diff --git a/clang/lib/AST/Interp/ByteCodeExprGen.cpp b/clang/lib/AST/Interp/ByteCodeExprGen.cpp
@@ -222,6 +222,64 @@ bool ByteCodeExprGen<Emitter>::VisitCastExpr(const CastExpr *CE) {
     return this->emitNE(PtrT, CE);
   }
 
+  case CK_IntegralComplexToBoolean:
+  case CK_FloatingComplexToBoolean: {
+    std::optional<PrimType> ElemT =
+        classifyComplexElementType(SubExpr->getType());
+    if (!ElemT)
+      return false;
+    // We emit the expression (__real(E) != 0 || __imag(E) != 0)
+    // for us, that means (bool)E[0] || (bool)E[1]
+    if (!this->visit(SubExpr))
+      return false;
+    if (!this->emitConstUint8(0, CE))
+      return false;
+    if (!this->emitArrayElemPtrUint8(CE))
+      return false;
+    if (!this->emitLoadPop(*ElemT, CE))
+      return false;
+    if (*ElemT == PT_Float) {
+      if (!this->emitCastFloatingIntegral(PT_Bool, CE))
+        return false;
+    } else {
+      if (!this->emitCast(*ElemT, PT_Bool, CE))
+        return false;
+    }
+
+    // We now have the bool value of E[0] on the stack.
+    LabelTy LabelTrue = this->getLabel();
+    if (!this->jumpTrue(LabelTrue))
+      return false;
+
+    if (!this->emitConstUint8(1, CE))
+      return false;
+    if (!this->emitArrayElemPtrPopUint8(CE))
+      return false;
+    if (!this->emitLoadPop(*ElemT, CE))
+      return false;
+    if (*ElemT == PT_Float) {
+      if (!this->emitCastFloatingIntegral(PT_Bool, CE))
+        return false;
+    } else {
+      if (!this->emitCast(*ElemT, PT_Bool, CE))
+        return false;
+    }
+    // Leave the boolean value of E[1] on the stack.
+    LabelTy EndLabel = this->getLabel();
+    this->jump(EndLabel);
+
+    this->emitLabel(LabelTrue);
+    if (!this->emitPopPtr(CE))
+      return false;
+    if (!this->emitConstBool(true, CE))
+      return false;
+
+    this->fallthrough(EndLabel);
+    this->emitLabel(EndLabel);
+
+    return true;
+  }
+
   case CK_ToVoid:
     return discard(SubExpr);
 
@@ -258,6 +316,9 @@ bool ByteCodeExprGen<Emitter>::VisitBinaryOperator(const BinaryOperator *BO) {
   if (BO->isLogicalOp())
     return this->VisitLogicalBinOp(BO);
 
+  if (BO->getType()->isAnyComplexType())
+    return this->VisitComplexBinOp(BO);
+
   const Expr *LHS = BO->getLHS();
   const Expr *RHS = BO->getRHS();
 
@@ -500,6 +561,107 @@ bool ByteCodeExprGen<Emitter>::VisitLogicalBinOp(const BinaryOperator *E) {
   return true;
 }
 
+template <class Emitter>
+bool ByteCodeExprGen<Emitter>::VisitComplexBinOp(const BinaryOperator *E) {
+  // FIXME: We expect a pointer on the stack here.
+  //   we should not do that, but that's part of a bigger rework.
+  const Expr *LHS = E->getLHS();
+  const Expr *RHS = E->getRHS();
+  PrimType LHSElemT = *this->classifyComplexElementType(LHS->getType());
+  PrimType RHSElemT = *this->classifyComplexElementType(RHS->getType());
+
+  unsigned LHSOffset = this->allocateLocalPrimitive(LHS, PT_Ptr, true, false);
+  unsigned RHSOffset = this->allocateLocalPrimitive(RHS, PT_Ptr, true, false);
+  unsigned ResultOffset = ~0u;
+  if (!this->DiscardResult)
+    ResultOffset = this->allocateLocalPrimitive(E, PT_Ptr, true, false);
+
+  assert(LHSElemT == RHSElemT);
+
+  // Save result pointer in ResultOffset
+  if (!this->DiscardResult) {
+    if (!this->emitDupPtr(E))
+      return false;
+    if (!this->emitSetLocal(PT_Ptr, ResultOffset, E))
+      return false;
+  }
+
+  // Evaluate LHS and save value to LHSOffset.
+  if (!this->visit(LHS))
+    return false;
+  if (!this->emitSetLocal(PT_Ptr, LHSOffset, E))
+    return false;
+
+  // Same with RHS.
+  if (!this->visit(RHS))
+    return false;
+  if (!this->emitSetLocal(PT_Ptr, RHSOffset, E))
+    return false;
+
+  // Now we can get pointers to the LHS and RHS from the offsets above.
+  BinaryOperatorKind Op = E->getOpcode();
+  for (unsigned ElemIndex = 0; ElemIndex != 2; ++ElemIndex) {
+    // Result pointer for the store later.
+    if (!this->DiscardResult) {
+      if (!this->emitGetLocal(PT_Ptr, ResultOffset, E))
+        return false;
+    }
+
+    if (!this->emitGetLocal(PT_Ptr, LHSOffset, E))
+      return false;
+    if (!this->emitConstUint8(ElemIndex, E))
+      return false;
+    if (!this->emitArrayElemPtrPopUint8(E))
+      return false;
+    if (!this->emitLoadPop(LHSElemT, E))
+      return false;
+
+    if (!this->emitGetLocal(PT_Ptr, RHSOffset, E))
+      return false;
+    if (!this->emitConstUint8(ElemIndex, E))
+      return false;
+    if (!this->emitArrayElemPtrPopUint8(E))
+      return false;
+    if (!this->emitLoadPop(RHSElemT, E))
+      return false;
+
+    // The actual operation.
+    switch (Op) {
+    case BO_Add:
+      if (LHSElemT == PT_Float) {
+        if (!this->emitAddf(getRoundingMode(E), E))
+          return false;
+      } else {
+        if (!this->emitAdd(LHSElemT, E))
+          return false;
+      }
+      break;
+    case BO_Sub:
+      if (LHSElemT == PT_Float) {
+        if (!this->emitSubf(getRoundingMode(E), E))
+          return false;
+      } else {
+        if (!this->emitSub(LHSElemT, E))
+          return false;
+      }
+      break;
+
+    default:
+      return false;
+    }
+
+    if (!this->DiscardResult) {
+      // Initialize array element with the value we just computed.
+      if (!this->emitInitElemPop(LHSElemT, ElemIndex, E))
+        return false;
+    } else {
+      if (!this->emitPop(LHSElemT, E))
+        return false;
+    }
+  }
+  return true;
+}
+
 template <class Emitter>
 bool ByteCodeExprGen<Emitter>::VisitImplicitValueInitExpr(const ImplicitValueInitExpr *E) {
   QualType QT = E->getType();
@@ -671,6 +833,32 @@ bool ByteCodeExprGen<Emitter>::VisitInitListExpr(const InitListExpr *E) {
     return true;
   }
 
+  if (T->isAnyComplexType()) {
+    unsigned NumInits = E->getNumInits();
+    QualType ElemQT = E->getType()->getAs<ComplexType>()->getElementType();
+    PrimType ElemT = classifyPrim(ElemQT);
+    if (NumInits == 0) {
+      // Zero-initialize both elements.
+      for (unsigned I = 0; I < 2; ++I) {
+        if (!this->visitZeroInitializer(ElemT, ElemQT, E))
+          return false;
+        if (!this->emitInitElem(ElemT, I, E))
+          return false;
+      }
+    } else if (NumInits == 2) {
+      unsigned InitIndex = 0;
+      for (const Expr *Init : E->inits()) {
+        if (!this->visit(Init))
+          return false;
+
+        if (!this->emitInitElem(ElemT, InitIndex, E))
+          return false;
+        ++InitIndex;
+      }
+    }
+    return true;
+  }
+
   return false;
 }
 
@@ -1647,7 +1835,8 @@ template <class Emitter> bool ByteCodeExprGen<Emitter>::visit(const Expr *E) {
     return this->discard(E);
 
   // Create local variable to hold the return value.
-  if (!E->isGLValue() && !classify(E->getType())) {
+  if (!E->isGLValue() && !E->getType()->isAnyComplexType() &&
+      !classify(E->getType())) {
     std::optional<unsigned> LocalIndex = allocateLocal(E, /*IsExtended=*/true);
     if (!LocalIndex)
       return false;
@@ -1833,6 +2022,9 @@ bool ByteCodeExprGen<Emitter>::dereference(
     return Indirect(*T);
   }
 
+  if (LV->getType()->isAnyComplexType())
+    return visit(LV);
+
   return false;
 }
 
@@ -2092,15 +2284,33 @@ const Function *ByteCodeExprGen<Emitter>::getFunction(const FunctionDecl *FD) {
 template <class Emitter>
 bool ByteCodeExprGen<Emitter>::visitExpr(const Expr *E) {
   ExprScope<Emitter> RootScope(this);
-  if (!visit(E))
-    return false;
-
-  if (E->getType()->isVoidType())
+  // Void expressions.
+  if (E->getType()->isVoidType()) {
+    if (!visit(E))
+      return false;
     return this->emitRetVoid(E);
+  }
 
-  if (std::optional<PrimType> T = classify(E))
+  // Expressions with a primitive return type.
+  if (std::optional<PrimType> T = classify(E)) {
+    if (!visit(E))
+      return false;
     return this->emitRet(*T, E);
-  return this->emitRetValue(E);
+  }
+
+  // Expressions with a composite return type.
+  // For us, that means everything we don't
+  // have a PrimType for.
+  if (std::optional<unsigned> LocalOffset = this->allocateLocal(E)) {
+    if (!this->visitLocalInitializer(E, *LocalOffset))
+      return false;
+
+    if (!this->emitGetPtrLocal(*LocalOffset, E))
+      return false;
+    return this->emitRetValue(E);
+  }
+
+  return false;
 }
 
 /// Toplevel visitDecl().
@@ -2550,8 +2760,36 @@ bool ByteCodeExprGen<Emitter>::VisitUnaryOperator(const UnaryOperator *E) {
     if (!this->visit(SubExpr))
       return false;
     return DiscardResult ? this->emitPop(*T, E) : this->emitComp(*T, E);
-  case UO_Real:   // __real x
-  case UO_Imag:   // __imag x
+  case UO_Real: { // __real x
+    assert(!T);
+    if (!this->visit(SubExpr))
+      return false;
+    if (!this->emitConstUint8(0, E))
+      return false;
+    if (!this->emitArrayElemPtrPopUint8(E))
+      return false;
+
+    // Since our _Complex implementation does not map to a primitive type,
+    // we sometimes have to do the lvalue-to-rvalue conversion here manually.
+    if (!SubExpr->isLValue())
+      return this->emitLoadPop(classifyPrim(E->getType()), E);
+    return true;
+  }
+  case UO_Imag: { // __imag x
+    assert(!T);
+    if (!this->visit(SubExpr))
+      return false;
+    if (!this->emitConstUint8(1, E))
+      return false;
+    if (!this->emitArrayElemPtrPopUint8(E))
+      return false;
+
+    // Since our _Complex implementation does not map to a primitive type,
+    // we sometimes have to do the lvalue-to-rvalue conversion here manually.
+    if (!SubExpr->isLValue())
+      return this->emitLoadPop(classifyPrim(E->getType()), E);
+    return true;
+  }
   case UO_Extension:
     return this->delegate(SubExpr);
   case UO_Coawait:

diff --git a/clang/lib/AST/Interp/ByteCodeExprGen.h b/clang/lib/AST/Interp/ByteCodeExprGen.h
@@ -65,6 +65,7 @@ class ByteCodeExprGen : public ConstStmtVisitor<ByteCodeExprGen<Emitter>, bool>,
   bool VisitBinaryOperator(const BinaryOperator *E);
   bool VisitLogicalBinOp(const BinaryOperator *E);
   bool VisitPointerArithBinOp(const BinaryOperator *E);
+  bool VisitComplexBinOp(const BinaryOperator *E);
   bool VisitCXXDefaultArgExpr(const CXXDefaultArgExpr *E);
   bool VisitCallExpr(const CallExpr *E);
   bool VisitBuiltinCallExpr(const CallExpr *E);
@@ -285,6 +286,14 @@ class ByteCodeExprGen : public ConstStmtVisitor<ByteCodeExprGen<Emitter>, bool>,
   }
 
   bool emitPrimCast(PrimType FromT, PrimType ToT, QualType ToQT, const Expr *E);
+  std::optional<PrimType> classifyComplexElementType(QualType T) const {
+    assert(T->isAnyComplexType());
+
+    QualType ElemType = T->getAs<ComplexType>()->getElementType();
+
+    return this->classify(ElemType);
+  }
+
   bool emitRecordDestruction(const Descriptor *Desc);
   unsigned collectBaseOffset(const RecordType *BaseType,
                              const RecordType *DerivedType);

diff --git a/clang/lib/AST/Interp/Context.cpp b/clang/lib/AST/Interp/Context.cpp
@@ -92,6 +92,9 @@ std::optional<PrimType> Context::classify(QualType T) const {
   if (T->isBooleanType())
     return PT_Bool;
 
+  if (T->isAnyComplexType())
+    return std::nullopt;
+
   if (T->isSignedIntegerOrEnumerationType()) {
     switch (Ctx.getIntWidth(T)) {
     case 64:

diff --git a/clang/lib/AST/Interp/EvalEmitter.cpp b/clang/lib/AST/Interp/EvalEmitter.cpp
@@ -208,6 +208,27 @@ bool EvalEmitter::emitRetValue(const SourceInfo &Info) {
       }
       return Ok;
     }
+
+    // Complex types.
+    if (const auto *CT = Ty->getAs<ComplexType>()) {
+      QualType ElemTy = CT->getElementType();
+      std::optional<PrimType> ElemT = Ctx.classify(ElemTy);
+      assert(ElemT);
+
+      if (ElemTy->isIntegerType()) {
+        INT_TYPE_SWITCH(*ElemT, {
+          auto V1 = Ptr.atIndex(0).deref<T>();
+          auto V2 = Ptr.atIndex(1).deref<T>();
+          Result = APValue(V1.toAPSInt(), V2.toAPSInt());
+          return true;
+        });
+      } else if (ElemTy->isFloatingType()) {
+        Result = APValue(Ptr.atIndex(0).deref<Floating>().getAPFloat(),
+                         Ptr.atIndex(1).deref<Floating>().getAPFloat());
+        return true;
+      }
+      return false;
+    }
     llvm_unreachable("invalid value to return");
   };
 

diff --git a/clang/lib/AST/Interp/Interp.cpp b/clang/lib/AST/Interp/Interp.cpp
@@ -350,11 +350,6 @@ bool CheckCallable(InterpState &S, CodePtr OpPC, const Function *F) {
   }
 
   if (!F->isConstexpr()) {
-    // Don't emit anything if we're checking for a potential constant
-    // expression. That will happen later when actually executing.
-    if (S.checkingPotentialConstantExpression())
-      return false;
-
     const SourceLocation &Loc = S.Current->getLocation(OpPC);
     if (S.getLangOpts().CPlusPlus11) {
       const FunctionDecl *DiagDecl = F->getDecl();
@@ -371,13 +366,21 @@ bool CheckCallable(InterpState &S, CodePtr OpPC, const Function *F) {
       // FIXME: If DiagDecl is an implicitly-declared special member function
       // or an inheriting constructor, we should be much more explicit about why
       // it's not constexpr.
-      if (CD && CD->isInheritingConstructor())
+      if (CD && CD->isInheritingConstructor()) {
         S.FFDiag(Loc, diag::note_constexpr_invalid_inhctor, 1)
           << CD->getInheritedConstructor().getConstructor()->getParent();
-      else
+        S.Note(DiagDecl->getLocation(), diag::note_declared_at);
+      } else {
+        // Don't emit anything if the function isn't defined and we're checking
+        // for a constant expression. It might be defined at the point we're
+        // actually calling it.
+        if (!DiagDecl->isDefined() && S.checkingPotentialConstantExpression())
+          return false;
+
         S.FFDiag(Loc, diag::note_constexpr_invalid_function, 1)
           << DiagDecl->isConstexpr() << (bool)CD << DiagDecl;
-      S.Note(DiagDecl->getLocation(), diag::note_declared_at);
+        S.Note(DiagDecl->getLocation(), diag::note_declared_at);
+      }
     } else {
       S.FFDiag(Loc, diag::note_invalid_subexpr_in_const_expr);
     }

diff --git a/clang/lib/AST/Mangle.cpp b/clang/lib/AST/Mangle.cpp
@@ -147,7 +147,7 @@ void MangleContext::mangleName(GlobalDecl GD, raw_ostream &Out) {
 
