[ADT] Alias llvm::Optional to std::optional

This avoids the continuous API churn when upgrading things to use
std::optional and makes trivial string replace upgrades possible.

I tested this with GCC 7.5, the oldest supported GCC I had around.

Differential Revision: https://reviews.llvm.org/D140332

Author: d0k

clang/include/clang/Basic/LLVM.h

@@ -37,7 +37,7 @@ namespace llvm {
   template<unsigned InternalLen> class SmallString;
   template<typename T, unsigned N> class SmallVector;
   template<typename T> class SmallVectorImpl;
-  template <typename T> class Optional;
+  template <typename T> using Optional = std::optional<T>;
   template <class T> class Expected;
 
   template<typename T>

clang/lib/StaticAnalyzer/Core/ExprEngine.cpp

@@ -481,7 +481,7 @@ Optional<unsigned> ExprEngine::getPendingInitLoop(ProgramStateRef State,
                                                   const CXXConstructExpr *E,
                                                   const LocationContext *LCtx) {
   const unsigned *V = State->get<PendingInitLoop>({E, LCtx->getStackFrame()});
-  return V ? Optional(*V) : std::nullopt;
+  return V ? std::make_optional(*V) : std::nullopt;
 }
 
 ProgramStateRef ExprEngine::removePendingInitLoop(ProgramStateRef State,
@@ -510,7 +510,7 @@ ExprEngine::getIndexOfElementToConstruct(ProgramStateRef State,
                                          const LocationContext *LCtx) {
   const unsigned *V =
       State->get<IndexOfElementToConstruct>({E, LCtx->getStackFrame()});
-  return V ? Optional(*V) : std::nullopt;
+  return V ? std::make_optional(*V) : std::nullopt;
 }
 
 ProgramStateRef
@@ -530,7 +530,7 @@ ExprEngine::getPendingArrayDestruction(ProgramStateRef State,
 
   const unsigned *V =
       State->get<PendingArrayDestruction>(LCtx->getStackFrame());
-  return V ? Optional(*V) : std::nullopt;
+  return V ? std::make_optional(*V) : std::nullopt;
 }
 
 ProgramStateRef ExprEngine::setPendingArrayDestruction(
@@ -600,7 +600,7 @@ ExprEngine::getObjectUnderConstruction(ProgramStateRef State,
                                        const LocationContext *LC) {
   ConstructedObjectKey Key(Item, LC->getStackFrame());
   const SVal *V = State->get<ObjectsUnderConstruction>(Key);
-  return V ? Optional(*V) : std::nullopt;
+  return V ? std::make_optional(*V) : std::nullopt;
 }
 
 ProgramStateRef

flang/include/flang/Lower/Runtime.h

@@ -16,9 +16,10 @@
 #ifndef FORTRAN_LOWER_RUNTIME_H
 #define FORTRAN_LOWER_RUNTIME_H
 
+#include <optional>
+
 namespace llvm {
-template <typename T>
-class Optional;
+template <typename T> using Optional = std::optional<T>;
 }
 
 namespace mlir {

lldb/source/Plugins/SymbolFile/DWARF/DWARFFormValue.cpp

@@ -190,7 +190,7 @@ static FormSize g_form_sizes[] = {
 llvm::Optional<uint8_t>
 DWARFFormValue::GetFixedSize(dw_form_t form, const DWARFUnit *u) {
   if (form <= DW_FORM_ref_sig8 && g_form_sizes[form].valid)
-    return g_form_sizes[form].size;
+    return static_cast<uint8_t>(g_form_sizes[form].size);
   if (form == DW_FORM_addr && u)
     return u->GetAddressByteSize();
   return std::nullopt;

lldb/source/Symbol/Type.cpp

@@ -343,7 +343,7 @@ Type *Type::GetEncodingType() {
 
 llvm::Optional<uint64_t> Type::GetByteSize(ExecutionContextScope *exe_scope) {
   if (m_byte_size_has_value)
-    return m_byte_size;
+    return static_cast<uint64_t>(m_byte_size);
 
   switch (m_encoding_uid_type) {
   case eEncodingInvalid:
@@ -360,14 +360,14 @@ llvm::Optional<uint64_t> Type::GetByteSize(ExecutionContextScope *exe_scope) {
       if (llvm::Optional<uint64_t> size = encoding_type->GetByteSize(exe_scope)) {
         m_byte_size = *size;
         m_byte_size_has_value = true;
-        return m_byte_size;
+        return static_cast<uint64_t>(m_byte_size);
       }
 
     if (llvm::Optional<uint64_t> size =
             GetLayoutCompilerType().GetByteSize(exe_scope)) {
       m_byte_size = *size;
       m_byte_size_has_value = true;
-        return m_byte_size;
+      return static_cast<uint64_t>(m_byte_size);
     }
   } break;
 
@@ -378,7 +378,7 @@ llvm::Optional<uint64_t> Type::GetByteSize(ExecutionContextScope *exe_scope) {
       if (ArchSpec arch = m_symbol_file->GetObjectFile()->GetArchitecture()) {
         m_byte_size = arch.GetAddressByteSize();
         m_byte_size_has_value = true;
-        return m_byte_size;
+        return static_cast<uint64_t>(m_byte_size);
       }
     } break;
   }