[LLDB] Add type casting to DIL, part 1 of 3. (#165199)

This is an alternative to
https://github.com/llvm/llvm-project/pull/159500, breaking that PR down
into three separate PRs, to make it easier to review.

This first PR of the three adds the basic framework for doing type
casing to the DIL code, but it does not actually do any casting: In this
PR the DIL parser only recognizes builtin type names, and the DIL
interpreter does not do anything except return the original operand (no
casting). The second and third PRs will add most of the type parsing,
and do the actual type casting, respectively.

lldb/docs/dil-expr-lang.ebnf

@@ -3,10 +3,13 @@
 (* This is currently a subset of the final DIL Language, matching the current
    DIL implementation. *)
 
-expression = unary_expression ;
+expression = cast_expression;
+
+cast_expression = unary_expression
+                | "(" type_id ")" cast_expression;
 
 unary_expression = postfix_expression
-                 | unary_operator expression ;
+                 | unary_operator cast_expression ;
 
 unary_operator = "*" | "&" | "+" | "-";
 
@@ -44,10 +47,28 @@ nested_name_specifier = type_name "::"
                       | namespace_name '::'
                       | nested_name_specifier identifier "::" ;
 
+type_id = type_specifier_seq [abstract_declarator] ;
+
+type_specifier_seq = type_specifier [type_specifier];
+
+type_specifier = ["::"] [nested_name_specifier] type_name
+               | builtin_typename ;
+
+nested_name_specifier = type_name "::"
+                      | namespace_name "::"
+                      | nested_name_specifier identifier "::" ;
+
+abstract_declarator = ptr_operator [abstract_declarator] ;
+
+ptr_operator = "*"
+             | "&";
+
 type_name = class_name
           | enum_name
           | typedef_name;
 
+builtin_typename = identifier_seq;
+
 class_name = identifier ;
 
 enum_name = identifier ;
@@ -56,6 +77,7 @@ typedef_name = identifier ;
 
 namespace_name = identifier ;
 
-
+identifier_seq = identifier
+               | identifier identifier_seq;
 
 

lldb/include/lldb/ValueObject/DILAST.h

@@ -21,6 +21,7 @@ enum class NodeKind {
   eArraySubscriptNode,
   eBitExtractionNode,
   eBooleanLiteralNode,
+  eCastNode,
   eErrorNode,
   eFloatLiteralNode,
   eIdentifierNode,
@@ -37,6 +38,14 @@ enum class UnaryOpKind {
   Plus,   // "+"
 };
 
+/// The type casts allowed by DIL.
+enum class CastKind {
+  eEnumeration, ///< Casting from a scalar to an enumeration type
+  eNullptr,     ///< Casting to a nullptr type
+  eReference,   ///< Casting to a reference type
+  eNone,        ///< Type promotion casting
+};
+
 /// Forward declaration, for use in DIL AST nodes. Definition is at the very
 /// end of this file.
 class Visitor;
@@ -246,6 +255,29 @@ private:
   bool m_value;
 };
 
+class CastNode : public ASTNode {
+public:
+  CastNode(uint32_t location, CompilerType type, ASTNodeUP operand,
+           CastKind kind)
+      : ASTNode(location, NodeKind::eCastNode), m_type(type),
+        m_operand(std::move(operand)), m_cast_kind(kind) {}
+
+  llvm::Expected<lldb::ValueObjectSP> Accept(Visitor *v) const override;
+
+  CompilerType GetType() const { return m_type; }
+  ASTNode *GetOperand() const { return m_operand.get(); }
+  CastKind GetCastKind() const { return m_cast_kind; }
+
+  static bool classof(const ASTNode *node) {
+    return node->GetKind() == NodeKind::eCastNode;
+  }
+
+private:
+  CompilerType m_type;
+  ASTNodeUP m_operand;
+  CastKind m_cast_kind;
+};
+
 /// This class contains one Visit method for each specialized type of
 /// DIL AST node. The Visit methods are used to dispatch a DIL AST node to
 /// the correct function in the DIL expression evaluator for evaluating that
@@ -269,6 +301,7 @@ public:
   Visit(const FloatLiteralNode *node) = 0;
   virtual llvm::Expected<lldb::ValueObjectSP>
   Visit(const BooleanLiteralNode *node) = 0;
+  virtual llvm::Expected<lldb::ValueObjectSP> Visit(const CastNode *node) = 0;
 };
 
 } // namespace lldb_private::dil

lldb/include/lldb/ValueObject/DILEval.h

@@ -60,6 +60,7 @@ private:
   Visit(const FloatLiteralNode *node) override;
   llvm::Expected<lldb::ValueObjectSP>
   Visit(const BooleanLiteralNode *node) override;
+  llvm::Expected<lldb::ValueObjectSP> Visit(const CastNode *node) override;
 
