https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98206
--- Comment #5 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Jakub Jelinek <ja...@gcc.gnu.org>: https://gcc.gnu.org/g:a9ec9902d7f1a9bf7a2778c3fb8fc75bc2df2cef commit r11-6375-ga9ec9902d7f1a9bf7a2778c3fb8fc75bc2df2cef Author: Jakub Jelinek <ja...@redhat.com> Date: Thu Dec 31 10:20:39 2020 +0100 fold-const: Avoid (cast) ((cast2) x p+ y) folding for -fsanitize=alignment [PR98206] The following testcase is diagnosed by UBSan as invalid, even when it is valid. We have a derived type Base2 at offset 1 with alignment 1 and do: (const Derived &) ((const Base2 *) this + -1) but the folder before ubsan in the FE gets a chance to instrument it optimizes that into: (const Derived &) this + -1 and so we require that this has 8-byte alignment which Derived class needs. Fixed by avoiding such an optimization when -fsanitize=alignment is in effect if it would affect the alignments (and guarded with !in_gimple_form because we don't really care during GIMPLE, though pointer conversions are useless then and so such folding isn't needed very much during GIMPLE). 2020-12-31 Jakub Jelinek <ja...@redhat.com> PR c++/98206 * fold-const.c: Include asan.h. (fold_unary_loc): Don't optimize (ptr_type) (((ptr_type2) x) p+ y) into ((ptr_type) x) p+ y if sanitizing alignment in GENERIC and ptr_type points to type with higher alignment than ptr_type2. * g++.dg/ubsan/align-4.C: New test.
