Fix a bug where the DWARF emitter in the JIT was not initializing alignment

[oota-llvm.git] / include / llvm / Use.h

diff --git a/include/llvm/Use.h b/include/llvm/Use.h
index 891eaf856579bfef901d6e091f4840adbd2e3184..489dbc50a041251ba870b0dadab7067bd13e6dfd 100644 (file)
--- a/include/llvm/Use.h
+++ b/include/llvm/Use.h
@@ -11,6 +11,15 @@
 // instruction or some other User instance which refers to a Value.  The Use
 // class keeps the "use list" of the referenced value up to date.
 //
+// Pointer tagging is used to efficiently find the User corresponding
+// to a Use without having to store a User pointer in every Use. A
+// User is preceded in memory by all the Uses corresponding to its
+// operands, and the low bits of one of the fields (Prev) of the Use
+// class are used to encode offsets to be able to find that User given
+// a pointer to any Use. For details, see:
+//
+//   http://www.llvm.org/docs/ProgrammersManual.html#UserLayout
+//
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_USE_H
@@ -18,58 +27,35 @@
 
 #include "llvm/Support/Casting.h"
 #include "llvm/ADT/iterator.h"
+#include "llvm/ADT/PointerIntPair.h"
 
 namespace llvm {
 
 class Value;
 class User;
-
-
-//===----------------------------------------------------------------------===//
-//                          Generic Tagging Functions
-//===----------------------------------------------------------------------===//
+class Use;
 
 /// Tag - generic tag type for (at least 32 bit) pointers
 enum Tag { noTag, tagOne, tagTwo, tagThree };
 
-/// addTag - insert tag bits into an (untagged) pointer
-template <typename T, typename TAG>
-inline T *addTag(const T *P, TAG Tag) {
-    return reinterpret_cast<T*>(ptrdiff_t(P) | Tag);
-}
-
-/// stripTag - remove tag bits from a pointer,
-/// making it dereferencable
-template <ptrdiff_t MASK, typename T>
-inline T *stripTag(const T *P) {
-  return reinterpret_cast<T*>(ptrdiff_t(P) & ~MASK);
-}
-
-/// extractTag - extract tag bits from a pointer
-template <typename TAG, TAG MASK, typename T>
-inline TAG extractTag(const T *P) {
-  return TAG(ptrdiff_t(P) & MASK);
-}
-
-/// transferTag - transfer tag bits from a pointer,
-/// to an untagged pointer
-template <ptrdiff_t MASK, typename T>
-inline T *transferTag(const T *From, const T *To) {
-  return reinterpret_cast<T*>((ptrdiff_t(From) & MASK) | ptrdiff_t(To));
-}
-
+// Use** is only 4-byte aligned.
+template<>
+class PointerLikeTypeTraits<Use**> {
+public:
+  static inline void *getAsVoidPointer(Use** P) { return P; }
+  static inline Use **getFromVoidPointer(void *P) {
+    return static_cast<Use**>(P);
+  }
+  enum { NumLowBitsAvailable = 2 };
+};
 
 //===----------------------------------------------------------------------===//
 //                                  Use Class
 //===----------------------------------------------------------------------===//
 
-// Use is here to make keeping the "use" list of a Value up-to-date really easy.
-//
+/// Use is here to make keeping the "use" list of a Value up-to-date really
+/// easy.
 class Use {
-private:
-  /// init - specify Value and User
-  /// @deprecated in 2.4, will be removed soon
-  inline void init(Value *V, User *U);
 public:
   /// swap - provide a fast substitute to std::swap<Use>
   /// that also works with less standard-compliant compilers
@@ -84,9 +70,8 @@ private:
     if (Val) removeFromList();
   }
 
-  /// Default ctor - This leaves the Use completely uninitialized.  The only thing
-  /// that is valid to do with this use is to call the "init" method.
-
+  /// Default ctor - This leaves the Use completely uninitialized.  The only
+  /// thing that is valid to do with this use is to call the "init" method.
   inline Use() {}
   enum PrevPtrTag { zeroDigitTag = noTag
                   , oneDigitTag = tagOne
@@ -94,12 +79,16 @@ private:
                   , fullStopTag = tagThree };
 
 public:
+  /// Normally Use will just implicitly convert to a Value* that it holds.
   operator Value*() const { return Val; }
+  
+  /// If implicit conversion to Value* doesn't work, the get() method returns
+  /// the Value*.
   Value *get() const { return Val; }
+  
+  /// getUser - This returns the User that contains this Use.  For an
+  /// instruction operand, for example, this will return the instruction.
   User *getUser() const;
-  const Use* getImpliedUser() const;
-  static Use *initTags(Use *Start, Use *Stop, ptrdiff_t Done = 0);
-  static void zap(Use *Start, const Use *Stop, bool del = false);
 
   inline void set(Value *Val);
 
@@ -116,12 +105,24 @@ public:
   const Value *operator->() const { return Val; }
 
   Use *getNext() const { return Next; }
+
+  
+  /// zap - This is used to destroy Use operands when the number of operands of
+  /// a User changes.
+  static void zap(Use *Start, const Use *Stop, bool del = false);
+
+  /// getPrefix - Return deletable pointer if appropriate
+  Use *getPrefix();
 private:
+  const Use* getImpliedUser() const;
+  static Use *initTags(Use *Start, Use *Stop, ptrdiff_t Done = 0);
+  
   Value *Val;
-  Use *Next, **Prev;
+  Use *Next;
+  PointerIntPair<Use**, 2, PrevPtrTag> Prev;
 
   void setPrev(Use **NewPrev) {
-    Prev = transferTag<fullStopTag>(Prev, NewPrev);
+    Prev.setPointer(NewPrev);
   }
   void addToList(Use **List) {
     Next = *List;
@@ -130,12 +131,13 @@ private:
     *List = this;
   }
   void removeFromList() {
-    Use **StrippedPrev = stripTag<fullStopTag>(Prev);
+    Use **StrippedPrev = Prev.getPointer();
     *StrippedPrev = Next;
     if (Next) Next->setPrev(StrippedPrev);
   }
 
   friend class Value;
+  friend class User;
 };
 
 // simplify_type - Allow clients to treat uses just like values when using
@@ -229,7 +231,7 @@ template<> struct simplify_type<value_use_iterator<const User> > {
 
 template<> struct simplify_type<const value_use_iterator<const User> >
   : public simplify_type<value_use_iterator<const User> > {};
-
+ 
 } // End llvm namespace
 
 #endif