https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105729
--- Comment #6 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The releases/gcc-11 branch has been updated by Jakub Jelinek <ja...@gcc.gnu.org>: https://gcc.gnu.org/g:e396f501f8a33439dee3ee5eef5b1d3a928852d9 commit r11-10079-ge396f501f8a33439dee3ee5eef5b1d3a928852d9 Author: Jakub Jelinek <ja...@redhat.com> Date: Fri May 27 11:40:42 2022 +0200 fold-const: Fix up -fsanitize=null in C++ [PR105729] The following testcase triggers a false positive UBSan binding a reference to null diagnostics. In the FE we instrument conversions from pointer to reference type to diagnose at runtime if the operand of such a conversion is 0. The problem is that a GENERIC folding folds ((const struct Bar *) ((const struct Foo *) this)->data) + (sizetype) range_check (x) conversion to const struct Bar & by converting to that the first operand of the POINTER_PLUS_EXPR. But that changes when the -fsanitize=null binding to reference runtime check occurs. Without the optimization, it is invoked on the result of the POINTER_PLUS_EXPR, and as range_check call throws, that means it never triggers in the testcase. With the optimization, it checks whether this->data is NULL and it is. The following patch avoids that optimization during GENERIC folding when -fsanitize=null is enabled and it is a cast from non-REFERENCE_TYPE to REFERENCE_TYPE. 2022-05-27 Jakub Jelinek <ja...@redhat.com> PR sanitizer/105729 * fold-const.c (fold_unary_loc): Don't optimize (X &) ((Y *) z + w) to (X &) z + w if -fsanitize=null during GENERIC folding. * g++.dg/ubsan/pr105729.C: New test. (cherry picked from commit e2f014fcefcd2ad56b31995329820bbd99072eae)