Implement a new type trait __is_trivially_constructible(T, Args...)

that provides the behavior of the C++11 library trait
std::is_trivially_constructible<T, Args...>, which can't be
implemented purely as a library.

Since __is_trivially_constructible can have zero or more arguments, I
needed to add Yet Another Type Trait Expression Class, this one
handling arbitrary arguments. The next step will be to migrate
UnaryTypeTrait and BinaryTypeTrait over to this new, more general
TypeTrait class.

Fixes the Clang side of <rdar://problem/10895483> / PR12038.

llvm-svn: 151352

2 files changed, 254 insertions, 0 deletions

diff --git a/clang/lib/Sema/SemaExprCXX.cpp b/clang/lib/Sema/SemaExprCXX.cpp
index 708db1c9a9c..a4ae9be41b4 100644
--- a/clang/lib/Sema/SemaExprCXX.cpp
+++ b/clang/lib/Sema/SemaExprCXX.cpp
@@ -3212,6 +3212,127 @@ ExprResult Sema::ActOnBinaryTypeTrait(BinaryTypeTrait BTT,
   return BuildBinaryTypeTrait(BTT, KWLoc, LhsTSInfo, RhsTSInfo, RParen);
 }
 
+static bool evaluateTypeTrait(Sema &S, TypeTrait Kind, SourceLocation KWLoc,
+                              ArrayRef<TypeSourceInfo *> Args,
+                              SourceLocation RParenLoc) {
+  switch (Kind) {
+  case clang::TT_IsTriviallyConstructible: {
+    // C++11 [meta.unary.prop]:
+    //   is_trivially_constructor is defined as:
+    //
+    //     is_constructible<T, Args...>::value is true and the variable 
+    //
+    ///  definition for is_constructible, as defined below, is known to call no
+    //   operation that is not trivial.
+    //
+    //   The predicate condition for a template specialization 
+    //   is_constructible<T, Args...> shall be satisfied if and only if the 
+    //   following variable definition would be well-formed for some invented 
+    //   variable t:
+    //
+    //     T t(create<Args>()...);
+    if (Args.empty()) {
+      S.Diag(KWLoc, diag::err_type_trait_arity)
+        << 1 << 1 << 1 << (int)Args.size();
+      return false;
+    }
+    
+    bool SawVoid = false;
+    for (unsigned I = 0, N = Args.size(); I != N; ++I) {
+      if (Args[I]->getType()->isVoidType()) {
+        SawVoid = true;
+        continue;
+      }
+      
+      if (!Args[I]->getType()->isIncompleteType() &&
+        S.RequireCompleteType(KWLoc, Args[I]->getType(), 
+          diag::err_incomplete_type_used_in_type_trait_expr))
+        return false;
+    }
+    
+    // If any argument was 'void', of course it won't type-check.
+    if (SawVoid)
+      return false;
+    
+    llvm::SmallVector<OpaqueValueExpr, 2> OpaqueArgExprs;
+    llvm::SmallVector<Expr *, 2> ArgExprs;
+    ArgExprs.reserve(Args.size() - 1);
+    for (unsigned I = 1, N = Args.size(); I != N; ++I) {
+      QualType T = Args[I]->getType();
+      if (T->isObjectType() || T->isFunctionType())
+        T = S.Context.getRValueReferenceType(T);
+      OpaqueArgExprs.push_back(
+        OpaqueValueExpr(Args[I]->getTypeLoc().getSourceRange().getBegin(), 
+                        T.getNonLValueExprType(S.Context),
+                        Expr::getValueKindForType(T)));
