> -----Original Message----- > From: Prathamesh Kulkarni <prathamesh.kulka...@linaro.org> > Sent: 24 August 2021 09:02 > To: gcc Patches <gcc-patches@gcc.gnu.org>; Kyrylo Tkachov > <kyrylo.tkac...@arm.com> > Subject: Re: [ARM] PR66791: Replace builtins for signed vmul_n intrinsics > > On Fri, 13 Aug 2021 at 16:40, Prathamesh Kulkarni > <prathamesh.kulka...@linaro.org> wrote: > > > > On Thu, 5 Aug 2021 at 15:44, Prathamesh Kulkarni > > <prathamesh.kulka...@linaro.org> wrote: > > > > > > On Mon, 12 Jul 2021 at 15:24, Prathamesh Kulkarni > > > <prathamesh.kulka...@linaro.org> wrote: > > > > > > > > On Mon, 12 Jul 2021 at 15:23, Prathamesh Kulkarni > > > > <prathamesh.kulka...@linaro.org> wrote: > > > > > > > > > > On Mon, 5 Jul 2021 at 14:47, Prathamesh Kulkarni > > > > > <prathamesh.kulka...@linaro.org> wrote: > > > > > > > > > > > > Hi, > > > > > > This patch replaces builtins with __a * __b for signed variants of > > > > > > vmul_n intrinsics. > > > > > > As discussed earlier, the patch has issue if __a * __b overflows, > > > > > > and > > > > > > whether we wish to leave > > > > > > that as UB. > > > > > ping > https://gcc.gnu.org/git/gitweb.cgi?p=gcc.git;h=6785eb595981abd93ad85ed > cfdf1d2e43c0841f5 > > > > Oops sorry, I meant this link: > > > > https://gcc.gnu.org/pipermail/gcc-patches/2021-July/574428.html > > > ping * 2 https://gcc.gnu.org/pipermail/gcc-patches/2021- > July/574428.html > > ping * 3 https://gcc.gnu.org/pipermail/gcc-patches/2021-July/574428.html > ping * 4 https://gcc.gnu.org/pipermail/gcc-patches/2021-July/576321.html
I'm not very comfortable with this change. We'd be introducing direct signed multiplications that are undefined on overflow in C, but the vmul instructions in Neon have well-defined overflow semantics. So they wouldn't be exactly equivalent. Thanks, Kyrill > > Thanks, > Prathamesh > > > > Thanks, > > Prathamesh > > > > > > Thanks, > > > Prathamesh > > > > > > > > Thanks, > > > > Prathamesh > > > > > > > > > > Thanks, > > > > > Prathamesh > > > > > > > > > > > > Thanks, > > > > > > Prathamesh
