[AbstractAttributor] Fold __kmpc_parallel_level if possible

[tianshilei1992]

Summary

Similar to D105787, this patch tries to fold __kmpc_parallel_level if possible.
Note that __kmpc_parallel_level doesn't take activeness into consideration,
based on current deviceRTLs, its return value can be such as 0, 1, 2, instead
of 0, 129, 130, etc. that also indicate activeness.

[tianshilei1992]

llvm/lib/Transforms/IPO/OpenMPOpt.cpp

450–452

These changes are covered by D106149, which will not be part of this patch eventually.

[tianshilei1992]

rebase

[tianshilei1992]

add missing feature and a trivial test case

[tianshilei1992]

llvm/lib/Transforms/IPO/OpenMPOpt.cpp

3415

The logic seems problematic here. Need to revise later.

llvm/test/Transforms/OpenMP/parallel_level_fold.ll

2

The enhancement of the test case is still WIP.

[tianshilei1992]

add assertion

[jdoerfert]

add noinline to the microtrask function to avoid us accidentally doing the wrong thing. I'll put a patch up that removes those noinline in the module pass.

[tianshilei1992]

more conservative

[tianshilei1992]

rebase

[jdoerfert]

llvm/lib/Transforms/IPO/OpenMPOpt.cpp

3433

3833

3852

[tianshilei1992]

llvm/lib/Transforms/IPO/OpenMPOpt.cpp

3433

Seems unnecessary because this variable is only written in the function call but I can do it.

[tianshilei1992]

rebase and fixed comments

[jdoerfert]

LG, some minor comments below.

llvm/lib/Transforms/IPO/OpenMPOpt.cpp

3415

mark __kmpc_parallel_51 as noinline to make this sound.

3845

3867–3868

[tianshilei1992]

fix comments

[tianshilei1992]

llvm/lib/Transforms/IPO/OpenMPOpt.cpp

3845

I changed this a little bit. If CallerKernelInfoAA.ParallelLevels is empty, we can only tell we currently cannot fold it, but it doesn't mean it cannot be folded in the future. If the size is more than 1, yeah, definitely it is pessimistic.

[tianshilei1992]

rebase

[jdoerfert]

llvm/lib/Transforms/IPO/OpenMPOpt.cpp

3871

not nullptr but it shuld continue to be none

[tianshilei1992]

llvm/lib/Transforms/IPO/OpenMPOpt.cpp

3871

Aha, I recall it. Yeah, will do it.

[tianshilei1992]

rebase and fix comments

[tianshilei1992]

update

[tianshilei1992]

add __attribute__((noinline)) to __kmpc_parallel_level

[jhuber6]

openmp/libomptarget/deviceRTLs/interface.h

444–448

Isn't there a NOINLINE definition in target_impl.h?

[tianshilei1992]

rebase

[tianshilei1992]

rebase and update

llvm/lib/Transforms/IPO/OpenMPOpt.cpp

#include "llvm/Frontend/OpenMP/OMPKinds.def"
   /// Collection of known kernels (\see Kernel) in the module.
   SmallPtrSetImpl<Kernel> &Kernels;
 
   /// Collection of known OpenMP runtime functions..
   DenseSet<const Function *> RTLFunctions;
 };
 
 template <typename Ty, bool InsertInvalidates = true>
 struct BooleanStateWithSetVector : public BooleanState {
   bool contains(const Ty &Elem) const { return Set.contains(Elem); }
   bool insert(const Ty &Elem) {
     if (InsertInvalidates)
       BooleanState::indicatePessimisticFixpoint();
     return Set.insert(Elem);
   }
 
   const Ty &operator[](int Idx) const { return Set[Idx]; }
   bool operator==(const BooleanStateWithSetVector &RHS) const {
     return BooleanState::operator==(RHS) && Set == RHS.Set;
struct KernelInfoState : AbstractState {
   CallBase *KernelDeinitCB = nullptr;
 
   /// Flag to indicate if the associated function is a kernel entry.
   bool IsKernelEntry = false;
 
