https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118409
--- Comment #29 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Alexandre Oliva <aol...@gcc.gnu.org>: https://gcc.gnu.org/g:52e4ede030979d8aff2f88364e1d11c61fb212aa commit r15-6866-g52e4ede030979d8aff2f88364e1d11c61fb212aa Author: Alexandre Oliva <ol...@adacore.com> Date: Mon Jan 13 10:49:51 2025 -0300 [ifcombine] propagate signbit mask to XOR right-hand operand If a single-bit bitfield takes up the sign bit of a storage unit, comparing the corresponding bitfield between two objects loads the storage units, XORs them, converts the result to signed char, and compares it with zero: ((signed char)(a.<byte> ^ c.<byte>) >= 0). fold_truth_andor_for_ifcombine recognizes the compare with zero as a sign bit test, then it decomposes the XOR into an equality test. The problem is that, after this decomposition, that figures out the width of the accessed fields, we apply the sign bit mask to the left-hand operand of the compare, but we failed to also apply it to the right-hand operand when both were taken from the same XOR. This patch fixes that. for gcc/ChangeLog PR tree-optimization/118409 * gimple-fold.cc (fold_truth_andor_for_ifcombine): Apply the signbit mask to the right-hand XOR operand too. for gcc/testsuite/ChangeLog PR tree-optimization/118409 * gcc.dg/field-merge-20.c: New.
