2 files changed, 20 insertions, 5 deletions
diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.cpp
index 5419a10f4f9..61b2c7e6584 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.cpp
@@ -86,7 +86,7 @@ bool DwarfExpression::AddMachineRegIndirect(const TargetRegisterInfo &TRI,
 }
 
 bool DwarfExpression::AddMachineReg(const TargetRegisterInfo &TRI,
-                                    unsigned MachineReg) {
+                                    unsigned MachineReg, unsigned MaxSize) {
   if (!TRI.isPhysicalRegister(MachineReg))
     return false;
 
@@ -137,10 +137,12 @@ bool DwarfExpression::AddMachineReg(const TargetRegisterInfo &TRI,
     // its range, emit a DWARF piece for it.
     if (Reg >= 0 && Intersection.any()) {
       AddReg(Reg, "sub-register");
+      if (Offset >= MaxSize)
+	break;
       // Emit a piece for the any gap in the coverage.
       if (Offset > CurPos)
         AddOpPiece(Offset - CurPos);
-      AddOpPiece(Size);
+      AddOpPiece(std::min<unsigned>(Size, MaxSize - Offset));
       CurPos = Offset + Size;
 
       // Mark it as emitted.
@@ -196,9 +198,12 @@ bool DwarfExpression::AddMachineRegExpression(const TargetRegisterInfo &TRI,
   bool ValidReg = false;
   auto Op = ExprCursor.peek();
   switch (Op->getOp()) {
-  default:
-    ValidReg = AddMachineReg(TRI, MachineReg);
+  default: {
+    auto Fragment = ExprCursor.getFragmentInfo();
+    ValidReg = AddMachineReg(TRI, MachineReg,
+			     Fragment ? Fragment->SizeInBits : ~1U);
     break;
+  }
   case dwarf::DW_OP_plus:
   case dwarf::DW_OP_minus: {
     // [DW_OP_reg,Offset,DW_OP_plus, DW_OP_deref] --> [DW_OP_breg, Offset].
diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.h b/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.h
index 96d9f09faf0..fd90fa05bc3 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.h
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.h
@@ -72,6 +72,11 @@ public:
   }
   /// Determine whether there are any operations left in this expression.
   operator bool() const { return Start != End; }
+
+  /// Retrieve the fragment information, if any.
+  Optional<DIExpression::FragmentInfo> getFragmentInfo() const {
+    return DIExpression::getFragmentInfo(Start, End);
+  }
 };
 
 /// Base class containing the logic for constructing DWARF expressions
@@ -145,6 +150,10 @@ public:
   /// Emit a partial DWARF register operation.
   ///
   /// \param MachineReg           The register number.
+  /// \param MaxSize              If the register must be composed from
+  ///                             sub-registers this is an upper bound
+  ///                             for how many bits the emitted DW_OP_piece
+  ///                             may cover.
   ///
   /// If size and offset is zero an operation for the entire register is
   /// emitted: Some targets do not provide a DWARF register number for every
@@ -153,7 +162,8 @@ public:
   /// multiple subregisters that alias the register.
   ///
   /// \return false if no DWARF register exists for MachineReg.
-  bool AddMachineReg(const TargetRegisterInfo &TRI, unsigned MachineReg);
+  bool AddMachineReg(const TargetRegisterInfo &TRI, unsigned MachineReg,
+                     unsigned MaxSize = ~1U);
 
   /// Emit a signed constant.
   void AddSignedConstant(int64_t Value);