https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94524
--- 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:f52eb4f988992d393c69ee4ab76f236dced80e36 commit r10-7639-gf52eb4f988992d393c69ee4ab76f236dced80e36 Author: Jakub Jelinek <ja...@redhat.com> Date: Wed Apr 8 21:22:05 2020 +0200 vect: Fix up lowering of TRUNC_MOD_EXPR by negative constant [PR94524] The first testcase below is miscompiled, because for the division part of the lowering we canonicalize negative divisors to their absolute value (similarly how expmed.c canonicalizes it), but when multiplying the division result back by the VECTOR_CST, we use the original constant, which can contain negative divisors. Fixed by computing ABS_EXPR of the VECTOR_CST. Unfortunately, fold-const.c doesn't support const_unop (ABS_EXPR, VECTOR_CST) and I think it is too late in GCC 10 cycle to add it now. Furthermore, while modulo by most negative constant happens to return the right value, it does that only by invoking UB in the IL, because we then expand division by that 1U+INT_MAX and say for INT_MIN % INT_MIN compute the division as -1, and then multiply by INT_MIN, which is signed integer overflow. We in theory could do the computation in unsigned vector types instead, but is it worth bothering. People that are doing % INT_MIN are either testing for standard conformance, or doing something wrong. So, I've also added punting on % INT_MIN, both in vect lowering and vect pattern recognition (we punt already for / INT_MIN). 2020-04-08 Jakub Jelinek <ja...@redhat.com> PR tree-optimization/94524 * tree-vect-generic.c (expand_vector_divmod): If any elt of op1 is negative for signed TRUNC_MOD_EXPR, multiply with absolute value of op1 rather than op1 itself at the end. Punt for signed modulo by most negative constant. * tree-vect-patterns.c (vect_recog_divmod_pattern): Punt for signed modulo by most negative constant. * gcc.c-torture/execute/pr94524-1.c: New test. * gcc.c-torture/execute/pr94524-2.c: New test.
