[Clang][OpenMP] Fixed an issue that `target team` is emitted incorrectly

[tianshilei1992]

Summary

This patch is trying to fix the bug 47039 (https://bugs.llvm.org/show_bug.cgi?id=47039).
The root cause is, in clang, if NumTeams is not nullptr, it will emit call
to target teams, even if the value of NumTeams is 0. This is wrong, but at
least the team number is 0, so if the runtime can handle this correct, it should
still be fine. However, in the runtime, we only check the boolean variable
IsTeamConstruct, and don't check the team number. The last straw is, in CUDA
plugin, if the team number is 0, and the loop count is also 0, then it will set
the team number to a default value, which is 128 now.

In this patch, instead of emitting TeamNum of value 0, we emit nullptr
instead, which is spec conformant at least, aside from the discussion on the
weekly meeting that no team can also mean one team with one thread.

Failed tests will be fixed accordingly.

[tianshilei1992]

This patch is abandoned and will propose a new patch to unify interface of target and target teams.

clang/lib/CodeGen/CGOpenMPRuntime.cpp

emitNumTeamsForTargetDirective(CodeGenFunction &CGF,
   case OMPD_target: {
     const auto *CS = D.getInnermostCapturedStmt();
     const auto *Body =
         CS->getCapturedStmt()->IgnoreContainers(/*IgnoreCaptured=*/true);
     const Stmt *ChildStmt =
         CGOpenMPRuntime::getSingleCompoundChild(CGF.getContext(), Body);
     if (const auto *NestedDir =
             dyn_cast_or_null<OMPExecutableDirective>(ChildStmt)) {
-      if (isOpenMPTeamsDirective(NestedDir->getDirectiveKind())) {
-        if (NestedDir->hasClausesOfKind<OMPNumTeamsClause>()) {
-          CGOpenMPInnerExprInfo CGInfo(CGF, *CS);
-          CodeGenFunction::CGCapturedStmtRAII CapInfoRAII(CGF, &CGInfo);
-          const Expr *NumTeams =
-              NestedDir->getSingleClause<OMPNumTeamsClause>()->getNumTeams();
-          llvm::Value *NumTeamsVal =
-              CGF.EmitScalarExpr(NumTeams,
-                                 /*IgnoreResultAssign*/ true);
-          return Bld.CreateIntCast(NumTeamsVal, CGF.Int32Ty,
-                                   /*isSigned=*/true);
-        }
-        return Bld.getInt32(0);
-      }
-      if (isOpenMPParallelDirective(NestedDir->getDirectiveKind()) ||
+      if (isOpenMPTeamsDirective(NestedDir->getDirectiveKind()) &&
+          NestedDir->hasClausesOfKind<OMPNumTeamsClause>()) {
+      } else if (isOpenMPParallelDirective(NestedDir->getDirectiveKind()) ||
                  isOpenMPSimdDirective(NestedDir->getDirectiveKind()))
         return Bld.getInt32(1);
-      return Bld.getInt32(0);
     }
     return nullptr;
   }
   case OMPD_target_teams:
   case OMPD_target_teams_distribute:
   case OMPD_target_teams_distribute_simd:
   case OMPD_target_teams_distribute_parallel_for:
   case OMPD_target_teams_distribute_parallel_for_simd: {