   /// State to track what kernel entries can reach the associated function.
   BooleanStateWithPtrSetVector<Function, false> ReachingKernelEntries;
 
+  /// State to indicate if we can track parallel level of the associated
+  /// function. We will give up tracking if we encounter unknown caller or the
+  /// caller is __kmpc_parallel_51.
+  BooleanStateWithSetVector<uint8_t> ParallelLevels;
+
   /// Abstract State interface
   ///{
 
   KernelInfoState() {}
   KernelInfoState(bool BestState) {
     if (!BestState)
       indicatePessimisticFixpoint();
   }
ChangeStatus updateImpl(Attributor &A) override {
     };
 
     bool UsedAssumedInformationInCheckRWInst = false;
     if (!SPMDCompatibilityTracker.isAtFixpoint())
       if (!A.checkForAllReadWriteInstructions(
               CheckRWInst, *this, UsedAssumedInformationInCheckRWInst))
         SPMDCompatibilityTracker.indicatePessimisticFixpoint();
 
-    if (!IsKernelEntry)
+    if (!IsKernelEntry) {
       updateReachingKernelEntries(A);
+      updateParallelLevels(A);
+    }
 
     // Callback to check a call instruction.
     bool AllSPMDStatesWereFixed = true;
     auto CheckCallInst = [&](Instruction &I) {
       auto &CB = cast<CallBase>(I);
       auto &CBAA = A.getAAFor<AAKernelInfo>(
           *this, IRPosition::callsite_function(CB), DepClassTy::OPTIONAL);
       getState() ^= CBAA.getState();
void updateReachingKernelEntries(Attributor &A) {
     };
 
     bool AllCallSitesKnown;
     if (!A.checkForAllCallSites(PredCallSite, *this,
                                 true /* RequireAllCallSites */,
                                 AllCallSitesKnown))
       ReachingKernelEntries.indicatePessimisticFixpoint();
   }
+
+  /// Update info regarding parallel levels.
+  void updateParallelLevels(Attributor &A) {
+    auto &OMPInfoCache = static_cast<OMPInformationCache &>(A.getInfoCache());
+    OMPInformationCache::RuntimeFunctionInfo &Parallel51RFI =
+        OMPInfoCache.RFIs[OMPRTL___kmpc_parallel_51];
+
+    auto PredCallSite = [&](AbstractCallSite ACS) {
+      Function *Caller = ACS.getInstruction()->getFunction();
+
+      assert(Caller && "Caller is nullptr");
+
+      auto &CAA =
+          A.getOrCreateAAFor<AAKernelInfo>(IRPosition::function(*Caller));
+      if (CAA.ParallelLevels.isValidState()) {
+        // Any function that is called by `__kmpc_parallel_51` will not be
+        // folded as the parallel level in the function is updated. In order to
+        // get it right, all the analysis would depend on the implentation. That
+        // said, if in the future any change to the implementation, the analysis
+        // could be wrong. As a consequence, we are just conservative here.
+        if (Caller == Parallel51RFI.Declaration) {
+          ParallelLevels.indicatePessimisticFixpoint();
+          return true;
+        }
+
+        ParallelLevels ^= CAA.ParallelLevels;
+
+        return true;
+      }
+
+      // We lost track of the caller of the associated function, any kernel
+      // could reach now.
+      ParallelLevels.indicatePessimisticFixpoint();
+
+      return true;
+    };
+
+    bool AllCallSitesKnown = true;
+    if (!A.checkForAllCallSites(PredCallSite, *this,
+                                true /* RequireAllCallSites */,
+                                AllCallSitesKnown))
+      ParallelLevels.indicatePessimisticFixpoint();
+  }
 };
 
