[OPENMP50]Codegen for inscan reductions in worksharing directives.

[ABataev]

Summary

Implemented codegen for reduction clauses with inscan modifiers in
worksharing constructs.

Emits the code for the directive with inscan reductions.
The code is the following:

size num_iters = <num_iters>;
<type> buffer[num_iters];
for (i: 0..<num_iters>) {
  <input phase>;
  buffer[i] = red;
}
for (int k = 0; k != ceil(log2(num_iters)); ++k)
for (size cnt = last_iter; cnt >= pow(2, k); --k)
  buffer[i] op= buffer[i-pow(2,k)];
for (0..<num_iters>) {
  red = InclusiveScan ? buffer[i] : buffer[i-1];
  <scan phase>;
}

[ABataev]

Rebase

[ABataev]

Rebase

[jdoerfert]

Looks good, puzzled about the one changed mentioned below.

clang/lib/Sema/SemaOpenMP.cpp

14900

Why would we continue after this error?

[ABataev]

clang/lib/Sema/SemaOpenMP.cpp

14900

The function, that uses VLAs, might be processed in Sema, but not actually used (and, thus, is not emitted and the error message won't be generated). Need to continue the normal processing as if the error is not emitted. If we leave continue in the old place, the list of the reduction variables might be empty and in this case, the reduction clause won't be built. The scan directive then diagnoses that it does not see a single reduction clause with the inscan modifier.

[jdoerfert]

Thx for the explanation. LGTM.

clang/include/clang/AST/OpenMPClause.h

class OMPReductionClause final
   /// Get the list of helper reduction expressions.
   MutableArrayRef<Expr *> getReductionOps() {
     return MutableArrayRef<Expr *>(getRHSExprs().end(), varlist_size());
   }
   ArrayRef<const Expr *> getReductionOps() const {
     return llvm::makeArrayRef(getRHSExprs().end(), varlist_size());
   }
 
+  /// Set list of helper copy operations for inscan reductions.
+  /// The form is: Temps[i] = LHS[i];
+  void setInscanCopyOps(ArrayRef<Expr *> Ops);
+
+  /// Get the list of helper inscan copy operations.
+  MutableArrayRef<Expr *> getInscanCopyOps() {
+    return MutableArrayRef<Expr *>(getReductionOps().end(), varlist_size());
+  }
+  ArrayRef<const Expr *> getInscanCopyOps() const {
+    return llvm::makeArrayRef(getReductionOps().end(), varlist_size());
+  }
+
+  /// Set list of helper temp vars for inscan copy array operations.
+  void setInscanCopyArrayTemps(ArrayRef<Expr *> CopyArrayTemps);
+
+  /// Get the list of helper inscan copy temps.
+  MutableArrayRef<Expr *> getInscanCopyArrayTemps() {
+    return MutableArrayRef<Expr *>(getInscanCopyOps().end(), varlist_size());
+  }
+  ArrayRef<const Expr *> getInscanCopyArrayTemps() const {
+    return llvm::makeArrayRef(getInscanCopyOps().end(), varlist_size());
+  }
+
+  /// Set list of helper temp elements vars for inscan copy array operations.
+  void setInscanCopyArrayElems(ArrayRef<Expr *> CopyArrayElems);
+
+  /// Get the list of helper inscan copy temps.
+  MutableArrayRef<Expr *> getInscanCopyArrayElems() {
+    return MutableArrayRef<Expr *>(getInscanCopyArrayTemps().end(),
+                                   varlist_size());
+  }
+  ArrayRef<const Expr *> getInscanCopyArrayElems() const {
+    return llvm::makeArrayRef(getInscanCopyArrayTemps().end(), varlist_size());
+  }
+
 public:
   /// Creates clause with a list of variables \a VL.
   ///
   /// \param StartLoc Starting location of the clause.
   /// \param LParenLoc Location of '('.
   /// \param ModifierLoc Modifier location.
   /// \param ColonLoc Location of ':'.
   /// \param EndLoc Ending location of the clause.
public:
   /// expressions:
   /// \code
   /// LHSExprs binop RHSExprs;
   /// operator binop(LHSExpr, RHSExpr);
   /// <CutomReduction>(LHSExpr, RHSExpr);
   /// \endcode
   /// Required for proper codegen of final reduction operation performed by the
   /// reduction clause.
+  /// \param CopyOps List of copy operations for inscan reductions:
+  /// \code
+  /// TempExprs = LHSExprs;
+  /// \endcode
+  /// \param CopyArrayTemps Temp arrays for prefix sums.
+  /// \param CopyArrayElems Temp arrays for prefix sums.
   /// \param PreInit Statement that must be executed before entering the OpenMP
   /// region with this clause.
   /// \param PostUpdate Expression that must be executed after exit from the
   /// OpenMP region with this clause.
   static OMPReductionClause *
   Create(const ASTContext &C, SourceLocation StartLoc, SourceLocation LParenLoc,
          SourceLocation ModifierLoc, SourceLocation ColonLoc,
          SourceLocation EndLoc, OpenMPReductionClauseModifier Modifier,
          ArrayRef<Expr *> VL, NestedNameSpecifierLoc QualifierLoc,
          const DeclarationNameInfo &NameInfo, ArrayRef<Expr *> Privates,
          ArrayRef<Expr *> LHSExprs, ArrayRef<Expr *> RHSExprs,
-         ArrayRef<Expr *> ReductionOps, Stmt *PreInit, Expr *PostUpdate);
+         ArrayRef<Expr *> ReductionOps, ArrayRef<Expr *> CopyOps,
+         ArrayRef<Expr *> CopyArrayTemps, ArrayRef<Expr *> CopyArrayElems,
+         Stmt *PreInit, Expr *PostUpdate);
 
   /// Creates an empty clause with the place for \a N variables.
   ///
   /// \param C AST context.
   /// \param N The number of variables.
-  static OMPReductionClause *CreateEmpty(const ASTContext &C, unsigned N);
+  /// \param Modifier Reduction modifier.
+  static OMPReductionClause *
+  CreateEmpty(const ASTContext &C, unsigned N,
+              OpenMPReductionClauseModifier Modifier);
 
   /// Returns modifier.
   OpenMPReductionClauseModifier getModifier() const { return Modifier; }
 
   /// Returns modifier location.
   SourceLocation getModifierLoc() const { return ModifierLoc; }
 
   /// Gets location of ':' symbol in clause.
return helper_expr_const_range(getReductionOps().begin(),
                                    getReductionOps().end());
   }
 
   helper_expr_range reduction_ops() {
     return helper_expr_range(getReductionOps().begin(),
                              getReductionOps().end());
   }
 
+  helper_expr_const_range copy_ops() const {
+    return helper_expr_const_range(getInscanCopyOps().begin(),
+                                   getInscanCopyOps().end());
+  }
+
+  helper_expr_range copy_ops() {
+    return helper_expr_range(getInscanCopyOps().begin(),
+                             getInscanCopyOps().end());
+  }
+
+  helper_expr_const_range copy_array_temps() const {
+    return helper_expr_const_range(getInscanCopyArrayTemps().begin(),
+                                   getInscanCopyArrayTemps().end());
+  }
+
+  helper_expr_range copy_array_temps() {
+    return helper_expr_range(getInscanCopyArrayTemps().begin(),
+                             getInscanCopyArrayTemps().end());
+  }
+
+  helper_expr_const_range copy_array_elems() const {
+    return helper_expr_const_range(getInscanCopyArrayElems().begin(),
+                                   getInscanCopyArrayElems().end());
+  }
+
+  helper_expr_range copy_array_elems() {
+    return helper_expr_range(getInscanCopyArrayElems().begin(),
+                             getInscanCopyArrayElems().end());
+  }
+
   child_range children() {
     return child_range(reinterpret_cast<Stmt **>(varlist_begin()),
                        reinterpret_cast<Stmt **>(varlist_end()));
   }
 
   const_child_range children() const {
     auto Children = const_cast<OMPReductionClause *>(this)->children();
     return const_child_range(Children.begin(), Children.end());

clang/include/clang/AST/RecursiveASTVisitor.h

for (auto *E : C->lhs_exprs()) {
     TRY_TO(TraverseStmt(E));
   }
   for (auto *E : C->rhs_exprs()) {
     TRY_TO(TraverseStmt(E));
   }
   for (auto *E : C->reduction_ops()) {
     TRY_TO(TraverseStmt(E));
   }
+  if (C->getModifier() == OMPC_REDUCTION_inscan) {
+    for (auto *E : C->copy_ops()) {
+      TRY_TO(TraverseStmt(E));
+    }
+    for (auto *E : C->copy_array_temps()) {
+      TRY_TO(TraverseStmt(E));
+    }
+    for (auto *E : C->copy_array_elems()) {
+      TRY_TO(TraverseStmt(E));
+    }
+  }
   return true;
 }
 
 template <typename Derived>
 bool RecursiveASTVisitor<Derived>::VisitOMPTaskReductionClause(
     OMPTaskReductionClause *C) {
   TRY_TO(TraverseNestedNameSpecifierLoc(C->getQualifierLoc()));
   TRY_TO(TraverseDeclarationNameInfo(C->getNameInfo()));

clang/lib/AST/OpenMPClause.cpp

 
 void OMPReductionClause::setReductionOps(ArrayRef<Expr *> ReductionOps) {
   assert(ReductionOps.size() == varlist_size() && "Number of reduction "
                                                   "expressions is not the same "
                                                   "as the preallocated buffer");
   std::copy(ReductionOps.begin(), ReductionOps.end(), getRHSExprs().end());
 }
 
+void OMPReductionClause::setInscanCopyOps(ArrayRef<Expr *> Ops) {
+  assert(Modifier == OMPC_REDUCTION_inscan && "Expected inscan reduction.");
+  assert(Ops.size() == varlist_size() && "Number of copy "
+                                         "expressions is not the same "
+                                         "as the preallocated buffer");
+  llvm::copy(Ops, getReductionOps().end());
+}
+
+void OMPReductionClause::setInscanCopyArrayTemps(
+    ArrayRef<Expr *> CopyArrayTemps) {
+  assert(Modifier == OMPC_REDUCTION_inscan && "Expected inscan reduction.");
+  assert(CopyArrayTemps.size() == varlist_size() &&
+         "Number of copy temp expressions is not the same as the preallocated "
+         "buffer");
+  llvm::copy(CopyArrayTemps, getInscanCopyOps().end());
+}
+
+void OMPReductionClause::setInscanCopyArrayElems(
+    ArrayRef<Expr *> CopyArrayElems) {
+  assert(Modifier == OMPC_REDUCTION_inscan && "Expected inscan reduction.");
+  assert(CopyArrayElems.size() == varlist_size() &&
+         "Number of copy temp expressions is not the same as the preallocated "
+         "buffer");
+  llvm::copy(CopyArrayElems, getInscanCopyArrayTemps().end());
+}
+
 OMPReductionClause *OMPReductionClause::Create(
     const ASTContext &C, SourceLocation StartLoc, SourceLocation LParenLoc,
     SourceLocation ModifierLoc, SourceLocation EndLoc, SourceLocation ColonLoc,
     OpenMPReductionClauseModifier Modifier, ArrayRef<Expr *> VL,
     NestedNameSpecifierLoc QualifierLoc, const DeclarationNameInfo &NameInfo,
     ArrayRef<Expr *> Privates, ArrayRef<Expr *> LHSExprs,
-    ArrayRef<Expr *> RHSExprs, ArrayRef<Expr *> ReductionOps, Stmt *PreInit,
-    Expr *PostUpdate) {
-  void *Mem = C.Allocate(totalSizeToAlloc<Expr *>(5 * VL.size()));
+    ArrayRef<Expr *> RHSExprs, ArrayRef<Expr *> ReductionOps,
+    ArrayRef<Expr *> CopyOps, ArrayRef<Expr *> CopyArrayTemps,
+    ArrayRef<Expr *> CopyArrayElems, Stmt *PreInit, Expr *PostUpdate) {
+  void *Mem = C.Allocate(totalSizeToAlloc<Expr *>(
+      (Modifier == OMPC_REDUCTION_inscan ? 8 : 5) * VL.size()));
   auto *Clause = new (Mem)
       OMPReductionClause(StartLoc, LParenLoc, ModifierLoc, EndLoc, ColonLoc,
                          Modifier, VL.size(), QualifierLoc, NameInfo);
   Clause->setVarRefs(VL);
   Clause->setPrivates(Privates);
   Clause->setLHSExprs(LHSExprs);
   Clause->setRHSExprs(RHSExprs);
   Clause->setReductionOps(ReductionOps);
   Clause->setPreInitStmt(PreInit);
   Clause->setPostUpdateExpr(PostUpdate);
+  if (Modifier == OMPC_REDUCTION_inscan) {
+    Clause->setInscanCopyOps(CopyOps);
+    Clause->setInscanCopyArrayTemps(CopyArrayTemps);
+    Clause->setInscanCopyArrayElems(CopyArrayElems);
+  } else {
+    assert(CopyOps.empty() &&
+           "copy operations are expected in inscan reductions only.");
+    assert(CopyArrayTemps.empty() &&
+           "copy array temps are expected in inscan reductions only.");
+    assert(CopyArrayElems.empty() &&
+           "copy array temps are expected in inscan reductions only.");
+  }
   return Clause;
 }
 