     // If the label isn't literal, or if this is an alias for an LLVM intrinsic,
     // do not add a "\01" prefix.
-    if (!ALA->getIsLiteralLabel() || ALA->getLabel().startswith("llvm.")) {
+    if (!ALA->getIsLiteralLabel() || ALA->getLabel().starts_with("llvm.")) {
       Out << ALA->getLabel();
       return;
     }

diff --git a/clang/lib/AST/MicrosoftMangle.cpp b/clang/lib/AST/MicrosoftMangle.cpp
@@ -63,7 +63,7 @@ struct msvc_hashing_ostream : public llvm::raw_svector_ostream {
       : llvm::raw_svector_ostream(Buffer), OS(OS) {}
   ~msvc_hashing_ostream() override {
     StringRef MangledName = str();
-    bool StartsWithEscape = MangledName.startswith("\01");
+    bool StartsWithEscape = MangledName.starts_with("\01");
     if (StartsWithEscape)
       MangledName = MangledName.drop_front(1);
     if (MangledName.size() < 4096) {

diff --git a/clang/lib/AST/PrintfFormatString.cpp b/clang/lib/AST/PrintfFormatString.cpp
@@ -140,7 +140,7 @@ static PrintfSpecifierResult ParsePrintfSpecifier(FormatStringHandler &H,
         // Set the privacy flag if the privacy annotation in the
         // comma-delimited segment is at least as strict as the privacy
         // annotations in previous comma-delimited segments.
-        if (MatchedStr.startswith("mask")) {
+        if (MatchedStr.starts_with("mask")) {
           StringRef MaskType = MatchedStr.substr(sizeof("mask.") - 1);
           unsigned Size = MaskType.size();
           if (Warn && (Size == 0 || Size > 8))

diff --git a/clang/lib/AST/RawCommentList.cpp b/clang/lib/AST/RawCommentList.cpp
@@ -141,8 +141,8 @@ RawComment::RawComment(const SourceManager &SourceMgr, SourceRange SR,
     Kind = K.first;
     IsTrailingComment |= K.second;
 
-    IsAlmostTrailingComment = RawText.startswith("//<") ||
-                                 RawText.startswith("/*<");
+    IsAlmostTrailingComment =
+        RawText.starts_with("//<") || RawText.starts_with("/*<");
   } else {
     Kind = RCK_Merged;
     IsTrailingComment =

diff --git a/clang/lib/AST/Stmt.cpp b/clang/lib/AST/Stmt.cpp
@@ -811,11 +811,12 @@ std::string MSAsmStmt::generateAsmString(const ASTContext &C) const {
     StringRef Instruction = Pieces[I];
     // For vex/vex2/vex3/evex masm style prefix, convert it to att style
     // since we don't support masm style prefix in backend.
-    if (Instruction.startswith("vex "))
+    if (Instruction.starts_with("vex "))
       MSAsmString += '{' + Instruction.substr(0, 3).str() + '}' +
                      Instruction.substr(3).str();
-    else if (Instruction.startswith("vex2 ") ||
-             Instruction.startswith("vex3 ") || Instruction.startswith("evex "))
+    else if (Instruction.starts_with("vex2 ") ||
+             Instruction.starts_with("vex3 ") ||
+             Instruction.starts_with("evex "))
       MSAsmString += '{' + Instruction.substr(0, 4).str() + '}' +
                      Instruction.substr(4).str();
     else

diff --git a/clang/lib/ASTMatchers/ASTMatchersInternal.cpp b/clang/lib/ASTMatchers/ASTMatchersInternal.cpp
@@ -480,11 +480,11 @@ HasNameMatcher::HasNameMatcher(std::vector<std::string> N)
 
 static bool consumeNameSuffix(StringRef &FullName, StringRef Suffix) {
   StringRef Name = FullName;
-  if (!Name.endswith(Suffix))
+  if (!Name.ends_with(Suffix))
     return false;
   Name = Name.drop_back(Suffix.size());
   if (!Name.empty()) {
-    if (!Name.endswith("::"))
+    if (!Name.ends_with("::"))
       return false;
     Name = Name.drop_back(2);
   }
@@ -530,7 +530,7 @@ class PatternSet {
   PatternSet(ArrayRef<std::string> Names) {
     Patterns.reserve(Names.size());
     for (StringRef Name : Names)
-      Patterns.push_back({Name, Name.startswith("::")});
+      Patterns.push_back({Name, Name.starts_with("::")});
   }
 
   /// Consumes the name suffix from each pattern in the set and removes the ones
@@ -652,11 +652,11 @@ bool HasNameMatcher::matchesNodeFullSlow(const NamedDecl &Node) const {
     const StringRef FullName = OS.str();
 
     for (const StringRef Pattern : Names) {
-      if (Pattern.startswith("::")) {
+      if (Pattern.starts_with("::")) {
         if (FullName == Pattern)
           return true;
-      } else if (FullName.endswith(Pattern) &&
-                 FullName.drop_back(Pattern.size()).endswith("::")) {
+      } else if (FullName.ends_with(Pattern) &&
+                 FullName.drop_back(Pattern.size()).ends_with("::")) {
         return true;
       }
     }

diff --git a/clang/lib/ASTMatchers/Dynamic/Parser.cpp b/clang/lib/ASTMatchers/Dynamic/Parser.cpp
@@ -187,10 +187,10 @@ class Parser::CodeTokenizer {
             break;
           ++TokenLength;
         }
-        if (TokenLength == 4 && Code.startswith("true")) {
+        if (TokenLength == 4 && Code.starts_with("true")) {
           Result.Kind = TokenInfo::TK_Literal;
           Result.Value = true;
-        } else if (TokenLength == 5 && Code.startswith("false")) {
+        } else if (TokenLength == 5 && Code.starts_with("false")) {
           Result.Kind = TokenInfo::TK_Literal;
           Result.Value = false;
         } else {
@@ -737,7 +737,7 @@ bool Parser::parseMatcherExpressionImpl(const TokenInfo &NameToken,
 // Completions minus the prefix.
 void Parser::addCompletion(const TokenInfo &CompToken,
                            const MatcherCompletion& Completion) {
-  if (StringRef(Completion.TypedText).startswith(CompToken.Text) &&
+  if (StringRef(Completion.TypedText).starts_with(CompToken.Text) &&
       Completion.Specificity > 0) {
     Completions.emplace_back(Completion.TypedText.substr(CompToken.Text.size()),
                              Completion.MatcherDecl, Completion.Specificity);

diff --git a/clang/lib/Analysis/BodyFarm.cpp b/clang/lib/Analysis/BodyFarm.cpp
@@ -726,8 +726,8 @@ Stmt *BodyFarm::getBody(const FunctionDecl *D) {
       FF = nullptr;
       break;
     }
-  } else if (Name.startswith("OSAtomicCompareAndSwap") ||
-             Name.startswith("objc_atomicCompareAndSwap")) {
+  } else if (Name.starts_with("OSAtomicCompareAndSwap") ||
+             Name.starts_with("objc_atomicCompareAndSwap")) {
     FF = create_OSAtomicCompareAndSwap;
   } else if (Name == "call_once" && D->getDeclContext()->isStdNamespace()) {
     FF = create_call_once;

diff --git a/clang/lib/Analysis/CallGraph.cpp b/clang/lib/Analysis/CallGraph.cpp
@@ -168,7 +168,7 @@ bool CallGraph::includeCalleeInGraph(const Decl *D) {
       return false;
 
     IdentifierInfo *II = FD->getIdentifier();
-    if (II && II->getName().startswith("__inline"))
+    if (II && II->getName().starts_with("__inline"))
       return false;
   }
 

diff --git a/clang/lib/Analysis/CalledOnceCheck.cpp b/clang/lib/Analysis/CalledOnceCheck.cpp
@@ -973,7 +973,7 @@ class CalledOnceChecker : public ConstStmtVisitor<CalledOnceChecker> {
   /// Return true if the given name has conventional suffixes.
   static bool hasConventionalSuffix(llvm::StringRef Name) {
     return llvm::any_of(CONVENTIONAL_SUFFIXES, [Name](llvm::StringRef Suffix) {
-      return Name.endswith(Suffix);
+      return Name.ends_with(Suffix);
     });
   }
 

diff --git a/clang/lib/Analysis/CocoaConventions.cpp b/clang/lib/Analysis/CocoaConventions.cpp
@@ -26,10 +26,10 @@ bool cocoa::isRefType(QualType RetTy, StringRef Prefix,
   // Recursively walk the typedef stack, allowing typedefs of reference types.
   while (const TypedefType *TD = RetTy->getAs<TypedefType>()) {
     StringRef TDName = TD->getDecl()->getIdentifier()->getName();
-    if (TDName.startswith(Prefix) && TDName.endswith("Ref"))
+    if (TDName.starts_with(Prefix) && TDName.ends_with("Ref"))
       return true;
     // XPC unfortunately uses CF-style function names, but aren't CF types.
-    if (TDName.startswith("xpc_"))
+    if (TDName.starts_with("xpc_"))
       return false;
     RetTy = TD->getDecl()->getUnderlyingType();
   }
@@ -43,7 +43,7 @@ bool cocoa::isRefType(QualType RetTy, StringRef Prefix,
     return false;
 
   // Does the name start with the prefix?
-  return Name.startswith(Prefix);
+  return Name.starts_with(Prefix);
 }
 
 /// Returns true when the passed-in type is a CF-style reference-counted
@@ -127,10 +127,9 @@ bool coreFoundation::followsCreateRule(const FunctionDecl *fn) {
     // Scan for *lowercase* 'reate' or 'opy', followed by no lowercase
     // character.
     StringRef suffix = functionName.substr(it - start);
-    if (suffix.startswith("reate")) {
+    if (suffix.starts_with("reate")) {
       it += 5;
-    }
-    else if (suffix.startswith("opy")) {
+    } else if (suffix.starts_with("opy")) {
       it += 3;
     } else {
       // Keep scanning.

diff --git a/clang/lib/Analysis/FlowSensitive/Models/ChromiumCheckModel.cpp b/clang/lib/Analysis/FlowSensitive/Models/ChromiumCheckModel.cpp
@@ -43,7 +43,7 @@ bool isCheckLikeMethod(llvm::SmallDenseSet<const CXXMethodDecl *> &CheckDecls,
       return false;
 
     for (const CXXMethodDecl *M : ParentClass->methods())
-      if (M->getDeclName().isIdentifier() && M->getName().endswith("Check"))
+      if (M->getDeclName().isIdentifier() && M->getName().ends_with("Check"))
         CheckDecls.insert(M);
   }
 

diff --git a/clang/lib/Analysis/RetainSummaryManager.cpp b/clang/lib/Analysis/RetainSummaryManager.cpp
@@ -174,7 +174,7 @@ static bool isOSObjectPtr(QualType QT) {
 }
 
 static bool isISLObjectRef(QualType Ty) {
-  return StringRef(Ty.getAsString()).startswith("isl_");
+  return StringRef(Ty.getAsString()).starts_with("isl_");
 }
 
 static bool isOSIteratorSubclass(const Decl *D) {
@@ -255,13 +255,13 @@ RetainSummaryManager::getSummaryForOSObject(const FunctionDecl *FD,
       // TODO: Add support for the slightly common *Matching(table) idiom.
       // Cf. IOService::nameMatching() etc. - these function have an unusual
       // contract of returning at +0 or +1 depending on their last argument.
-      if (FName.endswith("Matching")) {
+      if (FName.ends_with("Matching")) {
         return getPersistentStopSummary();
       }
 
       // All objects returned with functions *not* starting with 'get',
       // or iterators, are returned at +1.
-      if ((!FName.startswith("get") && !FName.startswith("Get")) ||
+      if ((!FName.starts_with("get") && !FName.starts_with("Get")) ||
           isOSIteratorSubclass(PD)) {
         return getOSSummaryCreateRule(FD);
       } else {
@@ -392,9 +392,9 @@ const RetainSummary *RetainSummaryManager::getSummaryForObjCOrCFObject(
     return getPersistentSummary(RetEffect::MakeNoRet(),
                                 ScratchArgs,
                                 ArgEffect(DoNothing), ArgEffect(DoNothing));
-  } else if (FName.startswith("NSLog")) {
+  } else if (FName.starts_with("NSLog")) {
     return getDoNothingSummary();
-  } else if (FName.startswith("NS") && FName.contains("Insert")) {
+  } else if (FName.starts_with("NS") && FName.contains("Insert")) {
     // Allowlist NSXXInsertXX, for example NSMapInsertIfAbsent, since they can
     // be deallocated by NSMapRemove.
     ScratchArgs = AF.add(ScratchArgs, 1, ArgEffect(StopTracking));
@@ -453,9 +453,9 @@ const RetainSummary *RetainSummaryManager::getSummaryForObjCOrCFObject(
 
   // Check for release functions, the only kind of functions that we care
   // about that don't return a pointer type.
-  if (FName.startswith("CG") || FName.startswith("CF")) {
+  if (FName.starts_with("CG") || FName.starts_with("CF")) {
     // Test for 'CGCF'.
-    FName = FName.substr(FName.startswith("CGCF") ? 4 : 2);
+    FName = FName.substr(FName.starts_with("CGCF") ? 4 : 2);
 
     if (isRelease(FD, FName))
       return getUnarySummary(FT, DecRef);

diff --git a/clang/lib/Basic/Attributes.cpp b/clang/lib/Basic/Attributes.cpp
@@ -33,7 +33,7 @@ int clang::hasAttribute(AttributeCommonInfo::Syntax Syntax,
                         const TargetInfo &Target, const LangOptions &LangOpts) {
   StringRef Name = Attr->getName();
   // Normalize the attribute name, __foo__ becomes foo.
-  if (Name.size() >= 4 && Name.startswith("__") && Name.endswith("__"))
+  if (Name.size() >= 4 && Name.starts_with("__") && Name.ends_with("__"))
     Name = Name.substr(2, Name.size() - 4);
 
   // Normalize the scope name, but only for gnu and clang attributes.
@@ -103,8 +103,8 @@ static StringRef normalizeAttrName(const IdentifierInfo *Name,
        (NormalizedScopeName.empty() || NormalizedScopeName == "gnu" ||
         NormalizedScopeName == "clang"));
   StringRef AttrName = Name->getName();
-  if (ShouldNormalize && AttrName.size() >= 4 && AttrName.startswith("__") &&
-      AttrName.endswith("__"))
+  if (ShouldNormalize && AttrName.size() >= 4 && AttrName.starts_with("__") &&
+      AttrName.ends_with("__"))
     AttrName = AttrName.slice(2, AttrName.size() - 2);
 
   return AttrName;

diff --git a/clang/lib/Basic/DiagnosticIDs.cpp b/clang/lib/Basic/DiagnosticIDs.cpp
@@ -853,5 +853,5 @@ bool DiagnosticIDs::isUnrecoverable(unsigned DiagID) const {
 
 bool DiagnosticIDs::isARCDiagnostic(unsigned DiagID) {
   unsigned cat = getCategoryNumberForDiag(DiagID);
-  return DiagnosticIDs::getCategoryNameFromID(cat).startswith("ARC ");
+  return DiagnosticIDs::getCategoryNameFromID(cat).starts_with("ARC ");
 }
diff --git a/clang/lib/Basic/IdentifierTable.cpp b/clang/lib/Basic/IdentifierTable.cpp
@@ -604,7 +604,7 @@ LLVM_DUMP_METHOD void Selector::dump() const { print(llvm::errs()); }
 static bool startsWithWord(StringRef name, StringRef word) {
   if (name.size() < word.size()) return false;
   return ((name.size() == word.size() || !isLowercase(name[word.size()])) &&
-          name.startswith(word));
+          name.starts_with(word));
 }
 
 ObjCMethodFamily Selector::getMethodFamilyImpl(Selector sel) {
@@ -742,7 +742,7 @@ SelectorTable::constructSetterSelector(IdentifierTable &Idents,
 
 std::string SelectorTable::getPropertyNameFromSetterSelector(Selector Sel) {
   StringRef Name = Sel.getNameForSlot(0);
-  assert(Name.startswith("set") && "invalid setter name");
+  assert(Name.starts_with("set") && "invalid setter name");
   return (Twine(toLowercase(Name[3])) + Name.drop_front(4)).str();
 }
 

diff --git a/clang/lib/Basic/Module.cpp b/clang/lib/Basic/Module.cpp
@@ -166,7 +166,8 @@ bool Module::isForBuilding(const LangOptions &LangOpts) const {
   // for either.
   if (!LangOpts.isCompilingModule() && getTopLevelModule()->IsFramework &&
       CurrentModule == LangOpts.ModuleName &&
-      !CurrentModule.endswith("_Private") && TopLevelName.endswith("_Private"))
+      !CurrentModule.ends_with("_Private") &&
+      TopLevelName.ends_with("_Private"))
     TopLevelName = TopLevelName.drop_back(8);
 
   return TopLevelName == CurrentModule;

diff --git a/clang/lib/Basic/Sarif.cpp b/clang/lib/Basic/Sarif.cpp
@@ -74,7 +74,7 @@ static std::string fileNameToURI(StringRef Filename) {
 
   // Get the root name to see if it has a URI authority.
   StringRef Root = sys::path::root_name(Filename);
-  if (Root.startswith("//")) {
+  if (Root.starts_with("//")) {
     // There is an authority, so add it to the URI.
     Ret += Root.drop_front(2).str();
   } else if (!Root.empty()) {

diff --git a/clang/lib/Basic/TargetInfo.cpp b/clang/lib/Basic/TargetInfo.cpp
@@ -551,26 +551,26 @@ ParsedTargetAttr TargetInfo::parseTargetAttr(StringRef Features) const {
     // TODO: Support the fpmath option. It will require checking
     // overall feature validity for the function with the rest of the
     // attributes on the function.
-    if (Feature.startswith("fpmath="))
+    if (Feature.starts_with("fpmath="))
       continue;
 
-    if (Feature.startswith("branch-protection=")) {
+    if (Feature.starts_with("branch-protection=")) {
       Ret.BranchProtection = Feature.split('=').second.trim();
       continue;
     }
 
     // While we're here iterating check for a different target cpu.
-    if (Feature.startswith("arch=")) {
+    if (Feature.starts_with("arch=")) {
       if (!Ret.CPU.empty())
         Ret.Duplicate = "arch=";
       else
         Ret.CPU = Feature.split("=").second.trim();
-    } else if (Feature.startswith("tune=")) {
+    } else if (Feature.starts_with("tune=")) {
       if (!Ret.Tune.empty())
         Ret.Duplicate = "tune=";
       else
         Ret.Tune = Feature.split("=").second.trim();
-    } else if (Feature.startswith("no-"))
+    } else if (Feature.starts_with("no-"))
       Ret.Features.push_back("-" + Feature.split("-").second.str());
     else
       Ret.Features.push_back("+" + Feature.str());

diff --git a/clang/lib/Basic/Targets/AArch64.cpp b/clang/lib/Basic/Targets/AArch64.cpp
@@ -1062,7 +1062,7 @@ ParsedTargetAttr AArch64TargetInfo::parseTargetAttr(StringRef Features) const {
       else
         // Pushing the original feature string to give a sema error later on
         // when they get checked.
-        if (Feature.startswith("no"))
+        if (Feature.starts_with("no"))
           Features.push_back("-" + Feature.drop_front(2).str());
         else
           Features.push_back("+" + Feature.str());
@@ -1071,15 +1071,15 @@ ParsedTargetAttr AArch64TargetInfo::parseTargetAttr(StringRef Features) const {
 
   for (auto &Feature : AttrFeatures) {
     Feature = Feature.trim();
-    if (Feature.startswith("fpmath="))
+    if (Feature.starts_with("fpmath="))
       continue;
 
-    if (Feature.startswith("branch-protection=")) {
+    if (Feature.starts_with("branch-protection=")) {
       Ret.BranchProtection = Feature.split('=').second.trim();
       continue;
     }
 
-    if (Feature.startswith("arch=")) {
+    if (Feature.starts_with("arch=")) {
       if (FoundArch)
         Ret.Duplicate = "arch=";
       FoundArch = true;
@@ -1095,7 +1095,7 @@ ParsedTargetAttr AArch64TargetInfo::parseTargetAttr(StringRef Features) const {
       Ret.Features.push_back(AI->ArchFeature.str());
       // Add any extra features, after the +
       SplitAndAddFeatures(Split.second, Ret.Features);
-    } else if (Feature.startswith("cpu=")) {
+    } else if (Feature.starts_with("cpu=")) {
       if (!Ret.CPU.empty())
         Ret.Duplicate = "cpu=";
       else {
@@ -1106,14 +1106,14 @@ ParsedTargetAttr AArch64TargetInfo::parseTargetAttr(StringRef Features) const {
         Ret.CPU = Split.first;
         SplitAndAddFeatures(Split.second, Ret.Features);
       }
-    } else if (Feature.startswith("tune=")) {
+    } else if (Feature.starts_with("tune=")) {
       if (!Ret.Tune.empty())
         Ret.Duplicate = "tune=";
       else
         Ret.Tune = Feature.split("=").second.trim();
-    } else if (Feature.startswith("+")) {
+    } else if (Feature.starts_with("+")) {
       SplitAndAddFeatures(Feature, Ret.Features);
-    } else if (Feature.startswith("no-")) {
+    } else if (Feature.starts_with("no-")) {
       StringRef FeatureName =
           llvm::AArch64::getArchExtFeature(Feature.split("-").second);
       if (!FeatureName.empty())

diff --git a/clang/lib/Basic/Targets/AMDGPU.cpp b/clang/lib/Basic/Targets/AMDGPU.cpp
@@ -279,7 +279,7 @@ void AMDGPUTargetInfo::getTargetDefines(const LangOptions &Opts,
     Builder.defineMacro(Twine("__") + Twine(CanonName) + Twine("__"));
     // Emit macros for gfx family e.g. gfx906 -> __GFX9__, gfx1030 -> __GFX10___
     if (isAMDGCN(getTriple())) {
-      assert(CanonName.startswith("gfx") && "Invalid amdgcn canonical name");
+      assert(CanonName.starts_with("gfx") && "Invalid amdgcn canonical name");
       Builder.defineMacro(Twine("__") + Twine(CanonName.drop_back(2).upper()) +
                           Twine("__"));
     }

diff --git a/clang/lib/Basic/Targets/Mips.cpp b/clang/lib/Basic/Targets/Mips.cpp
@@ -196,7 +196,7 @@ void MipsTargetInfo::getTargetDefines(const LangOptions &Opts,
   else
     Builder.defineMacro("_MIPS_ARCH_" + StringRef(CPU).upper());
 
-  if (StringRef(CPU).startswith("octeon"))
+  if (StringRef(CPU).starts_with("octeon"))
     Builder.defineMacro("__OCTEON__");
 
   if (CPU != "mips1") {

diff --git a/clang/lib/Basic/Targets/NVPTX.cpp b/clang/lib/Basic/Targets/NVPTX.cpp
@@ -42,7 +42,7 @@ NVPTXTargetInfo::NVPTXTargetInfo(const llvm::Triple &Triple,
   PTXVersion = 32;
   for (const StringRef Feature : Opts.FeaturesAsWritten) {
     int PTXV;
-    if (!Feature.startswith("+ptx") ||
+    if (!Feature.starts_with("+ptx") ||
         Feature.drop_front(4).getAsInteger(10, PTXV))
       continue;
     PTXVersion = PTXV; // TODO: should it be max(PTXVersion, PTXV)?

diff --git a/clang/lib/Basic/Targets/RISCV.cpp b/clang/lib/Basic/Targets/RISCV.cpp
@@ -434,14 +434,14 @@ ParsedTargetAttr RISCVTargetInfo::parseTargetAttr(StringRef Features) const {
     Feature = Feature.trim();
     StringRef AttrString = Feature.split("=").second.trim();
 
-    if (Feature.startswith("arch=")) {
+    if (Feature.starts_with("arch=")) {
       // Override last features
       Ret.Features.clear();
       if (FoundArch)
         Ret.Duplicate = "arch=";
       FoundArch = true;
 
-      if (AttrString.startswith("+")) {
+      if (AttrString.starts_with("+")) {
         // EXTENSION like arch=+v,+zbb
         SmallVector<StringRef, 1> Exts;
         AttrString.split(Exts, ",");
@@ -461,7 +461,7 @@ ParsedTargetAttr RISCVTargetInfo::parseTargetAttr(StringRef Features) const {
         // full-arch-string like arch=rv64gcv
         handleFullArchString(AttrString, Ret.Features);
       }
-    } else if (Feature.startswith("cpu=")) {
+    } else if (Feature.starts_with("cpu=")) {
       if (!Ret.CPU.empty())
         Ret.Duplicate = "cpu=";
 
@@ -475,7 +475,7 @@ ParsedTargetAttr RISCVTargetInfo::parseTargetAttr(StringRef Features) const {
           handleFullArchString(MarchFromCPU, Ret.Features);
         }
       }
-    } else if (Feature.startswith("tune=")) {
+    } else if (Feature.starts_with("tune=")) {
       if (!Ret.Tune.empty())
         Ret.Duplicate = "tune=";
 

diff --git a/clang/lib/Basic/Warnings.cpp b/clang/lib/Basic/Warnings.cpp
@@ -97,7 +97,7 @@ void clang::ProcessWarningOptions(DiagnosticsEngine &Diags,
       // Check to see if this warning starts with "no-", if so, this is a
       // negative form of the option.
       bool isPositive = true;
-      if (Opt.startswith("no-")) {
+      if (Opt.starts_with("no-")) {
         isPositive = false;
         Opt = Opt.substr(3);
       }
@@ -133,7 +133,7 @@ void clang::ProcessWarningOptions(DiagnosticsEngine &Diags,
       // table. It also has the "specifier" form of -Werror=foo. GCC supports
       // the deprecated -Werror-implicit-function-declaration which is used by
       // a few projects.
-      if (Opt.startswith("error")) {
+      if (Opt.starts_with("error")) {
         StringRef Specifier;
         if (Opt.size() > 5) {  // Specifier must be present.
           if (Opt[5] != '=' &&
@@ -162,7 +162,7 @@ void clang::ProcessWarningOptions(DiagnosticsEngine &Diags,
       }
 
       // -Wfatal-errors is yet another special case.
-      if (Opt.startswith("fatal-errors")) {
+      if (Opt.starts_with("fatal-errors")) {
         StringRef Specifier;
         if (Opt.size() != 12) {
           if ((Opt[12] != '=' && Opt[12] != '-') || Opt.size() == 13) {
@@ -204,7 +204,7 @@ void clang::ProcessWarningOptions(DiagnosticsEngine &Diags,
 
       // Check to see if this warning starts with "no-", if so, this is a
       // negative form of the option.
-      bool IsPositive = !Opt.startswith("no-");
+      bool IsPositive = !Opt.starts_with("no-");
       if (!IsPositive) Opt = Opt.substr(3);
 
       auto Severity = IsPositive ? diag::Severity::Remark

diff --git a/clang/lib/CodeGen/CGBuiltin.cpp b/clang/lib/CodeGen/CGBuiltin.cpp
@@ -9985,6 +9985,10 @@ CodeGenFunction::getSVEOverloadTypes(const SVETypeFlags &TypeFlags,
   if (TypeFlags.isOverloadCvt())
     return {Ops[0]->getType(), Ops.back()->getType()};
 
+  if (TypeFlags.isReductionQV() && !ResultType->isScalableTy() &&
+      ResultType->isVectorTy())
+    return {ResultType, Ops[1]->getType()};
+
   assert(TypeFlags.isOverloadDefault() && "Unexpected value for overloads");
   return {DefaultType};
 }

diff --git a/clang/lib/CodeGen/CGCall.cpp b/clang/lib/CodeGen/CGCall.cpp
@@ -5609,7 +5609,7 @@ RValue CodeGenFunction::EmitCall(const CGFunctionInfo &CallInfo,
     EmitBlock(Cont);
   }
   if (CI->getCalledFunction() && CI->getCalledFunction()->hasName() &&
-      CI->getCalledFunction()->getName().startswith("_Z4sqrt")) {
+      CI->getCalledFunction()->getName().starts_with("_Z4sqrt")) {
     SetSqrtFPAccuracy(CI);
   }
   if (callOrInvoke)

diff --git a/clang/lib/CodeGen/CGDebugInfo.cpp b/clang/lib/CodeGen/CGDebugInfo.cpp
@@ -637,7 +637,8 @@ void CGDebugInfo::CreateCompileUnit() {
     Sysroot = CGM.getHeaderSearchOpts().Sysroot;
     auto B = llvm::sys::path::rbegin(Sysroot);
     auto E = llvm::sys::path::rend(Sysroot);
-    auto It = std::find_if(B, E, [](auto SDK) { return SDK.endswith(".sdk"); });
+    auto It =
+        std::find_if(B, E, [](auto SDK) { return SDK.ends_with(".sdk"); });
     if (It != E)
       SDK = *It;
   }
@@ -2885,7 +2886,7 @@ llvm::DIModule *CGDebugInfo::getOrCreateModuleRef(ASTSourceDescriptor Mod,
   // clang::Module object, but it won't actually be built or imported; it will
   // be textual.
   if (CreateSkeletonCU && IsRootModule && Mod.getASTFile().empty() && M)
-    assert(StringRef(M->Name).startswith(CGM.getLangOpts().ModuleName) &&
+    assert(StringRef(M->Name).starts_with(CGM.getLangOpts().ModuleName) &&
            "clang module without ASTFile must be specified by -fmodule-name");
 
   // Return a StringRef to the remapped Path.
@@ -4249,7 +4250,7 @@ void CGDebugInfo::emitFunctionStart(GlobalDecl GD, SourceLocation Loc,
 
