diff --git a/lld/COFF/Chunks.h b/lld/COFF/Chunks.h
--- a/lld/COFF/Chunks.h
+++ b/lld/COFF/Chunks.h
@@ -50,7 +50,7 @@
 // doesn't even have actual data (if common or bss).
 class Chunk {
 public:
-  enum Kind { SectionKind, OtherKind };
+  enum Kind : uint8_t { SectionKind, OtherKind };
   Kind kind() const { return ChunkKind; }
   virtual ~Chunk() = default;
 
@@ -107,6 +107,12 @@
   Chunk(Kind K = OtherKind) : ChunkKind(K) {}
   const Kind ChunkKind;
 
+public:
+  // Whether this section needs to be kept distinct from other sections during
+  // ICF. This is set by the driver using address-significance tables.
+  bool KeepUnique = false;
+
+protected:
   // The RVA of this chunk in the output. The writer sets a value.
   uint64_t RVA = 0;
 
@@ -116,10 +122,6 @@
 public:
   // The offset from beginning of the output section. The writer sets a value.
   uint64_t OutputSectionOff = 0;
-
-  // Whether this section needs to be kept distinct from other sections during
-  // ICF. This is set by the driver using address-significance tables.
-  bool KeepUnique = false;
 };
 
 // A chunk corresponding a section of an input file.
@@ -192,8 +194,34 @@
                             symbol_iterator(File, Relocs.end()));
   }
 
+  // Single linked list iterator for associated comdat children.
+  class AssociatedIterator
+      : public llvm::iterator_facade_base<
+            AssociatedIterator, std::forward_iterator_tag, SectionChunk> {
+  public:
+    AssociatedIterator() = default;
+    AssociatedIterator(SectionChunk *Head) : Cur(Head) {}
+    AssociatedIterator &operator=(const AssociatedIterator &R) {
+      Cur = R.Cur;
+      return *this;
+    }
+    bool operator==(const AssociatedIterator &R) const { return Cur == R.Cur; }
+    const SectionChunk &operator*() const { return *Cur; }
+    SectionChunk &operator*() { return *Cur; }
+    AssociatedIterator &operator++() {
+      Cur = Cur->AssocChildren;
+      return *this;
+    }
+
+  private:
+    SectionChunk *Cur = nullptr;
+  };
+
   // Allow iteration over the associated child chunks for this section.
-  ArrayRef<SectionChunk *> children() const { return AssocChildren; }
+  llvm::iterator_range<AssociatedIterator> children() const {
+    return llvm::make_range(AssociatedIterator(AssocChildren),
+                            AssociatedIterator(nullptr));
+  }
 
   // The section ID this chunk belongs to in its Obj.
   uint32_t getSectionNumber() const;
@@ -208,35 +236,37 @@
 
   bool isHotPatchable() const override { return File->HotPatchable; }
 
-  // A pointer pointing to a replacement for this chunk.
-  // Initially it points to "this" object. If this chunk is merged
-  // with other chunk by ICF, it points to another chunk,
-  // and this chunk is considered as dead.
-  SectionChunk *Repl;
-
-  // The CRC of the contents as described in the COFF spec 4.5.5.
-  // Auxiliary Format 5: Section Definitions. Used for ICF.
-  uint32_t Checksum = 0;
-
-  const coff_section *Header;
-
   // The file that this chunk was created from.
   ObjFile *File;
 
+  // Pointer to the COFF section header in the input file.
+  const coff_section *Header;
+
   // The COMDAT leader symbol if this is a COMDAT chunk.
   DefinedRegular *Sym = nullptr;
 
-  // The COMDAT selection if this is a COMDAT chunk.
-  llvm::COFF::COMDATType Selection = (llvm::COFF::COMDATType)0;
-
+  // Relocations for this section.
   ArrayRef<coff_relocation> Relocs;
 
+  // The CRC of the contents as described in the COFF spec 4.5.5.
+  // Auxiliary Format 5: Section Definitions. Used for ICF.
+  uint32_t Checksum = 0;
+
   // Used by the garbage collector.
   bool Live;
 
+  // The COMDAT selection if this is a COMDAT chunk.
+  llvm::COFF::COMDATType Selection = (llvm::COFF::COMDATType)0;
+
+  // A pointer pointing to a replacement for this chunk.
+  // Initially it points to "this" object. If this chunk is merged
+  // with other chunk by ICF, it points to another chunk,
+  // and this chunk is considered as dead.
+  SectionChunk *Repl;
+
 private:
   StringRef SectionName;
-  std::vector<SectionChunk *> AssocChildren;
+  SectionChunk *AssocChildren = nullptr;
 
