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<'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<'tcx>(tcx: TyCtxt<'tcx, 'tcx>, body: &hir::Body) -> CFG {
34 let mut graph = graph::Graph::new();
35 let entry = graph.add_node(CFGNodeData::Entry);
37 // `fn_exit` is target of return exprs, which lies somewhere
38 // outside input `body`. (Distinguishing `fn_exit` and `body_exit`
39 // also resolves chicken-and-egg problem that arises if you try to
40 // have return exprs jump to `body_exit` during construction.)
41 let fn_exit = graph.add_node(CFGNodeData::Exit);
44 // Find the tables for this body.
45 let owner_def_id = tcx.hir().local_def_id(tcx.hir().body_owner(body.id()));
46 let tables = tcx.typeck_tables_of(owner_def_id);
48 let mut cfg_builder = CFGBuilder {
54 loop_scopes: Vec::new(),
55 breakable_block_scopes: Vec::new(),
57 body_exit = cfg_builder.expr(&body.value, entry);
58 cfg_builder.add_contained_edge(body_exit, fn_exit);
59 let CFGBuilder { graph, .. } = cfg_builder;
68 impl<'a, 'tcx> CFGBuilder<'a, 'tcx> {
69 fn block(&mut self, blk: &hir::Block, pred: CFGIndex) -> CFGIndex {
70 if blk.targeted_by_break {
71 let expr_exit = self.add_ast_node(blk.hir_id.local_id, &[]);
73 self.breakable_block_scopes.push(BlockScope {
74 block_expr_id: blk.hir_id.local_id,
75 break_index: expr_exit,
78 let mut stmts_exit = pred;
79 for stmt in &blk.stmts {
80 stmts_exit = self.stmt(stmt, stmts_exit);
82 let blk_expr_exit = self.opt_expr(&blk.expr, stmts_exit);
83 self.add_contained_edge(blk_expr_exit, expr_exit);
85 self.breakable_block_scopes.pop();
89 let mut stmts_exit = pred;
90 for stmt in &blk.stmts {
91 stmts_exit = self.stmt(stmt, stmts_exit);
94 let expr_exit = self.opt_expr(&blk.expr, stmts_exit);
96 self.add_ast_node(blk.hir_id.local_id, &[expr_exit])
100 fn stmt(&mut self, stmt: &hir::Stmt, pred: CFGIndex) -> CFGIndex {
101 let exit = match stmt.node {
102 hir::StmtKind::Local(ref local) => {
103 let init_exit = self.opt_expr(&local.init, pred);
104 self.pat(&local.pat, init_exit)
106 hir::StmtKind::Item(_) => {
109 hir::StmtKind::Expr(ref expr) |
110 hir::StmtKind::Semi(ref expr) => {
111 self.expr(&expr, pred)
114 self.add_ast_node(stmt.hir_id.local_id, &[exit])
117 fn pat(&mut self, pat: &hir::Pat, pred: CFGIndex) -> CFGIndex {
119 PatKind::Binding(.., None) |
123 PatKind::Wild => self.add_ast_node(pat.hir_id.local_id, &[pred]),
125 PatKind::Box(ref subpat) |
126 PatKind::Ref(ref subpat, _) |
127 PatKind::Binding(.., Some(ref subpat)) => {
128 let subpat_exit = self.pat(&subpat, pred);
129 self.add_ast_node(pat.hir_id.local_id, &[subpat_exit])
132 PatKind::TupleStruct(_, ref subpats, _) |
133 PatKind::Tuple(ref subpats, _) => {
134 let pats_exit = self.pats_all(subpats.iter(), pred);
135 self.add_ast_node(pat.hir_id.local_id, &[pats_exit])
138 PatKind::Struct(_, ref subpats, _) => {
139 let pats_exit = self.pats_all(subpats.iter().map(|f| &f.node.pat), pred);
140 self.add_ast_node(pat.hir_id.local_id, &[pats_exit])
143 PatKind::Slice(ref pre, ref vec, ref post) => {
144 let pre_exit = self.pats_all(pre.iter(), pred);
145 let vec_exit = self.pats_all(vec.iter(), pre_exit);
146 let post_exit = self.pats_all(post.iter(), vec_exit);
147 self.add_ast_node(pat.hir_id.local_id, &[post_exit])
152 fn pats_all<'b, I: Iterator<Item=&'b P<hir::Pat>>>(
157 //! Handles case where all of the patterns must match.
158 pats.fold(pred, |pred, pat| self.pat(&pat, pred))
161 fn expr(&mut self, expr: &hir::Expr, pred: CFGIndex) -> CFGIndex {
163 hir::ExprKind::Block(ref blk, _) => {
164 let blk_exit = self.block(&blk, pred);
165 self.add_ast_node(expr.hir_id.local_id, &[blk_exit])
168 hir::ExprKind::While(ref cond, ref body, _) => {
183 // Note that `break` and `continue` statements
184 // may cause additional edges.
186 let loopback = self.add_dummy_node(&[pred]); // 1
188 // Create expr_exit without pred (cond_exit)
189 let expr_exit = self.add_ast_node(expr.hir_id.local_id, &[]); // 3
191 // The LoopScope needs to be on the loop_scopes stack while evaluating the
192 // condition and the body of the loop (both can break out of the loop)
193 self.loop_scopes.push(LoopScope {
194 loop_id: expr.hir_id.local_id,
195 continue_index: loopback,
196 break_index: expr_exit
199 let cond_exit = self.expr(&cond, loopback); // 2
201 // Add pred (cond_exit) to expr_exit
202 self.add_contained_edge(cond_exit, expr_exit);
204 let body_exit = self.block(&body, cond_exit); // 4
205 self.add_contained_edge(body_exit, loopback); // 5
206 self.loop_scopes.pop();
210 hir::ExprKind::Loop(ref body, _, _) => {
222 // Note that `break` and `loop` statements
223 // may cause additional edges.
225 let loopback = self.add_dummy_node(&[pred]); // 1
226 let expr_exit = self.add_ast_node(expr.hir_id.local_id, &[]); // 2
227 self.loop_scopes.push(LoopScope {
228 loop_id: expr.hir_id.local_id,
229 continue_index: loopback,
230 break_index: expr_exit,
232 let body_exit = self.block(&body, loopback); // 3
233 self.add_contained_edge(body_exit, loopback); // 4
234 self.loop_scopes.pop();
238 hir::ExprKind::Match(ref discr, ref arms, _) => {
239 self.match_(expr.hir_id.local_id, &discr, &arms, pred)
242 hir::ExprKind::Binary(op, ref l, ref r) if op.node.is_lazy() => {
257 let l_exit = self.expr(&l, pred); // 1
258 let r_exit = self.expr(&r, l_exit); // 2
259 self.add_ast_node(expr.hir_id.local_id, &[l_exit, r_exit]) // 3,4
262 hir::ExprKind::Ret(ref v) => {
263 let v_exit = self.opt_expr(v, pred);
264 let b = self.add_ast_node(expr.hir_id.local_id, &[v_exit]);
265 self.add_returning_edge(expr, b);
266 self.add_unreachable_node()
269 hir::ExprKind::Break(destination, ref opt_expr) => {
270 let v = self.opt_expr(opt_expr, pred);
271 let (target_scope, break_dest) =
272 self.find_scope_edge(expr, destination, ScopeCfKind::Break);
273 let b = self.add_ast_node(expr.hir_id.local_id, &[v]);
274 self.add_exiting_edge(expr, b, target_scope, break_dest);
275 self.add_unreachable_node()
278 hir::ExprKind::Continue(destination) => {
279 let (target_scope, cont_dest) =
280 self.find_scope_edge(expr, destination, ScopeCfKind::Continue);
281 let a = self.add_ast_node(expr.hir_id.local_id, &[pred]);
282 self.add_exiting_edge(expr, a, target_scope, cont_dest);
283 self.add_unreachable_node()
286 hir::ExprKind::Array(ref elems) => {
287 self.straightline(expr, pred, elems.iter().map(|e| &*e))
290 hir::ExprKind::Call(ref func, ref args) => {
291 self.call(expr, pred, &func, args.iter().map(|e| &*e))
294 hir::ExprKind::MethodCall(.., ref args) => {
295 self.call(expr, pred, &args[0], args[1..].iter().map(|e| &*e))
298 hir::ExprKind::Index(ref l, ref r) |
299 hir::ExprKind::Binary(_, ref l, ref r) if self.tables.is_method_call(expr) => {
300 self.call(expr, pred, &l, Some(&**r).into_iter())
303 hir::ExprKind::Unary(_, ref e) if self.tables.is_method_call(expr) => {
304 self.call(expr, pred, &e, None::<hir::Expr>.iter())
307 hir::ExprKind::Tup(ref exprs) => {
308 self.straightline(expr, pred, exprs.iter().map(|e| &*e))
311 hir::ExprKind::Struct(_, ref fields, ref base) => {
312 let field_cfg = self.straightline(expr, pred, fields.iter().map(|f| &*f.expr));
313 self.opt_expr(base, field_cfg)
316 hir::ExprKind::Assign(ref l, ref r) |
317 hir::ExprKind::AssignOp(_, ref l, ref r) => {
318 self.straightline(expr, pred, [r, l].iter().map(|&e| &**e))
321 hir::ExprKind::Index(ref l, ref r) |
322 hir::ExprKind::Binary(_, ref l, ref r) => { // N.B., && and || handled earlier
323 self.straightline(expr, pred, [l, r].iter().map(|&e| &**e))
326 hir::ExprKind::Box(ref e) |
327 hir::ExprKind::AddrOf(_, ref e) |
328 hir::ExprKind::Cast(ref e, _) |
329 hir::ExprKind::Type(ref e, _) |
330 hir::ExprKind::DropTemps(ref e) |
331 hir::ExprKind::Unary(_, ref e) |
332 hir::ExprKind::Field(ref e, _) |
333 hir::ExprKind::Yield(ref e) |
334 hir::ExprKind::Repeat(ref e, _) => {
335 self.straightline(expr, pred, Some(&**e).into_iter())
338 hir::ExprKind::InlineAsm(_, ref outputs, ref inputs) => {
339 let post_outputs = self.exprs(outputs.iter().map(|e| &*e), pred);
340 let post_inputs = self.exprs(inputs.iter().map(|e| &*e), post_outputs);
341 self.add_ast_node(expr.hir_id.local_id, &[post_inputs])
344 hir::ExprKind::Closure(..) |
345 hir::ExprKind::Lit(..) |
346 hir::ExprKind::Path(_) |
347 hir::ExprKind::Err => {
348 self.straightline(expr, pred, None::<hir::Expr>.iter())
353 fn call<'b, I: Iterator<Item=&'b hir::Expr>>(&mut self,
354 call_expr: &hir::Expr,
356 func_or_rcvr: &hir::Expr,
357 args: I) -> CFGIndex {
358 let func_or_rcvr_exit = self.expr(func_or_rcvr, pred);
359 let ret = self.straightline(call_expr, func_or_rcvr_exit, args);
360 let m = self.tcx.hir().get_module_parent_by_hir_id(call_expr.hir_id);
361 if self.tcx.is_ty_uninhabited_from(m, self.tables.expr_ty(call_expr)) {
362 self.add_unreachable_node()
368 fn exprs<'b, I: Iterator<Item=&'b hir::Expr>>(&mut self,
370 pred: CFGIndex) -> CFGIndex {
371 //! Constructs graph for `exprs` evaluated in order
372 exprs.fold(pred, |p, e| self.expr(e, p))
375 fn opt_expr(&mut self,
376 opt_expr: &Option<P<hir::Expr>>,
377 pred: CFGIndex) -> CFGIndex {
378 //! Constructs graph for `opt_expr` evaluated, if Some
379 opt_expr.iter().fold(pred, |p, e| self.expr(&e, p))
382 fn straightline<'b, I: Iterator<Item=&'b hir::Expr>>(&mut self,
385 subexprs: I) -> CFGIndex {
386 //! Handles case of an expression that evaluates `subexprs` in order
388 let subexprs_exit = self.exprs(subexprs, pred);
389 self.add_ast_node(expr.hir_id.local_id, &[subexprs_exit])
392 fn match_(&mut self, id: hir::ItemLocalId, discr: &hir::Expr,
393 arms: &[hir::Arm], pred: CFGIndex) -> CFGIndex {
394 // The CFG for match expression is quite complex, so no ASCII
397 // The CFG generated below matches roughly what MIR contains.
398 // Each pattern and guard is visited in parallel, with
399 // arms containing multiple patterns generating multiple nodes
400 // for the same guard expression. The guard expressions chain
401 // into each other from top to bottom, with a specific
402 // exception to allow some additional valid programs
403 // (explained below). MIR differs slightly in that the
404 // pattern matching may continue after a guard but the visible
405 // behaviour should be the same.
407 // What is going on is explained in further comments.
409 // Visit the discriminant expression
410 let discr_exit = self.expr(discr, pred);
412 // Add a node for the exit of the match expression as a whole.
413 let expr_exit = self.add_ast_node(id, &[]);
415 // Keep track of the previous guard expressions
416 let mut prev_guards = Vec::new();
419 // Add an exit node for when we've visited all the
420 // patterns and the guard (if there is one) in the arm.
421 let bindings_exit = self.add_dummy_node(&[]);
423 for pat in &arm.pats {
424 // Visit the pattern, coming from the discriminant exit
425 let mut pat_exit = self.pat(&pat, discr_exit);
427 // If there is a guard expression, handle it here
428 if let Some(ref guard) = arm.guard {
429 // Add a dummy node for the previous guard
430 // expression to target
431 let guard_start = self.add_dummy_node(&[pat_exit]);
432 // Visit the guard expression
433 let guard_exit = match guard {
434 hir::Guard::If(ref e) => self.expr(e, guard_start),
436 // #47295: We used to have very special case code
437 // here for when a pair of arms are both formed
438 // solely from constants, and if so, not add these
439 // edges. But this was not actually sound without
440 // other constraints that we stopped enforcing at
442 while let Some(prev) = prev_guards.pop() {
443 self.add_contained_edge(prev, guard_start);
446 // Push the guard onto the list of previous guards
447 prev_guards.push(guard_exit);
449 // Update the exit node for the pattern
450 pat_exit = guard_exit;
453 // Add an edge from the exit of this pattern to the
455 self.add_contained_edge(pat_exit, bindings_exit);
458 // Visit the body of this arm
459 let body_exit = self.expr(&arm.body, bindings_exit);
461 let arm_exit = self.add_ast_node(arm.hir_id.local_id, &[body_exit]);
463 // Link the body to the exit of the expression
464 self.add_contained_edge(arm_exit, expr_exit);
470 fn add_dummy_node(&mut self, preds: &[CFGIndex]) -> CFGIndex {
471 self.add_node(CFGNodeData::Dummy, preds)
474 fn add_ast_node(&mut self, id: hir::ItemLocalId, preds: &[CFGIndex]) -> CFGIndex {
475 self.add_node(CFGNodeData::AST(id), preds)
478 fn add_unreachable_node(&mut self) -> CFGIndex {
479 self.add_node(CFGNodeData::Unreachable, &[])
482 fn add_node(&mut self, data: CFGNodeData, preds: &[CFGIndex]) -> CFGIndex {
483 let node = self.graph.add_node(data);
485 self.add_contained_edge(pred, node);
490 fn add_contained_edge(&mut self,
493 let data = CFGEdgeData {exiting_scopes: vec![] };
494 self.graph.add_edge(source, target, data);
497 fn add_exiting_edge(&mut self,
498 from_expr: &hir::Expr,
499 from_index: CFGIndex,
500 target_scope: region::Scope,
501 to_index: CFGIndex) {
502 let mut data = CFGEdgeData { exiting_scopes: vec![] };
503 let mut scope = region::Scope {
504 id: from_expr.hir_id.local_id,
505 data: region::ScopeData::Node
507 let region_scope_tree = self.tcx.region_scope_tree(self.owner_def_id);
508 while scope != target_scope {
509 data.exiting_scopes.push(scope.item_local_id());
510 scope = region_scope_tree.encl_scope(scope);
512 self.graph.add_edge(from_index, to_index, data);
515 fn add_returning_edge(&mut self,
516 _from_expr: &hir::Expr,
517 from_index: CFGIndex) {
518 let data = CFGEdgeData {
519 exiting_scopes: self.loop_scopes.iter()
521 .map(|&LoopScope { loop_id: id, .. }| id)
524 self.graph.add_edge(from_index, self.fn_exit, data);
527 fn find_scope_edge(&self,
529 destination: hir::Destination,
530 scope_cf_kind: ScopeCfKind) -> (region::Scope, CFGIndex) {
532 match destination.target_id {
534 for b in &self.breakable_block_scopes {
535 if b.block_expr_id == loop_id.local_id {
536 let scope = region::Scope {
537 id: loop_id.local_id,
538 data: region::ScopeData::Node
540 return (scope, match scope_cf_kind {
541 ScopeCfKind::Break => b.break_index,
542 ScopeCfKind::Continue => bug!("can't continue to block"),
546 for l in &self.loop_scopes {
547 if l.loop_id == loop_id.local_id {
548 let scope = region::Scope {
549 id: loop_id.local_id,
550 data: region::ScopeData::Node
552 return (scope, match scope_cf_kind {
553 ScopeCfKind::Break => l.break_index,
554 ScopeCfKind::Continue => l.continue_index,
558 span_bug!(expr.span, "no scope for id {}", loop_id);
560 Err(err) => span_bug!(expr.span, "scope error: {}", err),
565 #[derive(Copy, Clone, Eq, PartialEq)]