   /// Perform usual unary conversions on a value. At the moment this
   /// includes array-to-pointer and integral promotion for eligible types.

lldb/include/lldb/ValueObject/DILParser.h

@@ -101,6 +101,12 @@ private:
   ASTNodeUP ParseFloatingPointLiteral();
   ASTNodeUP ParseBooleanLiteral();
 
+  ASTNodeUP ParseCastExpression();
+  std::optional<CompilerType> ParseBuiltinType();
+  std::optional<CompilerType> ParseTypeId();
+  CompilerType ResolveTypeDeclarators(CompilerType type,
+                                      const std::vector<Token> &ptr_operators);
+
   void BailOut(const std::string &error, uint32_t loc, uint16_t err_len);
 
   void Expect(Token::Kind kind);

lldb/source/ValueObject/DILAST.cpp

@@ -51,4 +51,8 @@ BooleanLiteralNode::Accept(Visitor *v) const {
   return v->Visit(this);
 }
 
+llvm::Expected<lldb::ValueObjectSP> CastNode::Accept(Visitor *v) const {
+  return v->Visit(this);
+}
+
 } // namespace lldb_private::dil

lldb/source/ValueObject/DILEval.cpp

@@ -740,4 +740,16 @@ Interpreter::Visit(const BooleanLiteralNode *node) {
   return ValueObject::CreateValueObjectFromBool(m_target, value, "result");
 }
 
+llvm::Expected<lldb::ValueObjectSP> Interpreter::Visit(const CastNode *node) {
+  auto operand_or_err = Evaluate(node->GetOperand());
+  if (!operand_or_err)
+    return operand_or_err;
+
+  lldb::ValueObjectSP operand = *operand_or_err;
+  // Don't actually do the cast for now -- that code will be added later.
+  // For now just return an error message.
+  return llvm::make_error<DILDiagnosticError>(
+      m_expr, "Type casting is not supported here.", node->GetLocation());
+}
+
 } // namespace lldb_private::dil

lldb/source/ValueObject/DILParser.cpp

@@ -13,7 +13,9 @@
 
 #include "lldb/ValueObject/DILParser.h"
 #include "lldb/Host/common/DiagnosticsRendering.h"
+#include "lldb/Symbol/CompileUnit.h"
 #include "lldb/Target/ExecutionContextScope.h"
+#include "lldb/Target/LanguageRuntime.h"
 #include "lldb/ValueObject/DILAST.h"
 #include "lldb/ValueObject/DILEval.h"
 #include "llvm/ADT/StringRef.h"
@@ -80,15 +82,63 @@ ASTNodeUP DILParser::Run() {
 // Parse an expression.
 //
 //  expression:
-//    unary_expression
+//    cast_expression
 //
-ASTNodeUP DILParser::ParseExpression() { return ParseUnaryExpression(); }
+ASTNodeUP DILParser::ParseExpression() { return ParseCastExpression(); }
+
+// Parse a cast_expression.
+//
+// cast_expression:
+//   unary_expression
+//   "(" type_id ")" cast_expression
+
+ASTNodeUP DILParser::ParseCastExpression() {
+  if (!CurToken().Is(Token::l_paren))
+    return ParseUnaryExpression();
+
+  // This could be a type cast, try parsing the contents as a type declaration.
+  Token token = CurToken();
+  uint32_t loc = token.GetLocation();
+
+  // Enable lexer backtracking, so that we can rollback in case it's not
+  // actually a type declaration.
+
+  // Start tentative parsing (save token location/idx, for possible rollback).
+  uint32_t save_token_idx = m_dil_lexer.GetCurrentTokenIdx();
+
+  // Consume the token only after enabling the backtracking.
+  m_dil_lexer.Advance();
+
+  // Try parsing the type declaration. If the returned value is not valid,
+  // then we should rollback and try parsing the expression.
+  auto type_id = ParseTypeId();
+  if (type_id) {
+    // Successfully parsed the type declaration. Commit the backtracked
+    // tokens and parse the cast_expression.
+
+    if (!type_id.value().IsValid())
+      return std::make_unique<ErrorNode>();
+
+    Expect(Token::r_paren);
+    m_dil_lexer.Advance();
+    auto rhs = ParseCastExpression();
+
+    return std::make_unique<CastNode>(loc, type_id.value(), std::move(rhs),
+                                      CastKind::eNone);
+  }
+
+  // Failed to parse the contents of the parentheses as a type declaration.
+  // Rollback the lexer and try parsing it as unary_expression.
+  TentativeParsingRollback(save_token_idx);
+
+  return ParseUnaryExpression();
+}
 
