[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

Author: zygoloid

include/clang/AST/ExprCXX.h

@@ -220,6 +220,96 @@ class CXXMemberCallExpr final : public CallExpr {
   }
 };
 
+/// 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 @@ class alignas(void *) Stmt {
     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 @@ class alignas(void *) Stmt {
 
     // 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 @@ class ExprEvaluatorBase
     }
   }
 
+  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 @@ void CXXNameMangler::mangleExpression(const Expr *E, unsigned Arity) {
     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);