OpenMP 5.0: requires directive

This is a merge of:
https://gcc.gnu.org/pipermail/gcc-patches/2021-January/563393.html

This patch completes more of the reverse_offload, unified_address, and
unified_shared_memory clauses for the OpenMP 5.0 requires directive,
including runtime verification of the offload target.
(currently no offload devices actually support above features, only
warning messages are emitted)

This may possibly reverted/updated when a final patch is approved
for mainline.

2021-02-02  Chung-Lin Tang  <cltang@codesourcery.com>

gcc/c/ChangeLog:

	* c-parser.c (c_parser_declaration_or_fndef): Set
	OMP_REQUIRES_TARGET_USED in omp_requires_mask if function has
	"omp declare target" attribute.
	(c_parser_omp_target_data): Set    OMP_REQUIRES_TARGET_USED in
	omp_requires_mask.
	(c_parser_omp_target_enter_data): Likewise.
	(c_parser_omp_target_exit_data): Likewise.
	(c_parser_omp_requires): Adjust to only mention "not implemented yet"
	for OMP_REQUIRES_DYNAMIC_ALLOCATORS.

gcc/cp/ChangeLog:

	* parser.c (cp_parser_simple_declaration): Set
	OMP_REQUIRES_TARGET_USED in omp_requires_mask if function has
	"omp declare target" attribute.
	(cp_parser_omp_target_data): Set OMP_REQUIRES_TARGET_USED in
	omp_requires_mask.
	(cp_parser_omp_target_enter_data): Likewise.
	(cp_parser_omp_target_exit_data): Likewise.
	(cp_parser_omp_requires): Adjust to only mention "not implemented yet"
	for OMP_REQUIRES_DYNAMIC_ALLOCATORS.

gcc/fortran/ChangeLog:

	* openmp.c (gfc_check_omp_requires): Fix REVERSE_OFFLOAD typo.
	(gfc_match_omp_requires): Adjust to only mention "not implemented yet"
	for OMP_REQUIRES_DYNAMIC_ALLOCATORS.
	* parse.c ("tree.h"): Add include.
	("omp-general.h"): Likewise.
	(gfc_parse_file): Add code to merge omp_requires to omp_requires_mask.

gcc/ChangeLog:

	* omp-offload.c (omp_finish_file): Add code to reate OpenMP requires
	mask variable in .gnu.gomp_requires section if needed.

gcc/testsuite/ChangeLog:

	* c-c++-common/gomp/requires-4.c: Remove prune of "not supported yet".
	* gcc/testsuite/gfortran.dg/gomp/requires-4.f90: Fix REVERSE_OFFLOAD typo.
	* gcc/testsuite/gfortran.dg/gomp/requires-8.f90: Likewise.

include/ChangeLog:

	* gomp-constants.h (GOMP_REQUIRES_UNIFIED_ADDRESS): New symbol.
	(GOMP_REQUIRES_UNIFIED_SHARED_MEMORY): Likewise.
	(GOMP_REQUIRES_REVERSE_OFFLOAD): Likewise.

libgcc/ChangeLog:

	* offloadstuff.c (__requires_mask_table): New symbol to mark start of
	.gnu.gomp_requires section.
	(__requires_mask_table_end): New symbol to mark end of
	.gnu.gomp_requires section.

libgomp/ChangeLog:

	* libgomp-plugin.h (GOMP_OFFLOAD_supported_features): New declaration.
	* libgomp.h (struct gomp_device_descr): New 'supported_features_func'
	plugin hook field.
	* oacc-host.c (host_supported_features): New host hook function.
	(host_dispatch): Initialize 'supported_features_func' host hook.
	* plugin/plugin-gcn.c (GOMP_OFFLOAD_supported_features): New function.
	* plugin/plugin-nvptx.c (GOMP_OFFLOAD_supported_features): Likewise.
	* target.c (<stdio.h>): Add include of standard header.
	(gomp_requires_mask): New static variable.
	(__requires_mask_table): New declaration.
	(__requires_mask_table_end): Likewise.
	(gomp_load_plugin_for_device): Add loading of 'supported_features' hook.
	(gomp_target_init): Add code to summarize .gnu._gomp_requires section
	mask values, emit error if inconsistency found.