-OMPReductionClause *OMPReductionClause::CreateEmpty(const ASTContext &C,
-                                                    unsigned N) {
-  void *Mem = C.Allocate(totalSizeToAlloc<Expr *>(5 * N));
-  return new (Mem) OMPReductionClause(N);
+OMPReductionClause *
+OMPReductionClause::CreateEmpty(const ASTContext &C, unsigned N,
+                                OpenMPReductionClauseModifier Modifier) {
+  void *Mem = C.Allocate(totalSizeToAlloc<Expr *>(
+      (Modifier == OMPC_REDUCTION_inscan ? 8 : 5) * N));
+  auto *Clause = new (Mem) OMPReductionClause(N);
+  Clause->setModifier(Modifier);
+  return Clause;
 }
 
 void OMPTaskReductionClause::setPrivates(ArrayRef<Expr *> Privates) {
   assert(Privates.size() == varlist_size() &&
          "Number of private copies is not the same as the preallocated buffer");
   std::copy(Privates.begin(), Privates.end(), varlist_end());
 }
 

clang/lib/AST/StmtProfile.cpp

void OMPClauseProfiler::VisitOMPReductionClause(
   for (auto *E : C->rhs_exprs()) {
     if (E)
       Profiler->VisitStmt(E);
   }
   for (auto *E : C->reduction_ops()) {
     if (E)
       Profiler->VisitStmt(E);
   }
+  if (C->getModifier() == clang::OMPC_REDUCTION_inscan) {
+    for (auto *E : C->copy_ops()) {
+      if (E)
+        Profiler->VisitStmt(E);
+    }
+    for (auto *E : C->copy_array_temps()) {
+      if (E)
+        Profiler->VisitStmt(E);
+    }
+    for (auto *E : C->copy_array_elems()) {
+      if (E)
+        Profiler->VisitStmt(E);
+    }
+  }
 }
 void OMPClauseProfiler::VisitOMPTaskReductionClause(
     const OMPTaskReductionClause *C) {
   Profiler->VisitNestedNameSpecifier(
       C->getQualifierLoc().getNestedNameSpecifier());
   Profiler->VisitName(C->getNameInfo().getName());
   VisitOMPClauseList(C);
   VistOMPClauseWithPostUpdate(C);

clang/lib/CodeGen/CGStmt.cpp

case Stmt::OMPTaskgroupDirectiveClass:
     break;
   case Stmt::OMPFlushDirectiveClass:
     EmitOMPFlushDirective(cast<OMPFlushDirective>(*S));
     break;
   case Stmt::OMPDepobjDirectiveClass:
     EmitOMPDepobjDirective(cast<OMPDepobjDirective>(*S));
     break;
   case Stmt::OMPScanDirectiveClass:
-    llvm_unreachable("Scan directive not supported yet.");
+    EmitOMPScanDirective(cast<OMPScanDirective>(*S));
     break;
   case Stmt::OMPOrderedDirectiveClass:
     EmitOMPOrderedDirective(cast<OMPOrderedDirective>(*S));
     break;
   case Stmt::OMPAtomicDirectiveClass:
     EmitOMPAtomicDirective(cast<OMPAtomicDirective>(*S));
     break;
   case Stmt::OMPTargetDirectiveClass:

clang/lib/CodeGen/CGStmtOpenMP.cpp

if (const Expr *PostUpdate = C->getPostUpdateExpr())
       EmitIgnoredExpr(PostUpdate);
   }
   if (IsLastIterCond)
     EmitBlock(DoneBB, /*IsFinished=*/true);
 }
 
 void CodeGenFunction::EmitOMPReductionClauseInit(
     const OMPExecutableDirective &D,
-    CodeGenFunction::OMPPrivateScope &PrivateScope) {
+    CodeGenFunction::OMPPrivateScope &PrivateScope, bool ForInscan) {
   if (!HaveInsertPoint())
     return;
   SmallVector<const Expr *, 4> Shareds;
   SmallVector<const Expr *, 4> Privates;
   SmallVector<const Expr *, 4> ReductionOps;
   SmallVector<const Expr *, 4> LHSs;
   SmallVector<const Expr *, 4> RHSs;
   OMPTaskDataTy Data;
   SmallVector<const Expr *, 4> TaskLHSs;
   SmallVector<const Expr *, 4> TaskRHSs;
   for (const auto *C : D.getClausesOfKind<OMPReductionClause>()) {
+    if (ForInscan != (C->getModifier() == OMPC_REDUCTION_inscan))
+      continue;
     Shareds.append(C->varlist_begin(), C->varlist_end());
     Privates.append(C->privates().begin(), C->privates().end());
     ReductionOps.append(C->reduction_ops().begin(), C->reduction_ops().end());
     LHSs.append(C->lhs_exprs().begin(), C->lhs_exprs().end());
     RHSs.append(C->rhs_exprs().begin(), C->rhs_exprs().end());
     if (C->getModifier() == OMPC_REDUCTION_task) {
       Data.ReductionVars.append(C->privates().begin(), C->privates().end());
       Data.ReductionOrigs.append(C->varlist_begin(), C->varlist_end());
if (!HaveInsertPoint())
     return;
   llvm::SmallVector<const Expr *, 8> Privates;
   llvm::SmallVector<const Expr *, 8> LHSExprs;
   llvm::SmallVector<const Expr *, 8> RHSExprs;
   llvm::SmallVector<const Expr *, 8> ReductionOps;
   bool HasAtLeastOneReduction = false;
   bool IsReductionWithTaskMod = false;
   for (const auto *C : D.getClausesOfKind<OMPReductionClause>()) {
+    // Do not emit for inscan reductions.
+    if (C->getModifier() == OMPC_REDUCTION_inscan)
+      continue;
     HasAtLeastOneReduction = true;
     Privates.append(C->privates().begin(), C->privates().end());
     LHSExprs.append(C->lhs_exprs().begin(), C->lhs_exprs().end());
     RHSExprs.append(C->rhs_exprs().begin(), C->rhs_exprs().end());
     ReductionOps.append(C->reduction_ops().begin(), C->reduction_ops().end());
     IsReductionWithTaskMod =
         IsReductionWithTaskMod || C->getModifier() == OMPC_REDUCTION_task;
   }
if (!E)
       continue;
     // Check that loop counter in non-rectangular nest fits into the iteration
     // space.
     llvm::BasicBlock *NextBB = createBasicBlock("omp.body.next");
     EmitBranchOnBoolExpr(E, NextBB, Continue.getBlock(),
                          getProfileCount(D.getBody()));
     EmitBlock(NextBB);
   }
+
+  OMPPrivateScope InscanScope(*this);
+  EmitOMPReductionClauseInit(D, InscanScope, /*ForInscan=*/true);
+  bool IsInscanRegion = InscanScope.Privatize();
+  if (IsInscanRegion) {
+    // Need to remember the block before and after scan directive
+    // to dispatch them correctly depending on the clause used in
+    // this directive, inclusive or exclusive. For inclusive scan the natural
+    // order of the blocks is used, for exclusive clause the blocks must be
+    // executed in reverse order.
+    OMPBeforeScanBlock = createBasicBlock("omp.before.scan.bb");
+    OMPAfterScanBlock = createBasicBlock("omp.after.scan.bb");
+    OMPScanExitBlock = createBasicBlock("omp.exit.inscan.bb");
+    OMPScanDispatch = createBasicBlock("omp.inscan.dispatch");
+    EmitBranch(OMPScanDispatch);
+    EmitBlock(OMPBeforeScanBlock);
+  }
+
   // Emit loop variables for C++ range loops.
   const Stmt *Body =
       D.getInnermostCapturedStmt()->getCapturedStmt()->IgnoreContainers();
   // Emit loop body.
   emitBody(*this, Body,
            OMPLoopDirective::tryToFindNextInnerLoop(
                Body, /*TryImperfectlyNestedLoops=*/true),
            D.getCollapsedNumber());
 
+  // Jump to the dispatcher at the end of the loop body.
+  if (IsInscanRegion)
+    EmitBranch(OMPScanExitBlock);
+
   // The end (updates/cleanups).
   EmitBlock(Continue.getBlock());
   BreakContinueStack.pop_back();
 }
 
 void CodeGenFunction::EmitOMPInnerLoop(
     const Stmt &S, bool RequiresCleanup, const Expr *LoopCond,
     const Expr *IncExpr,
emitDispatchForLoopBounds(CodeGenFunction &CGF, const OMPExecutableDirective &S,
   const auto &LS = cast<OMPLoopDirective>(S);
   const Expr *IVExpr = LS.getIterationVariable();
   const unsigned IVSize = CGF.getContext().getTypeSize(IVExpr->getType());
   llvm::Value *LBVal = CGF.Builder.getIntN(IVSize, 0);
   llvm::Value *UBVal = CGF.EmitScalarExpr(LS.getLastIteration());
   return {LBVal, UBVal};
 }
 
+/// Emits the code for the directive with inscan reductions.
+/// The code is the following:
+/// \code
+/// size num_iters = <num_iters>;
+/// <type> buffer[num_iters];
+/// #pragma omp ...
+/// for (i: 0..<num_iters>) {
+///   <input phase>;
+///   buffer[i] = red;
+/// }
+/// for (int k = 0; k != ceil(log2(num_iters)); ++k)
+/// for (size cnt = last_iter; cnt >= pow(2, k); --k)
+///   buffer[i] op= buffer[i-pow(2,k)];
+/// #pragma omp ...
+/// for (0..<num_iters>) {
+///   red = InclusiveScan ? buffer[i] : buffer[i-1];
+///   <scan phase>;
+/// }
+/// \endcode
+static void emitScanBasedDirective(
+    CodeGenFunction &CGF, const OMPLoopDirective &S,
+    llvm::function_ref<llvm::Value *(CodeGenFunction &)> NumIteratorsGen,
+    llvm::function_ref<void(CodeGenFunction &)> FirstGen,
+    llvm::function_ref<void(CodeGenFunction &)> SecondGen) {
+  llvm::Value *OMPScanNumIterations = CGF.Builder.CreateIntCast(
+      NumIteratorsGen(CGF), CGF.SizeTy, /*isSigned=*/false);
+  SmallVector<const Expr *, 4> Shareds;
+  SmallVector<const Expr *, 4> Privates;
+  SmallVector<const Expr *, 4> ReductionOps;
+  SmallVector<const Expr *, 4> LHSs;
+  SmallVector<const Expr *, 4> RHSs;
+  SmallVector<const Expr *, 4> CopyOps;
+  SmallVector<const Expr *, 4> CopyArrayTemps;
+  SmallVector<const Expr *, 4> CopyArrayElems;
+  for (const auto *C : S.getClausesOfKind<OMPReductionClause>()) {
+    assert(C->getModifier() == OMPC_REDUCTION_inscan &&
+           "Only inscan reductions are expected.");
+    Shareds.append(C->varlist_begin(), C->varlist_end());
+    Privates.append(C->privates().begin(), C->privates().end());
+    ReductionOps.append(C->reduction_ops().begin(), C->reduction_ops().end());
+    LHSs.append(C->lhs_exprs().begin(), C->lhs_exprs().end());
+    RHSs.append(C->rhs_exprs().begin(), C->rhs_exprs().end());
+    CopyOps.append(C->copy_ops().begin(), C->copy_ops().end());
+    CopyArrayTemps.append(C->copy_array_temps().begin(),
+                          C->copy_array_temps().end());
+    CopyArrayElems.append(C->copy_array_elems().begin(),
+                          C->copy_array_elems().end());
+  }
+  {
+    // Emit buffers for each reduction variables.
+    // ReductionCodeGen is required to emit correctly the code for array
+    // reductions.
+    ReductionCodeGen RedCG(Shareds, Shareds, Privates, ReductionOps);
+    unsigned Count = 0;
+    auto *ITA = CopyArrayTemps.begin();
+    for (const Expr *IRef : Privates) {
+      const auto *PrivateVD = cast<VarDecl>(cast<DeclRefExpr>(IRef)->getDecl());
+      // Emit variably modified arrays, used for arrays/array sections
+      // reductions.
+      if (PrivateVD->getType()->isVariablyModifiedType()) {
+        RedCG.emitSharedOrigLValue(CGF, Count);
+        RedCG.emitAggregateType(CGF, Count);
+      }
+      CodeGenFunction::OpaqueValueMapping DimMapping(
+          CGF,
+          cast<OpaqueValueExpr>(
+              cast<VariableArrayType>((*ITA)->getType()->getAsArrayTypeUnsafe())
+                  ->getSizeExpr()),
+          RValue::get(OMPScanNumIterations));
+      // Emit temp buffer.
+      CGF.EmitVarDecl(*cast<VarDecl>(cast<DeclRefExpr>(*ITA)->getDecl()));
+      ++ITA;
+      ++Count;
+    }
+  }
+  CodeGenFunction::ParentLoopDirectiveForScanRegion ScanRegion(CGF, S);
+  {
+    // Emit loop with input phase:
+    // #pragma omp ...
+    // for (i: 0..<num_iters>) {
+    //   <input phase>;
+    //   buffer[i] = red;
+    // }
+    CGF.OMPFirstScanLoop = true;
+    CodeGenFunction::OMPLocalDeclMapRAII Scope(CGF);
+    FirstGen(CGF);
+  }
+  // Emit prefix reduction:
+  // for (int k = 0; k <= ceil(log2(n)); ++k)
+  llvm::BasicBlock *InputBB = CGF.Builder.GetInsertBlock();
+  llvm::BasicBlock *LoopBB = CGF.createBasicBlock("omp.outer.log.scan.body");
+  llvm::BasicBlock *ExitBB = CGF.createBasicBlock("omp.outer.log.scan.exit");
+  llvm::Function *F = CGF.CGM.getIntrinsic(llvm::Intrinsic::log2, CGF.DoubleTy);
+  llvm::Value *Arg =
+      CGF.Builder.CreateUIToFP(OMPScanNumIterations, CGF.DoubleTy);
+  llvm::Value *LogVal = CGF.EmitNounwindRuntimeCall(F, Arg);
+  F = CGF.CGM.getIntrinsic(llvm::Intrinsic::ceil, CGF.DoubleTy);
+  LogVal = CGF.EmitNounwindRuntimeCall(F, LogVal);
+  LogVal = CGF.Builder.CreateFPToUI(LogVal, CGF.IntTy);
+  llvm::Value *NMin1 = CGF.Builder.CreateNUWSub(
+      OMPScanNumIterations, llvm::ConstantInt::get(CGF.SizeTy, 1));
+  auto DL = ApplyDebugLocation::CreateDefaultArtificial(CGF, S.getBeginLoc());
+  CGF.EmitBlock(LoopBB);
+  auto *Counter = CGF.Builder.CreatePHI(CGF.IntTy, 2);
+  // size pow2k = 1;
+  auto *Pow2K = CGF.Builder.CreatePHI(CGF.SizeTy, 2);
+  Counter->addIncoming(llvm::ConstantInt::get(CGF.IntTy, 0), InputBB);
+  Pow2K->addIncoming(llvm::ConstantInt::get(CGF.SizeTy, 1), InputBB);
+  // for (size i = n - 1; i >= 2 ^ k; --i)
+  //   tmp[i] op= tmp[i-pow2k];
+  llvm::BasicBlock *InnerLoopBB =
+      CGF.createBasicBlock("omp.inner.log.scan.body");
+  llvm::BasicBlock *InnerExitBB =
+      CGF.createBasicBlock("omp.inner.log.scan.exit");
+  llvm::Value *CmpI = CGF.Builder.CreateICmpUGE(NMin1, Pow2K);
+  CGF.Builder.CreateCondBr(CmpI, InnerLoopBB, InnerExitBB);
+  CGF.EmitBlock(InnerLoopBB);
+  auto *IVal = CGF.Builder.CreatePHI(CGF.SizeTy, 2);
+  IVal->addIncoming(NMin1, LoopBB);
+  {
+    CodeGenFunction::OMPPrivateScope PrivScope(CGF);
+    auto *ILHS = LHSs.begin();
+    auto *IRHS = RHSs.begin();
+    for (const Expr *CopyArrayElem : CopyArrayElems) {
+      const auto *LHSVD = cast<VarDecl>(cast<DeclRefExpr>(*ILHS)->getDecl());
+      const auto *RHSVD = cast<VarDecl>(cast<DeclRefExpr>(*IRHS)->getDecl());
+      Address LHSAddr = Address::invalid();
+      {
+        CodeGenFunction::OpaqueValueMapping IdxMapping(
+            CGF,
+            cast<OpaqueValueExpr>(
+                cast<ArraySubscriptExpr>(CopyArrayElem)->getIdx()),
+            RValue::get(IVal));
+        LHSAddr = CGF.EmitLValue(CopyArrayElem).getAddress(CGF);
+      }
+      PrivScope.addPrivate(LHSVD, [LHSAddr]() { return LHSAddr; });
+      Address RHSAddr = Address::invalid();
+      {
+        llvm::Value *OffsetIVal = CGF.Builder.CreateNUWSub(IVal, Pow2K);
+        CodeGenFunction::OpaqueValueMapping IdxMapping(
+            CGF,
+            cast<OpaqueValueExpr>(
+                cast<ArraySubscriptExpr>(CopyArrayElem)->getIdx()),
+            RValue::get(OffsetIVal));
+        RHSAddr = CGF.EmitLValue(CopyArrayElem).getAddress(CGF);
+      }
+      PrivScope.addPrivate(RHSVD, [RHSAddr]() { return RHSAddr; });
+      ++ILHS;
+      ++IRHS;
+    }
+    PrivScope.Privatize();
+    CGF.CGM.getOpenMPRuntime().emitReduction(
+        CGF, S.getEndLoc(), Privates, LHSs, RHSs, ReductionOps,
+        {/*WithNowait=*/true, /*SimpleReduction=*/true, OMPD_unknown});
+  }
+  llvm::Value *NextIVal =
+      CGF.Builder.CreateNUWSub(IVal, llvm::ConstantInt::get(CGF.SizeTy, 1));
+  IVal->addIncoming(NextIVal, CGF.Builder.GetInsertBlock());
+  CmpI = CGF.Builder.CreateICmpUGE(NextIVal, Pow2K);
+  CGF.Builder.CreateCondBr(CmpI, InnerLoopBB, InnerExitBB);
+  CGF.EmitBlock(InnerExitBB);
+  llvm::Value *Next =
+      CGF.Builder.CreateNUWAdd(Counter, llvm::ConstantInt::get(CGF.IntTy, 1));
+  Counter->addIncoming(Next, CGF.Builder.GetInsertBlock());
+  // pow2k <<= 1;
+  llvm::Value *NextPow2K = CGF.Builder.CreateShl(Pow2K, 1, "", /*HasNUW=*/true);
+  Pow2K->addIncoming(NextPow2K, CGF.Builder.GetInsertBlock());
+  llvm::Value *Cmp = CGF.Builder.CreateICmpNE(Next, LogVal);
+  CGF.Builder.CreateCondBr(Cmp, LoopBB, ExitBB);
+  auto DL1 = ApplyDebugLocation::CreateDefaultArtificial(CGF, S.getEndLoc());
+  CGF.EmitBlock(ExitBB);
+
+  CGF.OMPFirstScanLoop = false;
+  SecondGen(CGF);
+}
+
 void CodeGenFunction::EmitOMPForDirective(const OMPForDirective &S) {
   bool HasLastprivates = false;
   auto &&CodeGen = [&S, &HasLastprivates](CodeGenFunction &CGF,
                                           PrePostActionTy &) {
+    if (llvm::any_of(S.getClausesOfKind<OMPReductionClause>(),
+                     [](const OMPReductionClause *C) {
+                       return C->getModifier() == OMPC_REDUCTION_inscan;
+                     })) {
+      const auto &&NumIteratorsGen = [&S](CodeGenFunction &CGF) {
+        OMPLocalDeclMapRAII Scope(CGF);
+        OMPLoopScope LoopScope(CGF, S);
+        return CGF.EmitScalarExpr(S.getNumIterations());
+      };
+      const auto &&FirstGen = [&S](CodeGenFunction &CGF) {
+        OMPCancelStackRAII CancelRegion(CGF, OMPD_for, S.hasCancel());
+        (void)CGF.EmitOMPWorksharingLoop(S, S.getEnsureUpperBound(),
+                                         emitForLoopBounds,
+                                         emitDispatchForLoopBounds);
+        // Emit an implicit barrier at the end.
+        CGF.CGM.getOpenMPRuntime().emitBarrierCall(CGF, S.getBeginLoc(),
+                                                   OMPD_for);
+      };
+      const auto &&SecondGen = [&S, &HasLastprivates](CodeGenFunction &CGF) {
         OMPCancelStackRAII CancelRegion(CGF, OMPD_for, S.hasCancel());
         HasLastprivates = CGF.EmitOMPWorksharingLoop(S, S.getEnsureUpperBound(),
                                                      emitForLoopBounds,
                                                      emitDispatchForLoopBounds);
       };
+      emitScanBasedDirective(CGF, S, NumIteratorsGen, FirstGen, SecondGen);
+    } else {
+      OMPCancelStackRAII CancelRegion(CGF, OMPD_for, S.hasCancel());
+      HasLastprivates = CGF.EmitOMPWorksharingLoop(S, S.getEnsureUpperBound(),
+                                                   emitForLoopBounds,
+                                                   emitDispatchForLoopBounds);
+    }
+  };
   {
     auto LPCRegion =
         CGOpenMPRuntime::LastprivateConditionalRAII::disable(*this, S);
     OMPLexicalScope Scope(*this, S, OMPD_unknown);
     CGM.getOpenMPRuntime().emitInlinedDirective(*this, OMPD_for, CodeGen,
                                                 S.hasCancel());
   }
 
void CodeGenFunction::EmitOMPDepobjDirective(const OMPDepobjDirective &S) {
   }
   if (const auto *UC = S.getSingleClause<OMPUpdateClause>()) {
     CGM.getOpenMPRuntime().emitUpdateClause(
         *this, DOLVal, UC->getDependencyKind(), UC->getBeginLoc());
     return;
   }
 }
 
+void CodeGenFunction::EmitOMPScanDirective(const OMPScanDirective &S) {
+  // Do not emit code for non-simd directives in simd-only mode.
+  if (getLangOpts().OpenMPSimd && !OMPParentLoopDirectiveForScan)
+    return;
+  const OMPExecutableDirective &ParentDir = *OMPParentLoopDirectiveForScan;
+  SmallVector<const Expr *, 4> Shareds;
+  SmallVector<const Expr *, 4> Privates;
+  SmallVector<const Expr *, 4> LHSs;
+  SmallVector<const Expr *, 4> RHSs;
+  SmallVector<const Expr *, 4> CopyOps;
+  SmallVector<const Expr *, 4> CopyArrayTemps;
+  SmallVector<const Expr *, 4> CopyArrayElems;
+  for (const auto *C : ParentDir.getClausesOfKind<OMPReductionClause>()) {
+    if (C->getModifier() != OMPC_REDUCTION_inscan)
+      continue;
+    Shareds.append(C->varlist_begin(), C->varlist_end());
+    Privates.append(C->privates().begin(), C->privates().end());
+    LHSs.append(C->lhs_exprs().begin(), C->lhs_exprs().end());
+    RHSs.append(C->rhs_exprs().begin(), C->rhs_exprs().end());
+    CopyOps.append(C->copy_ops().begin(), C->copy_ops().end());
+    CopyArrayTemps.append(C->copy_array_temps().begin(),
+                          C->copy_array_temps().end());
+    CopyArrayElems.append(C->copy_array_elems().begin(),
+                          C->copy_array_elems().end());
+  }
+  bool IsInclusive = S.hasClausesOfKind<OMPInclusiveClause>();
+  if (!IsInclusive) {
+    EmitBranch(BreakContinueStack.back().ContinueBlock.getBlock());
+    EmitBlock(OMPScanExitBlock);
+  }
+  if (OMPFirstScanLoop) {
+    // Emit buffer[i] = red; at the end of the input phase.
+    const auto *IVExpr = cast<OMPLoopDirective>(ParentDir)
+                             .getIterationVariable()
+                             ->IgnoreParenImpCasts();
+    LValue IdxLVal = EmitLValue(IVExpr);
+    llvm::Value *IdxVal = EmitLoadOfScalar(IdxLVal, IVExpr->getExprLoc());
+    IdxVal = Builder.CreateIntCast(IdxVal, SizeTy, /*isSigned=*/false);
+    for (unsigned I = 0, E = CopyArrayElems.size(); I < E; ++I) {
+      const Expr *PrivateExpr = Privates[I];
+      const Expr *OrigExpr = Shareds[I];
+      const Expr *CopyArrayElem = CopyArrayElems[I];
+      OpaqueValueMapping IdxMapping(
+          *this,
+          cast<OpaqueValueExpr>(
+              cast<ArraySubscriptExpr>(CopyArrayElem)->getIdx()),
+          RValue::get(IdxVal));
+      LValue DestLVal = EmitLValue(CopyArrayElem);
+      LValue SrcLVal = EmitLValue(OrigExpr);
+      EmitOMPCopy(PrivateExpr->getType(), DestLVal.getAddress(*this),
+                  SrcLVal.getAddress(*this),
+                  cast<VarDecl>(cast<DeclRefExpr>(LHSs[I])->getDecl()),
+                  cast<VarDecl>(cast<DeclRefExpr>(RHSs[I])->getDecl()),
+                  CopyOps[I]);
+    }
+  }
+  EmitBranch(BreakContinueStack.back().ContinueBlock.getBlock());
+  if (IsInclusive) {
+    EmitBlock(OMPScanExitBlock);
+    EmitBranch(BreakContinueStack.back().ContinueBlock.getBlock());
+  }
+  EmitBlock(OMPScanDispatch);
+  if (!OMPFirstScanLoop) {
+    // Emit red = buffer[i]; at the entrance to the scan phase.
+    const auto *IVExpr = cast<OMPLoopDirective>(ParentDir)
+                             .getIterationVariable()
+                             ->IgnoreParenImpCasts();
+    LValue IdxLVal = EmitLValue(IVExpr);
+    llvm::Value *IdxVal = EmitLoadOfScalar(IdxLVal, IVExpr->getExprLoc());
+    IdxVal = Builder.CreateIntCast(IdxVal, SizeTy, /*isSigned=*/false);
+    llvm::BasicBlock *ExclusiveExitBB = nullptr;
+    if (!IsInclusive) {
+      llvm::BasicBlock *ContBB = createBasicBlock("omp.exclusive.dec");
+      ExclusiveExitBB = createBasicBlock("omp.exclusive.copy.exit");
+      llvm::Value *Cmp = Builder.CreateIsNull(IdxVal);
+      Builder.CreateCondBr(Cmp, ExclusiveExitBB, ContBB);
+      EmitBlock(ContBB);
+      // Use idx - 1 iteration for exclusive scan.
+      IdxVal = Builder.CreateNUWSub(IdxVal, llvm::ConstantInt::get(SizeTy, 1));
+    }
+    for (unsigned I = 0, E = CopyArrayElems.size(); I < E; ++I) {
+      const Expr *PrivateExpr = Privates[I];
+      const Expr *OrigExpr = Shareds[I];
+      const Expr *CopyArrayElem = CopyArrayElems[I];
+      OpaqueValueMapping IdxMapping(
+          *this,
+          cast<OpaqueValueExpr>(
+              cast<ArraySubscriptExpr>(CopyArrayElem)->getIdx()),
+          RValue::get(IdxVal));
+      LValue SrcLVal = EmitLValue(CopyArrayElem);
+      LValue DestLVal = EmitLValue(OrigExpr);
+      EmitOMPCopy(PrivateExpr->getType(), DestLVal.getAddress(*this),
+                  SrcLVal.getAddress(*this),
+                  cast<VarDecl>(cast<DeclRefExpr>(LHSs[I])->getDecl()),
+                  cast<VarDecl>(cast<DeclRefExpr>(RHSs[I])->getDecl()),
+                  CopyOps[I]);
+    }
+    if (!IsInclusive) {
+      EmitBlock(ExclusiveExitBB);
+    }
+  }
+  EmitBranch((OMPFirstScanLoop == IsInclusive) ? OMPBeforeScanBlock
+                                               : OMPAfterScanBlock);
+  EmitBlock(OMPAfterScanBlock);
+}
+
 void CodeGenFunction::EmitOMPDistributeLoop(const OMPLoopDirective &S,
                                             const CodeGenLoopTy &CodeGenLoop,
                                             Expr *IncExpr) {
   // Emit the loop iteration variable.
   const auto *IVExpr = cast<DeclRefExpr>(S.getIterationVariable());
   const auto *IVDecl = cast<VarDecl>(IVExpr->getDecl());
   EmitVarDecl(*IVDecl);
 
if (const auto *C = S.getSingleClause<OMPDeviceClause>())
     Device = C->getDevice();
 
