https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78794
--- Comment #12 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:c027592d39b2968005aa28bc84a946bab2668db8 commit r14-2158-gc027592d39b2968005aa28bc84a946bab2668db8 Author: Roger Sayle <ro...@nextmovesoftware.com> Date: Wed Jun 28 11:07:47 2023 +0100 i386: Fix FAIL of gcc.target/i386/pr78794.c on ia32. This patch fixes that FAIL of gcc.target/i386/pr78794.c on ia32, which is caused by minor STV rtx_cost differences with -march=silvermont. It turns out that generic tuning results in pandn, but the lack of accurate parameterization for COMPARE in compute_convert_gain combined with small differences in scalar<->SSE costs on silvermont results in this DImode chain not being converted. The solution is to provide more accurate costs/gains for converting (DImode and SImode) comparisons. I'd been holding off of doing this as I'd thought it would be possible to turn pandn;ptestz into ptestc (for an even bigger scalar-to-vector win) but I've recently realized that these optimizations (as I've implemented them) occur in the wrong order (stv2 occurs after combine), so it isn't easy for STV to convert CCZmode into CCCmode. Doh! Perhaps something can be done in peephole2. 2023-06-28 Roger Sayle <ro...@nextmovesoftware.com> gcc/ChangeLog PR target/78794 * config/i386/i386-features.cc (compute_convert_gain): Provide more accurate gains for conversion of scalar comparisons to PTEST.