     Flags |= llvm::DINode::FlagPrototyped;
   }
-  if (Name.startswith("\01"))
+  if (Name.starts_with("\01"))
     Name = Name.substr(1);
 
   assert((!D || !isa<VarDecl>(D) ||

diff --git a/clang/lib/CodeGen/CGException.cpp b/clang/lib/CodeGen/CGException.cpp
@@ -277,7 +277,7 @@ static bool LandingPadHasOnlyCXXUses(llvm::LandingPadInst *LPI) {
       if (llvm::GlobalVariable *GV = dyn_cast<llvm::GlobalVariable>(Val))
         // ObjC EH selector entries are always global variables with
         // names starting like this.
-        if (GV->getName().startswith("OBJC_EHTYPE"))
+        if (GV->getName().starts_with("OBJC_EHTYPE"))
           return false;
     } else {
       // Check if any of the filter values have the ObjC prefix.
@@ -288,7 +288,7 @@ static bool LandingPadHasOnlyCXXUses(llvm::LandingPadInst *LPI) {
             cast<llvm::GlobalVariable>((*II)->stripPointerCasts()))
           // ObjC EH selector entries are always global variables with
           // names starting like this.
-          if (GV->getName().startswith("OBJC_EHTYPE"))
+          if (GV->getName().starts_with("OBJC_EHTYPE"))
             return false;
       }
     }
@@ -1917,7 +1917,7 @@ void CodeGenFunction::EmitCapturedLocals(CodeGenFunction &ParentCGF,
         const VarDecl *D = cast<VarDecl>(I.first);
         if (isa<ImplicitParamDecl>(D) &&
             D->getType() == getContext().VoidPtrTy) {
-          assert(D->getName().startswith("frame_pointer"));
+          assert(D->getName().starts_with("frame_pointer"));
           FramePtrAddrAlloca = cast<llvm::AllocaInst>(I.second.getPointer());
           break;
         }

diff --git a/clang/lib/CodeGen/CGExpr.cpp b/clang/lib/CodeGen/CGExpr.cpp
@@ -431,7 +431,7 @@ static Address createReferenceTemporary(CodeGenFunction &CGF,
 
 /// Helper method to check if the underlying ABI is AAPCS
 static bool isAAPCS(const TargetInfo &TargetInfo) {
-  return TargetInfo.getABI().startswith("aapcs");
+  return TargetInfo.getABI().starts_with("aapcs");
 }
 
 LValue CodeGenFunction::
@@ -3156,7 +3156,7 @@ LValue CodeGenFunction::EmitPredefinedLValue(const PredefinedExpr *E) {
   auto SL = E->getFunctionName();
   assert(SL != nullptr && "No StringLiteral name in PredefinedExpr");
   StringRef FnName = CurFn->getName();
-  if (FnName.startswith("\01"))
+  if (FnName.starts_with("\01"))
     FnName = FnName.substr(1);
   StringRef NameItems[] = {
       PredefinedExpr::getIdentKindName(E->getIdentKind()), FnName};

diff --git a/clang/lib/CodeGen/CGObjCMac.cpp b/clang/lib/CodeGen/CGObjCMac.cpp
@@ -1850,7 +1850,7 @@ static bool hasObjCExceptionAttribute(ASTContext &Context,
 static llvm::GlobalValue::LinkageTypes
 getLinkageTypeForObjCMetadata(CodeGenModule &CGM, StringRef Section) {
   if (CGM.getTriple().isOSBinFormatMachO() &&
-      (Section.empty() || Section.startswith("__DATA")))
+      (Section.empty() || Section.starts_with("__DATA")))
     return llvm::GlobalValue::InternalLinkage;
   return llvm::GlobalValue::PrivateLinkage;
 }
@@ -6162,7 +6162,7 @@ void CGObjCNonFragileABIMac::AddModuleClassList(
   // Section name is obtained by calling GetSectionName, which returns
   // sections in the __DATA segment on MachO.
   assert((!CGM.getTriple().isOSBinFormatMachO() ||
-          SectionName.startswith("__DATA")) &&
+          SectionName.starts_with("__DATA")) &&
          "SectionName expected to start with __DATA on MachO");
   llvm::GlobalVariable *GV = new llvm::GlobalVariable(
       CGM.getModule(), Init->getType(), false,

diff --git a/clang/lib/CodeGen/CGRecordLayoutBuilder.cpp b/clang/lib/CodeGen/CGRecordLayoutBuilder.cpp
@@ -111,7 +111,7 @@ struct CGRecordLowering {
 
   /// Helper function to check if we are targeting AAPCS.
   bool isAAPCS() const {
-    return Context.getTargetInfo().getABI().startswith("aapcs");
+    return Context.getTargetInfo().getABI().starts_with("aapcs");
   }
 
   /// Helper function to check if the target machine is BigEndian.

diff --git a/clang/lib/CodeGen/CGStmt.cpp b/clang/lib/CodeGen/CGStmt.cpp
@@ -2548,7 +2548,7 @@ void CodeGenFunction::EmitAsmStmt(const AsmStmt &S) {
       ResultRegQualTys.push_back(QTy);
       ResultRegDests.push_back(Dest);
 
-      bool IsFlagReg = llvm::StringRef(OutputConstraint).startswith("{@cc");
+      bool IsFlagReg = llvm::StringRef(OutputConstraint).starts_with("{@cc");
       ResultRegIsFlagReg.push_back(IsFlagReg);
 
       llvm::Type *Ty = ConvertTypeForMem(QTy);

diff --git a/clang/lib/CodeGen/CodeGenAction.cpp b/clang/lib/CodeGen/CodeGenAction.cpp
@@ -1139,7 +1139,7 @@ CodeGenAction::loadModule(MemoryBufferRef MBRef) {
 
   // Strip off a leading diagnostic code if there is one.
   StringRef Msg = Err.getMessage();
-  if (Msg.startswith("error: "))
+  if (Msg.starts_with("error: "))
     Msg = Msg.substr(7);
 
   unsigned DiagID =

diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -225,9 +225,9 @@ createTargetCodeGenInfo(CodeGenModule &CGM) {
     StringRef ABIStr = Target.getABI();
     unsigned XLen = Target.getPointerWidth(LangAS::Default);
     unsigned ABIFLen = 0;
-    if (ABIStr.endswith("f"))
+    if (ABIStr.ends_with("f"))
       ABIFLen = 32;
-    else if (ABIStr.endswith("d"))
+    else if (ABIStr.ends_with("d"))
       ABIFLen = 64;
     return createRISCVTargetCodeGenInfo(CGM, XLen, ABIFLen);
   }
@@ -308,9 +308,9 @@ createTargetCodeGenInfo(CodeGenModule &CGM) {
   case llvm::Triple::loongarch64: {
     StringRef ABIStr = Target.getABI();
     unsigned ABIFRLen = 0;
-    if (ABIStr.endswith("f"))
+    if (ABIStr.ends_with("f"))
       ABIFRLen = 32;
-    else if (ABIStr.endswith("d"))
+    else if (ABIStr.ends_with("d"))
       ABIFRLen = 64;
     return createLoongArchTargetCodeGenInfo(
         CGM, Target.getPointerWidth(LangAS::Default), ABIFRLen);
@@ -1715,7 +1715,7 @@ static void AppendTargetMangling(const CodeGenModule &CGM,
   llvm::sort(Info.Features, [&Target](StringRef LHS, StringRef RHS) {
     // Multiversioning doesn't allow "no-${feature}", so we can
     // only have "+" prefixes here.
-    assert(LHS.startswith("+") && RHS.startswith("+") &&
+    assert(LHS.starts_with("+") && RHS.starts_with("+") &&
            "Features should always have a prefix.");
     return Target.multiVersionSortPriority(LHS.substr(1)) >
            Target.multiVersionSortPriority(RHS.substr(1));
@@ -1769,7 +1769,7 @@ static void AppendTargetClonesMangling(const CodeGenModule &CGM,
   } else {
     Out << '.';
     StringRef FeatureStr = Attr->getFeatureStr(VersionIndex);
-    if (FeatureStr.startswith("arch="))
+    if (FeatureStr.starts_with("arch="))
       Out << "arch_" << FeatureStr.substr(sizeof("arch=") - 1);
     else
       Out << FeatureStr;
@@ -3828,7 +3828,7 @@ namespace {
       if (!BuiltinID || !BI.isLibFunction(BuiltinID))
         return false;
       StringRef BuiltinName = BI.getName(BuiltinID);
-      if (BuiltinName.startswith("__builtin_") &&
+      if (BuiltinName.starts_with("__builtin_") &&
           Name == BuiltinName.slice(strlen("__builtin_"), StringRef::npos)) {
         return true;
       }
@@ -4164,7 +4164,7 @@ void CodeGenModule::emitMultiVersionFunctions() {
               Feature.push_back(CurFeat.trim());
           }
         } else {
-          if (Version.startswith("arch="))
+          if (Version.starts_with("arch="))
             Architecture = Version.drop_front(sizeof("arch=") - 1);
           else if (Version != "default")
             Feature.push_back(Version);

diff --git a/clang/lib/CodeGen/CoverageMappingGen.cpp b/clang/lib/CodeGen/CoverageMappingGen.cpp
@@ -1623,8 +1623,12 @@ static void dump(llvm::raw_ostream &OS, StringRef FunctionName,
       OS << "Gap,";
       break;
     case CounterMappingRegion::BranchRegion:
+    case CounterMappingRegion::MCDCBranchRegion:
       OS << "Branch,";
       break;
+    case CounterMappingRegion::MCDCDecisionRegion:
+      OS << "Decision,";
+      break;
     }
 
     OS << "File " << R.FileID << ", " << R.LineStart << ":" << R.ColumnStart

diff --git a/clang/lib/CodeGen/Targets/SPIR.cpp b/clang/lib/CodeGen/Targets/SPIR.cpp
@@ -146,14 +146,14 @@ static llvm::Type *getSPIRVImageType(llvm::LLVMContext &Ctx, StringRef BaseType,
 
   // Choose the dimension of the image--this corresponds to the Dim enum in
   // SPIR-V (first integer parameter of OpTypeImage).
-  if (OpenCLName.startswith("image2d"))
+  if (OpenCLName.starts_with("image2d"))
     IntParams[0] = 1; // 1D
-  else if (OpenCLName.startswith("image3d"))
+  else if (OpenCLName.starts_with("image3d"))
     IntParams[0] = 2; // 2D
   else if (OpenCLName == "image1d_buffer")
     IntParams[0] = 5; // Buffer
   else
-    assert(OpenCLName.startswith("image1d") && "Unknown image type");
+    assert(OpenCLName.starts_with("image1d") && "Unknown image type");
 
   // Set the other integer parameters of OpTypeImage if necessary. Note that the
   // OpenCL image types don't provide any information for the Sampled or

diff --git a/clang/lib/Driver/Distro.cpp b/clang/lib/Driver/Distro.cpp
@@ -34,7 +34,7 @@ static Distro::DistroType DetectOsRelease(llvm::vfs::FileSystem &VFS) {
 
   // Obviously this can be improved a lot.
   for (StringRef Line : Lines)
-    if (Version == Distro::UnknownDistro && Line.startswith("ID="))
+    if (Version == Distro::UnknownDistro && Line.starts_with("ID="))
       Version = llvm::StringSwitch<Distro::DistroType>(Line.substr(3))
                     .Case("alpine", Distro::AlpineLinux)
                     .Case("fedora", Distro::Fedora)
@@ -60,7 +60,7 @@ static Distro::DistroType DetectLsbRelease(llvm::vfs::FileSystem &VFS) {
 
   for (StringRef Line : Lines)
     if (Version == Distro::UnknownDistro &&
-        Line.startswith("DISTRIB_CODENAME="))
+        Line.starts_with("DISTRIB_CODENAME="))
       Version = llvm::StringSwitch<Distro::DistroType>(Line.substr(17))
                     .Case("hardy", Distro::UbuntuHardy)
                     .Case("intrepid", Distro::UbuntuIntrepid)
@@ -119,10 +119,10 @@ static Distro::DistroType DetectDistro(llvm::vfs::FileSystem &VFS) {
 
   if (File) {
     StringRef Data = File.get()->getBuffer();
-    if (Data.startswith("Fedora release"))
+    if (Data.starts_with("Fedora release"))
       return Distro::Fedora;
-    if (Data.startswith("Red Hat Enterprise Linux") ||
-        Data.startswith("CentOS") || Data.startswith("Scientific Linux")) {
+    if (Data.starts_with("Red Hat Enterprise Linux") ||
+        Data.starts_with("CentOS") || Data.starts_with("Scientific Linux")) {
       if (Data.contains("release 7"))
         return Distro::RHEL7;
       else if (Data.contains("release 6"))
@@ -182,7 +182,7 @@ static Distro::DistroType DetectDistro(llvm::vfs::FileSystem &VFS) {
     SmallVector<StringRef, 8> Lines;
     Data.split(Lines, "\n");
     for (const StringRef &Line : Lines) {
-      if (!Line.trim().startswith("VERSION"))
+      if (!Line.trim().starts_with("VERSION"))
         continue;
       std::pair<StringRef, StringRef> SplitLine = Line.split('=');
       // Old versions have split VERSION and PATCHLEVEL

diff --git a/clang/lib/Driver/Driver.cpp b/clang/lib/Driver/Driver.cpp
@@ -1451,7 +1451,7 @@ Compilation *Driver::BuildCompilation(ArrayRef<const char *> ArgList) {
     case llvm::Triple::aarch64:
     case llvm::Triple::aarch64_be:
     case llvm::Triple::aarch64_32:
-      if (TC.getTriple().getEnvironmentName().startswith("eabi")) {
+      if (TC.getTriple().getEnvironmentName().starts_with("eabi")) {
         Diag(diag::warn_target_unrecognized_env)
             << TargetTriple
             << (TC.getTriple().getArchName().str() + "-none-elf");
@@ -1540,7 +1540,7 @@ bool Driver::getCrashDiagnosticFile(StringRef ReproCrashFilename,
   for (fs::directory_iterator File(CrashDiagDir, EC), FileEnd;
        File != FileEnd && !EC; File.increment(EC)) {
     StringRef FileName = path::filename(File->path());
-    if (!FileName.startswith(Name))
+    if (!FileName.starts_with(Name))
       continue;
     if (fs::status(File->path(), FileStatus))
       continue;
@@ -1551,7 +1551,7 @@ bool Driver::getCrashDiagnosticFile(StringRef ReproCrashFilename,
     // The first line should start with "Process:", otherwise this isn't a real
     // .crash file.
     StringRef Data = CrashFile.get()->getBuffer();
-    if (!Data.startswith("Process:"))
+    if (!Data.starts_with("Process:"))
       continue;
     // Parse parent process pid line, e.g: "Parent Process: clang-4.0 [79141]"
     size_t ParentProcPos = Data.find("Parent Process:");
@@ -1780,7 +1780,7 @@ void Driver::generateCompilationDiagnostics(
       ReproCrashFilename = TempFile;
       llvm::sys::path::replace_extension(ReproCrashFilename, ".crash");
     }
-    if (StringRef(TempFile).endswith(".cache")) {
+    if (StringRef(TempFile).ends_with(".cache")) {
       // In some cases (modules) we'll dump extra data to help with reproducing
       // the crash into a directory next to the output.
       VFS = llvm::sys::path::filename(TempFile);
@@ -2001,7 +2001,7 @@ void Driver::HandleAutocompletions(StringRef PassedFlags) const {
   // Distinguish "--autocomplete=-someflag" and "--autocomplete=-someflag,"
   // because the latter indicates that the user put space before pushing tab
   // which should end up in a file completion.
-  const bool HasSpace = PassedFlags.endswith(",");
+  const bool HasSpace = PassedFlags.ends_with(",");
 
   // Parse PassedFlags by "," as all the command-line flags are passed to this
   // function separated by ","
@@ -2041,7 +2041,7 @@ void Driver::HandleAutocompletions(StringRef PassedFlags) const {
 
