Fix alignment issues in LLVM.

Adds static_asserts to ensure alignment of concatenated objects is
correct, and fixes them where they are not.

Also changes the definition of AlignOf to use constexpr, except on
MSVC, to avoid enum comparison warnings from GCC.

(There's not too much of this in llvm itself, most of the fun is in
clang).

This seems to make LLVM actually work without Bus Error on 32bit
sparc.

Differential Revision: http://reviews.llvm.org/D10271

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@239872 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/IR/DerivedTypes.h

@@ -140,7 +140,8 @@ public:
     return T->getTypeID() == FunctionTyID;
   }
 };
-
+static_assert(AlignOf<FunctionType>::Alignment >= AlignOf<Type *>::Alignment,
+              "Alignment sufficient for objects appended to FunctionType");
 
 /// CompositeType - Common super class of ArrayType, StructType, PointerType
 /// and VectorType.

include/llvm/IR/User.h

@@ -22,6 +22,7 @@
 #include "llvm/ADT/iterator.h"
 #include "llvm/ADT/iterator_range.h"
 #include "llvm/IR/Value.h"
+#include "llvm/Support/AlignOf.h"
 #include "llvm/Support/ErrorHandling.h"
 
 namespace llvm {
@@ -226,6 +227,11 @@ public:
     return isa<Instruction>(V) || isa<Constant>(V);
   }
 };
+// Either Use objects, or a Use pointer can be prepended to User.
+static_assert(AlignOf<Use>::Alignment >= AlignOf<User>::Alignment,
+              "Alignment sufficient after objects prepended to User");
+static_assert(AlignOf<Use *>::Alignment >= AlignOf<User>::Alignment,
+              "Alignment sufficient after objects prepended to User");
 
 template<> struct simplify_type<User::op_iterator> {
   typedef Value* SimpleType;

include/llvm/Support/AlignOf.h

@@ -44,9 +44,18 @@ private:
 ///  compile-time constant (e.g., for template instantiation).
 template <typename T>
 struct AlignOf {
+#ifndef _MSC_VER
+  // Avoid warnings from GCC like:
+  //   comparison between 'enum llvm::AlignOf<X>::<anonymous>' and 'enum
+  //   llvm::AlignOf<Y>::<anonymous>' [-Wenum-compare]
+  // by using constexpr instead of enum.
+  // (except on MSVC, since it doesn't support constexpr yet).
+  static constexpr unsigned Alignment =
+      static_cast<unsigned int>(sizeof(AlignmentCalcImpl<T>) - sizeof(T));
+#else
   enum { Alignment =
          static_cast<unsigned int>(sizeof(AlignmentCalcImpl<T>) - sizeof(T)) };
-
+#endif
   enum { Alignment_GreaterEqual_2Bytes = Alignment >= 2 ? 1 : 0 };
   enum { Alignment_GreaterEqual_4Bytes = Alignment >= 4 ? 1 : 0 };
   enum { Alignment_GreaterEqual_8Bytes = Alignment >= 8 ? 1 : 0 };
@@ -58,6 +67,10 @@ struct AlignOf {
   enum { Alignment_LessEqual_16Bytes = Alignment <= 16 ? 1 : 0 };
 };
 
+#ifndef _MSC_VER
+template <typename T> constexpr unsigned AlignOf<T>::Alignment;
+#endif
+
 /// alignOf - A templated function that returns the minimum alignment of
 ///  of a type.  This provides no extra functionality beyond the AlignOf
 ///  class besides some cosmetic cleanliness.  Example usage:

lib/IR/AttributeImpl.h

@@ -181,6 +181,9 @@ public:
       AttrList[I].Profile(ID);
   }
 };
+static_assert(AlignOf<AttributeSetNode>::Alignment >=
+                  AlignOf<Attribute>::Alignment,
+              "Alignment sufficient for objects appended to AttributeSetNode");
 
 //===----------------------------------------------------------------------===//
 /// \class
@@ -189,9 +192,11 @@ public:
 class AttributeSetImpl : public FoldingSetNode {
   friend class AttributeSet;
 
-  LLVMContext &Context;
+public:
-
   typedef std::pair<unsigned, AttributeSetNode*> IndexAttrPair;
+
+private:
+  LLVMContext &Context;
   unsigned NumAttrs; ///< Number of entries in this set.
 
