Re: [PATCH] [PR24021] Implement PLUS_EXPR range-op entry for floats.

[Jakub Jelinek <jakub@redhat.com>]

On Tue, Nov 08, 2022 at 01:47:58PM +0100, Aldy Hernandez wrote:
> On Tue, Nov 8, 2022 at 12:07 PM Jakub Jelinek <jakub@redhat.com> wrote:
> >
> > On Mon, Nov 07, 2022 at 04:38:29PM +0100, Aldy Hernandez wrote:
> > > From d214bcdff2cb90ad1eb808d29bda6fb98d510b4c Mon Sep 17 00:00:00 2001
> > > From: Aldy Hernandez <aldyh@redhat.com>
> > > Date: Mon, 7 Nov 2022 14:18:57 +0100
> > > Subject: [PATCH] Provide normalized and denormal format version of
> > >  real_isdenormal.
> > >
> > > Implement real_isdenormal_target() to be used within real.cc where the
> > > argument is known to be in denormal format.  Rewrite real_isdenormal()
> > > for use outside of real.cc where the argument is known to be
> > > normalized.
> > >
> > > gcc/ChangeLog:
> > >
> > >       * real.cc (real_isdenormal_target): New.
> > >       (encode_ieee_single): Use real_isdenormal_target.
> > >       (encode_ieee_double): Same.
> > >       (encode_ieee_extended): Same.
> > >       (encode_ieee_quad): Same.
> > >       (encode_ieee_half): Same.
> > >       (encode_arm_bfloat_half): Same.
> > >       * value-range.cc (frange::flush_denormals_to_zero): Same.
> > >       * real.h (real_isdenormal): Rewrite to look at mode.
> >
> > I'd make real_isdenormal_target static inline bool
> > rather than inline bool, it is only defined in real.cc, so there is
> > no point exporting it.
> 
> Huh.  I thought inline alone would inhibit the exporting.  Thanks.

That is what happens with C99 inline (unless there is extern for the decl),
but C++ inline is different.  It isn't guaranteed to be exported, but
with -fkeep-inline-functions or if you say take address of the inline
in a way that can't be optimized back into a call to the inline (or even
just call it with -O0), it is exported.
> 
> > Though, as you've added the mode argument, the real.cc inline
> > could very well also be called real_isdenormal too, it wouldn't be
> > a redeclaration or ODR violation.
> 
> Great, even better.
> 
> OK pending tests?
> Aldy

> From c3ca1d606bfb22bf4f8bc7ac0ce561bd6afc3368 Mon Sep 17 00:00:00 2001
> From: Aldy Hernandez <aldyh@redhat.com>
> Date: Mon, 7 Nov 2022 14:18:57 +0100
> Subject: [PATCH] Provide normalized and denormal format version of
>  real_isdenormal.
> 
> Implement a variant of real_isdenormal() to be used within real.cc
> where the argument is known to be in denormal format.  Rewrite
> real_isdenormal() for use outside of real.cc where the argument is
> known to be normalized.
> 
> gcc/ChangeLog:
> 
> 	* real.cc (real_isdenormal): New.
> 	* real.h (real_isdenormal): Add mode argument.  Rewrite for
> 	normalized values.
> 	* value-range.cc (frange::flush_denormals_to_zero): Pass mode to
> 	real_isdenormal.
> ---
>  gcc/real.cc        | 10 ++++++++++
>  gcc/real.h         |  7 ++++---
>  gcc/value-range.cc |  5 +++--
>  3 files changed, 17 insertions(+), 5 deletions(-)
> 
> diff --git a/gcc/real.cc b/gcc/real.cc
> index aae7c335d59..028aad95ec4 100644
> --- a/gcc/real.cc
> +++ b/gcc/real.cc
> @@ -111,6 +111,16 @@ static const REAL_VALUE_TYPE * real_digit (int);
>  static void times_pten (REAL_VALUE_TYPE *, int);
>  
>  static void round_for_format (const struct real_format *, REAL_VALUE_TYPE *);
> +
> +/* Determine whether a floating-point value X is a denormal.  R is
> +   expected to be in denormal form, so this function is only
> +   meaningful after a call to round_for_format.  */
> +
> +static inline bool
> +real_isdenormal (const REAL_VALUE_TYPE *r)
> +{
> +  return (r->sig[SIGSZ-1] & SIG_MSB) == 0;

I would probably keep the r->cl == rvc_normal in here too.
I know the code in real.cc didn't do it before, but what
r->sig is for the rvc_zero/rvc_inf is unclear.  It is true
that get_zero/get_canonical_?nan/get_inf clear the whole sig,
but not really sure if we guarantee that everywhere.
The real.cc uses were like:
  bool denormal = ...;
at the start of the function and then
  switch (...)
    {
...
    case rvc_normal:
      if (denormal)
	...
    }
so another even better possibility would be to use your simple
real.cc (real_isdenormal) and drop all the denormal variables, so:
- bool denormal = ...;
  switch (...)
    {
...
    case rvc_normal:
-     if (denormal)
+     if (real_isdenormal (r))
	...
    }

Otherwise LGTM.

	Jakub