   OMPLexicalScope Scope(*this, S, OMPD_task);
   CGM.getOpenMPRuntime().emitTargetDataStandAloneCall(*this, S, IfCond, Device);
 }
 
 void CodeGenFunction::EmitSimpleOMPExecutableDirective(
     const OMPExecutableDirective &D) {
+  if (const auto *SD = dyn_cast<OMPScanDirective>(&D)) {
+    EmitOMPScanDirective(*SD);
+    return;
+  }
   if (!D.hasAssociatedStmt() || !D.getAssociatedStmt())
     return;
   auto &&CodeGen = [&D](CodeGenFunction &CGF, PrePostActionTy &Action) {
     OMPPrivateScope GlobalsScope(CGF);
     if (isOpenMPTaskingDirective(D.getDirectiveKind())) {
       // Capture global firstprivates to avoid crash.
       for (const auto *C : D.getClausesOfKind<OMPFirstprivateClause>()) {
         for (const Expr *Ref : C->varlists()) {

clang/lib/CodeGen/CodeGenFunction.h

public:
   /// Value returned by __exception_info intrinsic.
   llvm::Value *SEHInfo = nullptr;
 
   /// Emits a landing pad for the current EH stack.
   llvm::BasicBlock *EmitLandingPad();
 
   llvm::BasicBlock *getInvokeDestImpl();
 
+  /// Parent loop-based directive for scan directive.
+  const OMPExecutableDirective *OMPParentLoopDirectiveForScan = nullptr;
+  llvm::BasicBlock *OMPBeforeScanBlock = nullptr;
+  llvm::BasicBlock *OMPAfterScanBlock = nullptr;
+  llvm::BasicBlock *OMPScanExitBlock = nullptr;
+  llvm::BasicBlock *OMPScanDispatch = nullptr;
+  bool OMPFirstScanLoop = false;
+
+  /// Manages parent directive for scan directives.
+  class ParentLoopDirectiveForScanRegion {
+    CodeGenFunction &CGF;
+    const OMPExecutableDirective &ParentLoopDirectiveForScan;
+
+  public:
+    ParentLoopDirectiveForScanRegion(
+        CodeGenFunction &CGF,
+        const OMPExecutableDirective &ParentLoopDirectiveForScan)
+        : CGF(CGF),
+          ParentLoopDirectiveForScan(*CGF.OMPParentLoopDirectiveForScan) {
+      CGF.OMPParentLoopDirectiveForScan = &ParentLoopDirectiveForScan;
+    }
+    ~ParentLoopDirectiveForScanRegion() {
+      CGF.OMPParentLoopDirectiveForScan = &ParentLoopDirectiveForScan;
+    }
+  };
+
   template <class T>
   typename DominatingValue<T>::saved_type saveValueInCond(T value) {
     return DominatingValue<T>::save(*this, value);
   }
 
 public:
   /// ObjCEHValueStack - Stack of Objective-C exception values, used for
   /// rethrows.

   /// Emit initial code for reduction variables. Creates reduction copies
   /// and initializes them with the values according to OpenMP standard.
   ///
   /// \param D Directive (possibly) with the 'reduction' clause.
   /// \param PrivateScope Private scope for capturing reduction variables for
   /// proper codegen in internal captured statement.
   ///
   void EmitOMPReductionClauseInit(const OMPExecutableDirective &D,
-                                  OMPPrivateScope &PrivateScope);
+                                  OMPPrivateScope &PrivateScope,
+                                  bool ForInscan = false);
   /// Emit final update of reduction values to original variables at
   /// the end of the directive.
   ///
   /// \param D Directive that has at least one 'reduction' directives.
   /// \param ReductionKind The kind of reduction to perform.
   void EmitOMPReductionClauseFinal(const OMPExecutableDirective &D,
                                    const OpenMPDirectiveKind ReductionKind);
   /// Emit initial code for linear variables. Creates private copies

   void EmitOMPParallelMasterDirective(const OMPParallelMasterDirective &S);
   void EmitOMPTaskDirective(const OMPTaskDirective &S);
   void EmitOMPTaskyieldDirective(const OMPTaskyieldDirective &S);
   void EmitOMPBarrierDirective(const OMPBarrierDirective &S);
   void EmitOMPTaskwaitDirective(const OMPTaskwaitDirective &S);
   void EmitOMPTaskgroupDirective(const OMPTaskgroupDirective &S);
   void EmitOMPFlushDirective(const OMPFlushDirective &S);
   void EmitOMPDepobjDirective(const OMPDepobjDirective &S);
+  void EmitOMPScanDirective(const OMPScanDirective &S);
   void EmitOMPOrderedDirective(const OMPOrderedDirective &S);
   void EmitOMPAtomicDirective(const OMPAtomicDirective &S);
   void EmitOMPTargetDirective(const OMPTargetDirective &S);
   void EmitOMPTargetDataDirective(const OMPTargetDataDirective &S);
   void EmitOMPTargetEnterDataDirective(const OMPTargetEnterDataDirective &S);
   void EmitOMPTargetExitDataDirective(const OMPTargetExitDataDirective &S);
   void EmitOMPTargetUpdateDirective(const OMPTargetUpdateDirective &S);
   void EmitOMPTargetParallelDirective(const OMPTargetParallelDirective &S);

clang/lib/Sema/SemaOpenMP.cpp

StmtResult Sema::ActOnOpenMPScanDirective(ArrayRef<OMPClause *> Clauses,
                                           SourceLocation StartLoc,
                                           SourceLocation EndLoc) {
   // Check that exactly one clause is specified.
   if (Clauses.size() != 1) {
     Diag(Clauses.empty() ? EndLoc : Clauses[1]->getBeginLoc(),
          diag::err_omp_scan_single_clause_expected);
     return StmtError();
   }
+  // Check that scan directive is used in the scopeof the OpenMP loop body.
+  if (Scope *S = DSAStack->getCurScope()) {
+    Scope *ParentS = S->getParent();
+    if (!ParentS || ParentS->getParent() != ParentS->getBreakParent() ||
+        !ParentS->getBreakParent()->isOpenMPLoopScope())
+      return StmtError(Diag(StartLoc, diag::err_omp_orphaned_device_directive)
+                       << getOpenMPDirectiveName(OMPD_scan) << 5);
+  }
   // Check that only one instance of scan directives is used in the same outer
   // region.
   if (DSAStack->doesParentHasScanDirective()) {
     Diag(StartLoc, diag::err_omp_several_scan_directives_in_region);
     Diag(DSAStack->getParentScanDirectiveLoc(),
          diag::note_omp_previous_scan_directive);
     return StmtError();
   }
struct ReductionData {
   /// List of private copies of the reduction items.
   SmallVector<Expr *, 8> Privates;
   /// LHS expressions for the reduction_op expressions.
   SmallVector<Expr *, 8> LHSs;
   /// RHS expressions for the reduction_op expressions.
   SmallVector<Expr *, 8> RHSs;
   /// Reduction operation expression.
   SmallVector<Expr *, 8> ReductionOps;
+  /// inscan copy operation expressions.
+  SmallVector<Expr *, 8> InscanCopyOps;
+  /// inscan copy temp array expressions for prefix sums.
+  SmallVector<Expr *, 8> InscanCopyArrayTemps;
+  /// inscan copy temp array element expressions for prefix sums.
+  SmallVector<Expr *, 8> InscanCopyArrayElems;
   /// Taskgroup descriptors for the corresponding reduction items in
   /// in_reduction clauses.
   SmallVector<Expr *, 8> TaskgroupDescriptors;
   /// List of captures for clause.
   SmallVector<Decl *, 4> ExprCaptures;
   /// List of postupdate expressions.
   SmallVector<Expr *, 4> ExprPostUpdates;
   /// Reduction modifier.
   unsigned RedModifier = 0;
   ReductionData() = delete;
   /// Reserves required memory for the reduction data.
   ReductionData(unsigned Size, unsigned Modifier = 0) : RedModifier(Modifier) {
     Vars.reserve(Size);
     Privates.reserve(Size);
     LHSs.reserve(Size);
     RHSs.reserve(Size);
     ReductionOps.reserve(Size);
+    if (RedModifier == OMPC_REDUCTION_inscan) {
+      InscanCopyOps.reserve(Size);
+      InscanCopyArrayTemps.reserve(Size);
+      InscanCopyArrayElems.reserve(Size);
+    }
     TaskgroupDescriptors.reserve(Size);
     ExprCaptures.reserve(Size);
     ExprPostUpdates.reserve(Size);
   }
   /// Stores reduction item and reduction operation only (required for dependent
   /// reduction item).
   void push(Expr *Item, Expr *ReductionOp) {
     Vars.emplace_back(Item);
     Privates.emplace_back(nullptr);
     LHSs.emplace_back(nullptr);
     RHSs.emplace_back(nullptr);
     ReductionOps.emplace_back(ReductionOp);
     TaskgroupDescriptors.emplace_back(nullptr);
+    if (RedModifier == OMPC_REDUCTION_inscan) {
+      InscanCopyOps.push_back(nullptr);
+      InscanCopyArrayTemps.push_back(nullptr);
+      InscanCopyArrayElems.push_back(nullptr);
+    }
   }
   /// Stores reduction data.
   void push(Expr *Item, Expr *Private, Expr *LHS, Expr *RHS, Expr *ReductionOp,
-            Expr *TaskgroupDescriptor) {
+            Expr *TaskgroupDescriptor, Expr *CopyOp, Expr *CopyArrayTemp,
+            Expr *CopyArrayElem) {
     Vars.emplace_back(Item);
     Privates.emplace_back(Private);
     LHSs.emplace_back(LHS);
     RHSs.emplace_back(RHS);
     ReductionOps.emplace_back(ReductionOp);
     TaskgroupDescriptors.emplace_back(TaskgroupDescriptor);
+    if (RedModifier == OMPC_REDUCTION_inscan) {
+      InscanCopyOps.push_back(CopyOp);
+      InscanCopyArrayTemps.push_back(CopyArrayTemp);
+      InscanCopyArrayElems.push_back(CopyArrayElem);
+    } else {
+      assert(CopyOp == nullptr && CopyArrayTemp == nullptr &&
+             CopyArrayElem == nullptr &&
+             "Copy operation must be used for inscan reductions only.");
+    }
   }
 };
 } // namespace
 
 static bool checkOMPArraySectionConstantForReduction(
     ASTContext &Context, const OMPArraySectionExpr *OASE, bool &SingleElement,
     SmallVectorImpl<llvm::APSInt> &ArraySizes) {
   const Expr *Length = OASE->getLength();
for (Expr *RefExpr : VarList) {
 
     if ((OASE && !ConstantLengthOASE) ||
         (!OASE && !ASE &&
          D->getType().getNonReferenceType()->isVariablyModifiedType())) {
       if (!Context.getTargetInfo().isVLASupported()) {
         if (isOpenMPTargetExecutionDirective(Stack->getCurrentDirective())) {
           S.Diag(ELoc, diag::err_omp_reduction_vla_unsupported) << !!OASE;
           S.Diag(ELoc, diag::note_vla_unsupported);
+          continue;
         } else {
           S.targetDiag(ELoc, diag::err_omp_reduction_vla_unsupported) << !!OASE;
           S.targetDiag(ELoc, diag::note_vla_unsupported);
         }
-        continue;
       }
       // For arrays/array sections only:
       // Create pseudo array type for private copy. The size for this array will
       // be generated during codegen.
       // For array subscripts or single variables Private Ty is the same as Type
       // (type of the variable or single array element).
       PrivateTy = Context.getVariableArrayType(
           Type,
if (DeclareReductionRef.isUsable()) {
         if (ReductionOp.isUsable())
           ReductionOp = S.ActOnFinishFullExpr(ReductionOp.get(),
                                               /*DiscardedValue*/ false);
       }
       if (!ReductionOp.isUsable())
         continue;
     }
 
