https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110755
--- Comment #11 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:21da32d995c8b574c929ec420cd3b0fcfe6fa4fe commit r14-2782-g21da32d995c8b574c929ec420cd3b0fcfe6fa4fe Author: Jakub Jelinek <ja...@redhat.com> Date: Wed Jul 26 10:50:50 2023 +0200 range-op-float: Fix up -frounding-math frange_arithmetic +- handling [PR110755] IEEE754 says that x + (-x) and x - x result in +0 in all rounding modes but rounding towards negative infinity, in which case the result is -0 for all finite x. x + x and x - (-x) if it is zero retain sign of x. Now, range_arithmetic implements the normal rounds to even rounding, and as the addition or subtraction in those cases is exact, we don't do any further rounding etc. and e.g. on the testcase below distilled from glibc compute a range [+0, +INF], which is fine for -fno-rounding-math or if we'd have a guarantee that those statements aren't executed with rounding towards negative infinity. I believe it is only +- which has this problematic behavior and I think it is best to deal with it in frange_arithmetic; if we know -frounding-math is on, it is x + (-x) or x - x and we are asked to round to negative infinity (i.e. want low bound rather than high bound), change +0 result to -0. 2023-07-26 Jakub Jelinek <ja...@redhat.com> PR tree-optimization/110755 * range-op-float.cc (frange_arithmetic): Change +0 result to -0 for PLUS_EXPR or MINUS_EXPR if -frounding-math, inf is negative and it is exact op1 + (-op1) or op1 - op1. * gcc.dg/pr110755.c: New test.
