Introduce a new expression node, ImplicitValueInitExpr, that

represents an implicit value-initialization of a subobject of a
particular type. This replaces the (ab)use of CXXZeroValueInitExpr
within initializer lists for the "holes" that occur due to the use of
C99 designated initializers.

The new test case is currently XFAIL'd, because CodeGen's
ConstExprEmitter (in lib/CodeGen/CGExprConstant.cpp) needs to be
taught to value-initialize when it sees ImplicitValueInitExprs.

llvm-svn: 63317

clang/include/clang/AST/Expr.h

@@ -1645,7 +1645,7 @@ public:
 /// initializations into the subobject they initialize. Additionally,
 /// any "holes" in the initialization, where no initializer has been
 /// specified for a particular subobject, will be replaced with
-/// implicitly-generated CXXZeroInitValueExpr expressions that
+/// implicitly-generated ImplicitValueInitExpr expressions that
 /// value-initialize the subobjects. Note, however, that the
 /// initializer lists may still have fewer initializers than there are
 /// elements to initialize within the object.
@@ -1987,6 +1987,31 @@ public:
   virtual child_iterator child_end(); 
 };
 
+/// \brief Represents an implicitly-generated value initialization of
+/// an object of a given type.
+///
+/// Implicit value initializations occur within semantic initialize
+/// list expressions (\see InitListExpr) as placeholders for subobject
+/// initializations not explicitly specified by the user.
+class ImplicitValueInitExpr : public Expr { 
+public:
+  explicit ImplicitValueInitExpr(QualType ty) 
+    : Expr(ImplicitValueInitExprClass, ty) { }
+
+  static bool classof(const Stmt *T) { 
+    return T->getStmtClass() == ImplicitValueInitExprClass;
+  }
+  static bool classof(const ImplicitValueInitExpr *) { return true; }
+
+  virtual SourceRange getSourceRange() const {
+    return SourceRange();
+  }
+
+  // Iterators
+  virtual child_iterator child_begin();
+  virtual child_iterator child_end(); 
+};
+
 //===----------------------------------------------------------------------===//
 // Clang Extensions
 //===----------------------------------------------------------------------===//

clang/include/clang/AST/StmtNodes.def

@@ -86,6 +86,7 @@ STMT(CompoundLiteralExpr   , Expr)
 STMT(ExtVectorElementExpr  , Expr)
 STMT(InitListExpr          , Expr)
 STMT(DesignatedInitExpr    , Expr)
+STMT(ImplicitValueInitExpr , Expr)
 STMT(VAArgExpr             , Expr)
 
 // GNU Extensions.

clang/lib/AST/Expr.cpp

@@ -735,6 +735,8 @@ bool Expr::isConstantInitializer(ASTContext &Ctx) const {
     }
     return true;
   }
+  case ImplicitValueInitExprClass:
+    return true;
   case ParenExprClass: {
     return cast<ParenExpr>(this)->getSubExpr()->isConstantInitializer(Ctx);
   }
@@ -1672,7 +1674,7 @@ Stmt::child_iterator InitListExpr::child_end() {
   return InitExprs.size() ? &InitExprs[0] + InitExprs.size() : 0;
 }
 
-/// DesignatedInitExpr
+// DesignatedInitExpr
 Stmt::child_iterator DesignatedInitExpr::child_begin() {
   char* Ptr = static_cast<char*>(static_cast<void *>(this));
   Ptr += sizeof(DesignatedInitExpr);
@@ -1683,6 +1685,15 @@ Stmt::child_iterator DesignatedInitExpr::child_end() {
   return child_iterator(&*child_begin() + NumSubExprs);
 }
 
+// ImplicitValueInitExpr
+Stmt::child_iterator ImplicitValueInitExpr::child_begin() { 
+  return child_iterator(); 
+}
+
+Stmt::child_iterator ImplicitValueInitExpr::child_end() { 
+  return child_iterator(); 
+}
+
 // ObjCStringLiteral
 Stmt::child_iterator ObjCStringLiteral::child_begin() { 
   return child_iterator();

clang/lib/AST/StmtPrinter.cpp

@@ -906,6 +906,10 @@ void StmtPrinter::VisitDesignatedInitExpr(DesignatedInitExpr *Node) {
   PrintExpr(Node->getInit());
 }
 
+void StmtPrinter::VisitImplicitValueInitExpr(ImplicitValueInitExpr *Node) {
+  OS << "/*implicit*/" << Node->getType().getAsString() << "()";
+}
+
 void StmtPrinter::VisitVAArgExpr(VAArgExpr *Node) {
   OS << "va_arg(";
   PrintExpr(Node->getSubExpr());

clang/lib/CodeGen/CGExprAgg.cpp

@@ -339,10 +339,10 @@ void AggExprEmitter::EmitNonConstInit(InitListExpr *E) {
 
 void AggExprEmitter::EmitInitializationToLValue(Expr* E, LValue LV) {
   // FIXME: Are initializers affected by volatile?
-  if (E->getType()->isComplexType()) {
-    CGF.EmitComplexExprIntoAddr(E, LV.getAddress(), false);
-  } else if (isa<CXXZeroInitValueExpr>(E)) {
+  if (isa<ImplicitValueInitExpr>(E)) {
     EmitNullInitializationToLValue(LV, E->getType());
+  } else if (E->getType()->isComplexType()) {
+    CGF.EmitComplexExprIntoAddr(E, LV.getAddress(), false);
   } else if (CGF.hasAggregateLLVMType(E->getType())) {
     CGF.EmitAnyExpr(E, LV.getAddress(), false);
   } else {

clang/lib/CodeGen/CGExprComplex.cpp

@@ -130,6 +130,12 @@ public:
     llvm::Constant *Null = llvm::Constant::getNullValue(CGF.ConvertType(Elem));
     return ComplexPairTy(Null, Null);
   }
+  ComplexPairTy VisitImplicitValueInitExpr(ImplicitValueInitExpr *E) {
+    assert(E->getType()->isAnyComplexType() && "Expected complex type!");
+    QualType Elem = E->getType()->getAsComplexType()->getElementType();
+    llvm::Constant *Null = llvm::Constant::getNullValue(CGF.ConvertType(Elem));
+    return ComplexPairTy(Null, Null);
+  }
   
   struct BinOpInfo {
     ComplexPairTy LHS;

clang/lib/CodeGen/CGExprConstant.cpp

@@ -248,11 +248,6 @@ public:
 
     FieldDecl* curField = ILE->getInitializedFieldInUnion();
     if (!curField) {
-#ifndef NDEBUG
-#endif
-    }
-
-    if (!curField) {
       // There's no field to initialize, so value-initialize the union.
 #ifndef NDEBUG
       // Make sure that it's really an empty and not a failure of

clang/lib/CodeGen/CGExprScalar.cpp

@@ -200,6 +200,9 @@ public:
     return V;
   }
   
+  Value *VisitImplicitValueInitExpr(const ImplicitValueInitExpr *E) {
+    return llvm::Constant::getNullValue(ConvertType(E->getType()));
+  }
   Value *VisitImplicitCastExpr(const ImplicitCastExpr *E);
   Value *VisitCastExpr(const CastExpr *E) { 
     return EmitCastExpr(E->getSubExpr(), E->getType());

clang/lib/Sema/SemaDecl.cpp

@@ -2220,17 +2220,17 @@ bool Sema::CheckForConstantInitializer(Expr *Init, QualType DclT) {
   if (CompoundLiteralExpr *e = dyn_cast<CompoundLiteralExpr>(Init))
     return CheckForConstantInitializer(e->getInitializer(), DclT);
 
+  if (isa<ImplicitValueInitExpr>(Init)) {
+    // FIXME: In C++, check for non-POD types.
+    return false;
+  }
+
   if (InitListExpr *Exp = dyn_cast<InitListExpr>(Init)) {
     unsigned numInits = Exp->getNumInits();
     for (unsigned i = 0; i < numInits; i++) {
       // FIXME: Need to get the type of the declaration for C++,
       // because it could be a reference?
 
