Index: include/lld/Core/DefinedAtom.h
===================================================================
--- include/lld/Core/DefinedAtom.h
+++ include/lld/Core/DefinedAtom.h
@@ -255,6 +255,10 @@
   /// \brief constraints on whether the linker may dead strip away this atom.
   virtual SectionPosition sectionPosition() const = 0;
 
+  /// \brief If merge() == mergeByLargestSection, this returns the
+  /// size of the section for this atom.
+  virtual uint64_t sectionSize() const { return 0; }
+
   /// \brief constraints on whether the linker may dead strip away this atom.
   virtual DeadStripKind deadStrip() const = 0;
 
Index: lib/Core/SymbolTable.cpp
===================================================================
--- lib/Core/SymbolTable.cpp
+++ lib/Core/SymbolTable.cpp
@@ -135,36 +135,6 @@
   return mergeCases[first][second];
 }
 
-static const DefinedAtom *followReference(const DefinedAtom *atom,
-                                          uint32_t kind) {
-  for (const Reference *r : *atom)
-    if (r->kindNamespace() == Reference::KindNamespace::all &&
-        r->kindArch() == Reference::KindArch::all &&
-        r->kindValue() == kind)
-      return cast<const DefinedAtom>(r->target());
-  return nullptr;
-}
-
-static uint64_t getSizeFollowReferences(const DefinedAtom *atom,
-                                        uint32_t kind) {
-  uint64_t size = 0;
-  for (;;) {
-    atom = followReference(atom, kind);
-    if (!atom)
-      return size;
-    size += atom->size();
-  }
-}
-
-// Returns the size of the section containing the given atom. Atoms in the same
-// section are connected by layout-before and layout-after edges, so this
-// function traverses them to get the total size of atoms in the same section.
-static uint64_t sectionSize(const DefinedAtom *atom) {
-  return atom->size()
-      + getSizeFollowReferences(atom, lld::Reference::kindLayoutBefore)
-      + getSizeFollowReferences(atom, lld::Reference::kindLayoutAfter);
-}
-
 bool SymbolTable::addByName(const Atom &newAtom) {
   StringRef name = newAtom.name();
   assert(!name.empty());
@@ -200,14 +170,14 @@
       useNew = true;
       break;
     case MCR_Largest: {
-      uint64_t existingSize = sectionSize((DefinedAtom*)existing);
-      uint64_t newSize = sectionSize((DefinedAtom*)&newAtom);
+      uint64_t existingSize = ((DefinedAtom*)existing)->sectionSize();
+      uint64_t newSize = ((DefinedAtom*)&newAtom)->sectionSize();
       useNew = (newSize >= existingSize);
       break;
     }
     case MCR_SameSize: {
-      uint64_t existingSize = sectionSize((DefinedAtom*)existing);
-      uint64_t newSize = sectionSize((DefinedAtom*)&newAtom);
+      uint64_t existingSize = ((DefinedAtom*)existing)->sectionSize();
+      uint64_t newSize = ((DefinedAtom*)&newAtom)->sectionSize();
       if (existingSize == newSize) {
         useNew = true;
         break;
Index: lib/ReaderWriter/PECOFF/Atoms.h
===================================================================
--- lib/ReaderWriter/PECOFF/Atoms.h
+++ lib/ReaderWriter/PECOFF/Atoms.h
@@ -182,16 +182,19 @@
 public:
   COFFDefinedAtom(const File &file, StringRef name, StringRef sectionName,
                   Scope scope, ContentType type, bool isComdat,
-                  ContentPermissions perms, Merge merge, ArrayRef<uint8_t> data,
-                  uint64_t ordinal)
+                  ContentPermissions perms, Merge merge, uint64_t sectionSize,
+                  ArrayRef<uint8_t> data, uint64_t ordinal)
       : COFFDefinedFileAtom(file, name, sectionName, scope, type, perms,
                             ordinal),
-        _isComdat(isComdat), _merge(merge), _dataref(data) {}
+    _isComdat(isComdat), _merge(merge), _sectionSize(sectionSize),
+    _dataref(data) {}
 
   Merge merge() const override { return _merge; }
   uint64_t size() const override { return _dataref.size(); }
   ArrayRef<uint8_t> rawContent() const override { return _dataref; }
 
+  uint64_t sectionSize() const override { return _sectionSize; }
+
   DeadStripKind deadStrip() const override {
     // Only COMDAT symbols would be dead-stripped.
     return _isComdat ? deadStripNormal : deadStripNever;
@@ -200,6 +203,7 @@
 private:
   bool _isComdat;
   Merge _merge;
+  uint64_t _sectionSize;
   ArrayRef<uint8_t> _dataref;
 };
 
Index: lib/ReaderWriter/PECOFF/ReaderCOFF.cpp
===================================================================
--- lib/ReaderWriter/PECOFF/ReaderCOFF.cpp
+++ lib/ReaderWriter/PECOFF/ReaderCOFF.cpp
@@ -636,7 +636,7 @@
     ArrayRef<uint8_t> data(secData.data(), secData.size());
     auto *atom = new (_alloc) COFFDefinedAtom(
         *this, "", sectionName, Atom::scopeTranslationUnit, type, isComdat,
-        perms, _merge[section], data, _ordinal++);
+        perms, _merge[section], section->SizeOfRawData, data, _ordinal++);
     atoms.push_back(atom);
     _definedAtomLocations[section][0].push_back(atom);
     return error_code();
@@ -649,7 +649,7 @@
     ArrayRef<uint8_t> data(secData.data(), size);
     auto *atom = new (_alloc) COFFDefinedAtom(
         *this, "", sectionName, Atom::scopeTranslationUnit, type, isComdat,
-        perms, _merge[section], data, _ordinal++);
+        perms, _merge[section], section->SizeOfRawData, data, _ordinal++);
     atoms.push_back(atom);
     _definedAtomLocations[section][0].push_back(atom);
   }
@@ -662,7 +662,7 @@
     ArrayRef<uint8_t> data(start, end);
     auto *atom = new (_alloc) COFFDefinedAtom(
         *this, _symbolName[*si], sectionName, getScope(*si), type, isComdat,
-        perms, _merge[section], data, _ordinal++);
+        perms, _merge[section], section->SizeOfRawData, data, _ordinal++);
     atoms.push_back(atom);
     _symbolAtom[*si] = atom;
     _definedAtomLocations[section][(*si)->Value].push_back(atom);
@@ -834,7 +834,7 @@
   auto *atom = new (_alloc) COFFDefinedAtom(
       *this, "", ".sxdata", Atom::scopeTranslationUnit, DefinedAtom::typeData,
       false /*isComdat*/, DefinedAtom::permR__, DefinedAtom::mergeNo,
-      atomContent, _ordinal++);
+      0 /* sectionSize */, atomContent, _ordinal++);
 
   const ulittle32_t *symbolIndex =
       reinterpret_cast<const ulittle32_t *>(sxdata.data());