https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115921
--- Comment #4 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Jeff Law <l...@gcc.gnu.org>: https://gcc.gnu.org/g:4371f656288f461335c47e98b8c038937a89764a commit r15-3415-g4371f656288f461335c47e98b8c038937a89764a Author: Jeff Law <j...@ventanamicro.com> Date: Tue Sep 3 06:45:30 2024 -0600 [PR target/115921] Improve reassociation for rv64 As Jovan pointed out in pr115921, we're not reassociating expressions like this on rv64: (x & 0x3e) << 12 It generates something like this: li a5,258048 slli a0,a0,12 and a0,a0,a5 We have a pattern that's designed to clean this up. Essentially reassociating the operations so that we don't need to load the constant resulting in something like this: andi a0,a0,63 slli a0,a0,12 That pattern wasn't working for certain constants due to its condition. The condition is trying to avoid cases where this kind of reassociation would hinder shadd generation on rv64. That condition was just written poorly. This patch tightens up that condition in a few ways. First, there's no need to worry about shadd cases if ZBA is not enabled. Second we can't use shadd if the shift value isn't 1, 2 or 3. Finally rather than open-coding one of the tests, we can use an existing operand predicate. The net is we'll start performing this transformation in more cases on rv64 while still avoiding reassociation if it would spoil shadd generation. PR target/115921 gcc/ * config/riscv/riscv.md (reassociate bitwise ops): Tighten test for cases we do not want reassociate. gcc/testsuite/ * gcc.target/riscv/pr115921.c: New test.
