diff --git a/flang/include/flang/Lower/BoxAnalyzer.h b/flang/include/flang/Lower/BoxAnalyzer.h
index 2543c443acc96..07588e8410c96 100644
--- a/flang/include/flang/Lower/BoxAnalyzer.h
+++ b/flang/include/flang/Lower/BoxAnalyzer.h
@@ -17,6 +17,7 @@
 #include "flang/Lower/Support/Utils.h"
 #include "flang/Optimizer/Dialect/FIRType.h"
 #include "flang/Optimizer/Support/Matcher.h"
+#include <optional>
 
 namespace Fortran::lower {
 
diff --git a/flang/include/flang/Lower/ComponentPath.h b/flang/include/flang/Lower/ComponentPath.h
index b95f4a38dba2b..fb8395ba008d4 100644
--- a/flang/include/flang/Lower/ComponentPath.h
+++ b/flang/include/flang/Lower/ComponentPath.h
@@ -11,6 +11,7 @@
 
 #include "flang/Lower/IterationSpace.h"
 #include "llvm/ADT/SmallVector.h"
+#include <optional>
 
 namespace fir {
 class ArrayLoadOp;
diff --git a/flang/include/flang/Lower/ConvertCall.h b/flang/include/flang/Lower/ConvertCall.h
index c38e48685db4e..33008a17457f5 100644
--- a/flang/include/flang/Lower/ConvertCall.h
+++ b/flang/include/flang/Lower/ConvertCall.h
@@ -20,6 +20,7 @@
 #include "flang/Lower/AbstractConverter.h"
 #include "flang/Lower/CallInterface.h"
 #include "flang/Optimizer/Builder/HLFIRTools.h"
+#include <optional>
 
 namespace Fortran::lower {
 
diff --git a/flang/include/flang/Lower/ConvertExpr.h b/flang/include/flang/Lower/ConvertExpr.h
index 0fa0f5749dfc9..bf681e9a96924 100644
--- a/flang/include/flang/Lower/ConvertExpr.h
+++ b/flang/include/flang/Lower/ConvertExpr.h
@@ -20,6 +20,7 @@
 #include "flang/Lower/Support/Utils.h"
 #include "flang/Optimizer/Builder/BoxValue.h"
 #include "flang/Optimizer/Builder/FIRBuilder.h"
+#include <optional>
 
 namespace mlir {
 class Location;
diff --git a/flang/include/flang/Lower/CustomIntrinsicCall.h b/flang/include/flang/Lower/CustomIntrinsicCall.h
index 673c26b168387..9ae84fd62362a 100644
--- a/flang/include/flang/Lower/CustomIntrinsicCall.h
+++ b/flang/include/flang/Lower/CustomIntrinsicCall.h
@@ -27,6 +27,7 @@
 #include "flang/Lower/AbstractConverter.h"
 #include "llvm/ADT/Optional.h"
 #include <functional>
+#include <optional>
 
 namespace Fortran {
 
diff --git a/flang/include/flang/Lower/IntrinsicCall.h b/flang/include/flang/Lower/IntrinsicCall.h
index 0846c6d38c431..cd7c7a622cd05 100644
--- a/flang/include/flang/Lower/IntrinsicCall.h
+++ b/flang/include/flang/Lower/IntrinsicCall.h
@@ -11,6 +11,7 @@
 
 #include "flang/Optimizer/Builder/FIRBuilder.h"
 #include "llvm/ADT/Optional.h"
+#include <optional>
 
 namespace fir {
 class ExtendedValue;
diff --git a/flang/include/flang/Lower/IterationSpace.h b/flang/include/flang/Lower/IterationSpace.h
index 218e9e1d0fbd6..a7de970b4c74b 100644
--- a/flang/include/flang/Lower/IterationSpace.h
+++ b/flang/include/flang/Lower/IterationSpace.h
@@ -17,6 +17,7 @@
 #include "flang/Lower/StatementContext.h"
 #include "flang/Lower/SymbolMap.h"
 #include "flang/Optimizer/Builder/FIRBuilder.h"
+#include <optional>
 