   // When flag ends with '=' and there was no value completion, return empty
   // string and fall back to the file autocompletion.
-  if (SuggestedCompletions.empty() && !Cur.endswith("=")) {
+  if (SuggestedCompletions.empty() && !Cur.ends_with("=")) {
     // If the flag is in the form of "--autocomplete=-foo",
     // we were requested to print out all option names that start with "-foo".
     // For example, "--autocomplete=-fsyn" is expanded to "-fsyntax-only".
@@ -2053,7 +2053,7 @@ void Driver::HandleAutocompletions(StringRef PassedFlags) const {
     // TODO: Find a good way to add them to OptTable instead and them remove
     // this code.
     for (StringRef S : DiagnosticIDs::getDiagnosticFlags())
-      if (S.startswith(Cur))
+      if (S.starts_with(Cur))
         SuggestedCompletions.push_back(std::string(S));
   }
 
@@ -2535,7 +2535,7 @@ bool Driver::DiagnoseInputExistence(const DerivedArgList &Args, StringRef Value,
   // so we can't downgrade diagnostics for `/GR-` from an error to a warning
   // in cc mode. (We can in cl mode because cl.exe itself only warns on
   // unknown flags.)
-  if (IsCLMode() && Ty == types::TY_Object && !Value.startswith("/"))
+  if (IsCLMode() && Ty == types::TY_Object && !Value.starts_with("/"))
     return true;
 
   Diag(clang::diag::err_drv_no_such_file) << Value;
@@ -6565,7 +6565,7 @@ llvm::StringRef clang::driver::getDriverMode(StringRef ProgName,
       getDriverOptTable().getOption(options::OPT_driver_mode).getPrefixedName();
   llvm::StringRef Opt;
   for (StringRef Arg : Args) {
-    if (!Arg.startswith(OptName))
+    if (!Arg.starts_with(OptName))
       continue;
     Opt = Arg;
   }
@@ -6606,7 +6606,7 @@ llvm::Error driver::expandResponseFiles(SmallVectorImpl<const char *> &Args,
   else
     Tokenizer = &llvm::cl::TokenizeGNUCommandLine;
 
-  if (MarkEOLs && Args.size() > 1 && StringRef(Args[1]).startswith("-cc1"))
+  if (MarkEOLs && Args.size() > 1 && StringRef(Args[1]).starts_with("-cc1"))
     MarkEOLs = false;
 
   llvm::cl::ExpansionContext ECtx(Alloc, Tokenizer);
@@ -6620,7 +6620,7 @@ llvm::Error driver::expandResponseFiles(SmallVectorImpl<const char *> &Args,
   // If -cc1 came from a response file, remove the EOL sentinels.
   auto FirstArg = llvm::find_if(llvm::drop_begin(Args),
                                 [](const char *A) { return A != nullptr; });
-  if (FirstArg != Args.end() && StringRef(*FirstArg).startswith("-cc1")) {
+  if (FirstArg != Args.end() && StringRef(*FirstArg).starts_with("-cc1")) {
     // If -cc1 came from a response file, remove the EOL sentinels.
     if (MarkEOLs) {
       auto newEnd = std::remove(Args.begin(), Args.end(), nullptr);

diff --git a/clang/lib/Driver/Job.cpp b/clang/lib/Driver/Job.cpp
@@ -95,10 +95,10 @@ static bool skipArgs(const char *Flag, bool HaveCrashVFS, int &SkipNum,
 
   // These flags are treated as a single argument (e.g., -F<Dir>).
   StringRef FlagRef(Flag);
-  IsInclude = FlagRef.startswith("-F") || FlagRef.startswith("-I");
+  IsInclude = FlagRef.starts_with("-F") || FlagRef.starts_with("-I");
   if (IsInclude)
     return !HaveCrashVFS;
-  if (FlagRef.startswith("-fmodules-cache-path="))
+  if (FlagRef.starts_with("-fmodules-cache-path="))
     return true;
 
   SkipNum = 0;
@@ -185,8 +185,8 @@ rewriteIncludes(const llvm::ArrayRef<const char *> &Args, size_t Idx,
   SmallString<128> NewInc;
   if (NumArgs == 1) {
     StringRef FlagRef(Args[Idx + NumArgs - 1]);
-    assert((FlagRef.startswith("-F") || FlagRef.startswith("-I")) &&
-            "Expecting -I or -F");
+    assert((FlagRef.starts_with("-F") || FlagRef.starts_with("-I")) &&
+           "Expecting -I or -F");
     StringRef Inc = FlagRef.slice(2, StringRef::npos);
     if (getAbsPath(Inc, NewInc)) {
       SmallString<128> NewArg(FlagRef.slice(0, 2));

diff --git a/clang/lib/Driver/ToolChain.cpp b/clang/lib/Driver/ToolChain.cpp
@@ -315,7 +315,7 @@ static const DriverSuffix *FindDriverSuffix(StringRef ProgName, size_t &Pos) {
 
   for (const auto &DS : DriverSuffixes) {
     StringRef Suffix(DS.Suffix);
-    if (ProgName.endswith(Suffix)) {
+    if (ProgName.ends_with(Suffix)) {
       Pos = ProgName.size() - Suffix.size();
       return &DS;
     }
@@ -345,7 +345,7 @@ static const DriverSuffix *parseDriverSuffix(StringRef ProgName, size_t &Pos) {
   // added via -target as implicit first argument.
   const DriverSuffix *DS = FindDriverSuffix(ProgName, Pos);
 
-  if (!DS && ProgName.endswith(".exe")) {
+  if (!DS && ProgName.ends_with(".exe")) {
     // Try again after stripping the executable suffix:
     // clang++.exe -> clang++
     ProgName = ProgName.drop_back(StringRef(".exe").size());

diff --git a/clang/lib/Driver/ToolChains/AIX.cpp b/clang/lib/Driver/ToolChains/AIX.cpp
@@ -88,16 +88,16 @@ static bool hasExportListLinkerOpts(const ArgStringList &CmdArgs) {
   for (size_t i = 0, Size = CmdArgs.size(); i < Size; ++i) {
     llvm::StringRef ArgString(CmdArgs[i]);
 
-    if (ArgString.startswith("-bE:") || ArgString.startswith("-bexport:") ||
+    if (ArgString.starts_with("-bE:") || ArgString.starts_with("-bexport:") ||
         ArgString == "-bexpall" || ArgString == "-bexpfull")
       return true;
 
     // If we split -b option, check the next opt.
     if (ArgString == "-b" && i + 1 < Size) {
       ++i;
       llvm::StringRef ArgNextString(CmdArgs[i]);
-      if (ArgNextString.startswith("E:") ||
-          ArgNextString.startswith("export:") || ArgNextString == "expall" ||
+      if (ArgNextString.starts_with("E:") ||
+          ArgNextString.starts_with("export:") || ArgNextString == "expall" ||
           ArgNextString == "expfull")
         return true;
     }

diff --git a/clang/lib/Driver/ToolChains/AMDGPU.cpp b/clang/lib/Driver/ToolChains/AMDGPU.cpp
@@ -49,7 +49,7 @@ RocmInstallationDetector::findSPACKPackage(const Candidate &Cand,
                                      FileEnd;
        File != FileEnd && !EC; File.increment(EC)) {
     llvm::StringRef FileName = llvm::sys::path::filename(File->path());
-    if (FileName.startswith(Prefix)) {
+    if (FileName.starts_with(Prefix)) {
       SubDirs.push_back(FileName);
       if (SubDirs.size() > 1)
         break;
@@ -84,13 +84,13 @@ void RocmInstallationDetector::scanLibDevicePath(llvm::StringRef Path) {
        !EC && LI != LE; LI = LI.increment(EC)) {
     StringRef FilePath = LI->path();
     StringRef FileName = llvm::sys::path::filename(FilePath);
-    if (!FileName.endswith(Suffix))
+    if (!FileName.ends_with(Suffix))
       continue;
 
     StringRef BaseName;
-    if (FileName.endswith(Suffix2))
+    if (FileName.ends_with(Suffix2))
       BaseName = FileName.drop_back(Suffix2.size());
-    else if (FileName.endswith(Suffix))
+    else if (FileName.ends_with(Suffix))
       BaseName = FileName.drop_back(Suffix.size());
 
     const StringRef ABIVersionPrefix = "oclc_abi_version_";
@@ -124,7 +124,7 @@ void RocmInstallationDetector::scanLibDevicePath(llvm::StringRef Path) {
       WavefrontSize64.On = FilePath;
     } else if (BaseName == "oclc_wavefrontsize64_off") {
       WavefrontSize64.Off = FilePath;
-    } else if (BaseName.startswith(ABIVersionPrefix)) {
+    } else if (BaseName.starts_with(ABIVersionPrefix)) {
       unsigned ABIVersionNumber;
       if (BaseName.drop_front(ABIVersionPrefix.size())
               .getAsInteger(/*Redex=*/0, ABIVersionNumber))
@@ -134,7 +134,7 @@ void RocmInstallationDetector::scanLibDevicePath(llvm::StringRef Path) {
       // Process all bitcode filenames that look like
       // ocl_isa_version_XXX.amdgcn.bc
       const StringRef DeviceLibPrefix = "oclc_isa_version_";
-      if (!BaseName.startswith(DeviceLibPrefix))
+      if (!BaseName.starts_with(DeviceLibPrefix))
         continue;
 
       StringRef IsaVersionNumber =
@@ -230,7 +230,7 @@ RocmInstallationDetector::getInstallationPathCandidates() {
     // <rocm_root>/llvm-amdgpu-<rocm_release_string>-<hash>/bin directory.
     // We only consider the parent directory of llvm-amdgpu package as ROCm
     // installation candidate for SPACK.
-    if (ParentName.startswith("llvm-amdgpu-")) {
+    if (ParentName.starts_with("llvm-amdgpu-")) {
       auto SPACKPostfix =
           ParentName.drop_front(strlen("llvm-amdgpu-")).split('-');
       auto SPACKReleaseStr = SPACKPostfix.first;
@@ -243,7 +243,7 @@ RocmInstallationDetector::getInstallationPathCandidates() {
 
     // Some versions of the rocm llvm package install to /opt/rocm/llvm/bin
     // Some versions of the aomp package install to /opt/rocm/aomp/bin
-    if (ParentName == "llvm" || ParentName.startswith("aomp"))
+    if (ParentName == "llvm" || ParentName.starts_with("aomp"))
       ParentDir = llvm::sys::path::parent_path(ParentDir);
 
     return Candidate(ParentDir.str(), /*StrictChecking=*/true);
@@ -292,7 +292,7 @@ RocmInstallationDetector::getInstallationPathCandidates() {
            FileEnd;
        File != FileEnd && !EC; File.increment(EC)) {
     llvm::StringRef FileName = llvm::sys::path::filename(File->path());
-    if (!FileName.startswith("rocm-"))
+    if (!FileName.starts_with("rocm-"))
       continue;
     if (LatestROCm.empty()) {
       LatestROCm = FileName.str();

diff --git a/clang/lib/Driver/ToolChains/Arch/AArch64.cpp b/clang/lib/Driver/ToolChains/Arch/AArch64.cpp
@@ -228,7 +228,7 @@ getAArch64MicroArchFeaturesFromMtune(const Driver &D, StringRef Mtune,
   if (MtuneLowerCase == "native")
     MtuneLowerCase = std::string(llvm::sys::getHostCPUName());
   if (MtuneLowerCase == "cyclone" ||
-      StringRef(MtuneLowerCase).startswith("apple")) {
+      StringRef(MtuneLowerCase).starts_with("apple")) {
     Features.push_back("+zcm");
     Features.push_back("+zcz");
   }
@@ -262,7 +262,7 @@ void aarch64::getAArch64TargetFeatures(const Driver &D,
     for (const auto *A :
          Args.filtered(options::OPT_Wa_COMMA, options::OPT_Xassembler))
       for (StringRef Value : A->getValues())
-        if (Value.startswith("-march="))
+        if (Value.starts_with("-march="))
           WaMArch = Value.substr(7);
   // Call getAArch64ArchFeaturesFromMarch only if "-Wa,-march=" or
   // "-Xassembler -march" is detected. Otherwise it may return false

diff --git a/clang/lib/Driver/ToolChains/Arch/ARM.cpp b/clang/lib/Driver/ToolChains/Arch/ARM.cpp
@@ -67,9 +67,9 @@ void arm::getARMArchCPUFromArgs(const ArgList &Args, llvm::StringRef &Arch,
     // Use getValues because -Wa can have multiple arguments
     // e.g. -Wa,-mcpu=foo,-mcpu=bar
     for (StringRef Value : A->getValues()) {
-      if (Value.startswith("-mcpu="))
+      if (Value.starts_with("-mcpu="))
         CPU = Value.substr(6);
-      if (Value.startswith("-march="))
+      if (Value.starts_with("-march="))
         Arch = Value.substr(7);
     }
   }
@@ -285,9 +285,9 @@ void arm::setArchNameInTriple(const Driver &D, const ArgList &Args,
         // There is no assembler equivalent of -mno-thumb, -marm, or -mno-arm.
         if (Value == "-mthumb")
           IsThumb = true;
-        else if (Value.startswith("-march="))
+        else if (Value.starts_with("-march="))
           WaMArch = Value.substr(7);
-        else if (Value.startswith("-mcpu="))
+        else if (Value.starts_with("-mcpu="))
           WaMCPU = Value.substr(6);
       }
     }
@@ -528,13 +528,13 @@ llvm::ARM::FPUKind arm::getARMTargetFeatures(const Driver &D,
       // We use getValues here because you can have many options per -Wa
       // We will keep the last one we find for each of these
       for (StringRef Value : A->getValues()) {
-        if (Value.startswith("-mfpu=")) {
+        if (Value.starts_with("-mfpu=")) {
           WaFPU = std::make_pair(A, Value.substr(6));
-        } else if (Value.startswith("-mcpu=")) {
+        } else if (Value.starts_with("-mcpu=")) {
           WaCPU = std::make_pair(A, Value.substr(6));
-        } else if (Value.startswith("-mhwdiv=")) {
+        } else if (Value.starts_with("-mhwdiv=")) {
           WaHDiv = std::make_pair(A, Value.substr(8));
-        } else if (Value.startswith("-march=")) {
+        } else if (Value.starts_with("-march=")) {
           WaArch = std::make_pair(A, Value.substr(7));
         }
       }
@@ -796,7 +796,7 @@ llvm::ARM::FPUKind arm::getARMTargetFeatures(const Driver &D,
   // Propagate frame-chain model selection
   if (Arg *A = Args.getLastArg(options::OPT_mframe_chain)) {
     StringRef FrameChainOption = A->getValue();
-    if (FrameChainOption.startswith("aapcs"))
+    if (FrameChainOption.starts_with("aapcs"))
       Features.push_back("+aapcs-frame-chain");
     if (FrameChainOption == "aapcs+leaf")
       Features.push_back("+aapcs-frame-chain-leaf");

diff --git a/clang/lib/Driver/ToolChains/Arch/X86.cpp b/clang/lib/Driver/ToolChains/Arch/X86.cpp
@@ -234,15 +234,15 @@ void x86::getX86TargetFeatures(const Driver &D, const llvm::Triple &Triple,
     A->claim();
 
     // Skip over "-m".
-    assert(Name.startswith("m") && "Invalid feature name.");
+    assert(Name.starts_with("m") && "Invalid feature name.");
     Name = Name.substr(1);
 
-    bool IsNegative = Name.startswith("no-");
+    bool IsNegative = Name.starts_with("no-");
     if (IsNegative)
       Name = Name.substr(3);
 
