Re: [PATCH. fortran] Add automatic linking to caf_shmem using -fcoarray=shared

From 0fb3be9df144dec1a0bba475ae8e64ac81df3586 Mon Sep 17 00:00:00 2001
From: Jerry DeLisle <[email protected]>
Date: Sat, 9 May 2026 11:49:21 -0700
Subject: [PATCH] fortran: Add -fcoarray=shared option to auto-link -lcaf_shmem

The new -fcoarray=shared option provides a convenient shorthand for
the common invocation -fcoarray=lib -lcaf_shmem.  The driver transforms
-fcoarray=shared into -fcoarray=lib for the frontend and automatically
appends -lcaf_shmem to the link command.  Existing uses of -fcoarray=lib
are unaffected.

Assisted by: Claude Sonnet 4.6

gcc/:

	* flag-types.h (gfc_fcoarray): Add GFC_FCOARRAY_SHARED.

gcc/fortran/:

	* lang.opt (fcoarray=): Add shared enum value; update help text.
	* gfortranspec.cc (CAF_SHMEM_LIBRARY): New macro.
	(lang_specific_driver): Detect -fcoarray=shared in first pass and
	set need_caf_shmem flag.  In second pass, transform -fcoarray=shared
	to -fcoarray=lib for cc1.  Append -lcaf_shmem when need_caf_shmem
	is set and linking is active.

gcc/testsuite/:

	* gfortran.dg/coarray_51.f90: New test.
---
 gcc/flag-types.h                         |  3 ++-
 gcc/fortran/gfortranspec.cc              | 25 ++++++++++++++++++++++++
 gcc/fortran/lang.opt                     |  5 ++++-
 gcc/testsuite/gfortran.dg/coarray_51.f90 | 15 ++++++++++++++
 4 files changed, 46 insertions(+), 2 deletions(-)
 create mode 100644 gcc/testsuite/gfortran.dg/coarray_51.f90

diff --git a/gcc/flag-types.h b/gcc/flag-types.h
index 77dc1f658fb..3d182785c82 100644
--- a/gcc/flag-types.h
+++ b/gcc/flag-types.h
@@ -456,7 +456,8 @@ enum gfc_fcoarray
 {
   GFC_FCOARRAY_NONE = 0,
   GFC_FCOARRAY_SINGLE,
-  GFC_FCOARRAY_LIB
+  GFC_FCOARRAY_LIB,
+  GFC_FCOARRAY_SHARED
 };
 
 
diff --git a/gcc/fortran/gfortranspec.cc b/gcc/fortran/gfortranspec.cc
index d0df0ee6171..13b240013e8 100644
--- a/gcc/fortran/gfortranspec.cc
+++ b/gcc/fortran/gfortranspec.cc
@@ -62,6 +62,10 @@ along with GCC; see the file COPYING3.  If not see
 #define FORTRAN_LIBRARY "gfortran"
 #endif
 
+#ifndef CAF_SHMEM_LIBRARY
+#define CAF_SHMEM_LIBRARY "caf_shmem"
+#endif
+
 /* Name of the spec file.  */
 #define SPEC_FILE "libgfortran.spec"
 
@@ -205,6 +209,9 @@ lang_specific_driver (struct cl_decoded_option **in_decoded_options,
   /* Whether we need to link statically.  */
   int static_linking = 0;
 
+  /* Whether -fcoarray=shared was given; triggers auto-link of -lcaf_shmem.  */
+  int need_caf_shmem = 0;
+
   /* The number of input and output files in the incoming arg list.  */
   int n_infiles = 0;
   int n_outfiles = 0;
@@ -272,6 +279,11 @@ lang_specific_driver (struct cl_decoded_option **in_decoded_options,
 	  ++n_outfiles;
 	  break;
 
+	case OPT_fcoarray_:
+	  if (decoded_options[i].value == GFC_FCOARRAY_SHARED)
+	    need_caf_shmem = 1;
+	  break;
+
 	case OPT_v:
 	  verbose = 1;
 	  break;
@@ -349,6 +361,16 @@ warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.\n\n"
 	      saw_speclang = (strcmp (lang, "none") != 0);
 	    }
 
+	  /* -fcoarray=shared is a driver-level alias for -fcoarray=lib that
+	     also arranges for -lcaf_shmem to be linked automatically.  Pass
+	     -fcoarray=lib to cc1 so the frontend uses the library code path.  */
+	  if (decoded_options[i].opt_index == OPT_fcoarray_
+	      && decoded_options[i].value == GFC_FCOARRAY_SHARED)
+	    {
+	      append_option (OPT_fcoarray_, "lib", GFC_FCOARRAY_LIB);
+	      continue;
+	    }
+
 	  append_arg (&decoded_options[i]);
 
 	  continue;
@@ -404,6 +426,9 @@ warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.\n\n"
 	default:
 	  break;
 	}
+
+      if (need_caf_shmem)
+	append_option (OPT_l, CAF_SHMEM_LIBRARY, 1);
     }
 
 #ifdef ENABLE_SHARED_LIBGCC
diff --git a/gcc/fortran/lang.opt b/gcc/fortran/lang.opt
index 754e5c9115b..cbd13aa2019 100644
--- a/gcc/fortran/lang.opt
+++ b/gcc/fortran/lang.opt
@@ -833,7 +833,7 @@ Experimental unsigned numbers.
 
 fcoarray=
 Fortran RejectNegative Joined Enum(gfc_fcoarray) Var(flag_coarray) Init(GFC_FCOARRAY_NONE)
--fcoarray=<none|single|lib>	Specify which coarray parallelization should be used.
+-fcoarray=<none|single|lib|shared>	Specify which coarray parallelization should be used.
 
 Enum
 Name(gfc_fcoarray) Type(enum gfc_fcoarray) UnknownError(Unrecognized option: %qs)
@@ -847,6 +847,9 @@ Enum(gfc_fcoarray) String(single) Value(GFC_FCOARRAY_SINGLE)
 EnumValue
 Enum(gfc_fcoarray) String(lib) Value(GFC_FCOARRAY_LIB)
 
+EnumValue
+Enum(gfc_fcoarray) String(shared) Value(GFC_FCOARRAY_SHARED)
+
 fcheck=
 Fortran RejectNegative JoinedOrMissing
 -fcheck=[...]	Specify which runtime checks are to be performed.
diff --git a/gcc/testsuite/gfortran.dg/coarray_51.f90 b/gcc/testsuite/gfortran.dg/coarray_51.f90
new file mode 100644
index 00000000000..da8a270c262
--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/coarray_51.f90
@@ -0,0 +1,15 @@
+! { dg-do link }
+! { dg-options "-fcoarray=shared -fdump-tree-original" }
+!
+! Test that -fcoarray=shared is accepted and generates the same
+! library-based CAF calls as -fcoarray=lib.
+
+program test
+  implicit none
+  integer :: x[*]
+  x = this_image ()
+  sync all
+end program test
+
+! { dg-final { scan-tree-dump-times "_gfortran_caf_init \\(&argc, &argv\\);" 1 "original" } }
+! { dg-final { scan-tree-dump-times "_gfortran_caf_sync_all \\(" 1 "original" } }
-- 
2.54.0