 namespace llvm {
 class raw_ostream;
diff --git a/flang/include/flang/Lower/SymbolMap.h b/flang/include/flang/Lower/SymbolMap.h
index 1ad0427091eb5..f3450f5b23564 100644
--- a/flang/include/flang/Lower/SymbolMap.h
+++ b/flang/include/flang/Lower/SymbolMap.h
@@ -25,6 +25,7 @@
 #include "llvm/ADT/Optional.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/Support/Compiler.h"
+#include <optional>
 
 namespace Fortran::lower {
 
diff --git a/flang/include/flang/Optimizer/Builder/FIRBuilder.h b/flang/include/flang/Optimizer/Builder/FIRBuilder.h
index 4d89e5b2931ef..b44d9faf6fe23 100644
--- a/flang/include/flang/Optimizer/Builder/FIRBuilder.h
+++ b/flang/include/flang/Optimizer/Builder/FIRBuilder.h
@@ -25,6 +25,7 @@
 #include "mlir/IR/BuiltinOps.h"
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/Optional.h"
+#include <optional>
 
 namespace fir {
 class AbstractArrayBox;
diff --git a/flang/include/flang/Optimizer/Builder/HLFIRTools.h b/flang/include/flang/Optimizer/Builder/HLFIRTools.h
index d83766c9f0c7f..cb37484a934e0 100644
--- a/flang/include/flang/Optimizer/Builder/HLFIRTools.h
+++ b/flang/include/flang/Optimizer/Builder/HLFIRTools.h
@@ -17,6 +17,7 @@
 #include "flang/Optimizer/Dialect/FIROps.h"
 #include "flang/Optimizer/Dialect/FortranVariableInterface.h"
 #include "flang/Optimizer/HLFIR/HLFIRDialect.h"
+#include <optional>
 
 namespace fir {
 class FirOpBuilder;
diff --git a/flang/lib/Frontend/CompilerInvocation.cpp b/flang/lib/Frontend/CompilerInvocation.cpp
index 33ec6af3a2276..b17d197ff98b5 100644
--- a/flang/lib/Frontend/CompilerInvocation.cpp
+++ b/flang/lib/Frontend/CompilerInvocation.cpp
@@ -36,6 +36,7 @@
 #include "llvm/Support/Process.h"
 #include "llvm/Support/raw_ostream.h"
 #include <memory>
+#include <optional>
 
 using namespace Fortran::frontend;
 
diff --git a/flang/lib/Lower/Bridge.cpp b/flang/lib/Lower/Bridge.cpp
index fb94218b606ae..c5551ff0810e2 100644
--- a/flang/lib/Lower/Bridge.cpp
+++ b/flang/lib/Lower/Bridge.cpp
@@ -58,6 +58,7 @@
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/ErrorHandling.h"
+#include <optional>
 
 #define DEBUG_TYPE "flang-lower-bridge"
 
diff --git a/flang/lib/Lower/CallInterface.cpp b/flang/lib/Lower/CallInterface.cpp
index bc622f35e48cf..41be1b0eabcdc 100644
--- a/flang/lib/Lower/CallInterface.cpp
+++ b/flang/lib/Lower/CallInterface.cpp
@@ -21,6 +21,7 @@
 #include "flang/Optimizer/Support/InternalNames.h"
 #include "flang/Semantics/symbol.h"
 #include "flang/Semantics/tools.h"
+#include <optional>
 
 //===----------------------------------------------------------------------===//
 // BIND(C) mangling helpers
diff --git a/flang/lib/Lower/ConvertCall.cpp b/flang/lib/Lower/ConvertCall.cpp
index 4b69d972bc709..926f6ce207dd6 100644
--- a/flang/lib/Lower/ConvertCall.cpp
+++ b/flang/lib/Lower/ConvertCall.cpp
@@ -26,6 +26,7 @@
 #include "flang/Optimizer/Dialect/FIROpsSupport.h"
 #include "flang/Optimizer/HLFIR/HLFIROps.h"
 #include "llvm/Support/Debug.h"
+#include <optional>
 
