Re: [PATCH] Builtin function roundeven folding implementation

[Tejas Joshi <tejasjoshi9673@gmail.com>]

I have made the respective changes and fixed the indentations and it
passes the testing.

> I encourage a followup looking for and fixing further places in the source
> tree that handle round-to-integer function families (ceil / floor / trunc
> / round / rint / nearbyint) and should handle roundeven as well, as that
> would lead to more optimization of roundeven calls.  Such places aren't
> that easy to search for because most of those names are common words used
> in other contexts in the compiler.  But, for example, match.pd has
> patterns

I will follow up to make these optimizations for sure.

Thanks,
Tejas


On Sat, 24 Aug 2019 at 02:08, Joseph Myers <joseph@codesourcery.com> wrote:
>
> On Fri, 23 Aug 2019, Tejas Joshi wrote:
>
> > diff --git a/gcc/builtins.c b/gcc/builtins.c
> > index 9a766e4ad63..5149d901a96 100644
> > --- a/gcc/builtins.c
> > +++ b/gcc/builtins.c
> > @@ -2056,6 +2056,7 @@ mathfn_built_in_2 (tree type, combined_fn fn)
> >      CASE_MATHFN (REMQUO)
> >      CASE_MATHFN_FLOATN (RINT)
> >      CASE_MATHFN_FLOATN (ROUND)
> > +    CASE_MATHFN (ROUNDEVEN)
>
> This should use CASE_MATHFN_FLOATN, as for the other round-to-integer
> functions.
>
> > +  /* Check lowest bit, if not set, return true.  */
> > +  else if (REAL_EXP (r) <= SIGNIFICAND_BITS)
> > +  {
> > +    unsigned int n = SIGNIFICAND_BITS - REAL_EXP (r);
> > +    int w = n / HOST_BITS_PER_LONG;
> > +
> > +    unsigned long num = ((unsigned long)1 << (n % HOST_BITS_PER_LONG));
> > +
> > +    if ((r->sig[w] & num) == 0)
> > +      return true;
>
> Fix the indentation here (the braces should be indented two columns from
> the "else", the contents then two columns from the braces).
>
> > +  }
> > +
> > +  else
>
> And remove the stray blank line before "else".
>
> > +/* Return true if R is halfway between two integers, else return
> > +   false.  The function is not valid for rvc_inf and rvc_nan classes.  */
> > +
> > +bool
> > +is_halfway_below (const REAL_VALUE_TYPE *r)
> > +{
> > +  gcc_assert (r->cl != rvc_inf);
> > +  gcc_assert (r->cl != rvc_nan);
> > +  int i;
>
> Explicitly check for rvc_zero and return false in that case (that seems to
> be the convention in real.c, rather than relying on code using REAL_EXP to
> do something sensible for zero, which has REAL_EXP of 0).
>
> > +  else if (REAL_EXP (r) < SIGNIFICAND_BITS)
> > +  {
>
> Another place to fix indentation.
>
> > +void
> > +real_roundeven (REAL_VALUE_TYPE *r, format_helper fmt,
> > +             const REAL_VALUE_TYPE *x)
> > +{
> > +  if (is_halfway_below (x))
> > +  {
>
> Again, fix indentation throughout this function.
>
> The patch is OK with those fixes, assuming the fixed patch passes testing.
> I encourage a followup looking for and fixing further places in the source
> tree that handle round-to-integer function families (ceil / floor / trunc
> / round / rint / nearbyint) and should handle roundeven as well, as that
> would lead to more optimization of roundeven calls.  Such places aren't
> that easy to search for because most of those names are common words used
> in other contexts in the compiler.  But, for example, match.pd has
> patterns
>
> /* trunc(trunc(x)) -> trunc(x), etc.  */
>
> /* f(x) -> x if x is integer valued and f does nothing for such values.  */
>
>  /* truncl(extend(x)) -> extend(trunc(x)), etc., if x is a double.  */
>
>  /* truncl(extend(x)) and trunc(extend(x)) -> extend(truncf(x)), etc.,
>     if x is a float.  */
>
> which should apply to roundeven as well.
>
> --
> Joseph S. Myers
> joseph@codesourcery.com