path: root/lib/AST/ExprConstant.cpp

//===--- ExprConstant.cpp - Expression Constant Evaluator -----------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the Expr constant evaluator.
//
//===----------------------------------------------------------------------===//

#include "clang/AST/APValue.h"
#include "clang/AST/ASTContext.h"
#include "clang/AST/StmtVisitor.h"
#include "clang/Basic/Diagnostic.h"
#include "clang/Basic/TargetInfo.h"
#include "llvm/Support/Compiler.h"
using namespace clang;
using llvm::APSInt;
using llvm::APFloat;

/// EvalInfo - This is a private struct used by the evaluator to capture
/// information about a subexpression as it is folded.  It retains information
/// about the AST context, but also maintains information about the folded
/// expression.
///
/// If an expression could be evaluated, it is still possible it is not a C
/// "integer constant expression" or constant expression.  If not, this struct
/// captures information about how and why not.
///
/// One bit of information passed *into* the request for constant folding
/// indicates whether the subexpression is "evaluated" or not according to C
/// rules.  For example, the RHS of (0 && foo()) is not evaluated.  We can
/// evaluate the expression regardless of what the RHS is, but C only allows
/// certain things in certain situations.
struct EvalInfo {
  ASTContext &Ctx;
  
  /// isEvaluated - True if the subexpression is required to be evaluated, false
  /// if it is short-circuited (according to C rules).
  bool isEvaluated;
  
  /// ICEDiag - If the expression is unfoldable, then ICEDiag contains the 
  /// error diagnostic indicating why it is not foldable and DiagLoc indicates a
  /// caret position for the error.  If it is foldable, but the expression is
  /// not an integer constant expression, ICEDiag contains the extension
  /// diagnostic to emit which describes why it isn't an integer constant
  /// expression.  If this expression *is* an integer-constant-expr, then
  /// ICEDiag is zero.
  ///
  /// The caller can choose to emit this diagnostic or not, depending on whether
  /// they require an i-c-e or a constant or not.  DiagLoc indicates the caret
  /// position for the report.
  ///
  /// If ICEDiag is zero, then this expression is an i-c-e.  
  unsigned ICEDiag;
  SourceLocation DiagLoc;

  EvalInfo(ASTContext &ctx) : Ctx(ctx), isEvaluated(true), ICEDiag(0) {}
};


static bool EvaluatePointer(const Expr *E, APValue &Result, EvalInfo &Info);
static bool EvaluateInteger(const Expr *E, APSInt  &Result, EvalInfo &Info);
static bool EvaluateFloat(const Expr *E, APFloat &Result, EvalInfo &Info);

//===----------------------------------------------------------------------===//
// Pointer Evaluation
//===----------------------------------------------------------------------===//

namespace {
class VISIBILITY_HIDDEN PointerExprEvaluator
  : public StmtVisitor<PointerExprEvaluator, APValue> {
  EvalInfo &Info;
public:
    
  PointerExprEvaluator(EvalInfo &info) : Info(info) {}

  APValue VisitStmt(Stmt *S) {
    // FIXME: Remove this when we support more expressions.
    printf("Unhandled pointer statement\n");
    S->dump();  
    return APValue();
  }

  APValue VisitParenExpr(ParenExpr *E) { return Visit(E->getSubExpr()); }

  APValue VisitBinaryOperator(const BinaryOperator *E);
  APValue VisitCastExpr(const CastExpr* E);
};
} // end anonymous namespace

static bool EvaluatePointer(const Expr* E, APValue& Result, EvalInfo &Info) {
  if (!E->getType()->isPointerType())
    return false;
  Result = PointerExprEvaluator(Info).Visit(const_cast<Expr*>(E));
  return Result.isLValue();
}

APValue PointerExprEvaluator::VisitBinaryOperator(const BinaryOperator *E) {
  if (E->getOpcode() != BinaryOperator::Add &&
      E->getOpcode() != BinaryOperator::Sub)
    return APValue();
  
  const Expr *PExp = E->getLHS();
  const Expr *IExp = E->getRHS();
  if (IExp->getType()->isPointerType())
    std::swap(PExp, IExp);
  
  APValue ResultLValue;
  if (!EvaluatePointer(PExp, ResultLValue, Info))
    return APValue();
  
  llvm::APSInt AdditionalOffset(32);
  if (!EvaluateInteger(IExp, AdditionalOffset, Info))
    return APValue();

  uint64_t Offset = ResultLValue.getLValueOffset();
  if (E->getOpcode() == BinaryOperator::Add)
    Offset += AdditionalOffset.getZExtValue();
  else
    Offset -= AdditionalOffset.getZExtValue();
    
  return APValue(ResultLValue.getLValueBase(), Offset);
}
  

APValue PointerExprEvaluator::VisitCastExpr(const CastExpr* E) {
  const Expr* SubExpr = E->getSubExpr();

   // Check for pointer->pointer cast
  if (SubExpr->getType()->isPointerType()) {
    APValue Result;
    if (EvaluatePointer(SubExpr, Result, Info))
      return Result;
    return APValue();
  }
  
  if (SubExpr->getType()->isIntegralType()) {
    llvm::APSInt Result(32);
    if (EvaluateInteger(SubExpr, Result, Info)) {
      Result.extOrTrunc((unsigned)Info.Ctx.getTypeSize(E->getType()));
      return APValue(0, Result.getZExtValue());
    }
  }
  
  assert(0 && "Unhandled cast");
  return APValue();
}  


//===----------------------------------------------------------------------===//
// Integer Evaluation
//===----------------------------------------------------------------------===//

namespace {
class VISIBILITY_HIDDEN IntExprEvaluator
  : public StmtVisitor<IntExprEvaluator, bool> {
  EvalInfo &Info;
  APSInt &Result;
public:
  IntExprEvaluator(EvalInfo &info, APSInt &result)
    : Info(info), Result(result) {}

  unsigned getIntTypeSizeInBits(QualType T) const {
    return (unsigned)Info.Ctx.getIntWidth(T);
  }
  
  bool Extension(SourceLocation L, diag::kind D) {
    Info.DiagLoc = L;
    Info.ICEDiag = D;
    return true;  // still a constant.
  }
    
  bool Error(SourceLocation L, diag::kind D) {
    // If this is in an unevaluated portion of the subexpression, ignore the
    // error.
    if (!Info.isEvaluated)
      return true;
    
    Info.DiagLoc = L;
    Info.ICEDiag = D;
    return false;
  }
    
  //===--------------------------------------------------------------------===//
  //                            Visitor Methods
  //===--------------------------------------------------------------------===//
    
  bool VisitStmt(Stmt *S) {
    return Error(S->getLocStart(), diag::err_expr_not_constant);
  }
  
  bool VisitParenExpr(ParenExpr *E) { return Visit(E->getSubExpr()); }

  bool VisitIntegerLiteral(const IntegerLiteral *E) {
    Result = E->getValue();
    Result.setIsUnsigned(E->getType()->isUnsignedIntegerType());
    return true;
  }
  bool VisitCharacterLiteral(const CharacterLiteral *E) {
    Result.zextOrTrunc(getIntTypeSizeInBits(E->getType()));
    Result = E->getValue();
    Result.setIsUnsigned(E->getType()->isUnsignedIntegerType());
    return true;
  }
  bool VisitTypesCompatibleExpr(const TypesCompatibleExpr *E) {
    Result.zextOrTrunc(getIntTypeSizeInBits(E->getType()));
    Result = Info.Ctx.typesAreCompatible(E->getArgType1(), E->getArgType2());
    return true;
  }
  bool VisitDeclRefExpr(const DeclRefExpr *E);
  bool VisitCallExpr(const CallExpr *E);
  bool VisitBinaryOperator(const BinaryOperator *E);
  bool VisitUnaryOperator(const UnaryOperator *E);

  bool