 #ifndef NDEBUG
-    assert(Name.startswith("avx10.") && "Invalid AVX10 feature name.");
+    assert(Name.starts_with("avx10.") && "Invalid AVX10 feature name.");
     StringRef Version, Width;
     std::tie(Version, Width) = Name.substr(6).split('-');
     assert(Version == "1" && "Invalid AVX10 feature name.");
@@ -260,7 +260,7 @@ void x86::getX86TargetFeatures(const Driver &D, const llvm::Triple &Triple,
     A->claim();
 
     // Skip over "-m".
-    assert(Name.startswith("m") && "Invalid feature name.");
+    assert(Name.starts_with("m") && "Invalid feature name.");
     Name = Name.substr(1);
 
     // Replace -mgeneral-regs-only with -x87, -mmx, -sse
@@ -269,7 +269,7 @@ void x86::getX86TargetFeatures(const Driver &D, const llvm::Triple &Triple,
       continue;
     }
 
-    bool IsNegative = Name.startswith("no-");
+    bool IsNegative = Name.starts_with("no-");
     if (A->getOption().matches(options::OPT_mapx_features_EQ) ||
         A->getOption().matches(options::OPT_mno_apx_features_EQ)) {
 

diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -223,7 +223,7 @@ static void ParseMRecip(const Driver &D, const ArgList &Args,
   for (unsigned i = 0; i != NumOptions; ++i) {
     StringRef Val = A->getValue(i);
 
-    bool IsDisabled = Val.startswith(DisabledPrefixIn);
+    bool IsDisabled = Val.starts_with(DisabledPrefixIn);
     // Ignore the disablement token for string matching.
     if (IsDisabled)
       Val = Val.substr(1);
@@ -433,7 +433,7 @@ static void addDebugObjectName(const ArgList &Args, ArgStringList &CmdArgs,
                                const char *OutputFileName) {
   // No need to generate a value for -object-file-name if it was provided.
   for (auto *Arg : Args.filtered(options::OPT_Xclang))
-    if (StringRef(Arg->getValue()).startswith("-object-file-name"))
+    if (StringRef(Arg->getValue()).starts_with("-object-file-name"))
       return;
 
   if (Args.hasArg(options::OPT_object_file_name_EQ))
@@ -940,7 +940,7 @@ static void handleAMDGPUCodeObjectVersionOptions(const Driver &D,
 static bool hasClangPchSignature(const Driver &D, StringRef Path) {
   if (llvm::ErrorOr<std::unique_ptr<llvm::MemoryBuffer>> MemBuf =
           D.getVFS().getBufferForFile(Path))
-    return (*MemBuf)->getBuffer().startswith("CPCH");
+    return (*MemBuf)->getBuffer().starts_with("CPCH");
   return false;
 }
 
@@ -1715,7 +1715,7 @@ void Clang::AddAArch64TargetArgs(const ArgList &Args,
         Val.equals("256+") || Val.equals("512+") || Val.equals("1024+") ||
         Val.equals("2048+")) {
       unsigned Bits = 0;
-      if (Val.endswith("+"))
+      if (Val.ends_with("+"))
         Val = Val.substr(0, Val.size() - 1);
       else {
         bool Invalid = Val.getAsInteger(10, Bits); (void)Invalid;
@@ -2503,7 +2503,7 @@ static void CollectArgsForIntegratedAssembler(Compilation &C,
       case llvm::Triple::thumbeb:
       case llvm::Triple::arm:
       case llvm::Triple::armeb:
-        if (Value.startswith("-mimplicit-it=")) {
+        if (Value.starts_with("-mimplicit-it=")) {
           // Only store the value; the last value set takes effect.
           ImplicitIt = Value.split("=").second;
           if (CheckARMImplicitITArg(ImplicitIt))
@@ -2528,12 +2528,12 @@ static void CollectArgsForIntegratedAssembler(Compilation &C,
           CmdArgs.push_back("-use-tcc-in-div");
           continue;
         }
-        if (Value.startswith("-msoft-float")) {
+        if (Value.starts_with("-msoft-float")) {
           CmdArgs.push_back("-target-feature");
           CmdArgs.push_back("+soft-float");
           continue;
         }
-        if (Value.startswith("-mhard-float")) {
+        if (Value.starts_with("-mhard-float")) {
           CmdArgs.push_back("-target-feature");
           CmdArgs.push_back("-soft-float");
           continue;
@@ -2570,8 +2570,8 @@ static void CollectArgsForIntegratedAssembler(Compilation &C,
         CmdArgs.push_back("-massembler-no-warn");
       } else if (Value == "--noexecstack") {
         UseNoExecStack = true;
-      } else if (Value.startswith("-compress-debug-sections") ||
-                 Value.startswith("--compress-debug-sections") ||
+      } else if (Value.starts_with("-compress-debug-sections") ||
+                 Value.starts_with("--compress-debug-sections") ||
                  Value == "-nocompress-debug-sections" ||
                  Value == "--nocompress-debug-sections") {
         CmdArgs.push_back(Value.data());
@@ -2581,13 +2581,13 @@ static void CollectArgsForIntegratedAssembler(Compilation &C,
       } else if (Value == "-mrelax-relocations=no" ||
                  Value == "--mrelax-relocations=no") {
         UseRelaxRelocations = false;
-      } else if (Value.startswith("-I")) {
+      } else if (Value.starts_with("-I")) {
         CmdArgs.push_back(Value.data());
         // We need to consume the next argument if the current arg is a plain
         // -I. The next arg will be the include directory.
         if (Value == "-I")
           TakeNextArg = true;
-      } else if (Value.startswith("-gdwarf-")) {
+      } else if (Value.starts_with("-gdwarf-")) {
         // "-gdwarf-N" options are not cc1as options.
         unsigned DwarfVersion = DwarfVersionNum(Value);
         if (DwarfVersion == 0) { // Send it onward, and let cc1as complain.
@@ -2597,30 +2597,30 @@ static void CollectArgsForIntegratedAssembler(Compilation &C,
                                   llvm::codegenoptions::DebugInfoConstructor,
                                   DwarfVersion, llvm::DebuggerKind::Default);
         }
-      } else if (Value.startswith("-mcpu") || Value.startswith("-mfpu") ||
-                 Value.startswith("-mhwdiv") || Value.startswith("-march")) {
+      } else if (Value.starts_with("-mcpu") || Value.starts_with("-mfpu") ||
+                 Value.starts_with("-mhwdiv") || Value.starts_with("-march")) {
         // Do nothing, we'll validate it later.
       } else if (Value == "-defsym") {
-          if (A->getNumValues() != 2) {
-            D.Diag(diag::err_drv_defsym_invalid_format) << Value;
-            break;
-          }
-          const char *S = A->getValue(1);
-          auto Pair = StringRef(S).split('=');
-          auto Sym = Pair.first;
-          auto SVal = Pair.second;
-
-          if (Sym.empty() || SVal.empty()) {
-            D.Diag(diag::err_drv_defsym_invalid_format) << S;
-            break;
-          }
-          int64_t IVal;
-          if (SVal.getAsInteger(0, IVal)) {
-            D.Diag(diag::err_drv_defsym_invalid_symval) << SVal;
-            break;
-          }
-          CmdArgs.push_back(Value.data());
-          TakeNextArg = true;
+        if (A->getNumValues() != 2) {
+          D.Diag(diag::err_drv_defsym_invalid_format) << Value;
+          break;
+        }
+        const char *S = A->getValue(1);
+        auto Pair = StringRef(S).split('=');
+        auto Sym = Pair.first;
+        auto SVal = Pair.second;
+
+        if (Sym.empty() || SVal.empty()) {
+          D.Diag(diag::err_drv_defsym_invalid_format) << S;
+          break;
+        }
+        int64_t IVal;
+        if (SVal.getAsInteger(0, IVal)) {
+          D.Diag(diag::err_drv_defsym_invalid_symval) << SVal;
+          break;
+        }
+        CmdArgs.push_back(Value.data());
+        TakeNextArg = true;
       } else if (Value == "-fdebug-compilation-dir") {
         CmdArgs.push_back("-fdebug-compilation-dir");
         TakeNextArg = true;
@@ -3331,7 +3331,7 @@ static void RenderSSPOptions(const Driver &D, const ToolChain &TC,
   // --param ssp-buffer-size=
   for (const Arg *A : Args.filtered(options::OPT__param)) {
     StringRef Str(A->getValue());
-    if (Str.startswith("ssp-buffer-size=")) {
+    if (Str.starts_with("ssp-buffer-size=")) {
       if (StackProtectorLevel) {
         CmdArgs.push_back("-stack-protector-buffer-size");
         // FIXME: Verify the argument is a valid integer.
@@ -5615,6 +5615,10 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
                        options::OPT_fno_auto_import);
   }
 
+  if (Args.hasFlag(options::OPT_fms_volatile, options::OPT_fno_ms_volatile,
+                   Triple.isX86() && D.IsCLMode()))
+    CmdArgs.push_back("-fms-volatile");
+
   // Non-PIC code defaults to -fdirect-access-external-data while PIC code
   // defaults to -fno-direct-access-external-data. Pass the option if different
   // from the default.
@@ -5882,7 +5886,7 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
     StringRef Val = A->getValue();
     if (Triple.isX86() && Triple.isOSBinFormatELF()) {
       if (Val != "all" && Val != "labels" && Val != "none" &&
-          !Val.startswith("list="))
+          !Val.starts_with("list="))
         D.Diag(diag::err_drv_invalid_value)
             << A->getAsString(Args) << A->getValue();
       else
@@ -7947,18 +7951,6 @@ void Clang::AddClangCLArgs(const ArgList &Args, types::ID InputType,
     CmdArgs.push_back("-P");
   }
 
-  unsigned VolatileOptionID;
-  if (getToolChain().getTriple().isX86())
-    VolatileOptionID = options::OPT__SLASH_volatile_ms;
-  else
-    VolatileOptionID = options::OPT__SLASH_volatile_iso;
-
-  if (Arg *A = Args.getLastArg(options::OPT__SLASH_volatile_Group))
-    VolatileOptionID = A->getOption().getID();
-
-  if (VolatileOptionID == options::OPT__SLASH_volatile_ms)
-    CmdArgs.push_back("-fms-volatile");
-
  if (Args.hasFlag(options::OPT__SLASH_Zc_dllexportInlines_,
                   options::OPT__SLASH_Zc_dllexportInlines,
                   false)) {
@@ -8390,14 +8382,14 @@ void ClangAs::ConstructJob(Compilation &C, const JobAction &JA,
       continue;
     auto &JArgs = J.getArguments();
     for (unsigned I = 0; I < JArgs.size(); ++I) {
-      if (StringRef(JArgs[I]).startswith("-object-file-name=") &&
+      if (StringRef(JArgs[I]).starts_with("-object-file-name=") &&
           Output.isFilename()) {
-        ArgStringList NewArgs(JArgs.begin(), JArgs.begin() + I);
-        addDebugObjectName(Args, NewArgs, DebugCompilationDir,
-                           Output.getFilename());
-        NewArgs.append(JArgs.begin() + I + 1, JArgs.end());
-        J.replaceArguments(NewArgs);
-        break;
+       ArgStringList NewArgs(JArgs.begin(), JArgs.begin() + I);
+       addDebugObjectName(Args, NewArgs, DebugCompilationDir,
+                          Output.getFilename());
+       NewArgs.append(JArgs.begin() + I + 1, JArgs.end());
+       J.replaceArguments(NewArgs);
+       break;
       }
     }
   }
@@ -8661,7 +8653,7 @@ void OffloadPackager::ConstructJob(Compilation &C, const JobAction &JA,
     getTargetFeatures(TC->getDriver(), TC->getTriple(), TCArgs, Features,
                       false);
     llvm::copy_if(Features, std::back_inserter(FeatureArgs),
-                  [](StringRef Arg) { return !Arg.startswith("-target"); });
+                  [](StringRef Arg) { return !Arg.starts_with("-target"); });
 
     if (TC->getTriple().isAMDGPU()) {
       for (StringRef Feature : llvm::split(Arch.split(':').second, ':')) {

diff --git a/clang/lib/Driver/ToolChains/CommonArgs.cpp b/clang/lib/Driver/ToolChains/CommonArgs.cpp
@@ -303,7 +303,7 @@ void tools::handleTargetFeaturesGroup(const Driver &D,
     A->claim();
 
     // Skip over "-m".
-    assert(Name.startswith("m") && "Invalid feature name.");
+    assert(Name.starts_with("m") && "Invalid feature name.");
     Name = Name.substr(1);
 
     auto Proc = getCPUName(D, Args, Triple);
@@ -317,7 +317,7 @@ void tools::handleTargetFeaturesGroup(const Driver &D,
       continue;
     }
 
-    bool IsNegative = Name.startswith("no-");
+    bool IsNegative = Name.starts_with("no-");
     if (IsNegative)
       Name = Name.substr(3);
 
@@ -2336,20 +2336,20 @@ static void GetSDLFromOffloadArchive(
   llvm::Triple Triple(D.getTargetTriple());
   bool IsMSVC = Triple.isWindowsMSVCEnvironment();
   auto Ext = IsMSVC ? ".lib" : ".a";
-  if (!Lib.startswith(":") && !Lib.startswith("-l")) {
+  if (!Lib.starts_with(":") && !Lib.starts_with("-l")) {
     if (llvm::sys::fs::exists(Lib)) {
       ArchiveOfBundles = Lib;
       FoundAOB = true;
     }
   } else {
-    if (Lib.startswith("-l"))
+    if (Lib.starts_with("-l"))
       Lib = Lib.drop_front(2);
     for (auto LPath : LibraryPaths) {
       ArchiveOfBundles.clear();
-      auto LibFile =
-          (Lib.startswith(":") ? Lib.drop_front()
-                               : IsMSVC ? Lib + Ext : "lib" + Lib + Ext)
-              .str();
+      auto LibFile = (Lib.starts_with(":") ? Lib.drop_front()
+                      : IsMSVC             ? Lib + Ext
+                                           : "lib" + Lib + Ext)
+                         .str();
       for (auto Prefix : {"/libdevice/", "/"}) {
         auto AOB = Twine(LPath + Prefix + LibFile).str();
         if (llvm::sys::fs::exists(AOB)) {

diff --git a/clang/lib/Driver/ToolChains/Cuda.cpp b/clang/lib/Driver/ToolChains/Cuda.cpp
@@ -238,7 +238,7 @@ CudaInstallationDetector::CudaInstallationDetector(
         // Process all bitcode filenames that look like
         // libdevice.compute_XX.YY.bc
         const StringRef LibDeviceName = "libdevice.";
-        if (!(FileName.startswith(LibDeviceName) && FileName.endswith(".bc")))
+        if (!(FileName.starts_with(LibDeviceName) && FileName.ends_with(".bc")))
           continue;
         StringRef GpuArch = FileName.slice(
             LibDeviceName.size(), FileName.find('.', LibDeviceName.size()));

diff --git a/clang/lib/Driver/ToolChains/Darwin.cpp b/clang/lib/Driver/ToolChains/Darwin.cpp
@@ -1010,13 +1010,13 @@ static const char *ArmMachOArchNameCPU(StringRef CPU) {
 
   // FIXME: Make sure this MachO triple mangling is really necessary.
   // ARMv5* normalises to ARMv5.
-  if (Arch.startswith("armv5"))
+  if (Arch.starts_with("armv5"))
     Arch = Arch.substr(0, 5);
   // ARMv6*, except ARMv6M, normalises to ARMv6.
-  else if (Arch.startswith("armv6") && !Arch.endswith("6m"))
+  else if (Arch.starts_with("armv6") && !Arch.ends_with("6m"))
     Arch = Arch.substr(0, 5);
   // ARMv7A normalises to ARMv7.
-  else if (Arch.endswith("v7a"))
+  else if (Arch.ends_with("v7a"))
     Arch = Arch.substr(0, 5);
   return Arch.data();
 }
@@ -1319,8 +1319,8 @@ StringRef Darwin::getSDKName(StringRef isysroot) {
   auto EndSDK = llvm::sys::path::rend(isysroot);
   for (auto IT = BeginSDK; IT != EndSDK; ++IT) {
     StringRef SDK = *IT;
-    if (SDK.endswith(".sdk"))
-      return SDK.slice(0, SDK.size() - 4);
+    if (SDK.ends_with(".sdk"))
+        return SDK.slice(0, SDK.size() - 4);
   }
   return "";
 }
@@ -1959,22 +1959,23 @@ inferDeploymentTargetFromSDK(DerivedArgList &Args,
 
   auto CreatePlatformFromSDKName =
       [&](StringRef SDK) -> std::optional<DarwinPlatform> {
-    if (SDK.startswith("iPhoneOS") || SDK.startswith("iPhoneSimulator"))
+    if (SDK.starts_with("iPhoneOS") || SDK.starts_with("iPhoneSimulator"))
       return DarwinPlatform::createFromSDK(
           Darwin::IPhoneOS, Version,
-          /*IsSimulator=*/SDK.startswith("iPhoneSimulator"));
-    else if (SDK.startswith("MacOSX"))
+          /*IsSimulator=*/SDK.starts_with("iPhoneSimulator"));
+    else if (SDK.starts_with("MacOSX"))
       return DarwinPlatform::createFromSDK(Darwin::MacOS,
                                            getSystemOrSDKMacOSVersion(Version));
-    else if (SDK.startswith("WatchOS") || SDK.startswith("WatchSimulator"))
+    else if (SDK.starts_with("WatchOS") || SDK.starts_with("WatchSimulator"))
       return DarwinPlatform::createFromSDK(
           Darwin::WatchOS, Version,
-          /*IsSimulator=*/SDK.startswith("WatchSimulator"));
-    else if (SDK.startswith("AppleTVOS") || SDK.startswith("AppleTVSimulator"))
+          /*IsSimulator=*/SDK.starts_with("WatchSimulator"));
+    else if (SDK.starts_with("AppleTVOS") ||
+             SDK.starts_with("AppleTVSimulator"))
       return DarwinPlatform::createFromSDK(
           Darwin::TvOS, Version,
-          /*IsSimulator=*/SDK.startswith("AppleTVSimulator"));
-    else if (SDK.startswith("DriverKit"))
+          /*IsSimulator=*/SDK.starts_with("AppleTVSimulator"));
+    else if (SDK.starts_with("DriverKit"))
       return DarwinPlatform::createFromSDK(Darwin::DriverKit, Version);
     return std::nullopt;
   };
@@ -2339,8 +2340,8 @@ void Darwin::AddDeploymentTarget(DerivedArgList &Args) const {
     if (SDK.size() > 0) {
       size_t StartVer = SDK.find_first_of("0123456789");
       StringRef SDKName = SDK.slice(0, StartVer);
-      if (!SDKName.startswith(getPlatformFamily()) &&
-          !dropSDKNamePrefix(SDKName).startswith(getPlatformFamily()))
+      if (!SDKName.starts_with(getPlatformFamily()) &&
+          !dropSDKNamePrefix(SDKName).starts_with(getPlatformFamily()))
         getDriver().Diag(diag::warn_incompatible_sysroot)
             << SDKName << getPlatformFamily();
     }

diff --git a/clang/lib/Driver/ToolChains/Flang.cpp b/clang/lib/Driver/ToolChains/Flang.cpp
@@ -182,7 +182,7 @@ void Flang::AddAArch64TargetArgs(const ArgList &Args,
         Val.equals("256+") || Val.equals("512+") || Val.equals("1024+") ||
         Val.equals("2048+")) {
       unsigned Bits = 0;
-      if (Val.endswith("+"))
+      if (Val.ends_with("+"))
         Val = Val.substr(0, Val.size() - 1);
       else {
         [[maybe_unused]] bool Invalid = Val.getAsInteger(10, Bits);

diff --git a/clang/lib/Driver/ToolChains/Gnu.cpp b/clang/lib/Driver/ToolChains/Gnu.cpp
@@ -1084,7 +1084,7 @@ static bool findMipsCsMultilibs(const Multilib::flags_list &Flags,
             .FilterOut(NonExistent)
             .setIncludeDirsCallback([](const Multilib &M) {
               std::vector<std::string> Dirs({"/include"});
-              if (StringRef(M.includeSuffix()).startswith("/uclibc"))
+              if (StringRef(M.includeSuffix()).starts_with("/uclibc"))
                 Dirs.push_back(
                     "/../../../../mips-linux-gnu/libc/uclibc/usr/include");
               else
@@ -1288,7 +1288,7 @@ static bool findMipsMtiMultilibs(const Multilib::flags_list &Flags,
             .FilterOut(NonExistent)
             .setIncludeDirsCallback([](const Multilib &M) {
               std::vector<std::string> Dirs({"/include"});
-              if (StringRef(M.includeSuffix()).startswith("/uclibc"))
+              if (StringRef(M.includeSuffix()).starts_with("/uclibc"))
                 Dirs.push_back("/../../../../sysroot/uclibc/usr/include");
               else
                 Dirs.push_back("/../../../../sysroot/usr/include");
@@ -3055,7 +3055,7 @@ void Generic_GCC::AddMultilibPaths(const Driver &D,
     // the cross. Note that GCC does include some of these directories in some
     // configurations but this seems somewhere between questionable and simply
     // a bug.
-    if (StringRef(LibPath).startswith(SysRoot))
+    if (StringRef(LibPath).starts_with(SysRoot))
       addPathIfExists(D, LibPath + "/../" + OSLibDir, Paths);
   }
 }

diff --git a/clang/lib/Driver/ToolChains/Hexagon.cpp b/clang/lib/Driver/ToolChains/Hexagon.cpp
@@ -54,11 +54,11 @@ static void handleHVXTargetFeatures(const Driver &D, const ArgList &Args,
   auto makeFeature = [&Args](Twine T, bool Enable) -> StringRef {
     const std::string &S = T.str();
     StringRef Opt(S);
-    if (Opt.endswith("="))
+    if (Opt.ends_with("="))
       Opt = Opt.drop_back(1);
-    if (Opt.startswith("mno-"))
+    if (Opt.starts_with("mno-"))
       Opt = Opt.drop_front(4);
-    else if (Opt.startswith("m"))
+    else if (Opt.starts_with("m"))
       Opt = Opt.drop_front(1);
     return Args.MakeArgString(Twine(Enable ? "+" : "-") + Twine(Opt));
   };
@@ -801,7 +801,7 @@ StringRef HexagonToolChain::GetTargetCPUVersion(const ArgList &Args) {
     CpuArg = A;
 
   StringRef CPU = CpuArg ? CpuArg->getValue() : GetDefaultCPU();
-  if (CPU.startswith("hexagon"))
+  if (CPU.starts_with("hexagon"))
     return CPU.substr(sizeof("hexagon") - 1);
   return CPU;
 }
diff --git a/clang/lib/Driver/ToolChains/Hurd.cpp b/clang/lib/Driver/ToolChains/Hurd.cpp
@@ -92,7 +92,7 @@ Hurd::Hurd(const Driver &D, const llvm::Triple &Triple, const ArgList &Args)
   // those searched.
   // FIXME: It's not clear whether we should use the driver's installed
   // directory ('Dir' below) or the ResourceDir.
-  if (StringRef(D.Dir).startswith(SysRoot)) {
+  if (StringRef(D.Dir).starts_with(SysRoot)) {
     addPathIfExists(D, D.Dir + "/../lib/" + MultiarchTriple, Paths);
     addPathIfExists(D, D.Dir + "/../" + OSLibDir, Paths);
   }
@@ -110,7 +110,7 @@ Hurd::Hurd(const Driver &D, const llvm::Triple &Triple, const ArgList &Args)
   // searched.
   // FIXME: It's not clear whether we should use the driver's installed
   // directory ('Dir' below) or the ResourceDir.
-  if (StringRef(D.Dir).startswith(SysRoot))
+  if (StringRef(D.Dir).starts_with(SysRoot))
     addPathIfExists(D, D.Dir + "/../lib", Paths);
 
   addPathIfExists(D, SysRoot + "/lib", Paths);

diff --git a/clang/lib/Driver/ToolChains/MSP430.cpp b/clang/lib/Driver/ToolChains/MSP430.cpp
@@ -166,7 +166,7 @@ void MSP430ToolChain::addClangTargetOptions(const ArgList &DriverArgs,
     return;
 
   const StringRef MCU = MCUArg->getValue();
-  if (MCU.startswith("msp430i")) {
+  if (MCU.starts_with("msp430i")) {
     // 'i' should be in lower case as it's defined in TI MSP430-GCC headers
     CC1Args.push_back(DriverArgs.MakeArgString(
         "-D__MSP430i" + MCU.drop_front(7).upper() + "__"));

diff --git a/clang/lib/Driver/ToolChains/MSVC.cpp b/clang/lib/Driver/ToolChains/MSVC.cpp
@@ -302,7 +302,7 @@ void visualstudio::Linker::ConstructJob(Compilation &C, const JobAction &JA,
     if (A.getOption().matches(options::OPT_l)) {
       StringRef Lib = A.getValue();
       const char *LinkLibArg;
-      if (Lib.endswith(".lib"))
+      if (Lib.ends_with(".lib"))
         LinkLibArg = Args.MakeArgString(Lib);
       else
         LinkLibArg = Args.MakeArgString(Lib + ".lib");

diff --git a/clang/lib/Driver/ToolChains/MinGW.cpp b/clang/lib/Driver/ToolChains/MinGW.cpp
@@ -86,9 +86,9 @@ void tools::MinGW::Linker::AddLibGCC(const ArgList &Args,
   CmdArgs.push_back("-lmoldname");
   CmdArgs.push_back("-lmingwex");
   for (auto Lib : Args.getAllArgValues(options::OPT_l))
-    if (StringRef(Lib).startswith("msvcr") ||
-        StringRef(Lib).startswith("ucrt") ||
-        StringRef(Lib).startswith("crtdll"))
+    if (StringRef(Lib).starts_with("msvcr") ||
+        StringRef(Lib).starts_with("ucrt") ||
+        StringRef(Lib).starts_with("crtdll"))
       return;
   CmdArgs.push_back("-lmsvcrt");
 }

diff --git a/clang/lib/Driver/ToolChains/PPCLinux.cpp b/clang/lib/Driver/ToolChains/PPCLinux.cpp
@@ -31,10 +31,10 @@ static bool GlibcSupportsFloat128(const std::string &Linker) {
 
   // Since glibc 2.34, the installed .so file is not symlink anymore. But we can
   // still safely assume it's newer than 2.32.
-  if (LinkerName.startswith("ld64.so"))
+  if (LinkerName.starts_with("ld64.so"))
     return true;
 
-  if (!LinkerName.startswith("ld-2."))
+  if (!LinkerName.starts_with("ld-2."))
     return false;
   unsigned Minor = (LinkerName[5] - '0') * 10 + (LinkerName[6] - '0');
   if (Minor < 32)

diff --git a/clang/lib/Driver/ToolChains/Solaris.cpp b/clang/lib/Driver/ToolChains/Solaris.cpp
@@ -328,7 +328,7 @@ Solaris::Solaris(const Driver &D, const llvm::Triple &Triple,
 
   // If we are currently running Clang inside of the requested system root,
   // add its parent library path to those searched.
-  if (StringRef(D.Dir).startswith(D.SysRoot))
+  if (StringRef(D.Dir).starts_with(D.SysRoot))
     addPathIfExists(D, D.Dir + "/../lib", Paths);
 
   addPathIfExists(D, D.SysRoot + "/usr/lib" + LibSuffix, Paths);

diff --git a/clang/lib/Driver/ToolChains/WebAssembly.cpp b/clang/lib/Driver/ToolChains/WebAssembly.cpp
@@ -328,7 +328,7 @@ void WebAssembly::addClangTargetOptions(const ArgList &DriverArgs,
 
   for (const Arg *A : DriverArgs.filtered(options::OPT_mllvm)) {
     StringRef Opt = A->getValue(0);
-    if (Opt.startswith("-emscripten-cxx-exceptions-allowed")) {
+    if (Opt.starts_with("-emscripten-cxx-exceptions-allowed")) {
       // '-mllvm -emscripten-cxx-exceptions-allowed' should be used with
       // '-mllvm -enable-emscripten-cxx-exceptions'
       bool EmEHArgExists = false;
@@ -355,7 +355,7 @@ void WebAssembly::addClangTargetOptions(const ArgList &DriverArgs,
       }
     }
 
-    if (Opt.startswith("-wasm-enable-sjlj")) {
+    if (Opt.starts_with("-wasm-enable-sjlj")) {
       // '-mllvm -wasm-enable-sjlj' is not compatible with
       // '-mno-exception-handling'
       if (DriverArgs.hasFlag(options::OPT_mno_exception_handing,

diff --git a/clang/lib/Edit/Commit.cpp b/clang/lib/Edit/Commit.cpp
@@ -334,7 +334,7 @@ bool Commit::canReplaceText(SourceLocation loc, StringRef text,
     return false;
 
   Len = text.size();
-  return file.substr(Offs.getOffset()).startswith(text);
+  return file.substr(Offs.getOffset()).starts_with(text);
 }
 
 bool Commit::isAtStartOfMacroExpansion(SourceLocation loc,

diff --git a/clang/lib/Edit/RewriteObjCFoundationAPI.cpp b/clang/lib/Edit/RewriteObjCFoundationAPI.cpp
@@ -697,7 +697,7 @@ static bool getLiteralInfo(SourceRange literalRange,
 
   struct Suff {
     static bool has(StringRef suff, StringRef &text) {
-      if (text.endswith(suff)) {
+      if (text.ends_with(suff)) {
         text = text.substr(0, text.size()-suff.size());
         return true;
       }
@@ -739,9 +739,9 @@ static bool getLiteralInfo(SourceRange literalRange,
   Info.F = UpperF ? "F" : "f";
 
   Info.Hex = Info.Octal = false;
-  if (text.startswith("0x"))
+  if (text.starts_with("0x"))
     Info.Hex = true;
-  else if (!isFloat && !isIntZero && text.startswith("0"))
+  else if (!isFloat && !isIntZero && text.starts_with("0"))
     Info.Octal = true;
 
   SourceLocation B = literalRange.getBegin();

diff --git a/clang/lib/ExtractAPI/ExtractAPIConsumer.cpp b/clang/lib/ExtractAPI/ExtractAPIConsumer.cpp
@@ -105,10 +105,10 @@ std::optional<std::string> getRelativeIncludeName(const CompilerInstance &CI,
       // Special case Apple .sdk folders since the search path is typically a
       // symlink like `iPhoneSimulator14.5.sdk` while the file is instead
       // located in `iPhoneSimulator.sdk` (the real folder).
-      if (NI->endswith(".sdk") && DI->endswith(".sdk")) {
+      if (NI->ends_with(".sdk") && DI->ends_with(".sdk")) {
         StringRef NBasename = path::stem(*NI);
         StringRef DBasename = path::stem(*DI);
-        if (DBasename.startswith(NBasename))
+        if (DBasename.starts_with(NBasename))
           continue;
       }
 

diff --git a/clang/lib/ExtractAPI/Serialization/SymbolGraphSerializer.cpp b/clang/lib/ExtractAPI/Serialization/SymbolGraphSerializer.cpp
@@ -743,7 +743,7 @@ bool SymbolGraphSerializer::shouldSkip(const APIRecord &Record) const {
 