   // Used for ICF (Identical COMDAT Folding)
   void replace(SectionChunk *Other);
diff --git a/lld/COFF/Chunks.cpp b/lld/COFF/Chunks.cpp
--- a/lld/COFF/Chunks.cpp
+++ b/lld/COFF/Chunks.cpp
@@ -30,8 +30,8 @@
 namespace coff {
 
 SectionChunk::SectionChunk(ObjFile *F, const coff_section *H)
-    : Chunk(SectionKind), Repl(this), Header(H), File(F),
-      Relocs(File->getCOFFObj()->getRelocations(Header)) {
+    : Chunk(SectionKind), File(F), Header(H),
+      Relocs(File->getCOFFObj()->getRelocations(Header)), Repl(this) {
   // Initialize SectionName.
   File->getCOFFObj()->getSectionName(Header, SectionName);
 
@@ -44,6 +44,11 @@
   Live = !Config->DoGC || !isCOMDAT();
 }
 
+// SectionChunk is one of the most frequently allocated classes, so it is
+// important to keep it as compact as possible. As of this writing, the number
+// below is the size of this class on x64 platforms.
+static_assert(sizeof(SectionChunk) <= 128, "SectionChunk grew unexpectedly");
+
 static void add16(uint8_t *P, int16_t V) { write16le(P, read16le(P) + V); }
 static void add32(uint8_t *P, int32_t V) { write32le(P, read32le(P) + V); }
 static void add64(uint8_t *P, int64_t V) { write64le(P, read64le(P) + V); }
@@ -394,7 +399,11 @@
 }
 
 void SectionChunk::addAssociative(SectionChunk *Child) {
-  AssocChildren.push_back(Child);
+  // Insert this child at the head of the list.
+  assert(Child->AssocChildren == nullptr &&
+         "associated sections cannot have their own associated children");
+  Child->AssocChildren = AssocChildren;
+  AssocChildren = Child;
 }
 
 static uint8_t getBaserelType(const coff_relocation &Rel) {
diff --git a/lld/COFF/ICF.cpp b/lld/COFF/ICF.cpp
--- a/lld/COFF/ICF.cpp
+++ b/lld/COFF/ICF.cpp
@@ -129,10 +129,10 @@
 bool ICF::assocEquals(const SectionChunk *A, const SectionChunk *B) {
   auto ChildClasses = [&](const SectionChunk *SC) {
     std::vector<uint32_t> Classes;
-    for (const SectionChunk *C : SC->children())
-      if (!C->SectionName.startswith(".debug") &&
-          C->SectionName != ".gfids$y" && C->SectionName != ".gljmp$y")
-        Classes.push_back(C->Class[Cnt % 2]);
+    for (const SectionChunk &C : SC->children())
+      if (!C.SectionName.startswith(".debug") &&
+          C.SectionName != ".gfids$y" && C.SectionName != ".gljmp$y")
+        Classes.push_back(C.Class[Cnt % 2]);
     return Classes;
   };
   return ChildClasses(A) == ChildClasses(B);
diff --git a/lld/COFF/MarkLive.cpp b/lld/COFF/MarkLive.cpp
--- a/lld/COFF/MarkLive.cpp
+++ b/lld/COFF/MarkLive.cpp
@@ -64,8 +64,8 @@
         AddSym(B);
 
     // Mark associative sections if any.
-    for (SectionChunk *C : SC->children())
-      Enqueue(C);
+    for (SectionChunk &C : SC->children())
+      Enqueue(&C);
   }
 }
 
diff --git a/llvm/include/llvm/BinaryFormat/COFF.h b/llvm/include/llvm/BinaryFormat/COFF.h
--- a/llvm/include/llvm/BinaryFormat/COFF.h
+++ b/llvm/include/llvm/BinaryFormat/COFF.h
@@ -402,7 +402,7 @@
   IMAGE_REL_ARM64_REL32 = 0x0011,
 };
 
-enum COMDATType : unsigned {
+enum COMDATType : uint8_t {
   IMAGE_COMDAT_SELECT_NODUPLICATES = 1,
   IMAGE_COMDAT_SELECT_ANY,
   IMAGE_COMDAT_SELECT_SAME_SIZE,