diff --git a/clang/lib/AST/Decl.cpp b/clang/lib/AST/Decl.cpp
index 32dae5ccad3a..5ea091edcf4c 100644
--- a/clang/lib/AST/Decl.cpp
+++ b/clang/lib/AST/Decl.cpp
@@ -1663,8 +1663,7 @@ void NamedDecl::printNestedNameSpecifier(raw_ostream &OS,
     NameInScope = ND->getDeclName();
   }
 
-  for (unsigned I = Contexts.size(); I != 0; --I) {
-    const DeclContext *DC = Contexts[I - 1];
+  for (const DeclContext *DC : llvm::reverse(Contexts)) {
     if (const auto *Spec = dyn_cast<ClassTemplateSpecializationDecl>(DC)) {
       OS << Spec->getName();
       const TemplateArgumentList &TemplateArgs = Spec->getTemplateArgs();
diff --git a/clang/lib/CodeGen/CGExpr.cpp b/clang/lib/CodeGen/CGExpr.cpp
index e73782f2d317..0d83d6a0d966 100644
--- a/clang/lib/CodeGen/CGExpr.cpp
+++ b/clang/lib/CodeGen/CGExpr.cpp
@@ -568,8 +568,7 @@ EmitMaterializeTemporaryExpr(const MaterializeTemporaryExpr *M) {
   // Perform derived-to-base casts and/or field accesses, to get from the
   // temporary object we created (and, potentially, for which we extended
   // the lifetime) to the subobject we're binding the reference to.
-  for (unsigned I = Adjustments.size(); I != 0; --I) {
-    SubobjectAdjustment &Adjustment = Adjustments[I-1];
+  for (SubobjectAdjustment &Adjustment : llvm::reverse(Adjustments)) {
     switch (Adjustment.Kind) {
     case SubobjectAdjustment::DerivedToBaseAdjustment:
       Object =
diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index 9cedd9a9a35c..3d11da295654 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -2293,9 +2293,9 @@ static void addLinkOptionsPostorder(CodeGenModule &CGM, Module *Mod,
   }
 
   // Import this module's dependencies.
-  for (unsigned I = Mod->Imports.size(); I > 0; --I) {
-    if (Visited.insert(Mod->Imports[I - 1]).second)
-      addLinkOptionsPostorder(CGM, Mod->Imports[I-1], Metadata, Visited);
+  for (Module *Import : llvm::reverse(Mod->Imports)) {
+    if (Visited.insert(Import).second)
+      addLinkOptionsPostorder(CGM, Import, Metadata, Visited);
   }
 
   // Add linker options to link against the libraries/frameworks
@@ -2308,13 +2308,12 @@ static void addLinkOptionsPostorder(CodeGenModule &CGM, Module *Mod,
   if (Mod->UseExportAsModuleLinkName)
     return;
 
-  for (unsigned I = Mod->LinkLibraries.size(); I > 0; --I) {
+  for (const Module::LinkLibrary &LL : llvm::reverse(Mod->LinkLibraries)) {
     // Link against a framework.  Frameworks are currently Darwin only, so we
     // don't to ask TargetCodeGenInfo for the spelling of the linker option.
-    if (Mod->LinkLibraries[I-1].IsFramework) {
-      llvm::Metadata *Args[2] = {
-          llvm::MDString::get(Context, "-framework"),
-          llvm::MDString::get(Context, Mod->LinkLibraries[I - 1].Library)};
+    if (LL.IsFramework) {
+      llvm::Metadata *Args[2] = {llvm::MDString::get(Context, "-framework"),
+                                 llvm::MDString::get(Context, LL.Library)};
 
       Metadata.push_back(llvm::MDNode::get(Context, Args));
       continue;
@@ -2324,13 +2323,12 @@ static void addLinkOptionsPostorder(CodeGenModule &CGM, Module *Mod,
     if (IsELF) {
       llvm::Metadata *Args[2] = {
           llvm::MDString::get(Context, "lib"),
-          llvm::MDString::get(Context, Mod->LinkLibraries[I - 1].Library),
+          llvm::MDString::get(Context, LL.Library),
       };
       Metadata.push_back(llvm::MDNode::get(Context, Args));
     } else {
       llvm::SmallString<24> Opt;
-      CGM.getTargetCodeGenInfo().getDependentLibraryOption(
-          Mod->LinkLibraries[I - 1].Library, Opt);
+      CGM.getTargetCodeGenInfo().getDependentLibraryOption(LL.Library, Opt);
       auto *OptString = llvm::MDString::get(Context, Opt);
       Metadata.push_back(llvm::MDNode::get(Context, OptString));
     }
diff --git a/clang/lib/Lex/ModuleMap.cpp b/clang/lib/Lex/ModuleMap.cpp
index 6324cdc5a6b0..9fa170410da3 100644
--- a/clang/lib/Lex/ModuleMap.cpp
+++ b/clang/lib/Lex/ModuleMap.cpp
@@ -167,8 +167,8 @@ static void appendSubframeworkPaths(Module *Mod,
     return;
 
   // Add Frameworks/Name.framework for each subframework.
-  for (unsigned I = Paths.size() - 1; I != 0; --I)
-    llvm::sys::path::append(Path, "Frameworks", Paths[I-1] + ".framework");
+  for (StringRef Framework : llvm::drop_begin(llvm::reverse(Paths)))
+    llvm::sys::path::append(Path, "Frameworks", Framework + ".framework");
 }
 
 Optional<FileEntryRef> ModuleMap::findHeader(
@@ -618,18 +618,18 @@ ModuleMap::findOrCreateModuleForHeaderInUmbrellaDir(const FileEntry *File) {
       // the actual header is located.
       bool Explicit = UmbrellaModule->InferExplicitSubmodules;
 
-      for (unsigned I = SkippedDirs.size(); I != 0; --I) {
+      for (const DirectoryEntry *SkippedDir : llvm::reverse(SkippedDirs)) {
         // Find or create the module that corresponds to this directory name.
         SmallString<32> NameBuf;
         StringRef Name = sanitizeFilenameAsIdentifier(
-            llvm::sys::path::stem(SkippedDirs[I-1]->getName()), NameBuf);
+            llvm::sys::path::stem(SkippedDir->getName()), NameBuf);
         Result = findOrCreateModule(Name, Result, /*IsFramework=*/false,
                                     Explicit).first;
         InferredModuleAllowedBy[Result] = UmbrellaModuleMap;
         Result->IsInferred = true;
 
         // Associate the module and the directory.
-        UmbrellaDirs[SkippedDirs[I-1]] = Result;
+        UmbrellaDirs[SkippedDir] = Result;
 
         // If inferred submodules export everything they import, add a
         // wildcard to the set of exports.
@@ -745,12 +745,11 @@ ModuleMap::isHeaderUnavailableInModule(const FileEntry *Header,
         UmbrellaModule = UmbrellaModule->Parent;
 
       if (UmbrellaModule->InferSubmodules) {
-        for (unsigned I = SkippedDirs.size(); I != 0; --I) {
+        for (const DirectoryEntry *SkippedDir : llvm::reverse(SkippedDirs)) {
           // Find or create the module that corresponds to this directory name.
           SmallString<32> NameBuf;
           StringRef Name = sanitizeFilenameAsIdentifier(
-                             llvm::sys::path::stem(SkippedDirs[I-1]->getName()),
-                             NameBuf);
+              llvm::sys::path::stem(SkippedDir->getName()), NameBuf);
           Found = lookupModuleQualified(Name, Found);
           if (!Found)
             return false;
diff --git a/clang/lib/Sema/CodeCompleteConsumer.cpp b/clang/lib/Sema/CodeCompleteConsumer.cpp
index d2dfc96a6021..6c47cedfccf3 100644
--- a/clang/lib/Sema/CodeCompleteConsumer.cpp
+++ b/clang/lib/Sema/CodeCompleteConsumer.cpp
@@ -387,14 +387,13 @@ StringRef CodeCompletionTUInfo::getParentName(const DeclContext *DC) {
     SmallString<128> S;
     llvm::raw_svector_ostream OS(S);
     bool First = true;
-    for (unsigned I = Contexts.size(); I != 0; --I) {
+    for (const DeclContext *CurDC : llvm::reverse(Contexts)) {
       if (First)
         First = false;
       else {
         OS << "::";
       }
 
-      const DeclContext *CurDC = Contexts[I - 1];
       if (const auto *CatImpl = dyn_cast<ObjCCategoryImplDecl>(CurDC))
         CurDC = CatImpl->getCategoryDecl();