Hi,

this patch adds support for the 'seq_cst' memory order clause on the
'flush' directive which was introduced in OpenMP 5.1 (p.275ff of the
OpenMP 5.1 Specification):

"If neither memory-order-clause nor a list appears on the flush
construct then the behavior is as if memory-order-clause is seq_cst.

A flush construct with the seq_cst clause, executed on a given thread,
operates as if all data storage blocks that are accessible to the thread
are flushed by a strong flush operation.

...

An implementation may implement a flush construct with a list by
ignoring the list and treating it the same as a flush construct with the
seq_cst clause."

I am not completely sure about the correct memory model specification:
"MEMMODEL_SYNC_SEQ_CST" vs. "MEMMODEL_SEQ_CST".
As "MEMMODEL_SYNC_SEQ_CST" is already used for flush without a clause
(that should behave in the same way than using seq_cst), see
expand_builtin_sync_synchronize in gcc/builtins.c, and regarding the
discussion in https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65697 I found
it appropriate to use "MEMMODEL_SYNC_SEQ_CST" in order to guarantee a
strong flush.

I tested on x86_64-linux with nvptx offloading with no regressions.

Marcel



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C, C++, Fortran, OpenMP: Add support for 'flush seq_cst' construct.

This patch adds support for the 'seq_cst' memory order clause on the 'flush'
directive which was introduced in OpenMP 5.1.

gcc/c-family/ChangeLog:

        * c-omp.c (c_finish_omp_flush): Handle MEMMODEL_SEQ_CST.

gcc/c/ChangeLog:

        * c-parser.c (c_parser_omp_flush): Parse 'seq_cst' clause on 'flush' 
        directive.

gcc/cp/ChangeLog:

        * parser.c (cp_parser_omp_flush): Parse 'seq_cst' clause on 'flush'
        directive.
        * semantics.c (finish_omp_flush): Handle MEMMODEL_SEQ_CST.

gcc/fortran/ChangeLog:

        * openmp.c (gfc_match_omp_flush): Parse 'seq_cst' clause on 'flush'
        directive.
        * trans-openmp.c (gfc_trans_omp_flush): Handle OMP_MEMORDER_SEQ_CST.

gcc/testsuite/ChangeLog:

        * c-c++-common/gomp/flush-1.c: Add test case for 'seq_cst'.
        * c-c++-common/gomp/flush-2.c: Add test case for 'seq_cst'.
        * g++.dg/gomp/attrs-1.C:  Adapt test to handle all flush clauses.
        * gfortran.dg/gomp/flush-1.f90:  Add test case for 'seq_cst'.
        * gfortran.dg/gomp/flush-2.f90:  Add test case for 'seq_cst'.

diff --git a/gcc/c-family/c-omp.c b/gcc/c-family/c-omp.c
index 18de7e4..4b95fc1 100644
--- a/gcc/c-family/c-omp.c
+++ b/gcc/c-family/c-omp.c
@@ -606,7 +606,7 @@ c_finish_omp_flush (location_t loc, int mo)
 {
   tree x;
 
-  if (mo == MEMMODEL_LAST)
+  if (mo == MEMMODEL_LAST || mo == MEMMODEL_SEQ_CST)
     {
       x = builtin_decl_explicit (BUILT_IN_SYNC_SYNCHRONIZE);
       x = build_call_expr_loc (loc, x, 0);
diff --git a/gcc/c/c-parser.c b/gcc/c/c-parser.c
index 3b1d10f..4d074ec 100644
--- a/gcc/c/c-parser.c
+++ b/gcc/c/c-parser.c
@@ -18339,7 +18339,9 @@ c_parser_omp_flush (c_parser *parser)
       const char *p
        = IDENTIFIER_POINTER (c_parser_peek_token (parser)->value);
 
