[c++20] Add CXXRewrittenBinaryOperator to represent a comparison

operator that is rewritten as a call to multiple other operators.

No functionality change yet: nothing creates these expressions.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@375305 91177308-0d34-0410-b5e6-96231b3b80d8

include/clang/AST/ExprCXX.h

@@ -220,6 +220,96 @@ public:
   }
 };
 
+/// A rewritten comparison expression that was originally written using
+/// operator syntax.
+///
+/// In C++20, the following rewrites are performed:
+/// - <tt>a == b</tt> -> <tt>b == a</tt>
+/// - <tt>a != b</tt> -> <tt>!(a == b)</tt>
+/// - <tt>a != b</tt> -> <tt>!(b == a)</tt>
+/// - For \c \@ in \c <, \c <=, \c >, \c >=, \c <=>:
+///   - <tt>a @ b<tt> -> <tt>(a <=> b) @ 0</tt>
+///   - <tt>a @ b<tt> -> <tt>0 @ (b <=> a)</tt>
+///
+/// This expression provides access to both the original syntax and the
+/// rewritten expression.
+///
+/// Note that the rewritten calls to \c ==, \c <=>, and \c \@ are typically
+/// \c CXXOperatorCallExprs, but could theoretically be \c BinaryOperators.
+class CXXRewrittenBinaryOperator : public Expr {
+  friend class ASTStmtReader;
+
+  /// The rewritten semantic form.
+  Stmt *SemanticForm;
+
+public:
+  CXXRewrittenBinaryOperator(Expr *SemanticForm, bool IsReversed)
+      : Expr(CXXRewrittenBinaryOperatorClass, SemanticForm->getType(),
+             SemanticForm->getValueKind(), SemanticForm->getObjectKind(),
+             SemanticForm->isTypeDependent(), SemanticForm->isValueDependent(),
+             SemanticForm->isInstantiationDependent(),
+             SemanticForm->containsUnexpandedParameterPack()),
+        SemanticForm(SemanticForm) {
+    CXXRewrittenBinaryOperatorBits.IsReversed = IsReversed;
+  }
+  CXXRewrittenBinaryOperator(EmptyShell Empty)
+      : Expr(CXXRewrittenBinaryOperatorClass, Empty), SemanticForm() {}
+
+  /// Get an equivalent semantic form for this expression.
+  Expr *getSemanticForm() { return cast<Expr>(SemanticForm); }
+  const Expr *getSemanticForm() const { return cast<Expr>(SemanticForm); }
+
+  struct DecomposedForm {
+    /// The original opcode, prior to rewriting.
+    BinaryOperatorKind Opcode;
+    /// The original left-hand side.
+    const Expr *LHS;
+    /// The original right-hand side.
+    const Expr *RHS;
+    /// The inner \c == or \c <=> operator expression.
+    const Expr *InnerBinOp;
+  };
+
+  /// Decompose this operator into its syntactic form.
+  DecomposedForm getDecomposedForm() const LLVM_READONLY;
+
+  /// Determine whether this expression was rewritten in reverse form.
+  bool isReversed() const { return CXXRewrittenBinaryOperatorBits.IsReversed; }
+
+  BinaryOperatorKind getOperator() const { return getDecomposedForm().Opcode; }
+  const Expr *getLHS() const { return getDecomposedForm().LHS; }
+  const Expr *getRHS() const { return getDecomposedForm().RHS; }
+
+  SourceLocation getOperatorLoc() const LLVM_READONLY {
+    return getDecomposedForm().InnerBinOp->getExprLoc();
+  }
+  SourceLocation getExprLoc() const LLVM_READONLY { return getOperatorLoc(); }
+
+  /// Compute the begin and end locations from the decomposed form.
+  /// The locations of the semantic form are not reliable if this is
+  /// a reversed expression.
+  //@{
+  SourceLocation getBeginLoc() const LLVM_READONLY {
+    return getDecomposedForm().LHS->getBeginLoc();
+  }
+  SourceLocation getEndLoc() const LLVM_READONLY {
+    return getDecomposedForm().RHS->getEndLoc();
+  }
+  SourceRange getSourceRange() const LLVM_READONLY {
+    DecomposedForm DF = getDecomposedForm();
+    return SourceRange(DF.LHS->getBeginLoc(), DF.RHS->getEndLoc());
+  }
+  //@}
+
+  child_range children() {
+    return child_range(&SemanticForm, &SemanticForm + 1);
+  }
+
+  static bool classof(const Stmt *T) {
+    return T->getStmtClass() == CXXRewrittenBinaryOperatorClass;
+  }
+};
+
 /// Represents a call to a CUDA kernel function.
 class CUDAKernelCallExpr final : public CallExpr {
   friend class ASTStmtReader;