	* testsuite/libgomp.c-c++-common/requires-1.c: New test.
	* testsuite/libgomp.c-c++-common/requires-1-aux.c: New file linked with
	above test.
	* testsuite/libgomp.c-c++-common/requires-2.c: New test.
	* testsuite/libgomp.c-c++-common/requires-2-aux.c: New file linked with
	above test.

liboffloadmic/ChangeLog:

	* plugin/libgomp-plugin-intelmic.cpp (GOMP_OFFLOAD_supported_features):
	New function.

21 files changed, 236 insertions, 8 deletions

diff --git a/gcc/c/c-parser.c b/gcc/c/c-parser.c
index 6b9898a1c70..cb491d2d0a4 100644
--- a/gcc/c/c-parser.c
+++ b/gcc/c/c-parser.c
@@ -2444,6 +2444,12 @@ c_parser_declaration_or_fndef (c_parser *parser, bool fndef_ok,
 	  break;
 	}
 
+      if (flag_openmp
+	  && lookup_attribute ("omp declare target",
+			       DECL_ATTRIBUTES (current_function_decl)))
+	omp_requires_mask
+	  = (enum omp_requires) (omp_requires_mask | OMP_REQUIRES_TARGET_USED);
+
       if (DECL_DECLARED_INLINE_P (current_function_decl))
         tv = TV_PARSE_INLINE;
       else
@@ -19447,6 +19453,10 @@ c_parser_omp_teams (location_t loc, c_parser *parser,
 static tree
 c_parser_omp_target_data (location_t loc, c_parser *parser, bool *if_p)
 {
+  if (flag_openmp)
+    omp_requires_mask
+      = (enum omp_requires) (omp_requires_mask | OMP_REQUIRES_TARGET_USED);
+
   tree clauses
     = c_parser_omp_all_clauses (parser, OMP_TARGET_DATA_CLAUSE_MASK,
 				"#pragma omp target data");
@@ -19589,6 +19599,10 @@ c_parser_omp_target_enter_data (location_t loc, c_parser *parser,
       return NULL_TREE;
     }
 
+  if (flag_openmp)
+    omp_requires_mask
+      = (enum omp_requires) (omp_requires_mask | OMP_REQUIRES_TARGET_USED);
+
   tree clauses
     = c_parser_omp_all_clauses (parser, OMP_TARGET_ENTER_DATA_CLAUSE_MASK,
 				"#pragma omp target enter data");
@@ -19675,6 +19689,10 @@ c_parser_omp_target_exit_data (location_t loc, c_parser *parser,
       return NULL_TREE;
     }
 
+  if (flag_openmp)
+    omp_requires_mask
+      = (enum omp_requires) (omp_requires_mask | OMP_REQUIRES_TARGET_USED);
+
   tree clauses
     = c_parser_omp_all_clauses (parser, OMP_TARGET_EXIT_DATA_CLAUSE_MASK,
 				"#pragma omp target exit data");
@@ -21261,7 +21279,7 @@ c_parser_omp_requires (c_parser *parser)
 	      c_parser_skip_to_pragma_eol (parser, false);
 	      return;
 	    }
-	  if (p)
+	  if (this_req == OMP_REQUIRES_DYNAMIC_ALLOCATORS)
 	    sorry_at (cloc, "%qs clause on %<requires%> directive not "
 			    "supported yet", p);
 	  if (p)
diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index 6eb228099bc..1af233690a2 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -13813,6 +13813,11 @@ cp_parser_simple_declaration (cp_parser* parser,
 	  /* Otherwise, we're done with the list of declarators.  */
 	  else
 	    {
+	      if (flag_openmp && lookup_attribute ("omp declare target",
+						   DECL_ATTRIBUTES (decl)))
+		omp_requires_mask
+		  = (enum omp_requires) (omp_requires_mask
+					 | OMP_REQUIRES_TARGET_USED);
 	      pop_deferring_access_checks ();
 	      return;
 	    }
@@ -40412,6 +40417,10 @@ cp_parser_omp_teams (cp_parser *parser, cp_token *pragma_tok,
 static tree
 cp_parser_omp_target_data (cp_parser *parser, cp_token *pragma_tok, bool *if_p)
 {
+  if (flag_openmp)
+    omp_requires_mask
+      = (enum omp_requires) (omp_requires_mask | OMP_REQUIRES_TARGET_USED);
+
   tree clauses
     = cp_parser_omp_all_clauses (parser, OMP_TARGET_DATA_CLAUSE_MASK,
 				 "#pragma omp target data", pragma_tok);
@@ -40515,6 +40524,10 @@ cp_parser_omp_target_enter_data (cp_parser *parser, cp_token *pragma_tok,
       return NULL_TREE;
     }
 