+    // Add copy operations for inscan reductions.
+    // LHS = RHS;
+    ExprResult CopyOpRes, TempArrayRes, TempArrayElem;
+    if (ClauseKind == OMPC_reduction &&
+        RD.RedModifier == OMPC_REDUCTION_inscan) {
+      ExprResult RHS = S.DefaultLvalueConversion(RHSDRE);
+      CopyOpRes = S.BuildBinOp(Stack->getCurScope(), ELoc, BO_Assign, LHSDRE,
+                               RHS.get());
+      if (!CopyOpRes.isUsable())
+        continue;
+      CopyOpRes =
+          S.ActOnFinishFullExpr(CopyOpRes.get(), /*DiscardedValue=*/true);
+      if (!CopyOpRes.isUsable())
+        continue;
+      // Build temp array for prefix sum.
+      auto *Dim = new (S.Context)
+          OpaqueValueExpr(ELoc, S.Context.getSizeType(), VK_RValue);
+      QualType ArrayTy =
+          S.Context.getVariableArrayType(PrivateTy, Dim, ArrayType::Normal,
+                                         /*IndexTypeQuals=*/0, {ELoc, ELoc});
+      VarDecl *TempArrayVD =
+          buildVarDecl(S, ELoc, ArrayTy, D->getName(),
+                       D->hasAttrs() ? &D->getAttrs() : nullptr);
+      // Add a constructor to the temp decl.
+      S.ActOnUninitializedDecl(TempArrayVD);
+      TempArrayRes = buildDeclRefExpr(S, TempArrayVD, ArrayTy, ELoc);
+      TempArrayElem =
+          S.DefaultFunctionArrayLvalueConversion(TempArrayRes.get());
+      auto *Idx = new (S.Context)
+          OpaqueValueExpr(ELoc, S.Context.getSizeType(), VK_RValue);
+      TempArrayElem = S.CreateBuiltinArraySubscriptExpr(TempArrayElem.get(),
+                                                        ELoc, Idx, ELoc);
+    }
+
     // OpenMP [2.15.4.6, Restrictions, p.2]
     // A list item that appears in an in_reduction clause of a task construct
     // must appear in a task_reduction clause of a construct associated with a
     // taskgroup region that includes the participating task in its taskgroup
     // set. The construct associated with the innermost region that meets this
     // condition must specify the same reduction-identifier as the in_reduction
     // clause.
     if (ClauseKind == OMPC_in_reduction) {
if (Modifier == OMPC_REDUCTION_task &&
           !isOpenMPSimdDirective(CurrDir)))) {
       if (DeclareReductionRef.isUsable())
         Stack->addTaskgroupReductionData(D, ReductionIdRange,
                                          DeclareReductionRef.get());
       else
         Stack->addTaskgroupReductionData(D, ReductionIdRange, BOK);
     }
     RD.push(VarsExpr, PrivateDRE, LHSDRE, RHSDRE, ReductionOp.get(),
-            TaskgroupDescriptor);
+            TaskgroupDescriptor, CopyOpRes.get(), TempArrayRes.get(),
+            TempArrayElem.get());
   }
   return RD.Vars.empty();
 }
 
 OMPClause *Sema::ActOnOpenMPReductionClause(
     ArrayRef<Expr *> VarList, OpenMPReductionClauseModifier Modifier,
     SourceLocation StartLoc, SourceLocation LParenLoc,
     SourceLocation ModifierLoc, SourceLocation ColonLoc, SourceLocation EndLoc,
if (actOnOMPReductionKindClause(*this, DSAStack, OMPC_reduction, VarList,
                                   StartLoc, LParenLoc, ColonLoc, EndLoc,
                                   ReductionIdScopeSpec, ReductionId,
                                   UnresolvedReductions, RD))
     return nullptr;
 
   return OMPReductionClause::Create(
       Context, StartLoc, LParenLoc, ModifierLoc, ColonLoc, EndLoc, Modifier,
       RD.Vars, ReductionIdScopeSpec.getWithLocInContext(Context), ReductionId,
-      RD.Privates, RD.LHSs, RD.RHSs, RD.ReductionOps,
+      RD.Privates, RD.LHSs, RD.RHSs, RD.ReductionOps, RD.InscanCopyOps,
+      RD.InscanCopyArrayTemps, RD.InscanCopyArrayElems,
       buildPreInits(Context, RD.ExprCaptures),
       buildPostUpdate(*this, RD.ExprPostUpdates));
 }
 
 OMPClause *Sema::ActOnOpenMPTaskReductionClause(
     ArrayRef<Expr *> VarList, SourceLocation StartLoc, SourceLocation LParenLoc,
     SourceLocation ColonLoc, SourceLocation EndLoc,
     CXXScopeSpec &ReductionIdScopeSpec, const DeclarationNameInfo &ReductionId,

clang/lib/Serialization/ASTReader.cpp

case llvm::omp::OMPC_firstprivate:
     C = OMPFirstprivateClause::CreateEmpty(Context, Record.readInt());
     break;
   case llvm::omp::OMPC_lastprivate:
     C = OMPLastprivateClause::CreateEmpty(Context, Record.readInt());
     break;
   case llvm::omp::OMPC_shared:
     C = OMPSharedClause::CreateEmpty(Context, Record.readInt());
     break;
-  case llvm::omp::OMPC_reduction:
-    C = OMPReductionClause::CreateEmpty(Context, Record.readInt());
+  case llvm::omp::OMPC_reduction: {
+    unsigned N = Record.readInt();
+    auto Modifier = Record.readEnum<OpenMPReductionClauseModifier>();
+    C = OMPReductionClause::CreateEmpty(Context, N, Modifier);
     break;
+  }
   case llvm::omp::OMPC_task_reduction:
     C = OMPTaskReductionClause::CreateEmpty(Context, Record.readInt());
     break;
   case llvm::omp::OMPC_in_reduction:
     C = OMPInReductionClause::CreateEmpty(Context, Record.readInt());
     break;
   case llvm::omp::OMPC_linear:
     C = OMPLinearClause::CreateEmpty(Context, Record.readInt());
void OMPClauseReader::VisitOMPSharedClause(OMPSharedClause *C) {
   C->setVarRefs(Vars);
 }
 
 void OMPClauseReader::VisitOMPReductionClause(OMPReductionClause *C) {
   VisitOMPClauseWithPostUpdate(C);
   C->setLParenLoc(Record.readSourceLocation());
   C->setModifierLoc(Record.readSourceLocation());
   C->setColonLoc(Record.readSourceLocation());
-  C->setModifier(Record.readEnum<OpenMPReductionClauseModifier>());
   NestedNameSpecifierLoc NNSL = Record.readNestedNameSpecifierLoc();
   DeclarationNameInfo DNI = Record.readDeclarationNameInfo();
   C->setQualifierLoc(NNSL);
   C->setNameInfo(DNI);
 
   unsigned NumVars = C->varlist_size();
   SmallVector<Expr *, 16> Vars;
   Vars.reserve(NumVars);
void OMPClauseReader::VisitOMPReductionClause(OMPReductionClause *C) {
   Vars.clear();
   for (unsigned i = 0; i != NumVars; ++i)
     Vars.push_back(Record.readSubExpr());
   C->setRHSExprs(Vars);
   Vars.clear();
   for (unsigned i = 0; i != NumVars; ++i)
     Vars.push_back(Record.readSubExpr());
   C->setReductionOps(Vars);
+  if (C->getModifier() == OMPC_REDUCTION_inscan) {
+    Vars.clear();
+    for (unsigned i = 0; i != NumVars; ++i)
+      Vars.push_back(Record.readSubExpr());
+    C->setInscanCopyOps(Vars);
+    Vars.clear();
+    for (unsigned i = 0; i != NumVars; ++i)
+      Vars.push_back(Record.readSubExpr());
+    C->setInscanCopyArrayTemps(Vars);
+    Vars.clear();
+    for (unsigned i = 0; i != NumVars; ++i)
+      Vars.push_back(Record.readSubExpr());
+    C->setInscanCopyArrayElems(Vars);
+  }
 }
 
 void OMPClauseReader::VisitOMPTaskReductionClause(OMPTaskReductionClause *C) {
   VisitOMPClauseWithPostUpdate(C);
   C->setLParenLoc(Record.readSourceLocation());
   C->setColonLoc(Record.readSourceLocation());
   NestedNameSpecifierLoc NNSL = Record.readNestedNameSpecifierLoc();
   DeclarationNameInfo DNI = Record.readDeclarationNameInfo();

clang/lib/Serialization/ASTWriter.cpp

void OMPClauseWriter::VisitOMPSharedClause(OMPSharedClause *C) {
   Record.push_back(C->varlist_size());
   Record.AddSourceLocation(C->getLParenLoc());
   for (auto *VE : C->varlists())
     Record.AddStmt(VE);
 }
 
 void OMPClauseWriter::VisitOMPReductionClause(OMPReductionClause *C) {
   Record.push_back(C->varlist_size());
+  Record.writeEnum(C->getModifier());
   VisitOMPClauseWithPostUpdate(C);
   Record.AddSourceLocation(C->getLParenLoc());
   Record.AddSourceLocation(C->getModifierLoc());
   Record.AddSourceLocation(C->getColonLoc());
-  Record.writeEnum(C->getModifier());
   Record.AddNestedNameSpecifierLoc(C->getQualifierLoc());
   Record.AddDeclarationNameInfo(C->getNameInfo());
   for (auto *VE : C->varlists())
     Record.AddStmt(VE);
   for (auto *VE : C->privates())
     Record.AddStmt(VE);
   for (auto *E : C->lhs_exprs())
     Record.AddStmt(E);
   for (auto *E : C->rhs_exprs())
     Record.AddStmt(E);
   for (auto *E : C->reduction_ops())
     Record.AddStmt(E);
+  if (C->getModifier() == clang::OMPC_REDUCTION_inscan) {
+    for (auto *E : C->copy_ops())
+      Record.AddStmt(E);
+    for (auto *E : C->copy_array_temps())
+      Record.AddStmt(E);
+    for (auto *E : C->copy_array_elems())
+      Record.AddStmt(E);
+  }
 }
 
 void OMPClauseWriter::VisitOMPTaskReductionClause(OMPTaskReductionClause *C) {
   Record.push_back(C->varlist_size());
   VisitOMPClauseWithPostUpdate(C);
   Record.AddSourceLocation(C->getLParenLoc());
   Record.AddSourceLocation(C->getColonLoc());
   Record.AddNestedNameSpecifierLoc(C->getQualifierLoc());

