_id).to_filename_friendly_no_crate()
+            });
+            path.push(format!("rustc.{}.{}.dot", item_name, A::NAME));
+            path
+        }
+
+        None => return Ok(()),
+    };
+
+    let bits_per_block = results.analysis.bits_per_block(body);
+
+    let mut formatter: Box<dyn graphviz::StateFormatter<'tcx, _>> = match attrs.formatter {
+        Some(sym::two_phase) => Box::new(graphviz::TwoPhaseDiff::new(bits_per_block)),
+        Some(sym::gen_kill) => {
+            if let Some(trans_for_block) = block_transfer_functions {
+                Box::new(graphviz::BlockTransferFunc::new(body, trans_for_block))
+            } else {
+                Box::new(graphviz::SimpleDiff::new(body, &results))
+            }
+        }
+
+        // Default to the `SimpleDiff` output style.
+        _ => Box::new(graphviz::SimpleDiff::new(body, &results)),
+    };
+
+    debug!("printing dataflow results for {:?} to {}", def_id, path.display());
+    let mut buf = Vec::new();
+
+    let graphviz = graphviz::Formatter::new(body, def_id, results, &mut *formatter);
+    dot::render_opts(&graphviz, &mut buf, &[dot::RenderOption::Monospace])?;
+
+    if let Some(parent) = path.parent() {
+        fs::create_dir_all(parent)?;
+    }
+    fs::write(&path, buf)?;
+
+    Ok(())
+}
+
+#[derive(Default)]
+struct RustcMirAttrs {
+    basename_and_suffix: Option<PathBuf>,
+    formatter: Option<Symbol>,
+}
+
+impl RustcMirAttrs {
+    fn parse(tcx: TyCtxt<'tcx>, def_id: DefId) -> Result<Self, ()> {
+        let attrs = tcx.get_attrs(def_id);
+
+        let mut result = Ok(());
+        let mut ret = RustcMirAttrs::default();
+
+        let rustc_mir_attrs = attrs
+            .iter()
+            .filter(|attr| tcx.sess.check_name(attr, sym::rustc_mir))
+            .flat_map(|attr| attr.meta_item_list().into_iter().flat_map(|v| v.into_iter()));
+
+        for attr in rustc_mir_attrs {
+            let attr_result = if attr.has_name(sym::borrowck_graphviz_postflow) {
+                Self::set_field(&mut ret.basename_and_suffix, tcx, &attr, |s| {
+                    let path = PathBuf::from(s.to_string());
+                    match path.file_name() {
+                        Some(_) => Ok(path),
+                        None => {
+                            tcx.sess.span_err(attr.span(), "path must end in a filename");
+                            Err(())
+                        }
+                    }
+                })
+            } else if attr.has_name(sym::borrowck_graphviz_format) {
+                Self::set_field(&mut ret.formatter, tcx, &attr, |s| match s {
+                    sym::gen_kill | sym::two_phase => Ok(s),
+                    _ => {
+                        tcx.sess.span_err(attr.span(), "unknown formatter");
+                        Err(())
+                    }
+                })
+            } else {
+                Ok(())
+            };
+
+            result = result.and(attr_result);
+        }
+
+        result.map(|()| ret)
+    }
+
+    fn set_field<T>(
+        field: &mut Option<T>,
+        tcx: TyCtxt<'tcx>,
+        attr: &ast::NestedMetaItem,
+        mapper: impl FnOnce(Symbol) -> Result<T, ()>,
+    ) -> Result<(), ()> {
+        if field.is_some() {
+            tcx.sess
+                .span_err(attr.span(), &format!("duplicate values for `{}`", attr.name_or_empty()));
+
+            return Err(());
+        }
+
+        if let Some(s) = attr.value_str() {
+            *field = Some(mapper(s)?);
+            Ok(())
+        } else {
+            tcx.sess
+                .span_err(attr.span(), &format!("`{}` requires an argument", attr.name_or_empty()));
+            Err(())
+        }
+    }
+
+    /// Returns the path where dataflow results should be written, or `None`
+    /// `borrowck_graphviz_postflow` was not specified.
+    ///
+    /// This performs the following transformation to the argument of `borrowck_graphviz_postflow`:
+    ///
+    /// "path/suffix.dot" -> "path/analysis_name_suffix.dot"
+    fn output_path(&self, analysis_name: &str) -> Option<PathBuf> {
+        let mut ret = self.basename_and_suffix.as_ref().cloned()?;
+        let suffix = ret.file_name().unwrap(); // Checked when parsing attrs
+
+        let mut file_name: OsString = analysis_name.into();
+        file_name.push("_");
+        file_name.push(suffix);
+        ret.set_file_name(file_name);
+
+        Some(ret)
+    }
+}