diff --git a/llvm/include/llvm/CodeGen/MachineInstr.h b/llvm/include/llvm/CodeGen/MachineInstr.h
--- a/llvm/include/llvm/CodeGen/MachineInstr.h
+++ b/llvm/include/llvm/CodeGen/MachineInstr.h
@@ -121,16 +121,20 @@
 
   // Operands are allocated by an ArrayRecycler.
   MachineOperand *Operands = nullptr;   // Pointer to the first operand.
-  uint32_t Flags = 0;                   // Various bits of additional
-                                        // information about machine
-                                        // instruction.
-  uint16_t NumOperands = 0;             // Number of operands on instruction.
-  uint8_t AsmPrinterFlags = 0;          // Various bits of information used by
-                                        // the AsmPrinter to emit helpful
-                                        // comments.  This is *not* semantic
-                                        // information.  Do not use this for
-                                        // anything other than to convey comment
-                                        // information to AsmPrinter.
+
+  #define LLVM_MID_NUMOPERANDS_BITS 24
+  #define LLVM_MID_FLAGS_BITS 24
+  #define LLVM_MID_ASMPRINTERFLAGS_BITS 8
+  LLVM_PACKED(struct MachineInstrDetail {
+    /// Number of operands on instruction.
+    uint32_t NumOperands : LLVM_MID_NUMOPERANDS_BITS;
+    /// Various bits of additional information about the machine instruction.
+    uint32_t Flags : LLVM_MID_FLAGS_BITS;
+    /// Various bits of information used by the AsmPrinter to emit helpful
+    /// comments.  This is *not* semantic information.  Do not use this for
+    /// anything other than to convey comment information to AsmPrinter.
+    uint8_t AsmPrinterFlags : LLVM_MID_ASMPRINTERFLAGS_BITS;
+  }) Detail = { 0, 0, 0 };
 
   // OperandCapacity has uint8_t size, so it should be next to AsmPrinterFlags
   // to properly pack.
@@ -335,50 +339,53 @@
   }
 
   /// Return the asm printer flags bitvector.
-  uint8_t getAsmPrinterFlags() const { return AsmPrinterFlags; }
+  uint8_t getAsmPrinterFlags() const { return Detail.AsmPrinterFlags; }
 
   /// Clear the AsmPrinter bitvector.
-  void clearAsmPrinterFlags() { AsmPrinterFlags = 0; }
+  void clearAsmPrinterFlags() { Detail.AsmPrinterFlags = 0; }
 
   /// Return whether an AsmPrinter flag is set.
   bool getAsmPrinterFlag(CommentFlag Flag) const {
-    return AsmPrinterFlags & Flag;
+    return Detail.AsmPrinterFlags & Flag;
   }
 
   /// Set a flag for the AsmPrinter.
   void setAsmPrinterFlag(uint8_t Flag) {
-    AsmPrinterFlags |= Flag;
+    Detail.AsmPrinterFlags |= Flag;
   }
 
   /// Clear specific AsmPrinter flags.
   void clearAsmPrinterFlag(CommentFlag Flag) {
-    AsmPrinterFlags &= ~Flag;
+    Detail.AsmPrinterFlags &= ~Flag;
   }
 
   /// Return the MI flags bitvector.
   uint32_t getFlags() const {
-    return Flags;
+    return Detail.Flags;
   }
 
   /// Return whether an MI flag is set.
   bool getFlag(MIFlag Flag) const {
-    return Flags & Flag;
+    return Detail.Flags & Flag;
   }
 
   /// Set a MI flag.
   void setFlag(MIFlag Flag) {
-    Flags |= (uint32_t)Flag;
+    assert(unsigned(Flag) <= ((1u<<LLVM_MII_FLAGS_BITS)-1) && "set not in desirable range?");
+    Detail.Flags |= (uint32_t)Flag;
   }
 
   void setFlags(unsigned flags) {
+    assert(flags <= ((1u<<LLVM_MII_FLAGS_BITS)-1) && "multi-set not in desirable range?");
     // Filter out the automatically maintained flags.
     unsigned Mask = BundledPred | BundledSucc;
-    Flags = (Flags & Mask) | (flags & ~Mask);
+    Detail.Flags = (Detail.Flags & Mask) | (flags & ~Mask);
   }
 
   /// clearFlag - Clear a MI flag.
   void clearFlag(MIFlag Flag) {
-    Flags &= ~((uint32_t)Flag);
+    assert(unsigned(Flag) <= ((1u<<LLVM_MII_FLAGS_BITS)-1) && "clear not in desirable range?");
+    Detail.Flags &= ~((uint32_t)Flag);
   }
 
