From: Richard Smith <richard-llvm@metafoo.co.uk>
Date: Thu, 30 May 2019 23:21:14 +0000 (+0000)
Subject: Refactor OpenMP stack management.
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=a7fb0fca0bbe2fea51490be70f219d1d818fac8f;p=clang

Refactor OpenMP stack management.

Instead of duplicating access to the directive stack throughout
SemaOpenMP.cpp, consolidate it to a few methods and call those
everywhere else. In passing, simplify adjacent code where possible.

No functionality change intended.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@362172 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Sema/SemaOpenMP.cpp b/lib/Sema/SemaOpenMP.cpp
index 19a7d784c5..5a6b49961f 100644
--- a/lib/Sema/SemaOpenMP.cpp
+++ b/lib/Sema/SemaOpenMP.cpp
@@ -173,18 +173,78 @@ private:
   bool ForceCaptureByReferenceInTargetExecutable = false;
   CriticalsWithHintsTy Criticals;
 
-  using iterator = StackTy::const_reverse_iterator;
+  /// Iterators over the stack iterate in order from innermost to outermost
+  /// directive.
+  using const_iterator = StackTy::const_reverse_iterator;
+  const_iterator begin() const {
+    return Stack.empty() ? const_iterator() : Stack.back().first.rbegin();
+  }
+  const_iterator end() const {
+    return Stack.empty() ? const_iterator() : Stack.back().first.rend();
+  }
+  using iterator = StackTy::reverse_iterator;
+  iterator begin() {
+    return Stack.empty() ? iterator() : Stack.back().first.rbegin();
+  }
+  iterator end() {
+    return Stack.empty() ? iterator() : Stack.back().first.rend();
+  }
 
-  DSAVarData getDSA(iterator &Iter, ValueDecl *D) const;
-
-  /// Checks if the variable is a local for OpenMP region.
-  bool isOpenMPLocal(VarDecl *D, iterator Iter) const;
+  // Convenience operations to get at the elements of the stack.
 
   bool isStackEmpty() const {
     return Stack.empty() ||
            Stack.back().second != CurrentNonCapturingFunctionScope ||
            Stack.back().first.empty();
   }
+  size_t getStackSize() const {
+    return isStackEmpty() ? 0 : Stack.back().first.size();
+  }
+
+  SharingMapTy *getTopOfStackOrNull() {
+    if (isStackEmpty())
+      return nullptr;
+    return &Stack.back().first.back();
+  }
+  const SharingMapTy *getTopOfStackOrNull() const {
+    return const_cast<DSAStackTy&>(*this).getTopOfStackOrNull();
+  }
+  SharingMapTy &getTopOfStack() {
+    assert(!isStackEmpty() && "no current directive");
+    return *getTopOfStackOrNull();
+  }
+  const SharingMapTy &getTopOfStack() const {
+    return const_cast<DSAStackTy&>(*this).getTopOfStack();
+  }
+
+  SharingMapTy *getSecondOnStackOrNull() {
+    size_t Size = getStackSize();
+    if (Size <= 1)
+      return nullptr;
+    return &Stack.back().first[Size - 2];
+  }
+  const SharingMapTy *getSecondOnStackOrNull() const {
+    return const_cast<DSAStackTy&>(*this).getSecondOnStackOrNull();
+  }
+
+  /// Get the stack element at a certain level (previously returned by
+  /// \c getNestingLevel).
+  ///
+  /// Note that nesting levels count from outermost to innermost, and this is
+  /// the reverse of our iteration order where new inner levels are pushed at
+  /// the front of the stack.
+  SharingMapTy &getStackElemAtLevel(unsigned Level) {
+    assert(Level < getStackSize() && "no such stack element");
+    return Stack.back().first[Level];
+  }
+  const SharingMapTy &getStackElemAtLevel(unsigned Level) const {
+    return const_cast<DSAStackTy&>(*this).getStackElemAtLevel(Level);
+  }
+
+  DSAVarData getDSA(const_iterator &Iter, ValueDecl *D) const;
+
+  /// Checks if the variable is a local for OpenMP region.
+  bool isOpenMPLocal(VarDecl *D, const_iterator Iter) const;
 
   /// Vector of previously declared requires directives
   SmallVector<const OMPRequiresDecl *, 2> RequiresDecls;
@@ -249,28 +309,28 @@ public:
   void loopInit() {
     assert(isOpenMPLoopDirective(getCurrentDirective()) &&
            "Expected loop-based directive.");
-    Stack.back().first.back().LoopStart = true;
+    getTopOfStack().LoopStart = true;
   }
   /// Start capturing of the variables in the loop context.
   void loopStart() {
     assert(isOpenMPLoopDirective(getCurrentDirective()) &&
            "Expected loop-based directive.");
-    Stack.back().first.back().LoopStart = false;
+    getTopOfStack().LoopStart = false;
   }
   /// true, if variables are captured, false otherwise.
   bool isLoopStarted() const {
     assert(isOpenMPLoopDirective(getCurrentDirective()) &&
            "Expected loop-based directive.");
-    return !Stack.back().first.back().LoopStart;
+    return !getTopOfStack().LoopStart;
   }
   /// Marks (or clears) declaration as possibly loop counter.
   void resetPossibleLoopCounter(const Decl *D = nullptr) {
-    Stack.back().first.back().PossiblyLoopCounter =
+    getTopOfStack().PossiblyLoopCounter =
         D ? D->getCanonicalDecl() : D;
   }
   /// Gets the possible loop counter decl.
   const Decl *getPossiblyLoopCunter() const {
-    return Stack.back().first.back().PossiblyLoopCounter;
+    return getTopOfStack().PossiblyLoopCounter;
   }
   /// Start new OpenMP region stack in new non-capturing function.
   void pushFunction() {
@@ -350,16 +410,16 @@ public:
                                    Expr *&TaskgroupDescriptor) const;
   /// Return reduction reference expression for the current taskgroup.
   Expr *getTaskgroupReductionRef() const {
-    assert(Stack.back().first.back().Directive == OMPD_taskgroup &&
+    assert(getTopOfStack().Directive == OMPD_taskgroup &&
            "taskgroup reference expression requested for non taskgroup "
            "directive.");
-    return Stack.back().first.back().TaskgroupReductionRef;
+    return getTopOfStack().TaskgroupReductionRef;
   }
   /// Checks if the given \p VD declaration is actually a taskgroup reduction
   /// descriptor variable at the \p Level of OpenMP regions.
   bool isTaskgroupReductionRef(const ValueDecl *VD, unsigned Level) const {
-    return Stack.back().first[Level].TaskgroupReductionRef &&
-           cast<DeclRefExpr>(Stack.back().first[Level].TaskgroupReductionRef)
+    return getStackElemAtLevel(Level).TaskgroupReductionRef &&
+           cast<DeclRefExpr>(getStackElemAtLevel(Level).TaskgroupReductionRef)
                    ->getDecl() == VD;
   }
 
@@ -405,18 +465,18 @@ public:
 
   /// Returns currently analyzed directive.
   OpenMPDirectiveKind getCurrentDirective() const {
-    return isStackEmpty() ? OMPD_unknown : Stack.back().first.back().Directive;
+    const SharingMapTy *Top = getTopOfStackOrNull();
+    return Top ? Top->Directive : OMPD_unknown;
   }
   /// Returns directive kind at specified level.
   OpenMPDirectiveKind getDirective(unsigned Level) const {
     assert(!isStackEmpty() && "No directive at specified level.");
-    return Stack.back().first[Level].Directive;
+    return getStackElemAtLevel(Level).Directive;
   }
   /// Returns parent directive.
   OpenMPDirectiveKind getParentDirective() const {
-    if (isStackEmpty() || Stack.back().first.size() == 1)
-      return OMPD_unknown;
-    return std::next(Stack.back().first.rbegin())->Directive;
+    const SharingMapTy *Parent = getSecondOnStackOrNull();
+    return Parent ? Parent->Directive : OMPD_unknown;
   }
 
   /// Add requires decl to internal vector
@@ -468,41 +528,38 @@ public:
 
   /// Set default data sharing attribute to none.
   void setDefaultDSANone(SourceLocation Loc) {
-    assert(!isStackEmpty());
-    Stack.back().first.back().DefaultAttr = DSA_none;
-    Stack.back().first.back().DefaultAttrLoc = Loc;
+    getTopOfStack().DefaultAttr = DSA_none;
+    getTopOfStack().DefaultAttrLoc = Loc;
   }
   /// Set default data sharing attribute to shared.
   void setDefaultDSAShared(SourceLocation Loc) {
-    assert(!isStackEmpty());
-    Stack.back().first.back().DefaultAttr = DSA_shared;
-    Stack.back().first.back().DefaultAttrLoc = Loc;
+    getTopOfStack().DefaultAttr = DSA_shared;
+    getTopOfStack().DefaultAttrLoc = Loc;
   }
   /// Set default data mapping attribute to 'tofrom:scalar'.
   void setDefaultDMAToFromScalar(SourceLocation Loc) {
-    assert(!isStackEmpty());
-    Stack.back().first.back().DefaultMapAttr = DMA_tofrom_scalar;
-    Stack.back().first.back().DefaultMapAttrLoc = Loc;
+    getTopOfStack().DefaultMapAttr = DMA_tofrom_scalar;
+    getTopOfStack().DefaultMapAttrLoc = Loc;
   }
 
   DefaultDataSharingAttributes getDefaultDSA() const {
     return isStackEmpty() ? DSA_unspecified
-                          : Stack.back().first.back().DefaultAttr;
+                          : getTopOfStack().DefaultAttr;
   }
   SourceLocation getDefaultDSALocation() const {
     return isStackEmpty() ? SourceLocation()
-                          : Stack.back().first.back().DefaultAttrLoc;
+                          : getTopOfStack().DefaultAttrLoc;
   }
   DefaultMapAttributes getDefaultDMA() const {
     return isStackEmpty() ? DMA_unspecified
-                          : Stack.back().first.back().DefaultMapAttr;
+                          : getTopOfStack().DefaultMapAttr;
   }
   DefaultMapAttributes getDefaultDMAAtLevel(unsigned Level) const {
-    return Stack.back().first[Level].DefaultMapAttr;
+    return getStackElemAtLevel(Level).DefaultMapAttr;
   }
   SourceLocation getDefaultDMALocation() const {
     return isStackEmpty() ? SourceLocation()
-                          : Stack.back().first.back().DefaultMapAttrLoc;
+                          : getTopOfStack().DefaultMapAttrLoc;
   }
 
   /// Checks if the specified variable is a threadprivate.
@@ -514,82 +571,77 @@ public:
   /// Marks current region as ordered (it has an 'ordered' clause).
   void setOrderedRegion(bool IsOrdered, const Expr *Param,
                         OMPOrderedClause *Clause) {
-    assert(!isStackEmpty());
     if (IsOrdered)
-      Stack.back().first.back().OrderedRegion.emplace(Param, Clause);
+      getTopOfStack().OrderedRegion.emplace(Param, Clause);
     else
-      Stack.back().first.back().OrderedRegion.reset();
+      getTopOfStack().OrderedRegion.reset();
   }
   /// Returns true, if region is ordered (has associated 'ordered' clause),
   /// false - otherwise.
   bool isOrderedRegion() const {
-    if (isStackEmpty())
-      return false;
-    return Stack.back().first.rbegin()->OrderedRegion.hasValue();
+    if (const SharingMapTy *Top = getTopOfStackOrNull())
+      return Top->OrderedRegion.hasValue();
+    return false;
   }
   /// Returns optional parameter for the ordered region.
   std::pair<const Expr *, OMPOrderedClause *> getOrderedRegionParam() const {
-    if (isStackEmpty() ||
-        !Stack.back().first.rbegin()->OrderedRegion.hasValue())
-      return std::make_pair(nullptr, nullptr);
-    return Stack.back().first.rbegin()->OrderedRegion.getValue();
+    if (const SharingMapTy *Top = getTopOfStackOrNull())
+      if (Top->OrderedRegion.hasValue())
+        return Top->OrderedRegion.getValue();
+    return std::make_pair(nullptr, nullptr);
   }
   /// Returns true, if parent region is ordered (has associated
   /// 'ordered' clause), false - otherwise.
   bool isParentOrderedRegion() const {
-    if (isStackEmpty() || Stack.back().first.size() == 1)
-      return false;
-    return std::next(Stack.back().first.rbegin())->OrderedRegion.hasValue();
+    if (const SharingMapTy *Parent = getSecondOnStackOrNull())
+      return Parent->OrderedRegion.hasValue();
+    return false;
   }
   /// Returns optional parameter for the ordered region.
   std::pair<const Expr *, OMPOrderedClause *>
   getParentOrderedRegionParam() const {
-    if (isStackEmpty() || Stack.back().first.size() == 1 ||
-        !std::next(Stack.back().first.rbegin())->OrderedRegion.hasValue())
-      return std::make_pair(nullptr, nullptr);
-    return std::next(Stack.back().first.rbegin())->OrderedRegion.getValue();
+    if (const SharingMapTy *Parent = getSecondOnStackOrNull())
+      if (Parent->OrderedRegion.hasValue())
+        return Parent->OrderedRegion.getValue();
+    return std::make_pair(nullptr, nullptr);
   }
   /// Marks current region as nowait (it has a 'nowait' clause).
   void setNowaitRegion(bool IsNowait = true) {
-    assert(!isStackEmpty());
-    Stack.back().first.back().NowaitRegion = IsNowait;
+    getTopOfStack().NowaitRegion = IsNowait;
   }
   /// Returns true, if parent region is nowait (has associated
   /// 'nowait' clause), false - otherwise.
   bool isParentNowaitRegion() const {
-    if (isStackEmpty() || Stack.back().first.size() == 1)
-      return false;
-    return std::next(Stack.back().first.rbegin())->NowaitRegion;
+    if (const SharingMapTy *Parent = getSecondOnStackOrNull())
+      return Parent->NowaitRegion;
+    return false;
   }
   /// Marks parent region as cancel region.
   void setParentCancelRegion(bool Cancel = true) {
-    if (!isStackEmpty() && Stack.back().first.size() > 1) {
-      auto &StackElemRef = *std::next(Stack.back().first.rbegin());
-      StackElemRef.CancelRegion |= StackElemRef.CancelRegion || Cancel;
-    }
+    if (SharingMapTy *Parent = getSecondOnStackOrNull())
+      Parent->CancelRegion |= Cancel;
   }
   /// Return true if current region has inner cancel construct.
   bool isCancelRegion() const {
-    return isStackEmpty() ? false : Stack.back().first.back().CancelRegion;
+    const SharingMapTy *Top = getTopOfStackOrNull();
+    return Top ? Top->CancelRegion : false;
   }
 
   /// Set collapse value for the region.
   void setAssociatedLoops(unsigned Val) {
-    assert(!isStackEmpty());
-    Stack.back().first.back().AssociatedLoops = Val;
+    getTopOfStack().AssociatedLoops = Val;
   }
   /// Return collapse value for region.
   unsigned getAssociatedLoops() const {
-    return isStackEmpty() ? 0 : Stack.back().first.back().AssociatedLoops;
+    const SharingMapTy *Top = getTopOfStackOrNull();
+    return Top ? Top->AssociatedLoops : 0;
   }
 
   /// Marks current target region as one with closely nested teams
   /// region.
   void setParentTeamsRegionLoc(SourceLocation TeamsRegionLoc) {
-    if (!isStackEmpty() && Stack.back().first.size() > 1) {
-      std::next(Stack.back().first.rbegin())->InnerTeamsRegionLoc =
-          TeamsRegionLoc;
-    }
+    if (SharingMapTy *Parent = getSecondOnStackOrNull())
+      Parent->InnerTeamsRegionLoc = TeamsRegionLoc;
   }
   /// Returns true, if current region has closely nested teams region.
   bool hasInnerTeamsRegion() const {
@@ -597,16 +649,17 @@ public:
   }
   /// Returns location of the nested teams region (if any).
   SourceLocation getInnerTeamsRegionLoc() const {
-    return isStackEmpty() ? SourceLocation()
-                          : Stack.back().first.back().InnerTeamsRegionLoc;
+    const SharingMapTy *Top = getTopOfStackOrNull();
+    return Top ? Top->InnerTeamsRegionLoc : SourceLocation();
   }
 
   Scope *getCurScope() const {
-    return isStackEmpty() ? nullptr : Stack.back().first.back().CurScope;
+    const SharingMapTy *Top = getTopOfStackOrNull();
+    return Top ? Top->CurScope : nullptr;
   }
   SourceLocation getConstructLoc() const {
-    return isStackEmpty() ? SourceLocation()
-                          : Stack.back().first.back().ConstructLoc;
+    const SharingMapTy *Top = getTopOfStackOrNull();
+    return Top ? Top->ConstructLoc : SourceLocation();
   }
 
   /// Do the check specified in \a Check to all component lists and return true
@@ -619,8 +672,8 @@ public:
           Check) const {
     if (isStackEmpty())
       return false;
-    auto SI = Stack.back().first.rbegin();
-    auto SE = Stack.back().first.rend();
+    auto SI = begin();
+    auto SE = end();
 
     if (SI == SE)
       return false;
@@ -649,17 +702,12 @@ public:
           bool(OMPClauseMappableExprCommon::MappableExprComponentListRef,
                OpenMPClauseKind)>
           Check) const {
-    if (isStackEmpty())
-      return false;
-
-    auto StartI = Stack.back().first.begin();
-    auto EndI = Stack.back().first.end();
-    if (std::distance(StartI, EndI) <= (int)Level)
+    if (getStackSize() <= Level)
       return false;
-    std::advance(StartI, Level);
 
-    auto MI = StartI->MappedExprComponents.find(VD);
-    if (MI != StartI->MappedExprComponents.end())
+    const SharingMapTy &StackElem = getStackElemAtLevel(Level);
+    auto MI = StackElem.MappedExprComponents.find(VD);
+    if (MI != StackElem.MappedExprComponents.end())
       for (OMPClauseMappableExprCommon::MappableExprComponentListRef L :
            MI->second.Components)
         if (Check(L, MI->second.Kind))
@@ -673,10 +721,7 @@ public:
       const ValueDecl *VD,
       OMPClauseMappableExprCommon::MappableExprComponentListRef Components,
       OpenMPClauseKind WhereFoundClauseKind) {
-    assert(!isStackEmpty() &&
-           "Not expecting to retrieve components from a empty stack!");
-    MappedExprComponentTy &MEC =
-        Stack.back().first.back().MappedExprComponents[VD];
+    MappedExprComponentTy &MEC = getTopOfStack().MappedExprComponents[VD];
     // Create new entry and append the new components there.
     MEC.Components.resize(MEC.Components.size() + 1);
     MEC.Components.back().append(Components.begin(), Components.end());
@@ -685,19 +730,17 @@ public:
 
   unsigned getNestingLevel() const {
     assert(!isStackEmpty());
-    return Stack.back().first.size() - 1;
+    return getStackSize() - 1;
   }
   void addDoacrossDependClause(OMPDependClause *C,
                                const OperatorOffsetTy &OpsOffs) {
-    assert(!isStackEmpty() && Stack.back().first.size() > 1);
-    SharingMapTy &StackElem = *std::next(Stack.back().first.rbegin());
-    assert(isOpenMPWorksharingDirective(StackElem.Directive));
-    StackElem.DoacrossDepends.try_emplace(C, OpsOffs);
+    SharingMapTy *Parent = getSecondOnStackOrNull();
+    assert(Parent && isOpenMPWorksharingDirective(Parent->Directive));
+    Parent->DoacrossDepends.try_emplace(C, OpsOffs);
   }
   llvm::iterator_range<DoacrossDependMapTy::const_iterator>
   getDoacrossDependClauses() const {
-    assert(!isStackEmpty());
-    const SharingMapTy &StackElem = Stack.back().first.back();
+    const SharingMapTy &StackElem = getTopOfStack();
     if (isOpenMPWorksharingDirective(StackElem.Directive)) {
       const DoacrossDependMapTy &Ref = StackElem.DoacrossDepends;
       return llvm::make_range(Ref.begin(), Ref.end());
@@ -708,13 +751,13 @@ public:
 
   // Store types of classes which have been explicitly mapped
   void addMappedClassesQualTypes(QualType QT) {
-    SharingMapTy &StackElem = Stack.back().first.back();
+    SharingMapTy &StackElem = getTopOfStack();
     StackElem.MappedClassesQualTypes.insert(QT);
   }
 
   // Return set of mapped classes types
   bool isClassPreviouslyMapped(QualType QT) const {
-    const SharingMapTy &StackElem = Stack.back().first.back();
+    const SharingMapTy &StackElem = getTopOfStack();
     return StackElem.MappedClassesQualTypes.count(QT) != 0;
   }
 
@@ -723,16 +766,11 @@ public:
     assert(*OMPDeclareTargetDeclAttr::isDeclareTargetDeclaration(
                E->getDecl()) == OMPDeclareTargetDeclAttr::MT_Link &&
            "Expected declare target link global.");
-    if (isStackEmpty())
-      return;
-    auto It = Stack.back().first.rbegin();
-    while (It != Stack.back().first.rend() &&
-           !isOpenMPTargetExecutionDirective(It->Directive))
-      ++It;
-    if (It != Stack.back().first.rend()) {
-      assert(isOpenMPTargetExecutionDirective(It->Directive) &&
-             "Expected target executable directive.");
-      It->DeclareTargetLinkVarDecls.push_back(E);
+    for (auto &Elem : *this) {
+      if (isOpenMPTargetExecutionDirective(Elem.Directive)) {
+        Elem.DeclareTargetLinkVarDecls.push_back(E);
+        return;
+      }
     }
   }
 
@@ -741,7 +779,7 @@ public:
   ArrayRef<DeclRefExpr *> getLinkGlobals() const {
     assert(isOpenMPTargetExecutionDirective(getCurrentDirective()) &&
            "Expected target executable directive.");
-    return Stack.back().first.back().DeclareTargetLinkVarDecls;
+    return getTopOfStack().DeclareTargetLinkVarDecls;
   }
 };
 
@@ -797,13 +835,13 @@ static ValueDecl *getCanonicalDecl(ValueDecl *D) {
       getCanonicalDecl(const_cast<const ValueDecl *>(D)));
 }
 
-DSAStackTy::DSAVarData DSAStackTy::getDSA(iterator &Iter,
+DSAStackTy::DSAVarData DSAStackTy::getDSA(const_iterator &Iter,
                                           ValueDecl *D) const {
   D = getCanonicalDecl(D);
   auto *VD = dyn_cast<VarDecl>(D);
   const auto *FD = dyn_cast<FieldDecl>(D);
   DSAVarData DVar;
-  if (isStackEmpty() || Iter == Stack.back().first.rend()) {
+  if (Iter == end()) {
     // OpenMP [2.9.1.1, Data-sharing Attribute Rules for Variables Referenced
     // in a region but not in construct]
     //  File-scope or namespace-scope variables referenced in called routines
@@ -878,7 +916,7 @@ DSAStackTy::DSAVarData DSAStackTy::getDSA(iterator &Iter,
     //  bound to the current team is shared.
     if (isOpenMPTaskingDirective(DVar.DKind)) {
       DSAVarData DVarTemp;
-      iterator I = Iter, E = Stack.back().first.rend();
+      const_iterator I = Iter, E = end();
       do {
         ++I;
         // OpenMP [2.9.1.1, Data-sharing Attribute Rules for Variables
@@ -910,7 +948,7 @@ const Expr *DSAStackTy::addUniqueAligned(const ValueDecl *D,
                                          const Expr *NewDE) {
   assert(!isStackEmpty() && "Data sharing attributes stack is empty");
   D = getCanonicalDecl(D);
-  SharingMapTy &StackElem = Stack.back().first.back();
+  SharingMapTy &StackElem = getTopOfStack();
   auto It = StackElem.AlignedMap.find(D);
   if (It == StackElem.AlignedMap.end()) {
     assert(NewDE && "Unexpected nullptr expr to be added into aligned map");
@@ -924,7 +962,7 @@ const Expr *DSAStackTy::addUniqueAligned(const ValueDecl *D,
 void DSAStackTy::addLoopControlVariable(const ValueDecl *D, VarDecl *Capture) {
   assert(!isStackEmpty() && "Data-sharing attributes stack is empty");
   D = getCanonicalDecl(D);
-  SharingMapTy &StackElem = Stack.back().first.back();
+  SharingMapTy &StackElem = getTopOfStack();
   StackElem.LCVMap.try_emplace(
       D, LCDeclInfo(StackElem.LCVMap.size() + 1, Capture));
 }
@@ -933,7 +971,7 @@ const DSAStackTy::LCDeclInfo
 DSAStackTy::isLoopControlVariable(const ValueDecl *D) const {
   assert(!isStackEmpty() && "Data-sharing attributes stack is empty");
   D = getCanonicalDecl(D);
-  const SharingMapTy &StackElem = Stack.back().first.back();
+  const SharingMapTy &StackElem = getTopOfStack();
   auto It = StackElem.LCVMap.find(D);
   if (It != StackElem.LCVMap.end())
     return It->second;
@@ -942,23 +980,21 @@ DSAStackTy::isLoopControlVariable(const ValueDecl *D) const {
 
 const DSAStackTy::LCDeclInfo
 DSAStackTy::isParentLoopControlVariable(const ValueDecl *D) const {
-  assert(!isStackEmpty() && Stack.back().first.size() > 1 &&
-         "Data-sharing attributes stack is empty");
+  const SharingMapTy *Parent = getSecondOnStackOrNull();
+  assert(Parent && "Data-sharing attributes stack is empty");
   D = getCanonicalDecl(D);
-  const SharingMapTy &StackElem = *std::next(Stack.back().first.rbegin());
-  auto It = StackElem.LCVMap.find(D);
-  if (It != StackElem.LCVMap.end())
+  auto It = Parent->LCVMap.find(D);
+  if (It != Parent->LCVMap.end())
     return It->second;
   return {0, nullptr};
 }
 
 const ValueDecl *DSAStackTy::getParentLoopControlVariable(unsigned I) const {
-  assert(!isStackEmpty() && Stack.back().first.size() > 1 &&
-         "Data-sharing attributes stack is empty");
-  const SharingMapTy &StackElem = *std::next(Stack.back().first.rbegin());
-  if (StackElem.LCVMap.size() < I)
+  const SharingMapTy *Parent = getSecondOnStackOrNull();
+  assert(Parent && "Data-sharing attributes stack is empty");
+  if (Parent->LCVMap.size() < I)
     return nullptr;
-  for (const auto &Pair : StackElem.LCVMap)
+  for (const auto &Pair : Parent->LCVMap)
     if (Pair.second.first == I)
       return Pair.first;
   return nullptr;
@@ -973,8 +1009,7 @@ void DSAStackTy::addDSA(const ValueDecl *D, const Expr *E, OpenMPClauseKind A,
     Data.RefExpr.setPointer(E);
     Data.PrivateCopy = nullptr;
   } else {
-    assert(!isStackEmpty() && "Data-sharing attributes stack is empty");
-    DSAInfo &Data = Stack.back().first.back().SharingMap[D];
+    DSAInfo &Data = getTopOfStack().SharingMap[D];
     assert(Data.Attributes == OMPC_unknown || (A == Data.Attributes) ||
            (A == OMPC_firstprivate && Data.Attributes == OMPC_lastprivate) ||
            (A == OMPC_lastprivate && Data.Attributes == OMPC_firstprivate) ||
@@ -989,8 +1024,7 @@ void DSAStackTy::addDSA(const ValueDecl *D, const Expr *E, OpenMPClauseKind A,
     Data.RefExpr.setPointerAndInt(E, IsLastprivate);
     Data.PrivateCopy = PrivateCopy;
     if (PrivateCopy) {
-      DSAInfo &Data =
-          Stack.back().first.back().SharingMap[PrivateCopy->getDecl()];
+      DSAInfo &Data = getTopOfStack().SharingMap[PrivateCopy->getDecl()];
       Data.Attributes = A;
       Data.RefExpr.setPointerAndInt(PrivateCopy, IsLastprivate);
       Data.PrivateCopy = nullptr;
@@ -1035,16 +1069,16 @@ void DSAStackTy::addTaskgroupReductionData(const ValueDecl *D, SourceRange SR,
   D = getCanonicalDecl(D);
   assert(!isStackEmpty() && "Data-sharing attributes stack is empty");
   assert(
-      Stack.back().first.back().SharingMap[D].Attributes == OMPC_reduction &&
+      getTopOfStack().SharingMap[D].Attributes == OMPC_reduction &&
       "Additional reduction info may be specified only for reduction items.");
-  ReductionData &ReductionData = Stack.back().first.back().ReductionMap[D];
+  ReductionData &ReductionData = getTopOfStack().ReductionMap[D];
   assert(ReductionData.ReductionRange.isInvalid() &&
-         Stack.back().first.back().Directive == OMPD_taskgroup &&
+         getTopOfStack().Directive == OMPD_taskgroup &&
          "Additional reduction info may be specified only once for reduction "
          "items.");
   ReductionData.set(BOK, SR);
   Expr *&TaskgroupReductionRef =
-      Stack.back().first.back().TaskgroupReductionRef;
+      getTopOfStack().TaskgroupReductionRef;
   if (!TaskgroupReductionRef) {
     VarDecl *VD = buildVarDecl(SemaRef, SR.getBegin(),
                                SemaRef.Context.VoidPtrTy, ".task_red.");
@@ -1058,16 +1092,16 @@ void DSAStackTy::addTaskgroupReductionData(const ValueDecl *D, SourceRange SR,
   D = getCanonicalDecl(D);
   assert(!isStackEmpty() && "Data-sharing attributes stack is empty");
   assert(
-      Stack.back().first.back().SharingMap[D].Attributes == OMPC_reduction &&
+      getTopOfStack().SharingMap[D].Attributes == OMPC_reduction &&
       "Additional reduction info may be specified only for reduction items.");
-  ReductionData &ReductionData = Stack.back().first.back().ReductionMap[D];
+  ReductionData &ReductionData = getTopOfStack().ReductionMap[D];
   assert(ReductionData.ReductionRange.isInvalid() &&
-         Stack.back().first.back().Directive == OMPD_taskgroup &&
+         getTopOfStack().Directive == OMPD_taskgroup &&
          "Additional reduction info may be specified only once for reduction "
          "items.");
   ReductionData.set(ReductionRef, SR);
   Expr *&TaskgroupReductionRef =
-      Stack.back().first.back().TaskgroupReductionRef;
+      getTopOfStack().TaskgroupReductionRef;
   if (!TaskgroupReductionRef) {
     VarDecl *VD = buildVarDecl(SemaRef, SR.getBegin(),
                                SemaRef.Context.VoidPtrTy, ".task_red.");
@@ -1081,11 +1115,7 @@ const DSAStackTy::DSAVarData DSAStackTy::getTopMostTaskgroupReductionData(
     Expr *&TaskgroupDescriptor) const {
   D = getCanonicalDecl(D);
   assert(!isStackEmpty() && "Data-sharing attributes stack is empty.");
-  if (Stack.back().first.empty())
-      return DSAVarData();
-  for (iterator I = std::next(Stack.back().first.rbegin(), 1),
-                E = Stack.back().first.rend();
-       I != E; std::advance(I, 1)) {
+  for (const_iterator I = begin() + 1, E = end(); I != E; ++I) {
     const DSAInfo &Data = I->SharingMap.lookup(D);
     if (Data.Attributes != OMPC_reduction || I->Directive != OMPD_taskgroup)
       continue;
@@ -1110,11 +1140,7 @@ const DSAStackTy::DSAVarData DSAStackTy::getTopMostTaskgroupReductionData(
     Expr *&TaskgroupDescriptor) const {
   D = getCanonicalDecl(D);
   assert(!isStackEmpty() && "Data-sharing attributes stack is empty.");
-  if (Stack.back().first.empty())
-      return DSAVarData();
-  for (iterator I = std::next(Stack.back().first.rbegin(), 1),
-                E = Stack.back().first.rend();
-       I != E; std::advance(I, 1)) {
+  for (const_iterator I = begin() + 1, E = end(); I != E; ++I) {
     const DSAInfo &Data = I->SharingMap.lookup(D);
     if (Data.Attributes != OMPC_reduction || I->Directive != OMPD_taskgroup)
       continue;
@@ -1134,21 +1160,17 @@ const DSAStackTy::DSAVarData DSAStackTy::getTopMostTaskgroupReductionData(
   return DSAVarData();
 }
 
-bool DSAStackTy::isOpenMPLocal(VarDecl *D, iterator Iter) const {
+bool DSAStackTy::isOpenMPLocal(VarDecl *D, const_iterator I) const {
   D = D->getCanonicalDecl();
-  if (!isStackEmpty()) {
-    iterator I = Iter, E = Stack.back().first.rend();
-    Scope *TopScope = nullptr;
-    while (I != E && !isImplicitOrExplicitTaskingRegion(I->Directive) &&
-           !isOpenMPTargetExecutionDirective(I->Directive))
-      ++I;
-    if (I == E)
-      return false;
-    TopScope = I->CurScope ? I->CurScope->getParent() : nullptr;
-    Scope *CurScope = getCurScope();
-    while (CurScope && CurScope != TopScope && !CurScope->isDeclScope(D))
-      CurScope = CurScope->getParent();
-    return CurScope != TopScope;
+  for (const_iterator E = end(); I != E; ++I) {
+    if (isImplicitOrExplicitTaskingRegion(I->Directive) ||
+        isOpenMPTargetExecutionDirective(I->Directive)) {
+      Scope *TopScope = I->CurScope ? I->CurScope->getParent() : nullptr;
+      Scope *CurScope = getCurScope();
+      while (CurScope && CurScope != TopScope && !CurScope->isDeclScope(D))
+        CurScope = CurScope->getParent();
+      return CurScope != TopScope;
+    }
   }
   return false;
 }
@@ -1236,15 +1258,14 @@ const DSAStackTy::DSAVarData DSAStackTy::getTopDSA(ValueDecl *D,
   if (SemaRef.getLangOpts().OpenMPCUDAMode && VD &&
       VD->isLocalVarDeclOrParm() && !isStackEmpty() &&
       !isLoopControlVariable(D).first) {
-    iterator IterTarget =
-        std::find_if(Stack.back().first.rbegin(), Stack.back().first.rend(),
-                     [](const SharingMapTy &Data) {
-                       return isOpenMPTargetExecutionDirective(Data.Directive);
-                     });
-    if (IterTarget != Stack.back().first.rend()) {
-      iterator ParentIterTarget = std::next(IterTarget, 1);
-      for (iterator Iter = Stack.back().first.rbegin();
-           Iter != ParentIterTarget; std::advance(Iter, 1)) {
+    const_iterator IterTarget =
+        std::find_if(begin(), end(), [](const SharingMapTy &Data) {
+          return isOpenMPTargetExecutionDirective(Data.Directive);
+        });
+    if (IterTarget != end()) {
+      const_iterator ParentIterTarget = IterTarget + 1;
+      for (const_iterator Iter = begin();
+           Iter != ParentIterTarget; ++Iter) {
         if (isOpenMPLocal(VD, Iter)) {
           DVar.RefExpr =
               buildDeclRefExpr(SemaRef, VD, D->getType().getNonReferenceType(),
@@ -1253,7 +1274,7 @@ const DSAStackTy::DSAVarData DSAStackTy::getTopDSA(ValueDecl *D,
           return DVar;
         }
       }
-      if (!isClauseParsingMode() || IterTarget != Stack.back().first.rbegin()) {
+      if (!isClauseParsingMode() || IterTarget != begin()) {
         auto DSAIter = IterTarget->SharingMap.find(D);
         if (DSAIter != IterTarget->SharingMap.end() &&
             isOpenMPPrivate(DSAIter->getSecond().Attributes)) {
@@ -1261,7 +1282,7 @@ const DSAStackTy::DSAVarData DSAStackTy::getTopDSA(ValueDecl *D,
           DVar.CKind = OMPC_threadprivate;
           return DVar;
         }
-        iterator End = Stack.back().first.rend();
+        const_iterator End = end();
         if (!SemaRef.isOpenMPCapturedByRef(
                 D, std::distance(ParentIterTarget, End))) {
           DVar.RefExpr =
@@ -1321,10 +1342,10 @@ const DSAStackTy::DSAVarData DSAStackTy::getTopDSA(ValueDecl *D,
 
   // Explicitly specified attributes and local variables with predetermined
   // attributes.
-  iterator I = Stack.back().first.rbegin();
-  iterator EndI = Stack.back().first.rend();
+  const_iterator I = begin();
+  const_iterator EndI = end();
   if (FromParent && I != EndI)
-    std::advance(I, 1);
+    ++I;
   auto It = I->SharingMap.find(D);
   if (It != I->SharingMap.end()) {
     const DSAInfo &Data = It->getSecond();
@@ -1341,14 +1362,14 @@ const DSAStackTy::DSAVarData DSAStackTy::getTopDSA(ValueDecl *D,
 const DSAStackTy::DSAVarData DSAStackTy::getImplicitDSA(ValueDecl *D,
                                                         bool FromParent) const {
   if (isStackEmpty()) {
-    iterator I;
+    const_iterator I;
     return getDSA(I, D);
   }
   D = getCanonicalDecl(D);
-  iterator StartI = Stack.back().first.rbegin();
-  iterator EndI = Stack.back().first.rend();
+  const_iterator StartI = begin();
+  const_iterator EndI = end();
   if (FromParent && StartI != EndI)
-    std::advance(StartI, 1);
+    ++StartI;
   return getDSA(StartI, D);
 }
 
@@ -1360,14 +1381,15 @@ DSAStackTy::hasDSA(ValueDecl *D,
   if (isStackEmpty())
     return {};
   D = getCanonicalDecl(D);
-  iterator I = Stack.back().first.rbegin();
-  iterator EndI = Stack.back().first.rend();
+  const_iterator I = begin();
+  const_iterator EndI = end();
   if (FromParent && I != EndI)
-    std::advance(I, 1);
-  for (; I != EndI; std::advance(I, 1)) {
-    if (!DPred(I->Directive) && !isImplicitOrExplicitTaskingRegion(I->Directive))
+    ++I;
+  for (; I != EndI; ++I) {
+    if (!DPred(I->Directive) &&
+        !isImplicitOrExplicitTaskingRegion(I->Directive))
       continue;
-    iterator NewI = I;
+    const_iterator NewI = I;
     DSAVarData DVar = getDSA(NewI, D);
     if (I == NewI && CPred(DVar.CKind))
       return DVar;
@@ -1382,13 +1404,13 @@ const DSAStackTy::DSAVarData DSAStackTy::hasInnermostDSA(
   if (isStackEmpty())
     return {};
   D = getCanonicalDecl(D);
-  iterator StartI = Stack.back().first.rbegin();
-  iterator EndI = Stack.back().first.rend();
+  const_iterator StartI = begin();
+  const_iterator EndI = end();
   if (FromParent && StartI != EndI)
-    std::advance(StartI, 1);
+    ++StartI;
   if (StartI == EndI || !DPred(StartI->Directive))
     return {};
-  iterator NewI = StartI;
+  const_iterator NewI = StartI;
   DSAVarData DVar = getDSA(NewI, D);
   return (NewI == StartI && CPred(DVar.CKind)) ? DVar : DSAVarData();
 }
@@ -1396,23 +1418,19 @@ const DSAStackTy::DSAVarData DSAStackTy::hasInnermostDSA(
 bool DSAStackTy::hasExplicitDSA(
     const ValueDecl *D, const llvm::function_ref<bool(OpenMPClauseKind)> CPred,
     unsigned Level, bool NotLastprivate) const {
-  if (isStackEmpty())
+  if (getStackSize() <= Level)
     return false;
   D = getCanonicalDecl(D);
-  auto StartI = Stack.back().first.begin();
-  auto EndI = Stack.back().first.end();
-  if (std::distance(StartI, EndI) <= (int)Level)
-    return false;
-  std::advance(StartI, Level);
-  auto I = StartI->SharingMap.find(D);
-  if ((I != StartI->SharingMap.end()) &&
-         I->getSecond().RefExpr.getPointer() &&
-         CPred(I->getSecond().Attributes) &&
-         (!NotLastprivate || !I->getSecond().RefExpr.getInt()))
+  const SharingMapTy &StackElem = getStackElemAtLevel(Level);
+  auto I = StackElem.SharingMap.find(D);
+  if (I != StackElem.SharingMap.end() &&
+      I->getSecond().RefExpr.getPointer() &&
+      CPred(I->getSecond().Attributes) &&
+      (!NotLastprivate || !I->getSecond().RefExpr.getInt()))
     return true;
   // Check predetermined rules for the loop control variables.
-  auto LI = StartI->LCVMap.find(D);
-  if (LI != StartI->LCVMap.end())
+  auto LI = StackElem.LCVMap.find(D);
+  if (LI != StackElem.LCVMap.end())
     return CPred(OMPC_private);
   return false;
 }
@@ -1420,14 +1438,10 @@ bool DSAStackTy::hasExplicitDSA(
 bool DSAStackTy::hasExplicitDirective(
     const llvm::function_ref<bool(OpenMPDirectiveKind)> DPred,
     unsigned Level) const {
-  if (isStackEmpty())
+  if (getStackSize() <= Level)
     return false;
-  auto StartI = Stack.back().first.begin();
-  auto EndI = Stack.back().first.end();
-  if (std::distance(StartI, EndI) <= (int)Level)
-    return false;
-  std::advance(StartI, Level);
-  return DPred(StartI->Directive);
+  const SharingMapTy &StackElem = getStackElemAtLevel(Level);
+  return DPred(StackElem.Directive);
 }
 
 bool DSAStackTy::hasDirective(
@@ -1436,13 +1450,9 @@ bool DSAStackTy::hasDirective(
         DPred,
     bool FromParent) const {
   // We look only in the enclosing region.
-  if (isStackEmpty())
-    return false;
-  auto StartI = std::next(Stack.back().first.rbegin());
-  auto EndI = Stack.back().first.rend();
-  if (FromParent && StartI != EndI)
-    StartI = std::next(StartI);
-  for (auto I = StartI, EE = EndI; I != EE; ++I) {
+  size_t Skip = FromParent ? 2 : 1;
+  for (const_iterator I = begin() + std::min(Skip, getStackSize()), E = end();
+       I != E; ++I) {
     if (DPred(I->Directive, I->DirectiveName, I->ConstructLoc))
       return true;
   }