 /// The call site kernel info abstract attribute, basically, what can we say
 /// about a call site with regards to the KernelInfoState. For now this simply
 /// forwards the information from the callee.
 struct AAKernelInfoCallSite : AAKernelInfo {
   AAKernelInfoCallSite(const IRPosition &IRP, Attributor &A)
       : AAKernelInfo(IRP, A) {}
ChangeStatus updateImpl(Attributor &A) override {
 
     switch (RFKind) {
     case OMPRTL___kmpc_is_spmd_exec_mode:
       Changed |= foldIsSPMDExecMode(A);
       break;
     case OMPRTL___kmpc_is_generic_main_thread_id:
       Changed |= foldIsGenericMainThread(A);
       break;
+    case OMPRTL___kmpc_parallel_level:
+      Changed |= foldParallelLevel(A);
+      break;
     default:
       llvm_unreachable("Unhandled OpenMP runtime function!");
     }
 
     return Changed;
   }
 
   ChangeStatus manifest(Attributor &A) override {
ChangeStatus foldIsGenericMainThread(Attributor &A) {
     if (!ExecutionDomainAA.isValidState())
       return indicatePessimisticFixpoint();
 
     auto &Ctx = getAnchorValue().getContext();
     if (ExecutionDomainAA.isExecutedByInitialThreadOnly(CB))
       SimplifiedValue = ConstantInt::get(Type::getInt8Ty(Ctx), true);
     else
       return indicatePessimisticFixpoint();
 
     return SimplifiedValue == SimplifiedValueBefore ? ChangeStatus::UNCHANGED
                                                     : ChangeStatus::CHANGED;
   }
 
+  /// Fold __kmpc_parallel_level into a constant if possible.
+  ChangeStatus foldParallelLevel(Attributor &A) {
+    Optional<Value *> SimplifiedValueBefore = SimplifiedValue;
+
+    auto &CallerKernelInfoAA = A.getAAFor<AAKernelInfo>(
+        *this, IRPosition::function(*getAnchorScope()), DepClassTy::REQUIRED);
+
+    if (!CallerKernelInfoAA.ParallelLevels.isValidState())
+      return indicatePessimisticFixpoint();
+
+    if (!CallerKernelInfoAA.ReachingKernelEntries.isValidState())
+      return indicatePessimisticFixpoint();
+
+    if (CallerKernelInfoAA.ReachingKernelEntries.empty()) {
+      assert(!SimplifiedValue.hasValue() &&
+             "SimplifiedValue should keep none at this point");
+      return ChangeStatus::UNCHANGED;
+    }
+
+    unsigned AssumedSPMDCount = 0, KnownSPMDCount = 0;
+    unsigned AssumedNonSPMDCount = 0, KnownNonSPMDCount = 0;
+    for (Kernel K : CallerKernelInfoAA.ReachingKernelEntries) {
+      auto &AA = A.getAAFor<AAKernelInfo>(*this, IRPosition::function(*K),
+                                          DepClassTy::REQUIRED);
+      if (!AA.SPMDCompatibilityTracker.isValidState())
+        return indicatePessimisticFixpoint();
+
+      if (AA.SPMDCompatibilityTracker.isAssumed()) {
+        if (AA.SPMDCompatibilityTracker.isAtFixpoint())
+          ++KnownSPMDCount;
+        else
+          ++AssumedSPMDCount;
+      } else {
+        if (AA.SPMDCompatibilityTracker.isAtFixpoint())
+          ++KnownNonSPMDCount;
+        else
+          ++AssumedNonSPMDCount;
+      }
+    }
+
+    if ((AssumedSPMDCount + KnownSPMDCount) &&
+        (AssumedNonSPMDCount + KnownNonSPMDCount))
+      return indicatePessimisticFixpoint();
+
+    auto &Ctx = getAnchorValue().getContext();
+    // If the caller can only be reached by SPMD kernel entries, the parallel
+    // level is 1. Similarly, if the caller can only be reached by non-SPMD
+    // kernel entries, it is 0.
+    if (AssumedSPMDCount || KnownSPMDCount) {
+      assert(KnownNonSPMDCount == 0 && AssumedNonSPMDCount == 0 &&
+             "Expected only SPMD kernels!");
+      SimplifiedValue = ConstantInt::get(Type::getInt8Ty(Ctx), 1);
+    } else {
+      assert(KnownSPMDCount == 0 && AssumedSPMDCount == 0 &&
+             "Expected only non-SPMD kernels!");
+      SimplifiedValue = ConstantInt::get(Type::getInt8Ty(Ctx), 0);
+    }
+
+    return SimplifiedValue == SimplifiedValueBefore ? ChangeStatus::UNCHANGED
+                                                    : ChangeStatus::CHANGED;
+  }
+
   /// An optional value the associated value is assumed to fold to. That is, we
   /// assume the associated value (which is a call) can be replaced by this
   /// simplified value.
   Optional<Value *> SimplifiedValue;
 
