https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106831
--- Comment #13 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Aldy Hernandez <al...@gcc.gnu.org>: https://gcc.gnu.org/g:5dba8b2a91376d0518eb21c69a0700f099aa9cc4 commit r13-2714-g5dba8b2a91376d0518eb21c69a0700f099aa9cc4 Author: Jakub Jelinek <ja...@redhat.com> Date: Sat Sep 17 08:50:22 2022 +0200 [PR106831] Avoid propagating long doubles that may have multiple representations. Long doubles are tricky when it comes to considering singletons because small numbers and +-INF can have multiple representations for the same number. So we need to be very careful not to treat those as singletons, lest they be incorrectly propagated by VRP. This is similar to the -0.0 and +0.0 duality. In long doubles +INF can be represented with +INF in the MSB and either -0.0 or +0.0 in the LSB. Similarly for numbers that are exactly representable in DF. For example, 1.0 can be represented as either (1.0, +0.0) or (1.0, -0.0). This patch avoids treating these numbers as singletons. Note that NANs in long double format have a LSB of don't care, but this is irrelevant for singleton_p, because NANs are never considered singletons. Also, internally in the frange we store NANs as a pair of boolean flags indicating whether they are +NAN or -NAN, so we don't need any special treatment here for comparing range equality etc. We never see anything but the boolean flags. PR middle-end/106831 gcc/ChangeLog: * value-range.cc (frange::singleton_p): Avoid propagating long doubles that may have multiple representations.
