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*From*: Tejas Joshi <tejasjoshi9673 at gmail dot com>*To*: gcc at gcc dot gnu dot org*Cc*: Martin Jambor <mjambor at suse dot cz>, hubicka at ucw dot cz, segher at kernel dot crashing dot org, joseph at codesourcery dot com*Date*: Sun, 11 Aug 2019 18:22:26 +0530*Subject*: Re: Expansion of narrowing math built-ins into power instructions*References*: <87sgqnx4i6.fsf@oldenburg2.str.redhat.com> <alpine.DEB.2.21.1907301947090.10734@digraph.polyomino.org.uk> <CACMrGjBiEMp7jj=b30MQ-8SMYoPA_4BFTdQRQSbV7WkYmv+Opg@mail.gmail.com> <20190731144722.GS31406@gate.crashing.org> <CACMrGjC5T-BNowawG9WiKi-C6FRMrtNKnkUSsn1TVT3iFN-Zdg@mail.gmail.com> <20190808200514.GL31406@gate.crashing.org> <alpine.DEB.2.21.1908082304570.5719@digraph.polyomino.org.uk> <CACMrGjB1UmfKuTCwGLi5oTapr4EM-JxbfVGr_GvwucWwfg0oYg@mail.gmail.com> <20190810164600.GT31406@gate.crashing.org> <CACMrGjDk-VhA38LanK5uxprx-hQABQDX6XOdMTAqjyvSAdN+TA@mail.gmail.com> <20190811071955.GV31406@gate.crashing.org>

Hello. > with it, but first get DP->SP (fadd) working? Can you please review what have I have been trying and facing the issues on patch : <https://gcc.gnu.org/ml/gcc/2019-08/msg00078.html> Thanks, Tejas On Sun, 11 Aug 2019 at 12:50, Segher Boessenkool <segher@kernel.crashing.org> wrote: > > Hi Tejas, > > On Sun, Aug 11, 2019 at 10:34:26AM +0530, Tejas Joshi wrote: > > > As far as I understand that flag should set the behaviour of the fadd > > > function, not the __builtin_fadd one. So I don't know. > > > > According to ISO/IEC TS 18661, I am supposed to implement the fadd > > variants for folding and expand them inline, that take double and long > > double as arguments and return > > addition in appropriate narrower type, float and double. As far as I > > know, we use __builtin_ to call the internal functions? I do not know > > which the only fadd function is. > > See the manual, section "Other Built-in Functions Provided by GCC": > > @opindex fno-builtin > GCC includes built-in versions of many of the functions in the standard > C library. These functions come in two forms: one whose names start with > the @code{__builtin_} prefix, and the other without. Both forms have the > same type (including prototype), the same address (when their address is > taken), and the same meaning as the C library functions even if you specify > the @option{-fno-builtin} option @pxref{C Dialect Options}). Many of these > functions are only optimized in certain cases; if they are not optimized in > a particular case, a call to the library function is emitted. > > > > double precision one. But instead you want to add two double precision > > > numbers, producing a single precision one? The fadds instruction fits > > > > Yes. > > > > > well to that, but you'll have to check exactly how the fadd() function > > > should behave with respect to rounding and exceptions and the like. > > I read 18661-1 now... and yup, "fadds" will work fine, and there are > no complications like this as far as I see. > > For QP to either DP or SP, you can do round-to-odd followed by one of the > conversion instructions. The ISA manual describes this; I can help you > with it, but first get DP->SP (fadd) working? > > For the non-QP long doubles we have... There is the option of using DP > for it, which isn't standard-compliant, many other archs have it too, > and it is simple anyway, because you have all code for operations > already. You can mostly just ignore this option. > > For double-double... Well firstly, double-double is on the way out, so > adding new features to it is pretty useless? Just ignore it unless you > have time left, I'd say. > > > In Joseph's initial mail that describes what should be carried out in > > the course of project, about rounding and exceptions. I have strictly > > followed this description for my folding patch : > > > > * The narrowing functions, e.g. fadd, faddl, daddl, are a bit different > > from most other built-in math.h functions because the return type is > > different from the argument types. You could start by adding them to > > builtins.def similarly to roundeven (with new macros to handle adding such > > functions for relevant pairs of _FloatN, _FloatNx types). These functions > > could be folded for constant arguments only if the result is exact, or if > > -fno-rounding-math -fno-trapping-math (and -fno-math-errno if the result > > involves overflow / underflow). > > For Power, all five basic operations (add, sub, mul, div, fma) work fine > wrt rounding mode if using the fadds etc. insns, for DP->SP. All > exceptions work as expected, except maybe underflow and overflow, but > 18661 doesn't require much at all for those anyway :-) > > > Segher

**References**:**Re: Expansion of narrowing math built-ins into power instructions***From:*Tejas Joshi

**Re: Expansion of narrowing math built-ins into power instructions***From:*Segher Boessenkool

**Re: Expansion of narrowing math built-ins into power instructions***From:*Joseph Myers

**Re: Expansion of narrowing math built-ins into power instructions***From:*Tejas Joshi

**Re: Expansion of narrowing math built-ins into power instructions***From:*Segher Boessenkool

**Re: Expansion of narrowing math built-ins into power instructions***From:*Tejas Joshi

**Re: Expansion of narrowing math built-ins into power instructions***From:*Segher Boessenkool

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