+      ArgExprs.push_back(&OpaqueArgExprs.back());
+    }
+    
+    // Perform the initialization in an unevaluated context within a SFINAE 
+    // trap at translation unit scope.
+    EnterExpressionEvaluationContext Unevaluated(S, Sema::Unevaluated);
+    Sema::SFINAETrap SFINAE(S, /*AccessCheckingSFINAE=*/true);
+    Sema::ContextRAII TUContext(S, S.Context.getTranslationUnitDecl());
+    InitializedEntity To(InitializedEntity::InitializeTemporary(Args[0]));
+    InitializationKind InitKind(InitializationKind::CreateDirect(KWLoc, KWLoc,
+                                                                 RParenLoc));
+    InitializationSequence Init(S, To, InitKind, 
+                                ArgExprs.begin(), ArgExprs.size());
+    if (Init.Failed())
+      return false;
+    
+    ExprResult Result = Init.Perform(S, To, InitKind, 
+                                     MultiExprArg(ArgExprs.data(), 
+                                                  ArgExprs.size()));
+    if (Result.isInvalid() || SFINAE.hasErrorOccurred())
+      return false;
+    
+    // The initialization succeeded; not make sure there are no non-trivial 
+    // calls.
+    return !Result.get()->hasNonTrivialCall(S.Context);
+  }
+  }
+  
+  return false;
+}
+
+ExprResult Sema::BuildTypeTrait(TypeTrait Kind, SourceLocation KWLoc, 
+                                ArrayRef<TypeSourceInfo *> Args, 
+                                SourceLocation RParenLoc) {
+  bool Dependent = false;
+  for (unsigned I = 0, N = Args.size(); I != N; ++I) {
+    if (Args[I]->getType()->isDependentType()) {
+      Dependent = true;
+      break;
+    }
+  }
+  
+  bool Value = false;
+  if (!Dependent)
+    Value = evaluateTypeTrait(*this, Kind, KWLoc, Args, RParenLoc);
+  
+  return TypeTraitExpr::Create(Context, Context.BoolTy, KWLoc, Kind,
+                               Args, RParenLoc, Value);
+}
+
+ExprResult Sema::ActOnTypeTrait(TypeTrait Kind, SourceLocation KWLoc, 
+                                ArrayRef<ParsedType> Args, 
+                                SourceLocation RParenLoc) {
+  llvm::SmallVector<TypeSourceInfo *, 4> ConvertedArgs;
+  ConvertedArgs.reserve(Args.size());
+  
+  for (unsigned I = 0, N = Args.size(); I != N; ++I) {
+    TypeSourceInfo *TInfo;
+    QualType T = GetTypeFromParser(Args[I], &TInfo);
+    if (!TInfo)
+      TInfo = Context.getTrivialTypeSourceInfo(T, KWLoc);
+    
+    ConvertedArgs.push_back(TInfo);    
+  }
+  
+  return BuildTypeTrait(Kind, KWLoc, ConvertedArgs, RParenLoc);
+}
+
 static bool EvaluateBinaryTypeTrait(Sema &Self, BinaryTypeTrait BTT,
                                     QualType LhsT, QualType RhsT,
                                     SourceLocation KeyLoc) {
diff --git a/clang/lib/Sema/TreeTransform.h b/clang/lib/Sema/TreeTransform.h
index 58d6a22a288..f0b5f4e2419 100644
--- a/clang/lib/Sema/TreeTransform.h
+++ b/clang/lib/Sema/TreeTransform.h
@@ -2022,6 +2022,17 @@ public:
     return getSema().BuildBinaryTypeTrait(Trait, StartLoc, LhsT, RhsT, RParenLoc);
   }
 
