https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88808
--- Comment #2 from Uroš Bizjak <ubizjak at gmail dot com> --- (In reply to Jakub Jelinek from comment #1) > See PR88473 and PR88798. I'd personally probably revert the changes to make > the mask operations separate from GPR operations and just use special RTL > patterns if GPR operation can't do it (e.g. andn when not BMI, or 64-bit > logicals on 32-bit targets), but it is too late for that for GCC9. I'm not against the revert, [1] describes the rationale for the current approach from 2016. In the meantime, a couple of new constraint modifiers were introduced to better guide register allocation choices, and I believe that with appropriate RTX costs, it is possible to implement mask operations without UNSPECs. I certainly agree with Jakub to postpone new implementation to gcc-10. Without approporate cost model, we risk that under register pressure, RA will allocate mask registers for values, expected to live in general registers. At the time, it was warned that moves between mask and integer registers are quite costly, so we took the safe way and by introducin UNSPECs, avoided runtime regressions when mask registers were present. [1] https://gcc.gnu.org/ml/gcc-patches/2016-11/msg02612.html