+  if (flag_openmp)
+    omp_requires_mask
+      = (enum omp_requires) (omp_requires_mask | OMP_REQUIRES_TARGET_USED);
+
   tree clauses
     = cp_parser_omp_all_clauses (parser, OMP_TARGET_ENTER_DATA_CLAUSE_MASK,
 				 "#pragma omp target enter data", pragma_tok);
@@ -40605,6 +40618,10 @@ cp_parser_omp_target_exit_data (cp_parser *parser, cp_token *pragma_tok,
       return NULL_TREE;
     }
 
+  if (flag_openmp)
+    omp_requires_mask
+      = (enum omp_requires) (omp_requires_mask | OMP_REQUIRES_TARGET_USED);
+
   tree clauses
     = cp_parser_omp_all_clauses (parser, OMP_TARGET_EXIT_DATA_CLAUSE_MASK,
 				 "#pragma omp target exit data", pragma_tok);
@@ -42736,7 +42753,7 @@ cp_parser_omp_requires (cp_parser *parser, cp_token *pragma_tok)
 	      cp_parser_skip_to_pragma_eol (parser, pragma_tok);
 	      return false;
 	    }
-	  if (p)
+	  if (this_req == OMP_REQUIRES_DYNAMIC_ALLOCATORS)
 	    sorry_at (cloc, "%qs clause on %<requires%> directive not "
 			    "supported yet", p);
 	  if (p)
diff --git a/gcc/fortran/openmp.c b/gcc/fortran/openmp.c
index 8dc2871cd41..61a340d7f39 100644
--- a/gcc/fortran/openmp.c
+++ b/gcc/fortran/openmp.c
@@ -3545,7 +3545,7 @@ gfc_check_omp_requires (gfc_namespace *ns, int ref_omp_requires)
       if ((ref_omp_requires & OMP_REQ_REVERSE_OFFLOAD)
 	  && !(ns->omp_requires & OMP_REQ_REVERSE_OFFLOAD))
 	gfc_error ("Program unit at %L has OpenMP device constructs/routines "
-		   "but does not set !$OMP REQUIRES REVERSE_OFFSET but other "
+		   "but does not set !$OMP REQUIRES REVERSE_OFFLOAD but other "
 		   "program units do", &ns->proc_name->declared_at);
       if ((ref_omp_requires & OMP_REQ_UNIFIED_ADDRESS)
 	  && !(ns->omp_requires & OMP_REQ_UNIFIED_ADDRESS))
@@ -3732,7 +3732,8 @@ gfc_match_omp_requires (void)
       else
 	goto error;
 
-      if (requires_clause & ~OMP_REQ_ATOMIC_MEM_ORDER_MASK)
+      /* Currently, everything except 'dynamic_allocators' is allowed.  */
+      if (requires_clause == OMP_REQ_DYNAMIC_ALLOCATORS)
 	gfc_error_now ("Sorry, %qs clause at %L on REQUIRES directive is not "
 		       "yet supported", clause, &old_loc);
       if (!gfc_omp_requires_add_clause (requires_clause, clause, &old_loc, NULL))
diff --git a/gcc/fortran/parse.c b/gcc/fortran/parse.c
index bade7953acd..ef3e219a2d4 100644
--- a/gcc/fortran/parse.c
+++ b/gcc/fortran/parse.c
@@ -22,10 +22,12 @@ along with GCC; see the file COPYING3.  If not see
 #include "system.h"
 #include "coretypes.h"
 #include "options.h"
+#include "tree.h"
 #include "gfortran.h"
 #include <setjmp.h>
 #include "match.h"
 #include "parse.h"
+#include "omp-general.h"
 