clang/test/OpenMP/for_scan_codegen.cpp

+// RUN: %clang_cc1 -verify -fopenmp -fopenmp-version=50 -x c++ -triple x86_64-unknown-unknown -emit-llvm %s -o - | FileCheck %s
+// RUN: %clang_cc1 -fopenmp -fopenmp-version=50 -x c++ -std=c++11 -triple x86_64-unknown-unknown -emit-pch -o %t %s
+// RUN: %clang_cc1 -fopenmp -fopenmp-version=50 -x c++ -triple x86_64-unknown-unknown -std=c++11 -include-pch %t -verify %s -emit-llvm -o - | FileCheck %s
+
+// RUN: %clang_cc1 -verify -fopenmp-simd -fopenmp-version=50 -x c++ -triple x86_64-unknown-unknown -emit-llvm %s -o - | FileCheck --check-prefix SIMD-ONLY0 %s
+// RUN: %clang_cc1 -fopenmp-simd -fopenmp-version=50 -x c++ -std=c++11 -triple x86_64-unknown-unknown -emit-pch -o %t %s
+// RUN: %clang_cc1 -fopenmp-simd -fopenmp-version=50 -x c++ -triple x86_64-unknown-unknown -std=c++11 -include-pch %t -verify %s -emit-llvm -o - | FileCheck --check-prefix SIMD-ONLY0 %s
+// SIMD-ONLY0-NOT: {{__kmpc|__tgt}}
+// expected-no-diagnostics
+#ifndef HEADER
+#define HEADER
+
+void foo();
+void bar();
+
+// CHECK: define void @{{.*}}baz{{.*}}(i32 %n)
+void baz(int n) {
+  static float a[10];
+  static double b;
+  // CHECK: call i8* @llvm.stacksave()
+  // CHECK: [[A_BUF_SIZE:%.+]] = mul nuw i64 10, [[NUM_ELEMS:%[^,]+]]
+
+  // float a_buffer[10][n];
+  // CHECK: [[A_BUF:%.+]] = alloca float, i64 [[A_BUF_SIZE]],
+
+  // double b_buffer[10];
+  // CHECK: [[B_BUF:%.+]] = alloca double, i64 10,
+#pragma omp for reduction(inscan, +:a[:n], b)
+  for (int i = 0; i < 10; ++i) {
+    // CHECK: call void @__kmpc_for_static_init_4(
+    // CHECK: call i8* @llvm.stacksave()
+    // CHECK: store float 0.000000e+00, float* %
+    // CHECK: store double 0.000000e+00, double* [[B_PRIV_ADDR:%.+]],
+    // CHECK: br label %[[DISPATCH:[^,]+]]
+    // CHECK: [[INPUT_PHASE:.+]]:
+    // CHECK: call void @{{.+}}foo{{.+}}()
+
+    // a_buffer[i][0..n] = a_priv[[0..n];
+    // CHECK: [[BASE_IDX_I:%.+]] = load i32, i32* [[IV_ADDR:%.+]],
+    // CHECK: [[BASE_IDX:%.+]] = zext i32 [[BASE_IDX_I]] to i64
+    // CHECK: [[IDX:%.+]] = mul nsw i64 [[BASE_IDX]], [[NUM_ELEMS]]
+    // CHECK: [[A_BUF_IDX:%.+]] = getelementptr inbounds float, float* [[A_BUF]], i64 [[IDX]]
+    // CHECK: [[A_PRIV:%.+]] = getelementptr inbounds [10 x float], [10 x float]* [[A_PRIV_ADDR:%.+]], i64 0, i64 0
+    // CHECK: [[BYTES:%.+]] = mul nuw i64 [[NUM_ELEMS:%.+]], 4
+    // CHECK: [[DEST:%.+]] = bitcast float* [[A_BUF_IDX]] to i8*
+    // CHECK: [[SRC:%.+]] = bitcast float* [[A_PRIV]] to i8*
+    // CHECK: call void @llvm.memcpy.p0i8.p0i8.i64(i8* {{.*}}[[DEST]], i8* {{.*}}[[SRC]], i64 [[BYTES]], i1 false)
+
+    // b_buffer[i] = b_priv;
+    // CHECK: [[B_BUF_IDX:%.+]] = getelementptr inbounds double, double* [[B_BUF]], i64 [[BASE_IDX]]
+    // CHECK: [[B_PRIV:%.+]] = load double, double* [[B_PRIV_ADDR]],
+    // CHECK: store double [[B_PRIV]], double* [[B_BUF_IDX]],
+    // CHECK: br label %[[LOOP_CONTINUE:.+]]
+
+    // CHECK: [[DISPATCH]]:
+    // CHECK: br label %[[INPUT_PHASE]]
+    // CHECK: [[LOOP_CONTINUE]]:
+    // CHECK: call void @llvm.stackrestore(i8* %
+    // CHECK: call void @__kmpc_for_static_fini(
+    // CHECK: call void @__kmpc_barrier(
+    foo();
+#pragma omp scan inclusive(a[:n], b)
+    // CHECK: [[LOG2_10:%.+]] = call double @llvm.log2.f64(double 1.000000e+01)
+    // CHECK: [[CEIL_LOG2_10:%.+]] = call double @llvm.ceil.f64(double [[LOG2_10]])
+    // CHECK: [[CEIL_LOG2_10_INT:%.+]] = fptoui double [[CEIL_LOG2_10]] to i32
+    // CHECK: br label %[[OUTER_BODY:[^,]+]]
+    // CHECK: [[OUTER_BODY]]:
+    // CHECK: [[K:%.+]] = phi i32 [ 0, %{{.+}} ], [ [[K_NEXT:%.+]], %{{.+}} ]
+    // CHECK: [[K2POW:%.+]] = phi i64 [ 1, %{{.+}} ], [ [[K2POW_NEXT:%.+]], %{{.+}} ]
+    // CHECK: [[CMP:%.+]] = icmp uge i64 9, [[K2POW]]
+    // CHECK: br i1 [[CMP]], label %[[INNER_BODY:[^,]+]], label %[[INNER_EXIT:[^,]+]]
+    // CHECK: [[INNER_BODY]]:
+    // CHECK: [[I:%.+]] = phi i64 [ 9, %[[OUTER_BODY]] ], [ [[I_PREV:%.+]], %{{.+}} ]
+
+    // a_buffer[i] += a_buffer[i-pow(2, k)];
+    // CHECK: [[IDX:%.+]] = mul nsw i64 [[I]], [[NUM_ELEMS]]
+    // CHECK: [[A_BUF_IDX:%.+]] = getelementptr inbounds float, float* [[A_BUF]], i64 [[IDX]]
+    // CHECK: [[IDX_SUB_K2POW:%.+]] = sub nuw i64 [[I]], [[K2POW]]
+    // CHECK: [[IDX:%.+]] = mul nsw i64 [[IDX_SUB_K2POW]], [[NUM_ELEMS]]
+    // CHECK: [[A_BUF_IDX_SUB_K2POW:%.+]] = getelementptr inbounds float, float* [[A_BUF]], i64 [[IDX]]
+    // CHECK: [[B_BUF_IDX:%.+]] = getelementptr inbounds double, double* [[B_BUF]], i64 [[I]]
+    // CHECK: [[IDX_SUB_K2POW:%.+]] = sub nuw i64 [[I]], [[K2POW]]
+    // CHECK: [[B_BUF_IDX_SUB_K2POW:%.+]] = getelementptr inbounds double, double* [[B_BUF]], i64 [[IDX_SUB_K2POW]]
+    // CHECK: [[A_BUF_END:%.+]] = getelementptr float, float* [[A_BUF_IDX]], i64 [[NUM_ELEMS]]
+    // CHECK: [[ISEMPTY:%.+]] = icmp eq float* [[A_BUF_IDX]], [[A_BUF_END]]
+    // CHECK: br i1 [[ISEMPTY]], label %[[RED_DONE:[^,]+]], label %[[RED_BODY:[^,]+]]
+    // CHECK: [[RED_BODY]]:
+    // CHECK: [[A_BUF_IDX_SUB_K2POW_ELEM:%.+]] = phi float* [ [[A_BUF_IDX_SUB_K2POW]], %[[INNER_BODY]] ], [ [[A_BUF_IDX_SUB_K2POW_NEXT:%.+]], %[[RED_BODY]] ]
+    // CHECK: [[A_BUF_IDX_ELEM:%.+]] = phi float* [ [[A_BUF_IDX]], %[[INNER_BODY]] ], [ [[A_BUF_IDX_NEXT:%.+]], %[[RED_BODY]] ]
+    // CHECK: [[A_BUF_IDX_VAL:%.+]] = load float, float* [[A_BUF_IDX_ELEM]],
+    // CHECK: [[A_BUF_IDX_SUB_K2POW_VAL:%.+]] = load float, float* [[A_BUF_IDX_SUB_K2POW_ELEM]],
+    // CHECK: [[RED:%.+]] = fadd float [[A_BUF_IDX_VAL]], [[A_BUF_IDX_SUB_K2POW_VAL]]
+    // CHECK: store float [[RED]], float* [[A_BUF_IDX_ELEM]],
+    // CHECK: [[A_BUF_IDX_NEXT]] = getelementptr float, float* [[A_BUF_IDX_ELEM]], i32 1
+    // CHECK: [[A_BUF_IDX_SUB_K2POW_NEXT]] = getelementptr float, float* [[A_BUF_IDX_SUB_K2POW_ELEM]], i32 1
+    // CHECK: [[DONE:%.+]] = icmp eq float* [[A_BUF_IDX_NEXT]], [[A_BUF_END]]
+    // CHECK: br i1 [[DONE]], label %[[RED_DONE]], label %[[RED_BODY]]
+    // CHECK: [[RED_DONE]]:
+
+    // b_buffer[i] += b_buffer[i-pow(2, k)];
+    // CHECK: [[B_BUF_IDX_VAL:%.+]] = load double, double* [[B_BUF_IDX]],
+    // CHECK: [[B_BUF_IDX_SUB_K2POW_VAL:%.+]] = load double, double* [[B_BUF_IDX_SUB_K2POW]],
+    // CHECK: [[RED:%.+]] = fadd double [[B_BUF_IDX_VAL]], [[B_BUF_IDX_SUB_K2POW_VAL]]
+    // CHECK: store double [[RED]], double* [[B_BUF_IDX]],
+
+    // --i;
+    // CHECK: [[I_PREV:%.+]] = sub nuw i64 [[I]], 1
+    // CHECK: [[CMP:%.+]] = icmp uge i64 [[I_PREV]], [[K2POW]]
+    // CHECK: br i1 [[CMP]], label %[[INNER_BODY]], label %[[INNER_EXIT]]
+    // CHECK: [[INNER_EXIT]]:
+
+    // ++k;
+    // CHECK: [[K_NEXT]] = add nuw i32 [[K]], 1
+    // k2pow <<= 1;
+    // CHECK: [[K2POW_NEXT]] = shl nuw i64 [[K2POW]], 1
+    // CHECK: [[CMP:%.+]] = icmp ne i32 [[K_NEXT]], [[CEIL_LOG2_10_INT]]
+    // CHECK: br i1 [[CMP]], label %[[OUTER_BODY]], label %[[OUTER_EXIT:[^,]+]]
+    // CHECK: [[OUTER_EXIT]]:
+    bar();
+    // CHECK: call void @__kmpc_for_static_init_4(
+    // CHECK: call i8* @llvm.stacksave()
+    // CHECK: store float 0.000000e+00, float* %
+    // CHECK: store double 0.000000e+00, double* [[B_PRIV_ADDR:%.+]],
+    // CHECK: br label %[[DISPATCH:[^,]+]]
+
+    // Skip the before scan body.
+    // CHECK: call void @{{.+}}foo{{.+}}()
+
+    // CHECK: [[EXIT_INSCAN:[^,]+]]:
+    // CHECK: br label %[[LOOP_CONTINUE:[^,]+]]
+
+    // CHECK: [[DISPATCH]]:
+    // a_priv[[0..n] = a_buffer[i][0..n];
+    // CHECK: [[BASE_IDX_I:%.+]] = load i32, i32* [[IV_ADDR:%.+]],
+    // CHECK: [[BASE_IDX:%.+]] = zext i32 [[BASE_IDX_I]] to i64
+    // CHECK: [[IDX:%.+]] = mul nsw i64 [[BASE_IDX]], [[NUM_ELEMS]]
+    // CHECK: [[A_BUF_IDX:%.+]] = getelementptr inbounds float, float* [[A_BUF]], i64 [[IDX]]
+    // CHECK: [[A_PRIV:%.+]] = getelementptr inbounds [10 x float], [10 x float]* [[A_PRIV_ADDR:%.+]], i64 0, i64 0
+    // CHECK: [[BYTES:%.+]] = mul nuw i64 [[NUM_ELEMS:%.+]], 4
+    // CHECK: [[DEST:%.+]] = bitcast float* [[A_PRIV]] to i8*
+    // CHECK: [[SRC:%.+]] = bitcast float* [[A_BUF_IDX]] to i8*
+    // CHECK: call void @llvm.memcpy.p0i8.p0i8.i64(i8* {{.*}}[[DEST]], i8* {{.*}}[[SRC]], i64 [[BYTES]], i1 false)
+
+    // b_priv = b_buffer[i];
+    // CHECK: [[B_BUF_IDX:%.+]] = getelementptr inbounds double, double* [[B_BUF]], i64 [[BASE_IDX]]
+    // CHECK: [[B_BUF_IDX_VAL:%.+]] = load double, double* [[B_BUF_IDX]],
+    // CHECK: store double [[B_BUF_IDX_VAL]], double* [[B_PRIV_ADDR]],
