https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118069
--- Comment #6 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Patrick Palka <ppa...@gcc.gnu.org>: https://gcc.gnu.org/g:875f14e15d49dce7de501a6357a3d5811b5c36d4 commit r15-6374-g875f14e15d49dce7de501a6357a3d5811b5c36d4 Author: Patrick Palka <ppa...@redhat.com> Date: Thu Dec 19 12:00:29 2024 -0500 c++: integer overflow during constraint subsumption [PR118069] For the testcase in the PR we hang during constraint subsumption ultimately because one of the constraints is complex enough that its conjunctive normal form is calculated to have more than 2^31 clauses, which causes the size calculation (through an int) to overflow and so the optimization in subsumes_constraints_nonnull if (dnf_size (lhs) <= cnf_size (rhs)) // iterate over DNF of LHS else // iterate over CNF of RHS incorrectly decides to loop over the CNF (>> billions of clauses) instead of the DNF (thousands of clauses). I haven't verified that the result of cnf_size is correct for the problematic constraint but integer overflow is definitely plausible given that CNF/DNF can be exponentially larger than the original constraint in the worst case. This patch fixes this by using 64-bit saturating arithmetic during these size calculations (via new add/mul_sat_hwi functions) so that overflow is less likely and if it does occur we handle it gracefully. It should be highly unlikely that both the DNF and CNF sizes overflow, and if they do then it doesn't matter which form we select, subsumption will take forever either way. The testcase now compiles in ~3 seconds on my machine after this change. PR c++/118069 gcc/ChangeLog: * hwint.h (add_sat_hwi): New function. (mul_sat_hwi): Likewise. gcc/cp/ChangeLog: * logic.cc (dnf_size_r): Use HOST_WIDE_INT instead of int, and handle overflow gracefully via add_sat_hwi and mul_sat_hwi. (cnf_size_r): Likewise. (dnf_size): Use HOST_WIDE_INT instead of int. (cnf_size): Likewise. Reviewed-by: Jason Merrill <ja...@redhat.com>