 /* Current statement label.  Zero means no statement label.  Because new_st
    can get wiped during statement matching, we have to keep it separate.  */
@@ -6568,6 +6570,23 @@ done:
        gfc_current_ns = gfc_current_ns->sibling)
     gfc_check_omp_requires (gfc_current_ns, omp_requires);
 
+  if (omp_requires)
+    {
+      omp_requires_mask = (enum omp_requires) OMP_REQUIRES_TARGET_USED;
+      if (omp_requires & OMP_REQ_REVERSE_OFFLOAD)
+	omp_requires_mask
+	  = (enum omp_requires) (omp_requires_mask
+				 | OMP_REQUIRES_REVERSE_OFFLOAD);
+      if (omp_requires & OMP_REQ_UNIFIED_ADDRESS)
+	omp_requires_mask
+	  = (enum omp_requires) (omp_requires_mask
+				 | OMP_REQUIRES_UNIFIED_ADDRESS);
+      if (omp_requires & OMP_REQ_UNIFIED_SHARED_MEMORY)
+	omp_requires_mask
+	  = (enum omp_requires) (omp_requires_mask
+				 | OMP_REQUIRES_UNIFIED_SHARED_MEMORY);
+    }
+
   /* Do the parse tree dump.  */
   gfc_current_ns = flag_dump_fortran_original ? gfc_global_ns_list : NULL;
 
diff --git a/gcc/omp-offload.c b/gcc/omp-offload.c
index bb3bfd130ee..e2d99cb261b 100644
--- a/gcc/omp-offload.c
+++ b/gcc/omp-offload.c
@@ -418,6 +418,24 @@ omp_finish_file (void)
 