-      if (!strcmp (p, "acq_rel"))
+      if (!strcmp (p, "seq_cst"))
+       mo = MEMMODEL_SEQ_CST;
+      else if (!strcmp (p, "acq_rel"))
        mo = MEMMODEL_ACQ_REL;
       else if (!strcmp (p, "release"))
        mo = MEMMODEL_RELEASE;
@@ -18347,7 +18349,8 @@ c_parser_omp_flush (c_parser *parser)
        mo = MEMMODEL_ACQUIRE;
       else
        error_at (c_parser_peek_token (parser)->location,
-                 "expected %<acq_rel%>, %<release%> or %<acquire%>");
+                 "expected %<seq_cst%>, %<acq_rel%>, %<release%> or "
+                 "%<acquire%>");
       c_parser_consume_token (parser);
     }
   if (c_parser_next_token_is (parser, CPP_OPEN_PAREN))
diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index ea71f9c..f9c2c8a 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -40742,7 +40742,9 @@ cp_parser_omp_flush (cp_parser *parser, cp_token 
*pragma_tok)
     {
       tree id = cp_lexer_peek_token (parser->lexer)->u.value;
       const char *p = IDENTIFIER_POINTER (id);
-      if (!strcmp (p, "acq_rel"))
+      if (!strcmp (p, "seq_cst"))
+       mo = MEMMODEL_SEQ_CST;
+      else if (!strcmp (p, "acq_rel"))
        mo = MEMMODEL_ACQ_REL;
       else if (!strcmp (p, "release"))
        mo = MEMMODEL_RELEASE;
@@ -40750,7 +40752,8 @@ cp_parser_omp_flush (cp_parser *parser, cp_token 
*pragma_tok)
        mo = MEMMODEL_ACQUIRE;
       else
        error_at (cp_lexer_peek_token (parser->lexer)->location,
-                 "expected %<acq_rel%>, %<release%> or %<acquire%>");
+                 "expected %<seq_cst%>, %<acq_rel%>, %<release%> or "
+                 "%<acquire%>");
       cp_lexer_consume_token (parser->lexer);
     }
   if (cp_lexer_next_token_is (parser->lexer, CPP_OPEN_PAREN))
diff --git a/gcc/cp/semantics.c b/gcc/cp/semantics.c
index f4b042f..8b78e89 100644
--- a/gcc/cp/semantics.c
+++ b/gcc/cp/semantics.c
@@ -10039,7 +10039,7 @@ finish_omp_flush (int mo)
 {
   tree fn = builtin_decl_explicit (BUILT_IN_SYNC_SYNCHRONIZE);
   releasing_vec vec;
-  if (mo != MEMMODEL_LAST)
+  if (mo != MEMMODEL_LAST && mo != MEMMODEL_SEQ_CST)
     {
       fn = builtin_decl_explicit (BUILT_IN_ATOMIC_THREAD_FENCE);
       vec->quick_push (build_int_cst (integer_type_node, mo));
diff --git a/gcc/fortran/openmp.c b/gcc/fortran/openmp.c
index 64ecd54..a64b7f5 100644
--- a/gcc/fortran/openmp.c
+++ b/gcc/fortran/openmp.c
@@ -3782,7 +3782,9 @@ gfc_match_omp_flush (void)
   enum gfc_omp_memorder mo = OMP_MEMORDER_UNSET;
   if (gfc_match_omp_eos () == MATCH_NO && gfc_peek_ascii_char () != '(')
     {
-      if (gfc_match ("acq_rel") == MATCH_YES)
+      if (gfc_match ("seq_cst") == MATCH_YES)
+       mo = OMP_MEMORDER_SEQ_CST;
+      else if (gfc_match ("acq_rel") == MATCH_YES)
        mo = OMP_MEMORDER_ACQ_REL;
       else if (gfc_match ("release") == MATCH_YES)
        mo = OMP_MEMORDER_RELEASE;
@@ -3790,7 +3792,7 @@ gfc_match_omp_flush (void)
        mo = OMP_MEMORDER_ACQUIRE;
       else
        {
