Replace custom alignment enforcement with LLVM_ALIGNAS.

This isn't perfect as it still assumes sizeof(void*) == alignof(void*),
but we can fix that when compiler support gets better.

Shrinks some Stmts that happen to inherit from Stmt and have a
SourceLocation as the first member (64 bit archs only).

llvm-svn: 233911

clang/include/clang/AST/DeclGroup.h

@@ -14,6 +14,7 @@
 #ifndef LLVM_CLANG_AST_DECLGROUP_H
 #define LLVM_CLANG_AST_DECLGROUP_H
 
+#include "llvm/Support/Compiler.h"
 #include "llvm/Support/DataTypes.h"
 #include <cassert>
 
@@ -24,13 +25,9 @@ class Decl;
 class DeclGroup;
 class DeclGroupIterator;
 
-class DeclGroup {
+class LLVM_ALIGNAS(sizeof(void *)) DeclGroup {
   // FIXME: Include a TypeSpecifier object.
-  union {
-    unsigned NumDecls;
-
-    Decl *Aligner;
-  };
+  unsigned NumDecls;
 
 private:
   DeclGroup() : NumDecls(0) {}

clang/include/clang/AST/DeclTemplate.h

@@ -460,21 +460,12 @@ public:
 ///     friend void foo<>(T);
 ///   };
 /// \endcode
-class DependentFunctionTemplateSpecializationInfo {
-  struct CA {
-    /// The number of potential template candidates.
-    unsigned NumTemplates;
+class LLVM_ALIGNAS(sizeof(void *)) DependentFunctionTemplateSpecializationInfo {
+  /// The number of potential template candidates.
+  unsigned NumTemplates;
 
-    /// The number of template arguments.
-    unsigned NumArgs;
-  };
-
-  union {
-    // Force sizeof to be a multiple of sizeof(void*) so that the
-    // trailing data is aligned.
-    void *Aligner;
-    struct CA d;
-  };
+  /// The number of template arguments.
+  unsigned NumArgs;
 
   /// The locations of the left and right angle brackets.
   SourceRange AngleLocs;
@@ -490,9 +481,7 @@ public:
 
   /// \brief Returns the number of function templates that this might
   /// be a specialization of.
-  unsigned getNumTemplates() const {
-    return d.NumTemplates;
-  }
+  unsigned getNumTemplates() const { return NumTemplates; }
 
   /// \brief Returns the i'th template candidate.
   FunctionTemplateDecl *getTemplate(unsigned I) const {
@@ -507,9 +496,7 @@ public:
   }
 
   /// \brief Returns the number of explicit template arguments that were given.
-  unsigned getNumTemplateArgs() const {
-    return d.NumArgs;
-  }
+  unsigned getNumTemplateArgs() const { return NumArgs; }
 
   /// \brief Returns the nth template argument.
   const TemplateArgumentLoc &getTemplateArg(unsigned I) const {

clang/include/clang/AST/Stmt.h

@@ -101,7 +101,7 @@ namespace clang {
 
 /// Stmt - This represents one statement.
 ///
-class Stmt {
+class LLVM_ALIGNAS(sizeof(void *)) Stmt {
 public:
   enum StmtClass {
     NoStmtClass = 0,
@@ -287,9 +287,6 @@ protected:
   };
 
   union {
-    // FIXME: this is wasteful on 64-bit platforms.
-    void *Aligner;
-
     StmtBitfields StmtBits;
     CompoundStmtBitfields CompoundStmtBits;
     ExprBitfields ExprBits;
@@ -341,13 +338,12 @@ private:
 
 protected:
   /// \brief Construct an empty statement.
-  explicit Stmt(StmtClass SC, EmptyShell) {
-    StmtBits.sClass = SC;
-    if (StatisticsEnabled) Stmt::addStmtClass(SC);
-  }
+  explicit Stmt(StmtClass SC, EmptyShell) : Stmt(SC) {}
 
 public:
   Stmt(StmtClass SC) {
+    static_assert(sizeof(*this) % llvm::AlignOf<void *>::Alignment == 0,
+                  "Insufficient alignment!");
     StmtBits.sClass = SC;
     if (StatisticsEnabled) Stmt::addStmtClass(SC);
   }

clang/include/clang/Basic/SourceManager.h

@@ -82,7 +82,7 @@ namespace SrcMgr {
   /// \brief One instance of this struct is kept for every file loaded or used.
   ///
   /// This object owns the MemoryBuffer object.
-  class ContentCache {
+  class LLVM_ALIGNAS(8) ContentCache {
     enum CCFlags {
       /// \brief Whether the buffer is invalid.
       InvalidFlag = 0x01,
@@ -90,15 +90,6 @@ namespace SrcMgr {
       DoNotFreeFlag = 0x02
     };
 
-    // Note that the first member of this class is an aligned character buffer
-    // to ensure that this class has an alignment of 8 bytes. This wastes
-    // 8 bytes for every ContentCache object, but each of these corresponds to
-    // a file loaded into memory, so the 8 bytes doesn't seem terribly
-    // important. It is quite awkward to fit this aligner into any other part
-    // of the class due to the lack of portable ways to combine it with other
-    // members.
-    llvm::AlignedCharArray<8, 1> NonceAligner;
-
     /// \brief The actual buffer containing the characters from the input
     /// file.
     ///
@@ -142,14 +133,9 @@ namespace SrcMgr {
     /// \brief True if this content cache was initially created for a source
     /// file considered as a system one.
     unsigned IsSystemFile : 1;
-    
-    ContentCache(const FileEntry *Ent = nullptr)
-      : Buffer(nullptr, false), OrigEntry(Ent), ContentsEntry(Ent),
-        SourceLineCache(nullptr), NumLines(0), BufferOverridden(false),
-        IsSystemFile(false) {
-      (void)NonceAligner; // Silence warnings about unused member.
-    }
-    
+
+    ContentCache(const FileEntry *Ent = nullptr) : ContentCache(Ent, Ent) {}
+
     ContentCache(const FileEntry *Ent, const FileEntry *contentEnt)
       : Buffer(nullptr, false), OrigEntry(Ent), ContentsEntry(contentEnt),
         SourceLineCache(nullptr), NumLines(0), BufferOverridden(false),

clang/lib/AST/Decl.cpp

@@ -3103,10 +3103,10 @@ FunctionDecl::setDependentTemplateSpecialization(ASTContext &Context,
 DependentFunctionTemplateSpecializationInfo::
 DependentFunctionTemplateSpecializationInfo(const UnresolvedSetImpl &Ts,
                                       const TemplateArgumentListInfo &TArgs)
-  : AngleLocs(TArgs.getLAngleLoc(), TArgs.getRAngleLoc()) {
-
-  d.NumTemplates = Ts.size();
-  d.NumArgs = TArgs.size();
+  : NumTemplates(Ts.size()), NumArgs(TArgs.size()),
+    AngleLocs(TArgs.getLAngleLoc(), TArgs.getRAngleLoc()) {
+  static_assert(sizeof(*this) % llvm::AlignOf<void *>::Alignment == 0,
+                "Trailing data is unaligned!");
 
   FunctionTemplateDecl **TsArray =
     const_cast<FunctionTemplateDecl**>(getTemplates());

clang/lib/AST/DeclGroup.cpp

@@ -18,6 +18,8 @@
 using namespace clang;
 
 DeclGroup* DeclGroup::Create(ASTContext &C, Decl **Decls, unsigned NumDecls) {
+  static_assert(sizeof(DeclGroup) % llvm::AlignOf<void *>::Alignment == 0,
+                "Trailing data is unaligned!");
   assert(NumDecls > 1 && "Invalid DeclGroup");
   unsigned Size = sizeof(DeclGroup) + sizeof(Decl*) * NumDecls;
   void* Mem = C.Allocate(Size, llvm::AlignOf<DeclGroup>::Alignment);