   /// Return true if MI is in a bundle (but not the first MI in a bundle).
@@ -523,7 +530,7 @@
   unsigned getOpcode() const { return MCID->Opcode; }
 
   /// Retuns the total number of operands.
-  unsigned getNumOperands() const { return NumOperands; }
+  unsigned getNumOperands() const { return Detail.NumOperands; }
 
   /// Returns the total number of operands which are debug locations.
   unsigned getNumDebugOperands() const {
@@ -640,10 +647,10 @@
   using const_mop_iterator = const MachineOperand *;
 
   mop_iterator operands_begin() { return Operands; }
-  mop_iterator operands_end() { return Operands + NumOperands; }
+  mop_iterator operands_end() { return Operands + Detail.NumOperands; }
 
   const_mop_iterator operands_begin() const { return Operands; }
-  const_mop_iterator operands_end() const { return Operands + NumOperands; }
+  const_mop_iterator operands_end() const { return Operands + Detail.NumOperands; }
 
   iterator_range<mop_iterator> operands() {
     return make_range(operands_begin(), operands_end());
diff --git a/llvm/lib/CodeGen/MachineInstr.cpp b/llvm/lib/CodeGen/MachineInstr.cpp
--- a/llvm/lib/CodeGen/MachineInstr.cpp
+++ b/llvm/lib/CodeGen/MachineInstr.cpp
@@ -134,7 +134,7 @@
   }
 
   // Copy all the sensible flags.
-  setFlags(MI.Flags);
+  setFlags(MI.Detail.Flags);
 }
 
 void MachineInstr::moveBefore(MachineInstr *MovePos) {
@@ -192,11 +192,11 @@
 /// an explicit operand it is added at the end of the explicit operand list
 /// (before the first implicit operand).
 void MachineInstr::addOperand(MachineFunction &MF, const MachineOperand &Op) {
-  assert(NumOperands < USHRT_MAX && "Cannot add more operands.");
+  assert(NumOperands < ((1u<<LLVM_MID_NUMOPERANDS_BITS)-1) && "Cannot add more operands.");
   assert(MCID && "Cannot add operands before providing an instr descriptor");
 
   // Check if we're adding one of our existing operands.
-  if (&Op >= Operands && &Op < Operands + NumOperands) {
+  if (&Op >= Operands && &Op < Operands + Detail.NumOperands) {
     // This is unusual: MI->addOperand(MI->getOperand(i)).
     // If adding Op requires reallocating or moving existing operands around,
     // the Op reference could go stale. Support it by copying Op.
@@ -242,10 +242,10 @@
   }
 
   // Move the operands following the insertion point.
-  if (OpNo != NumOperands)
-    moveOperands(Operands + OpNo + 1, OldOperands + OpNo, NumOperands - OpNo,
+  if (OpNo != Detail.NumOperands)
+    moveOperands(Operands + OpNo + 1, OldOperands + OpNo, Detail.NumOperands - OpNo,
                  MRI);
-  ++NumOperands;
+  ++Detail.NumOperands;
 
   // Deallocate the old operand array.
   if (OldOperands != Operands && OldOperands)
@@ -303,9 +303,9 @@
   // MachineOperand having a trivial destructor anyway, and adding a call here
   // wouldn't make it 'destructor-correct'.
 
-  if (unsigned N = NumOperands - 1 - OpNo)
+  if (unsigned N = Detail.NumOperands - 1 - OpNo)
     moveOperands(Operands + OpNo, Operands + OpNo + 1, N, MRI);
-  --NumOperands;
+  --Detail.NumOperands;
 }
 
 void MachineInstr::setExtraInfo(MachineFunction &MF,
@@ -582,7 +582,7 @@
 }
 
 void MachineInstr::copyIRFlags(const Instruction &I) {
-  Flags = copyFlagsFromInstruction(I);
+  Detail.Flags = copyFlagsFromInstruction(I);
 }
 
 bool MachineInstr::hasPropertyInBundle(uint64_t Mask, QueryType Type) const {
@@ -947,7 +947,7 @@
           OpndIt.getOperandNo(), Reg, CurRC, TII, TRI);
   else
     // Otherwise, just check the current operands.
-    for (unsigned i = 0, e = NumOperands; i < e && CurRC; ++i)
+    for (unsigned i = 0, e = Detail.NumOperands; i < e && CurRC; ++i)
       CurRC = getRegClassConstraintEffectForVRegImpl(i, Reg, CurRC, TII, TRI);
   return CurRC;
 }