include/clang/AST/RecursiveASTVisitor.h

@@ -2606,6 +2606,15 @@ DEF_TRAVERSE_STMT(SEHLeaveStmt, {})
 DEF_TRAVERSE_STMT(CapturedStmt, { TRY_TO(TraverseDecl(S->getCapturedDecl())); })
 
 DEF_TRAVERSE_STMT(CXXOperatorCallExpr, {})
+DEF_TRAVERSE_STMT(CXXRewrittenBinaryOperator, {
+  if (!getDerived().shouldVisitImplicitCode()) {
+    CXXRewrittenBinaryOperator::DecomposedForm Decomposed =
+        S->getDecomposedForm();
+    TRY_TO(TraverseStmt(const_cast<Expr*>(Decomposed.LHS)));
+    TRY_TO(TraverseStmt(const_cast<Expr*>(Decomposed.RHS)));
+    ShouldVisitChildren = false;
+  }
+})
 DEF_TRAVERSE_STMT(OpaqueValueExpr, {})
 DEF_TRAVERSE_STMT(TypoExpr, {})
 DEF_TRAVERSE_STMT(CUDAKernelCallExpr, {})

include/clang/AST/Stmt.h

@@ -604,6 +604,15 @@ protected:
     unsigned FPFeatures : 3;
   };
 
+  class CXXRewrittenBinaryOperatorBitfields {
+    friend class ASTStmtReader;
+    friend class CXXRewrittenBinaryOperator;
+
+    unsigned : NumCallExprBits;
+
+    unsigned IsReversed : 1;
+  };
+
   class CXXBoolLiteralExprBitfields {
     friend class CXXBoolLiteralExpr;
 
@@ -978,6 +987,7 @@ protected:
 
     // C++ Expressions
     CXXOperatorCallExprBitfields CXXOperatorCallExprBits;
+    CXXRewrittenBinaryOperatorBitfields CXXRewrittenBinaryOperatorBits;
     CXXBoolLiteralExprBitfields CXXBoolLiteralExprBits;
     CXXNullPtrLiteralExprBitfields CXXNullPtrLiteralExprBits;
     CXXThisExprBitfields CXXThisExprBits;

include/clang/Basic/StmtNodes.td

@@ -114,6 +114,7 @@ def GNUNullExpr : DStmt<Expr>;
 // C++ Expressions.
 def CXXOperatorCallExpr : DStmt<CallExpr>;
 def CXXMemberCallExpr : DStmt<CallExpr>;
+def CXXRewrittenBinaryOperator : DStmt<Expr>;
 def CXXNamedCastExpr : DStmt<ExplicitCastExpr, 1>;
 def CXXStaticCastExpr : DStmt<CXXNamedCastExpr>;
 def CXXDynamicCastExpr : DStmt<CXXNamedCastExpr>;

include/clang/Serialization/ASTBitCodes.h

@@ -1845,6 +1845,9 @@ namespace serialization {
       /// A CXXMemberCallExpr record.
       EXPR_CXX_MEMBER_CALL,
 
+      /// A CXXRewrittenBinaryOperator record.
+      EXPR_CXX_REWRITTEN_BINARY_OPERATOR,
+
       /// A CXXConstructExpr record.
       EXPR_CXX_CONSTRUCT,
 

lib/AST/Expr.cpp

@@ -3473,6 +3473,7 @@ bool Expr::HasSideEffects(const ASTContext &Ctx,
   case ArrayInitLoopExprClass:
   case ParenListExprClass:
   case CXXPseudoDestructorExprClass:
+  case CXXRewrittenBinaryOperatorClass:
   case CXXStdInitializerListExprClass:
   case SubstNonTypeTemplateParmExprClass:
   case MaterializeTemporaryExprClass:

lib/AST/ExprCXX.cpp

@@ -58,6 +58,76 @@ bool CXXOperatorCallExpr::isInfixBinaryOp() const {
   }
 }
 
+CXXRewrittenBinaryOperator::DecomposedForm
+CXXRewrittenBinaryOperator::getDecomposedForm() const {
+  DecomposedForm Result = {};
+  const Expr *E = getSemanticForm()->IgnoreImplicit();
+
+  // Remove an outer '!' if it exists (only happens for a '!=' rewrite).
+  bool SkippedNot = false;
+  if (auto *NotEq = dyn_cast<UnaryOperator>(E)) {
+    assert(NotEq->getOpcode() == UO_LNot);
+    E = NotEq->getSubExpr()->IgnoreImplicit();
+    SkippedNot = true;
+  }
+
+  // Decompose the outer binary operator.
+  if (auto *BO = dyn_cast<BinaryOperator>(E)) {
+    assert(!SkippedNot || BO->getOpcode() == BO_EQ);
+    Result.Opcode = SkippedNot ? BO_NE : BO->getOpcode();
+    Result.LHS = BO->getLHS();
+    Result.RHS = BO->getRHS();
+    Result.InnerBinOp = BO;
+  } else if (auto *BO = dyn_cast<CXXOperatorCallExpr>(E)) {
+    assert(!SkippedNot || BO->getOperator() == OO_Equal);
+    assert(BO->isInfixBinaryOp());
+    switch (BO->getOperator()) {
+    case OO_Less: Result.Opcode = BO_LT; break;
+    case OO_LessEqual: Result.Opcode = BO_LE; break;
+    case OO_Greater: Result.Opcode = BO_GT; break;
+    case OO_GreaterEqual: Result.Opcode = BO_GE; break;
+    case OO_Spaceship: Result.Opcode = BO_Cmp; break;
+    case OO_EqualEqual: Result.Opcode = SkippedNot ? BO_NE : BO_EQ; break;
+    default: llvm_unreachable("unexpected binop in rewritten operator expr");
+    }
+    Result.LHS = BO->getArg(0);
+    Result.RHS = BO->getArg(1);
+    Result.InnerBinOp = BO;
+  } else {
+    llvm_unreachable("unexpected rewritten operator form");
+  }
+
+  // Put the operands in the right order for == and !=, and canonicalize the
+  // <=> subexpression onto the LHS for all other forms.
+  if (isReversed())
+    std::swap(Result.LHS, Result.RHS);
+
+  // If this isn't a spaceship rewrite, we're done.
+  if (Result.Opcode == BO_EQ || Result.Opcode == BO_NE)
+    return Result;
+
+  // Otherwise, we expect a <=> to now be on the LHS.
+  E = Result.InnerBinOp->IgnoreImplicit();
+  if (auto *BO = dyn_cast<BinaryOperator>(E)) {
+    assert(BO->getOpcode() == BO_Cmp);
+    Result.LHS = BO->getLHS();
+    Result.RHS = BO->getRHS();
+    Result.InnerBinOp = BO;
+  } else if (auto *BO = dyn_cast<CXXOperatorCallExpr>(E)) {
+    assert(BO->getOperator() == OO_Spaceship);
+    Result.LHS = BO->getArg(0);
+    Result.RHS = BO->getArg(1);
+    Result.InnerBinOp = BO;
+  } else {
+    llvm_unreachable("unexpected rewritten operator form");
+  }
+
+  // Put the comparison operands in the right order.
+  if (isReversed())
+    std::swap(Result.LHS, Result.RHS);
+  return Result;
+}
+
 bool CXXTypeidExpr::isPotentiallyEvaluated() const {
   if (isTypeOperand())
     return false;

lib/AST/ExprClassification.cpp

@@ -307,6 +307,10 @@ static Cl::Kinds ClassifyInternal(ASTContext &Ctx, const Expr *E) {
   case Expr::CUDAKernelCallExprClass:
     return ClassifyUnnamed(Ctx, cast<CallExpr>(E)->getCallReturnType(Ctx));
 
+  case Expr::CXXRewrittenBinaryOperatorClass:
+    return ClassifyInternal(
+        Ctx, cast<CXXRewrittenBinaryOperator>(E)->getSemanticForm());
+
     // __builtin_choose_expr is equivalent to the chosen expression.
   case Expr::ChooseExprClass:
     return ClassifyInternal(Ctx, cast<ChooseExpr>(E)->getChosenSubExpr());

lib/AST/ExprConstant.cpp

@@ -6765,6 +6765,10 @@ public:
     }
   }
 
+  bool VisitCXXRewrittenBinaryOperator(const CXXRewrittenBinaryOperator *E) {
+    return StmtVisitorTy::Visit(E->getSemanticForm());
+  }
+
   bool VisitBinaryConditionalOperator(const BinaryConditionalOperator *E) {
     // Evaluate and cache the common expression. We treat it as a temporary,
     // even though it's not quite the same thing.
@@ -13945,6 +13949,9 @@ static ICEDiag CheckICE(const Expr* E, const ASTContext &Ctx) {
       return CheckEvalInICE(E, Ctx);
     return ICEDiag(IK_NotICE, E->getBeginLoc());
   }
+  case Expr::CXXRewrittenBinaryOperatorClass:
+    return CheckICE(cast<CXXRewrittenBinaryOperator>(E)->getSemanticForm(),
+                    Ctx);
   case Expr::DeclRefExprClass: {
     if (isa<EnumConstantDecl>(cast<DeclRefExpr>(E)->getDecl()))
       return NoDiag();

lib/AST/ItaniumMangle.cpp

@@ -4090,6 +4090,17 @@ recurse:
     break;
   }
 
+  case Expr::CXXRewrittenBinaryOperatorClass: {
+    // The mangled form represents the original syntax.
+    CXXRewrittenBinaryOperator::DecomposedForm Decomposed =
+        cast<CXXRewrittenBinaryOperator>(E)->getDecomposedForm();
+    mangleOperatorName(BinaryOperator::getOverloadedOperator(Decomposed.Opcode),
+                       /*Arity=*/2);
+    mangleExpression(Decomposed.LHS);
+    mangleExpression(Decomposed.RHS);
+    break;
+  }
+
   case Expr::ConditionalOperatorClass: {
     const ConditionalOperator *CO = cast<ConditionalOperator>(E);
     mangleOperatorName(OO_Conditional, /*Arity=*/3);

lib/AST/StmtPrinter.cpp

@@ -1697,6 +1697,15 @@ void StmtPrinter::VisitCUDAKernelCallExpr(CUDAKernelCallExpr *Node) {
   OS << ")";
 }
 
+void StmtPrinter::VisitCXXRewrittenBinaryOperator(
+    CXXRewrittenBinaryOperator *Node) {
+  CXXRewrittenBinaryOperator::DecomposedForm Decomposed =
+      Node->getDecomposedForm();
+  PrintExpr(const_cast<Expr*>(Decomposed.LHS));
+  OS << ' ' << BinaryOperator::getOpcodeStr(Decomposed.Opcode) << ' ';
+  PrintExpr(const_cast<Expr*>(Decomposed.RHS));
+}
+
 void StmtPrinter::VisitCXXNamedCastExpr(CXXNamedCastExpr *Node) {
   OS << Node->getCastName() << '<';
   Node->getTypeAsWritten().print(OS, Policy);

lib/AST/StmtProfile.cpp

@@ -1557,6 +1557,16 @@ void StmtProfiler::VisitCXXOperatorCallExpr(const CXXOperatorCallExpr *S) {
   ID.AddInteger(S->getOperator());
 }
 
+void StmtProfiler::VisitCXXRewrittenBinaryOperator(
+    const CXXRewrittenBinaryOperator *S) {
+  // If a rewritten operator were ever to be type-dependent, we should profile
+  // it following its syntactic operator.
+  assert(!S->isTypeDependent() &&
+         "resolved rewritten operator should never be type-dependent");
+  ID.AddBoolean(S->isReversed());
+  VisitExpr(S->getSemanticForm());
+}
+
 #if defined(_MSC_VER) && !defined(__clang__)
 #if _MSC_VER == 1911
 #pragma optimize("", on)

lib/CodeGen/CGExpr.cpp

@@ -1267,6 +1267,8 @@ LValue CodeGenFunction::EmitLValue(const Expr *E) {
   case Expr::CXXOperatorCallExprClass:
   case Expr::UserDefinedLiteralClass:
     return EmitCallExprLValue(cast<CallExpr>(E));
+  case Expr::CXXRewrittenBinaryOperatorClass:
+    return EmitLValue(cast<CXXRewrittenBinaryOperator>(E)->getSemanticForm());
   case Expr::VAArgExprClass:
     return EmitVAArgExprLValue(cast<VAArgExpr>(E));
   case Expr::DeclRefExprClass:

lib/CodeGen/CGExprAgg.cpp

@@ -150,6 +150,9 @@ public:
   void VisitBinAssign(const BinaryOperator *E);
   void VisitBinComma(const BinaryOperator *E);
   void VisitBinCmp(const BinaryOperator *E);
+  void VisitCXXRewrittenBinaryOperator(CXXRewrittenBinaryOperator *E) {
+    Visit(E->getSemanticForm());
+  }
 
   void VisitObjCMessageExpr(ObjCMessageExpr *E);
   void VisitObjCIvarRefExpr(ObjCIvarRefExpr *E) {

lib/CodeGen/CGExprComplex.cpp

@@ -279,6 +279,10 @@ public:
     return EmitBinDiv(EmitBinOps(E));
   }
 
+  ComplexPairTy VisitCXXRewrittenBinaryOperator(CXXRewrittenBinaryOperator *E) {
+    return Visit(E->getSemanticForm());
+  }
+
   // Compound assignments.
   ComplexPairTy VisitBinAddAssign(const CompoundAssignOperator *E) {
     return EmitCompoundAssign(E, &ComplexExprEmitter::EmitBinAdd);

lib/CodeGen/CGExprScalar.cpp

@@ -817,6 +817,10 @@ public:
   Value *VisitBinPtrMemD(const Expr *E) { return EmitLoadOfLValue(E); }
   Value *VisitBinPtrMemI(const Expr *E) { return EmitLoadOfLValue(E); }
 
+  Value *VisitCXXRewrittenBinaryOperator(CXXRewrittenBinaryOperator *E) {
+    return Visit(E->getSemanticForm());
+  }
+
   // Other Operators.
   Value *VisitBlockExpr(const BlockExpr *BE);
   Value *VisitAbstractConditionalOperator(const AbstractConditionalOperator *);

lib/Sema/SemaExceptionSpec.cpp

@@ -1201,6 +1201,7 @@ CanThrowResult Sema::canThrow(const Expr *E) {
   case Expr::CoyieldExprClass:
   case Expr::CXXConstCastExprClass:
   case Expr::CXXReinterpretCastExprClass:
+  case Expr::CXXRewrittenBinaryOperatorClass:
   case Expr::BuiltinBitCastExprClass:
   case Expr::CXXStdInitializerListExprClass:
   case Expr::DesignatedInitExprClass:

lib/Sema/TreeTransform.h

@@ -2353,6 +2353,17 @@ public:
     return getSema().BuildBinOp(/*Scope=*/nullptr, OpLoc, Opc, LHS, RHS);
   }
 
+  /// Build a new rewritten operator expression.
+  ///
+  /// By default, builds the rewritten operator without performing any semantic
+  /// analysis. Subclasses may override this routine to provide different
+  /// behavior.
+  ExprResult RebuildCXXRewrittenBinaryOperator(Expr *SemanticForm,
+                                             bool IsReversed) {
+    return new (getSema().Context)
+        CXXRewrittenBinaryOperator(SemanticForm, IsReversed);
+  }
+
   /// Build a new conditional operator expression.
   ///
   /// By default, performs semantic analysis to build the new expression.
@@ -9769,6 +9780,29 @@ TreeTransform<Derived>::TransformBinaryOperator(BinaryOperator *E) {
                                             LHS.get(), RHS.get());
 }
 
