path: root/lib/Sema/SemaTemplateDeduction.cpp

//===------- 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 "Sema.h"
#include "clang/AST/ASTContext.h"
#include "clang/AST/DeclTemplate.h"
#include "clang/AST/StmtVisitor.h"
#include "clang/AST/Expr.h"
#include "clang/AST/ExprCXX.h"
#include "clang/Parse/DeclSpec.h"
#include "llvm/Support/Compiler.h"
using namespace clang;

static Sema::TemplateDeductionResult
DeduceTemplateArguments(ASTContext &Context, 
                        TemplateParameterList *TemplateParams,
                        const TemplateArgument &Param,
                        const TemplateArgument &Arg,
                        Sema::TemplateDeductionInfo &Info,
                        llvm::SmallVectorImpl<TemplateArgument> &Deduced);

/// \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 (ImplicitCastExpr *IC = dyn_cast<ImplicitCastExpr>(E))
    E = IC->getSubExpr();
  
  if (DeclRefExpr *DRE = dyn_cast<DeclRefExpr>(E))
    return dyn_cast<NonTypeTemplateParmDecl>(DRE->getDecl());
  
  return 0;
}

/// \brief Deduce the value of the given non-type template parameter 
/// from the given constant.
static Sema::TemplateDeductionResult
DeduceNonTypeTemplateArgument(ASTContext &Context, 
                              NonTypeTemplateParmDecl *NTTP, 
                              llvm::APInt Value,
                              Sema::TemplateDeductionInfo &Info,
                              llvm::SmallVectorImpl<TemplateArgument> &Deduced) {
  assert(NTTP->getDepth() == 0 && 
         "Cannot deduce non-type template argument with depth > 0");
  
  if (Deduced[NTTP->getIndex()].isNull()) {
    Deduced[NTTP->getIndex()] = TemplateArgument(SourceLocation(), 
                                                 llvm::APSInt(Value),
                                                 NTTP->getType());
    return Sema::TDK_Success;
  }
  
  assert(Deduced[NTTP->getIndex()].getKind() == TemplateArgument::Integral);
  
  // If the template argument was previously deduced to a negative value, 
  // then our deduction fails.
  const llvm::APSInt *PrevValuePtr = Deduced[NTTP->getIndex()].getAsIntegral();
  if (PrevValuePtr->isSigned() && PrevValuePtr->isNegative()) {
    // FIXME: This is wacky; we should be dealing with APSInts and
    // checking the actual signs.
    Info.Param = NTTP;
    Info.FirstArg = Deduced[NTTP->getIndex()];
    Info.SecondArg = TemplateArgument(SourceLocation(), 
                                      llvm::APSInt(Value),
                                      NTTP->getType());
    return Sema::TDK_Inconsistent;
  }

  llvm::APInt PrevValue = *PrevValuePtr;
  if (Value.getBitWidth() > PrevValue.getBitWidth())
    PrevValue.zext(Value.getBitWidth());
  else if (Value.getBitWidth() < PrevValue.getBitWidth())
    Value.zext(PrevValue.getBitWidth());

  if (Value != PrevValue) {
    Info.Param = NTTP;
    Info.FirstArg = Deduced[NTTP->getIndex()];
    Info.SecondArg = TemplateArgument(SourceLocation(), 
                                      llvm::APSInt(Value),
                                      NTTP->getType());
    return Sema::TDK_Inconsistent;
  }

  return Sema::TDK_Success;
}

/// \brief Deduce the value of the given non-type template parameter 
/// from the given type- or value-dependent expression.
///
/// \returns true if deduction succeeded, false otherwise.

static Sema::TemplateDeductionResult
DeduceNonTypeTemplateArgument(ASTContext &Context, 
                              NonTypeTemplateParmDecl *NTTP,
                              Expr *Value,
                              Sema::TemplateDeductionInfo &Info,
                           llvm::SmallVectorImpl<TemplateArgument> &Deduced) {
  assert(NTTP->getDepth() == 0 && 
         "Cannot deduce non-type template argument with depth > 0");
  assert((Value->isTypeDependent() || Value->isValueDependent()) &&
         "Expression template argument must be type- or value-dependent.");
  
  if (Deduced[NTTP->getIndex()].isNull()) {
    // FIXME: Clone the Value?
    Deduced[NTTP->getIndex()] = TemplateArgument(Value);
    return Sema::TDK_Success;
  }
  
  if (