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From: "dominiq at lps dot ens.fr" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug fortran/57871] gfortran -freal-4-real-16 gives wrong result for
 selected_real_kind(1)
Date: Sun, 07 Mar 2021 13:19:47 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D57871

--- Comment #12 from Dominique d'Humieres <dominiq at lps dot ens.fr> ---
> As this issue is about documentation, if I read the later comments correc=
tly:
> Can you check whether the documentation is now sufficient or whether more=
 is needed? > If so, what is needed? =E2=80=94 If not, can this bug now be =
closed?

I don't like the sentence

Note that for @code{REAL(KIND=3DKIND(1.0))} the literal may get promoted and
then the result may get promoted again.

There is only one promotion for -freal-4-real-X, and it does not matter if
1.0 is promoted first KIND(1.0) is then X, or after KIND(1.0) is 4 then=20
REAL(KIND=3D4) is promoted to REAL(KIND=3DX).

The situation for SELECTED_REAL_KIND(1) is quite different: if the promotio=
n of
-freal-4-real-X is done first, then the smallest kind available is 8,
if it is done after then SELECTED_REAL_KIND(1) will be 4, then promoted to =
X.

What about a sentence such as:

Note that while @code{REAL(KIND=3DKIND(1.0))} is always promoted to X by
-freal-4-real-X, @code{SELECTED_REAL_KIND(1)} returns always 4 which is then
promoted to X.

?

It may be also useful to add a sentence saying that the promotion options a=
re
provided as such and that the observed behavior is not a bug but a feature.

As said in comment 8, I did not find any other circonstance, by
SELECTED_REAL_KIND
for which such ambiguity exists.=