C++1y constexpr extensions, round 1: Allow most forms of declaration and

statement in constexpr functions. Everything which doesn't require variable
mutation is also allowed as an extension in C++11. 'void' becomes a literal
type to support constexpr functions which return 'void'.

llvm-svn: 180022

clang/include/clang/AST/Type.h

@@ -1443,8 +1443,8 @@ class Type : public ExtQualsTypeCommonBase {
   }
 
   /// isLiteralType - Return true if this is a literal type
-  /// (C++0x [basic.types]p10)
-  bool isLiteralType() const;
+  /// (C++11 [basic.types]p10)
+  bool isLiteralType(ASTContext &Ctx) const;
 
   /// \brief Test if this type is a standard-layout type.
   /// (C++0x [basic.type]p9)

clang/include/clang/Basic/DiagnosticASTKinds.td

@@ -26,6 +26,8 @@ def note_constexpr_lshift_discards : Note<"signed left shift discards bits">;
 def note_constexpr_invalid_function : Note<
   "%select{non-constexpr|undefined}0 %select{function|constructor}1 %2 cannot "
   "be used in a constant expression">;
+def note_constexpr_no_return : Note<
+  "control reached end of constexpr function">;
 def note_constexpr_virtual_call : Note<
   "cannot evaluate virtual function call in a constant expression">;
 def note_constexpr_virtual_base : Note<

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -1593,20 +1593,54 @@ def err_constexpr_non_literal_param : Error<
   "not a literal type">;
 def err_constexpr_body_invalid_stmt : Error<
   "statement not allowed in constexpr %select{function|constructor}0">;
-def err_constexpr_type_definition : Error<
-  "types cannot be defined in a constexpr %select{function|constructor}0">;
+def ext_constexpr_body_invalid_stmt : ExtWarn<
+  "use of this statement in a constexpr %select{function|constructor}0 "
+  "is a C++1y extension">, InGroup<CXX1y>;
+def warn_cxx11_compat_constexpr_body_invalid_stmt : Warning<
+  "use of this statement in a constexpr %select{function|constructor}0 "
+  "is incompatible with C++ standards before C++1y">,
+  InGroup<CXXPre1yCompat>, DefaultIgnore;
+def ext_constexpr_type_definition : ExtWarn<
+  "type definition in a constexpr %select{function|constructor}0 "
+  "is a C++1y extension">, InGroup<CXX1y>;
+def warn_cxx11_compat_constexpr_type_definition : Warning<
+  "type definition in a constexpr %select{function|constructor}0 "
+  "is incompatible with C++ standards before C++1y">,
+  InGroup<CXXPre1yCompat>, DefaultIgnore;
 def err_constexpr_vla : Error<
   "variably-modified type %0 cannot be used in a constexpr "
   "%select{function|constructor}1">;
-def err_constexpr_var_declaration : Error<
-  "variables cannot be declared in a constexpr %select{function|constructor}0">;
+def ext_constexpr_local_var : ExtWarn<
+  "variable declaration in a constexpr %select{function|constructor}0 "
+  "is a C++1y extension">, InGroup<CXX1y>;
+def warn_cxx11_compat_constexpr_local_var : Warning<
+  "variable declaration in a constexpr %select{function|constructor}0 "
+  "is incompatible with C++ standards before C++1y">,
+  InGroup<CXXPre1yCompat>, DefaultIgnore;
+def err_constexpr_local_var_static : Error<
+  "%select{static|thread_local}1 variable not permitted in a constexpr "
+  "%select{function|constructor}0">;
+def err_constexpr_local_var_non_literal_type : Error<
+  "variable of non-literal type %1 cannot be defined in a constexpr "
+  "%select{function|constructor}0">;
+def err_constexpr_local_var_no_init : Error<
+  "variables defined in a constexpr %select{function|constructor}0 must be "
+  "initialized">;
 def ext_constexpr_function_never_constant_expr : ExtWarn<
   "constexpr %select{function|constructor}0 never produces a "
   "constant expression">, InGroup<DiagGroup<"invalid-constexpr">>, DefaultError;
 def err_constexpr_body_no_return : Error<
   "no return statement in constexpr function">;
-def err_constexpr_body_multiple_return : Error<
-  "multiple return statements in constexpr function">;
+def warn_cxx11_compat_constexpr_body_no_return : Warning<
+  "constexpr function with no return statements is incompatible with C++ "
+  "standards before C++1y">, InGroup<CXXPre1yCompat>, DefaultIgnore;
+def ext_constexpr_body_multiple_return : ExtWarn<
+  "multiple return statements in constexpr function is a C++1y extension">,
+  InGroup<CXX1y>;
+def warn_cxx11_compat_constexpr_body_multiple_return : Warning<
+  "multiple return statements in constexpr function "
+  "is incompatible with C++ standards before C++1y">,
+  InGroup<CXXPre1yCompat>, DefaultIgnore;
 def note_constexpr_body_previous_return : Note<
   "previous return statement is here">;
 def err_constexpr_function_try_block : Error<

clang/lib/AST/DeclCXX.cpp

@@ -186,7 +186,7 @@ CXXRecordDecl::setBases(CXXBaseSpecifier const * const *Bases,
       data().IsStandardLayout = false;
 
