SemaTemplateDeduction.cpp - Android社区 - https://www.androidos.net.cn/

//===------- SemaTemplateDeduction.cpp - Template Argument Deduction ------===/
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//===----------------------------------------------------------------------===/
//
//  This file implements C++ template argument deduction.
//
//===----------------------------------------------------------------------===/

#include "clang/Sema/TemplateDeduction.h"
#include "TreeTransform.h"
#include "clang/AST/ASTContext.h"
#include "clang/AST/ASTLambda.h"
#include "clang/AST/DeclObjC.h"
#include "clang/AST/DeclTemplate.h"
#include "clang/AST/Expr.h"
#include "clang/AST/ExprCXX.h"
#include "clang/AST/StmtVisitor.h"
#include "clang/Sema/DeclSpec.h"
#include "clang/Sema/Sema.h"
#include "clang/Sema/Template.h"
#include "llvm/ADT/SmallBitVector.h"
#include <algorithm>

namespace clang {
  using namespace sema;
  /// \brief Various flags that control template argument deduction.
  ///
  /// These flags can be bitwise-OR'd together.
  enum TemplateDeductionFlags {
    /// \brief No template argument deduction flags, which indicates the
    /// strictest results for template argument deduction (as used for, e.g.,
    /// matching class template partial specializations).
    TDF_None = 0,
    /// \brief Within template argument deduction from a function call, we are
    /// matching with a parameter type for which the original parameter was
    /// a reference.
    TDF_ParamWithReferenceType = 0x1,
    /// \brief Within template argument deduction from a function call, we
    /// are matching in a case where we ignore cv-qualifiers.
    TDF_IgnoreQualifiers = 0x02,
    /// \brief Within template argument deduction from a function call,
    /// we are matching in a case where we can perform template argument
    /// deduction from a template-id of a derived class of the argument type.
    TDF_DerivedClass = 0x04,
    /// \brief Allow non-dependent types to differ, e.g., when performing
    /// template argument deduction from a function call where conversions
    /// may apply.
    TDF_SkipNonDependent = 0x08,
    /// \brief Whether we are performing template argument deduction for
    /// parameters and arguments in a top-level template argument
    TDF_TopLevelParameterTypeList = 0x10,
    /// \brief Within template argument deduction from overload resolution per
    /// C++ [over.over] allow matching function types that are compatible in
    /// terms of noreturn and default calling convention adjustments.
    TDF_InOverloadResolution = 0x20
  };
}

using namespace clang;

/// \brief Compare two APSInts, extending and switching the sign as
/// necessary to compare their values regardless of underlying type.
static bool hasSameExtendedValue(llvm::APSInt X, llvm::APSInt Y) {
  if (Y.getBitWidth() > X.getBitWidth())
    X = X.extend(Y.getBitWidth());
  else if (Y.getBitWidth() < X.getBitWidth())
    Y = Y.extend(X.getBitWidth());

// If there is a signedness mismatch, correct it.
  if (X.isSigned() != Y.isSigned()) {
    // If the signed value is negative, then the values cannot be the same.
    if ((Y.isSigned() && Y.isNegative()) || (X.isSigned() && X.isNegative()))
      return false;

Y.setIsSigned(true);
    X.setIsSigned(true);
  }

return X == Y;
}

static Sema::TemplateDeductionResult
DeduceTemplateArgumentsByTypeMatch(Sema &S,
                                   TemplateParameterList *TemplateParams,
                                   QualType Param,
                                   QualType Arg,
                                   TemplateDeductionInfo &Info,
                                   SmallVectorImpl<DeducedTemplateArgument> &
                                                      Deduced,
                                   unsigned TDF,
                                   bool PartialOrdering = false);

/// \brief If the given expression is of a form that permits the deduction
/// of a non-type template parameter, return the declaration of that
/// non-type template parameter.
static NonTypeTemplateParmDecl *getDeducedParameterFromExpr(Expr *E) {
  // If we are within an alias template, the expression may have undergone
  // any number of parameter substitutions already.
  while (1) {
    if (ImplicitCastExpr *IC = dyn_cast<ImplicitCastExpr>(E))
      E = IC->getSubExpr();
    else if (SubstNonTypeTemplateParmExpr *Subst =
               dyn_cast<SubstNonTypeTemplateParmExpr>(E))
      E = Subst->getReplacement();
    else
      break;
  }

if (DeclRefExpr *DRE = dyn_cast<DeclRefExpr>(E))
    return dyn_cast<NonTypeTemplateParmDecl>(DRE->getDecl());

return nullptr;
}

/// \brief Determine whether two declaration pointers refer to the same
/// declaration.
static bool isSameDeclaration(Decl *X, Decl *Y) {
  if (NamedDecl *NX = dyn_cast<NamedDecl>(X))
    X = NX->getUnderlyingDecl();
  if (NamedDecl *NY = dyn_cast<NamedDecl>(Y))
    Y = NY->getUnderlyingDecl();

return X->getCanonicalDecl() == Y->getCanonicalDecl();
}

/// \brief Verify that the given, deduced template arguments are compatible.
///
/// \returns The deduced template argument, or a NULL template argument if
/// the deduced template arguments were incompatible.
static DeducedTemplateArgument
checkDeducedTemplateArguments(ASTContext &Context,
                              const DeducedTemplateArgument &X,
                              const DeducedTemplateArgument &Y) {
  // We have no deduction for one or both of the arguments; they're compatible.
  if (X.isNull())
    return Y;
  if (Y.isNull())
    return X;

switch (X.getKind()) {
  case TemplateArgument::Null:
    llvm_unreachable("Non-deduced template arguments handled above");

case TemplateArgument::Type:
    // If two template type arguments have the same type, they're compatible.
    if (Y.getKind() == TemplateArgument::Type &&
        Context.hasSameType(X.getAsType(), Y.getAsType()))
      return X;

return DeducedTemplateArgument();

case TemplateArgument::Integral:
    // If we deduced a constant in one case and either a dependent expression or
    // declaration in another case, keep the integral constant.
    // If both are integral constants with the same value, keep that value.
    if (Y.getKind() == TemplateArgument::Expression ||
        Y.getKind() == TemplateArgument::Declaration ||
        (Y.getKind() == TemplateArgument::Integral &&
         hasSameExtendedValue(X.getAsIntegral(), Y.getAsIntegral())))
      return DeducedTemplateArgument(X,
                                     X.wasDeducedFromArrayBound() &&
                                     Y.wasDeducedFromArrayBound());