   // Filter out symbols prefixed with an underscored as they are understood to
   // be symbols clients should not use.
-  if (Record.Name.startswith("_"))
+  if (Record.Name.starts_with("_"))
     return true;
 
   return false;

diff --git a/clang/lib/Format/BreakableToken.cpp b/clang/lib/Format/BreakableToken.cpp
@@ -55,7 +55,7 @@ static StringRef getLineCommentIndentPrefix(StringRef Comment,
       }));
 
   for (StringRef KnownPrefix : KnownPrefixes) {
-    if (Comment.startswith(KnownPrefix)) {
+    if (Comment.starts_with(KnownPrefix)) {
       const auto PrefixLength =
           Comment.find_first_not_of(' ', KnownPrefix.size());
       return Comment.substr(0, PrefixLength);
@@ -220,8 +220,8 @@ bool switchesFormatting(const FormatToken &Token) {
   assert((Token.is(TT_BlockComment) || Token.is(TT_LineComment)) &&
          "formatting regions are switched by comment tokens");
   StringRef Content = Token.TokenText.substr(2).ltrim();
-  return Content.startswith("clang-format on") ||
-         Content.startswith("clang-format off");
+  return Content.starts_with("clang-format on") ||
+         Content.starts_with("clang-format off");
 }
 
 unsigned
@@ -271,7 +271,7 @@ BreakableStringLiteral::BreakableStringLiteral(
     : BreakableToken(Tok, InPPDirective, Encoding, Style),
       StartColumn(StartColumn), Prefix(Prefix), Postfix(Postfix),
       UnbreakableTailLength(UnbreakableTailLength) {
-  assert(Tok.TokenText.startswith(Prefix) && Tok.TokenText.endswith(Postfix));
+  assert(Tok.TokenText.starts_with(Prefix) && Tok.TokenText.ends_with(Postfix));
   Line = Tok.TokenText.substr(
       Prefix.size(), Tok.TokenText.size() - Prefix.size() - Postfix.size());
 }
@@ -454,7 +454,7 @@ static bool mayReflowContent(StringRef Content) {
   bool hasSpecialMeaningPrefix = false;
   for (StringRef Prefix :
        {"@", "TODO", "FIXME", "XXX", "-# ", "- ", "+ ", "* "}) {
-    if (Content.startswith(Prefix)) {
+    if (Content.starts_with(Prefix)) {
       hasSpecialMeaningPrefix = true;
       break;
     }
@@ -471,7 +471,7 @@ static bool mayReflowContent(StringRef Content) {
   // characters and either the first or second character must be
   // non-punctuation.
   return Content.size() >= 2 && !hasSpecialMeaningPrefix &&
-         !Content.endswith("\\") &&
+         !Content.ends_with("\\") &&
          // Note that this is UTF-8 safe, since if isPunctuation(Content[0]) is
          // true, then the first code point must be 1 byte long.
          (!isPunctuation(Content[0]) || !isPunctuation(Content[1]));
@@ -488,7 +488,7 @@ BreakableBlockComment::BreakableBlockComment(
          "block comment section must start with a block comment");
 
   StringRef TokenText(Tok.TokenText);
-  assert(TokenText.startswith("/*") && TokenText.endswith("*/"));
+  assert(TokenText.starts_with("/*") && TokenText.ends_with("*/"));
   TokenText.substr(2, TokenText.size() - 4)
       .split(Lines, UseCRLF ? "\r\n" : "\n");
 
@@ -511,7 +511,7 @@ BreakableBlockComment::BreakableBlockComment(
   // /*
   // ** blah blah blah
   // */
-  if (Lines.size() >= 2 && Content[1].startswith("**") &&
+  if (Lines.size() >= 2 && Content[1].starts_with("**") &&
       static_cast<unsigned>(ContentColumn[1]) == StartColumn) {
     DecorationColumn = StartColumn;
   }
@@ -531,10 +531,10 @@ BreakableBlockComment::BreakableBlockComment(
       // If the last line is empty, the closing "*/" will have a star.
       if (Text.empty())
         break;
-    } else if (!Text.empty() && Decoration.startswith(Text)) {
+    } else if (!Text.empty() && Decoration.starts_with(Text)) {
       continue;
     }
-    while (!Text.startswith(Decoration))
+    while (!Text.starts_with(Decoration))
       Decoration = Decoration.drop_back(1);
   }
 
@@ -562,13 +562,13 @@ BreakableBlockComment::BreakableBlockComment(
     // The last line excludes the star if LastLineNeedsDecoration is false.
     // For all other lines, adjust the line to exclude the star and
     // (optionally) the first whitespace.
-    unsigned DecorationSize = Decoration.startswith(Content[i])
+    unsigned DecorationSize = Decoration.starts_with(Content[i])
                                   ? Content[i].size()
                                   : Decoration.size();
     if (DecorationSize)
       ContentColumn[i] = DecorationColumn + DecorationSize;
     Content[i] = Content[i].substr(DecorationSize);
-    if (!Decoration.startswith(Content[i])) {
+    if (!Decoration.starts_with(Content[i])) {
       IndentAtLineBreak =
           std::min<int>(IndentAtLineBreak, std::max(0, ContentColumn[i]));
     }
@@ -577,10 +577,10 @@ BreakableBlockComment::BreakableBlockComment(
 
   // Detect a multiline jsdoc comment and set DelimitersOnNewline in that case.
   if (Style.isJavaScript() || Style.Language == FormatStyle::LK_Java) {
-    if ((Lines[0] == "*" || Lines[0].startswith("* ")) && Lines.size() > 1) {
+    if ((Lines[0] == "*" || Lines[0].starts_with("* ")) && Lines.size() > 1) {
       // This is a multiline jsdoc comment.
       DelimitersOnNewline = true;
-    } else if (Lines[0].startswith("* ") && Lines.size() == 1) {
+    } else if (Lines[0].starts_with("* ") && Lines.size() == 1) {
       // Detect a long single-line comment, like:
       // /** long long long */
       // Below, '2' is the width of '*/'.
@@ -612,7 +612,7 @@ BreakableToken::Split BreakableBlockComment::getSplit(
     return Split(StringRef::npos, 0);
   return getCommentSplit(Content[LineIndex].substr(TailOffset),
                          ContentStartColumn, ColumnLimit, Style.TabWidth,
-                         Encoding, Style, Decoration.endswith("*"));
+                         Encoding, Style, Decoration.ends_with("*"));
 }
 
 void BreakableBlockComment::adjustWhitespace(unsigned LineIndex,
@@ -623,7 +623,7 @@ void BreakableBlockComment::adjustWhitespace(unsigned LineIndex,
   // trimming the trailing whitespace. The backslash will be re-added later when
   // inserting a line break.
   size_t EndOfPreviousLine = Lines[LineIndex - 1].size();
-  if (InPPDirective && Lines[LineIndex - 1].endswith("\\"))
+  if (InPPDirective && Lines[LineIndex - 1].ends_with("\\"))
     --EndOfPreviousLine;
 
   // Calculate the end of the non-whitespace text in the previous line.
@@ -672,7 +672,7 @@ unsigned BreakableBlockComment::getRemainingLength(unsigned LineIndex,
     // We never need a decoration when breaking just the trailing "*/" postfix.
     bool HasRemainingText = Offset < Content[LineIndex].size();
     if (!HasRemainingText) {
-      bool HasDecoration = Lines[LineIndex].ltrim().startswith(Decoration);
+      bool HasDecoration = Lines[LineIndex].ltrim().starts_with(Decoration);
       if (HasDecoration)
         LineLength -= Decoration.size();
     }
@@ -700,7 +700,7 @@ unsigned BreakableBlockComment::getContentIndent(unsigned LineIndex) const {
   // /** line 0 */
   // is "* line 0", so we need to skip over the decoration in that case.
   StringRef ContentWithNoDecoration = Content[LineIndex];
-  if (LineIndex == 0 && ContentWithNoDecoration.startswith("*"))
+  if (LineIndex == 0 && ContentWithNoDecoration.starts_with("*"))
     ContentWithNoDecoration = ContentWithNoDecoration.substr(1).ltrim(Blanks);
   StringRef FirstWord = ContentWithNoDecoration.substr(
       0, ContentWithNoDecoration.find_first_of(Blanks));
@@ -853,7 +853,7 @@ bool BreakableBlockComment::mayReflow(
   // Content[LineIndex] may exclude the indent after the '*' decoration. In that
   // case, we compute the start of the comment pragma manually.
   StringRef IndentContent = Content[LineIndex];
-  if (Lines[LineIndex].ltrim(Blanks).startswith("*"))
+  if (Lines[LineIndex].ltrim(Blanks).starts_with("*"))
     IndentContent = Lines[LineIndex].ltrim(Blanks).substr(1);
   return LineIndex > 0 && !CommentPragmasRegex.match(IndentContent) &&
          mayReflowContent(Content[LineIndex]) && !Tok.Finalized &&
@@ -876,7 +876,7 @@ BreakableLineCommentSection::BreakableLineCommentSection(
        CurrentTok = CurrentTok->Next) {
     LastLineTok = LineTok;
     StringRef TokenText(CurrentTok->TokenText);
-    assert((TokenText.startswith("//") || TokenText.startswith("#")) &&
+    assert((TokenText.starts_with("//") || TokenText.starts_with("#")) &&
            "unsupported line comment prefix, '//' and '#' are supported");
     size_t FirstLineIndex = Lines.size();
     TokenText.split(Lines, "\n");
@@ -913,7 +913,7 @@ BreakableLineCommentSection::BreakableLineCommentSection(
         // #########
         // # section
         // #########
-        if (FirstCommentChar == '#' && !TokenText.startswith("#"))
+        if (FirstCommentChar == '#' && !TokenText.starts_with("#"))
           return false;
         return FirstCommentChar == '\\' || isPunctuation(FirstCommentChar) ||
                isHorizontalWhitespace(FirstCommentChar);
@@ -1152,7 +1152,7 @@ bool BreakableLineCommentSection::mayReflow(
   // Line comments have the indent as part of the prefix, so we need to
   // recompute the start of the line.
   StringRef IndentContent = Content[LineIndex];
-  if (Lines[LineIndex].startswith("//"))
+  if (Lines[LineIndex].starts_with("//"))
     IndentContent = Lines[LineIndex].substr(2);
   // FIXME: Decide whether we want to reflow non-regular indents:
   // Currently, we only reflow when the OriginalPrefix[LineIndex] matches the

diff --git a/clang/lib/Format/ContinuationIndenter.cpp b/clang/lib/Format/ContinuationIndenter.cpp
@@ -161,7 +161,7 @@ static bool opensProtoMessageField(const FormatToken &LessTok,
 // string.  For example, the delimiter of R"deli(cont)deli" is deli.
 static std::optional<StringRef> getRawStringDelimiter(StringRef TokenText) {
   if (TokenText.size() < 5 // The smallest raw string possible is 'R"()"'.
-      || !TokenText.startswith("R\"") || !TokenText.endswith("\"")) {
+      || !TokenText.starts_with("R\"") || !TokenText.ends_with("\"")) {
     return std::nullopt;
   }
 
@@ -177,7 +177,7 @@ static std::optional<StringRef> getRawStringDelimiter(StringRef TokenText) {
   size_t RParenPos = TokenText.size() - Delimiter.size() - 2;
   if (TokenText[RParenPos] != ')')
     return std::nullopt;
-  if (!TokenText.substr(RParenPos + 1).startswith(Delimiter))
+  if (!TokenText.substr(RParenPos + 1).starts_with(Delimiter))
     return std::nullopt;
   return Delimiter;
 }
@@ -608,7 +608,7 @@ bool ContinuationIndenter::mustBreak(const LineState &State) {
 
   if (Current.is(tok::lessless) &&
       ((Previous.is(tok::identifier) && Previous.TokenText == "endl") ||
-       (Previous.Tok.isLiteral() && (Previous.TokenText.endswith("\\n\"") ||
+       (Previous.Tok.isLiteral() && (Previous.TokenText.ends_with("\\n\"") ||
                                      Previous.TokenText == "\'\\n\'")))) {
     return true;
   }
@@ -2293,12 +2293,13 @@ ContinuationIndenter::createBreakableToken(const FormatToken &Current,
     if (Style.isVerilog() || Style.Language == FormatStyle::LK_Java ||
         Style.isJavaScript() || Style.isCSharp()) {
       BreakableStringLiteralUsingOperators::QuoteStyleType QuoteStyle;
-      if (Style.isJavaScript() && Text.startswith("'") && Text.endswith("'")) {
+      if (Style.isJavaScript() && Text.starts_with("'") &&
+          Text.ends_with("'")) {
         QuoteStyle = BreakableStringLiteralUsingOperators::SingleQuotes;
-      } else if (Style.isCSharp() && Text.startswith("@\"") &&
-                 Text.endswith("\"")) {
+      } else if (Style.isCSharp() && Text.starts_with("@\"") &&
+                 Text.ends_with("\"")) {
         QuoteStyle = BreakableStringLiteralUsingOperators::AtDoubleQuotes;
-      } else if (Text.startswith("\"") && Text.endswith("\"")) {
+      } else if (Text.starts_with("\"") && Text.ends_with("\"")) {
         QuoteStyle = BreakableStringLiteralUsingOperators::DoubleQuotes;
       } else {
         return nullptr;
@@ -2315,12 +2316,14 @@ ContinuationIndenter::createBreakableToken(const FormatToken &Current,
     // FIXME: Store Prefix and Suffix (or PrefixLength and SuffixLength to
     // reduce the overhead) for each FormatToken, which is a string, so that we
     // don't run multiple checks here on the hot path.
-    if ((Text.endswith(Postfix = "\"") &&
-         (Text.startswith(Prefix = "@\"") || Text.startswith(Prefix = "\"") ||
-          Text.startswith(Prefix = "u\"") || Text.startswith(Prefix = "U\"") ||
-          Text.startswith(Prefix = "u8\"") ||
-          Text.startswith(Prefix = "L\""))) ||
-        (Text.startswith(Prefix = "_T(\"") && Text.endswith(Postfix = "\")"))) {
+    if ((Text.ends_with(Postfix = "\"") &&
+         (Text.starts_with(Prefix = "@\"") || Text.starts_with(Prefix = "\"") ||
+          Text.starts_with(Prefix = "u\"") ||
+          Text.starts_with(Prefix = "U\"") ||
+          Text.starts_with(Prefix = "u8\"") ||
+          Text.starts_with(Prefix = "L\""))) ||
+        (Text.starts_with(Prefix = "_T(\"") &&
+         Text.ends_with(Postfix = "\")"))) {
       return std::make_unique<BreakableStringLiteral>(
           Current, StartColumn, Prefix, Postfix, UnbreakableTailLength,
           State.Line->InPPDirective, Encoding, Style);
@@ -2342,7 +2345,7 @@ ContinuationIndenter::createBreakableToken(const FormatToken &Current,
     bool RegularComments = [&]() {
       for (const FormatToken *T = &Current; T && T->is(TT_LineComment);
            T = T->Next) {
-        if (!(T->TokenText.startswith("//") || T->TokenText.startswith("#")))
+        if (!(T->TokenText.starts_with("//") || T->TokenText.starts_with("#")))
           return false;
       }
       return true;
@@ -2754,7 +2757,7 @@ bool ContinuationIndenter::nextIsMultilineString(const LineState &State) {
   // We never consider raw string literals "multiline" for the purpose of
   // AlwaysBreakBeforeMultilineStrings implementation as they are special-cased
   // (see TokenAnnotator::mustBreakBefore().
-  if (Current.TokenText.startswith("R\""))
+  if (Current.TokenText.starts_with("R\""))
     return false;
   if (Current.IsMultiline)
     return true;