Date: Mon, 23 Mar 2015 09:33:15 +0000 From: David Chisnall <theraven@FreeBSD.org> To: Craig Rodrigues <rodrigc@FreeBSD.org> Cc: "freebsd-testing@freebsd.org" <freebsd-testing@freebsd.org>, "jenkins-admin@freebsd.org" <jenkins-admin@freebsd.org>, freebsd-current Current <freebsd-current@freebsd.org>, Dimitry Andric <dim@freebsd.org>, freebsd-toolchain@freebsd.org Subject: Re: Jenkins build is still unstable: FreeBSD_HEAD-tests2 #867 Message-ID: <C8D88048-8CC6-40B8-A778-A33287CA2897@FreeBSD.org> In-Reply-To: <CAG=rPVdP_TAmerKh_82EravEw=sCj4LyEBu-NfGCK0Obg=HMVw@mail.gmail.com> References: <1669399171.13.1427029129760.JavaMail.jenkins@jenkins-9.freebsd.org> <799490341.14.1427048792932.JavaMail.jenkins@jenkins-9.freebsd.org> <CAG=rPVeyamLPnC5i05_=Ub0D%2BV256U_8t8R5tfDitC=NkjBOFQ@mail.gmail.com> <BE5A3694-E1D1-4A47-8707-D6214E997363@FreeBSD.org> <494AEF4B-0AF8-449A-9B41-9AC4F4552AF0@FreeBSD.org> <CAG=rPVchdm_VaTshq%2BRN%2BkHX0YC0_Tsx22oJVNNnoOamdm00mQ@mail.gmail.com> <864EB4DB-2DF7-4294-9498-95E54E6B49CC@FreeBSD.org> <CAG=rPVdP_TAmerKh_82EravEw=sCj4LyEBu-NfGCK0Obg=HMVw@mail.gmail.com>
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On 22 Mar 2015, at 22:01, Craig Rodrigues <rodrigc@FreeBSD.org> wrote: >=20 >> Volatile is not the solution, it is completely orthogonal. The = correct >> way would be to use unsigned integers, for which wrapping is defined, >> then convert those back and forth when presenting the results to the >> user. >>=20 >=20 > OK, converting expr.y to use unsigned integers would require a bit of = work. Note that clang has, for a few releases, had builtins that allow = overflow-checked operations and will generate very efficient code. In = op_times, I believe the following should work: long long mul; #if __has_builtin(__builtin_smulll_overflow) if (__builtin_smulll_overflow(a->u.i, b->u.i, &mul)) errx(ERR_EXIT, "overflow");=20 #else mul =3D a->u.i * b->u.i; #endif r =3D make_integer(mul); I don't know if recent versions of gcc implement these builtins yet. I = think they were added to clang around 3.4, possibly slightly earlier. =20= David
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