diff --git a/clang/include/clang/AST/JSONNodeDumper.h b/clang/include/clang/AST/JSONNodeDumper.h
--- a/clang/include/clang/AST/JSONNodeDumper.h
+++ b/clang/include/clang/AST/JSONNodeDumper.h
@@ -380,7 +380,7 @@
       case TSK_ExplicitInstantiationDefinition:
         if (!DumpExplicitInst)
           break;
-        LLVM_FALLTHROUGH;
+        [[fallthrough]];
       case TSK_Undeclared:
       case TSK_ImplicitInstantiation:
         if (DumpRefOnly)
diff --git a/clang/lib/ARCMigrate/TransRetainReleaseDealloc.cpp b/clang/lib/ARCMigrate/TransRetainReleaseDealloc.cpp
--- a/clang/lib/ARCMigrate/TransRetainReleaseDealloc.cpp
+++ b/clang/lib/ARCMigrate/TransRetainReleaseDealloc.cpp
@@ -78,7 +78,7 @@
         }
       }
       // Pass through.
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case OMF_retain:
     case OMF_release:
       if (E->getReceiverKind() == ObjCMessageExpr::Instance)
diff --git a/clang/lib/ARCMigrate/TransformActions.cpp b/clang/lib/ARCMigrate/TransformActions.cpp
--- a/clang/lib/ARCMigrate/TransformActions.cpp
+++ b/clang/lib/ARCMigrate/TransformActions.cpp
@@ -540,7 +540,7 @@
       return;
     case Range_Contains:
       RI->End = newRange.End;
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case Range_ExtendsBegin:
       newRange.End = RI->End;
       Removals.erase(RI);
diff --git a/clang/lib/AST/APValue.cpp b/clang/lib/AST/APValue.cpp
--- a/clang/lib/AST/APValue.cpp
+++ b/clang/lib/AST/APValue.cpp
@@ -871,7 +871,7 @@
           Out << "...}";
           return;
         }
-        LLVM_FALLTHROUGH;
+        [[fallthrough]];
       default:
         getArrayInitializedElt(I).printPretty(Out, Policy, ElemTy, Ctx);
       }
diff --git a/clang/lib/AST/ASTContext.cpp b/clang/lib/AST/ASTContext.cpp
--- a/clang/lib/AST/ASTContext.cpp
+++ b/clang/lib/AST/ASTContext.cpp
@@ -4420,7 +4420,7 @@
       case EST_Unparsed: case EST_Unevaluated: case EST_Uninstantiated:
         // We don't know yet. It shouldn't matter what we pick here; no-one
         // should ever look at this.
-        LLVM_FALLTHROUGH;
+        [[fallthrough]];
       case EST_None: case EST_MSAny: case EST_NoexceptFalse:
         CanonicalEPI.ExceptionSpec.Type = EST_None;
         break;
@@ -8286,7 +8286,7 @@
       return;
     }
     // TODO: Double check to make sure this intentionally falls through.
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   }
 
   case Type::ObjCInterface: {
diff --git a/clang/lib/AST/ASTDiagnostic.cpp b/clang/lib/AST/ASTDiagnostic.cpp
--- a/clang/lib/AST/ASTDiagnostic.cpp
+++ b/clang/lib/AST/ASTDiagnostic.cpp
@@ -425,7 +425,7 @@
       Modifier = StringRef();
       Argument = StringRef();
       // Fall through
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     }
     case DiagnosticsEngine::ak_qualtype: {
       assert(Modifier.empty() && Argument.empty() &&
diff --git a/clang/lib/AST/ASTDumper.cpp b/clang/lib/AST/ASTDumper.cpp
--- a/clang/lib/AST/ASTDumper.cpp
+++ b/clang/lib/AST/ASTDumper.cpp
@@ -96,7 +96,7 @@
     case TSK_ExplicitInstantiationDefinition:
       if (!DumpExplicitInst)
         break;
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case TSK_Undeclared:
     case TSK_ImplicitInstantiation:
       if (DumpRefOnly)
diff --git a/clang/lib/AST/ASTStructuralEquivalence.cpp b/clang/lib/AST/ASTStructuralEquivalence.cpp
--- a/clang/lib/AST/ASTStructuralEquivalence.cpp
+++ b/clang/lib/AST/ASTStructuralEquivalence.cpp
@@ -900,7 +900,7 @@
       return false;
 
     // Fall through to check the bits common with FunctionNoProtoType.
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   }
 
   case Type::FunctionNoProto: {
diff --git a/clang/lib/AST/Comment.cpp b/clang/lib/AST/Comment.cpp
--- a/clang/lib/AST/Comment.cpp
+++ b/clang/lib/AST/Comment.cpp
@@ -301,7 +301,7 @@
       TemplateKind = TemplateSpecialization;
       TemplateParameters = VTD->getTemplateParameters();
     }
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case Decl::Field:
   case Decl::EnumConstant:
   case Decl::ObjCIvar:
diff --git a/clang/lib/AST/Expr.cpp b/clang/lib/AST/Expr.cpp
--- a/clang/lib/AST/Expr.cpp
+++ b/clang/lib/AST/Expr.cpp
@@ -277,7 +277,7 @@
   case APValue::Int:
     if (!Value.getInt().needsCleanup())
       return ConstantExpr::RSK_Int64;
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   default:
     return ConstantExpr::RSK_APValue;
   }
@@ -2633,7 +2633,7 @@
     }
 
     // Fallthrough for generic call handling.
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   }
   case CallExprClass:
   case CXXMemberCallExprClass:
@@ -3609,7 +3609,7 @@
         DCE->getCastKind() == CK_Dynamic)
       return true;
     }
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case ImplicitCastExprClass:
   case CStyleCastExprClass:
   case CXXStaticCastExprClass:
diff --git a/clang/lib/AST/ExprCXX.cpp b/clang/lib/AST/ExprCXX.cpp
--- a/clang/lib/AST/ExprCXX.cpp
+++ b/clang/lib/AST/ExprCXX.cpp
@@ -1097,7 +1097,7 @@
   switch (Kind) {
   case LCK_StarThis:
     Bits |= Capture_ByCopy;
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case LCK_This:
     assert(!Var && "'this' capture cannot have a variable!");
     Bits |= Capture_This;
@@ -1105,7 +1105,7 @@
 
   case LCK_ByCopy:
     Bits |= Capture_ByCopy;
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case LCK_ByRef:
     assert(Var && "capture must have a variable!");
     break;
diff --git a/clang/lib/AST/ExprConstant.cpp b/clang/lib/AST/ExprConstant.cpp
--- a/clang/lib/AST/ExprConstant.cpp
+++ b/clang/lib/AST/ExprConstant.cpp
@@ -1132,7 +1132,7 @@
           if (!HasFoldFailureDiagnostic)
             break;
           // We've already failed to fold something. Keep that diagnostic.
-          LLVM_FALLTHROUGH;
+          [[fallthrough]];
         case EM_ConstantExpression:
         case EM_ConstantExpressionUnevaluated:
           setActiveDiagnostic(false);
@@ -9217,7 +9217,7 @@
         << (std::string("'") + Info.Ctx.BuiltinInfo.getName(BuiltinOp) + "'");
     else
       Info.CCEDiag(E, diag::note_invalid_subexpr_in_const_expr);
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case Builtin::BI__builtin_strchr:
   case Builtin::BI__builtin_wcschr:
   case Builtin::BI__builtin_memchr:
@@ -9278,7 +9278,7 @@
                                Desired))
         return ZeroInitialization(E);
       StopAtNull = true;
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case Builtin::BImemchr:
     case Builtin::BI__builtin_memchr:
     case Builtin::BI__builtin_char_memchr:
@@ -9291,7 +9291,7 @@
     case Builtin::BIwcschr:
     case Builtin::BI__builtin_wcschr:
       StopAtNull = true;
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case Builtin::BIwmemchr:
     case Builtin::BI__builtin_wmemchr:
       // wcschr and wmemchr are given a wchar_t to look for. Just use it.
@@ -9325,7 +9325,7 @@
         << (std::string("'") + Info.Ctx.BuiltinInfo.getName(BuiltinOp) + "'");
     else
       Info.CCEDiag(E, diag::note_invalid_subexpr_in_const_expr);
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case Builtin::BI__builtin_memcpy:
   case Builtin::BI__builtin_memmove:
   case Builtin::BI__builtin_wmemcpy:
@@ -12122,7 +12122,7 @@
         << (std::string("'") + Info.Ctx.BuiltinInfo.getName(BuiltinOp) + "'");
     else
       Info.CCEDiag(E, diag::note_invalid_subexpr_in_const_expr);
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case Builtin::BI__builtin_strlen:
   case Builtin::BI__builtin_wcslen: {
     // As an extension, we support __builtin_strlen() as a constant expression,
@@ -12147,7 +12147,7 @@
         << (std::string("'") + Info.Ctx.BuiltinInfo.getName(BuiltinOp) + "'");
     else
       Info.CCEDiag(E, diag::note_invalid_subexpr_in_const_expr);
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case Builtin::BI__builtin_strcmp:
   case Builtin::BI__builtin_wcscmp:
   case Builtin::BI__builtin_strncmp:
diff --git a/clang/lib/AST/FormatString.cpp b/clang/lib/AST/FormatString.cpp
--- a/clang/lib/AST/FormatString.cpp
+++ b/clang/lib/AST/FormatString.cpp
@@ -747,7 +747,7 @@
             break;
         }
       }
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case LengthModifier::AsChar:
     case LengthModifier::AsLongLong:
     case LengthModifier::AsQuad:
diff --git a/clang/lib/AST/ItaniumMangle.cpp b/clang/lib/AST/ItaniumMangle.cpp
--- a/clang/lib/AST/ItaniumMangle.cpp
+++ b/clang/lib/AST/ItaniumMangle.cpp
@@ -1659,7 +1659,7 @@
         if (!MD->isStatic())
           Arity++;
     }
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case DeclarationName::CXXConversionFunctionName:
   case DeclarationName::CXXLiteralOperatorName:
     mangleOperatorName(Name, Arity);
@@ -4671,7 +4671,7 @@
         Out << 'E';
         break;
       }
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case UETT_AlignOf:
       Out << 'a';
       MangleAlignofSizeofArg();
diff --git a/clang/lib/AST/NestedNameSpecifier.cpp b/clang/lib/AST/NestedNameSpecifier.cpp
--- a/clang/lib/AST/NestedNameSpecifier.cpp
+++ b/clang/lib/AST/NestedNameSpecifier.cpp
@@ -280,7 +280,7 @@
   case TypeSpecWithTemplate:
     OS << "template ";
     // Fall through to print the type.
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
 
   case TypeSpec: {
     const auto *Record =
diff --git a/clang/lib/AST/PrintfFormatString.cpp b/clang/lib/AST/PrintfFormatString.cpp
--- a/clang/lib/AST/PrintfFormatString.cpp
+++ b/clang/lib/AST/PrintfFormatString.cpp
@@ -500,7 +500,7 @@
       case LengthModifier::AsShort:
         if (Ctx.getTargetInfo().getTriple().isOSMSVCRT())
           return Ctx.IntTy;
-        LLVM_FALLTHROUGH;
+        [[fallthrough]];
       default:
         return ArgType::Invalid();
     }
diff --git a/clang/lib/AST/ScanfFormatString.cpp b/clang/lib/AST/ScanfFormatString.cpp
--- a/clang/lib/AST/ScanfFormatString.cpp
+++ b/clang/lib/AST/ScanfFormatString.cpp
@@ -345,7 +345,7 @@
         case LengthModifier::AsShort:
           if (Ctx.getTargetInfo().getTriple().isOSMSVCRT())
             return ArgType::PtrTo(ArgType::AnyCharTy);
-          LLVM_FALLTHROUGH;
+          [[fallthrough]];
         default:
           return ArgType::Invalid();
       }
@@ -362,7 +362,7 @@
         case LengthModifier::AsShort:
           if (Ctx.getTargetInfo().getTriple().isOSMSVCRT())
             return ArgType::PtrTo(ArgType::AnyCharTy);
-          LLVM_FALLTHROUGH;
+          [[fallthrough]];
         default:
           return ArgType::Invalid();
       }
diff --git a/clang/lib/AST/TypeLoc.cpp b/clang/lib/AST/TypeLoc.cpp
--- a/clang/lib/AST/TypeLoc.cpp
+++ b/clang/lib/AST/TypeLoc.cpp
@@ -208,7 +208,7 @@
         LeftMost = Cur;
         break;
       }
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case FunctionNoProto:
     case ConstantArray:
     case DependentSizedArray:
@@ -260,7 +260,7 @@
       // `id` and `id<...>` have no star location.
       if (Cur.castAs<ObjCObjectPointerTypeLoc>().getStarLoc().isInvalid())
         break;
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case Pointer:
     case BlockPointer:
     case MemberPointer:
diff --git a/clang/lib/AST/TypePrinter.cpp b/clang/lib/AST/TypePrinter.cpp
--- a/clang/lib/AST/TypePrinter.cpp
+++ b/clang/lib/AST/TypePrinter.cpp
@@ -262,7 +262,7 @@
     case Type::VariableArray:
     case Type::DependentSizedArray:
       NeedARCStrongQualifier = true;
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
 