-      // Implicitly-generated value initializations are okay.
-      if (isa<CXXZeroInitValueExpr>(Exp->getInit(i)) &&
-          cast<CXXZeroInitValueExpr>(Exp->getInit(i))->isImplicit()) 
-        continue;
-
       if (CheckForConstantInitializer(Exp->getInit(i),
                                       Exp->getInit(i)->getType()))
         return true;

clang/lib/Sema/SemaInit.cpp

@@ -17,7 +17,6 @@
 #include "clang/Parse/Designator.h"
 #include "clang/AST/ASTContext.h"
 #include "clang/AST/Expr.h"
-#include "clang/AST/ExprCXX.h"
 #include <map>
 using namespace clang;
 
@@ -137,10 +136,9 @@ static void fillInValueInitializations(ASTContext &Context, InitListExpr *ILE) {
       // FIXME: Check for fields with reference type in C++?
       if (!ILE->getInit(Init))
         ILE->setInit(Init, 
-                     new (Context) CXXZeroInitValueExpr(Field->getType(), 
-                                                        SourceLocation(),
-                                                        SourceLocation()));
-      else if (InitListExpr *InnerILE = dyn_cast<InitListExpr>(ILE->getInit(Init)))
+                     new (Context) ImplicitValueInitExpr(Field->getType()));
+      else if (InitListExpr *InnerILE 
+                 = dyn_cast<InitListExpr>(ILE->getInit(Init)))
         fillInValueInitializations(Context, InnerILE);
       ++Init;
     }
@@ -160,9 +158,7 @@ static void fillInValueInitializations(ASTContext &Context, InitListExpr *ILE) {
   for (unsigned Init = 0, NumInits = ILE->getNumInits(); Init != NumInits; 
        ++Init) {
     if (!ILE->getInit(Init))
-      ILE->setInit(Init, new (Context) CXXZeroInitValueExpr(ElementType, 
-                                                            SourceLocation(),
-                                                            SourceLocation()));
+      ILE->setInit(Init, new (Context) ImplicitValueInitExpr(ElementType));
     else if (InitListExpr *InnerILE =dyn_cast<InitListExpr>(ILE->getInit(Init)))
       fillInValueInitializations(Context, InnerILE);
   }
@@ -550,6 +546,22 @@ void InitListChecker::CheckStructUnionTypes(InitListExpr *IList,
     hadError = true;
     return;
   }    
+
+  if (DeclType->isUnionType() && IList->getNumInits() == 0) {
+    // Value-initialize the first named member of the union.
+    RecordDecl *RD = DeclType->getAsRecordType()->getDecl();
+    for (RecordDecl::field_iterator FieldEnd = RD->field_end();
+         Field != FieldEnd; ++Field) {
+      if (Field->getDeclName()) {
+        StructuredList->setInitializedFieldInUnion(*Field);
+        break;
+      }
+    }
+    return;
+  }
+
+
+
   // If structDecl is a forward declaration, this loop won't do
   // anything except look at designated initializers; That's okay,
   // because an error should get printed out elsewhere. It might be

clang/test/CodeGen/designated-initializers.c

@@ -0,0 +1,17 @@
+// RUN: clang %s -emit-llvm -o -
+// XFAIL
+struct foo {
+    void *a;
+    int b;
+};
+
+union { int i; float f; } u = { };
+
+int main(int argc, char **argv)
+{
+  union { int i; float f; } u2 = { };
+    static struct foo foo = {
+        .b = 1024,
+    };
+}
+