[PATCH, Fortran] DEC Compatibility: Default missing exponents to 0 with -fdec

[Fritz Reese <fritzoreese at gmail dot com>]

All,

Attached is a patch to the GNU Fortran front-end and runtime library
(libgfortran) which accepts real numbers with missing exponents as if
'0' was given as the exponent when the compile flag -fdec is given,
for further compatibility with legacy compilers. By default, GNU
Fortran will reject real constants such as '9e' or '15.2e'. With the
patch and -fdec, such numbers are accepted and treated as '9e0' (9) or
'15.2e0' (15.2), both at compile-time through the front-end and at
runtime through libgfortran.

For compile-time this is trivial. For runtime, An IOPARM_DT flag bit
is added to the usual flags to track whether a program was compiled
with the "default exponent" behavior, which the library can detect at
runtime for programs individually. No space is required in the
st_parameter_dt structure, and the behavior should be
backwards-compatible (by design of the IOPARM structures/flags).

Bootstraps and regtests on x86_64-redhat-linux. OK for trunk?

---
Fritz Reese

From: Fritz Reese <fritzoreese@gmail.com>
Date: Wed, 5 Oct 2016 18:27:56 -0400
Subject: [PATCH] Default missing exponents to 0 with -fdec.

        gcc/fortran/
        * gfortran.texi: Document.
        * gfortran.h (gfc_dt): New field default_exp.
        * primary.c (match_real_constant): Default exponent with -fdec.
        * io.c (match_io): Set dt.default_exp with -fdec.
        * ioparm.def (IOPARM_dt_default_exp): New.
        * trans-io.c (build_dt): Set IOPARM_dt_default_exp with -fdec.

        libgfortran/io/
        * io.h (IOPARM_DT_DEFAULT_EXP): New flag bit.
        * list_read.c (parse_real, read_real): Allow omission of exponent with
        IOPARM_DT_DEFAULT_EXP.
        * read.c (read_f): Ditto.

        gcc/testsuite/gfortran.dg/
        * dec_exp_1.f90, dec_exp_2.f90, dec_exp_3.f90: New testcases.
---
 gcc/fortran/gfortran.h                  |    1 +
 gcc/fortran/gfortran.texi               |   10 ++++++++
 gcc/fortran/io.c                        |    4 +++
 gcc/fortran/ioparm.def                  |    1 +
 gcc/fortran/primary.c                   |   19 ++++++++++++----
 gcc/fortran/trans-io.c                  |    3 ++
 gcc/testsuite/gfortran.dg/dec_exp_1.f90 |   35 +++++++++++++++++++++++++++++++
 gcc/testsuite/gfortran.dg/dec_exp_2.f90 |   13 +++++++++++
 gcc/testsuite/gfortran.dg/dec_exp_3.f90 |   15 +++++++++++++
 libgfortran/io/io.h                     |    1 +
 libgfortran/io/list_read.c              |   22 +++++++++++++++++-
 libgfortran/io/read.c                   |    8 ++++++-
 12 files changed, 124 insertions(+), 8 deletions(-)
 create mode 100644 gcc/testsuite/gfortran.dg/dec_exp_1.f90
 create mode 100644 gcc/testsuite/gfortran.dg/dec_exp_2.f90
 create mode 100644 gcc/testsuite/gfortran.dg/dec_exp_3.f90

Attachment: dec_default_exp.diff
Description: Text document