   /// The runtime function kind of the callee of the associated call site.
   RuntimeFunction RFKind;
 };
IsSPMDRFI.foreachUse(SCC, [&](Use &U, Function &) {
       if (!CI)
         return false;
       A.getOrCreateAAFor<AAFoldRuntimeCall>(
           IRPosition::callsite_returned(*CI), /* QueryingAA */ nullptr,
           DepClassTy::NONE, /* ForceUpdate */ false,
           /* UpdateAfterInit */ false);
       return false;
     });
+
+    auto &ParallelLevelRFI = OMPInfoCache.RFIs[OMPRTL___kmpc_parallel_level];
+    ParallelLevelRFI.foreachUse(SCC, [&](Use &U, Function &) {
+      CallInst *CI = OpenMPOpt::getCallIfRegularCall(U, &ParallelLevelRFI);
+      if (!CI)
+        return false;
+      A.getOrCreateAAFor<AAFoldRuntimeCall>(
+          IRPosition::callsite_returned(*CI), /* QueryingAA */ nullptr,
+          DepClassTy::NONE, /* ForceUpdate */ false,
+          /* UpdateAfterInit */ false);
+
+      return false;
+    });
   }
 
   // Create CallSite AA for all Getters.
   for (int Idx = 0; Idx < OMPInfoCache.ICVs.size() - 1; ++Idx) {
     auto ICVInfo = OMPInfoCache.ICVs[static_cast<InternalControlVar>(Idx)];
 
     auto &GetterRFI = OMPInfoCache.RFIs[ICVInfo.Getter];
 