+    // CHECK: br label %[[SCAN_PHASE:[^,]+]]
+
+    // CHECK: [[SCAN_PHASE]]:
+    // CHECK: call void @{{.+}}bar{{.+}}()
+    // CHECK: br label %[[EXIT_INSCAN]]
+
+    // CHECK: [[LOOP_CONTINUE]]:
+    // CHECK: call void @llvm.stackrestore(i8* %
+    // CHECK: call void @__kmpc_for_static_fini(
+    // CHECK: call void @llvm.stackrestore(i8*
+    // CHECK: call void @__kmpc_barrier(
+  }
+
+  // CHECK: call i8* @llvm.stacksave()
+  // CHECK: [[A_BUF_SIZE:%.+]] = mul nuw i64 10, [[NUM_ELEMS:%[^,]+]]
+
+  // float a_buffer[10][n];
+  // CHECK: [[A_BUF:%.+]] = alloca float, i64 [[A_BUF_SIZE]],
+
+  // double b_buffer[10];
+  // CHECK: [[B_BUF:%.+]] = alloca double, i64 10,
+#pragma omp for reduction(inscan, +:a[:n], b)
+  for (int i = 0; i < 10; ++i) {
+    // CHECK: call void @__kmpc_for_static_init_4(
+    // CHECK: call i8* @llvm.stacksave()
+    // CHECK: store float 0.000000e+00, float* %
+    // CHECK: store double 0.000000e+00, double* [[B_PRIV_ADDR:%.+]],
+    // CHECK: br label %[[DISPATCH:[^,]+]]
+
+    // Skip the before scan body.
+    // CHECK: call void @{{.+}}foo{{.+}}()
+
+    // CHECK: [[EXIT_INSCAN:[^,]+]]:
+
+    // a_buffer[i][0..n] = a_priv[[0..n];
+    // CHECK: [[BASE_IDX_I:%.+]] = load i32, i32* [[IV_ADDR:%.+]],
+    // CHECK: [[BASE_IDX:%.+]] = zext i32 [[BASE_IDX_I]] to i64
+    // CHECK: [[IDX:%.+]] = mul nsw i64 [[BASE_IDX]], [[NUM_ELEMS]]
+    // CHECK: [[A_BUF_IDX:%.+]] = getelementptr inbounds float, float* [[A_BUF]], i64 [[IDX]]
+    // CHECK: [[A_PRIV:%.+]] = getelementptr inbounds [10 x float], [10 x float]* [[A_PRIV_ADDR:%.+]], i64 0, i64 0
+    // CHECK: [[BYTES:%.+]] = mul nuw i64 [[NUM_ELEMS:%.+]], 4
+    // CHECK: [[DEST:%.+]] = bitcast float* [[A_BUF_IDX]] to i8*
+    // CHECK: [[SRC:%.+]] = bitcast float* [[A_PRIV]] to i8*
+    // CHECK: call void @llvm.memcpy.p0i8.p0i8.i64(i8* {{.*}}[[DEST]], i8* {{.*}}[[SRC]], i64 [[BYTES]], i1 false)
+
+    // b_buffer[i] = b_priv;
+    // CHECK: [[B_BUF_IDX:%.+]] = getelementptr inbounds double, double* [[B_BUF]], i64 [[BASE_IDX]]
+    // CHECK: [[B_PRIV:%.+]] = load double, double* [[B_PRIV_ADDR]],
+    // CHECK: store double [[B_PRIV]], double* [[B_BUF_IDX]],
+    // CHECK: br label %[[LOOP_CONTINUE:[^,]+]]
+
+    // CHECK: [[DISPATCH]]:
+    // CHECK: br label %[[INPUT_PHASE:[^,]+]]
+
+    // CHECK: [[INPUT_PHASE]]:
+    // CHECK: call void @{{.+}}bar{{.+}}()
+    // CHECK: br label %[[EXIT_INSCAN]]
+
+    // CHECK: [[LOOP_CONTINUE]]:
+    // CHECK: call void @llvm.stackrestore(i8* %
+    // CHECK: call void @__kmpc_for_static_fini(
+    // CHECK: call void @__kmpc_barrier(
+    foo();
+#pragma omp scan exclusive(a[:n], b)
+    // CHECK: [[LOG2_10:%.+]] = call double @llvm.log2.f64(double 1.000000e+01)
+    // CHECK: [[CEIL_LOG2_10:%.+]] = call double @llvm.ceil.f64(double [[LOG2_10]])
+    // CHECK: [[CEIL_LOG2_10_INT:%.+]] = fptoui double [[CEIL_LOG2_10]] to i32
+    // CHECK: br label %[[OUTER_BODY:[^,]+]]
+    // CHECK: [[OUTER_BODY]]:
+    // CHECK: [[K:%.+]] = phi i32 [ 0, %{{.+}} ], [ [[K_NEXT:%.+]], %{{.+}} ]
+    // CHECK: [[K2POW:%.+]] = phi i64 [ 1, %{{.+}} ], [ [[K2POW_NEXT:%.+]], %{{.+}} ]
+    // CHECK: [[CMP:%.+]] = icmp uge i64 9, [[K2POW]]
+    // CHECK: br i1 [[CMP]], label %[[INNER_BODY:[^,]+]], label %[[INNER_EXIT:[^,]+]]
+    // CHECK: [[INNER_BODY]]:
+    // CHECK: [[I:%.+]] = phi i64 [ 9, %[[OUTER_BODY]] ], [ [[I_PREV:%.+]], %{{.+}} ]
+
+    // a_buffer[i] += a_buffer[i-pow(2, k)];
+    // CHECK: [[IDX:%.+]] = mul nsw i64 [[I]], [[NUM_ELEMS]]
+    // CHECK: [[A_BUF_IDX:%.+]] = getelementptr inbounds float, float* [[A_BUF]], i64 [[IDX]]
+    // CHECK: [[IDX_SUB_K2POW:%.+]] = sub nuw i64 [[I]], [[K2POW]]
+    // CHECK: [[IDX:%.+]] = mul nsw i64 [[IDX_SUB_K2POW]], [[NUM_ELEMS]]
+    // CHECK: [[A_BUF_IDX_SUB_K2POW:%.+]] = getelementptr inbounds float, float* [[A_BUF]], i64 [[IDX]]
+    // CHECK: [[B_BUF_IDX:%.+]] = getelementptr inbounds double, double* [[B_BUF]], i64 [[I]]
+    // CHECK: [[IDX_SUB_K2POW:%.+]] = sub nuw i64 [[I]], [[K2POW]]
+    // CHECK: [[B_BUF_IDX_SUB_K2POW:%.+]] = getelementptr inbounds double, double* [[B_BUF]], i64 [[IDX_SUB_K2POW]]
+    // CHECK: [[A_BUF_END:%.+]] = getelementptr float, float* [[A_BUF_IDX]], i64 [[NUM_ELEMS]]
+    // CHECK: [[ISEMPTY:%.+]] = icmp eq float* [[A_BUF_IDX]], [[A_BUF_END]]
+    // CHECK: br i1 [[ISEMPTY]], label %[[RED_DONE:[^,]+]], label %[[RED_BODY:[^,]+]]
+    // CHECK: [[RED_BODY]]:
+    // CHECK: [[A_BUF_IDX_SUB_K2POW_ELEM:%.+]] = phi float* [ [[A_BUF_IDX_SUB_K2POW]], %[[INNER_BODY]] ], [ [[A_BUF_IDX_SUB_K2POW_NEXT:%.+]], %[[RED_BODY]] ]
+    // CHECK: [[A_BUF_IDX_ELEM:%.+]] = phi float* [ [[A_BUF_IDX]], %[[INNER_BODY]] ], [ [[A_BUF_IDX_NEXT:%.+]], %[[RED_BODY]] ]
+    // CHECK: [[A_BUF_IDX_VAL:%.+]] = load float, float* [[A_BUF_IDX_ELEM]],
+    // CHECK: [[A_BUF_IDX_SUB_K2POW_VAL:%.+]] = load float, float* [[A_BUF_IDX_SUB_K2POW_ELEM]],
+    // CHECK: [[RED:%.+]] = fadd float [[A_BUF_IDX_VAL]], [[A_BUF_IDX_SUB_K2POW_VAL]]
+    // CHECK: store float [[RED]], float* [[A_BUF_IDX_ELEM]],
+    // CHECK: [[A_BUF_IDX_NEXT]] = getelementptr float, float* [[A_BUF_IDX_ELEM]], i32 1
+    // CHECK: [[A_BUF_IDX_SUB_K2POW_NEXT]] = getelementptr float, float* [[A_BUF_IDX_SUB_K2POW_ELEM]], i32 1
+    // CHECK: [[DONE:%.+]] = icmp eq float* [[A_BUF_IDX_NEXT]], [[A_BUF_END]]
+    // CHECK: br i1 [[DONE]], label %[[RED_DONE]], label %[[RED_BODY]]
+    // CHECK: [[RED_DONE]]:
+
+    // b_buffer[i] += b_buffer[i-pow(2, k)];
+    // CHECK: [[B_BUF_IDX_VAL:%.+]] = load double, double* [[B_BUF_IDX]],
+    // CHECK: [[B_BUF_IDX_SUB_K2POW_VAL:%.+]] = load double, double* [[B_BUF_IDX_SUB_K2POW]],
+    // CHECK: [[RED:%.+]] = fadd double [[B_BUF_IDX_VAL]], [[B_BUF_IDX_SUB_K2POW_VAL]]
+    // CHECK: store double [[RED]], double* [[B_BUF_IDX]],
+
+    // --i;
+    // CHECK: [[I_PREV:%.+]] = sub nuw i64 [[I]], 1
+    // CHECK: [[CMP:%.+]] = icmp uge i64 [[I_PREV]], [[K2POW]]
+    // CHECK: br i1 [[CMP]], label %[[INNER_BODY]], label %[[INNER_EXIT]]
+    // CHECK: [[INNER_EXIT]]:
+
+    // ++k;
+    // CHECK: [[K_NEXT]] = add nuw i32 [[K]], 1
+    // k2pow <<= 1;
+    // CHECK: [[K2POW_NEXT]] = shl nuw i64 [[K2POW]], 1
+    // CHECK: [[CMP:%.+]] = icmp ne i32 [[K_NEXT]], [[CEIL_LOG2_10_INT]]
+    // CHECK: br i1 [[CMP]], label %[[OUTER_BODY]], label %[[OUTER_EXIT:[^,]+]]
+    // CHECK: [[OUTER_EXIT]]:
+    bar();
+    // CHECK: call void @__kmpc_for_static_init_4(
+    // CHECK: call i8* @llvm.stacksave()
+    // CHECK: store float 0.000000e+00, float* %
+    // CHECK: store double 0.000000e+00, double* [[B_PRIV_ADDR:%.+]],
+    // CHECK: br label %[[DISPATCH:[^,]+]]
+
+    // CHECK: [[SCAN_PHASE:.+]]:
+    // CHECK: call void @{{.+}}foo{{.+}}()
+    // CHECK: br label %[[LOOP_CONTINUE:.+]]
+
+    // CHECK: [[DISPATCH]]:
+    // if (i >0)
+    //   a_priv[[0..n] = a_buffer[i-1][0..n];
+    // CHECK: [[BASE_IDX_I:%.+]] = load i32, i32* [[IV_ADDR:%.+]],
+    // CHECK: [[BASE_IDX:%.+]] = zext i32 [[BASE_IDX_I]] to i64
+    // CHECK: [[CMP:%.+]] = icmp eq i64 [[BASE_IDX]], 0
+    // CHECK: br i1 [[CMP]], label %[[IF_DONE:[^,]+]], label %[[IF_THEN:[^,]+]]
+    // CHECK: [[IF_THEN]]:
+    // CHECK: [[BASE_IDX_SUB_1:%.+]] = sub nuw i64 [[BASE_IDX]], 1
+    // CHECK: [[IDX:%.+]] = mul nsw i64 [[BASE_IDX_SUB_1]], [[NUM_ELEMS]]
+    // CHECK: [[A_BUF_IDX:%.+]] = getelementptr inbounds float, float* [[A_BUF]], i64 [[IDX]]
+    // CHECK: [[A_PRIV:%.+]] = getelementptr inbounds [10 x float], [10 x float]* [[A_PRIV_ADDR:%.+]], i64 0, i64 0
+    // CHECK: [[BYTES:%.+]] = mul nuw i64 [[NUM_ELEMS:%.+]], 4
+    // CHECK: [[DEST:%.+]] = bitcast float* [[A_PRIV]] to i8*
+    // CHECK: [[SRC:%.+]] = bitcast float* [[A_BUF_IDX]] to i8*
+    // CHECK: call void @llvm.memcpy.p0i8.p0i8.i64(i8* {{.*}}[[DEST]], i8* {{.*}}[[SRC]], i64 [[BYTES]], i1 false)
+
+    // b_priv = b_buffer[i];
+    // CHECK: [[B_BUF_IDX:%.+]] = getelementptr inbounds double, double* [[B_BUF]], i64 [[BASE_IDX_SUB_1]]
+    // CHECK: [[B_BUF_IDX_VAL:%.+]] = load double, double* [[B_BUF_IDX]],
+    // CHECK: store double [[B_BUF_IDX_VAL]], double* [[B_PRIV_ADDR]],
+    // CHECK: br label %[[SCAN_PHASE]]
+
+    // CHECK: [[LOOP_CONTINUE]]:
+    // CHECK: call void @llvm.stackrestore(i8* %
+    // CHECK: call void @__kmpc_for_static_fini(
+    // CHECK: call void @llvm.stackrestore(i8*
+    // CHECK: call void @__kmpc_barrier(
+  }
+}
+
+#endif
+

