https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108806
--- Comment #1 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by David Malcolm <dmalc...@gcc.gnu.org>: https://gcc.gnu.org/g:4d3b7be281e73ecdaa233598db1a8390422b7770 commit r13-6101-g4d3b7be281e73ecdaa233598db1a8390422b7770 Author: David Malcolm <dmalc...@redhat.com> Date: Thu Feb 16 18:12:55 2023 -0500 analyzer: respect some conditions from bit masks [PR108806] PR analyzer/108806 reports false +ves seen from -fanalyzer on code like this in qemu-7.2.0's hw/intc/omap_intc.c: [...snip...] struct omap_intr_handler_bank_s* bank = NULL; if ((offset & 0xf80) == 0x80) { [...set "bank" to non-NULL...] } switch (offset) { [...snip various cases that don't deref "bank"...] case 0x80: return bank->inputs; case 0x84: return bank->mask; [...etc...] } where the analyzer falsely complains about execution paths in which "(offset & 0xf80) == 0x80" was false (leaving "bank" as NULL), but then in which "switch (offset)" goes to a case for which "(offset & 0xf80) == 0x80" is true and dereferences NULL "bank", i.e. paths in which "(offset & 0xf80) == 0x80" is both true *and* false. This patch adds enough logic to constraint_manager for -fanalyzer to reject such execution paths as impossible, fixing the false +ves. Integration testing shows this eliminates 20 probable false positives: Comparison: 9.08% -> 9.34% GOOD: 66 BAD: 661 -> 641 (-20) where the affected warnings/projects are: -Wanalyzer-null-dereference: 0.00% GOOD: 0 BAD: 279 -> 269 (-10) qemu-7.2.0: 175 -> 165 (-10) -Wanalyzer-use-of-uninitialized-value: 0.00% GOOD: 0 BAD: 153 -> 143 (-10) coreutils-9.1: 18 -> 14 (-4) qemu-7.2.0: 54 -> 48 (-6) gcc/analyzer/ChangeLog: PR analyzer/108806 * constraint-manager.cc (bounded_range::dump_to_pp): Use bounded_range::singleton_p. (constraint_manager::add_bounded_ranges): Handle singleton ranges by adding an EQ_EXPR constraint. (constraint_manager::impossible_derived_conditions_p): New. (constraint_manager::eval_condition): Reject EQ_EXPR when it would imply impossible derived conditions. (selftest::test_bits): New. (selftest::run_constraint_manager_tests): Run it. * constraint-manager.h (bounded_range::singleton_p): New. (constraint_manager::impossible_derived_conditions_p): New decl. * region-model.cc (region_model::get_rvalue_1): Handle BIT_AND_EXPR, BIT_IOR_EXPR, and BIT_XOR_EXPR. gcc/testsuite/ChangeLog: PR analyzer/108806 * gcc.dg/analyzer/null-deref-pr108806-qemu.c: New test. * gcc.dg/analyzer/pr103217.c: Add -Wno-analyzer-too-complex. * gcc.dg/analyzer/switch.c (test_bitmask_1): New. (test_bitmask_2): New. * gcc.dg/analyzer/uninit-pr108806-qemu.c: New test. Signed-off-by: David Malcolm <dmalc...@redhat.com>