     // Record if this base is the first non-literal field or base.
-    if (!hasNonLiteralTypeFieldsOrBases() && !BaseType->isLiteralType())
+    if (!hasNonLiteralTypeFieldsOrBases() && !BaseType->isLiteralType(C))
       data().HasNonLiteralTypeFieldsOrBases = true;
 
     // Now go through all virtual bases of this base and add them.
@@ -676,7 +676,7 @@ void CXXRecordDecl::addedMember(Decl *D) {
     }
 
     // Record if this field is the first non-literal or volatile field or base.
-    if (!T->isLiteralType() || T.isVolatileQualified())
+    if (!T->isLiteralType(Context) || T.isVolatileQualified())
       data().HasNonLiteralTypeFieldsOrBases = true;
 
     if (Field->hasInClassInitializer()) {
@@ -845,7 +845,7 @@ void CXXRecordDecl::addedMember(Decl *D) {
       }
     } else {
       // Base element type of field is a non-class type.
-      if (!T->isLiteralType() ||
+      if (!T->isLiteralType(Context) ||
           (!Field->hasInClassInitializer() && !isUnion()))
         data().DefaultedDefaultConstructorIsConstexpr = false;
 

clang/lib/AST/Expr.cpp

@@ -289,7 +289,7 @@ static void computeDeclRefDependence(ASTContext &Ctx, NamedDecl *D, QualType T,
   //          expression that is value-dependent [C++11]
   if (VarDecl *Var = dyn_cast<VarDecl>(D)) {
     if ((Ctx.getLangOpts().CPlusPlus11 ?
-           Var->getType()->isLiteralType() :
+           Var->getType()->isLiteralType(Ctx) :
            Var->getType()->isIntegralOrEnumerationType()) &&
         (Var->getType().isConstQualified() ||
          Var->getType()->isReferenceType())) {

clang/lib/AST/ExprConstant.cpp

@@ -290,7 +290,7 @@ namespace {
 
     // Note that we intentionally use std::map here so that references to
     // values are stable.
-    typedef std::map<const Expr*, APValue> MapTy;
+    typedef std::map<const void*, APValue> MapTy;
     typedef MapTy::const_iterator temp_iterator;
     /// Temporaries - Temporary lvalues materialized within this stack frame.
     MapTy Temporaries;
@@ -913,6 +913,14 @@ static bool EvaluateComplex(const Expr *E, ComplexValue &Res, EvalInfo &Info);
 // Misc utilities
 //===----------------------------------------------------------------------===//
 
+/// Evaluate an expression to see if it had side-effects, and discard its
+/// result.
+static void EvaluateIgnoredValue(EvalInfo &Info, const Expr *E) {
+  APValue Scratch;
+  if (!Evaluate(Scratch, Info, E))
+    Info.EvalStatus.HasSideEffects = true;
+}
+
 /// Should this call expression be treated as a string literal?
 static bool IsStringLiteralCall(const CallExpr *E) {
   unsigned Builtin = E->isBuiltinCall();
@@ -1046,7 +1054,7 @@ static bool CheckLValueConstantExpression(EvalInfo &Info, SourceLocation Loc,
 /// Check that this core constant expression is of literal type, and if not,
 /// produce an appropriate diagnostic.
 static bool CheckLiteralType(EvalInfo &Info, const Expr *E) {
-  if (!E->isRValue() || E->getType()->isLiteralType())
+  if (!E->isRValue() || E->getType()->isLiteralType(Info.Ctx))
     return true;
 
   // Prvalue constant expressions must be of literal types.
@@ -1461,6 +1469,15 @@ static bool EvaluateVarDeclInit(EvalInfo &Info, const Expr *E,
     return true;
   }
 
+  // If this is a local variable, dig out its value.
+  if (VD->hasLocalStorage() && Frame && Frame->Index > 1) {
+    Result = Frame->Temporaries[VD];
+    // If we've carried on past an unevaluatable local variable initializer,
+    // we can't go any further. This can happen during potential constant
+    // expression checking.
+    return !Result.isUninit();
+  }
+
   // Dig out the initializer, and use the declaration which it's attached to.
   const Expr *Init = VD->getAnyInitializer(VD);
   if (!Init || Init->isValueDependent()) {
@@ -1803,7 +1820,9 @@ static bool HandleLValueToRValueConversion(EvalInfo &Info, const Expr *Conv,
       return false;
     }
 