+template <typename Derived>
+ExprResult TreeTransform<Derived>::TransformCXXRewrittenBinaryOperator(
+    CXXRewrittenBinaryOperator *E) {
+  // FIXME: C++ [temp.deduct]p7 "The substitution proceeds in lexical order and
+  // stops when a condition that causes deduction to fail is encountered."
+  // requires us to substitute into the LHS before the RHS, even in a rewrite
+  // that reversed the operand order.
+  //
+  // We can't decompose back to a binary operator here, because that would lose
+  // the unqualified lookup results from the phase 1 name lookup.
+
+  ExprResult SemanticForm = getDerived().TransformExpr(E->getSemanticForm());
+  if (SemanticForm.isInvalid())
+    return ExprError();
+
+  if (!getDerived().AlwaysRebuild() &&
+      SemanticForm.get() == E->getSemanticForm())
+    return E;
+
+  return getDerived().RebuildCXXRewrittenBinaryOperator(SemanticForm.get(),
+                                                      E->isReversed());
+}
+
 template<typename Derived>
 ExprResult
 TreeTransform<Derived>::TransformCompoundAssignOperator(

lib/Serialization/ASTReaderStmt.cpp

@@ -1440,6 +1440,13 @@ void ASTStmtReader::VisitCXXOperatorCallExpr(CXXOperatorCallExpr *E) {
   E->Range = Record.readSourceRange();
 }
 
+void ASTStmtReader::VisitCXXRewrittenBinaryOperator(
+    CXXRewrittenBinaryOperator *E) {
+  VisitExpr(E);
+  E->CXXRewrittenBinaryOperatorBits.IsReversed = Record.readInt();
+  E->SemanticForm = Record.readSubExpr();
+}
+
 void ASTStmtReader::VisitCXXConstructExpr(CXXConstructExpr *E) {
   VisitExpr(E);
 
@@ -3252,6 +3259,10 @@ Stmt *ASTReader::ReadStmtFromStream(ModuleFile &F) {
           Context, /*NumArgs=*/Record[ASTStmtReader::NumExprFields], Empty);
       break;
 
+    case EXPR_CXX_REWRITTEN_BINARY_OPERATOR:
+      S = new (Context) CXXRewrittenBinaryOperator(Empty);
+      break;
+
     case EXPR_CXX_CONSTRUCT:
       S = CXXConstructExpr::CreateEmpty(
           Context,

lib/Serialization/ASTWriter.cpp

@@ -1024,6 +1024,7 @@ static void AddStmtsExprs(llvm::BitstreamWriter &Stream,
   RECORD(STMT_CXX_FOR_RANGE);
   RECORD(EXPR_CXX_OPERATOR_CALL);
   RECORD(EXPR_CXX_MEMBER_CALL);
+  RECORD(EXPR_CXX_REWRITTEN_BINARY_OPERATOR);
   RECORD(EXPR_CXX_CONSTRUCT);
   RECORD(EXPR_CXX_TEMPORARY_OBJECT);
   RECORD(EXPR_CXX_STATIC_CAST);

lib/Serialization/ASTWriterStmt.cpp

@@ -1375,6 +1375,14 @@ void ASTStmtWriter::VisitCXXMemberCallExpr(CXXMemberCallExpr *E) {
   Code = serialization::EXPR_CXX_MEMBER_CALL;
 }
 
+void ASTStmtWriter::VisitCXXRewrittenBinaryOperator(
+    CXXRewrittenBinaryOperator *E) {
+  VisitExpr(E);
+  Record.push_back(E->isReversed());
+  Record.AddStmt(E->getSemanticForm());
+  Code = serialization::EXPR_CXX_REWRITTEN_BINARY_OPERATOR;
+}
+
 void ASTStmtWriter::VisitCXXConstructExpr(CXXConstructExpr *E) {
   VisitExpr(E);
 

lib/StaticAnalyzer/Core/ExprEngine.cpp

@@ -1372,6 +1372,7 @@ void ExprEngine::Visit(const Stmt *S, ExplodedNode *Pred,
     case Stmt::OpaqueValueExprClass:
     case Stmt::AsTypeExprClass:
     case Stmt::ConceptSpecializationExprClass:
+    case Stmt::CXXRewrittenBinaryOperatorClass:
       // Fall through.
 
     // Cases we intentionally don't evaluate, since they don't need

tools/libclang/CXCursor.cpp

@@ -263,6 +263,7 @@ CXCursor cxcursor::MakeCXCursor(const Stmt *S, const Decl *Parent,
   case Stmt::CXXDefaultArgExprClass:
   case Stmt::CXXDefaultInitExprClass:
   case Stmt::CXXFoldExprClass:
+  case Stmt::CXXRewrittenBinaryOperatorClass:
   case Stmt::CXXStdInitializerListExprClass:
   case Stmt::CXXScalarValueInitExprClass:
   case Stmt::CXXUuidofExprClass: