diff --git a/clang/include/clang/CodeGen/CGFunctionInfo.h b/clang/include/clang/CodeGen/CGFunctionInfo.h
index 040ee025afaa8..50be51769f1a8 100644
--- a/clang/include/clang/CodeGen/CGFunctionInfo.h
+++ b/clang/include/clang/CodeGen/CGFunctionInfo.h
@@ -828,10 +828,8 @@ class CGFunctionInfo final
         ID.AddInteger(paramInfo.getOpaqueValue());
     }
     resultType.Profile(ID);
-    for (ArrayRef<CanQualType>::iterator
-           i = argTypes.begin(), e = argTypes.end(); i != e; ++i) {
-      i->Profile(ID);
-    }
+    for (const CanQualType &argType : argTypes)
+      argType.Profile(ID);
   }
 };
 
diff --git a/clang/lib/CodeGen/CGOpenMPRuntime.cpp b/clang/lib/CodeGen/CGOpenMPRuntime.cpp
index 4173355491fd4..8ccc37ef98a74 100644
--- a/clang/lib/CodeGen/CGOpenMPRuntime.cpp
+++ b/clang/lib/CodeGen/CGOpenMPRuntime.cpp
@@ -4168,8 +4168,7 @@ void CGOpenMPRuntime::emitDepobjElements(CodeGenFunction &CGF,
         CGF, cast_or_null<OMPIteratorExpr>(
                  Data.IteratorExpr ? Data.IteratorExpr->IgnoreParenImpCasts()
                                    : nullptr));
-    for (unsigned I = 0, End = Data.DepExprs.size(); I < End; ++I) {
-      const Expr *E = Data.DepExprs[I];
+    for (const Expr *E : Data.DepExprs) {
       llvm::Value *NumDeps;
       LValue Base;
       LValue DepobjLVal = CGF.EmitLValue(E->IgnoreParenImpCasts());
@@ -4289,31 +4288,26 @@ std::pair<llvm::Value *, Address> CGOpenMPRuntime::emitDependClause(
                                            /*isSigned=*/false);
   }
   unsigned Pos = 0;
-  for (unsigned I = 0, End = Dependencies.size(); I < End; ++I) {
-    if (Dependencies[I].DepKind == OMPC_DEPEND_depobj ||
-        Dependencies[I].IteratorExpr)
+  for (const OMPTaskDataTy::DependData &Dep : Dependencies) {
+    if (Dep.DepKind == OMPC_DEPEND_depobj || Dep.IteratorExpr)
       continue;
-    emitDependData(CGF, KmpDependInfoTy, &Pos, Dependencies[I],
-                   DependenciesArray);
+    emitDependData(CGF, KmpDependInfoTy, &Pos, Dep, DependenciesArray);
   }
   // Copy regular dependencies with iterators.
   LValue PosLVal = CGF.MakeAddrLValue(
       CGF.CreateMemTemp(C.getSizeType(), "dep.counter.addr"), C.getSizeType());
   CGF.EmitStoreOfScalar(llvm::ConstantInt::get(CGF.SizeTy, Pos), PosLVal);
-  for (unsigned I = 0, End = Dependencies.size(); I < End; ++I) {
-    if (Dependencies[I].DepKind == OMPC_DEPEND_depobj ||
-        !Dependencies[I].IteratorExpr)
+  for (const OMPTaskDataTy::DependData &Dep : Dependencies) {
+    if (Dep.DepKind == OMPC_DEPEND_depobj || !Dep.IteratorExpr)
       continue;
-    emitDependData(CGF, KmpDependInfoTy, &PosLVal, Dependencies[I],
-                   DependenciesArray);
+    emitDependData(CGF, KmpDependInfoTy, &PosLVal, Dep, DependenciesArray);
   }
   // Copy final depobj arrays without iterators.
   if (HasDepobjDeps) {
-    for (unsigned I = 0, End = Dependencies.size(); I < End; ++I) {
-      if (Dependencies[I].DepKind != OMPC_DEPEND_depobj)
+    for (const OMPTaskDataTy::DependData &Dep : Dependencies) {
+      if (Dep.DepKind != OMPC_DEPEND_depobj)
         continue;
-      emitDepobjElements(CGF, KmpDependInfoTy, PosLVal, Dependencies[I],
-                         DependenciesArray);
+      emitDepobjElements(CGF, KmpDependInfoTy, PosLVal, Dep, DependenciesArray);
     }
   }
   DependenciesArray = CGF.Builder.CreatePointerBitCastOrAddrSpaceCast(
diff --git a/clang/lib/CodeGen/CGRecordLayoutBuilder.cpp b/clang/lib/CodeGen/CGRecordLayoutBuilder.cpp
index 232e2d8b43ca1..e1310aed818ad 100644
--- a/clang/lib/CodeGen/CGRecordLayoutBuilder.cpp
+++ b/clang/lib/CodeGen/CGRecordLayoutBuilder.cpp
@@ -972,18 +972,16 @@ void CGRecordLowering::determinePacked(bool NVBaseType) {
   CharUnits NVAlignment = CharUnits::One();
   CharUnits NVSize =
       !NVBaseType && RD ? Layout.getNonVirtualSize() : CharUnits::Zero();
-  for (std::vector<MemberInfo>::const_iterator Member = Members.begin(),
-                                               MemberEnd = Members.end();
-       Member != MemberEnd; ++Member) {
-    if (!Member->Data)
+  for (const MemberInfo &Member : Members) {
+    if (!Member.Data)
       continue;
     // If any member falls at an offset that it not a multiple of its alignment,
     // then the entire record must be packed.
-    if (Member->Offset % getAlignment(Member->Data))
+    if (Member.Offset % getAlignment(Member.Data))
       Packed = true;
-    if (Member->Offset < NVSize)
-      NVAlignment = std::max(NVAlignment, getAlignment(Member->Data));
-    Alignment = std::max(Alignment, getAlignment(Member->Data));
+    if (Member.Offset < NVSize)
+      NVAlignment = std::max(NVAlignment, getAlignment(Member.Data));
+    Alignment = std::max(Alignment, getAlignment(Member.Data));
   }
   // If the size of the record (the capstone's offset) is not a multiple of the
   // record's alignment, it must be packed.
@@ -1002,45 +1000,39 @@ void CGRecordLowering::determinePacked(bool NVBaseType) {
 void CGRecordLowering::insertPadding() {
   std::vector<std::pair<CharUnits, CharUnits> > Padding;
   CharUnits Size = CharUnits::Zero();
-  for (std::vector<MemberInfo>::const_iterator Member = Members.begin(),
-                                               MemberEnd = Members.end();
-       Member != MemberEnd; ++Member) {
-    if (!Member->Data)
+  for (const MemberInfo &Member : Members) {
+    if (!Member.Data)
       continue;
-    CharUnits Offset = Member->Offset;
+    CharUnits Offset = Member.Offset;
     assert(Offset >= Size);
     // Insert padding if we need to.
     if (Offset !=
-        Size.alignTo(Packed ? CharUnits::One() : getAlignment(Member->Data)))
+        Size.alignTo(Packed ? CharUnits::One() : getAlignment(Member.Data)))
       Padding.push_back(std::make_pair(Size, Offset - Size));
-    Size = Offset + getSize(Member->Data);
+    Size = Offset + getSize(Member.Data);
   }
   if (Padding.empty())
     return;
   // Add the padding to the Members list and sort it.
-  for (std::vector<std::pair<CharUnits, CharUnits> >::const_iterator
-        Pad = Padding.begin(), PadEnd = Padding.end();
-        Pad != PadEnd; ++Pad)
-    Members.push_back(StorageInfo(Pad->first, getByteArrayType(Pad->second)));
+  for (const auto &Pad : Padding)
+    Members.push_back(StorageInfo(Pad.first, getByteArrayType(Pad.second)));
   llvm::stable_sort(Members);
 }
 
 void CGRecordLowering::fillOutputFields() {
-  for (std::vector<MemberInfo>::const_iterator Member = Members.begin(),
-                                               MemberEnd = Members.end();
-       Member != MemberEnd; ++Member) {
-    if (Member->Data)
-      FieldTypes.push_back(Member->Data);
-    if (Member->Kind == MemberInfo::Field) {
-      if (Member->FD)
-        Fields[Member->FD->getCanonicalDecl()] = FieldTypes.size() - 1;
+  for (const MemberInfo &Member : Members) {
+    if (Member.Data)
+      FieldTypes.push_back(Member.Data);
+    if (Member.Kind == MemberInfo::Field) {
+      if (Member.FD)
+        Fields[Member.FD->getCanonicalDecl()] = FieldTypes.size() - 1;
       // A field without storage must be a bitfield.
-      if (!Member->Data)
-        setBitFieldInfo(Member->FD, Member->Offset, FieldTypes.back());
-    } else if (Member->Kind == MemberInfo::Base)
-      NonVirtualBases[Member->RD] = FieldTypes.size() - 1;
-    else if (Member->Kind == MemberInfo::VBase)
-      VirtualBases[Member->RD] = FieldTypes.size() - 1;
+      if (!Member.Data)
+        setBitFieldInfo(Member.FD, Member.Offset, FieldTypes.back());
+    } else if (Member.Kind == MemberInfo::Base)
+      NonVirtualBases[Member.RD] = FieldTypes.size() - 1;
+    else if (Member.Kind == MemberInfo::VBase)
+      VirtualBases[Member.RD] = FieldTypes.size() - 1;
   }
 }
 
@@ -1224,20 +1216,18 @@ void CGRecordLayout::print(raw_ostream &OS) const {
 
   // Print bit-field infos in declaration order.
   std::vector<std::pair<unsigned, const CGBitFieldInfo*> > BFIs;
-  for (llvm::DenseMap<const FieldDecl*, CGBitFieldInfo>::const_iterator
-         it = BitFields.begin(), ie = BitFields.end();
-       it != ie; ++it) {
-    const RecordDecl *RD = it->first->getParent();
+  for (const auto &BitField : BitFields) {
+    const RecordDecl *RD = BitField.first->getParent();
     unsigned Index = 0;
-    for (RecordDecl::field_iterator
-           it2 = RD->field_begin(); *it2 != it->first; ++it2)
+    for (RecordDecl::field_iterator it2 = RD->field_begin();
+         *it2 != BitField.first; ++it2)
       ++Index;
-    BFIs.push_back(std::make_pair(Index, &it->second));
+    BFIs.push_back(std::make_pair(Index, &BitField.second));
   }
   llvm::array_pod_sort(BFIs.begin(), BFIs.end());
-  for (unsigned i = 0, e = BFIs.size(); i != e; ++i) {
+  for (auto &BFI : BFIs) {
     OS.indent(4);
-    BFIs[i].second->print(OS);
+    BFI.second->print(OS);
     OS << "\n";
   }
 
diff --git a/clang/lib/CodeGen/CGStmt.cpp b/clang/lib/CodeGen/CGStmt.cpp
index 8742f8e0fc04a..e0650067b9547 100644
--- a/clang/lib/CodeGen/CGStmt.cpp
+++ b/clang/lib/CodeGen/CGStmt.cpp
@@ -757,10 +757,9 @@ void CodeGenFunction::LexicalScope::rescopeLabels() {
     = CGF.EHStack.getInnermostNormalCleanup();
 
   // Change the scope depth of all the labels.
-  for (SmallVectorImpl<const LabelDecl*>::const_iterator
-         i = Labels.begin(), e = Labels.end(); i != e; ++i) {
-    assert(CGF.LabelMap.count(*i));
-    JumpDest &dest = CGF.LabelMap.find(*i)->second;
+  for (const LabelDecl *Label : Labels) {
+    assert(CGF.LabelMap.count(Label));
+    JumpDest &dest = CGF.LabelMap.find(Label)->second;
     assert(dest.getScopeDepth().isValid());
     assert(innermostScope.encloses(dest.getScopeDepth()));
     dest.setScopeDepth(innermostScope);
@@ -2302,8 +2301,8 @@ void CodeGenFunction::EmitSwitchStmt(const SwitchStmt &S) {
 
       // Okay, we can dead code eliminate everything except this case.  Emit the
       // specified series of statements and we're good.
-      for (unsigned i = 0, e = CaseStmts.size(); i != e; ++i)
-        EmitStmt(CaseStmts[i]);
+      for (const Stmt *CaseStmt : CaseStmts)
+        EmitStmt(CaseStmt);
       incrementProfileCounter(&S);
       PGO->markStmtMaybeUsed(S.getBody());
 
diff --git a/clang/lib/CodeGen/MicrosoftCXXABI.cpp b/clang/lib/CodeGen/MicrosoftCXXABI.cpp
index 514cc1d9015ee..a181559834296 100644
--- a/clang/lib/CodeGen/MicrosoftCXXABI.cpp
+++ b/clang/lib/CodeGen/MicrosoftCXXABI.cpp
@@ -1836,9 +1836,9 @@ llvm::GlobalVariable *MicrosoftCXXABI::getAddrOfVTable(const CXXRecordDecl *RD,
     // Create all the vftables at once in order to make sure each vftable has
     // a unique mangled name.
     llvm::StringSet<> ObservedMangledNames;
-    for (size_t J = 0, F = VFPtrs.size(); J != F; ++J) {
+    for (const auto &VFPtr : VFPtrs) {
       SmallString<256> Name;
-      mangleVFTableName(getMangleContext(), RD, *VFPtrs[J], Name);
+      mangleVFTableName(getMangleContext(), RD, *VFPtr, Name);
       if (!ObservedMangledNames.insert(Name.str()).second)
         llvm_unreachable("Already saw this mangling before?");
     }
diff --git a/clang/lib/CodeGen/ModuleBuilder.cpp b/clang/lib/CodeGen/ModuleBuilder.cpp
index 09a7d79ae4afb..8c1fee8c974f1 100644
--- a/clang/lib/CodeGen/ModuleBuilder.cpp
+++ b/clang/lib/CodeGen/ModuleBuilder.cpp
@@ -186,8 +186,8 @@ namespace {
       HandlingTopLevelDeclRAII HandlingDecl(*this);
 