-    if (!isa<ParmVarDecl>(VD)) {
+    // Unless we're looking at a local variable or argument in a constexpr call,
+    // the variable we're reading must be const.
+    if (LVal.CallIndex <= 1 || !VD->hasLocalStorage()) {
       if (VD->isConstexpr()) {
         // OK, we can read this variable.
       } else if (VT->isIntegralOrEnumerationType()) {
@@ -1911,7 +1930,7 @@ static bool EvaluateObjectArgument(EvalInfo &Info, const Expr *Object,
   if (Object->isGLValue())
     return EvaluateLValue(Object, This, Info);
 
-  if (Object->getType()->isLiteralType())
+  if (Object->getType()->isLiteralType(Info.Ctx))
     return EvaluateTemporary(Object, This, Info);
 
   return false;
@@ -2060,20 +2079,61 @@ enum EvalStmtResult {
 };
 }
 
+static bool EvaluateDecl(EvalInfo &Info, const Decl *D) {
+  if (const VarDecl *VD = dyn_cast<VarDecl>(D)) {
+    // We don't need to evaluate the initializer for a static local.
+    if (!VD->hasLocalStorage())
+      return true;
+
+    LValue Result;
+    Result.set(VD, Info.CurrentCall->Index);
+    APValue &Val = Info.CurrentCall->Temporaries[VD];
+
+    if (!EvaluateInPlace(Val, Info, Result, VD->getInit())) {
+      // Wipe out any partially-computed value, to allow tracking that this
+      // evaluation failed.
+      Val = APValue();
+      return false;
+    }
+  }
+
+  return true;
+}
+
 // Evaluate a statement.
 static EvalStmtResult EvaluateStmt(APValue &Result, EvalInfo &Info,
                                    const Stmt *S) {
+  // FIXME: Mark all temporaries in the current frame as destroyed at
+  // the end of each full-expression.
   switch (S->getStmtClass()) {
   default:
+    if (const Expr *E = dyn_cast<Expr>(S)) {
+      EvaluateIgnoredValue(Info, E);
+      // Don't bother evaluating beyond an expression-statement which couldn't
+      // be evaluated.
+      if (Info.EvalStatus.HasSideEffects && !Info.keepEvaluatingAfterFailure())
+        return ESR_Failed;
+      return ESR_Succeeded;
+    }
+
+    Info.Diag(S->getLocStart());
     return ESR_Failed;
 
   case Stmt::NullStmtClass:
-  case Stmt::DeclStmtClass:
     return ESR_Succeeded;
 
+  case Stmt::DeclStmtClass: {
+    const DeclStmt *DS = cast<DeclStmt>(S);
+    for (DeclStmt::const_decl_iterator DclIt = DS->decl_begin(),
+           DclEnd = DS->decl_end(); DclIt != DclEnd; ++DclIt)
+      if (!EvaluateDecl(Info, *DclIt) && !Info.keepEvaluatingAfterFailure())
+        return ESR_Failed;
+    return ESR_Succeeded;
+  }
+
   case Stmt::ReturnStmtClass: {
     const Expr *RetExpr = cast<ReturnStmt>(S)->getRetValue();
-    if (!Evaluate(Result, Info, RetExpr))
+    if (RetExpr && !Evaluate(Result, Info, RetExpr))
       return ESR_Failed;
     return ESR_Returned;
   }
@@ -2088,6 +2148,28 @@ static EvalStmtResult EvaluateStmt(APValue &Result, EvalInfo &Info,
     }
     return ESR_Succeeded;
   }
+
+  case Stmt::IfStmtClass: {
+    const IfStmt *IS = cast<IfStmt>(S);
+
+    // Evaluate the condition, as either a var decl or as an expression.
+    bool Cond;
+    if (VarDecl *CondDecl = IS->getConditionVariable()) {
+      if (!EvaluateDecl(Info, CondDecl))
+        return ESR_Failed;
+      if (!HandleConversionToBool(Info.CurrentCall->Temporaries[CondDecl],
+                                  Cond))
+        return ESR_Failed;
+    } else if (!EvaluateAsBooleanCondition(IS->getCond(), Cond, Info))
+      return ESR_Failed;
+
+    if (const Stmt *SubStmt = Cond ? IS->getThen() : IS->getElse()) {
+      EvalStmtResult ESR = EvaluateStmt(Result, Info, SubStmt);
+      if (ESR != ESR_Succeeded)
+        return ESR;
+    }
+    return ESR_Succeeded;
+  }
   }
 }
 
@@ -2181,7 +2263,10 @@ static bool HandleFunctionCall(SourceLocation CallLoc,
     return false;
 
   CallStackFrame Frame(Info, CallLoc, Callee, This, ArgValues.data());
-  return EvaluateStmt(Result, Info, Body) == ESR_Returned;
+  EvalStmtResult ESR = EvaluateStmt(Result, Info, Body);
+  if (ESR == ESR_Succeeded)
+    Info.Diag(Callee->getLocEnd(), diag::note_constexpr_no_return);
+  return ESR == ESR_Returned;
 }
 
 /// Evaluate a constructor call.
@@ -2207,7 +2292,9 @@ static bool HandleConstructorCall(SourceLocation CallLoc, const LValue &This,
   // If it's a delegating constructor, just delegate.
   if (Definition->isDelegatingConstructor()) {
     CXXConstructorDecl::init_const_iterator I = Definition->init_begin();
-    return EvaluateInPlace(Result, Info, This, (*I)->getInit());
+    if (!EvaluateInPlace(Result, Info, This, (*I)->getInit()))
+      return false;
+    return EvaluateStmt(Result, Info, Definition->getBody()) != ESR_Failed;
   }
 
   // For a trivial copy or move constructor, perform an APValue copy. This is
@@ -2307,7 +2394,8 @@ static bool HandleConstructorCall(SourceLocation CallLoc, const LValue &This,
     }
   }
 
-  return Success;
+  return Success &&
+         EvaluateStmt(Result, Info, Definition->getBody()) != ESR_Failed;
 }
 
 //===----------------------------------------------------------------------===//
@@ -2660,9 +2748,7 @@ class ExprEvaluatorBase
 
   /// Visit a value which is evaluated, but whose value is ignored.
   void VisitIgnoredValue(const Expr *E) {
-    APValue Scratch;
-    if (!Evaluate(Scratch, Info, E))
-      Info.EvalStatus.HasSideEffects = true;
+    EvaluateIgnoredValue(Info, E);
   }
 };
 
@@ -2868,7 +2954,7 @@ bool LValueExprEvaluator::VisitDeclRefExpr(const DeclRefExpr *E) {
 
 bool LValueExprEvaluator::VisitVarDecl(const Expr *E, const VarDecl *VD) {
   if (!VD->getType()->isReferenceType()) {
-    if (isa<ParmVarDecl>(VD)) {
+    if (VD->hasLocalStorage() && Info.CurrentCall->Index > 1) {
       Result.set(VD, Info.CurrentCall->Index);
       return true;
     }

clang/lib/AST/Type.cpp

@@ -1142,16 +1142,20 @@ bool QualType::isTriviallyCopyableType(ASTContext &Context) const {
 
 
 
-bool Type::isLiteralType() const {
+bool Type::isLiteralType(ASTContext &Ctx) const {
   if (isDependentType())
     return false;
 
-  // C++0x [basic.types]p10:
+  // C++1y [basic.types]p10:
+  //   A type is a literal type if it is:
+  //   -- cv void; or
+  if (Ctx.getLangOpts().CPlusPlus1y && isVoidType())
+    return true;
+
+  // C++11 [basic.types]p10:
   //   A type is a literal type if it is:
   //   [...]
-  //   -- an array of literal type.
-  // Extension: variable arrays cannot be literal types, since they're
-  // runtime-sized.
+  //   -- an array of literal type other than an array of runtime bound; or
   if (isVariableArrayType())
     return false;
   const Type *BaseTy = getBaseElementTypeUnsafe();
@@ -1162,7 +1166,7 @@ bool Type::isLiteralType() const {
   if (BaseTy->isIncompleteType())
     return false;
 
-  // C++0x [basic.types]p10:
+  // C++11 [basic.types]p10:
   //   A type is a literal type if it is:
   //    -- a scalar type; or
   // As an extension, Clang treats vector types and complex types as

clang/lib/Sema/SemaDecl.cpp

@@ -7626,7 +7626,7 @@ void Sema::AddInitializerToDecl(Decl *RealDecl, Expr *Init,
       }
 
     // Suggest adding 'constexpr' in C++11 for literal types.
-    } else if (getLangOpts().CPlusPlus11 && DclT->isLiteralType()) {
+    } else if (getLangOpts().CPlusPlus11 && DclT->isLiteralType(Context)) {
       Diag(VDecl->getLocation(), diag::err_in_class_initializer_literal_type)
         << DclT << Init->getSourceRange()
         << FixItHint::CreateInsertion(VDecl->getLocStart(), "constexpr ");