2 use crate::middle::region;
3 use rustc_data_structures::graph::implementation as graph;
5 use crate::ty::{self, TyCtxt};
7 use crate::hir::{self, PatKind};
8 use crate::hir::def_id::DefId;
10 struct CFGBuilder<'a, 'tcx: 'a> {
11 tcx: TyCtxt<'a, 'tcx, 'tcx>,
13 tables: &'a ty::TypeckTables<'tcx>,
16 loop_scopes: Vec<LoopScope>,
17 breakable_block_scopes: Vec<BlockScope>,
20 #[derive(Copy, Clone)]
22 block_expr_id: hir::ItemLocalId, // id of breakable block expr node
23 break_index: CFGIndex, // where to go on `break`
26 #[derive(Copy, Clone)]
28 loop_id: hir::ItemLocalId, // id of loop/while node
29 continue_index: CFGIndex, // where to go on a `loop`
30 break_index: CFGIndex, // where to go on a `break`
33 pub fn construct<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
34 body: &hir::Body) -> CFG {
35 let mut graph = graph::Graph::new();
36 let entry = graph.add_node(CFGNodeData::Entry);
38 // `fn_exit` is target of return exprs, which lies somewhere
39 // outside input `body`. (Distinguishing `fn_exit` and `body_exit`
40 // also resolves chicken-and-egg problem that arises if you try to
41 // have return exprs jump to `body_exit` during construction.)
42 let fn_exit = graph.add_node(CFGNodeData::Exit);
45 // Find the tables for this body.
46 let owner_def_id = tcx.hir().local_def_id(tcx.hir().body_owner(body.id()));
47 let tables = tcx.typeck_tables_of(owner_def_id);
49 let mut cfg_builder = CFGBuilder {
55 loop_scopes: Vec::new(),
56 breakable_block_scopes: Vec::new(),
58 body_exit = cfg_builder.expr(&body.value, entry);
59 cfg_builder.add_contained_edge(body_exit, fn_exit);
60 let CFGBuilder { graph, .. } = cfg_builder;
69 impl<'a, 'tcx> CFGBuilder<'a, 'tcx> {
70 fn block(&mut self, blk: &hir::Block, pred: CFGIndex) -> CFGIndex {
71 if blk.targeted_by_break {
72 let expr_exit = self.add_ast_node(blk.hir_id.local_id, &[]);
74 self.breakable_block_scopes.push(BlockScope {
75 block_expr_id: blk.hir_id.local_id,
76 break_index: expr_exit,
79 let mut stmts_exit = pred;
80 for stmt in &blk.stmts {
81 stmts_exit = self.stmt(stmt, stmts_exit);
83 let blk_expr_exit = self.opt_expr(&blk.expr, stmts_exit);
84 self.add_contained_edge(blk_expr_exit, expr_exit);
86 self.breakable_block_scopes.pop();
90 let mut stmts_exit = pred;
91 for stmt in &blk.stmts {
92 stmts_exit = self.stmt(stmt, stmts_exit);
95 let expr_exit = self.opt_expr(&blk.expr, stmts_exit);
97 self.add_ast_node(blk.hir_id.local_id, &[expr_exit])
101 fn stmt(&mut self, stmt: &hir::Stmt, pred: CFGIndex) -> CFGIndex {
102 let exit = match stmt.node {
103 hir::StmtKind::Local(ref local) => {
104 let init_exit = self.opt_expr(&local.init, pred);
105 self.pat(&local.pat, init_exit)
107 hir::StmtKind::Item(_) => {
110 hir::StmtKind::Expr(ref expr) |
111 hir::StmtKind::Semi(ref expr) => {
112 self.expr(&expr, pred)
115 self.add_ast_node(stmt.hir_id.local_id, &[exit])
118 fn pat(&mut self, pat: &hir::Pat, pred: CFGIndex) -> CFGIndex {
