IR: Add MDExpression::ExprOperand

Port `DIExpression::Operand` over to `MDExpression::ExprOperand`.  The
logic is needed directly in `MDExpression` to support printing in
assembly.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@229002 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/IR/DebugInfoMetadata.h

@@ -1401,6 +1401,85 @@ public:
   element_iterator elements_begin() const { return getElements().begin(); }
   element_iterator elements_end() const { return getElements().end(); }
 
+  /// \brief A lightweight wrapper around an expression operand.
+  ///
+  /// TODO: Store arguments directly and change \a MDExpression to store a
+  /// range of these.
+  class ExprOperand {
+    const uint64_t *Op;
+
+  public:
+    explicit ExprOperand(const uint64_t *Op) : Op(Op) {}
+
+    const uint64_t *get() const { return Op; }
+
+    /// \brief Get the operand code.
+    uint64_t getOp() const { return *Op; }
+
+    /// \brief Get an argument to the operand.
+    ///
+    /// Never returns the operand itself.
+    uint64_t getArg(unsigned I) const { return Op[I + 1]; }
+
+    unsigned getNumArgs() const { return getSize() - 1; }
+
+    /// \brief Return the size of the operand.
+    ///
+    /// Return the number of elements in the operand (1 + args).
+    unsigned getSize() const;
+  };
+
+  /// \brief An iterator for expression operands.
+  class expr_op_iterator
+      : public std::iterator<std::input_iterator_tag, ExprOperand> {
+    ExprOperand Op;
+
+  public:
+    explicit expr_op_iterator(element_iterator I) : Op(I) {}
+
+    element_iterator getBase() const { return Op.get(); }
+    const ExprOperand &operator*() const { return Op; }
+    const ExprOperand *operator->() const { return &Op; }
+
+    expr_op_iterator &operator++() {
+      increment();
+      return *this;
+    }
+    expr_op_iterator operator++(int) {
+      expr_op_iterator T(*this);
+      increment();
+      return T;
+    }
+
+    bool operator==(const expr_op_iterator &X) const {
+      return getBase() == X.getBase();
+    }
+    bool operator!=(const expr_op_iterator &X) const {
+      return getBase() != X.getBase();
+    }
+
+  private:
+    void increment() { Op = ExprOperand(getBase() + Op.getSize()); }
+  };
+
+  /// \brief Visit the elements via ExprOperand wrappers.
+  ///
+  /// These range iterators visit elements through \a ExprOperand wrappers.
+  /// This is not guaranteed to be a valid range unless \a isValid() gives \c
+  /// true.
+  ///
+  /// \pre \a isValid() gives \c true.
+  /// @{
+  expr_op_iterator expr_op_begin() const {
+    return expr_op_iterator(elements_begin());
+  }
+  expr_op_iterator expr_op_end() const {
+    return expr_op_iterator(elements_end());
+  }
+  /// @}
+
+  bool isValid() const;
+
   static bool classof(const Metadata *MD) {
     return MD->getMetadataID() == MDExpressionKind;
   }

lib/IR/DebugInfoMetadata.cpp

@@ -350,6 +350,38 @@ MDExpression *MDExpression::getImpl(LLVMContext &Context,
   DEFINE_GETIMPL_STORE_NO_OPS(MDExpression, (Elements));
 }
 
+unsigned MDExpression::ExprOperand::getSize() const {
+  switch (getOp()) {
+  case dwarf::DW_OP_bit_piece:
+    return 3;
+  case dwarf::DW_OP_plus:
+    return 2;
+  default:
+    return 1;
+  }
+}
+
+bool MDExpression::isValid() const {
+  for (auto I = expr_op_begin(), E = expr_op_end(); I != E; ++I) {
+    // Check that there's space for the operand.
+    if (I->get() + I->getSize() > E->get())
+      return false;
+
+    // Check that the operand is valid.
+    switch (I->getOp()) {
+    default:
+      return false;
+    case dwarf::DW_OP_bit_piece:
+      // Piece expressions must be at the end.
+      return I->get() + I->getSize() == E->get();
+    case dwarf::DW_OP_plus:
+    case dwarf::DW_OP_deref:
+      break;
+    }
+  }
+  return true;
+}
+
 MDObjCProperty *MDObjCProperty::getImpl(
     LLVMContext &Context, MDString *Name, Metadata *File, unsigned Line,
     MDString *GetterName, MDString *SetterName, unsigned Attributes,

lib/IR/Verifier.cpp

@@ -780,6 +780,7 @@ void Verifier::visitMDLocalVariable(const MDLocalVariable &N) {
 
 void Verifier::visitMDExpression(const MDExpression &N) {
   Assert1(N.getTag() == dwarf::DW_TAG_expression, "invalid tag", &N);
+  Assert1(N.isValid(), "invalid expression", &N);
 }
 
 void Verifier::visitMDObjCProperty(const MDObjCProperty &N) {

unittests/IR/MetadataTest.cpp

@@ -1407,6 +1407,42 @@ TEST_F(MDExpressionTest, get) {
   EXPECT_EQ(0u, N->getElement(4));
 }
 
+TEST_F(MDExpressionTest, isValid) {
+#define EXPECT_VALID(...)                                                      \
+  do {                                                                         \
+    uint64_t Elements[] = {__VA_ARGS__};                                       \
+    EXPECT_TRUE(MDExpression::get(Context, Elements)->isValid());              \
+  } while (false)
+#define EXPECT_INVALID(...)                                                    \
+  do {                                                                         \
+    uint64_t Elements[] = {__VA_ARGS__};                                       \
+    EXPECT_FALSE(MDExpression::get(Context, Elements)->isValid());             \
+  } while (false)
+
+  // Empty expression should be valid.
+  EXPECT_TRUE(MDExpression::get(Context, None));
+
+  // Valid constructions.
+  EXPECT_VALID(dwarf::DW_OP_plus, 6);
+  EXPECT_VALID(dwarf::DW_OP_deref);
+  EXPECT_VALID(dwarf::DW_OP_bit_piece, 3, 7);
+  EXPECT_VALID(dwarf::DW_OP_plus, 6, dwarf::DW_OP_deref);
+  EXPECT_VALID(dwarf::DW_OP_deref, dwarf::DW_OP_plus, 6);
+  EXPECT_VALID(dwarf::DW_OP_deref, dwarf::DW_OP_bit_piece, 3, 7);
+  EXPECT_VALID(dwarf::DW_OP_deref, dwarf::DW_OP_plus, 6, dwarf::DW_OP_bit_piece, 3, 7);
+
+  // Invalid constructions.
+  EXPECT_INVALID(~0u);
+  EXPECT_INVALID(dwarf::DW_OP_plus);
+  EXPECT_INVALID(dwarf::DW_OP_bit_piece);
+  EXPECT_INVALID(dwarf::DW_OP_bit_piece, 3);
+  EXPECT_INVALID(dwarf::DW_OP_bit_piece, 3, 7, dwarf::DW_OP_plus, 3);
+  EXPECT_INVALID(dwarf::DW_OP_bit_piece, 3, 7, dwarf::DW_OP_deref);
+
+#undef EXPECT_VALID
+#undef EXPECT_INVALID
+}
+
 typedef MetadataTest MDObjCPropertyTest;
 
 TEST_F(MDObjCPropertyTest, get) {