       varpool_node::finalize_decl (vars_decl);
       varpool_node::finalize_decl (funcs_decl);
+
+      if (flag_openmp && (omp_requires_mask & OMP_REQUIRES_TARGET_USED) != 0)
+	{
+	  const char *requires_section = ".gnu.gomp_requires";
+	  tree maskvar = build_decl (UNKNOWN_LOCATION, VAR_DECL,
+				     get_identifier (".gomp_requires_mask"),
+				     unsigned_type_node);
+	  SET_DECL_ALIGN (maskvar, TYPE_ALIGN (unsigned_type_node));
+	  TREE_STATIC (maskvar) = 1;
+	  DECL_INITIAL (maskvar)
+	    = build_int_cst (unsigned_type_node,
+			     ((unsigned int) omp_requires_mask
+			      & (OMP_REQUIRES_UNIFIED_ADDRESS
+				 | OMP_REQUIRES_UNIFIED_SHARED_MEMORY
+				 | OMP_REQUIRES_REVERSE_OFFLOAD)));
+	  set_decl_section_name (maskvar, requires_section);
+	  varpool_node::finalize_decl (maskvar);
+	}
     }
   else
     {
diff --git a/gcc/testsuite/c-c++-common/gomp/requires-4.c b/gcc/testsuite/c-c++-common/gomp/requires-4.c
index 88ba7746cf8..8f45d83ea6e 100644
--- a/gcc/testsuite/c-c++-common/gomp/requires-4.c
+++ b/gcc/testsuite/c-c++-common/gomp/requires-4.c
@@ -9,5 +9,3 @@ foo (void)
 #pragma omp requires unified_shared_memory	/* { dg-error "'unified_shared_memory' clause used lexically after first target construct or offloading API" } */
 #pragma omp requires unified_address	/* { dg-error "'unified_address' clause used lexically after first target construct or offloading API" } */
 #pragma omp requires reverse_offload	/* { dg-error "'reverse_offload' clause used lexically after first target construct or offloading API" } */
-
-/* { dg-prune-output "not supported yet" } */
diff --git a/gcc/testsuite/gfortran.dg/gomp/requires-4.f90 b/gcc/testsuite/gfortran.dg/gomp/requires-4.f90
index e0eb4dbc603..cc4bc3e7040 100644
--- a/gcc/testsuite/gfortran.dg/gomp/requires-4.f90
+++ b/gcc/testsuite/gfortran.dg/gomp/requires-4.f90
@@ -9,7 +9,7 @@ end module m
 subroutine foo
   !$omp target
   !$omp end target
-! { dg-error "OpenMP device constructs/routines but does not set !.OMP REQUIRES REVERSE_OFFSET but other program units do" "" { target *-*-* } 9 }
+! { dg-error "OpenMP device constructs/routines but does not set !.OMP REQUIRES REVERSE_OFFLOAD but other program units do" "" { target *-*-* } 9 }
 ! { dg-error "OpenMP device constructs/routines but does not set !.OMP REQUIRES UNIFIED_ADDRESS but other program units do" "" { target *-*-* } 9 }
 ! { dg-error "OpenMP device constructs/routines but does not set !.OMP REQUIRES UNIFIED_SHARED_MEMORY but other program units do" "" { target *-*-* } 9 }
 end
diff --git a/gcc/testsuite/gfortran.dg/gomp/requires-8.f90 b/gcc/testsuite/gfortran.dg/gomp/requires-8.f90
index 3c32ae9860e..3819b0c28cc 100644
--- a/gcc/testsuite/gfortran.dg/gomp/requires-8.f90
+++ b/gcc/testsuite/gfortran.dg/gomp/requires-8.f90
@@ -13,7 +13,7 @@ contains
  end subroutine foo
 end module m
 
-subroutine bar  ! { dg-error "has OpenMP device constructs/routines but does not set !.OMP REQUIRES REVERSE_OFFSET but other program units do" }
+subroutine bar  ! { dg-error "has OpenMP device constructs/routines but does not set !.OMP REQUIRES REVERSE_OFFLOAD but other program units do" }
   !use m
   !$omp requires unified_shared_memory
   !$omp declare target
diff --git a/include/gomp-constants.h b/include/gomp-constants.h
index d3d4514c84b..b8efb30b1e1 100644
--- a/include/gomp-constants.h
+++ b/include/gomp-constants.h
@@ -344,6 +344,12 @@ enum gomp_map_kind
 #define GOMP_DEPEND_INOUT		3
 #define GOMP_DEPEND_MUTEXINOUTSET	4
 
+/* Flag values for requires-directive features, must match corresponding
+   OMP_REQUIRES_* values in gcc/omp-general.h.  */
+#define GOMP_REQUIRES_UNIFIED_ADDRESS       0x10
+#define GOMP_REQUIRES_UNIFIED_SHARED_MEMORY 0x20
+#define GOMP_REQUIRES_REVERSE_OFFLOAD       0x80
+
 /* HSA specific data structures.  */
 
 /* Identifiers of device-specific target arguments.  */
diff --git a/libgcc/offloadstuff.c b/libgcc/offloadstuff.c
index 0bbe1c240e2..6caaaa09656 100644
--- a/libgcc/offloadstuff.c
+++ b/libgcc/offloadstuff.c
@@ -54,6 +54,9 @@ const void *const __offload_var_table[0]
   __attribute__ ((__used__, visibility ("hidden"),
 		  section (OFFLOAD_VAR_TABLE_SECTION_NAME))) = { };
 
+const unsigned int const __requires_mask_table[0]
+  __attribute__ ((__used__, section (".gnu.gomp_requires"))) = { };
+
 #elif defined CRT_END
 
 const void *const __offload_funcs_end[0]
@@ -63,6 +66,9 @@ const void *const __offload_vars_end[0]
   __attribute__ ((__used__, visibility ("hidden"),
 		  section (OFFLOAD_VAR_TABLE_SECTION_NAME))) = { };
 
+const unsigned int const __requires_mask_table_end[0]
+  __attribute__ ((__used__, section (".gnu.gomp_requires"))) = { };
+
 #elif defined CRT_TABLE
 
 extern const void *const __offload_func_table[];
@@ -77,6 +83,9 @@ const void *const __OFFLOAD_TABLE__[]
   &__offload_var_table, &__offload_vars_end
 };
 
+extern const unsigned int const __requires_mask_table[];
+extern const unsigned int const __requires_mask_table_end[];
+
 #else /* ! CRT_BEGIN && ! CRT_END && ! CRT_TABLE  */
 #error "One of CRT_BEGIN, CRT_END or CRT_TABLE must be defined."
 #endif
diff --git a/libgomp/libgomp-plugin.h b/libgomp/libgomp-plugin.h
index e8eebee55ec..43f62bad9b5 100644
--- a/libgomp/libgomp-plugin.h
+++ b/libgomp/libgomp-plugin.h
@@ -122,6 +122,7 @@ extern int GOMP_OFFLOAD_get_type (void);
 extern int GOMP_OFFLOAD_get_num_devices (void);
 extern bool GOMP_OFFLOAD_init_device (int);
 extern bool GOMP_OFFLOAD_fini_device (int);
+extern bool GOMP_OFFLOAD_supported_features (unsigned *);
 extern unsigned GOMP_OFFLOAD_version (void);
 extern int GOMP_OFFLOAD_load_image (int, unsigned, const void *,
 				    struct addr_pair **);
diff --git a/libgomp/libgomp.h b/libgomp/libgomp.h
index 096029fb8b0..c4efa1aa843 100644
--- a/libgomp/libgomp.h
+++ b/libgomp/libgomp.h
@@ -1180,6 +1180,7 @@ struct gomp_device_descr
   __typeof (GOMP_OFFLOAD_get_num_devices) *get_num_devices_func;
   __typeof (GOMP_OFFLOAD_init_device) *init_device_func;
   __typeof (GOMP_OFFLOAD_fini_device) *fini_device_func;
+  __typeof (GOMP_OFFLOAD_supported_features) *supported_features_func;
   __typeof (GOMP_OFFLOAD_version) *version_func;
   __typeof (GOMP_OFFLOAD_load_image) *load_image_func;
   __typeof (GOMP_OFFLOAD_unload_image) *unload_image_func;
diff --git a/libgomp/oacc-host.c b/libgomp/oacc-host.c
index 550c0b300fa..e61687755be 100644
--- a/libgomp/oacc-host.c
+++ b/libgomp/oacc-host.c
@@ -71,6 +71,12 @@ host_fini_device (int n __attribute__ ((unused)))
   return true;
 }
 
+static bool
+host_supported_features (unsigned int *n)
+{
+  return (*n == 0);
+}
+
 static unsigned
 host_version (void)
 {
@@ -297,6 +303,7 @@ static struct gomp_device_descr host_dispatch =
     .get_num_devices_func = host_get_num_devices,
     .init_device_func = host_init_device,
     .fini_device_func = host_fini_device,
+    .supported_features_func = host_supported_features,
     .version_func = host_version,
     .load_image_func = host_load_image,
     .unload_image_func = host_unload_image,
diff --git a/libgomp/plugin/plugin-gcn.c b/libgomp/plugin/plugin-gcn.c
index 24504a032c6..d2786c65138 100644
--- a/libgomp/plugin/plugin-gcn.c
+++ b/libgomp/plugin/plugin-gcn.c
@@ -4064,4 +4064,12 @@ GOMP_OFFLOAD_openacc_destroy_thread_data (void *data)
   free (data);
 }
 