+  /// \brief Build a new type trait expression.
+  ///
+  /// By default, performs semantic analysis to build the new expression.
+  /// Subclasses may override this routine to provide different behavior.
+  ExprResult RebuildTypeTrait(TypeTrait Trait,
+                              SourceLocation StartLoc,
+                              ArrayRef<TypeSourceInfo *> Args,
+                              SourceLocation RParenLoc) {
+    return getSema().BuildTypeTrait(Trait, StartLoc, Args, RParenLoc);
+  }
+  
   /// \brief Build a new array type trait expression.
   ///
   /// By default, performs semantic analysis to build the new expression.
@@ -7436,6 +7447,128 @@ TreeTransform<Derived>::TransformBinaryTypeTraitExpr(BinaryTypeTraitExpr *E) {
 
 template<typename Derived>
 ExprResult
+TreeTransform<Derived>::TransformTypeTraitExpr(TypeTraitExpr *E) {
+  bool ArgChanged = false;
+  llvm::SmallVector<TypeSourceInfo *, 4> Args;
+  for (unsigned I = 0, N = E->getNumArgs(); I != N; ++I) {
+    TypeSourceInfo *From = E->getArg(I);
+    TypeLoc FromTL = From->getTypeLoc();
+    if (!isa<PackExpansionTypeLoc>(FromTL)) {
+      TypeLocBuilder TLB;
+      TLB.reserve(FromTL.getFullDataSize());
+      QualType To = getDerived().TransformType(TLB, FromTL);
+      if (To.isNull())
+        return ExprError();
+      
+      if (To == From->getType())
+        Args.push_back(From);
+      else {
+        Args.push_back(TLB.getTypeSourceInfo(SemaRef.Context, To));
+        ArgChanged = true;
+      }
+      continue;
+    }
+    
+    ArgChanged = true;
+    
+    // We have a pack expansion. Instantiate it.
+    PackExpansionTypeLoc ExpansionTL = cast<PackExpansionTypeLoc>(FromTL);      
+    TypeLoc PatternTL = ExpansionTL.getPatternLoc();
+    SmallVector<UnexpandedParameterPack, 2> Unexpanded;
+    SemaRef.collectUnexpandedParameterPacks(PatternTL, Unexpanded);
+    
+    // Determine whether the set of unexpanded parameter packs can and should
+    // be expanded.
+    bool Expand = true;
+    bool RetainExpansion = false;
+    llvm::Optional<unsigned> OrigNumExpansions
+      = ExpansionTL.getTypePtr()->getNumExpansions();
+    llvm::Optional<unsigned> NumExpansions = OrigNumExpansions;
+    if (getDerived().TryExpandParameterPacks(ExpansionTL.getEllipsisLoc(),
+                                             PatternTL.getSourceRange(),
+                                             Unexpanded,
+                                             Expand, RetainExpansion,
+                                             NumExpansions))
+      return ExprError();
+    
+    if (!Expand) {
+      // The transform has determined that we should perform a simple
+      // transformation on the pack expansion, producing another pack 
+      // expansion.
+      Sema::ArgumentPackSubstitutionIndexRAII SubstIndex(getSema(), -1);
+      
+      TypeLocBuilder TLB;
+      TLB.reserve(From->getTypeLoc().getFullDataSize());
+
+      QualType To = getDerived().TransformType(TLB, PatternTL);
+      if (To.isNull())
+        return ExprError();
+
+      To = getDerived().RebuildPackExpansionType(To, 
+                                                 PatternTL.getSourceRange(),
+                                                 ExpansionTL.getEllipsisLoc(),
+                                                 NumExpansions);
+      if (To.isNull())
+        return ExprError();
+      
+      PackExpansionTypeLoc ToExpansionTL
+        = TLB.push<PackExpansionTypeLoc>(To);
+      ToExpansionTL.setEllipsisLoc(ExpansionTL.getEllipsisLoc());
+      Args.push_back(TLB.getTypeSourceInfo(SemaRef.Context, To));
+      continue;
+    }
+
+    // Expand the pack expansion by substituting for each argument in the
+    // pack(s).
+    for (unsigned I = 0; I != *NumExpansions; ++I) {
+      Sema::ArgumentPackSubstitutionIndexRAII SubstIndex(SemaRef, I);
+      TypeLocBuilder TLB;
+      TLB.reserve(PatternTL.getFullDataSize());
+      QualType To = getDerived().TransformType(TLB, PatternTL);
+      if (To.isNull())
+        return ExprError();
+
+      Args.push_back(TLB.getTypeSourceInfo(SemaRef.Context, To));
+    }
+    
+    if (!RetainExpansion)
+      continue;
+    
+    // If we're supposed to retain a pack expansion, do so by temporarily
+    // forgetting the partially-substituted parameter pack.
+    ForgetPartiallySubstitutedPackRAII Forget(getDerived());
+
+    TypeLocBuilder TLB;
+    TLB.reserve(From->getTypeLoc().getFullDataSize());
+    
+    QualType To = getDerived().TransformType(TLB, PatternTL);
+    if (To.isNull())
+      return ExprError();
+    
+    To = getDerived().RebuildPackExpansionType(To, 
+                                               PatternTL.getSourceRange(),
+                                               ExpansionTL.getEllipsisLoc(),
+                                               NumExpansions);
+    if (To.isNull())
+      return ExprError();
+    
+    PackExpansionTypeLoc ToExpansionTL
+      = TLB.push<PackExpansionTypeLoc>(To);
+    ToExpansionTL.setEllipsisLoc(ExpansionTL.getEllipsisLoc());
+    Args.push_back(TLB.getTypeSourceInfo(SemaRef.Context, To));
+  }
+  
+  if (!getDerived().AlwaysRebuild() && !ArgChanged)
+    return SemaRef.Owned(E);
+
+  return getDerived().RebuildTypeTrait(E->getTrait(),
+                                       E->getLocStart(),
+                                       Args,
+                                       E->getLocEnd());
+}
+
+template<typename Derived>
+ExprResult
 TreeTransform<Derived>::TransformArrayTypeTraitExpr(ArrayTypeTraitExpr *E) {
   TypeSourceInfo *T = getDerived().TransformType(E->getQueriedTypeSourceInfo());
   if (!T)