       // Make sure to emit all elements of a Decl.
-      for (DeclGroupRef::iterator I = DG.begin(), E = DG.end(); I != E; ++I)
-        Builder->EmitTopLevelDecl(*I);
+      for (auto &I : DG)
+        Builder->EmitTopLevelDecl(I);
 
       return true;
     }
diff --git a/clang/lib/CodeGen/TargetBuiltins/ARM.cpp b/clang/lib/CodeGen/TargetBuiltins/ARM.cpp
index dab311903f6dd..6738d4be6dd21 100644
--- a/clang/lib/CodeGen/TargetBuiltins/ARM.cpp
+++ b/clang/lib/CodeGen/TargetBuiltins/ARM.cpp
@@ -4560,10 +4560,10 @@ Value *CodeGenFunction::EmitAArch64SVEBuiltinExpr(unsigned BuiltinID,
       Ops.insert(&Ops[1], Builder.getInt32(/*SV_ALL*/ 31));
 
     // Predicates must match the main datatype.
-    for (unsigned i = 0, e = Ops.size(); i != e; ++i)
-      if (auto PredTy = dyn_cast<llvm::VectorType>(Ops[i]->getType()))
+    for (Value *&Op : Ops)
+      if (auto PredTy = dyn_cast<llvm::VectorType>(Op->getType()))
         if (PredTy->getElementType()->isIntegerTy(1))
-          Ops[i] = EmitSVEPredicateCast(Ops[i], getSVEType(TypeFlags));
+          Op = EmitSVEPredicateCast(Op, getSVEType(TypeFlags));
 
     // Splat scalar operand to vector (intrinsics with _n infix)
     if (TypeFlags.hasSplatOperand()) {
@@ -4936,10 +4936,10 @@ Value *CodeGenFunction::EmitAArch64SMEBuiltinExpr(unsigned BuiltinID,
   }
 
   // Predicates must match the main datatype.
-  for (unsigned i = 0, e = Ops.size(); i != e; ++i)
-    if (auto PredTy = dyn_cast<llvm::VectorType>(Ops[i]->getType()))
+  for (Value *&Op : Ops)
+    if (auto PredTy = dyn_cast<llvm::VectorType>(Op->getType()))
       if (PredTy->getElementType()->isIntegerTy(1))
-        Ops[i] = EmitSVEPredicateCast(Ops[i], getSVEType(TypeFlags));
+        Op = EmitSVEPredicateCast(Op, getSVEType(TypeFlags));
 
   Function *F =
       TypeFlags.isOverloadNone()
@@ -8036,8 +8036,8 @@ BuildVector(ArrayRef<llvm::Value*> Ops) {
   // If this is a constant vector, create a ConstantVector.
   if (AllConstants) {
     SmallVector<llvm::Constant*, 16> CstOps;
-    for (unsigned i = 0, e = Ops.size(); i != e; ++i)
-      CstOps.push_back(cast<Constant>(Ops[i]));
+    for (llvm::Value *Op : Ops)
+      CstOps.push_back(cast<Constant>(Op));
     return llvm::ConstantVector::get(CstOps);
   }
 
diff --git a/clang/lib/CodeGen/Targets/X86.cpp b/clang/lib/CodeGen/Targets/X86.cpp
index b36a6e1396653..0f59caac2323e 100644
--- a/clang/lib/CodeGen/Targets/X86.cpp
+++ b/clang/lib/CodeGen/Targets/X86.cpp
@@ -1462,9 +1462,8 @@ class X86_64TargetCodeGenInfo : public TargetCodeGenInfo {
     // defines varargs anyway.
     if (fnType->getCallConv() == CC_C) {
       bool HasAVXType = false;
-      for (CallArgList::const_iterator
-             it = args.begin(), ie = args.end(); it != ie; ++it) {
-        if (getABIInfo<X86_64ABIInfo>().isPassedUsingAVXType(it->Ty)) {
+      for (const CallArg &arg : args) {
+        if (getABIInfo<X86_64ABIInfo>().isPassedUsingAVXType(arg.Ty)) {
           HasAVXType = true;
           break;
         }