+/* Indicate which GOMP_REQUIRES_* features are supported, currently none.  */
+
+bool
+GOMP_OFFLOAD_supported_features (unsigned int *mask)
+{
+  return (*mask == 0);
+}
+
 /* }}} */
diff --git a/libgomp/plugin/plugin-nvptx.c b/libgomp/plugin/plugin-nvptx.c
index d2ee232f4f6..942fb989bac 100644
--- a/libgomp/plugin/plugin-nvptx.c
+++ b/libgomp/plugin/plugin-nvptx.c
@@ -1233,6 +1233,14 @@ GOMP_OFFLOAD_fini_device (int n)
   return true;
 }
 
+/* Indicate which GOMP_REQUIRES_* features are supported, currently none.  */
+
+bool
+GOMP_OFFLOAD_supported_features (unsigned int *mask)
+{
+  return (*mask == 0);
+}
+
 /* Return the libgomp version number we're compatible with.  There is
    no requirement for cross-version compatibility.  */
 
diff --git a/libgomp/target.c b/libgomp/target.c
index 0c9fe58e14d..699dc72cb72 100644
--- a/libgomp/target.c
+++ b/libgomp/target.c
@@ -31,6 +31,7 @@
 #include "gomp-constants.h"
 #include <limits.h>
 #include <stdbool.h>
+#include <stdio.h>
 #include <stdlib.h>
 #ifdef HAVE_INTTYPES_H
 # include <inttypes.h>  /* For PRIu64.  */
@@ -96,6 +97,16 @@ static int num_devices;
 /* Number of GOMP_OFFLOAD_CAP_OPENMP_400 devices.  */
 static int num_devices_openmp;
 
+/* Mask of requires directive clause values, summarized from .gnu.gomp.requires
+   section. Offload plugins are queried with this mask to see if all required
+   features are supported.  */
+static unsigned int gomp_requires_mask;
+
+/* Start/end of .gnu.gomp.requires section of program, defined in
+   crtoffloadbegin/end.o.  */
+extern const unsigned int __requires_mask_table[];
+extern const unsigned int __requires_mask_table_end[];
+
 /* Similar to gomp_realloc, but release register_lock before gomp_fatal.  */
 
 static void *
@@ -2384,6 +2395,20 @@ gomp_init_device (struct gomp_device_descr *devicep)
       gomp_fatal ("device initialization failed");
     }
 
+  unsigned int features = gomp_requires_mask;
+  if (!devicep->supported_features_func (&features))
+    {
+      char buf[64], *end = buf + sizeof (buf), *p = buf;
+      if (features & GOMP_REQUIRES_UNIFIED_ADDRESS)
+	p += snprintf (p, end - p, "unified_address");
+      if (features & GOMP_REQUIRES_UNIFIED_SHARED_MEMORY)
+	p += snprintf (p, end - p, "%sunified_shared_memory",
+		       (p == buf ? "" : ", "));
+      if (features & GOMP_REQUIRES_REVERSE_OFFLOAD)
+	p += snprintf (p, end - p, "%sreverse_offload", (p == buf ? "" : ", "));
+      gomp_error ("device does not support required features: %s", buf);
+    }
+
   /* Load to device all images registered by the moment.  */
   for (i = 0; i < num_offload_images; i++)
     {
@@ -3664,6 +3689,7 @@ gomp_load_plugin_for_device (struct gomp_device_descr *device,
   DLSYM (get_num_devices);
   DLSYM (init_device);
   DLSYM (fini_device);
+  DLSYM (supported_features);
   DLSYM (load_image);
   DLSYM (unload_image);
   DLSYM (alloc);
@@ -3776,6 +3802,28 @@ gomp_target_init (void)
   if (gomp_target_offload_var == GOMP_TARGET_OFFLOAD_DISABLED)
     return;
 
