limit repeated DIE comparisons
Commit Message
Exponential explosion of DIE comparison has been possible since the
limit of at most 5 pending struct/union DIE comparison pairs was
lifted.
This commit adds two things to control this (with a negligible chance of
falsely finding that two DIEs are equivalent when they are not).
- DIE self-comparisons immediately return true
- once a DIE pair has been compared 10000 times, always return true
* src/abg-dwarf-reader.cc (read_context): Add mutable
die_comparison_visits_ member.
(compare_dies): Return true if this is a self-comparison.
Return true if we have visited this comparison 10000 times.
Signed-off-by: Giuliano Procida <gprocida@google.com>
---
src/abg-dwarf-reader.cc | 10 ++++++++++
1 file changed, 10 insertions(+)
@@ -2094,6 +2094,9 @@ public:
/// A map that associates a function type representations to
/// function types, inside a translation unit.
mutable istring_fn_type_map_type per_tu_repr_to_fn_type_maps_;
+ mutable std::unordered_map<std::pair<Dwarf_Off, Dwarf_Off>,
+ size_t,
+ dwarf_offset_pair_hash> die_comparison_visits_;
die_class_or_union_map_type die_wip_classes_map_;
die_class_or_union_map_type alternate_die_wip_classes_map_;
@@ -10216,6 +10219,13 @@ compare_dies(const read_context& ctxt,
Dwarf_Off l_offset = dwarf_dieoffset(const_cast<Dwarf_Die*>(l)),
r_offset = dwarf_dieoffset(const_cast<Dwarf_Die*>(r));
+
+ if (l_offset == r_offset)
+ return true;
+ auto& visit = ctxt.die_comparison_visits_[std::make_pair(l_offset, r_offset)];
+ if (++visit == 10000)
+ return true;
+
Dwarf_Off l_canonical_die_offset = 0, r_canonical_die_offset = 0;
const die_source l_die_source = ctxt.get_die_source(l);
const die_source r_die_source = ctxt.get_die_source(r);