     case Type::ConstantArray:
     case Type::IncompleteArray:
diff --git a/clang/lib/Analysis/CalledOnceCheck.cpp b/clang/lib/Analysis/CalledOnceCheck.cpp
--- a/clang/lib/Analysis/CalledOnceCheck.cpp
+++ b/clang/lib/Analysis/CalledOnceCheck.cpp
@@ -319,7 +319,7 @@
       // We care about logical not only if we care about comparisons.
       if (!ShouldRetrieveFromComparisons)
         return nullptr;
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     // Function pointer/references can be dereferenced before a call.
     // That doesn't make it, however, any different from a regular call.
     // For this reason, dereference operation is a "no-op".
diff --git a/clang/lib/Analysis/ReachableCode.cpp b/clang/lib/Analysis/ReachableCode.cpp
--- a/clang/lib/Analysis/ReachableCode.cpp
+++ b/clang/lib/Analysis/ReachableCode.cpp
@@ -218,7 +218,7 @@
       return isConfigurationValue(cast<DeclRefExpr>(S)->getDecl(), PP);
     case Stmt::ObjCBoolLiteralExprClass:
       IgnoreYES_NO = true;
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case Stmt::CXXBoolLiteralExprClass:
     case Stmt::IntegerLiteralClass: {
       const Expr *E = cast<Expr>(S);
diff --git a/clang/lib/Analysis/ThreadSafety.cpp b/clang/lib/Analysis/ThreadSafety.cpp
--- a/clang/lib/Analysis/ThreadSafety.cpp
+++ b/clang/lib/Analysis/ThreadSafety.cpp
@@ -2013,7 +2013,7 @@
       case OO_LessLessEqual:
       case OO_GreaterGreaterEqual:
         checkAccess(OE->getArg(1), AK_Read);
-        LLVM_FALLTHROUGH;
+        [[fallthrough]];
       case OO_PlusPlus:
       case OO_MinusMinus:
         checkAccess(OE->getArg(0), AK_Written);
@@ -2026,7 +2026,7 @@
           // Grrr.  operator* can be multiplication...
           checkPtAccess(OE->getArg(0), AK_Read);
         }
-        LLVM_FALLTHROUGH;
+        [[fallthrough]];
       default: {
         // TODO: get rid of this, and rely on pass-by-ref instead.
         const Expr *Obj = OE->getArg(0);
diff --git a/clang/lib/Basic/BuiltinTargetFeatures.h b/clang/lib/Basic/BuiltinTargetFeatures.h
--- a/clang/lib/Basic/BuiltinTargetFeatures.h
+++ b/clang/lib/Basic/BuiltinTargetFeatures.h
@@ -54,7 +54,7 @@
       case ')':
         --InParentheses;
         assert(InParentheses >= 0 && "Parentheses are not in pair");
-        LLVM_FALLTHROUGH;
+        [[fallthrough]];
       case '|':
       case ',':
         if (InParentheses == 0) {
diff --git a/clang/lib/Basic/TargetInfo.cpp b/clang/lib/Basic/TargetInfo.cpp
--- a/clang/lib/Basic/TargetInfo.cpp
+++ b/clang/lib/Basic/TargetInfo.cpp
@@ -208,11 +208,11 @@
   case UnsignedChar:
     if (getCharWidth() < getIntWidth())
       return "";
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case UnsignedShort:
     if (getShortWidth() < getIntWidth())
       return "";
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case UnsignedInt:      return "U";
   case UnsignedLong:     return "UL";
   case UnsignedLongLong: return "ULL";
diff --git a/clang/lib/Basic/Targets/AMDGPU.cpp b/clang/lib/Basic/Targets/AMDGPU.cpp
--- a/clang/lib/Basic/Targets/AMDGPU.cpp
+++ b/clang/lib/Basic/Targets/AMDGPU.cpp
@@ -234,7 +234,7 @@
       Features["dot5-insts"] = true;
       Features["dot6-insts"] = true;
       Features["dot7-insts"] = true;
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case GK_GFX1013:
     case GK_GFX1010:
       Features["dl-insts"] = true;
@@ -251,30 +251,30 @@
     case GK_GFX940:
       Features["gfx940-insts"] = true;
       Features["fp8-insts"] = true;
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case GK_GFX90A:
       Features["gfx90a-insts"] = true;
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case GK_GFX908:
       Features["dot3-insts"] = true;
       Features["dot4-insts"] = true;
       Features["dot5-insts"] = true;
       Features["dot6-insts"] = true;
       Features["mai-insts"] = true;
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case GK_GFX906:
       Features["dl-insts"] = true;
       Features["dot1-insts"] = true;
       Features["dot2-insts"] = true;
       Features["dot7-insts"] = true;
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case GK_GFX90C:
     case GK_GFX909:
     case GK_GFX904:
     case GK_GFX902:
     case GK_GFX900:
       Features["gfx9-insts"] = true;
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case GK_GFX810:
     case GK_GFX805:
     case GK_GFX803:
@@ -284,7 +284,7 @@
       Features["16-bit-insts"] = true;
       Features["dpp"] = true;
       Features["s-memrealtime"] = true;
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case GK_GFX705:
     case GK_GFX704:
     case GK_GFX703:
@@ -293,7 +293,7 @@
     case GK_GFX700:
       Features["ci-insts"] = true;
       Features["flat-address-space"] = true;
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case GK_GFX602:
     case GK_GFX601:
     case GK_GFX600:
diff --git a/clang/lib/Basic/Targets/OSTargets.h b/clang/lib/Basic/Targets/OSTargets.h
--- a/clang/lib/Basic/Targets/OSTargets.h
+++ b/clang/lib/Basic/Targets/OSTargets.h
@@ -477,7 +477,7 @@
     case llvm::Triple::x86:
     case llvm::Triple::x86_64:
       this->HasFloat128 = true;
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     default:
       this->MCountName = "__mcount";
       break;
diff --git a/clang/lib/Basic/Targets/PPC.h b/clang/lib/Basic/Targets/PPC.h
--- a/clang/lib/Basic/Targets/PPC.h
+++ b/clang/lib/Basic/Targets/PPC.h
@@ -216,7 +216,7 @@
       // Don't use floating point registers on soft float ABI.
       if (FloatABI == SoftFloat)
         return false;
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case 'b': // Base register
       Info.setAllowsRegister();
       break;
@@ -295,7 +295,7 @@
     case 'Q': // Memory operand that is an offset from a register (it is
               // usually better to use `m' or `es' in asm statements)
       Info.setAllowsRegister();
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case 'Z': // Memory operand that is an indexed or indirect from a
               // register (it is usually better to use `m' or `es' in
               // asm statements)
diff --git a/clang/lib/Basic/Targets/SystemZ.cpp b/clang/lib/Basic/Targets/SystemZ.cpp
--- a/clang/lib/Basic/Targets/SystemZ.cpp
+++ b/clang/lib/Basic/Targets/SystemZ.cpp
@@ -69,7 +69,7 @@
     case 'T': // Likewise, plus an index
       break;
     }
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case 'a': // Address register
   case 'd': // Data register (equivalent to 'r')
   case 'f': // Floating-point register
diff --git a/clang/lib/Basic/Targets/WebAssembly.cpp b/clang/lib/Basic/Targets/WebAssembly.cpp
--- a/clang/lib/Basic/Targets/WebAssembly.cpp
+++ b/clang/lib/Basic/Targets/WebAssembly.cpp
@@ -104,10 +104,10 @@
     switch (Level) {
     case RelaxedSIMD:
       Features["relaxed-simd"] = true;
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case SIMD128:
       Features["simd128"] = true;
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case NoSIMD:
       break;
     }
@@ -118,7 +118,7 @@
   case NoSIMD:
   case SIMD128:
     Features["simd128"] = false;
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case RelaxedSIMD:
     Features["relaxed-simd"] = false;
     break;
diff --git a/clang/lib/Basic/Targets/X86.cpp b/clang/lib/Basic/Targets/X86.cpp
--- a/clang/lib/Basic/Targets/X86.cpp
+++ b/clang/lib/Basic/Targets/X86.cpp
@@ -444,7 +444,7 @@
   case CK_PentiumMMX:
     Builder.defineMacro("__pentium_mmx__");
     Builder.defineMacro("__tune_pentium_mmx__");
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case CK_i586:
   case CK_Pentium:
     defineCPUMacros(Builder, "i586");
@@ -453,11 +453,11 @@
   case CK_Pentium3:
   case CK_PentiumM:
     Builder.defineMacro("__tune_pentium3__");
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case CK_Pentium2:
   case CK_C3_2:
     Builder.defineMacro("__tune_pentium2__");
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case CK_PentiumPro:
   case CK_i686:
     defineCPUMacros(Builder, "i686");
@@ -525,7 +525,7 @@
   case CK_K6_2:
     Builder.defineMacro("__k6_2__");
     Builder.defineMacro("__tune_k6_2__");
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case CK_K6_3:
     if (CPU != CK_K6_2) { // In case of fallthrough
       // FIXME: GCC may be enabling these in cases where some other k6
@@ -534,7 +534,7 @@
       Builder.defineMacro("__k6_3__");
       Builder.defineMacro("__tune_k6_3__");
     }
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case CK_K6:
     defineCPUMacros(Builder, "k6");
     break;
@@ -660,13 +660,13 @@
   switch (XOPLevel) {
   case XOP:
     Builder.defineMacro("__XOP__");
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case FMA4:
     Builder.defineMacro("__FMA4__");
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case SSE4A:
     Builder.defineMacro("__SSE4A__");
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case NoXOP:
     break;
   }
@@ -786,33 +786,33 @@
   switch (SSELevel) {
   case AVX512F:
     Builder.defineMacro("__AVX512F__");
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case AVX2:
     Builder.defineMacro("__AVX2__");
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case AVX:
     Builder.defineMacro("__AVX__");
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case SSE42:
     Builder.defineMacro("__SSE4_2__");
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case SSE41:
     Builder.defineMacro("__SSE4_1__");
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case SSSE3:
     Builder.defineMacro("__SSSE3__");
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case SSE3:
     Builder.defineMacro("__SSE3__");
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case SSE2:
     Builder.defineMacro("__SSE2__");
     Builder.defineMacro("__SSE2_MATH__"); // -mfp-math=sse always implied.
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case SSE1:
     Builder.defineMacro("__SSE__");
     Builder.defineMacro("__SSE_MATH__"); // -mfp-math=sse always implied.
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case NoSSE:
     break;
   }
@@ -842,13 +842,13 @@
   switch (MMX3DNowLevel) {
   case AMD3DNowAthlon:
     Builder.defineMacro("__3dNOW_A__");
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case AMD3DNow:
     Builder.defineMacro("__3dNOW__");
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case MMX:
     Builder.defineMacro("__MMX__");
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case NoMMX3DNow:
     break;
   }
@@ -1521,7 +1521,7 @@
       // to the next constraint.
       return std::string("^") + std::string(Constraint++, 2);
     }
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   default:
     return std::string(1, *Constraint);
   }
diff --git a/clang/lib/CodeGen/CGAtomic.cpp b/clang/lib/CodeGen/CGAtomic.cpp
--- a/clang/lib/CodeGen/CGAtomic.cpp
+++ b/clang/lib/CodeGen/CGAtomic.cpp
@@ -609,7 +609,7 @@
   case AtomicExpr::AO__atomic_add_fetch:
     PostOp = E->getValueType()->isFloatingType() ? llvm::Instruction::FAdd
                                                  : llvm::Instruction::Add;
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case AtomicExpr::AO__c11_atomic_fetch_add:
   case AtomicExpr::AO__hip_atomic_fetch_add:
   case AtomicExpr::AO__opencl_atomic_fetch_add:
@@ -621,7 +621,7 @@
   case AtomicExpr::AO__atomic_sub_fetch:
     PostOp = E->getValueType()->isFloatingType() ? llvm::Instruction::FSub
                                                  : llvm::Instruction::Sub;
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case AtomicExpr::AO__c11_atomic_fetch_sub:
   case AtomicExpr::AO__opencl_atomic_fetch_sub:
   case AtomicExpr::AO__atomic_fetch_sub:
@@ -631,7 +631,7 @@
 
   case AtomicExpr::AO__atomic_min_fetch:
     PostOpMinMax = true;
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case AtomicExpr::AO__c11_atomic_fetch_min:
   case AtomicExpr::AO__hip_atomic_fetch_min:
   case AtomicExpr::AO__opencl_atomic_fetch_min:
@@ -642,7 +642,7 @@
 
   case AtomicExpr::AO__atomic_max_fetch:
     PostOpMinMax = true;
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case AtomicExpr::AO__c11_atomic_fetch_max:
   case AtomicExpr::AO__hip_atomic_fetch_max:
   case AtomicExpr::AO__opencl_atomic_fetch_max:
@@ -653,7 +653,7 @@
 
   case AtomicExpr::AO__atomic_and_fetch:
     PostOp = llvm::Instruction::And;
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case AtomicExpr::AO__c11_atomic_fetch_and:
   case AtomicExpr::AO__hip_atomic_fetch_and:
   case AtomicExpr::AO__opencl_atomic_fetch_and:
@@ -663,7 +663,7 @@
 
