1 // Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 use rustc_data_structures::graph;
15 use ty::{self, TyCtxt};
19 use hir::{self, PatKind};
21 struct CFGBuilder<'a, 'tcx: 'a> {
22 tcx: TyCtxt<'a, 'tcx, 'tcx>,
25 loop_scopes: Vec<LoopScope>,
28 #[derive(Copy, Clone)]
30 loop_id: ast::NodeId, // id of loop/while node
31 continue_index: CFGIndex, // where to go on a `loop`
32 break_index: CFGIndex, // where to go on a `break
35 pub fn construct<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
36 blk: &hir::Block) -> CFG {
37 let mut graph = graph::Graph::new();
38 let entry = graph.add_node(CFGNodeData::Entry);
40 // `fn_exit` is target of return exprs, which lies somewhere
41 // outside input `blk`. (Distinguishing `fn_exit` and `block_exit`
42 // also resolves chicken-and-egg problem that arises if you try to
43 // have return exprs jump to `block_exit` during construction.)
44 let fn_exit = graph.add_node(CFGNodeData::Exit);
47 let mut cfg_builder = CFGBuilder {
51 loop_scopes: Vec::new()
53 block_exit = cfg_builder.block(blk, entry);
54 cfg_builder.add_contained_edge(block_exit, fn_exit);
55 let CFGBuilder {graph, ..} = cfg_builder;
61 impl<'a, 'tcx> CFGBuilder<'a, 'tcx> {
62 fn block(&mut self, blk: &hir::Block, pred: CFGIndex) -> CFGIndex {
63 let mut stmts_exit = pred;
64 for stmt in &blk.stmts {
65 stmts_exit = self.stmt(stmt, stmts_exit);
68 let expr_exit = self.opt_expr(&blk.expr, stmts_exit);
70 self.add_ast_node(blk.id, &[expr_exit])
73 fn stmt(&mut self, stmt: &hir::Stmt, pred: CFGIndex) -> CFGIndex {
75 hir::StmtDecl(ref decl, id) => {
76 let exit = self.decl(&decl, pred);
77 self.add_ast_node(id, &[exit])
80 hir::StmtExpr(ref expr, id) | hir::StmtSemi(ref expr, id) => {
81 let exit = self.expr(&expr, pred);
82 self.add_ast_node(id, &[exit])
87 fn decl(&mut self, decl: &hir::Decl, pred: CFGIndex) -> CFGIndex {
89 hir::DeclLocal(ref local) => {
90 let init_exit = self.opt_expr(&local.init, pred);
91 self.pat(&local.pat, init_exit)
100 fn pat(&mut self, pat: &hir::Pat, pred: CFGIndex) -> CFGIndex {
102 PatKind::Binding(_, _, None) |
108 self.add_ast_node(pat.id, &[pred])
111 PatKind::Box(ref subpat) |
112 PatKind::Ref(ref subpat, _) |
113 PatKind::Binding(_, _, Some(ref subpat)) => {
114 let subpat_exit = self.pat(&subpat, pred);
115 self.add_ast_node(pat.id, &[subpat_exit])
118 PatKind::TupleStruct(_, ref subpats, _) |
119 PatKind::Tuple(ref subpats, _) => {
120 let pats_exit = self.pats_all(subpats.iter(), pred);
121 self.add_ast_node(pat.id, &[pats_exit])
124 PatKind::Struct(_, ref subpats, _) => {
126 self.pats_all(subpats.iter().map(|f| &f.node.pat), pred);
127 self.add_ast_node(pat.id, &[pats_exit])
130 PatKind::Vec(ref pre, ref vec, ref post) => {
131 let pre_exit = self.pats_all(pre.iter(), pred);
132 let vec_exit = self.pats_all(vec.iter(), pre_exit);
133 let post_exit = self.pats_all(post.iter(), vec_exit);
134 self.add_ast_node(pat.id, &[post_exit])
139 fn pats_all<'b, I: Iterator<Item=&'b P<hir::Pat>>>(&mut self,
141 pred: CFGIndex) -> CFGIndex {
142 //! Handles case where all of the patterns must match.
143 pats.fold(pred, |pred, pat| self.pat(&pat, pred))
146 fn expr(&mut self, expr: &hir::Expr, pred: CFGIndex) -> CFGIndex {
148 hir::ExprBlock(ref blk) => {
149 let blk_exit = self.block(&blk, pred);
150 self.add_ast_node(expr.id, &[blk_exit])
153 hir::ExprIf(ref cond, ref then, None) => {
168 let cond_exit = self.expr(&cond, pred); // 1
169 let then_exit = self.block(&then, cond_exit); // 2
170 self.add_ast_node(expr.id, &[cond_exit, then_exit]) // 3,4
173 hir::ExprIf(ref cond, ref then, Some(ref otherwise)) => {
188 let cond_exit = self.expr(&cond, pred); // 1
189 let then_exit = self.block(&then, cond_exit); // 2
190 let else_exit = self.expr(&otherwise, cond_exit); // 3
191 self.add_ast_node(expr.id, &[then_exit, else_exit]) // 4, 5
194 hir::ExprWhile(ref cond, ref body, _) => {
209 // Note that `break` and `continue` statements
210 // may cause additional edges.
212 // Is the condition considered part of the loop?
213 let loopback = self.add_dummy_node(&[pred]); // 1
214 let cond_exit = self.expr(&cond, loopback); // 2
215 let expr_exit = self.add_ast_node(expr.id, &[cond_exit]); // 3
216 self.loop_scopes.push(LoopScope {
218 continue_index: loopback,
219 break_index: expr_exit
221 let body_exit = self.block(&body, cond_exit); // 4
222 self.add_contained_edge(body_exit, loopback); // 5
223 self.loop_scopes.pop();
227 hir::ExprLoop(ref body, _) => {
239 // Note that `break` and `loop` statements
240 // may cause additional edges.
242 let loopback = self.add_dummy_node(&[pred]); // 1
243 let expr_exit = self.add_ast_node(expr.id, &[]); // 2
244 self.loop_scopes.push(LoopScope {
246 continue_index: loopback,
247 break_index: expr_exit,
249 let body_exit = self.block(&body, loopback); // 3
250 self.add_contained_edge(body_exit, loopback); // 4
251 self.loop_scopes.pop();
255 hir::ExprMatch(ref discr, ref arms, _) => {
256 self.match_(expr.id, &discr, &arms, pred)
259 hir::ExprBinary(op, ref l, ref r) if op.node.is_lazy() => {
274 let l_exit = self.expr(&l, pred); // 1
275 let r_exit = self.expr(&r, l_exit); // 2
276 self.add_ast_node(expr.id, &[l_exit, r_exit]) // 3,4
279 hir::ExprRet(ref v) => {
280 let v_exit = self.opt_expr(v, pred);
281 let b = self.add_ast_node(expr.id, &[v_exit]);
282 self.add_returning_edge(expr, b);
283 self.add_unreachable_node()
286 hir::ExprBreak(label) => {
287 let loop_scope = self.find_scope(expr, label.map(|l| l.node));
288 let b = self.add_ast_node(expr.id, &[pred]);
289 self.add_exiting_edge(expr, b,
290 loop_scope, loop_scope.break_index);
291 self.add_unreachable_node()
294 hir::ExprAgain(label) => {
295 let loop_scope = self.find_scope(expr, label.map(|l| l.node));
296 let a = self.add_ast_node(expr.id, &[pred]);
297 self.add_exiting_edge(expr, a,
298 loop_scope, loop_scope.continue_index);
299 self.add_unreachable_node()
302 hir::ExprVec(ref elems) => {
303 self.straightline(expr, pred, elems.iter().map(|e| &**e))
306 hir::ExprCall(ref func, ref args) => {
307 self.call(expr, pred, &func, args.iter().map(|e| &**e))
310 hir::ExprMethodCall(_, _, ref args) => {
311 self.call(expr, pred, &args[0], args[1..].iter().map(|e| &**e))
314 hir::ExprIndex(ref l, ref r) |
315 hir::ExprBinary(_, ref l, ref r) if self.tcx.is_method_call(expr.id) => {
316 self.call(expr, pred, &l, Some(&**r).into_iter())
319 hir::ExprUnary(_, ref e) if self.tcx.is_method_call(expr.id) => {
320 self.call(expr, pred, &e, None::<hir::Expr>.iter())
323 hir::ExprTup(ref exprs) => {
324 self.straightline(expr, pred, exprs.iter().map(|e| &**e))
327 hir::ExprStruct(_, ref fields, ref base) => {
328 let field_cfg = self.straightline(expr, pred, fields.iter().map(|f| &*f.expr));
329 self.opt_expr(base, field_cfg)
332 hir::ExprRepeat(ref elem, ref count) => {
333 self.straightline(expr, pred, [elem, count].iter().map(|&e| &**e))
336 hir::ExprAssign(ref l, ref r) |
337 hir::ExprAssignOp(_, ref l, ref r) => {
338 self.straightline(expr, pred, [r, l].iter().map(|&e| &**e))
341 hir::ExprIndex(ref l, ref r) |
342 hir::ExprBinary(_, ref l, ref r) => { // NB: && and || handled earlier
343 self.straightline(expr, pred, [l, r].iter().map(|&e| &**e))
346 hir::ExprBox(ref e) |
347 hir::ExprAddrOf(_, ref e) |
348 hir::ExprCast(ref e, _) |
349 hir::ExprType(ref e, _) |
350 hir::ExprUnary(_, ref e) |
351 hir::ExprField(ref e, _) |
352 hir::ExprTupField(ref e, _) => {
353 self.straightline(expr, pred, Some(&**e).into_iter())
356 hir::ExprInlineAsm(_, ref outputs, ref inputs) => {
357 let post_outputs = self.exprs(outputs.iter().map(|e| &**e), pred);
358 let post_inputs = self.exprs(inputs.iter().map(|e| &**e), post_outputs);
359 self.add_ast_node(expr.id, &[post_inputs])
362 hir::ExprClosure(..) |
364 hir::ExprPath(..) => {
365 self.straightline(expr, pred, None::<hir::Expr>.iter())
370 fn call<'b, I: Iterator<Item=&'b hir::Expr>>(&mut self,
371 call_expr: &hir::Expr,
373 func_or_rcvr: &hir::Expr,
374 args: I) -> CFGIndex {
375 let method_call = ty::MethodCall::expr(call_expr.id);
376 let fn_ty = match self.tcx.tables.borrow().method_map.get(&method_call) {
377 Some(method) => method.ty,
378 None => self.tcx.expr_ty_adjusted(func_or_rcvr)
381 let func_or_rcvr_exit = self.expr(func_or_rcvr, pred);
382 let ret = self.straightline(call_expr, func_or_rcvr_exit, args);
383 if fn_ty.fn_ret().diverges() {
384 self.add_unreachable_node()
390 fn exprs<'b, I: Iterator<Item=&'b hir::Expr>>(&mut self,
392 pred: CFGIndex) -> CFGIndex {
393 //! Constructs graph for `exprs` evaluated in order
394 exprs.fold(pred, |p, e| self.expr(e, p))
397 fn opt_expr(&mut self,
398 opt_expr: &Option<P<hir::Expr>>,
399 pred: CFGIndex) -> CFGIndex {
400 //! Constructs graph for `opt_expr` evaluated, if Some
401 opt_expr.iter().fold(pred, |p, e| self.expr(&e, p))
404 fn straightline<'b, I: Iterator<Item=&'b hir::Expr>>(&mut self,
407 subexprs: I) -> CFGIndex {
408 //! Handles case of an expression that evaluates `subexprs` in order
410 let subexprs_exit = self.exprs(subexprs, pred);
411 self.add_ast_node(expr.id, &[subexprs_exit])
414 fn match_(&mut self, id: ast::NodeId, discr: &hir::Expr,
415 arms: &[hir::Arm], pred: CFGIndex) -> CFGIndex {
416 // The CFG for match expression is quite complex, so no ASCII
419 // The CFG generated below matches roughly what trans puts
420 // out. Each pattern and guard is visited in parallel, with
421 // arms containing multiple patterns generating multiple nodes
422 // for the same guard expression. The guard expressions chain
423 // into each other from top to bottom, with a specific
424 // exception to allow some additional valid programs
425 // (explained below). Trans differs slightly in that the
426 // pattern matching may continue after a guard but the visible
427 // behaviour should be the same.
429 // What is going on is explained in further comments.
431 // Visit the discriminant expression
432 let discr_exit = self.expr(discr, pred);
434 // Add a node for the exit of the match expression as a whole.
435 let expr_exit = self.add_ast_node(id, &[]);
437 // Keep track of the previous guard expressions
438 let mut prev_guards = Vec::new();
439 // Track if the previous pattern contained bindings or wildcards
440 let mut prev_has_bindings = false;
443 // Add an exit node for when we've visited all the
444 // patterns and the guard (if there is one) in the arm.
445 let arm_exit = self.add_dummy_node(&[]);
447 for pat in &arm.pats {
448 // Visit the pattern, coming from the discriminant exit
449 let mut pat_exit = self.pat(&pat, discr_exit);
451 // If there is a guard expression, handle it here
452 if let Some(ref guard) = arm.guard {
453 // Add a dummy node for the previous guard
454 // expression to target
455 let guard_start = self.add_dummy_node(&[pat_exit]);
456 // Visit the guard expression
457 let guard_exit = self.expr(&guard, guard_start);
459 let this_has_bindings = pat_util::pat_contains_bindings_or_wild(&pat);
461 // If both this pattern and the previous pattern
462 // were free of bindings, they must consist only
463 // of "constant" patterns. Note we cannot match an
464 // all-constant pattern, fail the guard, and then
465 // match *another* all-constant pattern. This is
466 // because if the previous pattern matches, then
467 // we *cannot* match this one, unless all the
468 // constants are the same (which is rejected by
471 // We can use this to be smarter about the flow
472 // along guards. If the previous pattern matched,
473 // then we know we will not visit the guard in
474 // this one (whether or not the guard succeeded),
475 // if the previous pattern failed, then we know
476 // the guard for that pattern will not have been
477 // visited. Thus, it is not possible to visit both
478 // the previous guard and the current one when
479 // both patterns consist only of constant
482 // However, if the above does not hold, then all
483 // previous guards need to be wired to visit the
484 // current guard pattern.
485 if prev_has_bindings || this_has_bindings {
486 while let Some(prev) = prev_guards.pop() {
487 self.add_contained_edge(prev, guard_start);
491 prev_has_bindings = this_has_bindings;
493 // Push the guard onto the list of previous guards
494 prev_guards.push(guard_exit);
496 // Update the exit node for the pattern
497 pat_exit = guard_exit;
500 // Add an edge from the exit of this pattern to the
502 self.add_contained_edge(pat_exit, arm_exit);
505 // Visit the body of this arm
506 let body_exit = self.expr(&arm.body, arm_exit);
508 // Link the body to the exit of the expression
509 self.add_contained_edge(body_exit, expr_exit);
515 fn add_dummy_node(&mut self, preds: &[CFGIndex]) -> CFGIndex {
516 self.add_node(CFGNodeData::Dummy, preds)
519 fn add_ast_node(&mut self, id: ast::NodeId, preds: &[CFGIndex]) -> CFGIndex {
520 assert!(id != ast::DUMMY_NODE_ID);
521 self.add_node(CFGNodeData::AST(id), preds)
524 fn add_unreachable_node(&mut self) -> CFGIndex {
525 self.add_node(CFGNodeData::Unreachable, &[])
528 fn add_node(&mut self, data: CFGNodeData, preds: &[CFGIndex]) -> CFGIndex {
529 let node = self.graph.add_node(data);
531 self.add_contained_edge(pred, node);
536 fn add_contained_edge(&mut self,
539 let data = CFGEdgeData {exiting_scopes: vec!() };
540 self.graph.add_edge(source, target, data);
543 fn add_exiting_edge(&mut self,
544 from_expr: &hir::Expr,
545 from_index: CFGIndex,
547 to_index: CFGIndex) {
548 let mut data = CFGEdgeData {exiting_scopes: vec!() };
549 let mut scope = self.tcx.region_maps.node_extent(from_expr.id);
550 let target_scope = self.tcx.region_maps.node_extent(to_loop.loop_id);
551 while scope != target_scope {
552 data.exiting_scopes.push(scope.node_id(&self.tcx.region_maps));
553 scope = self.tcx.region_maps.encl_scope(scope);
555 self.graph.add_edge(from_index, to_index, data);
558 fn add_returning_edge(&mut self,
559 _from_expr: &hir::Expr,
560 from_index: CFGIndex) {
561 let mut data = CFGEdgeData {
562 exiting_scopes: vec!(),
564 for &LoopScope { loop_id: id, .. } in self.loop_scopes.iter().rev() {
565 data.exiting_scopes.push(id);
567 self.graph.add_edge(from_index, self.fn_exit, data);
572 label: Option<ast::Name>) -> LoopScope {
574 return *self.loop_scopes.last().unwrap();
577 match self.tcx.expect_def(expr.id) {
578 Def::Label(loop_id) => {
579 for l in &self.loop_scopes {
580 if l.loop_id == loop_id {
584 span_bug!(expr.span, "no loop scope for id {}", loop_id);
588 span_bug!(expr.span, "bad entry `{:?}` in def_map for label", r);