-         gfc_error ("Expected AQC_REL, RELEASE, or ACQUIRE at %C");
+         gfc_error ("Expected SEQ_CST, AQC_REL, RELEASE, or ACQUIRE at %C");
          return MATCH_ERROR;
        }
       c = gfc_get_omp_clauses ();
diff --git a/gcc/fortran/trans-openmp.c b/gcc/fortran/trans-openmp.c
index 6f9b0e3..e55e0c8 100644
--- a/gcc/fortran/trans-openmp.c
+++ b/gcc/fortran/trans-openmp.c
@@ -5413,7 +5413,8 @@ gfc_trans_omp_flush (gfc_code *code)
 {
   tree call;
   if (!code->ext.omp_clauses
-      || code->ext.omp_clauses->memorder == OMP_MEMORDER_UNSET)
+      || code->ext.omp_clauses->memorder == OMP_MEMORDER_UNSET
+      || code->ext.omp_clauses->memorder == OMP_MEMORDER_SEQ_CST)
     {
       call = builtin_decl_explicit (BUILT_IN_SYNC_SYNCHRONIZE);
       call = build_call_expr_loc (input_location, call, 0);
diff --git a/gcc/testsuite/c-c++-common/gomp/flush-1.c 
b/gcc/testsuite/c-c++-common/gomp/flush-1.c
index 7c3e529..717b951 100644
--- a/gcc/testsuite/c-c++-common/gomp/flush-1.c
+++ b/gcc/testsuite/c-c++-common/gomp/flush-1.c
@@ -1,4 +1,5 @@
 /* { dg-additional-options "-fdump-tree-gimple" } */
+/* { dg-final { scan-tree-dump "foo \\(6\\);\[\n\r]*  __sync_synchronize 
\\(\\);\[\n\r]*  foo \\(6\\);" "gimple" } } */
 /* { dg-final { scan-tree-dump "foo \\(4\\);\[\n\r]*  __atomic_thread_fence 
\\(4\\);\[\n\r]*  foo \\(4\\);" "gimple" } } */
 /* { dg-final { scan-tree-dump "foo \\(3\\);\[\n\r]*  __atomic_thread_fence 
\\(3\\);\[\n\r]*  foo \\(3\\);" "gimple" } } */
 /* { dg-final { scan-tree-dump "foo \\(2\\);\[\n\r]*  __atomic_thread_fence 
\\(2\\);\[\n\r]*  foo \\(2\\);" "gimple" } } */
@@ -37,3 +38,11 @@ f4 (void)
   #pragma omp flush
   foo (5);
 }
+
+void
+f5 (void)
+{
+  foo (6);
+  #pragma omp flush seq_cst
+  foo (6);
+}
diff --git a/gcc/testsuite/c-c++-common/gomp/flush-2.c 
b/gcc/testsuite/c-c++-common/gomp/flush-2.c
index 00baa8a..30ef598 100644
--- a/gcc/testsuite/c-c++-common/gomp/flush-2.c
+++ b/gcc/testsuite/c-c++-common/gomp/flush-2.c
@@ -8,10 +8,11 @@ foo (void)
   #pragma omp flush acquire
   #pragma omp flush release
   #pragma omp flush acq_rel
-  #pragma omp flush relaxed            /* { dg-error "expected 'acq_rel', 
'release' or 'acquire'" } */
-  #pragma omp flush seq_cst            /* { dg-error "expected 'acq_rel', 
'release' or 'acquire'" } */
-  #pragma omp flush foobar             /* { dg-error "expected 'acq_rel', 
'release' or 'acquire'" } */
+  #pragma omp flush seq_cst
+  #pragma omp flush relaxed            /* { dg-error "expected 'seq_cst', 
'acq_rel', 'release' or 'acquire'" } */
+  #pragma omp flush foobar             /* { dg-error "expected 'seq_cst', 
'acq_rel', 'release' or 'acquire'" } */
   #pragma omp flush acquire (a, b)     /* { dg-error "'flush' list specified 
together with memory order clause" } */
   #pragma omp flush release (a, b)     /* { dg-error "'flush' list specified 
together with memory order clause" } */
   #pragma omp flush acq_rel (a, b)     /* { dg-error "'flush' list specified 
