X-Git-Url: http://demsky.eecs.uci.edu/git/?a=blobdiff_plain;f=include%2Fllvm%2FUse.h;h=a496325c1fc667e5416cf35986993917ca4373bf;hb=06138ac5690383166e1e4f6414af846911ae9c28;hp=b4d4bda620e8e6de7c4e3bcabc0ad62121f8aa64;hpb=efe65369a74871c3140a540a6c95ce5d1f080954;p=oota-llvm.git

diff --git a/include/llvm/Use.h b/include/llvm/Use.h
index b4d4bda620e..a496325c1fc 100644
--- a/include/llvm/Use.h
+++ b/include/llvm/Use.h
@@ -11,94 +11,89 @@
 // 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
 #define LLVM_USE_H
 
-#include "llvm/Support/Casting.h"
-#include "llvm/ADT/iterator"
+#include "llvm/ADT/PointerIntPair.h"
+#include <cstddef>
+#include <iterator>
 
 namespace llvm {
 
 class Value;
 class User;
+class Use;
+template<typename>
+struct simplify_type;
 
-
-//===----------------------------------------------------------------------===//
-//                          Generic Tagging Functions
-//===----------------------------------------------------------------------===//
-
-/// 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 {
 public:
-  inline void init(Value *V, User *U);
+  /// swap - provide a fast substitute to std::swap<Use>
+  /// that also works with less standard-compliant compilers
+  void swap(Use &RHS);
 
-private:
-  /// Allow std::swap some intimacy
-  template <typename U> friend void std::swap(U&, U&);
+  // A type for the word following an array of hung-off Uses in memory, which is
+  // a pointer back to their User with the bottom bit set.
+  typedef PointerIntPair<User*, 1, unsigned> UserRef;
 
-  /// Copy ctor - Only for std::swap
-  Use(const Use &U) { init(U.get(), 0); }
+private:
+  /// Copy ctor - do not implement
+  Use(const Use &U);
 
-  /// Destructor - Only for zap() and std::swap
-  inline ~Use() {
-    if (get()) removeFromList();
+  /// Destructor - Only for zap()
+  ~Use() {
+    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.
+  enum PrevPtrTag { zeroDigitTag
+                  , oneDigitTag
+                  , stopTag
+                  , fullStopTag };
 
-  inline Use() {}
-  enum PrevPtrTag { zeroDigitTag = noTag
-                  , oneDigitTag = tagOne
-                  , stopTag = tagTwo
-                  , fullStopTag = tagThree };
+  /// Constructor
+  Use(PrevPtrTag tag) : Val(0) {
+    Prev.setInt(tag);
+  }
 
 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);
 
@@ -107,7 +102,7 @@ public:
     return RHS;
   }
   const Use &operator=(const Use &RHS) {
-    set(RHS.get());
+    set(RHS.Val);
     return *this;
   }
 
@@ -115,12 +110,25 @@ public:
   const Value *operator->() const { return Val; }
 
   Use *getNext() const { return Next; }
+
+  
+  /// initTags - initialize the waymarking tags on an array of Uses, so that
+  /// getUser() can find the User from any of those Uses.
+  static Use *initTags(Use *Start, Use *Stop);
+
+  /// 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);
+
 private:
+  const Use* getImpliedUser() const;
+  
   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;
@@ -129,7 +137,7 @@ private:
     *List = this;
   }
   void removeFromList() {
-    Use **StrippedPrev = stripTag<fullStopTag>(Prev);
+    Use **StrippedPrev = Prev.getPointer();
     *StrippedPrev = Next;
     if (Next) Next->setPrev(StrippedPrev);
   }
@@ -155,8 +163,9 @@ template<> struct simplify_type<const Use> {
 
 
 template<typename UserTy>  // UserTy == 'User' or 'const User'
-class value_use_iterator : public forward_iterator<UserTy*, ptrdiff_t> {
-  typedef forward_iterator<UserTy*, ptrdiff_t> super;
+class value_use_iterator : public std::iterator<std::forward_iterator_tag,
+                                                UserTy*, ptrdiff_t> {
+  typedef std::iterator<std::forward_iterator_tag, UserTy*, ptrdiff_t> super;
   typedef value_use_iterator<UserTy> _Self;
 
   Use *U;
@@ -189,7 +198,7 @@ public:
     _Self tmp = *this; ++*this; return tmp;
   }
 
-  // Retrieve a reference to the current User
+  // Retrieve a pointer to the current User.
   UserTy *operator*() const {
     assert(U && "Cannot dereference end iterator!");
     return U->getUser();
@@ -205,30 +214,6 @@ public:
   unsigned getOperandNo() const;
 };
 
-
-template<> struct simplify_type<value_use_iterator<User> > {
-  typedef User* SimpleType;
-  
-  static SimpleType getSimplifiedValue(const value_use_iterator<User> &Val) {
-    return *Val;
-  }
-};
-
-template<> struct simplify_type<const value_use_iterator<User> >
- : public simplify_type<value_use_iterator<User> > {};
-
-template<> struct simplify_type<value_use_iterator<const User> > {
-  typedef const User* SimpleType;
-  
-  static SimpleType getSimplifiedValue(const 
-                                       value_use_iterator<const User> &Val) {
-    return *Val;
-  }
-};
-
-template<> struct simplify_type<const value_use_iterator<const User> >
-  : public simplify_type<value_use_iterator<const User> > {};
-
 } // End llvm namespace
 
 #endif