Implement dependent alignment attribute support. This is a bit gross given the

current attribute system, but it is enough to handle class templates which
specify parts of their alignment in terms of their template parameters.

This also replaces the attributes test in SemaTemplate with one that actually
tests working attributes instead of broken ones. I plan to add more tests here
for non-dependent attributes in a subsequent patch.

Thanks to John for walking me through some of this. =D


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@106818 91177308-0d34-0410-b5e6-96231b3b80d8

include/clang/AST/Attr.h

@@ -26,6 +26,7 @@ namespace clang {
   class ASTContext;
   class IdentifierInfo;
   class ObjCInterfaceDecl;
+  class Expr;
 }
 
 // Defined in ASTContext.h
@@ -147,22 +148,44 @@ public:
 
 DEF_SIMPLE_ATTR(AlignMac68k);
 
+/// \brief Atribute for specifying the alignment of a variable or type.
+///
+/// This node will either contain the precise Alignment (in bits, not bytes!)
+/// or will contain the expression for the alignment attribute in the case of
+/// a dependent expression within a class or function template. At template
+/// instantiation time these are transformed into concrete attributes.
 class AlignedAttr : public Attr {
   unsigned Alignment;
+  Expr *AlignmentExpr;
 public:
   AlignedAttr(unsigned alignment)
-    : Attr(attr::Aligned), Alignment(alignment) {}
+    : Attr(attr::Aligned), Alignment(alignment), AlignmentExpr(0) {}
+  AlignedAttr(Expr *E)
+    : Attr(attr::Aligned), Alignment(0), AlignmentExpr(E) {}
+
+  /// getAlignmentExpr - Get a dependent alignment expression if one is present.
+  Expr *getAlignmentExpr() const {
+    return AlignmentExpr;
+  }
+
+  /// isDependent - Is the alignment a dependent expression
+  bool isDependent() const {
+    return getAlignmentExpr();
+  }
+
+  /// getAlignment - The specified alignment in bits. Requires !isDependent().
+  unsigned getAlignment() const {
+    assert(!isDependent() && "Cannot get a value dependent alignment");
+    return Alignment;
+  }
 
-  /// getAlignment - The specified alignment in bits.
-  unsigned getAlignment() const { return Alignment; }
-  
   /// getMaxAlignment - Get the maximum alignment of attributes on this list.
   unsigned getMaxAlignment() const {
     const AlignedAttr *Next = getNext<AlignedAttr>();
     if (Next)
-      return std::max(Next->getMaxAlignment(), Alignment);
+      return std::max(Next->getMaxAlignment(), getAlignment());
     else
-      return Alignment;
+      return getAlignment();
   }
 
   virtual Attr* clone(ASTContext &C) const;

lib/Sema/Sema.h

@@ -4088,6 +4088,9 @@ public:
   /// FreePackedContext - Deallocate and null out PackContext.
   void FreePackedContext();
 
+  /// AddAlignedAttr - Adds an aligned attribute to a particular declaration.
+  void AddAlignedAttr(SourceLocation AttrLoc, Decl *D, Expr *E);
+
   /// ImpCastExprToType - If Expr is not of type 'Type', insert an implicit
   /// cast.  If there is already an implicit cast, merge into the existing one.
   /// If isLvalue, the result of the cast is an lvalue.

lib/Sema/SemaDeclAttr.cpp

@@ -1458,7 +1458,7 @@ static void HandleAnnotateAttr(Decl *d, const AttributeList &Attr, Sema &S) {
   d->addAttr(::new (S.Context) AnnotateAttr(S.Context, SE->getString()));
 }
 
-static void HandleAlignedAttr(Decl *d, const AttributeList &Attr, Sema &S) {
+static void HandleAlignedAttr(Decl *D, const AttributeList &Attr, Sema &S) {
   // check the attribute arguments.
   if (Attr.getNumArgs() > 1) {
     S.Diag(Attr.getLoc(), diag::err_attribute_wrong_number_arguments) << 1;
@@ -1469,30 +1469,36 @@ static void HandleAlignedAttr(Decl *d, const AttributeList &Attr, Sema &S) {
   //       than GNU's, and should error out when it is used to specify a
   //       weaker alignment, rather than being silently ignored.
 
-  unsigned Align = 0;
   if (Attr.getNumArgs() == 0) {
     // FIXME: This should be the target specific maximum alignment.
     // (For now we just use 128 bits which is the maximum on X86).
-    Align = 128;
-    d->addAttr(::new (S.Context) AlignedAttr(Align));
+    D->addAttr(::new (S.Context) AlignedAttr(128));
+    return;
+  }
+
+  S.AddAlignedAttr(Attr.getLoc(), D, static_cast<Expr *>(Attr.getArg(0)));
+}
+
+void Sema::AddAlignedAttr(SourceLocation AttrLoc, Decl *D, Expr *E) {
+  if (E->isTypeDependent() || E->isValueDependent()) {
+    // Save dependent expressions in the AST to be instantiated.
+    D->addAttr(::new (Context) AlignedAttr(E));
     return;
   }
 
-  Expr *alignmentExpr = static_cast<Expr *>(Attr.getArg(0));
   llvm::APSInt Alignment(32);
-  if (alignmentExpr->isTypeDependent() || alignmentExpr->isValueDependent() ||
-      !alignmentExpr->isIntegerConstantExpr(Alignment, S.Context)) {
-    S.Diag(Attr.getLoc(), diag::err_attribute_argument_not_int)
-      << "aligned" << alignmentExpr->getSourceRange();
+  if (!E->isIntegerConstantExpr(Alignment, Context)) {
+    Diag(AttrLoc, diag::err_attribute_argument_not_int)
+      << "aligned" << E->getSourceRange();
     return;
   }
   if (!llvm::isPowerOf2_64(Alignment.getZExtValue())) {
-    S.Diag(Attr.getLoc(), diag::err_attribute_aligned_not_power_of_two)
-      << alignmentExpr->getSourceRange();
+    Diag(AttrLoc, diag::err_attribute_aligned_not_power_of_two)
+      << E->getSourceRange();
     return;
   }
 
-  d->addAttr(::new (S.Context) AlignedAttr(Alignment.getZExtValue() * 8));
+  D->addAttr(::new (Context) AlignedAttr(Alignment.getZExtValue() * 8));
 }
 
 /// HandleModeAttr - This attribute modifies the width of a decl with primitive

lib/Sema/SemaTemplateInstantiateDecl.cpp

@@ -143,14 +143,29 @@ bool TemplateDeclInstantiator::SubstQualifier(const TagDecl *OldDecl,
   return false;
 }
 
-// FIXME: Is this too simple?
+// FIXME: Is this still too simple?
 void TemplateDeclInstantiator::InstantiateAttrs(Decl *Tmpl, Decl *New) {
-  for (const Attr *TmplAttr = Tmpl->getAttrs(); TmplAttr; 
+  for (const Attr *TmplAttr = Tmpl->getAttrs(); TmplAttr;
        TmplAttr = TmplAttr->getNext()) {
-    
+    // FIXME: This should be generalized to more than just the AlignedAttr.
+    if (const AlignedAttr *Aligned = dyn_cast<AlignedAttr>(TmplAttr)) {
+      if (Aligned->isDependent()) {
+        // The alignment expression is not potentially evaluated.
+        EnterExpressionEvaluationContext Unevaluated(SemaRef,
+                                                     Action::Unevaluated);
+
+        OwningExprResult Result = SemaRef.SubstExpr(Aligned->getAlignmentExpr(),
+                                                    TemplateArgs);
+        if (!Result.isInvalid())
+          // FIXME: Is this the correct source location?
+          SemaRef.AddAlignedAttr(Aligned->getAlignmentExpr()->getExprLoc(),
+                                 New, Result.takeAs<Expr>());
+        continue;
+      }
+    }
+
     // FIXME: Is cloning correct for all attributes?
     Attr *NewAttr = TmplAttr->clone(SemaRef.Context);
-    
     New->addAttr(NewAttr);
   }
 }

test/SemaTemplate/attributes.cpp

@@ -1,8 +1,21 @@
 // RUN: %clang_cc1 -fsyntax-only -verify %s
 
-template<int N>
-struct X {
-  struct __attribute__((__aligned__((N)))) Aligned { }; // expected-error{{'aligned' attribute requires integer constant}}
+namespace attribute_aligned {
+  template<int N>
+  struct X {
+    char c[1] __attribute__((__aligned__((N)))); // expected-error {{alignment is not a power of 2}}
+  };
 
-  int __attribute__((__address_space__(N))) *ptr; // expected-error{{attribute requires 1 argument(s)}}
-};
+  template <bool X> struct check {
+    int check_failed[X ? 1 : -1]; // expected-error {{array size is negative}}
+  };
+
+  template <int N> struct check_alignment {
+    typedef check<N == sizeof(X<N>)> t; // expected-note {{in instantiation}}
+  };
+
+  check_alignment<1>::t c1;
+  check_alignment<2>::t c2;
+  check_alignment<3>::t c3; // expected-note 2 {{in instantiation}}
+  check_alignment<4>::t c4;
+}