Fortran manual: Revise introductory chapter.

Fix various bit-rot in the discussion of standards conformance, remove
material that is only of historical interest, copy-editing.  Also move
discussion of preprocessing out of the introductory chapter.

2021-11-01  Sandra Loosemore  <sandra@codesourcery.com>

	gcc/fortran/
	* gfortran.texi (About GNU Fortran): Consolidate material
	formerly in other sections.  Copy-editing.
	(Preprocessing and conditional compilation): Delete, moving
	most material to invoke.texi.
	(GNU Fortran and G77): Delete.
	(Project Status): Delete.
	(Standards): Update.
	(Fortran 95 status): Mention conditional compilation here.
	(Fortran 2003 status): Rewrite to mention the 1 missing feature
	instead of all the ones implemented.
	(Fortran 2008 status): Similarly for the 2 missing features.
	(Fortran 2018 status): Rewrite to reflect completion of TS29113
	feature support.
	* invoke.texi (Preprocessing Options): Move material formerly
	in introductory chapter here.

1 files changed, 40 insertions, 4 deletions

diff --git a/gcc/fortran/invoke.texi b/gcc/fortran/invoke.texi
index 0fb7e1a..3533e86 100644
--- a/gcc/fortran/invoke.texi
+++ b/gcc/fortran/invoke.texi
@@ -570,10 +570,46 @@ Enhance test coverage by forcing most forall assignments to use temporary.
 @cindex preprocessor
 @cindex options, preprocessor
 @cindex CPP
-
-Preprocessor related options. See section 
-@ref{Preprocessing and conditional compilation} for more detailed
-information on preprocessing in @command{gfortran}.
+@cindex FPP
+@cindex Conditional compilation
+@cindex Preprocessing
+@cindex preprocessor, include file handling
+
+Many Fortran compilers including GNU Fortran allow passing the source code
+through a C preprocessor (CPP; sometimes also called the Fortran preprocessor,
+FPP) to allow for conditional compilation.  In the case of GNU Fortran,
+this is the GNU C Preprocessor in the traditional mode.  On systems with
+case-preserving file names, the preprocessor is automatically invoked if the
+filename extension is @file{.F}, @file{.FOR}, @file{.FTN}, @file{.fpp},
+@file{.FPP}, @file{.F90}, @file{.F95}, @file{.F03} or @file{.F08}.  To manually
+invoke the preprocessor on any file, use @option{-cpp}, to disable
+preprocessing on files where the preprocessor is run automatically, use
+@option{-nocpp}.
+
+If a preprocessed file includes another file with the Fortran @code{INCLUDE}
+statement, the included file is not preprocessed.  To preprocess included
+files, use the equivalent preprocessor statement @code{#include}.
+
+If GNU Fortran invokes the preprocessor, @code{__GFORTRAN__}
+is defined.  The macros @code{__GNUC__}, @code{__GNUC_MINOR__} and
+@code{__GNUC_PATCHLEVEL__} can be used to determine the version of the
+compiler.  See @ref{Top,,Overview,cpp,The C Preprocessor} for details.
+
+GNU Fortran supports a number of @code{INTEGER} and @code{REAL} kind types
+in additional to the kind types required by the Fortran standard.
+The availability of any given kind type is architecture dependent.  The
+following pre-defined preprocessor macros can be used to conditionally
+include code for these additional kind types: @code{__GFC_INT_1__},
+@code{__GFC_INT_2__}, @code{__GFC_INT_8__}, @code{__GFC_INT_16__},
+@code{__GFC_REAL_10__}, and @code{__GFC_REAL_16__}.
+
+While CPP is the de-facto standard for preprocessing Fortran code,
+Part 3 of the Fortran 95 standard (ISO/IEC 1539-3:1998) defines
+Conditional Compilation, which is not widely used and not directly
+supported by the GNU Fortran compiler.  You can use the program coco
+to preprocess such files (@uref{http://www.daniellnagle.com/coco.html}).
+
+The following options control preprocessing of Fortran code:
 
 @table @gcctabopt
 @item -cpp