1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
|
use rustc_data_structures::graph::iterate::{
NodeStatus, TriColorDepthFirstSearch, TriColorVisitor,
};
use rustc_hir::def::DefKind;
use rustc_middle::mir::{BasicBlock, BasicBlocks, Body, Operand, TerminatorKind};
use rustc_middle::ty::subst::{GenericArg, InternalSubsts};
use rustc_middle::ty::{self, Instance, TyCtxt};
use rustc_session::lint::builtin::UNCONDITIONAL_RECURSION;
use rustc_span::Span;
use std::ops::ControlFlow;
pub(crate) fn check<'tcx>(tcx: TyCtxt<'tcx>, body: &Body<'tcx>) {
let def_id = body.source.def_id().expect_local();
if let DefKind::Fn | DefKind::AssocFn = tcx.def_kind(def_id) {
// If this is trait/impl method, extract the trait's substs.
let trait_substs = match tcx.trait_of_item(def_id.to_def_id()) {
Some(trait_def_id) => {
let trait_substs_count = tcx.generics_of(trait_def_id).count();
&InternalSubsts::identity_for_item(tcx, def_id.to_def_id())[..trait_substs_count]
}
_ => &[],
};
let mut vis = Search { tcx, body, reachable_recursive_calls: vec![], trait_substs };
if let Some(NonRecursive) =
TriColorDepthFirstSearch::new(&body.basic_blocks).run_from_start(&mut vis)
{
return;
}
if vis.reachable_recursive_calls.is_empty() {
return;
}
vis.reachable_recursive_calls.sort();
let sp = tcx.def_span(def_id);
let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
tcx.struct_span_lint_hir(UNCONDITIONAL_RECURSION, hir_id, sp, |lint| {
let mut db = lint.build("function cannot return without recursing");
db.span_label(sp, "cannot return without recursing");
// offer some help to the programmer.
for call_span in vis.reachable_recursive_calls {
db.span_label(call_span, "recursive call site");
}
db.help("a `loop` may express intention better if this is on purpose");
db.emit();
});
}
}
struct NonRecursive;
struct Search<'mir, 'tcx> {
tcx: TyCtxt<'tcx>,
body: &'mir Body<'tcx>,
trait_substs: &'tcx [GenericArg<'tcx>],
reachable_recursive_calls: Vec<Span>,
}
impl<'mir, 'tcx> Search<'mir, 'tcx> {
/// Returns `true` if `func` refers to the function we are searching in.
fn is_recursive_call(&self, func: &Operand<'tcx>, args: &[Operand<'tcx>]) -> bool {
let Search { tcx, body, trait_substs, .. } = *self;
// Resolving function type to a specific instance that is being called is expensive. To
// avoid the cost we check the number of arguments first, which is sufficient to reject
// most of calls as non-recursive.
if args.len() != body.arg_count {
return false;
}
let caller = body.source.def_id();
let param_env = tcx.param_env(caller);
let func_ty = func.ty(body, tcx);
if let ty::FnDef(callee, substs) = *func_ty.kind() {
let normalized_substs = tcx.normalize_erasing_regions(param_env, substs);
let (callee, call_substs) = if let Ok(Some(instance)) =
Instance::resolve(tcx, param_env, callee, normalized_substs)
{
(instance.def_id(), instance.substs)
} else {
(callee, normalized_substs)
};
// FIXME(#57965): Make this work across function boundaries
// If this is a trait fn, the substs on the trait have to match, or we might be
// calling into an entirely different method (for example, a call from the default
// method in the trait to `<A as Trait<B>>::method`, where `A` and/or `B` are
// specific types).
return callee == caller && &call_substs[..trait_substs.len()] == trait_substs;
}
false
}
}
impl<'mir, 'tcx> TriColorVisitor<BasicBlocks<'tcx>> for Search<'mir, 'tcx> {
type BreakVal = NonRecursive;
fn node_examined(
&mut self,
bb: BasicBlock,
prior_status: Option<NodeStatus>,
) -> ControlFlow<Self::BreakVal> {
// Back-edge in the CFG (loop).
if let Some(NodeStatus::Visited) = prior_status {
return ControlFlow::Break(NonRecursive);
}
match self.body[bb].terminator().kind {
// These terminators return control flow to the caller.
TerminatorKind::Abort
| TerminatorKind::GeneratorDrop
| TerminatorKind::Resume
| TerminatorKind::Return
| TerminatorKind::Unreachable
| TerminatorKind::Yield { .. } => ControlFlow::Break(NonRecursive),
// A diverging InlineAsm is treated as non-recursing
TerminatorKind::InlineAsm { destination, .. } => {
if destination.is_some() {
ControlFlow::CONTINUE
} else {
ControlFlow::Break(NonRecursive)
}
}
// These do not.
TerminatorKind::Assert { .. }
| TerminatorKind::Call { .. }
| TerminatorKind::Drop { .. }
| TerminatorKind::DropAndReplace { .. }
| TerminatorKind::FalseEdge { .. }
| TerminatorKind::FalseUnwind { .. }
| TerminatorKind::Goto { .. }
| TerminatorKind::SwitchInt { .. } => ControlFlow::CONTINUE,
}
}
fn node_settled(&mut self, bb: BasicBlock) -> ControlFlow<Self::BreakVal> {
// When we examine a node for the last time, remember it if it is a recursive call.
let terminator = self.body[bb].terminator();
if let TerminatorKind::Call { func, args, .. } = &terminator.kind {
if self.is_recursive_call(func, args) {
self.reachable_recursive_calls.push(terminator.source_info.span);
}
}
ControlFlow::CONTINUE
}
fn ignore_edge(&mut self, bb: BasicBlock, target: BasicBlock) -> bool {
let terminator = self.body[bb].terminator();
if terminator.unwind() == Some(&Some(target)) && terminator.successors().count() > 1 {
return true;
}
// Don't traverse successors of recursive calls or false CFG edges.
match self.body[bb].terminator().kind {
TerminatorKind::Call { ref func, ref args, .. } => self.is_recursive_call(func, args),
TerminatorKind::FalseEdge { imaginary_target, .. } => imaginary_target == target,
_ => false,
}
}
}
|