llvm/test/Transforms/OpenMP/parallel_level_fold.ll

+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --function-signature --check-globals
+; RUN: opt -S -passes=openmp-opt < %s | FileCheck %s
+target triple = "nvptx64"
+
+%struct.ident_t = type { i32, i32, i32, i32, i8* }
+
+@no_spmd_exec_mode = weak constant i8 1
+@spmd_exec_mode = weak constant i8 0
+@parallel_exec_mode = weak constant i8 0
+@G = external global i8
[e-mail] = appending global [3 x i8*] [i8* @no_spmd_exec_mode, i8* @spmd_exec_mode, i8* @parallel_exec_mode], section "llvm.metadata"
+
+;.
+; CHECK: @[[NO_SPMD_EXEC_MODE:[a-zA-Z0-9_$"\\.-]+]] = weak constant i8 1
+; CHECK: @[[SPMD_EXEC_MODE:[a-zA-Z0-9_$"\\.-]+]] = weak constant i8 0
+; CHECK: @[[PARALLEL_EXEC_MODE:[a-zA-Z0-9_$"\\.-]+]] = weak constant i8 0
+; CHECK: @[[G:[a-zA-Z0-9_$"\\.-]+]] = external global i8
+; CHECK: @[[LLVM_COMPILER_USED:[a-zA-Z0-9_$"\\.-]+]] = appending global [3 x i8*] [i8* @no_spmd_exec_mode, i8* @spmd_exec_mode, i8* @parallel_exec_mode], section "llvm.metadata"
+;.
+define weak void @none_spmd() {
+; CHECK-LABEL: define {{[^@]+}}@none_spmd() {
+; CHECK-NEXT:    [[I:%.*]] = call i32 @__kmpc_target_init(%struct.ident_t* null, i1 false, i1 false, i1 false)
+; CHECK-NEXT:    call void @none_spmd_helper()
+; CHECK-NEXT:    call void @mixed_helper()
+; CHECK-NEXT:    call void @__kmpc_target_deinit(%struct.ident_t* null, i1 false, i1 false)
+; CHECK-NEXT:    ret void
+;
+  %i = call i32 @__kmpc_target_init(%struct.ident_t* null, i1 false, i1 false, i1 false)
+  call void @none_spmd_helper()
+  call void @mixed_helper()
+  call void @__kmpc_target_deinit(%struct.ident_t* null, i1 false, i1 false)
+  ret void
+}
+
+define weak void @spmd() {
+; CHECK-LABEL: define {{[^@]+}}@spmd() {
+; CHECK-NEXT:    [[I:%.*]] = call i32 @__kmpc_target_init(%struct.ident_t* null, i1 true, i1 false, i1 false)
+; CHECK-NEXT:    call void @spmd_helper()
+; CHECK-NEXT:    call void @mixed_helper()
+; CHECK-NEXT:    call void @__kmpc_target_deinit(%struct.ident_t* null, i1 true, i1 false)
+; CHECK-NEXT:    ret void
+;
+  %i = call i32 @__kmpc_target_init(%struct.ident_t* null, i1 true, i1 false, i1 false)
+  call void @spmd_helper()
+  call void @mixed_helper()
+  call void @__kmpc_target_deinit(%struct.ident_t* null, i1 true, i1 false)
+  ret void
+}
+
+define weak void @parallel() {
+; CHECK-LABEL: define {{[^@]+}}@parallel() {
+; CHECK-NEXT:    [[I:%.*]] = call i32 @__kmpc_target_init(%struct.ident_t* align 536870912 null, i1 true, i1 false, i1 false)
+; CHECK-NEXT:    call void @spmd_helper()
+; CHECK-NEXT:    call void @__kmpc_parallel_51(%struct.ident_t* noalias noundef align 536870912 null, i32 noundef 0, i32 noundef 0, i32 noundef 0, i32 noundef 0, i8* noalias noundef align 536870912 null, i8* noalias noundef align 536870912 null, i8** noalias noundef align 536870912 null, i64 noundef 0)
+; CHECK-NEXT:    call void @__kmpc_target_deinit(%struct.ident_t* null, i1 true, i1 false)
+; CHECK-NEXT:    ret void
+;
+  %i = call i32 @__kmpc_target_init(%struct.ident_t* null, i1 true, i1 false, i1 false)
+  call void @spmd_helper()
+  call void @__kmpc_parallel_51(%struct.ident_t* null, i32 0, i32 0, i32 0, i32 0, i8* null, i8* null, i8** null, i64 0)