+  gomp_requires_mask = 0;
+  const unsigned int *mask_ptr = __requires_mask_table;
+  bool error_emitted = false;
+  while (mask_ptr != __requires_mask_table_end)
+    {
+      if (gomp_requires_mask == 0)
+	gomp_requires_mask = *mask_ptr;
+      else if (gomp_requires_mask != *mask_ptr)
+	{
+	  if (!error_emitted)
+	    {
+	      gomp_error ("requires-directive clause inconsistency between "
+			  "compilation units detected");
+	      error_emitted = true;
+	    }
+	  /* This is inconsistent, but still merge to query for all features
+	     later.  */
+	  gomp_requires_mask |= *mask_ptr;
+	}
+      mask_ptr++;
+    }
+
   cur = OFFLOAD_PLUGINS;
   if (*cur)
     do
diff --git a/libgomp/testsuite/libgomp.c-c++-common/requires-1-aux.c b/libgomp/testsuite/libgomp.c-c++-common/requires-1-aux.c
new file mode 100644
index 00000000000..8b9341523c6
--- /dev/null
+++ b/libgomp/testsuite/libgomp.c-c++-common/requires-1-aux.c
@@ -0,0 +1,11 @@
+/* { dg-skip-if "" { *-*-* } } */
+
+#pragma omp requires reverse_offload
+
+int x;
+
+void foo (void)
+{
+  #pragma omp target
+  x = 1;
+}
diff --git a/libgomp/testsuite/libgomp.c-c++-common/requires-1.c b/libgomp/testsuite/libgomp.c-c++-common/requires-1.c
new file mode 100644
index 00000000000..02585adfb6f
--- /dev/null
+++ b/libgomp/testsuite/libgomp.c-c++-common/requires-1.c
@@ -0,0 +1,20 @@
+/* { dg-additional-sources requires-1-aux.c } */
+
+#pragma omp requires unified_shared_memory
+
+int a[10];
+extern void foo (void);
+
+int
+main (void)
+{
+  #pragma omp target
+  for (int i = 0; i < 10; i++)
+    a[i] = 0;
+
+  foo ();
+  return 0;
+}
+
+/* { dg-output "libgomp: requires-directive clause inconsistency between compilation units detected" } */
+/* { dg-prune-output "device does not support required features" } */
diff --git a/libgomp/testsuite/libgomp.c-c++-common/requires-2-aux.c b/libgomp/testsuite/libgomp.c-c++-common/requires-2-aux.c
new file mode 100644
index 00000000000..8b9341523c6
--- /dev/null
+++ b/libgomp/testsuite/libgomp.c-c++-common/requires-2-aux.c
@@ -0,0 +1,11 @@
+/* { dg-skip-if "" { *-*-* } } */
+
+#pragma omp requires reverse_offload
+
+int x;
+
+void foo (void)
+{
+  #pragma omp target
+  x = 1;
+}
diff --git a/libgomp/testsuite/libgomp.c-c++-common/requires-2.c b/libgomp/testsuite/libgomp.c-c++-common/requires-2.c
new file mode 100644
index 00000000000..0302f891c9c
--- /dev/null
+++ b/libgomp/testsuite/libgomp.c-c++-common/requires-2.c
@@ -0,0 +1,19 @@
+/* { dg-additional-sources requires-2-aux.c } */
+
+#pragma omp requires reverse_offload
+
+int a[10];
+extern void foo (void);
+
+int
+main (void)
+{
+  #pragma omp target
+  for (int i = 0; i < 10; i++)
+    a[i] = 0;
+
+  foo ();
+  return 0;
+}
+
+/* { dg-output "libgomp: device does not support required features: reverse_offload" } */
diff --git a/liboffloadmic/plugin/libgomp-plugin-intelmic.cpp b/liboffloadmic/plugin/libgomp-plugin-intelmic.cpp
index d1678d0514e..f92418fa416 100644
--- a/liboffloadmic/plugin/libgomp-plugin-intelmic.cpp
+++ b/liboffloadmic/plugin/libgomp-plugin-intelmic.cpp
@@ -233,6 +233,14 @@ GOMP_OFFLOAD_fini_device (int device)
   return true;
 }
 
+/* Indicate which GOMP_REQUIRES_* features are supported, currently none.  */
+
+extern "C" bool
+GOMP_OFFLOAD_supported_features (unsigned int *mask)
+{
+  return (*mask == 0);
+}
+
 static bool
 get_target_table (int device, int &num_funcs, int &num_vars, void **&table)
 {