+use crate::cfg::*;
+use rustc_data_structures::graph::implementation as graph;
+use rustc::middle::region;
+use rustc::ty::{self, TyCtxt};
+
+use rustc::hir::{self, PatKind};
+use rustc::hir::def_id::DefId;
+use rustc::hir::ptr::P;
+
+struct CFGBuilder<'a, 'tcx> {
+ tcx: TyCtxt<'tcx>,
+ owner_def_id: DefId,
+ tables: &'a ty::TypeckTables<'tcx>,
+ graph: CFGGraph,
+ fn_exit: CFGIndex,
+ loop_scopes: Vec<LoopScope>,
+ breakable_block_scopes: Vec<BlockScope>,
+}
+
+#[derive(Copy, Clone)]
+struct BlockScope {
+ block_expr_id: hir::ItemLocalId, // id of breakable block expr node
+ break_index: CFGIndex, // where to go on `break`
+}
+
+#[derive(Copy, Clone)]
+struct LoopScope {
+ loop_id: hir::ItemLocalId, // id of loop/while node
+ continue_index: CFGIndex, // where to go on a `loop`
+ break_index: CFGIndex, // where to go on a `break`
+}
+
+pub(super) fn construct(tcx: TyCtxt<'_>, body: &hir::Body) -> CFG {
+ let mut graph = graph::Graph::new();
+ let entry = graph.add_node(CFGNodeData::Entry);
+
+ // `fn_exit` is target of return exprs, which lies somewhere
+ // outside input `body`. (Distinguishing `fn_exit` and `body_exit`
+ // also resolves chicken-and-egg problem that arises if you try to
+ // have return exprs jump to `body_exit` during construction.)
+ let fn_exit = graph.add_node(CFGNodeData::Exit);
+ let body_exit;
+
+ // Find the tables for this body.
+ let owner_def_id = tcx.hir().body_owner_def_id(body.id());
+ let tables = tcx.typeck_tables_of(owner_def_id);
+
+ let mut cfg_builder = CFGBuilder {
+ tcx,
+ owner_def_id,
+ tables,
+ graph,
+ fn_exit,
+ loop_scopes: Vec::new(),
+ breakable_block_scopes: Vec::new(),
+ };
+ body_exit = cfg_builder.expr(&body.value, entry);
+ cfg_builder.add_contained_edge(body_exit, fn_exit);
+ let CFGBuilder { graph, .. } = cfg_builder;
+ CFG {
+ owner_def_id,
+ graph,
+ entry,
+ exit: fn_exit,
+ }
+}
+
+impl<'a, 'tcx> CFGBuilder<'a, 'tcx> {
+ fn block(&mut self, blk: &hir::Block, pred: CFGIndex) -> CFGIndex {
+ if blk.targeted_by_break {
+ let expr_exit = self.add_ast_node(blk.hir_id.local_id, &[]);
+
+ self.breakable_block_scopes.push(BlockScope {
+ block_expr_id: blk.hir_id.local_id,
+ break_index: expr_exit,
+ });
+
+ let mut stmts_exit = pred;
+ for stmt in &blk.stmts {
+ stmts_exit = self.stmt(stmt, stmts_exit);
+ }
+ let blk_expr_exit = self.opt_expr(&blk.expr, stmts_exit);
+ self.add_contained_edge(blk_expr_exit, expr_exit);
+
+ self.breakable_block_scopes.pop();
+
+ expr_exit
+ } else {
+ let mut stmts_exit = pred;
+ for stmt in &blk.stmts {
+ stmts_exit = self.stmt(stmt, stmts_exit);
+ }
+
+ let expr_exit = self.opt_expr(&blk.expr, stmts_exit);
+
+ self.add_ast_node(blk.hir_id.local_id, &[expr_exit])
+ }
+ }
+
+ fn stmt(&mut self, stmt: &hir::Stmt, pred: CFGIndex) -> CFGIndex {
+ let exit = match stmt.node {
+ hir::StmtKind::Local(ref local) => {
+ let init_exit = self.opt_expr(&local.init, pred);
+ self.pat(&local.pat, init_exit)
+ }
+ hir::StmtKind::Item(_) => {
+ pred
+ }
+ hir::StmtKind::Expr(ref expr) |
+ hir::StmtKind::Semi(ref expr) => {
+ self.expr(&expr, pred)
+ }
+ };
+ self.add_ast_node(stmt.hir_id.local_id, &[exit])
+ }
+
+ fn pat(&mut self, pat: &hir::Pat, pred: CFGIndex) -> CFGIndex {
+ match pat.node {
+ PatKind::Binding(.., None) |
+ PatKind::Path(_) |
+ PatKind::Lit(..) |
+ PatKind::Range(..) |
+ PatKind::Wild => self.add_ast_node(pat.hir_id.local_id, &[pred]),
+
+ PatKind::Box(ref subpat) |
+ PatKind::Ref(ref subpat, _) |
+ PatKind::Binding(.., Some(ref subpat)) => {
+ let subpat_exit = self.pat(&subpat, pred);
+ self.add_ast_node(pat.hir_id.local_id, &[subpat_exit])
+ }
+
+ PatKind::TupleStruct(_, ref subpats, _) |
+ PatKind::Tuple(ref subpats, _) => {
+ let pats_exit = self.pats_all(subpats.iter(), pred);
+ self.add_ast_node(pat.hir_id.local_id, &[pats_exit])
+ }
+
+ PatKind::Struct(_, ref subpats, _) => {
+ let pats_exit = self.pats_all(subpats.iter().map(|f| &f.pat), pred);
+ self.add_ast_node(pat.hir_id.local_id, &[pats_exit])
+ }
+
+ PatKind::Or(ref pats) => {
+ let branches: Vec<_> = pats.iter().map(|p| self.pat(p, pred)).collect();
+ self.add_ast_node(pat.hir_id.local_id, &branches)
+ }
+
+ PatKind::Slice(ref pre, ref vec, ref post) => {
+ let pre_exit = self.pats_all(pre.iter(), pred);
+ let vec_exit = self.pats_all(vec.iter(), pre_exit);
+ let post_exit = self.pats_all(post.iter(), vec_exit);
+ self.add_ast_node(pat.hir_id.local_id, &[post_exit])
+ }
+ }
+ }
+
+ fn pats_all<'b, I: Iterator<Item=&'b P<hir::Pat>>>(
+ &mut self,
+ pats: I,
+ pred: CFGIndex
+ ) -> CFGIndex {
+ //! Handles case where all of the patterns must match.
+ pats.fold(pred, |pred, pat| self.pat(&pat, pred))
+ }
+
+ fn expr(&mut self, expr: &hir::Expr, pred: CFGIndex) -> CFGIndex {
+ match expr.node {
+ hir::ExprKind::Block(ref blk, _) => {
+ let blk_exit = self.block(&blk, pred);
+ self.add_ast_node(expr.hir_id.local_id, &[blk_exit])
+ }
+
+ hir::ExprKind::Loop(ref body, _, _) => {
+ //
+ // [pred]
+ // |
+ // v 1
+ // [loopback] <---+
+ // | 4 |
+ // v 3 |
+ // [body] ------+
+ //
+ // [expr] 2
+ //
+ // Note that `break` and `loop` statements
+ // may cause additional edges.
+
+ let loopback = self.add_dummy_node(&[pred]); // 1
+ let expr_exit = self.add_ast_node(expr.hir_id.local_id, &[]); // 2
+ self.loop_scopes.push(LoopScope {
+ loop_id: expr.hir_id.local_id,
+ continue_index: loopback,
+ break_index: expr_exit,
+ });
+ let body_exit = self.block(&body, loopback); // 3
+ self.add_contained_edge(body_exit, loopback); // 4
+ self.loop_scopes.pop();
+ expr_exit
+ }
+
+ hir::ExprKind::Match(ref discr, ref arms, _) => {
+ self.match_(expr.hir_id.local_id, &discr, &arms, pred)
+ }
+
+ hir::ExprKind::Binary(op, ref l, ref r) if op.node.is_lazy() => {
+ //
+ // [pred]
+ // |
+ // v 1
+ // [l]
+ // |
+ // / \
+ // / \
+ // v 2 *
+ // [r] |
+ // | |
+ // v 3 v 4
+ // [..exit..]
+ //
+ let l_exit = self.expr(&l, pred); // 1
+ let r_exit = self.expr(&r, l_exit); // 2
+ self.add_ast_node(expr.hir_id.local_id, &[l_exit, r_exit]) // 3,4
+ }
+
+ hir::ExprKind::Ret(ref v) => {
+ let v_exit = self.opt_expr(v, pred);
+ let b = self.add_ast_node(expr.hir_id.local_id, &[v_exit]);
+ self.add_returning_edge(expr, b);
+ self.add_unreachable_node()
+ }
+
+ hir::ExprKind::Break(destination, ref opt_expr) => {
+ let v = self.opt_expr(opt_expr, pred);
+ let (target_scope, break_dest) =
+ self.find_scope_edge(expr, destination, ScopeCfKind::Break);
+ let b = self.add_ast_node(expr.hir_id.local_id, &[v]);
+ self.add_exiting_edge(expr, b, target_scope, break_dest);
+ self.add_unreachable_node()
+ }
+
+ hir::ExprKind::Continue(destination) => {
+ let (target_scope, cont_dest) =
+ self.find_scope_edge(expr, destination, ScopeCfKind::Continue);
+ let a = self.add_ast_node(expr.hir_id.local_id, &[pred]);
+ self.add_exiting_edge(expr, a, target_scope, cont_dest);
+ self.add_unreachable_node()
+ }
+
+ hir::ExprKind::Array(ref elems) => {
+ self.straightline(expr, pred, elems.iter().map(|e| &*e))
+ }
+
+ hir::ExprKind::Call(ref func, ref args) => {
+ self.call(expr, pred, &func, args.iter().map(|e| &*e))
+ }
+
+ hir::ExprKind::MethodCall(.., ref args) => {
+ self.call(expr, pred, &args[0], args[1..].iter().map(|e| &*e))
+ }
+
+ hir::ExprKind::Index(ref l, ref r) |
+ hir::ExprKind::Binary(_, ref l, ref r) if self.tables.is_method_call(expr) => {
+ self.call(expr, pred, &l, Some(&**r).into_iter())
+ }
+
+ hir::ExprKind::Unary(_, ref e) if self.tables.is_method_call(expr) => {
+ self.call(expr, pred, &e, None::<hir::Expr>.iter())
+ }
+
+ hir::ExprKind::Tup(ref exprs) => {
+ self.straightline(expr, pred, exprs.iter().map(|e| &*e))
+ }
+
+ hir::ExprKind::Struct(_, ref fields, ref base) => {
+ let field_cfg = self.straightline(expr, pred, fields.iter().map(|f| &*f.expr));
+ self.opt_expr(base, field_cfg)
+ }
+
+ hir::ExprKind::Assign(ref l, ref r) |
+ hir::ExprKind::AssignOp(_, ref l, ref r) => {
+ self.straightline(expr, pred, [r, l].iter().map(|&e| &**e))
+ }
+
+ hir::ExprKind::Index(ref l, ref r) |
+ hir::ExprKind::Binary(_, ref l, ref r) => { // N.B., && and || handled earlier
+ self.straightline(expr, pred, [l, r].iter().map(|&e| &**e))
+ }
+
+ hir::ExprKind::Box(ref e) |
+ hir::ExprKind::AddrOf(_, ref e) |
+ hir::ExprKind::Cast(ref e, _) |
+ hir::ExprKind::Type(ref e, _) |
+ hir::ExprKind::DropTemps(ref e) |
+ hir::ExprKind::Unary(_, ref e) |
+ hir::ExprKind::Field(ref e, _) |
+ hir::ExprKind::Yield(ref e, _) |
+ hir::ExprKind::Repeat(ref e, _) => {
+ self.straightline(expr, pred, Some(&**e).into_iter())
+ }
+
+ hir::ExprKind::InlineAsm(_, ref outputs, ref inputs) => {
+ let post_outputs = self.exprs(outputs.iter().map(|e| &*e), pred);
+ let post_inputs = self.exprs(inputs.iter().map(|e| &*e), post_outputs);
+ self.add_ast_node(expr.hir_id.local_id, &[post_inputs])
+ }
+
+ hir::ExprKind::Closure(..) |
+ hir::ExprKind::Lit(..) |
+ hir::ExprKind::Path(_) |
+ hir::ExprKind::Err => {
+ self.straightline(expr, pred, None::<hir::Expr>.iter())
+ }
+ }
+ }
+
+ fn call<'b, I: Iterator<Item=&'b hir::Expr>>(&mut self,
+ call_expr: &hir::Expr,
+ pred: CFGIndex,
+ func_or_rcvr: &hir::Expr,
+ args: I) -> CFGIndex {
+ let func_or_rcvr_exit = self.expr(func_or_rcvr, pred);
+ let ret = self.straightline(call_expr, func_or_rcvr_exit, args);
+ let m = self.tcx.hir().get_module_parent(call_expr.hir_id);
+ if self.tcx.is_ty_uninhabited_from(m, self.tables.expr_ty(call_expr)) {
+ self.add_unreachable_node()
+ } else {
+ ret
+ }
+ }
+
+ fn exprs<'b, I: Iterator<Item=&'b hir::Expr>>(&mut self,
+ exprs: I,
+ pred: CFGIndex) -> CFGIndex {
+ //! Constructs graph for `exprs` evaluated in order
+ exprs.fold(pred, |p, e| self.expr(e, p))
+ }
+
+ fn opt_expr(&mut self,
+ opt_expr: &Option<P<hir::Expr>>,
+ pred: CFGIndex) -> CFGIndex {
+ //! Constructs graph for `opt_expr` evaluated, if Some
+ opt_expr.iter().fold(pred, |p, e| self.expr(&e, p))
+ }
+
+ fn straightline<'b, I: Iterator<Item=&'b hir::Expr>>(&mut self,
+ expr: &hir::Expr,
+ pred: CFGIndex,
+ subexprs: I) -> CFGIndex {
+ //! Handles case of an expression that evaluates `subexprs` in order
+
+ let subexprs_exit = self.exprs(subexprs, pred);
+ self.add_ast_node(expr.hir_id.local_id, &[subexprs_exit])
+ }
+
+ fn match_(&mut self, id: hir::ItemLocalId, discr: &hir::Expr,
+ arms: &[hir::Arm], pred: CFGIndex) -> CFGIndex {
+ // The CFG for match expression is quite complex, so no ASCII
+ // art for it (yet).
+ //
+ // The CFG generated below matches roughly what MIR contains.
+ // Each pattern and guard is visited in parallel, with
+ // arms containing multiple patterns generating multiple nodes
+ // for the same guard expression. The guard expressions chain
+ // into each other from top to bottom, with a specific
+ // exception to allow some additional valid programs
+ // (explained below). MIR differs slightly in that the
+ // pattern matching may continue after a guard but the visible
+ // behaviour should be the same.
+ //
+ // What is going on is explained in further comments.
+
+ // Visit the discriminant expression
+ let discr_exit = self.expr(discr, pred);
+
+ // Add a node for the exit of the match expression as a whole.
+ let expr_exit = self.add_ast_node(id, &[]);
+
+ // Keep track of the previous guard expressions
+ let mut prev_guard = None;
+ let match_scope = region::Scope { id, data: region::ScopeData::Node };
+
+ for arm in arms {
+ // Add an exit node for when we've visited all the
+ // patterns and the guard (if there is one) in the arm.
+ let bindings_exit = self.add_dummy_node(&[]);
+
+ for pat in &arm.pats {
+ // Visit the pattern, coming from the discriminant exit
+ let mut pat_exit = self.pat(&pat, discr_exit);
+
+ // If there is a guard expression, handle it here
+ if let Some(ref guard) = arm.guard {
+ // Add a dummy node for the previous guard
+ // expression to target
+ let guard_start = self.add_dummy_node(&[pat_exit]);
+ // Visit the guard expression
+ let guard_exit = match guard {
+ hir::Guard::If(ref e) => (&**e, self.expr(e, guard_start)),
+ };
+ // #47295: We used to have very special case code
+ // here for when a pair of arms are both formed
+ // solely from constants, and if so, not add these
+ // edges. But this was not actually sound without
+ // other constraints that we stopped enforcing at
+ // some point.
+ if let Some((prev_guard, prev_index)) = prev_guard.take() {
+ self.add_exiting_edge(prev_guard, prev_index, match_scope, guard_start);
+ }
+
+ // Push the guard onto the list of previous guards
+ prev_guard = Some(guard_exit);
+
+ // Update the exit node for the pattern
+ pat_exit = guard_exit.1;
+ }
+
+ // Add an edge from the exit of this pattern to the
+ // exit of the arm
+ self.add_contained_edge(pat_exit, bindings_exit);
+ }
+
+ // Visit the body of this arm
+ let body_exit = self.expr(&arm.body, bindings_exit);
+
+ let arm_exit = self.add_ast_node(arm.hir_id.local_id, &[body_exit]);
+
+ // Link the body to the exit of the expression
+ self.add_contained_edge(arm_exit, expr_exit);
+ }
+
+ expr_exit
+ }
+
+ fn add_dummy_node(&mut self, preds: &[CFGIndex]) -> CFGIndex {
+ self.add_node(CFGNodeData::Dummy, preds)
+ }
+
+ fn add_ast_node(&mut self, id: hir::ItemLocalId, preds: &[CFGIndex]) -> CFGIndex {
+ self.add_node(CFGNodeData::AST(id), preds)
+ }
+
+ fn add_unreachable_node(&mut self) -> CFGIndex {
+ self.add_node(CFGNodeData::Unreachable, &[])
+ }
+
+ fn add_node(&mut self, data: CFGNodeData, preds: &[CFGIndex]) -> CFGIndex {
+ let node = self.graph.add_node(data);
+ for &pred in preds {
+ self.add_contained_edge(pred, node);
+ }
+ node
+ }
+
+ fn add_contained_edge(&mut self,
+ source: CFGIndex,
+ target: CFGIndex) {
+ let data = CFGEdgeData {exiting_scopes: vec![] };
+ self.graph.add_edge(source, target, data);
+ }
+
+ fn add_exiting_edge(&mut self,
+ from_expr: &hir::Expr,
+ from_index: CFGIndex,
+ target_scope: region::Scope,
+ to_index: CFGIndex) {
+ let mut data = CFGEdgeData { exiting_scopes: vec![] };
+ let mut scope = region::Scope {
+ id: from_expr.hir_id.local_id,
+ data: region::ScopeData::Node
+ };
+ let region_scope_tree = self.tcx.region_scope_tree(self.owner_def_id);
+ while scope != target_scope {
+ data.exiting_scopes.push(scope.item_local_id());
+ scope = region_scope_tree.encl_scope(scope);
+ }
+ self.graph.add_edge(from_index, to_index, data);
+ }
+
+ fn add_returning_edge(&mut self,
+ _from_expr: &hir::Expr,
+ from_index: CFGIndex) {
+ let data = CFGEdgeData {
+ exiting_scopes: self.loop_scopes.iter()
+ .rev()
+ .map(|&LoopScope { loop_id: id, .. }| id)
+ .collect()
+ };
+ self.graph.add_edge(from_index, self.fn_exit, data);
+ }
+
+ fn find_scope_edge(&self,
+ expr: &hir::Expr,
+ destination: hir::Destination,
+ scope_cf_kind: ScopeCfKind) -> (region::Scope, CFGIndex) {
+
+ match destination.target_id {
+ Ok(loop_id) => {
+ for b in &self.breakable_block_scopes {
+ if b.block_expr_id == loop_id.local_id {
+ let scope = region::Scope {
+ id: loop_id.local_id,
+ data: region::ScopeData::Node
+ };
+ return (scope, match scope_cf_kind {
+ ScopeCfKind::Break => b.break_index,
+ ScopeCfKind::Continue => bug!("can't continue to block"),
+ });
+ }
+ }
+ for l in &self.loop_scopes {
+ if l.loop_id == loop_id.local_id {
+ let scope = region::Scope {
+ id: loop_id.local_id,
+ data: region::ScopeData::Node
+ };
+ return (scope, match scope_cf_kind {
+ ScopeCfKind::Break => l.break_index,
+ ScopeCfKind::Continue => l.continue_index,
+ });
+ }
+ }
+ span_bug!(expr.span, "no scope for id {}", loop_id);
+ }
+ Err(err) => span_bug!(expr.span, "scope error: {}", err),
+ }
+ }
+}
+
+#[derive(Copy, Clone, Eq, PartialEq)]
+enum ScopeCfKind {
+ Break,
+ Continue,
+}