   /// \brief Return a pointer to the IndexAttrPair for the specified slot.
@@ -206,6 +211,7 @@ public:
   AttributeSetImpl(LLVMContext &C,
                    ArrayRef<std::pair<unsigned, AttributeSetNode *> > Attrs)
       : Context(C), NumAttrs(Attrs.size()) {
+
 #ifndef NDEBUG
     if (Attrs.size() >= 2) {
       for (const std::pair<unsigned, AttributeSetNode *> *i = Attrs.begin() + 1,
@@ -267,6 +273,9 @@ public:
 
   void dump() const;
 };
+static_assert(AlignOf<AttributeSetImpl>::Alignment >=
+                  AlignOf<AttributeSetImpl::IndexAttrPair>::Alignment,
+              "Alignment sufficient for objects appended to AttributeSetImpl");
 
 } // end llvm namespace
 

lib/IR/Metadata.cpp

@@ -381,20 +381,35 @@ StringRef MDString::getString() const {
 // MDNode implementation.
 //
 
+// Assert that the MDNode types will not be unaligned by the objects
+// prepended to them.
+#define HANDLE_MDNODE_LEAF(CLASS)                                              \
+  static_assert(llvm::AlignOf<uint64_t>::Alignment >=                          \
+                    llvm::AlignOf<CLASS>::Alignment,                           \
+                "Alignment sufficient after objects prepended to " #CLASS);
+#include "llvm/IR/Metadata.def"
+
 void *MDNode::operator new(size_t Size, unsigned NumOps) {
-  void *Ptr = ::operator new(Size + NumOps * sizeof(MDOperand));
+  size_t OpSize = NumOps * sizeof(MDOperand);
+  // uint64_t is the most aligned type we need support (ensured by static_assert
+  // above)
+  OpSize = RoundUpToAlignment(OpSize, llvm::alignOf<uint64_t>());
+  void *Ptr = reinterpret_cast<char *>(::operator new(OpSize + Size)) + OpSize;
   MDOperand *O = static_cast<MDOperand *>(Ptr);
-  for (MDOperand *E = O + NumOps; O != E; ++O)
+  for (MDOperand *E = O - NumOps; O != E; --O)
-    (void)new (O) MDOperand;
+    (void)new (O - 1) MDOperand;
-  return O;
+  return Ptr;
 }
 
 void MDNode::operator delete(void *Mem) {
   MDNode *N = static_cast<MDNode *>(Mem);
+  size_t OpSize = N->NumOperands * sizeof(MDOperand);
+  OpSize = RoundUpToAlignment(OpSize, llvm::alignOf<uint64_t>());
+
   MDOperand *O = static_cast<MDOperand *>(Mem);
   for (MDOperand *E = O - N->NumOperands; O != E; --O)
     (O - 1)->~MDOperand();
-  ::operator delete(O);
+  ::operator delete(reinterpret_cast<char *>(Mem) - OpSize);
 }
 
 MDNode::MDNode(LLVMContext &Context, unsigned ID, StorageType Storage,

lib/IR/User.cpp

@@ -42,6 +42,12 @@ void User::replaceUsesOfWith(Value *From, Value *To) {
 
 void User::allocHungoffUses(unsigned N, bool IsPhi) {
   assert(HasHungOffUses && "alloc must have hung off uses");
+
+  static_assert(AlignOf<Use>::Alignment >= AlignOf<Use::UserRef>::Alignment,
+                "Alignment sufficient for hung-off-uses pieces");
+  static_assert(AlignOf<Use::UserRef>::Alignment >= AlignOf<BasicBlock *>::Alignment,
+                "Alignment sufficient for hung-off-uses pieces");
+
   // Allocate the array of Uses, followed by a pointer (with bottom bit set) to
   // the User.
   size_t size = N * sizeof(Use) + sizeof(Use::UserRef);