 #define DEBUG_TYPE "flang-lower-expr"
 
diff --git a/flang/lib/Lower/ConvertExpr.cpp b/flang/lib/Lower/ConvertExpr.cpp
index 035ccad37b875..bbac1d8967e5e 100644
--- a/flang/lib/Lower/ConvertExpr.cpp
+++ b/flang/lib/Lower/ConvertExpr.cpp
@@ -57,6 +57,7 @@
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/raw_ostream.h"
 #include <algorithm>
+#include <optional>
 
 #define DEBUG_TYPE "flang-lower-expr"
 
diff --git a/flang/lib/Lower/ConvertExprToHLFIR.cpp b/flang/lib/Lower/ConvertExprToHLFIR.cpp
index 481c04fdbd4db..35d4047722f36 100644
--- a/flang/lib/Lower/ConvertExprToHLFIR.cpp
+++ b/flang/lib/Lower/ConvertExprToHLFIR.cpp
@@ -25,6 +25,7 @@
 #include "flang/Optimizer/Builder/Todo.h"
 #include "flang/Optimizer/HLFIR/HLFIROps.h"
 #include "llvm/ADT/TypeSwitch.h"
+#include <optional>
 
 namespace {
 
diff --git a/flang/lib/Lower/ConvertVariable.cpp b/flang/lib/Lower/ConvertVariable.cpp
index 2279d745c1ead..b7931ae9c0080 100644
--- a/flang/lib/Lower/ConvertVariable.cpp
+++ b/flang/lib/Lower/ConvertVariable.cpp
@@ -38,6 +38,7 @@
 #include "flang/Semantics/runtime-type-info.h"
 #include "flang/Semantics/tools.h"
 #include "llvm/Support/Debug.h"
+#include <optional>
 
 #define DEBUG_TYPE "flang-lower-variable"
 
diff --git a/flang/lib/Lower/CustomIntrinsicCall.cpp b/flang/lib/Lower/CustomIntrinsicCall.cpp
index 7772be4071e57..b4fb1463a01dd 100644
--- a/flang/lib/Lower/CustomIntrinsicCall.cpp
+++ b/flang/lib/Lower/CustomIntrinsicCall.cpp
@@ -16,6 +16,7 @@
 #include "flang/Evaluate/tools.h"
 #include "flang/Lower/IntrinsicCall.h"
 #include "flang/Optimizer/Builder/Todo.h"
+#include <optional>
 
 /// Is this a call to MIN or MAX intrinsic with arguments that may be absent at
 /// runtime? This is a special case because MIN and MAX can have any number of
diff --git a/flang/lib/Lower/HostAssociations.cpp b/flang/lib/Lower/HostAssociations.cpp
index 1c36b263e6baf..90a43bca29a87 100644
--- a/flang/lib/Lower/HostAssociations.cpp
+++ b/flang/lib/Lower/HostAssociations.cpp
@@ -23,6 +23,7 @@
 #include "flang/Semantics/tools.h"
 #include "llvm/ADT/TypeSwitch.h"
 #include "llvm/Support/Debug.h"
+#include <optional>
 
 #define DEBUG_TYPE "flang-host-assoc"
 
diff --git a/flang/lib/Lower/IO.cpp b/flang/lib/Lower/IO.cpp
index 288878c830183..d1e9af5d0d8d8 100644
--- a/flang/lib/Lower/IO.cpp
+++ b/flang/lib/Lower/IO.cpp
@@ -34,6 +34,7 @@
 #include "flang/Semantics/tools.h"
 #include "mlir/Dialect/ControlFlow/IR/ControlFlowOps.h"
 #include "llvm/Support/Debug.h"
+#include <optional>
 
 #define DEBUG_TYPE "flang-lower-io"
 
diff --git a/flang/lib/Lower/IntrinsicCall.cpp b/flang/lib/Lower/IntrinsicCall.cpp
index cdccd451b9a69..f6bc94cec47ac 100644
--- a/flang/lib/Lower/IntrinsicCall.cpp
+++ b/flang/lib/Lower/IntrinsicCall.cpp
@@ -40,6 +40,7 @@
 #include "mlir/Dialect/Math/IR/Math.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Debug.h"
+#include <optional>
 
 #define DEBUG_TYPE "flang-lower-intrinsic"
 
diff --git a/flang/lib/Lower/IterationSpace.cpp b/flang/lib/Lower/IterationSpace.cpp
index 0bcdae6845f70..c41aa0ef0eecd 100644
--- a/flang/lib/Lower/IterationSpace.cpp
+++ b/flang/lib/Lower/IterationSpace.cpp
@@ -15,6 +15,7 @@
 #include "flang/Lower/AbstractConverter.h"
 #include "flang/Lower/Support/Utils.h"
 #include "llvm/Support/Debug.h"
+#include <optional>
 
 #define DEBUG_TYPE "flang-lower-iteration-space"
 
diff --git a/flang/lib/Lower/Mangler.cpp b/flang/lib/Lower/Mangler.cpp
index 5bc85209abc02..0aec674411559 100644
--- a/flang/lib/Lower/Mangler.cpp
+++ b/flang/lib/Lower/Mangler.cpp
@@ -19,6 +19,7 @@
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/Twine.h"
 #include "llvm/Support/MD5.h"
+#include <optional>
 
 // recursively build the vector of module scopes
 static void moduleNames(const Fortran::semantics::Scope &scope,
diff --git a/flang/lib/Lower/Runtime.cpp b/flang/lib/Lower/Runtime.cpp
index cf6cf0657de7f..e0dfdf5696a81 100644
--- a/flang/lib/Lower/Runtime.cpp
+++ b/flang/lib/Lower/Runtime.cpp
@@ -21,6 +21,7 @@
 #include "flang/Runtime/time-intrinsic.h"
 #include "flang/Semantics/tools.h"
 #include "llvm/Support/Debug.h"
+#include <optional>
 
 #define DEBUG_TYPE "flang-lower-runtime"
 
diff --git a/flang/lib/Lower/SymbolMap.cpp b/flang/lib/Lower/SymbolMap.cpp
index a8f59ee3852e2..ff0c75f12db25 100644
--- a/flang/lib/Lower/SymbolMap.cpp
+++ b/flang/lib/Lower/SymbolMap.cpp
@@ -14,6 +14,7 @@
 #include "flang/Optimizer/Builder/Todo.h"
 #include "mlir/IR/BuiltinTypes.h"
 #include "llvm/Support/Debug.h"
+#include <optional>
 
 #define DEBUG_TYPE "flang-lower-symbol-map"
 
diff --git a/flang/lib/Optimizer/Builder/FIRBuilder.cpp b/flang/lib/Optimizer/Builder/FIRBuilder.cpp
index 50e28e9966477..a82c218f49644 100644
--- a/flang/lib/Optimizer/Builder/FIRBuilder.cpp
+++ b/flang/lib/Optimizer/Builder/FIRBuilder.cpp
@@ -23,6 +23,7 @@
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/MD5.h"
+#include <optional>
 
 static llvm::cl::opt<std::size_t>
     nameLengthHashSize("length-to-hash-string-literal",
diff --git a/flang/lib/Optimizer/Builder/HLFIRTools.cpp b/flang/lib/Optimizer/Builder/HLFIRTools.cpp
index ca645cf97cbb2..818347e375eb0 100644
--- a/flang/lib/Optimizer/Builder/HLFIRTools.cpp
+++ b/flang/lib/Optimizer/Builder/HLFIRTools.cpp
@@ -16,6 +16,7 @@
 #include "flang/Optimizer/Builder/Todo.h"
 #include "flang/Optimizer/HLFIR/HLFIROps.h"
 #include "mlir/IR/BlockAndValueMapping.h"
+#include <optional>
 
