openmp: Add nothing directive support

As has been clarified, it is intentional that nothing directive is accepted
in substatements of selection and looping statements and after labels and
is handled as if the directive just isn't there, so that
void
foo (int x)
{
  if (x)
    #pragma omp metadirective when (...:nothing) when (...:parallel)
    bar ();
}
behaves consistently; declarative and stand-alone directives aren't allowed
at that point, but constructs are parsed with the following statement as
the construct body and nothing or missing default on metadirective therefore
should handle the following statement as part of the if substatement instead
of having nothing as the substatement and bar done unconditionally after the
if.

2021-08-18  Jakub Jelinek  <jakub@redhat.com>

gcc/c-family/
	* c-pragma.h (enum pragma_kind): Add PRAGMA_OMP_NOTHING.
	* c-pragma.c (omp_pragmas): Add nothing directive.
	* c-omp.c (omp_directives): Uncomment nothing directive entry.
gcc/c/
	* c-parser.c (c_parser_omp_nothing): New function.
	(c_parser_pragma): Handle PRAGMA_OMP_NOTHING.
gcc/cp/
	* parser.c (cp_parser_omp_nothing): New function.
	(cp_parser_pragma): Handle PRAGMA_OMP_NOTHING.
gcc/testsuite/
	* c-c++-common/gomp/nothing-1.c: New test.
	* g++.dg/gomp/attrs-1.C (bar): Add nothing directive test.
	* g++.dg/gomp/attrs-2.C (bar): Likewise.
	* g++.dg/gomp/attrs-9.C: Likewise.
libgomp/
	* testsuite/libgomp.c-c++-common/nothing-1.c: New test.

9 files changed, 73 insertions, 2 deletions

diff --git a/gcc/c-family/c-omp.c b/gcc/c-family/c-omp.c
index de49d26..d4e98bf 100644
--- a/gcc/c-family/c-omp.c
+++ b/gcc/c-family/c-omp.c
@@ -3007,8 +3007,8 @@ static const struct c_omp_directive omp_directives[] = {
     C_OMP_DIR_CONSTRUCT, true },
   /* { "metadirective", nullptr, nullptr, PRAGMA_OMP_METADIRECTIVE,
     C_OMP_DIR_???, ??? },  */
-  /* { "nothing", nullptr, nullptr, PRAGMA_OMP_NOTHING,
-    C_OMP_DIR_UTILITY, false },  */
+  { "nothing", nullptr, nullptr, PRAGMA_OMP_NOTHING,
+    C_OMP_DIR_UTILITY, false },
   /* ordered with depend clause is C_OMP_DIR_STANDALONE.  */
   { "ordered", nullptr, nullptr, PRAGMA_OMP_ORDERED,
     C_OMP_DIR_CONSTRUCT, true },
diff --git a/gcc/c-family/c-pragma.c b/gcc/c-family/c-pragma.c
index 5f0096f..238309d 100644
--- a/gcc/c-family/c-pragma.c
+++ b/gcc/c-family/c-pragma.c
@@ -1328,6 +1328,7 @@ static const struct omp_pragma_def omp_pragmas[] = {
   { "depobj", PRAGMA_OMP_DEPOBJ },
   { "end", PRAGMA_OMP_END_DECLARE_TARGET },
   { "flush", PRAGMA_OMP_FLUSH },
+  { "nothing", PRAGMA_OMP_NOTHING },
   { "requires", PRAGMA_OMP_REQUIRES },
   { "scope", PRAGMA_OMP_SCOPE },
   { "section", PRAGMA_OMP_SECTION },
diff --git a/gcc/c-family/c-pragma.h b/gcc/c-family/c-pragma.h
index 2b9e5ea..dc9e8a6 100644
--- a/gcc/c-family/c-pragma.h
+++ b/gcc/c-family/c-pragma.h
@@ -57,6 +57,7 @@ enum pragma_kind {
   PRAGMA_OMP_FLUSH,
   PRAGMA_OMP_FOR,
   PRAGMA_OMP_LOOP,
+  PRAGMA_OMP_NOTHING,
   PRAGMA_OMP_MASKED,
   PRAGMA_OMP_MASTER,
   PRAGMA_OMP_ORDERED,
diff --git a/gcc/c/c-parser.c b/gcc/c/c-parser.c
index 565efc4..d5f51b1 100644
--- a/gcc/c/c-parser.c
+++ b/gcc/c/c-parser.c
@@ -1578,6 +1578,7 @@ static tree c_parser_omp_for_loop (location_t, c_parser *, enum tree_code,
 static void c_parser_omp_taskwait (c_parser *);
 static void c_parser_omp_taskyield (c_parser *);
 static void c_parser_omp_cancel (c_parser *);
+static void c_parser_omp_nothing (c_parser *);
 
 enum pragma_context { pragma_external, pragma_struct, pragma_param,
 		      pragma_stmt, pragma_compound };
@@ -12480,6 +12481,10 @@ c_parser_pragma (c_parser *parser, enum pragma_context context, bool *if_p)
       c_parser_omp_requires (parser);
       return false;
 