 // Parse an unary_expression.
 //
 //  unary_expression:
 //    postfix_expression
-//    unary_operator expression
+//    unary_operator cast_expression
 //
 //  unary_operator:
 //    "&"
@@ -102,7 +152,7 @@ ASTNodeUP DILParser::ParseUnaryExpression() {
     Token token = CurToken();
     uint32_t loc = token.GetLocation();
     m_dil_lexer.Advance();
-    auto rhs = ParseExpression();
+    auto rhs = ParseCastExpression();
     switch (token.GetKind()) {
     case Token::star:
       return std::make_unique<UnaryOpNode>(loc, UnaryOpKind::Deref,
@@ -282,6 +332,81 @@ std::string DILParser::ParseNestedNameSpecifier() {
   }
 }
 
+// Parse a type_id.
+//
+//  type_id:
+//    type_specifier_seq [abstract_declarator]
+//
+//  type_specifier_seq:
+//    type_specifier [type_specifier]
+//
+//  type_specifier:
+//    ["::"] [nested_name_specifier] type_name // not handled for now!
+//    builtin_typename
+//
+std::optional<CompilerType> DILParser::ParseTypeId() {
+  CompilerType type;
+  // For now only allow builtin types -- will expand add to this later.
+  auto maybe_builtin_type = ParseBuiltinType();
+  if (maybe_builtin_type) {
+    type = *maybe_builtin_type;
+  } else
+    return {};
+
+  //
+  //  abstract_declarator:
+  //    ptr_operator [abstract_declarator]
+  //
+  std::vector<Token> ptr_operators;
+  while (CurToken().IsOneOf({Token::star, Token::amp})) {
+    Token tok = CurToken();
+    ptr_operators.push_back(std::move(tok));
+    m_dil_lexer.Advance();
+  }
+  type = ResolveTypeDeclarators(type, ptr_operators);
+
+  return type;
+}
+
+// Parse a built-in type
+//
+// builtin_typename:
+//   identifer_seq
+//
+//  identifier_seq
+//    identifer [identifier_seq]
+//
+// A built-in type can be a single identifier or a space-separated
+// list of identifiers (e.g. "short" or "long long").
+std::optional<CompilerType> DILParser::ParseBuiltinType() {
+  std::string type_name = "";
+  uint32_t save_token_idx = m_dil_lexer.GetCurrentTokenIdx();
+  bool first_word = true;
+  while (CurToken().GetKind() == Token::identifier) {
+    if (CurToken().GetSpelling() == "const" ||
+        CurToken().GetSpelling() == "volatile")
+      continue;
+    if (!first_word)
+      type_name.push_back(' ');
+    else
+      first_word = false;
+    type_name.append(CurToken().GetSpelling());
+    m_dil_lexer.Advance();
+  }
+
+  if (type_name.size() > 0) {
+    lldb::TargetSP target_sp = m_ctx_scope->CalculateTarget();
+    ConstString const_type_name(type_name.c_str());
+    for (auto type_system_sp : target_sp->GetScratchTypeSystems())
+      if (auto compiler_type =
+              type_system_sp->GetBuiltinTypeByName(const_type_name))
+        return compiler_type;
+  }
+
+  TentativeParsingRollback(save_token_idx);
+  return {};
+}
+
 // Parse an id_expression.
 //
 //  id_expression:
@@ -347,6 +472,40 @@ std::string DILParser::ParseUnqualifiedId() {
   return identifier;
 }
 
+CompilerType
+DILParser::ResolveTypeDeclarators(CompilerType type,
+                                  const std::vector<Token> &ptr_operators) {
+  // Resolve pointers/references.
+  for (Token tk : ptr_operators) {
+    uint32_t loc = tk.GetLocation();
+    if (tk.GetKind() == Token::star) {
+      // Pointers to reference types are forbidden.
+      if (type.IsReferenceType()) {
+        BailOut(llvm::formatv("'type name' declared as a pointer to a "
+                              "reference of type {0}",
+                              type.TypeDescription()),
+                loc, CurToken().GetSpelling().length());
+        return {};
+      }
+      // Get pointer type for the base type: e.g. int* -> int**.
+      type = type.GetPointerType();
+
+    } else if (tk.GetKind() == Token::amp) {
+      // References to references are forbidden.
+      // FIXME: In future we may want to allow rvalue references (i.e. &&).
+      if (type.IsReferenceType()) {
+        BailOut("type name declared as a reference to a reference", loc,
+                CurToken().GetSpelling().length());
+        return {};
+      }
+      // Get reference type for the base type: e.g. int -> int&.
+      type = type.GetLValueReferenceType();
+    }
+  }
+
+  return type;
+}
+
 // Parse an boolean_literal.
 //
 //  boolean_literal: