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

1 files changed, 121 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) {