[Clang][OpenMP] Support for omp nothing

[koops]

Summary

Patch to support "#pragma omp nothing"

[tianshilei1992]

Can we have test for right usage?

clang/lib/Parse/ParseOpenMP.cpp

2496

clang-format plz, and remove the { and } as there is only one statement.

[koops]

changes to support clang format.

[koops]

In D123286#3513797, @tianshilei1992 wrote:

Can we have test for right usage?

I do not understand "test for right usage". From the specifications the only right usage for "omp nothing" will be in the metadirective. If you have meeting notes when "omp nothing" was framed please share it.

[koops]

In D123286#3527374, @koops wrote:

In D123286#3513797, @tianshilei1992 wrote:

Can we have test for right usage?

I do not understand "test for right usage". From the specifications the only right usage for "omp nothing" will be in the metadirective. If you have meeting notes when "omp nothing" was framed please share it.

In gcc sources support "#pragma omp nothing" has been implemented. Test cases for it are in:

gcc/gcc/testsuite/c-c++-common/gomp/nothing-1.c
gcc/gcc/testsuite/c-c++-common/gomp/nothing-2.c

These 2 test cases indicate a similar kind of test cases as those which have been added in this support for "omp nothing". There does not seem to be a test for right usage.

[tianshilei1992]

LG

clang/lib/Basic/OpenMPKinds.cpp

case OMPD_target_teams_distribute_parallel_for_simd:
     CaptureRegions.push_back(OMPD_task);
     CaptureRegions.push_back(OMPD_target);
     CaptureRegions.push_back(OMPD_teams);
     CaptureRegions.push_back(OMPD_parallel);
     break;
   case OMPD_teams_loop:
     CaptureRegions.push_back(OMPD_teams);
     break;
+  case OMPD_nothing:
+    CaptureRegions.push_back(OMPD_nothing);
+    break;
   case OMPD_loop:
     // TODO: 'loop' may require different capture regions depending on the bind
     // clause or the parent directive when there is no bind clause. Use
     // OMPD_unknown for now.
   case OMPD_simd:
   case OMPD_for:
   case OMPD_for_simd:
   case OMPD_sections:

clang/lib/Parse/ParseOpenMP.cpp

StmtResult Parser::ParseOpenMPDeclarativeOrExecutableDirective(
   }
   OpenMPDirectiveKind CancelRegion = OMPD_unknown;
   // Name of critical directive.
   DeclarationNameInfo DirName;
   StmtResult Directive = StmtError();
   bool HasAssociatedStatement = true;
 
   switch (DKind) {
+  case OMPD_nothing:
+    if ((StmtCtx & ParsedStmtContext::AllowStandaloneOpenMPDirectives) ==
+        ParsedStmtContext()) {
+      Diag(Tok, diag::err_omp_immediate_directive)
+        << getOpenMPDirectiveName(DKind) << 0;
+    }
+    ConsumeToken();
+    skipUntilPragmaOpenMPEnd(DKind);
+    if (Tok.is(tok::annot_pragma_openmp_end))
+      ConsumeAnnotationToken();
+    break;
   case OMPD_metadirective: {
     ConsumeToken();
     SmallVector<VariantMatchInfo, 4> VMIs;
 
     // First iteration of parsing all clauses of metadirective.
     // This iteration only parses and collects all context selector ignoring the
     // associated directives.
     TentativeParsingAction TPA(*this);

clang/test/OpenMP/nothing_messages.cpp

+// RUN: %clang_cc1 -verify=expected -fopenmp -ferror-limit 100 %s -Wuninitialized
+
+int mixed() {
+  int x = 0;
+  int d = 4;
+  
+#pragma omp nothing
+  x=d;
+
+  if(!x) {
+#pragma omp nothing
+    x=d;
+  }
+
+// expected-error@+2 {{#pragma omp nothing' cannot be an immediate substatement}}
+  if(!x)
+#pragma omp nothing
+    x=d;
+
+// expected-warning@+2 {{extra tokens at the end of '#pragma omp nothing' are ignored}}
+  if(!x) {
+#pragma omp nothing seq_cst
+    x=d;
+  }
+
+  return 0;
+}

llvm/include/llvm/Frontend/OpenMP/OMP.td

let allowedClauses = [
     //
     // TODO: Correct this supprted version number whenever complete
     // implementation of reverse_offload is available.
     VersionedClause<OMPC_ReverseOffload, 99>,
     VersionedClause<OMPC_DynamicAllocators>,
     VersionedClause<OMPC_AtomicDefaultMemOrder>
   ];
 }
+def OMP_Nothing : Directive<"nothing"> {}
 def OMP_TargetData : Directive<"target data"> {
   let allowedClauses = [
     VersionedClause<OMPC_UseDevicePtr>,
     VersionedClause<OMPC_UseDeviceAddr, 50>
   ];
   let allowedOnceClauses = [
     VersionedClause<OMPC_Device>,
     VersionedClause<OMPC_If>