| use crate::cfg::*; |
| |
| use rustc::hir::{self, PatKind}; |
| use rustc::hir::def_id::DefId; |
| use rustc::hir::ptr::P; |
| use rustc::middle::region; |
| use rustc::ty::{self, TyCtxt}; |
| |
| use rustc_data_structures::graph::implementation as graph; |
| |
| 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]) |
| } |
| } |
| } |
| |
| /// Handles case where all of the patterns must match. |
| fn pats_all<'b, I: Iterator<Item = &'b P<hir::Pat>>>( |
| &mut self, |
| pats: I, |
| pred: CFGIndex, |
| ) -> CFGIndex { |
| 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 |
| } |
| } |
| |
| /// Constructs graph for `exprs` evaluated in order. |
| fn exprs<'b, I: Iterator<Item = &'b hir::Expr>>( |
| &mut self, |
| exprs: I, |
| pred: CFGIndex, |
| ) -> CFGIndex { |
| exprs.fold(pred, |p, e| self.expr(e, p)) |
| } |
| |
| /// Constructs graph for `opt_expr` evaluated, if `Some`. |
| fn opt_expr( |
| &mut self, |
| opt_expr: &Option<P<hir::Expr>>, |
| pred: CFGIndex, |
| ) -> CFGIndex { |
| opt_expr.iter().fold(pred, |p, e| self.expr(&e, p)) |
| } |
| |
| /// Handles case of an expression that evaluates `subexprs` in order. |
| fn straightline<'b, I: Iterator<Item = &'b hir::Expr>>( |
| &mut self, |
| expr: &hir::Expr, |
| pred: CFGIndex, |
| subexprs: I, |
| ) -> CFGIndex { |
| 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 expressions 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.top_pats_hack() { |
| // 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, |
| } |