   case AtomicExpr::AO__atomic_or_fetch:
     PostOp = llvm::Instruction::Or;
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case AtomicExpr::AO__c11_atomic_fetch_or:
   case AtomicExpr::AO__hip_atomic_fetch_or:
   case AtomicExpr::AO__opencl_atomic_fetch_or:
@@ -673,7 +673,7 @@
 
   case AtomicExpr::AO__atomic_xor_fetch:
     PostOp = llvm::Instruction::Xor;
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case AtomicExpr::AO__c11_atomic_fetch_xor:
   case AtomicExpr::AO__hip_atomic_fetch_xor:
   case AtomicExpr::AO__opencl_atomic_fetch_xor:
@@ -683,7 +683,7 @@
 
   case AtomicExpr::AO__atomic_nand_fetch:
     PostOp = llvm::Instruction::And; // the NOT is special cased below
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case AtomicExpr::AO__c11_atomic_fetch_nand:
   case AtomicExpr::AO__atomic_fetch_nand:
     Op = llvm::AtomicRMWInst::Nand;
@@ -914,13 +914,13 @@
       EmitStoreOfScalar(Val1Scalar, MakeAddrLValue(Temp, Val1Ty));
       break;
     }
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case AtomicExpr::AO__atomic_fetch_add:
   case AtomicExpr::AO__atomic_fetch_sub:
   case AtomicExpr::AO__atomic_add_fetch:
   case AtomicExpr::AO__atomic_sub_fetch:
     ShouldCastToIntPtrTy = !MemTy->isFloatingType();
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
 
   case AtomicExpr::AO__c11_atomic_store:
   case AtomicExpr::AO__c11_atomic_exchange:
@@ -1045,7 +1045,7 @@
       // suitably aligned for the optimized version.
       if (Misaligned)
         break;
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case AtomicExpr::AO__c11_atomic_load:
     case AtomicExpr::AO__c11_atomic_store:
     case AtomicExpr::AO__c11_atomic_exchange:
@@ -1176,7 +1176,7 @@
     // T __atomic_fetch_add_N(T *mem, T val, int order)
     case AtomicExpr::AO__atomic_add_fetch:
       PostOp = llvm::Instruction::Add;
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case AtomicExpr::AO__c11_atomic_fetch_add:
     case AtomicExpr::AO__opencl_atomic_fetch_add:
     case AtomicExpr::AO__atomic_fetch_add:
@@ -1189,7 +1189,7 @@
     // T __atomic_fetch_and_N(T *mem, T val, int order)
     case AtomicExpr::AO__atomic_and_fetch:
       PostOp = llvm::Instruction::And;
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case AtomicExpr::AO__c11_atomic_fetch_and:
     case AtomicExpr::AO__opencl_atomic_fetch_and:
     case AtomicExpr::AO__hip_atomic_fetch_and:
@@ -1202,7 +1202,7 @@
     // T __atomic_fetch_or_N(T *mem, T val, int order)
     case AtomicExpr::AO__atomic_or_fetch:
       PostOp = llvm::Instruction::Or;
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case AtomicExpr::AO__c11_atomic_fetch_or:
     case AtomicExpr::AO__opencl_atomic_fetch_or:
     case AtomicExpr::AO__hip_atomic_fetch_or:
@@ -1215,7 +1215,7 @@
     // T __atomic_fetch_sub_N(T *mem, T val, int order)
     case AtomicExpr::AO__atomic_sub_fetch:
       PostOp = llvm::Instruction::Sub;
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case AtomicExpr::AO__c11_atomic_fetch_sub:
     case AtomicExpr::AO__opencl_atomic_fetch_sub:
     case AtomicExpr::AO__atomic_fetch_sub:
@@ -1227,7 +1227,7 @@
     // T __atomic_fetch_xor_N(T *mem, T val, int order)
     case AtomicExpr::AO__atomic_xor_fetch:
       PostOp = llvm::Instruction::Xor;
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case AtomicExpr::AO__c11_atomic_fetch_xor:
     case AtomicExpr::AO__opencl_atomic_fetch_xor:
     case AtomicExpr::AO__hip_atomic_fetch_xor:
@@ -1238,7 +1238,7 @@
       break;
     case AtomicExpr::AO__atomic_min_fetch:
       PostOpMinMax = true;
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case AtomicExpr::AO__c11_atomic_fetch_min:
     case AtomicExpr::AO__atomic_fetch_min:
     case AtomicExpr::AO__hip_atomic_fetch_min:
@@ -1251,7 +1251,7 @@
       break;
     case AtomicExpr::AO__atomic_max_fetch:
       PostOpMinMax = true;
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case AtomicExpr::AO__c11_atomic_fetch_max:
     case AtomicExpr::AO__atomic_fetch_max:
     case AtomicExpr::AO__hip_atomic_fetch_max:
@@ -1266,7 +1266,7 @@
     // T __atomic_fetch_nand_N(T *mem, T val, int order)
     case AtomicExpr::AO__atomic_nand_fetch:
       PostOp = llvm::Instruction::And; // the NOT is special cased below
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case AtomicExpr::AO__c11_atomic_fetch_nand:
     case AtomicExpr::AO__atomic_fetch_nand:
       LibCallName = "__atomic_fetch_nand";
diff --git a/clang/lib/CodeGen/CGBuiltin.cpp b/clang/lib/CodeGen/CGBuiltin.cpp
--- a/clang/lib/CodeGen/CGBuiltin.cpp
+++ b/clang/lib/CodeGen/CGBuiltin.cpp
@@ -5034,7 +5034,7 @@
         EmitLifetimeEnd(TmpSize, TmpPtr);
       return Call;
     }
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   }
   // OpenCL v2.0 s6.13.17.6 - Kernel query functions need bitcast of block
   // parameter.
@@ -6634,7 +6634,7 @@
   case NEON::BI__builtin_neon_vcalt_v:
   case NEON::BI__builtin_neon_vcaltq_v:
     std::swap(Ops[0], Ops[1]);
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case NEON::BI__builtin_neon_vcage_v:
   case NEON::BI__builtin_neon_vcageq_v:
   case NEON::BI__builtin_neon_vcagt_v:
@@ -8037,7 +8037,7 @@
       int Indices[] = {1 - Lane, Lane};
       return Builder.CreateShuffleVector(Ops[1], Ld, Indices, "vld1q_lane");
     }
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case NEON::BI__builtin_neon_vld1_lane_v: {
     Ops[1] = Builder.CreateBitCast(Ops[1], Ty);
     PtrOp0 = Builder.CreateElementBitCast(PtrOp0, VTy->getElementType());
@@ -8077,7 +8077,7 @@
   case NEON::BI__builtin_neon_vsri_n_v:
   case NEON::BI__builtin_neon_vsriq_n_v:
     rightShift = true;
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case NEON::BI__builtin_neon_vsli_n_v:
   case NEON::BI__builtin_neon_vsliq_n_v:
     Ops[2] = EmitNeonShiftVector(Ops[2], Ty, rightShift);
@@ -8100,7 +8100,7 @@
       return Builder.CreateCall(CGM.getIntrinsic(Intrinsic::arm_neon_vst1,
                                                  Tys), Ops);
     }
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case NEON::BI__builtin_neon_vst1_lane_v: {
     Ops[1] = Builder.CreateBitCast(Ops[1], Ty);
     Ops[1] = Builder.CreateExtractElement(Ops[1], Ops[2]);
@@ -10119,7 +10119,7 @@
   case NEON::BI__builtin_neon_vcvts_f32_u32:
   case NEON::BI__builtin_neon_vcvtd_f64_u64:
     usgn = true;
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case NEON::BI__builtin_neon_vcvts_f32_s32:
   case NEON::BI__builtin_neon_vcvtd_f64_s64: {
     Ops.push_back(EmitScalarExpr(E->getArg(0)));
@@ -10135,7 +10135,7 @@
   case NEON::BI__builtin_neon_vcvth_f16_u32:
   case NEON::BI__builtin_neon_vcvth_f16_u64:
     usgn = true;
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case NEON::BI__builtin_neon_vcvth_f16_s16:
   case NEON::BI__builtin_neon_vcvth_f16_s32:
   case NEON::BI__builtin_neon_vcvth_f16_s64: {
@@ -11268,7 +11268,7 @@
   case NEON::BI__builtin_neon_vaddv_u8:
     // FIXME: These are handled by the AArch64 scalar code.
     usgn = true;
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case NEON::BI__builtin_neon_vaddv_s8: {
     Int = usgn ? Intrinsic::aarch64_neon_uaddv : Intrinsic::aarch64_neon_saddv;
     Ty = Int32Ty;
@@ -11280,7 +11280,7 @@
   }
   case NEON::BI__builtin_neon_vaddv_u16:
     usgn = true;
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case NEON::BI__builtin_neon_vaddv_s16: {
     Int = usgn ? Intrinsic::aarch64_neon_uaddv : Intrinsic::aarch64_neon_saddv;
     Ty = Int32Ty;
@@ -11292,7 +11292,7 @@
   }
   case NEON::BI__builtin_neon_vaddvq_u8:
     usgn = true;
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case NEON::BI__builtin_neon_vaddvq_s8: {
     Int = usgn ? Intrinsic::aarch64_neon_uaddv : Intrinsic::aarch64_neon_saddv;
     Ty = Int32Ty;
@@ -11304,7 +11304,7 @@
   }
   case NEON::BI__builtin_neon_vaddvq_u16:
     usgn = true;
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case NEON::BI__builtin_neon_vaddvq_s16: {
     Int = usgn ? Intrinsic::aarch64_neon_uaddv : Intrinsic::aarch64_neon_saddv;
     Ty = Int32Ty;
@@ -12347,7 +12347,7 @@
   default: break;
   case clang::X86::BI__builtin_ia32_vfmsubph512_mask3:
     Subtract = true;
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case clang::X86::BI__builtin_ia32_vfmaddph512_mask:
   case clang::X86::BI__builtin_ia32_vfmaddph512_maskz:
   case clang::X86::BI__builtin_ia32_vfmaddph512_mask3:
@@ -12355,7 +12355,7 @@
     break;
   case clang::X86::BI__builtin_ia32_vfmsubaddph512_mask3:
     Subtract = true;
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case clang::X86::BI__builtin_ia32_vfmaddsubph512_mask:
   case clang::X86::BI__builtin_ia32_vfmaddsubph512_maskz:
   case clang::X86::BI__builtin_ia32_vfmaddsubph512_mask3:
@@ -12363,21 +12363,21 @@
     break;
   case clang::X86::BI__builtin_ia32_vfmsubps512_mask3:
     Subtract = true;
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case clang::X86::BI__builtin_ia32_vfmaddps512_mask:
   case clang::X86::BI__builtin_ia32_vfmaddps512_maskz:
   case clang::X86::BI__builtin_ia32_vfmaddps512_mask3:
     IID = llvm::Intrinsic::x86_avx512_vfmadd_ps_512; break;
   case clang::X86::BI__builtin_ia32_vfmsubpd512_mask3:
     Subtract = true;
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case clang::X86::BI__builtin_ia32_vfmaddpd512_mask:
   case clang::X86::BI__builtin_ia32_vfmaddpd512_maskz:
   case clang::X86::BI__builtin_ia32_vfmaddpd512_mask3:
     IID = llvm::Intrinsic::x86_avx512_vfmadd_pd_512; break;
   case clang::X86::BI__builtin_ia32_vfmsubaddps512_mask3:
     Subtract = true;
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case clang::X86::BI__builtin_ia32_vfmaddsubps512_mask:
   case clang::X86::BI__builtin_ia32_vfmaddsubps512_maskz:
   case clang::X86::BI__builtin_ia32_vfmaddsubps512_mask3:
@@ -12385,7 +12385,7 @@
     break;
   case clang::X86::BI__builtin_ia32_vfmsubaddpd512_mask3:
     Subtract = true;
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case clang::X86::BI__builtin_ia32_vfmaddsubpd512_mask:
   case clang::X86::BI__builtin_ia32_vfmaddsubpd512_maskz:
   case clang::X86::BI__builtin_ia32_vfmaddsubpd512_mask3:
@@ -14725,7 +14725,7 @@
   case X86::BI__builtin_ia32_cmppd256_mask:
   case X86::BI__builtin_ia32_cmppd512_mask:
     IsMaskFCmp = true;
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case X86::BI__builtin_ia32_cmpps:
   case X86::BI__builtin_ia32_cmpps256:
   case X86::BI__builtin_ia32_cmppd:
@@ -15214,7 +15214,7 @@
   }
   case X86::BI__builtin_ia32_vfcmaddcph512_mask:
     IsConjFMA = true;
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case X86::BI__builtin_ia32_vfmaddcph512_mask: {
     Intrinsic::ID IID = IsConjFMA
                             ? Intrinsic::x86_avx512fp16_mask_vfcmadd_cph_512
@@ -15224,7 +15224,7 @@
   }
   case X86::BI__builtin_ia32_vfcmaddcsh_round_mask:
     IsConjFMA = true;
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case X86::BI__builtin_ia32_vfmaddcsh_round_mask: {
     Intrinsic::ID IID = IsConjFMA ? Intrinsic::x86_avx512fp16_mask_vfcmadd_csh
                                   : Intrinsic::x86_avx512fp16_mask_vfmadd_csh;
@@ -15234,7 +15234,7 @@
   }
   case X86::BI__builtin_ia32_vfcmaddcsh_round_mask3:
     IsConjFMA = true;
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case X86::BI__builtin_ia32_vfmaddcsh_round_mask3: {
     Intrinsic::ID IID = IsConjFMA ? Intrinsic::x86_avx512fp16_mask_vfcmadd_csh
                                   : Intrinsic::x86_avx512fp16_mask_vfmadd_csh;
diff --git a/clang/lib/CodeGen/CGCall.cpp b/clang/lib/CodeGen/CGCall.cpp
--- a/clang/lib/CodeGen/CGCall.cpp
+++ b/clang/lib/CodeGen/CGCall.cpp
@@ -2340,7 +2340,7 @@
       RetAttrs.addAttribute(llvm::Attribute::SExt);
     else
       RetAttrs.addAttribute(llvm::Attribute::ZExt);
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case ABIArgInfo::Direct:
     if (RetAI.getInReg())
       RetAttrs.addAttribute(llvm::Attribute::InReg);
@@ -2476,7 +2476,7 @@
         Attrs.addAttribute(llvm::Attribute::SExt);
       else
         Attrs.addAttribute(llvm::Attribute::ZExt);
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case ABIArgInfo::Direct:
       if (ArgNo == 0 && FI.isChainCall())
         Attrs.addAttribute(llvm::Attribute::Nest);
@@ -5550,7 +5550,7 @@
         Builder.CreateStore(elt, eltAddr);
       }
       // FALLTHROUGH
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     }
 
     case ABIArgInfo::InAlloca:
diff --git a/clang/lib/CodeGen/CGClass.cpp b/clang/lib/CodeGen/CGClass.cpp
--- a/clang/lib/CodeGen/CGClass.cpp
+++ b/clang/lib/CodeGen/CGClass.cpp
@@ -1505,7 +1505,7 @@
     }
 
     // Fallthrough: act like we're in the base variant.
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
 
   case Dtor_Base:
     assert(Body);
diff --git a/clang/lib/CodeGen/CGCoroutine.cpp b/clang/lib/CodeGen/CGCoroutine.cpp
--- a/clang/lib/CodeGen/CGCoroutine.cpp
+++ b/clang/lib/CodeGen/CGCoroutine.cpp
@@ -689,7 +689,7 @@
     CGM.Error(E->getBeginLoc(), "this builtin expect that __builtin_coro_id has"
                                 " been used earlier in this function");
     // Fallthrough to the next case to add TokenNone as the first argument.
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   }
   // @llvm.coro.suspend takes a token parameter. Add token 'none' as the first
   // argument.
diff --git a/clang/lib/CodeGen/CGDebugInfo.cpp b/clang/lib/CodeGen/CGDebugInfo.cpp
--- a/clang/lib/CodeGen/CGDebugInfo.cpp
+++ b/clang/lib/CodeGen/CGDebugInfo.cpp
@@ -3613,7 +3613,7 @@
     // them distinct if they are ODR-uniqued.
     if (Identifier.empty())
       break;
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
 
   case llvm::dwarf::DW_TAG_structure_type:
   case llvm::dwarf::DW_TAG_union_type:
diff --git a/clang/lib/CodeGen/CGDecl.cpp b/clang/lib/CodeGen/CGDecl.cpp
--- a/clang/lib/CodeGen/CGDecl.cpp
+++ b/clang/lib/CodeGen/CGDecl.cpp
@@ -839,7 +839,7 @@
     // If D is pseudo-strong, treat it like __unsafe_unretained here. This means
     // that we omit the retain, and causes non-autoreleased return values to be
     // immediately released.
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   }
 
   case Qualifiers::OCL_ExplicitNone:
diff --git a/clang/lib/CodeGen/CGException.cpp b/clang/lib/CodeGen/CGException.cpp
--- a/clang/lib/CodeGen/CGException.cpp
+++ b/clang/lib/CodeGen/CGException.cpp
@@ -158,7 +158,7 @@
   case ObjCRuntime::GNUstep:
     if (L.ObjCRuntime.getVersion() >= VersionTuple(1, 7))
       return EHPersonality::GNUstep_ObjC;
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case ObjCRuntime::GCC:
   case ObjCRuntime::ObjFW:
     if (L.hasSjLjExceptions())
diff --git a/clang/lib/CodeGen/CGExprAgg.cpp b/clang/lib/CodeGen/CGExprAgg.cpp
--- a/clang/lib/CodeGen/CGExprAgg.cpp
+++ b/clang/lib/CodeGen/CGExprAgg.cpp
@@ -850,7 +850,7 @@
       return;
     }
 
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
 
 
   case CK_NoOp:
diff --git a/clang/lib/CodeGen/CGExprCXX.cpp b/clang/lib/CodeGen/CGExprCXX.cpp
--- a/clang/lib/CodeGen/CGExprCXX.cpp
+++ b/clang/lib/CodeGen/CGExprCXX.cpp
@@ -646,7 +646,7 @@
 
      case CXXConstructExpr::CK_VirtualBase:
       ForVirtualBase = true;
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
 
      case CXXConstructExpr::CK_NonVirtualBase:
       Type = Ctor_Base;
diff --git a/clang/lib/CodeGen/CGExprScalar.cpp b/clang/lib/CodeGen/CGExprScalar.cpp
--- a/clang/lib/CodeGen/CGExprScalar.cpp
+++ b/clang/lib/CodeGen/CGExprScalar.cpp
@@ -718,7 +718,7 @@
       case LangOptions::SOB_Undefined:
         if (!CGF.SanOpts.has(SanitizerKind::SignedIntegerOverflow))
           return Builder.CreateNSWMul(Ops.LHS, Ops.RHS, "mul");
-        LLVM_FALLTHROUGH;
+        [[fallthrough]];
       case LangOptions::SOB_Trapping:
         if (CanElideOverflowCheck(CGF.getContext(), Ops))
           return Builder.CreateNSWMul(Ops.LHS, Ops.RHS, "mul");
@@ -2478,7 +2478,7 @@
   case LangOptions::SOB_Undefined:
     if (!CGF.SanOpts.has(SanitizerKind::SignedIntegerOverflow))
       return Builder.CreateNSWAdd(InVal, Amount, Name);
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case LangOptions::SOB_Trapping:
     if (!E->canOverflow())
       return Builder.CreateNSWAdd(InVal, Amount, Name);
@@ -3650,7 +3650,7 @@
     case LangOptions::SOB_Undefined:
       if (!CGF.SanOpts.has(SanitizerKind::SignedIntegerOverflow))
         return Builder.CreateNSWAdd(op.LHS, op.RHS, "add");
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case LangOptions::SOB_Trapping:
       if (CanElideOverflowCheck(CGF.getContext(), op))
         return Builder.CreateNSWAdd(op.LHS, op.RHS, "add");
@@ -3800,7 +3800,7 @@
       case LangOptions::SOB_Undefined:
         if (!CGF.SanOpts.has(SanitizerKind::SignedIntegerOverflow))
           return Builder.CreateNSWSub(op.LHS, op.RHS, "sub");
-        LLVM_FALLTHROUGH;
+        [[fallthrough]];
       case LangOptions::SOB_Trapping:
         if (CanElideOverflowCheck(CGF.getContext(), op))
           return Builder.CreateNSWSub(op.LHS, op.RHS, "sub");
diff --git a/clang/lib/CodeGen/CGObjCRuntime.cpp b/clang/lib/CodeGen/CGObjCRuntime.cpp
--- a/clang/lib/CodeGen/CGObjCRuntime.cpp
+++ b/clang/lib/CodeGen/CGObjCRuntime.cpp
@@ -293,7 +293,7 @@
   switch (paramDecl->getType().getQualifiers().getObjCLifetime()) {
   case Qualifiers::OCL_Strong:
     exn = CGF.EmitARCRetainNonBlock(exn);
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
 
   case Qualifiers::OCL_None:
   case Qualifiers::OCL_ExplicitNone:
diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -5475,7 +5475,7 @@
 
     switch (CFRuntime) {
     default: break;
-    case LangOptions::CoreFoundationABI::Swift: LLVM_FALLTHROUGH;
+    case LangOptions::CoreFoundationABI::Swift: [[fallthrough]];
     case LangOptions::CoreFoundationABI::Swift5_0:
       CFConstantStringClassName =
           Triple.isOSDarwin() ? "$s15SwiftFoundation19_NSCFConstantStringCN"
@@ -6132,7 +6132,7 @@
               TSK_ExplicitInstantiationDefinition &&
           Spec->hasDefinition())
         DI->completeTemplateDefinition(*Spec);
-  } LLVM_FALLTHROUGH;
+  } [[fallthrough]];
   case Decl::CXXRecord: {
     CXXRecordDecl *CRD = cast<CXXRecordDecl>(D);
     if (CGDebugInfo *DI = getModuleDebugInfo()) {
diff --git a/clang/lib/CodeGen/ItaniumCXXABI.cpp b/clang/lib/CodeGen/ItaniumCXXABI.cpp
--- a/clang/lib/CodeGen/ItaniumCXXABI.cpp
+++ b/clang/lib/CodeGen/ItaniumCXXABI.cpp
@@ -3542,7 +3542,7 @@
     }
 
     assert(isa<ObjCInterfaceType>(Ty));
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
 
   case Type::ObjCInterface:
     if (cast<ObjCInterfaceType>(Ty)->getDecl()->getSuperClass()) {
@@ -4515,7 +4515,7 @@
       switch (CatchType.getQualifiers().getObjCLifetime()) {
       case Qualifiers::OCL_Strong:
         CastExn = CGF.EmitARCRetainNonBlock(CastExn);
-        LLVM_FALLTHROUGH;
+        [[fallthrough]];
 
       case Qualifiers::OCL_None:
       case Qualifiers::OCL_ExplicitNone:
diff --git a/clang/lib/CodeGen/MacroPPCallbacks.cpp b/clang/lib/CodeGen/MacroPPCallbacks.cpp
--- a/clang/lib/CodeGen/MacroPPCallbacks.cpp
+++ b/clang/lib/CodeGen/MacroPPCallbacks.cpp
@@ -120,7 +120,7 @@
     if (PP.getSourceManager().isWrittenInCommandLineFile(Loc))
       return;
     updateStatusToNextScope();
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case CommandLineIncludeScope:
     EnteredCommandLineIncludeFiles++;
     break;
diff --git a/clang/lib/CodeGen/VarBypassDetector.cpp b/clang/lib/CodeGen/VarBypassDetector.cpp
--- a/clang/lib/CodeGen/VarBypassDetector.cpp
+++ b/clang/lib/CodeGen/VarBypassDetector.cpp
@@ -77,7 +77,7 @@
         return false;
       ++StmtsToSkip;
     }
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
 
   case Stmt::GotoStmtClass:
     FromScopes.push_back({S, ParentScope});
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -555,7 +555,7 @@
     case llvm::Triple::thumbeb:
       if (Triple.isAndroid())
         return true;
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case llvm::Triple::mips64:
     case llvm::Triple::mips64el:
     case llvm::Triple::mips:
@@ -3010,7 +3010,7 @@
       // If -Ofast is the optimization level, then -ffast-math should be enabled
       if (!OFastEnabled)
         continue;
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case options::OPT_ffast_math:
       HonorINFs = false;
       HonorNaNs = false;
diff --git a/clang/lib/Driver/ToolChains/Gnu.cpp b/clang/lib/Driver/ToolChains/Gnu.cpp
--- a/clang/lib/Driver/ToolChains/Gnu.cpp
+++ b/clang/lib/Driver/ToolChains/Gnu.cpp
@@ -227,7 +227,7 @@
   case llvm::Triple::armeb:
   case llvm::Triple::thumbeb:
     IsBigEndian = true;
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case llvm::Triple::arm:
   case llvm::Triple::thumb:
     if (Arg *A = Args.getLastArg(options::OPT_mlittle_endian,
diff --git a/clang/lib/Driver/ToolChains/Myriad.cpp b/clang/lib/Driver/ToolChains/Myriad.cpp
--- a/clang/lib/Driver/ToolChains/Myriad.cpp
+++ b/clang/lib/Driver/ToolChains/Myriad.cpp
@@ -218,7 +218,7 @@
   default:
     D.Diag(clang::diag::err_target_unsupported_arch)
         << Triple.getArchName() << "myriad";
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case llvm::Triple::shave:
     return;
   case llvm::Triple::sparc:
diff --git a/clang/lib/Edit/RewriteObjCFoundationAPI.cpp b/clang/lib/Edit/RewriteObjCFoundationAPI.cpp
--- a/clang/lib/Edit/RewriteObjCFoundationAPI.cpp
+++ b/clang/lib/Edit/RewriteObjCFoundationAPI.cpp
@@ -796,28 +796,28 @@
   case NSAPI::NSNumberWithUnsignedInt:
   case NSAPI::NSNumberWithUnsignedInteger:
     CallIsUnsigned = true;
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case NSAPI::NSNumberWithInt:
   case NSAPI::NSNumberWithInteger:
     break;
 
   case NSAPI::NSNumberWithUnsignedLong:
     CallIsUnsigned = true;
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case NSAPI::NSNumberWithLong:
     CallIsLong = true;
     break;
 
   case NSAPI::NSNumberWithUnsignedLongLong:
     CallIsUnsigned = true;
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case NSAPI::NSNumberWithLongLong:
     CallIsLongLong = true;
     break;
 
   case NSAPI::NSNumberWithDouble:
     CallIsDouble = true;
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case NSAPI::NSNumberWithFloat:
     CallIsFloating = true;
     break;
diff --git a/clang/lib/ExtractAPI/DeclarationFragments.cpp b/clang/lib/ExtractAPI/DeclarationFragments.cpp
--- a/clang/lib/ExtractAPI/DeclarationFragments.cpp
+++ b/clang/lib/ExtractAPI/DeclarationFragments.cpp
@@ -136,7 +136,7 @@
     Fragments.append("template", DeclarationFragments::FragmentKind::Keyword);
     Fragments.appendSpace();
     // Fallthrough after adding the keyword to handle the actual type.
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
 
   case NestedNameSpecifier::TypeSpec: {
     const Type *T = NNS->getAsType();
diff --git a/clang/lib/Format/FormatTokenLexer.cpp b/clang/lib/Format/FormatTokenLexer.cpp
--- a/clang/lib/Format/FormatTokenLexer.cpp
+++ b/clang/lib/Format/FormatTokenLexer.cpp
@@ -1027,7 +1027,7 @@
         // the same as a single LF.
         if (i + 1 < e && Text[i + 1] == '\n')
           break;
-        LLVM_FALLTHROUGH;
+        [[fallthrough]];
       case '\n':
         ++FormatTok->NewlinesBefore;
         if (!InEscape)
diff --git a/clang/lib/Format/TokenAnnotator.cpp b/clang/lib/Format/TokenAnnotator.cpp
--- a/clang/lib/Format/TokenAnnotator.cpp
+++ b/clang/lib/Format/TokenAnnotator.cpp
@@ -1061,7 +1061,7 @@
           CurrentToken->isOneOf(tok::kw_constexpr, tok::identifier)) {
         next();
       }
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case tok::kw_while:
       if (CurrentToken && CurrentToken->is(tok::l_paren)) {
         next();
diff --git a/clang/lib/Format/UnwrappedLineParser.cpp b/clang/lib/Format/UnwrappedLineParser.cpp
--- a/clang/lib/Format/UnwrappedLineParser.cpp
+++ b/clang/lib/Format/UnwrappedLineParser.cpp
@@ -573,7 +573,7 @@
         break;
       }
       // Else, if it is 'default:', fall through to the case handling.
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     }
     case tok::kw_case:
       if (Style.isVerilog() ||
@@ -600,7 +600,7 @@
       }
       if (handleCppAttributes())
         break;
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     default:
       ParseDefault();
       break;
@@ -736,7 +736,7 @@
     case tok::identifier:
       if (!Tok->is(TT_StatementMacro))
         break;
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case tok::at:
     case tok::semi:
     case tok::kw_if:
@@ -1627,7 +1627,7 @@
     if (!Style.isCpp())
       break;
     // Handle C++ "(inline|export) namespace".
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case tok::kw_inline:
     nextToken();
     if (FormatTok->is(tok::kw_namespace)) {
@@ -1804,7 +1804,7 @@
         addUnwrappedLine();
         return;
       }
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case tok::kw_struct:
     case tok::kw_union:
       if (parseStructLike())
@@ -2531,7 +2531,7 @@
     case tok::ampamp:
       if (AmpAmpTokenType != TT_Unknown)
         FormatTok->setFinalizedType(AmpAmpTokenType);
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     default:
       nextToken();
       break;
diff --git a/clang/lib/Frontend/CompilerInstance.cpp b/clang/lib/Frontend/CompilerInstance.cpp
--- a/clang/lib/Frontend/CompilerInstance.cpp
+++ b/clang/lib/Frontend/CompilerInstance.cpp
@@ -1441,7 +1441,7 @@
           << Module->Name << Locked.getErrorMessage();
       // Clear out any potential leftover.
       Locked.unsafeRemoveLockFile();
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case llvm::LockFileManager::LFS_Owned:
       // We're responsible for building the module ourselves.
       return compileModuleAndReadASTImpl(ImportingInstance, ImportLoc,
@@ -1879,7 +1879,7 @@
                               diag::warn_module_config_mismatch)
           << ModuleFilename;
     // Fall through to error out.
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case ASTReader::VersionMismatch:
   case ASTReader::HadErrors:
     ModuleLoader::HadFatalFailure = true;
diff --git a/clang/lib/Frontend/SerializedDiagnosticReader.cpp b/clang/lib/Frontend/SerializedDiagnosticReader.cpp
--- a/clang/lib/Frontend/SerializedDiagnosticReader.cpp
+++ b/clang/lib/Frontend/SerializedDiagnosticReader.cpp
@@ -184,7 +184,7 @@
         consumeError(std::move(Err));
         return SDError::MalformedMetadataBlock;
       }
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case Cursor::BlockEnd:
       if (!VersionChecked)
         return SDError::MissingVersion;
diff --git a/clang/lib/Index/USRGeneration.cpp b/clang/lib/Index/USRGeneration.cpp
--- a/clang/lib/Index/USRGeneration.cpp
+++ b/clang/lib/Index/USRGeneration.cpp
@@ -963,7 +963,7 @@
 
   case TemplateArgument::TemplateExpansion:
     Out << 'P'; // pack expansion of...
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case TemplateArgument::Template:
     VisitTemplateName(Arg.getAsTemplateOrTemplatePattern());
     break;
diff --git a/clang/lib/Interpreter/IncrementalParser.cpp b/clang/lib/Interpreter/IncrementalParser.cpp
--- a/clang/lib/Interpreter/IncrementalParser.cpp
+++ b/clang/lib/Interpreter/IncrementalParser.cpp
@@ -59,22 +59,22 @@
                 CI.getFrontendOpts().ProgramAction);
             return Act;
           case frontend::ASTDump:
-            LLVM_FALLTHROUGH;
+            [[fallthrough]];
           case frontend::ASTPrint:
-            LLVM_FALLTHROUGH;
+            [[fallthrough]];
           case frontend::ParseSyntaxOnly:
             Act = CreateFrontendAction(CI);
             break;
           case frontend::PluginAction:
-            LLVM_FALLTHROUGH;
+            [[fallthrough]];
           case frontend::EmitAssembly:
-            LLVM_FALLTHROUGH;
+            [[fallthrough]];
           case frontend::EmitBC:
-            LLVM_FALLTHROUGH;
+            [[fallthrough]];
           case frontend::EmitObj:
-            LLVM_FALLTHROUGH;
+            [[fallthrough]];
           case frontend::PrintPreprocessedInput:
-            LLVM_FALLTHROUGH;
+            [[fallthrough]];
           case frontend::EmitLLVMOnly:
             Act.reset(new EmitLLVMOnlyAction(&LLVMCtx));
             break;
diff --git a/clang/lib/Lex/InitHeaderSearch.cpp b/clang/lib/Lex/InitHeaderSearch.cpp
--- a/clang/lib/Lex/InitHeaderSearch.cpp
+++ b/clang/lib/Lex/InitHeaderSearch.cpp
@@ -246,7 +246,7 @@
     case llvm::Triple::Win32:
       if (triple.getEnvironment() != llvm::Triple::Cygnus)
         break;
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     default:
       // FIXME: temporary hack: hard-coded paths.
       AddPath("/usr/local/include", System, false);
diff --git a/clang/lib/Lex/Lexer.cpp b/clang/lib/Lex/Lexer.cpp
--- a/clang/lib/Lex/Lexer.cpp
+++ b/clang/lib/Lex/Lexer.cpp
@@ -2905,7 +2905,7 @@
         break;
       }
       // FALL THROUGH.
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case '\r':
     case '\n':
       // Okay, we found the end of the line. First, back up past the \0, \r, \n.
@@ -3591,7 +3591,7 @@
   case '\r':
     if (CurPtr[0] == '\n')
       (void)getAndAdvanceChar(CurPtr, Result);
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case '\n':
     // If we are inside a preprocessor directive and we see the end of line,
     // we know we are done with the directive, so return an EOD token.
@@ -3788,7 +3788,7 @@
       return LexCharConstant(Result, ConsumeChar(CurPtr, SizeTmp, Result),
                              tok::wide_char_constant);
     // FALL THROUGH, treating L like the start of an identifier.
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
 
   // C99 6.4.2: Identifiers.
   case 'A': case 'B': case 'C': case 'D': case 'E': case 'F': case 'G':
diff --git a/clang/lib/Lex/LiteralSupport.cpp b/clang/lib/Lex/LiteralSupport.cpp
--- a/clang/lib/Lex/LiteralSupport.cpp
+++ b/clang/lib/Lex/LiteralSupport.cpp
@@ -766,13 +766,13 @@
   switch (bytesToWrite) { // note: everything falls through.
   case 4:
     *--ResultBuf = (UTF8)((UcnVal | byteMark) & byteMask); UcnVal >>= 6;
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case 3:
     *--ResultBuf = (UTF8)((UcnVal | byteMark) & byteMask); UcnVal >>= 6;
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case 2:
     *--ResultBuf = (UTF8)((UcnVal | byteMark) & byteMask); UcnVal >>= 6;
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case 1:
     *--ResultBuf = (UTF8) (UcnVal | firstByteMark[bytesToWrite]);
   }
@@ -1037,7 +1037,7 @@
           break;
         }
       }
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case 'j':
     case 'J':
       if (isImaginary) break;   // Cannot be repeated.
diff --git a/clang/lib/Lex/ModuleMap.cpp b/clang/lib/Lex/ModuleMap.cpp
--- a/clang/lib/Lex/ModuleMap.cpp
+++ b/clang/lib/Lex/ModuleMap.cpp
@@ -1668,7 +1668,7 @@
         break;
       }
     }
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
 
   default:
     Diags.Report(Tok.getLocation(), diag::err_mmap_unknown_token);
diff --git a/clang/lib/Lex/Preprocessor.cpp b/clang/lib/Lex/Preprocessor.cpp
--- a/clang/lib/Lex/Preprocessor.cpp
+++ b/clang/lib/Lex/Preprocessor.cpp
@@ -986,7 +986,7 @@
         TrackGMFState.handleModule(ImportSeqState.afterTopLevelSeq());
         break;
       }
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     default:
       TrackGMFState.handleMisc();
       ImportSeqState.handleMisc();
@@ -1232,7 +1232,7 @@
       Suffix.back().setLocation(SemiLoc);
       Suffix.back().setAnnotationEndLoc(SemiLoc);
       Suffix.back().setAnnotationValue(Action.ModuleForHeader);
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
 
     case ImportAction::ModuleImport:
     case ImportAction::HeaderUnitImport:
diff --git a/clang/lib/Lex/TokenConcatenation.cpp b/clang/lib/Lex/TokenConcatenation.cpp
--- a/clang/lib/Lex/TokenConcatenation.cpp
+++ b/clang/lib/Lex/TokenConcatenation.cpp
@@ -240,7 +240,7 @@
     // it as an identifier.
     if (!PrevTok.hasUDSuffix())
       return false;
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case tok::identifier:   // id+id or id+number or id+L"foo".
     // id+'.'... will not append.
     if (Tok.is(tok::numeric_constant))
diff --git a/clang/lib/Parse/ParseCXXInlineMethods.cpp b/clang/lib/Parse/ParseCXXInlineMethods.cpp
--- a/clang/lib/Parse/ParseCXXInlineMethods.cpp
+++ b/clang/lib/Parse/ParseCXXInlineMethods.cpp
@@ -880,7 +880,7 @@
     case tok::semi:
       if (StopAtSemi)
         return false;
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     default:
       // consume this token.
       Toks.push_back(Tok);
@@ -1258,13 +1258,13 @@
         goto consume_token;
       if (AngleCount) --AngleCount;
       if (KnownTemplateCount) --KnownTemplateCount;
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case tok::greatergreater:
       if (!getLangOpts().CPlusPlus11)
         goto consume_token;
       if (AngleCount) --AngleCount;
       if (KnownTemplateCount) --KnownTemplateCount;
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case tok::greater:
       if (AngleCount) --AngleCount;
       if (KnownTemplateCount) --KnownTemplateCount;
@@ -1369,7 +1369,7 @@
     case tok::semi:
       if (CIK == CIK_DefaultInitializer)
         return true; // End of the default initializer.
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     default:
     consume_token:
       Toks.push_back(Tok);
diff --git a/clang/lib/Parse/ParseDecl.cpp b/clang/lib/Parse/ParseDecl.cpp
--- a/clang/lib/Parse/ParseDecl.cpp
+++ b/clang/lib/Parse/ParseDecl.cpp
@@ -2802,7 +2802,7 @@
         }
       }
       // Fall through.
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     }
     case tok::comma:
     case tok::equal:
@@ -4240,13 +4240,13 @@
         isInvalid = true;
         break;
       }
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case tok::kw_private:
       // It's fine (but redundant) to check this for __generic on the
       // fallthrough path; we only form the __generic token in OpenCL mode.
       if (!getLangOpts().OpenCL)
         goto DoneWithDeclSpec;
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case tok::kw___private:
     case tok::kw___global:
     case tok::kw___local:
@@ -5161,7 +5161,7 @@
   case tok::identifier:   // foo::bar
     if (TryAltiVecVectorToken())
       return true;
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case tok::kw_typename:  // typename T::type
     // Annotate typenames and C++ scope specifiers.  If we get one, just
     // recurse to handle whatever we get.
@@ -5304,7 +5304,7 @@
       return false;
     if (TryAltiVecVectorToken())
       return true;
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case tok::kw_decltype: // decltype(T())::type
   case tok::kw_typename: // typename T::type
     // Annotate typenames and C++ scope specifiers.  If we get one, just
@@ -5719,7 +5719,7 @@
     case tok::kw_private:
       if (!getLangOpts().OpenCL)
         goto DoneWithTypeQuals;
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case tok::kw___private:
     case tok::kw___global:
     case tok::kw___local:
@@ -5743,7 +5743,7 @@
         if (TryKeywordIdentFallback(false))
           continue;
       }
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case tok::kw___sptr:
     case tok::kw___w64:
     case tok::kw___ptr64:
@@ -5794,7 +5794,7 @@
         continue; // do *not* consume the next token!
       }
       // otherwise, FALL THROUGH!
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     default:
       DoneWithTypeQuals:
       // If this is not a type-qualifier token, we're done reading type
diff --git a/clang/lib/Parse/ParseDeclCXX.cpp b/clang/lib/Parse/ParseDeclCXX.cpp
--- a/clang/lib/Parse/ParseDeclCXX.cpp
+++ b/clang/lib/Parse/ParseDeclCXX.cpp
@@ -404,7 +404,7 @@
     case tok::r_brace:
       if (!NestedModules)
         break;
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     default:
       ParsedAttributes Attrs(AttrFactory);
       MaybeParseCXX11Attributes(Attrs);
@@ -3242,7 +3242,7 @@
     // yet.
     if (getLangOpts().OpenCL && !NextToken().is(tok::colon))
       return ParseCXXClassMemberDeclaration(AS, AccessAttrs);
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case tok::kw_public:
   case tok::kw_protected: {
     if (getLangOpts().HLSL)
@@ -4717,7 +4717,7 @@
     Diag(Result.KeywordLoc, diag::warn_microsoft_dependent_exists)
         << Result.IsIfExists;
     // Fall through to skip.
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
 
   case IEB_Skip:
     Braces.skipToEnd();
diff --git a/clang/lib/Parse/ParseExpr.cpp b/clang/lib/Parse/ParseExpr.cpp
--- a/clang/lib/Parse/ParseExpr.cpp
+++ b/clang/lib/Parse/ParseExpr.cpp
@@ -945,7 +945,7 @@
       case CastParseKind::UnaryExprOnly:
         if (!getLangOpts().CPlusPlus)
           ParenExprType = CompoundLiteral;
-        LLVM_FALLTHROUGH;
+        [[fallthrough]];
       case CastParseKind::AnyCastExpr:
         ParenExprType = ParenParseOption::CastExpr;
         break;
@@ -1413,7 +1413,7 @@
   case tok::kw__Alignof:   // unary-expression: '_Alignof' '(' type-name ')'
     if (!getLangOpts().C11)
       Diag(Tok, diag::ext_c11_feature) << Tok.getName();
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case tok::kw_alignof:    // unary-expression: 'alignof' '(' type-id ')'
   case tok::kw___alignof:  // unary-expression: '__alignof' unary-expression
                            // unary-expression: '__alignof' '(' type-name ')'
@@ -1502,7 +1502,7 @@
                                            Ty.get(), nullptr);
       break;
     }
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
 
   case tok::annot_decltype:
   case tok::kw_char:
@@ -1621,7 +1621,7 @@
     }
 
     // Fall through to treat the template-id as an id-expression.
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   }
 
   case tok::kw_operator: // [C++] id-expression: operator/conversion-function-id
@@ -1764,7 +1764,7 @@
       Res = ParseObjCMessageExpression();
       break;
     }
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   default:
     NotCastExpr = true;
     return ExprError();
@@ -1795,7 +1795,7 @@
       if (Tok.isAtStartOfLine())
         return Res;
 
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case tok::period:
     case tok::arrow:
       break;
@@ -1883,7 +1883,7 @@
         break;
       }
       // Fall through; this isn't a message send.
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
 
     default:  // Not a postfix-expression suffix.
       return LHS;
diff --git a/clang/lib/Parse/ParseInit.cpp b/clang/lib/Parse/ParseInit.cpp
--- a/clang/lib/Parse/ParseInit.cpp
+++ b/clang/lib/Parse/ParseInit.cpp
@@ -565,7 +565,7 @@
     Diag(Result.KeywordLoc, diag::warn_microsoft_dependent_exists)
       << Result.IsIfExists;
     // Fall through to skip.
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
 
   case IEB_Skip:
     Braces.skipToEnd();
diff --git a/clang/lib/Parse/ParseOpenMP.cpp b/clang/lib/Parse/ParseOpenMP.cpp
--- a/clang/lib/Parse/ParseOpenMP.cpp
+++ b/clang/lib/Parse/ParseOpenMP.cpp
@@ -259,7 +259,7 @@
   case tok::identifier: // identifier
     if (!WithOperator)
       break;
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   default:
     P.Diag(Tok.getLocation(), diag::err_omp_expected_reduction_identifier);
     P.SkipUntil(tok::colon, tok::r_paren, tok::annot_pragma_openmp_end,
@@ -2761,7 +2761,7 @@
     }
     HasAssociatedStatement = false;
     // Fall through for further analysis.
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case OMPD_parallel:
   case OMPD_simd:
   case OMPD_tile:
@@ -3253,7 +3253,7 @@
           << getOpenMPDirectiveName(DKind) << getOpenMPClauseName(CKind) << 0;
       ErrorFound = true;
     }
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case OMPC_if:
     Clause = ParseOpenMPSingleExprWithArgClause(DKind, CKind, WrongDirective);
     break;
@@ -3351,7 +3351,7 @@
       Clause = ParseOpenMPClause(CKind, WrongDirective);
       break;
     }
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case OMPC_init:
   case OMPC_use:
     Clause = ParseOpenMPInteropClause(CKind, WrongDirective);
diff --git a/clang/lib/Parse/ParseStmt.cpp b/clang/lib/Parse/ParseStmt.cpp
--- a/clang/lib/Parse/ParseStmt.cpp
+++ b/clang/lib/Parse/ParseStmt.cpp
@@ -222,7 +222,7 @@
     }
 
     // Fall through
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   }
 
   default: {
@@ -448,7 +448,7 @@
     // processing a #pragma omp clause.
     ProhibitAttributes(CXX11Attrs);
     ProhibitAttributes(GNUAttrs);
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case tok::annot_attr_openmp:
     // Do not prohibit attributes if they were OpenMP attributes.
     return ParseOpenMPDeclarativeOrExecutableDirective(StmtCtx);
diff --git a/clang/lib/Parse/ParseTentative.cpp b/clang/lib/Parse/ParseTentative.cpp
--- a/clang/lib/Parse/ParseTentative.cpp
+++ b/clang/lib/Parse/ParseTentative.cpp
@@ -158,7 +158,7 @@
       ConsumeToken();
       break;
     }
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case tok::kw_typeof:
   case tok::kw___attribute:
   case tok::kw___underlying_type: {
@@ -203,7 +203,7 @@
 
   case tok::annot_cxxscope:
     ConsumeAnnotationToken();
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   default:
     ConsumeAnyToken();
 
@@ -1334,7 +1334,7 @@
     if (Next.isOneOf(tok::kw_new,       // ::new
                      tok::kw_delete))   // ::delete
       return TPResult::False;
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   }
   case tok::kw___super:
   case tok::kw_decltype:
@@ -1401,7 +1401,7 @@
   case tok::kw_private:
     if (!getLangOpts().OpenCL)
       return TPResult::False;
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case tok::kw___private:
   case tok::kw___local:
   case tok::kw___global:
@@ -1573,7 +1573,7 @@
       return TPResult::False;
     }
     // If that succeeded, fallthrough into the generic simple-type-id case.
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
 
     // The ambiguity resides in a simple-type-specifier/typename-specifier
     // followed by a '('. The '(' could either be the start of:
@@ -1616,7 +1616,7 @@
 
       return TPResult::True;
     }
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
 
   case tok::kw_char:
   case tok::kw_wchar_t:
diff --git a/clang/lib/Parse/Parser.cpp b/clang/lib/Parse/Parser.cpp
--- a/clang/lib/Parse/Parser.cpp
+++ b/clang/lib/Parse/Parser.cpp
@@ -386,7 +386,7 @@
     case tok::semi:
       if (HasFlagsSet(Flags, StopAtSemi))
         return false;
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     default:
       // Skip this token.
       ConsumeAnyToken();
@@ -932,7 +932,7 @@
     }
     // This must be 'export template'. Parse it so we can diagnose our lack
     // of support.
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case tok::kw_using:
   case tok::kw_namespace:
   case tok::kw_typedef:
@@ -1830,7 +1830,7 @@
         AnnotateScopeToken(SS, !WasScopeAnnotation);
       return ANK_TemplateName;
     }
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case Sema::NC_VarTemplate:
   case Sema::NC_FunctionTemplate:
   case Sema::NC_UndeclaredTemplate: {
@@ -2167,7 +2167,7 @@
     Diag(Tok, diag::err_invalid_token_after_declarator_suggest_equal)
         << Kind
         << FixItHint::CreateReplacement(SourceRange(Tok.getLocation()), "=");
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case tok::equal:
     return true;
   }
diff --git a/clang/lib/Rewrite/HTMLRewrite.cpp b/clang/lib/Rewrite/HTMLRewrite.cpp
--- a/clang/lib/Rewrite/HTMLRewrite.cpp
+++ b/clang/lib/Rewrite/HTMLRewrite.cpp
@@ -488,14 +488,14 @@
       ++TokOffs;
       --TokLen;
       // FALL THROUGH to chop the 8
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case tok::wide_string_literal:
     case tok::utf16_string_literal:
     case tok::utf32_string_literal:
       // Chop off the L, u, U or 8 prefix
       ++TokOffs;
       --TokLen;
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case tok::string_literal:
       // FIXME: Exclude the optional ud-suffix from the highlighted range.
       HighlightRange(RB, TokOffs, TokOffs+TokLen, BufferStart,
diff --git a/clang/lib/Sema/CodeCompleteConsumer.cpp b/clang/lib/Sema/CodeCompleteConsumer.cpp
--- a/clang/lib/Sema/CodeCompleteConsumer.cpp
+++ b/clang/lib/Sema/CodeCompleteConsumer.cpp
@@ -776,7 +776,7 @@
       // Do nothing: Patterns can come with cursor kinds!
       break;
     }
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
 
   case RK_Declaration: {
     // Set the availability based on attributes.
diff --git a/clang/lib/Sema/JumpDiagnostics.cpp b/clang/lib/Sema/JumpDiagnostics.cpp
--- a/clang/lib/Sema/JumpDiagnostics.cpp
+++ b/clang/lib/Sema/JumpDiagnostics.cpp
@@ -354,7 +354,7 @@
       BuildScopeInformation(Var, ParentScope);
       ++StmtsToSkip;
     }
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
 
   case Stmt::GotoStmtClass:
     // Remember both what scope a goto is in as well as the fact that we have
diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -2108,7 +2108,7 @@
   case Builtin::BI__builtin_alloca_with_align_uninitialized:
     if (SemaBuiltinAllocaWithAlign(TheCall))
       return ExprError();
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case Builtin::BI__builtin_alloca:
   case Builtin::BI__builtin_alloca_uninitialized:
     Diag(TheCall->getBeginLoc(), diag::warn_alloca)
@@ -2485,7 +2485,7 @@
     break;
   case Builtin::BI__builtin_os_log_format:
     Cleanup.setExprNeedsCleanups(true);
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case Builtin::BI__builtin_os_log_format_buffer_size:
     if (SemaBuiltinOSLogFormat(TheCall))
       return ExprError();
@@ -4039,7 +4039,7 @@
   case PPC::BI__builtin_unpack_longdouble:
     if (SemaBuiltinConstantArgRange(TheCall, 1, 0, 1))
       return true;
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case PPC::BI__builtin_pack_longdouble:
     if (&TI.getLongDoubleFormat() != &llvm::APFloat::PPCDoubleDouble())
       return Diag(TheCall->getBeginLoc(), diag::err_ppc_builtin_requires_abi)
@@ -12322,7 +12322,7 @@
           return IntRange(R.Width, /*NonNegative*/ true);
         }
       }
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
 
     case BO_ShlAssign:
       return IntRange::forValueOfType(C, GetExprType(E));
diff --git a/clang/lib/Sema/SemaCodeComplete.cpp b/clang/lib/Sema/SemaCodeComplete.cpp
--- a/clang/lib/Sema/SemaCodeComplete.cpp
+++ b/clang/lib/Sema/SemaCodeComplete.cpp
@@ -1807,7 +1807,7 @@
       Results.AddResult(Result("mutable"));
       Results.AddResult(Result("virtual"));
     }
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
 
   case Sema::PCC_ObjCInterface:
   case Sema::PCC_ObjCImplementation:
@@ -2095,7 +2095,7 @@
       AddObjCTopLevelResults(Results, true);
 
     AddTypedefResult(Results);
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
 
   case Sema::PCC_Class:
     if (SemaRef.getLangOpts().CPlusPlus) {
@@ -2153,7 +2153,7 @@
                            Builder);
       }
     }
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
 
   case Sema::PCC_Template:
   case Sema::PCC_MemberTemplate:
@@ -2423,14 +2423,14 @@
 
     AddStaticAssertResult(Builder, Results, SemaRef.getLangOpts());
   }
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
 
   // Fall through (for statement expressions).
   case Sema::PCC_ForInit:
   case Sema::PCC_Condition:
     AddStorageSpecifiers(CCC, SemaRef.getLangOpts(), Results);
     // Fall through: conditions and statements can have expressions.
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
 
   case Sema::PCC_ParenthesizedExpression:
     if (SemaRef.getLangOpts().ObjCAutoRefCount &&
@@ -2460,7 +2460,7 @@
       Results.AddResult(Result(Builder.TakeString()));
     }
     // Fall through
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
 
   case Sema::PCC_Expression: {
     if (SemaRef.getLangOpts().CPlusPlus) {
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -456,7 +456,7 @@
       }
     }
     // If typo correction failed or was not performed, fall through
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case LookupResult::FoundOverloaded:
   case LookupResult::FoundUnresolvedValue:
     Result.suppressDiagnostics();
@@ -7637,7 +7637,7 @@
     Diag(D.getDeclSpec().getConstexprSpecLoc(),
          diag::err_constexpr_wrong_decl_kind)
         << static_cast<int>(D.getDeclSpec().getConstexprSpecifier());
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
 
   case ConstexprSpecKind::Constexpr:
     NewVD->setConstexpr(true);
@@ -13292,7 +13292,7 @@
       // that has an in-class initializer, so we type-check this like
       // a declaration.
       //
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
 
     case VarDecl::DeclarationOnly:
       // It's only a declaration.
diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -10797,7 +10797,7 @@
           PastFunctionChunk = true;
           break;
         }
-        LLVM_FALLTHROUGH;
+        [[fallthrough]];
       case DeclaratorChunk::Array:
         NeedsTypedef = true;
         extendRight(After, Chunk.getSourceRange());
@@ -15424,7 +15424,7 @@
     if (!Args[1]->isDefaultArgument())
       return false;
 
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case 1:
     return !Args[0]->isDefaultArgument();
   }
@@ -18118,7 +18118,7 @@
   case EST_NoexceptTrue:
     if (!Finder.TraverseStmt(Proto->getNoexceptExpr()))
       return true;
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
 
   case EST_Dynamic:
     for (const auto &E : Proto->exceptions()) {
diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -976,7 +976,7 @@
     DiagRuntimeBehavior(
         E->getBeginLoc(), nullptr,
         PDiag(diag::warn_cxx98_compat_pass_non_pod_arg_to_vararg) << Ty << CT);
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case VAK_Valid:
     if (Ty->isRecordType()) {
       // This is unlikely to be what the user intended. If the class has a
@@ -3391,7 +3391,7 @@
       valueKind = VK_PRValue;
       break;
     }
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
 
   case Decl::ImplicitParam:
   case Decl::ParmVar: {
@@ -3488,7 +3488,7 @@
       valueKind = VK_LValue;
       break;
     }
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
 
   case Decl::CXXConversion:
   case Decl::CXXDestructor:
@@ -14961,7 +14961,7 @@
     break;
   case BO_And:
     checkObjCPointerIntrospection(*this, LHS, RHS, OpLoc);
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case BO_Xor:
   case BO_Or:
     ResultTy = CheckBitwiseOperands(LHS, RHS, OpLoc, Opc);
@@ -15013,7 +15013,7 @@
   case BO_AndAssign:
   case BO_OrAssign: // fallthrough
     DiagnoseSelfAssignment(*this, LHS.get(), RHS.get(), OpLoc, true);
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case BO_XorAssign:
     CompResultTy = CheckBitwiseOperands(LHS, RHS, OpLoc, Opc);
     CompLHSTy = CompResultTy;
diff --git a/clang/lib/Sema/SemaExprCXX.cpp b/clang/lib/Sema/SemaExprCXX.cpp
--- a/clang/lib/Sema/SemaExprCXX.cpp
+++ b/clang/lib/Sema/SemaExprCXX.cpp
@@ -4817,7 +4817,7 @@
   case UTT_HasTrivialDestructor:
   case UTT_HasVirtualDestructor:
     ArgTy = QualType(ArgTy->getBaseElementTypeUnsafe(), 0);
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
 
   // C++1z [meta.unary.prop]:
   //   T shall be a complete type, cv void, or an array of unknown bound.
diff --git a/clang/lib/Sema/SemaExprMember.cpp b/clang/lib/Sema/SemaExprMember.cpp
--- a/clang/lib/Sema/SemaExprMember.cpp
+++ b/clang/lib/Sema/SemaExprMember.cpp
@@ -249,7 +249,7 @@
   case IMA_Field_Uneval_Context:
     Diag(R.getNameLoc(), diag::warn_cxx98_compat_non_static_member_use)
       << R.getLookupNameInfo().getName();
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case IMA_Static:
   case IMA_Abstract:
   case IMA_Mixed_StaticContext:
diff --git a/clang/lib/Sema/SemaInit.cpp b/clang/lib/Sema/SemaInit.cpp
--- a/clang/lib/Sema/SemaInit.cpp
+++ b/clang/lib/Sema/SemaInit.cpp
@@ -86,7 +86,7 @@
     // char8_t array can be initialized with a UTF-8 string.
     if (ElemTy->isChar8Type())
       return SIF_None;
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case StringLiteral::Ordinary:
     // char array can be initialized with a narrow string.
     // Only allow char x[] = "foo";  not char x[] = L"foo";
@@ -7572,7 +7572,7 @@
     case IndirectLocalPathEntry::VarInit:
       if (cast<VarDecl>(Path[I].D)->isImplicit())
         return SourceRange();
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case IndirectLocalPathEntry::DefaultInit:
       return Path[I].E->getSourceRange();
 
@@ -8739,7 +8739,7 @@
         << Step->Type << CurInit.get()->getType()
         << CurInit.get()->getSourceRange();
       updateGNUCompoundLiteralRValue(CurInit.get());
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case SK_ArrayInit:
       // If the destination type is an incomplete array type, update the
       // type accordingly.
@@ -9201,7 +9201,7 @@
       << Args[0]->getSourceRange();
       break;
     }
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
 
   case FK_NonConstLValueReferenceBindingToUnrelated:
     S.Diag(Kind.getLocation(),
diff --git a/clang/lib/Sema/SemaLambda.cpp b/clang/lib/Sema/SemaLambda.cpp
--- a/clang/lib/Sema/SemaLambda.cpp
+++ b/clang/lib/Sema/SemaLambda.cpp
@@ -335,7 +335,7 @@
     if (!IsInNonspecializedTemplate)
       return std::make_tuple(nullptr, ManglingContextDecl);
     // Fall through to get the current context.
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
 
   case DataMember:
     //  -- the in-class initializers of class members
diff --git a/clang/lib/Sema/SemaLookup.cpp b/clang/lib/Sema/SemaLookup.cpp
--- a/clang/lib/Sema/SemaLookup.cpp
+++ b/clang/lib/Sema/SemaLookup.cpp
@@ -3142,7 +3142,7 @@
       for (const auto &Arg : Proto->param_types())
         Queue.push_back(Arg.getTypePtr());
       // fallthrough
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     }
     case Type::FunctionNoProto: {
       const FunctionType *FnType = cast<FunctionType>(T);
diff --git a/clang/lib/Sema/SemaOpenMP.cpp b/clang/lib/Sema/SemaOpenMP.cpp
--- a/clang/lib/Sema/SemaOpenMP.cpp
+++ b/clang/lib/Sema/SemaOpenMP.cpp
@@ -12279,7 +12279,7 @@
     case OMPC_write:
     case OMPC_update:
       MutexClauseEncountered = true;
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case OMPC_capture:
     case OMPC_compare: {
       if (AtomicKind != OMPC_unknown && MutexClauseEncountered) {
@@ -15168,7 +15168,7 @@
         CaptureRegion = OMPD_parallel;
         break;
       }
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case OMPD_target_parallel:
     case OMPD_target_parallel_for:
     case OMPD_target_parallel_loop:
@@ -15183,7 +15183,7 @@
         CaptureRegion = OMPD_parallel;
         break;
       }
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case OMPD_target_teams_distribute_parallel_for:
       // If this clause applies to the nested 'parallel' region, capture within
       // the 'teams' region, otherwise do not capture.
@@ -15196,7 +15196,7 @@
         CaptureRegion = OMPD_parallel;
         break;
       }
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case OMPD_teams_distribute_parallel_for:
       CaptureRegion = OMPD_teams;
       break;
diff --git a/clang/lib/Sema/SemaOverload.cpp b/clang/lib/Sema/SemaOverload.cpp
--- a/clang/lib/Sema/SemaOverload.cpp
+++ b/clang/lib/Sema/SemaOverload.cpp
@@ -6241,7 +6241,7 @@
                                      HadMultipleCandidates,
                                      ExplicitConversions))
         return ExprError();
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case OR_Deleted:
       // We'll complain below about a non-integral condition type.
       break;
@@ -9311,7 +9311,7 @@
   case OO_Plus: // '+' is either unary or binary
     if (Args.size() == 1)
       OpBuilder.addUnaryPlusPointerOverloads();
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
 
   case OO_Minus: // '-' is either unary or binary
     if (Args.size() == 1) {
@@ -9386,12 +9386,12 @@
 
   case OO_Equal:
     OpBuilder.addAssignmentMemberPointerOrEnumeralOverloads();
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
 
   case OO_PlusEqual:
   case OO_MinusEqual:
     OpBuilder.addAssignmentPointerOverloads(Op == OO_Equal);
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
 
   case OO_StarEqual:
   case OO_SlashEqual:
diff --git a/clang/lib/Sema/SemaStmt.cpp b/clang/lib/Sema/SemaStmt.cpp
--- a/clang/lib/Sema/SemaStmt.cpp
+++ b/clang/lib/Sema/SemaStmt.cpp
@@ -2660,7 +2660,7 @@
                                   SemaRef.PDiag(diag::err_for_range_invalid)
                                       << BeginRange->getType() << BEFFound),
               SemaRef, OCD_AllCandidates, BeginRange);
-          LLVM_FALLTHROUGH;
+          [[fallthrough]];
 
         case Sema::FRS_DiagnosticIssued:
           for (NamedDecl *D : OldFound) {
diff --git a/clang/lib/Sema/SemaStmtAsm.cpp b/clang/lib/Sema/SemaStmtAsm.cpp
--- a/clang/lib/Sema/SemaStmtAsm.cpp
+++ b/clang/lib/Sema/SemaStmtAsm.cpp
@@ -330,7 +330,7 @@
       if (RequireCompleteType(OutputExpr->getBeginLoc(), Exprs[i]->getType(),
                               diag::err_dereference_incomplete_type))
         return StmtError();
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     default:
       return StmtError(Diag(OutputExpr->getBeginLoc(),
                             diag::err_asm_invalid_lvalue_in_output)
diff --git a/clang/lib/Sema/SemaTemplate.cpp b/clang/lib/Sema/SemaTemplate.cpp
--- a/clang/lib/Sema/SemaTemplate.cpp
+++ b/clang/lib/Sema/SemaTemplate.cpp
@@ -5085,7 +5085,7 @@
       }
     }
     // fallthrough
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   }
   default: {
     // We have a template type parameter but the template argument
@@ -8849,7 +8849,7 @@
         return false;
       }
       // Fall through
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
 
     case TSK_ExplicitInstantiationDeclaration:
     case TSK_ExplicitInstantiationDefinition:
@@ -10750,7 +10750,7 @@
   }
   // Fall through to create a dependent typename type, from which we can recover
   // better.
-  LLVM_FALLTHROUGH;
+  [[fallthrough]];
 
   case LookupResult::NotFoundInCurrentInstantiation:
     // Okay, it's a member of an unknown instantiation.
diff --git a/clang/lib/Sema/SemaTemplateDeduction.cpp b/clang/lib/Sema/SemaTemplateDeduction.cpp
--- a/clang/lib/Sema/SemaTemplateDeduction.cpp
+++ b/clang/lib/Sema/SemaTemplateDeduction.cpp
@@ -1587,7 +1587,7 @@
       // FIXME: Implement deduction in dependent case.
       if (P->isDependentType())
         return Sema::TDK_Success;
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case Type::Builtin:
     case Type::VariableArray:
     case Type::Vector:
@@ -1775,7 +1775,7 @@
         switch (FPA->canThrow()) {
         case CT_Cannot:
           Noexcept = 1;
-          LLVM_FALLTHROUGH;
+          [[fallthrough]];
 
         case CT_Can:
           // We give E in noexcept(E) the "deduced from array bound" treatment.
@@ -5741,7 +5741,7 @@
                                cast<DependentSizedArrayType>(T)->getSizeExpr(),
                                OnlyDeduced, Depth, Used);
     // Fall through to check the element type
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
 
   case Type::ConstantArray:
   case Type::IncompleteArray:
@@ -5851,7 +5851,7 @@
 
   case Type::InjectedClassName:
     T = cast<InjectedClassNameType>(T)->getInjectedSpecializationType();
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
 
   case Type::TemplateSpecialization: {
     const TemplateSpecializationType *Spec
diff --git a/clang/lib/Sema/SemaTemplateInstantiate.cpp b/clang/lib/Sema/SemaTemplateInstantiate.cpp
--- a/clang/lib/Sema/SemaTemplateInstantiate.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiate.cpp
@@ -864,7 +864,7 @@
       // context, depending on what else is on the stack.
       if (isa<TypeAliasTemplateDecl>(Active->Entity))
         break;
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case CodeSynthesisContext::DefaultFunctionArgumentInstantiation:
     case CodeSynthesisContext::ExceptionSpecInstantiation:
     case CodeSynthesisContext::ConstraintsCheck:
diff --git a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
--- a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -633,7 +633,7 @@
           FD->getReturnType()->isLValueReferenceType()) {
         return false;
       }
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case Builtin::BImove:
     case Builtin::BImove_if_noexcept:
       // HACK: Super-old versions of libc++ (3.1 and earlier) provide
diff --git a/clang/lib/Sema/SemaType.cpp b/clang/lib/Sema/SemaType.cpp
--- a/clang/lib/Sema/SemaType.cpp
+++ b/clang/lib/Sema/SemaType.cpp
@@ -430,7 +430,7 @@
           if (onlyBlockPointers)
             continue;
 
-          LLVM_FALLTHROUGH;
+          [[fallthrough]];
 
         case DeclaratorChunk::BlockPointer:
           result = &ptrChunk;
@@ -1369,7 +1369,7 @@
       }
     }
 
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case DeclSpec::TST_int: {
     if (DS.getTypeSpecSign() != TypeSpecifierSign::Unsigned) {
       switch (DS.getTypeSpecWidth()) {
@@ -3540,7 +3540,7 @@
           !D.getNumTypeObjects() &&
           D.getDeclSpec().getParsedSpecifiers() == DeclSpec::PQ_TypeSpecifier)
         break;
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case DeclaratorContext::TemplateTypeArg:
       Error = 10; // Template type argument
       break;
@@ -3565,7 +3565,7 @@
       if (SemaRef.getLangOpts().CPlusPlus2b && IsCXXAutoType &&
           !Auto->isDecltypeAuto())
         break; // auto(x)
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case DeclaratorContext::TypeName:
     case DeclaratorContext::Association:
       Error = 15; // Generic
@@ -3834,7 +3834,7 @@
     case DeclaratorChunk::Paren:
       if (&C == &Paren)
         continue;
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case DeclaratorChunk::Pointer:
       StartsWithDeclaratorId = false;
       continue;
@@ -4674,7 +4674,7 @@
     case DeclaratorContext::TrailingReturn:
     case DeclaratorContext::TrailingReturnVar:
       isFunctionOrMethod = true;
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
 
     case DeclaratorContext::Member:
       if (state.getDeclarator().isObjCIvar() && !isFunctionOrMethod) {
@@ -4688,7 +4688,7 @@
         break;
       }
 
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
 
     case DeclaratorContext::File:
     case DeclaratorContext::KNRTypeList: {
@@ -4843,7 +4843,7 @@
     case CAMN_InnerPointers:
       if (NumPointersRemaining == 0)
         break;
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
 
     case CAMN_Yes:
       checkNullabilityConsistency(S, pointerKind, pointerLoc, pointerEndLoc);
@@ -7714,7 +7714,7 @@
       case EST_NoexceptTrue:
       case EST_NoThrow:
         // Exception spec doesn't conflict with nothrow, so don't warn.
-        LLVM_FALLTHROUGH;
+        [[fallthrough]];
       case EST_Unparsed:
       case EST_Uninstantiated:
       case EST_DependentNoexcept:
@@ -8443,7 +8443,7 @@
     // clang, so revert to attribute-based handling for C.
       if (!state.getSema().getLangOpts().CPlusPlus)
         break;
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     FUNCTION_TYPE_ATTRS_CASELIST:
       attr.setUsedAsTypeAttr();
 
diff --git a/clang/lib/Serialization/ASTReader.cpp b/clang/lib/Serialization/ASTReader.cpp
--- a/clang/lib/Serialization/ASTReader.cpp
+++ b/clang/lib/Serialization/ASTReader.cpp
@@ -1275,10 +1275,10 @@
         switch (NumArgs) {
         case 3:
           Arg3 = Diag.getStringArg(2);
-          LLVM_FALLTHROUGH;
+          [[fallthrough]];
         case 2:
           Arg2 = Diag.getStringArg(1);
-          LLVM_FALLTHROUGH;
+          [[fallthrough]];
         case 1:
           Arg1 = Diag.getStringArg(0);
         }
diff --git a/clang/lib/StaticAnalyzer/Checkers/DeadStoresChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/DeadStoresChecker.cpp
--- a/clang/lib/StaticAnalyzer/Checkers/DeadStoresChecker.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/DeadStoresChecker.cpp
@@ -240,7 +240,7 @@
 
       case DeadIncrement:
         BugType = "Dead increment";
-        LLVM_FALLTHROUGH;
+        [[fallthrough]];
       case Standard:
         if (!BugType) BugType = "Dead assignment";
         os << "Value stored to '" << *V << "' is never read";
diff --git a/clang/lib/StaticAnalyzer/Checkers/MoveChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/MoveChecker.cpp
--- a/clang/lib/StaticAnalyzer/Checkers/MoveChecker.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/MoveChecker.cpp
@@ -309,7 +309,7 @@
 
       // If it's not a dereference, we don't care if it was reset to null
       // or that it is even a smart pointer.
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case SK_NonStd:
     case SK_Safe:
       OS << "Object";
@@ -587,7 +587,7 @@
         break;
 
       // We only care about the type if it's a dereference.
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case SK_Unsafe:
       OS << " of type '" << RD->getQualifiedNameAsString() << "'";
       break;
diff --git a/clang/lib/StaticAnalyzer/Checkers/RetainCountChecker/RetainCountChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/RetainCountChecker/RetainCountChecker.cpp
--- a/clang/lib/StaticAnalyzer/Checkers/RetainCountChecker/RetainCountChecker.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/RetainCountChecker/RetainCountChecker.cpp
@@ -767,7 +767,7 @@
         break;
       }
 
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
 
     case DoNothing:
       return state;
diff --git a/clang/lib/StaticAnalyzer/Core/ExprEngine.cpp b/clang/lib/StaticAnalyzer/Core/ExprEngine.cpp
--- a/clang/lib/StaticAnalyzer/Core/ExprEngine.cpp
+++ b/clang/lib/StaticAnalyzer/Core/ExprEngine.cpp
@@ -1793,7 +1793,7 @@
         }
       }
       // FALLTHROUGH
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     }
 
     case Stmt::CallExprClass:
diff --git a/clang/lib/StaticAnalyzer/Core/ExprEngineC.cpp b/clang/lib/StaticAnalyzer/Core/ExprEngineC.cpp
--- a/clang/lib/StaticAnalyzer/Core/ExprEngineC.cpp
+++ b/clang/lib/StaticAnalyzer/Core/ExprEngineC.cpp
@@ -524,7 +524,7 @@
         }
         // Explicitly proceed with default handler for this case cascade.
       }
-        LLVM_FALLTHROUGH;
+        [[fallthrough]];
       // Various C++ casts that are not handled yet.
       case CK_ToUnion:
       case CK_MatrixCast:
@@ -1001,7 +1001,7 @@
     }
     case UO_Plus:
       assert(!U->isGLValue());
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case UO_Deref:
     case UO_Extension: {
       handleUOExtension(I, U, Bldr);
diff --git a/clang/lib/StaticAnalyzer/Core/ExprEngineCXX.cpp b/clang/lib/StaticAnalyzer/Core/ExprEngineCXX.cpp
--- a/clang/lib/StaticAnalyzer/Core/ExprEngineCXX.cpp
+++ b/clang/lib/StaticAnalyzer/Core/ExprEngineCXX.cpp
@@ -263,7 +263,7 @@
       // a simple temporary.
       CallOpts = PreElideCallOpts;
       CallOpts.IsElidableCtorThatHasNotBeenElided = true;
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     }
     case ConstructionContext::SimpleTemporaryObjectKind: {
       const auto *TCC = cast<TemporaryObjectConstructionContext>(CC);
@@ -455,7 +455,7 @@
       }
       // If we decided not to elide the constructor, proceed as if
       // it's a simple temporary.
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     }
     case ConstructionContext::SimpleTemporaryObjectKind: {
       const auto *TCC = cast<TemporaryObjectConstructionContext>(CC);
@@ -620,7 +620,7 @@
         ("This virtual base should have already been initialized by "
          "the most derived class!"));
     (void)OuterCtor;
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   }
   case CXXConstructExpr::CK_NonVirtualBase:
     // In C++17, classes with non-virtual bases may be aggregates, so they would
@@ -640,7 +640,7 @@
       CallOpts.IsCtorOrDtorWithImproperlyModeledTargetRegion = true;
       break;
     }
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case CXXConstructExpr::CK_Delegating: {
     const CXXMethodDecl *CurCtor = cast<CXXMethodDecl>(LCtx->getDecl());
     Loc ThisPtr = getSValBuilder().getCXXThis(CurCtor,
diff --git a/clang/lib/StaticAnalyzer/Core/ExprEngineCallAndReturn.cpp b/clang/lib/StaticAnalyzer/Core/ExprEngineCallAndReturn.cpp
--- a/clang/lib/StaticAnalyzer/Core/ExprEngineCallAndReturn.cpp
+++ b/clang/lib/StaticAnalyzer/Core/ExprEngineCallAndReturn.cpp
@@ -894,7 +894,7 @@
     break;
   }
   case CE_CXXDeallocator:
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case CE_CXXAllocator:
     if (Opts.MayInlineCXXAllocator)
       break;
diff --git a/clang/lib/StaticAnalyzer/Core/RegionStore.cpp b/clang/lib/StaticAnalyzer/Core/RegionStore.cpp
--- a/clang/lib/StaticAnalyzer/Core/RegionStore.cpp
+++ b/clang/lib/StaticAnalyzer/Core/RegionStore.cpp
@@ -1354,11 +1354,11 @@
   case GFK_All:
     B = invalidateGlobalRegion(MemRegion::GlobalInternalSpaceRegionKind,
                                Ex, Count, LCtx, B, Invalidated);
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case GFK_SystemOnly:
     B = invalidateGlobalRegion(MemRegion::GlobalSystemSpaceRegionKind,
                                Ex, Count, LCtx, B, Invalidated);
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case GFK_None:
     break;
   }
diff --git a/clang/lib/StaticAnalyzer/Core/SValBuilder.cpp b/clang/lib/StaticAnalyzer/Core/SValBuilder.cpp
--- a/clang/lib/StaticAnalyzer/Core/SValBuilder.cpp
+++ b/clang/lib/StaticAnalyzer/Core/SValBuilder.cpp
@@ -396,7 +396,7 @@
     }
     }
     // FALLTHROUGH
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   }
 
   // If we don't have a special case, fall back to the AST's constant evaluator.
diff --git a/clang/lib/StaticAnalyzer/Core/SimpleSValBuilder.cpp b/clang/lib/StaticAnalyzer/Core/SimpleSValBuilder.cpp
--- a/clang/lib/StaticAnalyzer/Core/SimpleSValBuilder.cpp
+++ b/clang/lib/StaticAnalyzer/Core/SimpleSValBuilder.cpp
@@ -544,7 +544,7 @@
       case BO_LE:
       case BO_GE:
         op = BinaryOperator::reverseComparisonOp(op);
-        LLVM_FALLTHROUGH;
+        [[fallthrough]];
       case BO_EQ:
       case BO_NE:
       case BO_Add:
@@ -558,7 +558,7 @@
         // (~0)>>a
         if (LHSValue.isAllOnes() && LHSValue.isSigned())
           return evalCast(lhs, resultTy, QualType{});
-        LLVM_FALLTHROUGH;
+        [[fallthrough]];
       case BO_Shl:
         // 0<<a and 0>>a
         if (LHSValue == 0)
@@ -570,7 +570,7 @@
         // 0 % x == 0
         if (LHSValue == 0)
           return makeZeroVal(resultTy);
-        LLVM_FALLTHROUGH;
+        [[fallthrough]];
       default:
         return makeSymExprValNN(op, InputLHS, InputRHS, resultTy);
       }
diff --git a/clang/utils/TableGen/NeonEmitter.cpp b/clang/utils/TableGen/NeonEmitter.cpp
--- a/clang/utils/TableGen/NeonEmitter.cpp
+++ b/clang/utils/TableGen/NeonEmitter.cpp
@@ -817,19 +817,19 @@
       break;
     case 'h':
       Kind = Float;
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case 's':
       ElementBitwidth = 16;
       break;
     case 'f':
       Kind = Float;
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case 'i':
       ElementBitwidth = 32;
       break;
     case 'd':
       Kind = Float;
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case 'l':
       ElementBitwidth = 64;
       break;
diff --git a/clang/utils/TableGen/SveEmitter.cpp b/clang/utils/TableGen/SveEmitter.cpp
--- a/clang/utils/TableGen/SveEmitter.cpp
+++ b/clang/utils/TableGen/SveEmitter.cpp
@@ -523,7 +523,7 @@
     break;
   case 'c':
     Constant = true;
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   case 'p':
     Pointer = true;
     Bitwidth = ElementBitwidth;