[GSoC-19] Implementing narrowing functions like fadd

[Tejas Joshi]

Hello.
I am trying to add fadd function variants and as fadd takes two
arguments, the function should be called from fold_const_call_sss ().
The function is closely modeled on function calls and cases according
to real_nextafter (), also used gdb to look at backtrace. Although I
have made changes according to real_nextafter, the function real_fadd
is not called by the test program but real_nextafter does get called.
I cant find any other places to add calls for fadd. What is missing?
The patch is attached herewith.

int
main ()
{
  float x;
  x = __builtin_fadd (3.5,1.4);
}

Also, fadd function should not have faddf variant, but is introduced
only for the sake.

Thanks,
-Tejas

On Wed, 3 Jul 2019 at 18:29, Tejas Joshi <tejasjoshi9673@gmail.com> wrote:
>
> Hello.
> Functions like fadd, faddl take two arguments, do the addition and
> return the answer in narrower precision than the argument type. The
> thing that might be helpful is using the do_add function directly, if
> appropriate?
> The thing to consider about narrowed down return type is how it can be
> achieved. The functions that operate on real numbers like real_round
> and so on, do not consider the return type and do calculations on the
> entire real number representation. So just defining these functions
> and their return type in builtins.def and other appropriate places
> would do the trick?
> like:
> BT_FN_FLOAT_DOUBLE_DOUBLE as return and argument type for FADD
>
> Or it has to be narrowed down by zeroing down the trailing
> out-of-precision bits?
> Also, if the addition or any one of the argument exceeds the return
> size, the integer part of the addition would not fit in the narrowed
> type. Like, 2^32 would easily fit in double but will lose its least
> significant bit in float and become 2^31. How these types are supposed
> to be handled?
>
> Thanks,
> -Tejas
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