https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105189
--- Comment #9 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The releases/gcc-10 branch has been updated by Jakub Jelinek <ja...@gcc.gnu.org>: https://gcc.gnu.org/g:a954df6a075d5d1e91f98e3c686e5da62c829cf9 commit r10-10705-ga954df6a075d5d1e91f98e3c686e5da62c829cf9 Author: Jakub Jelinek <ja...@redhat.com> Date: Fri Apr 8 09:14:44 2022 +0200 fold-const: Fix up make_range_step [PR105189] The following testcase is miscompiled, because fold_truth_andor incorrectly folds (unsigned) foo () >= 0U && 1 into foo () >= 0 For the unsigned comparison (which is useless in this case, as >= 0U is always true, but hasn't been folded yet), previous make_range_step derives exp (unsigned) foo () and +[0U, -] range for it. Next we process the NOP_EXPR. We have special code for unsigned to signed casts, already earlier punt if low or high aren't representable in arg0_type or if it is a narrowing conversion. For the signed to unsigned casts, I think if high is specified we are still fine, as we punt for non-representable values in arg0_type, n_high is then still representable and so was smaller or equal to signed maximum and either low is not present (equivalent to 0U), or low must be smaller or equal to high and so for unsigned exp +[low, high] the signed exp +[n_low, n_high] will be correct. Similarly, if both low and high aren't specified (always true or always false), it is ok too. But if we have for unsigned exp +[low, -] or -[low, -], using +[n_low, -] or -[n_high, -] is incorrect. Because low is smaller or equal to signed maximum and high is unspecified (i.e. unsigned maximum), when signed that range is a union of +[n_low, -] and +[-, -1] which is equivalent to -[0, n_low-1], unless low is 0, in that case we can treat it as [-, -]. 2022-04-08 Jakub Jelinek <ja...@redhat.com> PR tree-optimization/105189 * fold-const.c (make_range_step): Fix up handling of (unsigned) x +[low, -] ranges for signed x if low fits into typeof (x). * g++.dg/torture/pr105189.C: New test. (cherry picked from commit 5e6597064b0c7eb93b8f720afc4aa970eefb0628)
