re PR fortran/20178 (COMPLEX function returns incompatible with g77)

gcc/fortran/
	PR fortran/20178
	* gfortran.h (gfc_option): Add flag_f2c.
	* invoke.texi: Document '-ff2c' command line option.  Adapt
	documentation for '-fno-second-underscore' and '-fno-underscoring'.
	* lang.opt (ff2c): New entry.
	* options.c (gfc-init_options): Set default calling convention
	to -fno-f2c.  Mark -fsecond-underscore unset.
	(gfc_post_options): Set -fsecond-underscore if not explicitly set
	by user.
	(handle_options): Set gfc_option.flag_f2c according to requested
	calling	convention.
	* trans-decl.c (gfc_get_extern_function_decl): Use special f2c
	intrinsics where necessary.
	(gfc_trans_deferred_vars): Change todo error to	assertion.
	* trans-expr.c (gfc_conv_variable): Dereference access
	to hidden result argument.
	(gfc_conv_function_call): Add hidden result argument to argument
	list if f2c calling conventions requested.  Slightly restructure
	tests.  Convert result of default REAL function to requested type
	if f2c calling conventions are used.  Dereference COMPLEX result
	if f2c cc are used.
	* trans-types.c (gfc_sym_type):  Return double for default REAL
	function if f2c cc are used.
	(gfc_return_by_reference): Slightly restructure logic.  Return
	COMPLEX by reference depending on calling conventions.
	(gfc_get_function_type): Correctly make hidden result argument a
	pass-by-reference argument for COMPLEX.  Remove old code which does
	this for derived types.
libgfortran/
	PR fortran/20178
	* Makefile.am (gfor_specific_src): Add 'intrinsics/f2c_intrinsics.F90'
	to dependencies.
	* Makefile.in: Regenerate.
	* intrinsics/f2c_specific.F90: New file.
gcc/testsuite/
	PR fortran/20178
	* gfortran.dg/f2c_1.f90, gfortran.dg/f2c_2.f90,
	gfortran.dg/f2c_3.f90: New tests.

From-SVN: r99544

1 files changed, 63 insertions, 18 deletions

diff --git a/gcc/fortran/invoke.texi b/gcc/fortran/invoke.texi
index 22f20dc..5385bba 100644
--- a/gcc/fortran/invoke.texi
+++ b/gcc/fortran/invoke.texi
@@ -143,7 +143,7 @@ by type.  Explanations are in the following sections.
 @item Code Generation Options
 @xref{Code Gen Options,,Options for Code Generation Conventions}.
 @gccoptlist{
--fno-underscoring  -fno-second-underscore @gol
+-ff2c -fno-underscoring  -fsecond-underscore @gol
 -fbounds-check  -fmax-stack-var-size=@var{n} @gol
 -fpackderived  -frepack-arrays}
 @end table
@@ -518,8 +518,43 @@ it.
 
 
 @table @gcctabopt
-@cindex -fno-underscoring option
-@cindex options, -fno-underscoring
+@cindex @option{-ff2c} option
+@cindex options, @option{-ff2c}
+@item -ff2c
+@cindex calling convention
+@cindex @command{f2c} calling convention
+@cindex @command{g77} calling convention
+@cindex libf2c calling convention
+Generate code designed to be compatible with code generated
+by @command{g77} and @command{f2c}.
+
+The calling conventions used by @command{g77} (originally implemented
+in @command{f2c}) require functions that return type
+default @code{REAL} to actually return the C type @code{double}, and
+functions that return type @code{COMPLEX} to return the values via an
+extra argument in the calling sequence that points to where to
+store the return value.  Under the default GNU calling conventions, such
+functions simply return their results as they would in GNU
+C -- default @code{REAL} functions return the C type @code{float}, and
+@code{COMPLEX} functions return the GNU C type @code{complex}.
+Additionally, this option implies the @options{-fsecond-underscore}
+option, unless @options{-fno-second-underscore} is explicitly requested.
+
+This does not affect the generation of code that interfaces with
+the @command{libgfortran} library.
+
+@emph{Caution:} It is not a good idea to mix Fortran code compiled
+with @code{-ff2c} with code compiled with the default @code{-fno-f2c}
+calling conventions as, calling @code{COMPLEX} or default @code{REAL}
+functions between program parts which were compiled with different
+calling conventions will break at execution time.
+
+@emph{Caution:} This will break code which passes intrinsic functions
+of type default @code{REAL} or @code{COMPLEX} as actual arguments, as
+the library implementations use the @command{-fno-f2c} calling conventions.
+
+@cindex @option{-fno-underscoring option}
+@cindex options, @option{-fno-underscoring}
 @item -fno-underscoring
 @cindex underscore
 @cindex symbol names, underscores
@@ -528,16 +563,17 @@ it.
 Do not transform names of entities specified in the Fortran
 source file by appending underscores to them.
 
-With @option{-funderscoring} in effect, @command{gfortran} appends two
-underscores to names with underscores and one underscore to external names
-with no underscores.  (@command{gfortran} also appends two underscores to
-internal names with underscores to avoid naming collisions with external
-names.  The @option{-fno-second-underscore} option disables appending of the
-second underscore in all cases.)
+With @option{-funderscoring} in effect, @command{gfortran} appends one
+underscore to external names with no underscores.
 
 This is done to ensure compatibility with code produced by many
-UNIX Fortran compilers, including @command{f2c} which perform the
-same transformations.
+UNIX Fortran compilers.
+
+@emph{Caution}: The default behavior of @command{gfortran} is
+incompatible with @command{f2c} and @command{g77}, please use the
+@option{-ff2c} and @option{-fsecond-underscore} options if you want
+object files compiled with @option{gfortran} to be compatible with
+object code created with these tools.
 
 Use of @option{-fno-underscoring} is not recommended unless you are
 experimenting with issues such as integration of (GNU) Fortran into
@@ -593,22 +629,31 @@ in the source, even if the names as seen by the linker are mangled to
 prevent accidental linking between procedures with incompatible
 interfaces.
 
-@cindex -fno-second-underscore option
-@cindex options, -fno-second-underscore
-@item -fno-second-underscore
+@cindex @option{-fsecond-underscore option}
+@cindex options, @option{-fsecond-underscore}
+@item -fsecond-underscore
 @cindex underscore
 @cindex symbol names, underscores
 @cindex transforming symbol names
 @cindex symbol names, transforming
-Do not append a second underscore to names of entities specified
-in the Fortran source file.
+@cindex @command{f2c} calling convention
+@cindex @command{g77} calling convention
+@cindex libf2c calling convention
+By default, @command{gfortran} appends an underscore to external
+names.  If this option is used @command{gfortran} appends two
+underscores to names with underscores and one underscore to external names
+with no underscores.  (@command{gfortran} also appends two underscores to
+internal names with underscores to avoid naming collisions with external
+names.
 
 This option has no effect if @option{-fno-underscoring} is
-in effect.
+in effect.  It is implied by the @option{-ff2c} option.
 
 Otherwise, with this option, an external name such as @samp{MAX_COUNT}
 is implemented as a reference to the link-time external symbol
-@samp{max_count_}, instead of @samp{max_count__}.
+@samp{max_count__}, instead of @samp{max_count_}.  This is required
+for compatibility with @command{g77} and @command{f2c}, and is implied
+by use of the @option{-ff2c} option.
 
 
 @cindex -fbounds-check option