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use crate::errors::UnconditionalRecursion;
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.emit_spanned_lint(
UNCONDITIONAL_RECURSION,
hir_id,
sp,
UnconditionalRecursion { span: sp, call_sites: vis.reachable_recursive_calls },
);
}
}
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,
}
}
}
|