clang/test/OpenMP/scan_messages.cpp

#pragma omp for
   for (int i = 0; i < 10; ++i) {
 #pragma omp scan allocate(argc)  // expected-error {{unexpected OpenMP clause 'allocate' in directive '#pragma omp scan'}} expected-error {{exactly one of 'inclusive' or 'exclusive' clauses is expected}}
 #pragma omp scan untied  // expected-error {{unexpected OpenMP clause 'untied' in directive '#pragma omp scan'}} expected-error {{exactly one of 'inclusive' or 'exclusive' clauses is expected}}
 #pragma omp scan unknown // expected-warning {{extra tokens at the end of '#pragma omp scan' are ignored}} expected-error {{exactly one of 'inclusive' or 'exclusive' clauses is expected}}
   }
 #pragma omp for simd reduction(inscan, +: argc)
   for (int i = 0; i < 10; ++i)
     if (argc)
-#pragma omp scan inclusive(argc) // expected-error {{'#pragma omp scan' cannot be an immediate substatement}}
+#pragma omp scan inclusive(argc) // expected-error {{'#pragma omp scan' cannot be an immediate substatement}} expected-error {{orphaned 'omp scan' directives are prohibited; perhaps you forget to enclose the directive into a for, simd, for simd, parallel for, or parallel for simd region?}}
     if (argc) {
 #pragma omp scan inclusive(argc) // expected-error {{orphaned 'omp scan' directives are prohibited; perhaps you forget to enclose the directive into a for, simd, for simd, parallel for, or parallel for simd region?}}
     }
 #pragma omp simd reduction(inscan, +: argc)
   for (int i = 0; i < 10; ++i)
   while (argc)
-#pragma omp scan inclusive(argc) // expected-error {{'#pragma omp scan' cannot be an immediate substatement}}
+#pragma omp scan inclusive(argc) // expected-error {{'#pragma omp scan' cannot be an immediate substatement}} expected-error {{orphaned 'omp scan' directives are prohibited; perhaps you forget to enclose the directive into a for, simd, for simd, parallel for, or parallel for simd region?}}
     while (argc) {
 #pragma omp scan inclusive(argc) // expected-error {{orphaned 'omp scan' directives are prohibited; perhaps you forget to enclose the directive into a for, simd, for simd, parallel for, or parallel for simd region?}}
     }
 #pragma omp simd reduction(inscan, +: argc)
   for (int i = 0; i < 10; ++i)
   do
-#pragma omp scan inclusive(argc) // expected-error {{'#pragma omp scan' cannot be an immediate substatement}}
+#pragma omp scan inclusive(argc) // expected-error {{'#pragma omp scan' cannot be an immediate substatement}} expected-error {{orphaned 'omp scan' directives are prohibited; perhaps you forget to enclose the directive into a for, simd, for simd, parallel for, or parallel for simd region?}}
     while (argc)
       ;
-#pragma omp simd reduction(inscan, +: argc)
+#pragma omp simd reduction(inscan, +: argc) // expected-error {{the inscan reduction list item must appear as a list item in an 'inclusive' or 'exclusive' clause on an inner 'omp scan' directive}}
   for (int i = 0; i < 10; ++i)
   do {
-#pragma omp scan inclusive(argc)
+#pragma omp scan inclusive(argc) // expected-error {{orphaned 'omp scan' directives are prohibited; perhaps you forget to enclose the directive into a for, simd, for simd, parallel for, or parallel for simd region?}}
   } while (argc);
 #pragma omp simd reduction(inscan, +: argc)
   for (int i = 0; i < 10; ++i)
   switch (argc)
-#pragma omp scan inclusive(argc) // expected-error {{'#pragma omp scan' cannot be an immediate substatement}}
+#pragma omp scan inclusive(argc) // expected-error {{'#pragma omp scan' cannot be an immediate substatement}} expected-error {{orphaned 'omp scan' directives are prohibited; perhaps you forget to enclose the directive into a for, simd, for simd, parallel for, or parallel for simd region?}}
     switch (argc)
     case 1:
 #pragma omp scan inclusive(argc) // expected-error {{'#pragma omp scan' cannot be an immediate substatement}} expected-error {{orphaned 'omp scan' directives are prohibited; perhaps you forget to enclose the directive into a for, simd, for simd, parallel for, or parallel for simd region?}}
   switch (argc)
   case 1: {
 #pragma omp scan inclusive(argc) // expected-error {{orphaned 'omp scan' directives are prohibited; perhaps you forget to enclose the directive into a for, simd, for simd, parallel for, or parallel for simd region?}}
   }
-#pragma omp simd reduction(inscan, +: argc)
+#pragma omp simd reduction(inscan, +: argc) // expected-error {{the inscan reduction list item must appear as a list item in an 'inclusive' or 'exclusive' clause on an inner 'omp scan' directive}}
   for (int i = 0; i < 10; ++i)
   switch (argc) {
-#pragma omp scan exclusive(argc) // expected-note 2 {{previous 'scan' directive used here}}
+#pragma omp scan exclusive(argc) // expected-error {{orphaned 'omp scan' directives are prohibited; perhaps you forget to enclose the directive into a for, simd, for simd, parallel for, or parallel for simd region?}}
   case 1:
-#pragma omp scan exclusive(argc) // expected-error {{exactly one 'scan' directive must appear in the loop body of an enclosing directive}}
+#pragma omp scan exclusive(argc) // expected-error {{orphaned 'omp scan' directives are prohibited; perhaps you forget to enclose the directive into a for, simd, for simd, parallel for, or parallel for simd region?}}
     break;
   default: {
-#pragma omp scan exclusive(argc) // expected-error {{exactly one 'scan' directive must appear in the loop body of an enclosing directive}}
+#pragma omp scan exclusive(argc) // expected-error {{orphaned 'omp scan' directives are prohibited; perhaps you forget to enclose the directive into a for, simd, for simd, parallel for, or parallel for simd region?}}
   } break;
   }
 #pragma omp simd reduction(inscan, +: argc)
   for (int i = 0; i < 10; ++i)
   for (;;)
-#pragma omp scan exclusive(argc) // expected-error {{'#pragma omp scan' cannot be an immediate substatement}}
+#pragma omp scan exclusive(argc) // expected-error {{'#pragma omp scan' cannot be an immediate substatement}} expected-error {{orphaned 'omp scan' directives are prohibited; perhaps you forget to enclose the directive into a for, simd, for simd, parallel for, or parallel for simd region?}}
     for (;;) {
 #pragma omp scan exclusive(argc) // expected-error {{orphaned 'omp scan' directives are prohibited; perhaps you forget to enclose the directive into a for, simd, for simd, parallel for, or parallel for simd region?}}
     }
 #pragma omp simd reduction(inscan, +: argc)
   for (int i = 0; i < 10; ++i) {
 label:
 #pragma omp scan exclusive(argc)
   }
 #pragma omp simd reduction(inscan, +: argc)
   for (int i = 0; i < 10; ++i) {
+#pragma omp scan inclusive(argc) // expected-note {{previous 'scan' directive used here}}
+#pragma omp scan inclusive(argc) // expected-error {{exactly one 'scan' directive must appear in the loop body of an enclosing directive}}
 label1 : {
-#pragma omp scan inclusive(argc)
+#pragma omp scan inclusive(argc) // expected-error {{orphaned 'omp scan' directives are prohibited; perhaps you forget to enclose the directive into a for, simd, for simd, parallel for, or parallel for simd region?}}
 }}
 
   return T();
 }
 
 int main() {
   static int argc;
 #pragma omp simd reduction(inscan, +: argc)

 #pragma omp simd reduction(inscan, +: argc) // expected-error {{the inscan reduction list item must appear as a list item in an 'inclusive' or 'exclusive' clause on an inner 'omp scan' directive}}
   for (int i = 0; i < 10; ++i) {
 #pragma omp scan untied  // expected-error {{unexpected OpenMP clause 'untied' in directive '#pragma omp scan'}} expected-error {{exactly one of 'inclusive' or 'exclusive' clauses is expected}}
 #pragma omp scan unknown // expected-warning {{extra tokens at the end of '#pragma omp scan' are ignored}} expected-error {{exactly one of 'inclusive' or 'exclusive' clauses is expected}}
   }
 #pragma omp simd reduction(inscan, +: argc)
   for (int i = 0; i < 10; ++i)
   if (argc)
-#pragma omp scan inclusive(argc) // expected-error {{'#pragma omp scan' cannot be an immediate substatement}}
+#pragma omp scan inclusive(argc) // expected-error {{'#pragma omp scan' cannot be an immediate substatement}} expected-error {{orphaned 'omp scan' directives are prohibited; perhaps you forget to enclose the directive into a for, simd, for simd, parallel for, or parallel for simd region?}}
     if (argc) {
 #pragma omp scan inclusive(argc) // expected-error {{orphaned 'omp scan' directives are prohibited; perhaps you forget to enclose the directive into a for, simd, for simd, parallel for, or parallel for simd region?}} expected-error {{the list item must appear in 'reduction' clause with the 'inscan' modifier of the parent directive}}
     }
 #pragma omp simd reduction(inscan, +: argc)
   for (int i = 0; i < 10; ++i)
   while (argc)
-#pragma omp scan inclusive(argc) // expected-error {{'#pragma omp scan' cannot be an immediate substatement}}
+#pragma omp scan inclusive(argc) // expected-error {{'#pragma omp scan' cannot be an immediate substatement}} expected-error {{orphaned 'omp scan' directives are prohibited; perhaps you forget to enclose the directive into a for, simd, for simd, parallel for, or parallel for simd region?}}
     while (argc) {
 #pragma omp scan inclusive(argc) // expected-error {{orphaned 'omp scan' directives are prohibited; perhaps you forget to enclose the directive into a for, simd, for simd, parallel for, or parallel for simd region?}} expected-error {{the list item must appear in 'reduction' clause with the 'inscan' modifier of the parent directive}}
     }
 #pragma omp simd reduction(inscan, +: argc)
   for (int i = 0; i < 10; ++i)
   do
-#pragma omp scan inclusive(argc) // expected-error {{'#pragma omp scan' cannot be an immediate substatement}}
+#pragma omp scan inclusive(argc) // expected-error {{'#pragma omp scan' cannot be an immediate substatement}} expected-error {{orphaned 'omp scan' directives are prohibited; perhaps you forget to enclose the directive into a for, simd, for simd, parallel for, or parallel for simd region?}}
     while (argc)
       ;
 #pragma omp simd reduction(inscan, +: argc)
   for (int i = 0; i < 10; ++i)
   do {
-#pragma omp scan exclusive(argc)
+#pragma omp scan exclusive(argc) // expected-error {{orphaned 'omp scan' directives are prohibited; perhaps you forget to enclose the directive into a for, simd, for simd, parallel for, or parallel for simd region?}}
   } while (argc);
 #pragma omp simd reduction(inscan, +: argc)
   for (int i = 0; i < 10; ++i)
   switch (argc)
-#pragma omp scan exclusive(argc) // expected-error {{'#pragma omp scan' cannot be an immediate substatement}}
+#pragma omp scan exclusive(argc) // expected-error {{'#pragma omp scan' cannot be an immediate substatement}} expected-error {{orphaned 'omp scan' directives are prohibited; perhaps you forget to enclose the directive into a for, simd, for simd, parallel for, or parallel for simd region?}}
     switch (argc)
     case 1:
 #pragma omp scan exclusive(argc) // expected-error {{'#pragma omp scan' cannot be an immediate substatement}} expected-error {{orphaned 'omp scan' directives are prohibited; perhaps you forget to enclose the directive into a for, simd, for simd, parallel for, or parallel for simd region?}} expected-error {{the list item must appear in 'reduction' clause with the 'inscan' modifier of the parent directive}}
   switch (argc)
   case 1: {
 #pragma omp scan exclusive(argc) // expected-error {{orphaned 'omp scan' directives are prohibited; perhaps you forget to enclose the directive into a for, simd, for simd, parallel for, or parallel for simd region?}} expected-error {{the list item must appear in 'reduction' clause with the 'inscan' modifier of the parent directive}}
   }
 #pragma omp simd reduction(inscan, +: argc)
   for (int i = 0; i < 10; ++i)
   switch (argc) {
-#pragma omp scan inclusive(argc) // expected-note 2 {{previous 'scan' directive used here}}
+#pragma omp scan inclusive(argc) // expected-error {{orphaned 'omp scan' directives are prohibited; perhaps you forget to enclose the directive into a for, simd, for simd, parallel for, or parallel for simd region?}}
   case 1:
-#pragma omp scan inclusive(argc) // expected-error {{exactly one 'scan' directive must appear in the loop body of an enclosing directive}}
+#pragma omp scan inclusive(argc) // expected-error {{orphaned 'omp scan' directives are prohibited; perhaps you forget to enclose the directive into a for, simd, for simd, parallel for, or parallel for simd region?}}
     break;
   default: {
-#pragma omp scan inclusive(argc) // expected-error {{exactly one 'scan' directive must appear in the loop body of an enclosing directive}}
+#pragma omp scan inclusive(argc) // expected-error {{orphaned 'omp scan' directives are prohibited; perhaps you forget to enclose the directive into a for, simd, for simd, parallel for, or parallel for simd region?}}
   } break;
   }
 #pragma omp simd reduction(inscan, +: argc)
   for (int i = 0; i < 10; ++i)
   for (;;)
-#pragma omp scan inclusive(argc) // expected-error {{'#pragma omp scan' cannot be an immediate substatement}}
+#pragma omp scan inclusive(argc) // expected-error {{'#pragma omp scan' cannot be an immediate substatement}} expected-error {{orphaned 'omp scan' directives are prohibited; perhaps you forget to enclose the directive into a for, simd, for simd, parallel for, or parallel for simd region?}}
     for (;;) {
 #pragma omp scan inclusive(argc) // expected-error {{orphaned 'omp scan' directives are prohibited; perhaps you forget to enclose the directive into a for, simd, for simd, parallel for, or parallel for simd region?}} expected-error {{the list item must appear in 'reduction' clause with the 'inscan' modifier of the parent directive}}
     }
 #pragma omp simd reduction(inscan, +: argc)
   for (int i = 0; i < 10; ++i) {
 label:
 #pragma omp scan inclusive(argc)
   }
 #pragma omp simd reduction(inscan, +: argc)
   for (int i = 0; i < 10; ++i) {
+#pragma omp scan inclusive(argc) // expected-note {{previous 'scan' directive used here}}
+#pragma omp scan inclusive(argc) // expected-error {{exactly one 'scan' directive must appear in the loop body of an enclosing directive}}
 label1 : {
-#pragma omp scan inclusive(argc)
+#pragma omp scan inclusive(argc) // expected-error {{orphaned 'omp scan' directives are prohibited; perhaps you forget to enclose the directive into a for, simd, for simd, parallel for, or parallel for simd region?}}
 }
 }
 
-  return tmain<int>();
+  return tmain<int>(); // expected-note {{in instantiation of function template specialization 'tmain<int>' requested here}}
 }

clang/tools/libclang/CIndex.cpp

for (auto *E : C->lhs_exprs()) {
     Visitor->AddStmt(E);
   }
   for (auto *E : C->rhs_exprs()) {
     Visitor->AddStmt(E);
   }
   for (auto *E : C->reduction_ops()) {
     Visitor->AddStmt(E);
   }
+  if (C->getModifier() == clang::OMPC_REDUCTION_inscan) {
+    for (auto *E : C->copy_ops()) {
+      Visitor->AddStmt(E);
+    }
+    for (auto *E : C->copy_array_temps()) {
+      Visitor->AddStmt(E);
+    }
+    for (auto *E : C->copy_array_elems()) {
+      Visitor->AddStmt(E);
+    }
+  }
 }
 void OMPClauseEnqueue::VisitOMPTaskReductionClause(
     const OMPTaskReductionClause *C) {
   VisitOMPClauseList(C);
   VisitOMPClauseWithPostUpdate(C);
   for (auto *E : C->privates()) {
     Visitor->AddStmt(E);
   }