120 PatKind::Binding(.., None) |
124 PatKind::Wild => self.add_ast_node(pat.hir_id.local_id, &[pred]),
126 PatKind::Box(ref subpat) |
127 PatKind::Ref(ref subpat, _) |
128 PatKind::Binding(.., Some(ref subpat)) => {
129 let subpat_exit = self.pat(&subpat, pred);
130 self.add_ast_node(pat.hir_id.local_id, &[subpat_exit])
133 PatKind::TupleStruct(_, ref subpats, _) |
134 PatKind::Tuple(ref subpats, _) => {
135 let pats_exit = self.pats_all(subpats.iter(), pred);
136 self.add_ast_node(pat.hir_id.local_id, &[pats_exit])
139 PatKind::Struct(_, ref subpats, _) => {
140 let pats_exit = self.pats_all(subpats.iter().map(|f| &f.node.pat), pred);
141 self.add_ast_node(pat.hir_id.local_id, &[pats_exit])
144 PatKind::Slice(ref pre, ref vec, ref post) => {
145 let pre_exit = self.pats_all(pre.iter(), pred);
146 let vec_exit = self.pats_all(vec.iter(), pre_exit);
147 let post_exit = self.pats_all(post.iter(), vec_exit);
148 self.add_ast_node(pat.hir_id.local_id, &[post_exit])
153 fn pats_all<'b, I: Iterator<Item=&'b P<hir::Pat>>>(
158 //! Handles case where all of the patterns must match.
159 pats.fold(pred, |pred, pat| self.pat(&pat, pred))
162 fn expr(&mut self, expr: &hir::Expr, pred: CFGIndex) -> CFGIndex {
164 hir::ExprKind::Block(ref blk, _) => {
165 let blk_exit = self.block(&blk, pred);
166 self.add_ast_node(expr.hir_id.local_id, &[blk_exit])
169 hir::ExprKind::If(ref cond, ref then, None) => {
184 let cond_exit = self.expr(&cond, pred); // 1
185 let then_exit = self.expr(&then, cond_exit); // 2
186 self.add_ast_node(expr.hir_id.local_id, &[cond_exit, then_exit]) // 3,4
189 hir::ExprKind::If(ref cond, ref then, Some(ref otherwise)) => {
204 let cond_exit = self.expr(&cond, pred); // 1
205 let then_exit = self.expr(&then, cond_exit); // 2
206 let else_exit = self.expr(&otherwise, cond_exit); // 3
207 self.add_ast_node(expr.hir_id.local_id, &[then_exit, else_exit]) // 4, 5
210 hir::ExprKind::While(ref cond, ref body, _) => {
225 // Note that `break` and `continue` statements
226 // may cause additional edges.
228 let loopback = self.add_dummy_node(&[pred]); // 1
230 // Create expr_exit without pred (cond_exit)
231 let expr_exit = self.add_ast_node(expr.hir_id.local_id, &[]); // 3
233 // The LoopScope needs to be on the loop_scopes stack while evaluating the
234 // condition and the body of the loop (both can break out of the loop)
235 self.loop_scopes.push(LoopScope {
236 loop_id: expr.hir_id.local_id,
237 continue_index: loopback,
238 break_index: expr_exit
241 let cond_exit = self.expr(&cond, loopback); // 2
243 // Add pred (cond_exit) to expr_exit
244 self.add_contained_edge(cond_exit, expr_exit);
246 let body_exit = self.block(&body, cond_exit); // 4
247 self.add_contained_edge(body_exit, loopback); // 5
248 self.loop_scopes.pop();
252 hir::ExprKind::Loop(ref body, _, _) => {
264 // Note that `break` and `loop` statements
265 // may cause additional edges.
267 let loopback = self.add_dummy_node(&[pred]); // 1
268 let expr_exit = self.add_ast_node(expr.hir_id.local_id, &[]); // 2
269 self.loop_scopes.push(LoopScope {
270 loop_id: expr.hir_id.local_id,
271 continue_index: loopback,
272 break_index: expr_exit,
274 let body_exit = self.block(&body, loopback); // 3
275 self.add_contained_edge(body_exit, loopback); // 4
276 self.loop_scopes.pop();
280 hir::ExprKind::Match(ref discr, ref arms, _) => {
281 self.match_(expr.hir_id.local_id, &discr, &arms, pred)
284 hir::ExprKind::Binary(op, ref l, ref r) if op.node.is_lazy() => {
299 let l_exit = self.expr(&l, pred); // 1
300 let r_exit = self.expr(&r, l_exit); // 2
301 self.add_ast_node(expr.hir_id.local_id, &[l_exit, r_exit]) // 3,4
304 hir::ExprKind::Ret(ref v) => {
305 let v_exit = self.opt_expr(v, pred);
306 let b = self.add_ast_node(expr.hir_id.local_id, &[v_exit]);
307 self.add_returning_edge(expr, b);
308 self.add_unreachable_node()
311 hir::ExprKind::Break(destination, ref opt_expr) => {
312 let v = self.opt_expr(opt_expr, pred);
313 let (target_scope, break_dest) =
314 self.find_scope_edge(expr, destination, ScopeCfKind::Break);
315 let b = self.add_ast_node(expr.hir_id.local_id, &[v]);
316 self.add_exiting_edge(expr, b, target_scope, break_dest);
317 self.add_unreachable_node()
320 hir::ExprKind::Continue(destination) => {
321 let (target_scope, cont_dest) =
322 self.find_scope_edge(expr, destination, ScopeCfKind::Continue);
323 let a = self.add_ast_node(expr.hir_id.local_id, &[pred]);
324 self.add_exiting_edge(expr, a, target_scope, cont_dest);
325 self.add_unreachable_node()
328 hir::ExprKind::Array(ref elems) => {
329 self.straightline(expr, pred, elems.iter().map(|e| &*e))
332 hir::ExprKind::Call(ref func, ref args) => {
333 self.call(expr, pred, &func, args.iter().map(|e| &*e))
336 hir::ExprKind::MethodCall(.., ref args) => {
337 self.call(expr, pred, &args[0], args[1..].iter().map(|e| &*e))
340 hir::ExprKind::Index(ref l, ref r) |
341 hir::ExprKind::Binary(_, ref l, ref r) if self.tables.is_method_call(expr) => {
342 self.call(expr, pred, &l, Some(&**r).into_iter())
345 hir::ExprKind::Unary(_, ref e) if self.tables.is_method_call(expr) => {
346 self.call(expr, pred, &e, None::<hir::Expr>.iter())
349 hir::ExprKind::Tup(ref exprs) => {
350 self.straightline(expr, pred, exprs.iter().map(|e| &*e))
353 hir::ExprKind::Struct(_, ref fields, ref base) => {
354 let field_cfg = self.straightline(expr, pred, fields.iter().map(|f| &*f.expr));
355 self.opt_expr(base, field_cfg)
358 hir::ExprKind::Assign(ref l, ref r) |
359 hir::ExprKind::AssignOp(_, ref l, ref r) => {
360 self.straightline(expr, pred, [r, l].iter().map(|&e| &**e))
363 hir::ExprKind::Index(ref l, ref r) |
364 hir::ExprKind::Binary(_, ref l, ref r) => { // N.B., && and || handled earlier
365 self.straightline(expr, pred, [l, r].iter().map(|&e| &**e))
368 hir::ExprKind::Box(ref e) |
369 hir::ExprKind::AddrOf(_, ref e) |
370 hir::ExprKind::Cast(ref e, _) |
371 hir::ExprKind::Type(ref e, _) |
372 hir::ExprKind::DropTemps(ref e) |
373 hir::ExprKind::Unary(_, ref e) |
374 hir::ExprKind::Field(ref e, _) |
375 hir::ExprKind::Yield(ref e) |
376 hir::ExprKind::Repeat(ref e, _) => {
377 self.straightline(expr, pred, Some(&**e).into_iter())
380 hir::ExprKind::InlineAsm(_, ref outputs, ref inputs) => {
381 let post_outputs = self.exprs(outputs.iter().map(|e| &*e), pred);
382 let post_inputs = self.exprs(inputs.iter().map(|e| &*e), post_outputs);
383 self.add_ast_node(expr.hir_id.local_id, &[post_inputs])
386 hir::ExprKind::Closure(..) |
387 hir::ExprKind::Lit(..) |
388 hir::ExprKind::Path(_) |
389 hir::ExprKind::Err => {
390 self.straightline(expr, pred, None::<hir::Expr>.iter())
395 fn call<'b, I: Iterator<Item=&'b hir::Expr>>(&mut self,
396 call_expr: &hir::Expr,
398 func_or_rcvr: &hir::Expr,
399 args: I) -> CFGIndex {
400 let func_or_rcvr_exit = self.expr(func_or_rcvr, pred);
401 let ret = self.straightline(call_expr, func_or_rcvr_exit, args);
402 let m = self.tcx.hir().get_module_parent_by_hir_id(call_expr.hir_id);
403 if self.tcx.is_ty_uninhabited_from(m, self.tables.expr_ty(call_expr)) {
404 self.add_unreachable_node()
410 fn exprs<'b, I: Iterator<Item=&'b hir::Expr>>(&mut self,
412 pred: CFGIndex) -> CFGIndex {
413 //! Constructs graph for `exprs` evaluated in order
414 exprs.fold(pred, |p, e| self.expr(e, p))
417 fn opt_expr(&mut self,
418 opt_expr: &Option<P<hir::Expr>>,
419 pred: CFGIndex) -> CFGIndex {
420 //! Constructs graph for `opt_expr` evaluated, if Some
421 opt_expr.iter().fold(pred, |p, e| self.expr(&e, p))
424 fn straightline<'b, I: Iterator<Item=&'b hir::Expr>>(&mut self,
427 subexprs: I) -> CFGIndex {
428 //! Handles case of an expression that evaluates `subexprs` in order
430 let subexprs_exit = self.exprs(subexprs, pred);
431 self.add_ast_node(expr.hir_id.local_id, &[subexprs_exit])
434 fn match_(&mut self, id: hir::ItemLocalId, discr: &hir::Expr,
435 arms: &[hir::Arm], pred: CFGIndex) -> CFGIndex {
436 // The CFG for match expression is quite complex, so no ASCII
439 // The CFG generated below matches roughly what MIR contains.
440 // Each pattern and guard is visited in parallel, with
441 // arms containing multiple patterns generating multiple nodes
442 // for the same guard expression. The guard expressions chain
443 // into each other from top to bottom, with a specific
444 // exception to allow some additional valid programs
445 // (explained below). MIR differs slightly in that the
446 // pattern matching may continue after a guard but the visible
447 // behaviour should be the same.
449 // What is going on is explained in further comments.
451 // Visit the discriminant expression
452 let discr_exit = self.expr(discr, pred);
454 // Add a node for the exit of the match expression as a whole.
455 let expr_exit = self.add_ast_node(id, &[]);
457 // Keep track of the previous guard expressions
458 let mut prev_guards = Vec::new();
461 // Add an exit node for when we've visited all the
462 // patterns and the guard (if there is one) in the arm.
463 let arm_exit = self.add_dummy_node(&[]);
465 for pat in &arm.pats {
466 // Visit the pattern, coming from the discriminant exit
467 let mut pat_exit = self.pat(&pat, discr_exit);
469 // If there is a guard expression, handle it here
470 if let Some(ref guard) = arm.guard {
471 // Add a dummy node for the previous guard
472 // expression to target
473 let guard_start = self.add_dummy_node(&[pat_exit]);
474 // Visit the guard expression
475 let guard_exit = match guard {
476 hir::Guard::If(ref e) => self.expr(e, guard_start),
478 // #47295: We used to have very special case code
479 // here for when a pair of arms are both formed
480 // solely from constants, and if so, not add these
481 // edges. But this was not actually sound without
482 // other constraints that we stopped enforcing at
484 while let Some(prev) = prev_guards.pop() {
485 self.add_contained_edge(prev, guard_start);
488 // Push the guard onto the list of previous guards
489 prev_guards.push(guard_exit);
491 // Update the exit node for the pattern
492 pat_exit = guard_exit;
495 // Add an edge from the exit of this pattern to the
497 self.add_contained_edge(pat_exit, arm_exit);
500 // Visit the body of this arm
501 let body_exit = self.expr(&arm.body, arm_exit);
503 // Link the body to the exit of the expression
504 self.add_contained_edge(body_exit, expr_exit);
510 fn add_dummy_node(&mut self, preds: &[CFGIndex]) -> CFGIndex {
511 self.add_node(CFGNodeData::Dummy, preds)
514 fn add_ast_node(&mut self, id: hir::ItemLocalId, preds: &[CFGIndex]) -> CFGIndex {
515 self.add_node(CFGNodeData::AST(id), preds)
518 fn add_unreachable_node(&mut self) -> CFGIndex {
519 self.add_node(CFGNodeData::Unreachable, &[])
522 fn add_node(&mut self, data: CFGNodeData, preds: &[CFGIndex]) -> CFGIndex {
523 let node = self.graph.add_node(data);
525 self.add_contained_edge(pred, node);
530 fn add_contained_edge(&mut self,
533 let data = CFGEdgeData {exiting_scopes: vec![] };
534 self.graph.add_edge(source, target, data);
537 fn add_exiting_edge(&mut self,
538 from_expr: &hir::Expr,
539 from_index: CFGIndex,
540 target_scope: region::Scope,
541 to_index: CFGIndex) {
542 let mut data = CFGEdgeData { exiting_scopes: vec![] };
543 let mut scope = region::Scope {
544 id: from_expr.hir_id.local_id,
545 data: region::ScopeData::Node
547 let region_scope_tree = self.tcx.region_scope_tree(self.owner_def_id);
548 while scope != target_scope {
549 data.exiting_scopes.push(scope.item_local_id());
550 scope = region_scope_tree.encl_scope(scope);
552 self.graph.add_edge(from_index, to_index, data);
555 fn add_returning_edge(&mut self,
556 _from_expr: &hir::Expr,
557 from_index: CFGIndex) {
558 let data = CFGEdgeData {
559 exiting_scopes: self.loop_scopes.iter()
561 .map(|&LoopScope { loop_id: id, .. }| id)
564 self.graph.add_edge(from_index, self.fn_exit, data);
567 fn find_scope_edge(&self,
569 destination: hir::Destination,
570 scope_cf_kind: ScopeCfKind) -> (region::Scope, CFGIndex) {
572 match destination.target_id {
574 for b in &self.breakable_block_scopes {
575 if b.block_expr_id == loop_id.local_id {
576 let scope = region::Scope {
577 id: loop_id.local_id,
578 data: region::ScopeData::Node
580 return (scope, match scope_cf_kind {
581 ScopeCfKind::Break => b.break_index,
582 ScopeCfKind::Continue => bug!("can't continue to block"),
586 for l in &self.loop_scopes {
587 if l.loop_id == loop_id.local_id {
588 let scope = region::Scope {
589 id: loop_id.local_id,
590 data: region::ScopeData::Node
592 return (scope, match scope_cf_kind {
593 ScopeCfKind::Break => l.break_index,
594 ScopeCfKind::Continue => l.continue_index,
598 span_bug!(expr.span, "no scope for id {}", loop_id);
600 Err(err) => span_bug!(expr.span, "scope error: {}", err),
605 #[derive(Copy, Clone, Eq, PartialEq)]