diff --git a/llvm/include/llvm/MC/MCAsmBackend.h b/llvm/include/llvm/MC/MCAsmBackend.h
index a7d7db834b50e6..279c2300565eae 100644
--- a/llvm/include/llvm/MC/MCAsmBackend.h
+++ b/llvm/include/llvm/MC/MCAsmBackend.h
@@ -46,6 +46,9 @@ class MCAsmBackend {
 
   const support::endianness Endian;
 
+  /// Give the target a chance to manipulate state related to instruction
+  /// alignment (e.g. padding for optimization) before and after actually
+  /// emitting the instruction.
   virtual void alignBranchesBegin(MCObjectStreamer &OS, const MCInst &Inst) {}
   virtual void alignBranchesEnd(MCObjectStreamer &OS, const MCInst &Inst) {}
 
diff --git a/llvm/include/llvm/MC/MCFragment.h b/llvm/include/llvm/MC/MCFragment.h
index 5e3d5b783365f9..892b65c43cf7f8 100644
--- a/llvm/include/llvm/MC/MCFragment.h
+++ b/llvm/include/llvm/MC/MCFragment.h
@@ -565,15 +565,18 @@ class MCCVDefRangeFragment : public MCEncodedFragmentWithFixups<32, 4> {
   }
 };
 
+/// Represents required padding such that a particular other set of fragments
+/// does not cross a particular power-of-two boundary. The other fragments must
+/// follow this one within the same section.
 class MCBoundaryAlignFragment : public MCFragment {
 private:
-  /// The size of the MCBoundaryAlignFragment.
-  /// Note: The size is lazily set during relaxation, and is not meaningful
-  /// before that.
+  /// The size of the fragment.  The size is lazily set during relaxation, and
+  /// is not meaningful before that.
   uint64_t Size = 0;
   /// The alignment requirement of the branch to be aligned.
   Align AlignBoundary;
-  /// Flag to indicate whether the branch is fused.
+  /// Flag to indicate whether the branch is fused.  Use in determining the
+  /// region of fragments being aligned.
   bool Fused : 1;
   /// Flag to indicate whether NOPs should be emitted.
   bool EmitNops : 1;
@@ -586,21 +589,16 @@ class MCBoundaryAlignFragment : public MCFragment {
 
   /// \name Accessors
   /// @{
-
-  Align getAlignment() const { return AlignBoundary; }
-
   uint64_t getSize() const { return Size; }
+  void setSize(uint64_t Value) { Size = Value; }
 
-  bool canEmitNops() const { return EmitNops; }
-
+  Align getAlignment() const { return AlignBoundary; }  
+  
   bool isFused() const { return Fused; }
-
   void setFused(bool Value) { Fused = Value; }
 
+  bool canEmitNops() const { return EmitNops; }
   void setEmitNops(bool Value) { EmitNops = Value; }
-
-  void setSize(uint64_t Value) { Size = Value; }
-
   /// @}
   //