+  call void @__kmpc_target_deinit(%struct.ident_t* null, i1 true, i1 false)
+  ret void
+}
+
+define internal void @mixed_helper() {
+; CHECK-LABEL: define {{[^@]+}}@mixed_helper() {
+; CHECK-NEXT:    [[LEVEL:%.*]] = call i8 @__kmpc_parallel_level()
+; CHECK-NEXT:    store i8 [[LEVEL]], i8* @G, align 1
+; CHECK-NEXT:    ret void
+;
+  %level = call i8 @__kmpc_parallel_level()
+  store i8 %level, i8* @G
+  ret void
+}
+
+define internal void @none_spmd_helper() {
+; CHECK-LABEL: define {{[^@]+}}@none_spmd_helper() {
+; CHECK-NEXT:    [[LEVEL12:%.*]] = call i8 @__kmpc_parallel_level()
+; CHECK-NEXT:    [[C:%.*]] = icmp eq i8 [[LEVEL12]], 0
+; CHECK-NEXT:    br i1 [[C]], label [[T:%.*]], label [[F:%.*]]
+; CHECK:       t:
+; CHECK-NEXT:    call void @foo()
+; CHECK-NEXT:    ret void
+; CHECK:       f:
+; CHECK-NEXT:    call void @bar()
+; CHECK-NEXT:    ret void
+;
+  %level12 = call i8 @__kmpc_parallel_level()
+  %c = icmp eq i8 %level12, 0
+  br i1 %c, label %t, label %f
+t:
+  call void @foo()
+  ret void
+f:
+  call void @bar()
+  ret void
+}
+
+define internal void @spmd_helper() {
+; CHECK-LABEL: define {{[^@]+}}@spmd_helper() {
+; CHECK-NEXT:    store i8 1, i8* @G, align 1
+; CHECK-NEXT:    ret void
+;
+  %level = call i8 @__kmpc_parallel_level()
+  store i8 %level, i8* @G
+  ret void
+}
+
+define internal void @__kmpc_parallel_51(%struct.ident_t*, i32, i32, i32, i32, i8*, i8*, i8**, i64) {
+; CHECK-LABEL: define {{[^@]+}}@__kmpc_parallel_51
+; CHECK-SAME: (%struct.ident_t* noalias nocapture nofree readnone align 536870912 [[TMP0:%.*]], i32 [[TMP1:%.*]], i32 [[TMP2:%.*]], i32 [[TMP3:%.*]], i32 [[TMP4:%.*]], i8* noalias nocapture nofree readnone align 536870912 [[TMP5:%.*]], i8* noalias nocapture nofree readnone align 536870912 [[TMP6:%.*]], i8** noalias nocapture nofree readnone align 536870912 [[TMP7:%.*]], i64 [[TMP8:%.*]]) {
+; CHECK-NEXT:    call void @parallel_helper()
+; CHECK-NEXT:    ret void
+;
+  call void @parallel_helper()
+  ret void
+}
+
+define internal void @parallel_helper() {
+; CHECK-LABEL: define {{[^@]+}}@parallel_helper() {
+; CHECK-NEXT:    [[LEVEL:%.*]] = call i8 @__kmpc_parallel_level()
+; CHECK-NEXT:    store i8 [[LEVEL]], i8* @G, align 1
+; CHECK-NEXT:    ret void
+;
+  %level = call i8 @__kmpc_parallel_level()
+  store i8 %level, i8* @G
+  ret void
+}
+
+declare void @foo()
+declare void @bar()
+declare i8 @__kmpc_parallel_level()
+declare i32 @__kmpc_target_init(%struct.ident_t*, i1 zeroext, i1 zeroext, i1 zeroext) #1
+declare void @__kmpc_target_deinit(%struct.ident_t* nocapture readnone, i1 zeroext, i1 zeroext) #1
+
+!llvm.module.flags = !{!0, !1}
+!nvvm.annotations = !{!2, !3, !4}
+
+!0 = !{i32 7, !"openmp", i32 50}
+!1 = !{i32 7, !"openmp-device", i32 50}
+!2 = !{void ()* @none_spmd, !"kernel", i32 1}
+!3 = !{void ()* @spmd, !"kernel", i32 1}
+!4 = !{void ()* @parallel, !"kernel", i32 1}
+;.
+; CHECK: [[META0:![0-9]+]] = !{i32 7, !"openmp", i32 50}
+; CHECK: [[META1:![0-9]+]] = !{i32 7, !"openmp-device", i32 50}
+; CHECK: [[META2:![0-9]+]] = !{void ()* @none_spmd, !"kernel", i32 1}
+; CHECK: [[META3:![0-9]+]] = !{void ()* @spmd, !"kernel", i32 1}
+; CHECK: [[META4:![0-9]+]] = !{void ()* @parallel, !"kernel", i32 1}
+;.