 // Return explicit extents. If the base is a fir.box, this won't read it to
 // return the extents and will instead return an empty vector.
diff --git a/flang/lib/Optimizer/CodeGen/TargetRewrite.cpp b/flang/lib/Optimizer/CodeGen/TargetRewrite.cpp
index 87206c12efde0..b19bb5efb0851 100644
--- a/flang/lib/Optimizer/CodeGen/TargetRewrite.cpp
+++ b/flang/lib/Optimizer/CodeGen/TargetRewrite.cpp
@@ -29,6 +29,7 @@
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/TypeSwitch.h"
 #include "llvm/Support/Debug.h"
+#include <optional>
 
 namespace fir {
 #define GEN_PASS_DEF_TARGETREWRITEPASS
diff --git a/flang/lib/Optimizer/HLFIR/IR/HLFIROps.cpp b/flang/lib/Optimizer/HLFIR/IR/HLFIROps.cpp
index ba62f511e5348..2111f502aa3d8 100644
--- a/flang/lib/Optimizer/HLFIR/IR/HLFIROps.cpp
+++ b/flang/lib/Optimizer/HLFIR/IR/HLFIROps.cpp
@@ -19,6 +19,7 @@
 #include "mlir/IR/OpImplementation.h"
 #include "llvm/ADT/TypeSwitch.h"
 #include <tuple>
+#include <optional>
 
 //===----------------------------------------------------------------------===//
 // DeclareOp
diff --git a/flang/lib/Optimizer/Support/InternalNames.cpp b/flang/lib/Optimizer/Support/InternalNames.cpp
index 8a12bfb69a6eb..3c455e1bc57ef 100644
--- a/flang/lib/Optimizer/Support/InternalNames.cpp
+++ b/flang/lib/Optimizer/Support/InternalNames.cpp
@@ -15,6 +15,7 @@
 #include "mlir/IR/BuiltinTypes.h"
 #include "mlir/IR/Diagnostics.h"
 #include "llvm/Support/CommandLine.h"
+#include <optional>
 
 static llvm::cl::opt<std::string> mainEntryName(
     "main-entry-name",
diff --git a/flang/lib/Optimizer/Transforms/AffinePromotion.cpp b/flang/lib/Optimizer/Transforms/AffinePromotion.cpp
index 0762b6f4d6aeb..998b063f7d1a2 100644
--- a/flang/lib/Optimizer/Transforms/AffinePromotion.cpp
+++ b/flang/lib/Optimizer/Transforms/AffinePromotion.cpp
@@ -29,6 +29,7 @@
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/Optional.h"
 #include "llvm/Support/Debug.h"
+#include <optional>
 
 namespace fir {
 #define GEN_PASS_DEF_AFFINEDIALECTPROMOTION
diff --git a/flang/lib/Optimizer/Transforms/MemRefDataFlowOpt.cpp b/flang/lib/Optimizer/Transforms/MemRefDataFlowOpt.cpp
index 668391201df7c..51e8561dee380 100644
--- a/flang/lib/Optimizer/Transforms/MemRefDataFlowOpt.cpp
+++ b/flang/lib/Optimizer/Transforms/MemRefDataFlowOpt.cpp
@@ -17,6 +17,7 @@
 #include "llvm/ADT/Optional.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SmallVector.h"
+#include <optional>
 
 namespace fir {
 #define GEN_PASS_DEF_MEMREFDATAFLOWOPT
diff --git a/flang/lib/Optimizer/Transforms/SimplifyIntrinsics.cpp b/flang/lib/Optimizer/Transforms/SimplifyIntrinsics.cpp
index b1c1f6ac71d5a..5628f0c7999df 100644
--- a/flang/lib/Optimizer/Transforms/SimplifyIntrinsics.cpp
+++ b/flang/lib/Optimizer/Transforms/SimplifyIntrinsics.cpp
@@ -40,6 +40,7 @@
 #include "llvm/ADT/Optional.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/raw_ostream.h"
+#include <optional>
 
 namespace fir {
 #define GEN_PASS_DEF_SIMPLIFYINTRINSICS