together with memory order clause" } */
+  #pragma omp flush seq_cst (a, b)     /* { dg-error "'flush' list specified 
together with memory order clause" } */
 }
diff --git a/gcc/testsuite/g++.dg/gomp/attrs-1.C 
b/gcc/testsuite/g++.dg/gomp/attrs-1.C
index cd20845..c871c51 100644
--- a/gcc/testsuite/g++.dg/gomp/attrs-1.C
+++ b/gcc/testsuite/g++.dg/gomp/attrs-1.C
@@ -528,6 +528,12 @@ bar (int d, int m, int i1, int i2, int i3, int p, int 
*idp, int s,
   ;
   [[omp::directive (flush acq_rel)]]
   ;
+  [[omp::directive (flush acquire)]]
+  ;
+  [[omp::directive (flush release)]]
+  ;
+  [[omp::directive (flush seq_cst)]]
+  ;
   [[omp::directive (flush (p, f))]]
   ;
   [[omp::directive (simd
diff --git a/gcc/testsuite/gfortran.dg/gomp/flush-1.f90 
b/gcc/testsuite/gfortran.dg/gomp/flush-1.f90
index d0b7f9e..904bb1d 100644
--- a/gcc/testsuite/gfortran.dg/gomp/flush-1.f90
+++ b/gcc/testsuite/gfortran.dg/gomp/flush-1.f90
@@ -1,4 +1,5 @@
 ! { dg-additional-options "-fdump-tree-gimple" }
+! { dg-final { scan-tree-dump "foo \\(6\\);\[\n\r]*  __sync_synchronize 
\\(\\);\[\n\r]*  foo \\(6\\);" "gimple" } }
 ! { dg-final { scan-tree-dump "foo \\(4\\);\[\n\r]*  __atomic_thread_fence 
\\(4\\);\[\n\r]*  foo \\(4\\);" "gimple" } }
 ! { dg-final { scan-tree-dump "foo \\(3\\);\[\n\r]*  __atomic_thread_fence 
\\(3\\);\[\n\r]*  foo \\(3\\);" "gimple" } }
 ! { dg-final { scan-tree-dump "foo \\(2\\);\[\n\r]*  __atomic_thread_fence 
\\(2\\);\[\n\r]*  foo \\(2\\);" "gimple" } }
@@ -39,3 +40,10 @@ subroutine f4
   !$omp flush
   call foo (5)
 end
+
+subroutine f5
+  use m
+  call foo (6)
+  !$omp flush seq_cst
+  call foo (6)
+end
diff --git a/gcc/testsuite/gfortran.dg/gomp/flush-2.f90 
b/gcc/testsuite/gfortran.dg/gomp/flush-2.f90
index 6857371..ba23444 100644
--- a/gcc/testsuite/gfortran.dg/gomp/flush-2.f90
+++ b/gcc/testsuite/gfortran.dg/gomp/flush-2.f90
@@ -9,10 +9,11 @@ subroutine foo (void)
   !$omp flush acquire
   !$omp flush release
   !$omp flush acq_rel
-  !$omp flush relaxed          ! { dg-error "Expected AQC_REL, RELEASE, or 
ACQUIRE" }
-  !$omp flush seq_cst          ! { dg-error "Expected AQC_REL, RELEASE, or 
ACQUIRE" }
-  !$omp flush foobar           ! { dg-error "Expected AQC_REL, RELEASE, or 
ACQUIRE" }
+  !$omp flush seq_cst
+  !$omp flush relaxed          ! { dg-error "Expected SEQ_CST, AQC_REL, 
RELEASE, or ACQUIRE" }
+  !$omp flush foobar           ! { dg-error "Expected SEQ_CST, AQC_REL, 
RELEASE, or ACQUIRE" }
   !$omp flush acquire (a, b)   ! { dg-error "List specified together with 
memory order clause in FLUSH directive" }
   !$omp flush release (a, b)   ! { dg-error "List specified together with 
memory order clause in FLUSH directive" }
   !$omp flush acq_rel (a, b)   ! { dg-error "List specified together with 
memory order clause in FLUSH directive" }
-end
+  !$omp flush seq_cst (a, b)   ! { dg-error "List specified together with 
memory order clause in FLUSH directive" }
+  end

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