openmp/libomptarget/deviceRTLs/common/src/parallel.cu

EXTERN void __kmpc_end_serialized_parallel(kmp_Ident *loc,
   omptarget_nvptx_threadPrivateContext->SetTopLevelTaskDescr(
       threadId, currTaskDescr->GetPrevTaskDescr());
   // free
   SafeFree(currTaskDescr, "new seq parallel task");
   currTaskDescr = getMyTopTaskDescriptor(threadId);
   currTaskDescr->RestoreLoopData();
 }
 
-EXTERN uint8_t __kmpc_parallel_level() {
+NOINLINE EXTERN uint8_t __kmpc_parallel_level() {
   return parallelLevel[GetWarpId()] & (OMP_ACTIVE_PARALLEL_LEVEL - 1);
 }
 
 // This kmpc call returns the thread id across all teams. It's value is
 // cached by the compiler and used when calling the runtime. On nvptx
 // it's cheap to recalculate this value so we never use the result
 // of this call.
 EXTERN int32_t __kmpc_global_thread_num(kmp_Ident *loc) {

 EXTERN void __kmpc_push_proc_bind(kmp_Ident *loc, uint32_t tid, int proc_bind) {
   PRINT(LD_IO, "call kmpc_push_proc_bind %d\n", (int)proc_bind);
 }
 
 ////////////////////////////////////////////////////////////////////////////////
 // parallel interface
 ////////////////////////////////////////////////////////////////////////////////
 
-EXTERN void __kmpc_parallel_51(kmp_Ident *ident, kmp_int32 global_tid,
-                               kmp_int32 if_expr, kmp_int32 num_threads,
-                               int proc_bind, void *fn, void *wrapper_fn,
-                               void **args, size_t nargs) {
-
+NOINLINE EXTERN void __kmpc_parallel_51(kmp_Ident *ident, kmp_int32 global_tid,
+                                        kmp_int32 if_expr,
+                                        kmp_int32 num_threads, int proc_bind,
+                                        void *fn, void *wrapper_fn, void **args,
+                                        size_t nargs) {
   // Handle the serialized case first, same for SPMD/non-SPMD except that in
   // SPMD mode we already incremented the parallel level counter, account for
   // that.
   bool InParallelRegion =
       (__kmpc_parallel_level() > __kmpc_is_spmd_exec_mode());
   if (!if_expr || InParallelRegion) {
     __kmpc_serialized_parallel(ident, global_tid);
     __kmp_invoke_microtask(global_tid, 0, fn, args, nargs);

openmp/libomptarget/deviceRTLs/interface.h

 ////////////////////////////////////////////////////////////////////////////////
 
 // parallel
 EXTERN int32_t __kmpc_global_thread_num(kmp_Ident *loc);
 EXTERN void __kmpc_push_num_threads(kmp_Ident *loc, int32_t global_tid,
                                     int32_t num_threads);
 EXTERN void __kmpc_serialized_parallel(kmp_Ident *loc, uint32_t global_tid);
 EXTERN void __kmpc_end_serialized_parallel(kmp_Ident *loc, uint32_t global_tid);
-EXTERN uint8_t __kmpc_parallel_level();
+NOINLINE EXTERN uint8_t __kmpc_parallel_level();
 
 // proc bind
 EXTERN void __kmpc_push_proc_bind(kmp_Ident *loc, uint32_t global_tid,
                                   int proc_bind);
 EXTERN int omp_get_num_places(void);
 EXTERN int omp_get_place_num_procs(int place_num);
 EXTERN void omp_get_place_proc_ids(int place_num, int *ids);
 EXTERN int omp_get_place_num(void);

 /// \param global_tid  The global thread ID.
 /// \param if_expr     The if(expr), or 1 if none given.
 /// \param num_threads The num_threads(expr), or -1 if none given.
 /// \param proc_bind   The proc_bind, or `proc_bind_default` if none given.
 /// \param fn          The outlined parallel region function.
 /// \param wrapper_fn  The worker wrapper function of fn.
 /// \param args        The pointer array of arguments to fn.
 /// \param nargs       The number of arguments to fn.
-EXTERN void __kmpc_parallel_51(ident_t *ident, kmp_int32 global_tid,
-                               kmp_int32 if_expr, kmp_int32 num_threads,
-                               int proc_bind, void *fn, void *wrapper_fn,
-                               void **args, size_t nargs);
+NOINLINE EXTERN void __kmpc_parallel_51(ident_t *ident, kmp_int32 global_tid,
+                                        kmp_int32 if_expr,
+                                        kmp_int32 num_threads, int proc_bind,
+                                        void *fn, void *wrapper_fn, void **args,
+                                        size_t nargs);
 
 // SPMD execution mode interrogation function.
 EXTERN int8_t __kmpc_is_spmd_exec_mode();
 
 /// Return true if the hardware thread id \p Tid represents the OpenMP main
 /// thread in generic mode outside of a parallel region.
 EXTERN int8_t __kmpc_is_generic_main_thread(kmp_int32 Tid);