+    case PRAGMA_OMP_NOTHING:
+      c_parser_omp_nothing (parser);
+      return false;
+
     case PRAGMA_OMP_ORDERED:
       return c_parser_omp_ordered (parser, context, if_p);
 
@@ -21908,6 +21913,16 @@ c_parser_omp_taskloop (location_t loc, c_parser *parser,
   return ret;
 }
 
+/* OpenMP 5.1
+   #pragma omp nothing new-line  */
+
+static void
+c_parser_omp_nothing (c_parser *parser)
+{
+  c_parser_consume_pragma (parser);
+  c_parser_skip_to_pragma_eol (parser);
+}
+
 /* Main entry point to parsing most OpenMP pragmas.  */
 
 static void
diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index 8f2d0fc..04116fb 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -45564,6 +45564,16 @@ cp_parser_omp_requires (cp_parser *parser, cp_token *pragma_tok)
 }
 
 
+/* OpenMP 5.1:
+   #pragma omp nothing new-line  */
+
+static void
+cp_parser_omp_nothing (cp_parser *parser, cp_token *pragma_tok)
+{
+  cp_parser_skip_to_pragma_eol (parser, pragma_tok);
+}
+
+
 /* OpenMP 4.5:
    #pragma omp taskloop taskloop-clause[optseq] new-line
      for-loop
@@ -46673,6 +46683,10 @@ cp_parser_pragma (cp_parser *parser, enum pragma_context context, bool *if_p)
 	}
       return cp_parser_omp_requires (parser, pragma_tok);
 
+    case PRAGMA_OMP_NOTHING:
+      cp_parser_omp_nothing (parser, pragma_tok);
+      return false;
+
     case PRAGMA_OMP_ORDERED:
       if (context != pragma_stmt && context != pragma_compound)
 	goto bad_stmt;
diff --git a/gcc/testsuite/c-c++-common/gomp/nothing-1.c b/gcc/testsuite/c-c++-common/gomp/nothing-1.c
new file mode 100644
index 0000000..d50c92a
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/gomp/nothing-1.c
@@ -0,0 +1,37 @@
+#pragma omp nothing
+
+struct S
+{
+  #pragma omp nothing
+  int s;
+};
+
+int
+foo (int i)
+{
+  #pragma omp nothing
+  if (0)
+    #pragma omp nothing
+    i++;
+  if (1)
+    ;
+  else
+    #pragma omp nothing
+    i++;
+  switch (0)
+    #pragma omp nothing
+    {
+    default:
+      break;
+    }
+  while (0)
+    #pragma omp nothing
+    i++;
+  for (; 0;)
+    #pragma omp nothing
+    i++;
+  lab:
+  #pragma omp nothing
+  i++;
+  return i;
+}
diff --git a/gcc/testsuite/g++.dg/gomp/attrs-1.C b/gcc/testsuite/g++.dg/gomp/attrs-1.C
index 686acf5..435d54f 100644
--- a/gcc/testsuite/g++.dg/gomp/attrs-1.C
+++ b/gcc/testsuite/g++.dg/gomp/attrs-1.C
@@ -111,6 +111,7 @@ void
 bar (int d, int m, int i1, int i2, int i3, int p, int *idp, int s,
      int nte, int tl, int nth, int g, int nta, int fi, int pp, int *q, int *dd, int ntm)
 {
+  [[omp::directive (nothing)]];
   [[omp::directive (for simd
     private (p) firstprivate (f) lastprivate (l) linear (ll:1) reduction(+:r) schedule(static, 4) collapse(1) nowait
     safelen(8) simdlen(4) aligned(q: 32) nontemporal(ntm) if(i1) order(concurrent) allocate (f))]]
diff --git a/gcc/testsuite/g++.dg/gomp/attrs-2.C b/gcc/testsuite/g++.dg/gomp/attrs-2.C
index 2190457..bea657f 100644
--- a/gcc/testsuite/g++.dg/gomp/attrs-2.C
+++ b/gcc/testsuite/g++.dg/gomp/attrs-2.C
@@ -111,6 +111,7 @@ void
 bar (int d, int m, int i1, int i2, int i3, int p, int *idp, int s,
      int nte, int tl, int nth, int g, int nta, int fi, int pp, int *q, int *dd, int ntm)
 {
+  [[omp::directive (nothing)]];
   [[omp::directive (for simd,
     private (p),firstprivate (f),lastprivate (l),linear (ll:1),reduction(+:r),schedule(static, 4),collapse(1),nowait,
     safelen(8),simdlen(4),aligned(q: 32),nontemporal(ntm),if(i1),order(concurrent),allocate (f))]]
diff --git a/gcc/testsuite/g++.dg/gomp/attrs-9.C b/gcc/testsuite/g++.dg/gomp/attrs-9.C
index 0af556c..08cd2b1 100644
--- a/gcc/testsuite/g++.dg/gomp/attrs-9.C
+++ b/gcc/testsuite/g++.dg/gomp/attrs-9.C
@@ -13,3 +13,4 @@ int b, c;
 int d;
 [[omp::directive (end declare target)]];
 [[omp::directive (end declare target)]];
+[[omp::directive (nothing)]];