https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98865
--- Comment #6 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Roger Sayle <sa...@gcc.gnu.org>: https://gcc.gnu.org/g:4a9be8d51182076222d707d9d68f6eda78e8ee2c commit r13-624-g4a9be8d51182076222d707d9d68f6eda78e8ee2c Author: Roger Sayle <ro...@nextmovesoftware.com> Date: Wed May 18 16:23:01 2022 +0100 Correct ix86_rtx_cost for multi-word multiplication. This is the i386 backend specific piece of my revised patch for PR middle-end/98865, where Richard Biener has suggested that I perform the desired transformation during RTL expansion where the backend can control whether it is profitable to convert a multiplication into a bit-wise AND and a negation. This works well for x86_64, but alas exposes a latent bug with -m32, where a DImode multiplication incorrectly appears to be cheaper than negdi2+anddi3(!?). The fix to ix86_rtx_costs is to report that a DImode (multi-word) multiplication actually requires three SImode multiplications and two SImode additions. This also corrects the cost of TImode multiplication on TARGET_64BIT. 2022-05-18 Roger Sayle <ro...@nextmovesoftware.com> gcc/ChangeLog * config/i386/i386.cc (ix86_rtx_costs) [MULT]: When mode size is wider than word_mode, a multiplication costs three word_mode multiplications and two word_mode additions.
