X-Git-Url: http://demsky.eecs.uci.edu/git/?a=blobdiff_plain;f=include%2Fllvm%2FUse.h;h=a496325c1fc667e5416cf35986993917ca4373bf;hb=2c10ecbe4c800bd8a2e1b3e05c4eedf75658b565;hp=c81a903e8b0e6e1074fe3e7ca53e233e27b6463c;hpb=59dc98de2f79c027eb6860443daee260710b1405;p=oota-llvm.git

diff --git a/include/llvm/Use.h b/include/llvm/Use.h
index c81a903e8b0..a496325c1fc 100644
--- a/include/llvm/Use.h
+++ b/include/llvm/Use.h
@@ -11,44 +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;
 
+// 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);
+
+  // 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;
+
+private:
+  /// Copy ctor - do not implement
+  Use(const Use &U);
 
-  Use(Value *V, User *U) { init(V, U); }
-  Use(const Use &U) { init(U.Val, U.U); }
-  inline ~Use() {
+  /// Destructor - Only for zap()
+  ~Use() {
     if (Val) removeFromList();
   }
 
-  /// Default ctor - This leaves the Use completely unitialized.  The only thing
-  /// that is valid to do with this use is to call the "init" method.
-  inline Use() : Val(0) {}
+  enum PrevPtrTag { zeroDigitTag
+                  , oneDigitTag
+                  , stopTag
+                  , fullStopTag };
 
+  /// 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; }
-  User *getUser() const { return U; }
+  
+  /// getUser - This returns the User that contains this Use.  For an
+  /// instruction operand, for example, this will return the instruction.
+  User *getUser() const;
 
   inline void set(Value *Val);
 
@@ -65,20 +110,36 @@ 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:
-  Use *Next, **Prev;
+  const Use* getImpliedUser() const;
+  
   Value *Val;
-  User *U;
+  Use *Next;
+  PointerIntPair<Use**, 2, PrevPtrTag> Prev;
 
+  void setPrev(Use **NewPrev) {
+    Prev.setPointer(NewPrev);
+  }
   void addToList(Use **List) {
     Next = *List;
-    if (Next) Next->Prev = &Next;
-    Prev = List;
+    if (Next) Next->setPrev(&Next);
+    setPrev(List);
     *List = this;
   }
   void removeFromList() {
-    *Prev = Next;
-    if (Next) Next->Prev = Prev;
+    Use **StrippedPrev = Prev.getPointer();
+    *StrippedPrev = Next;
+    if (Next) Next->setPrev(StrippedPrev);
   }
 
   friend class Value;
@@ -102,12 +163,13 @@ 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;
-  value_use_iterator(Use *u) : U(u) {}
+  explicit value_use_iterator(Use *u) : U(u) {}
   friend class Value;
 public:
   typedef typename super::reference reference;
@@ -122,7 +184,7 @@ public:
   bool operator!=(const _Self &x) const {
     return !operator==(x);
   }
-  
+
   /// atEnd - return true if this iterator is equal to use_end() on the value.
   bool atEnd() const { return U == 0; }
 
@@ -136,9 +198,9 @@ public:
     _Self tmp = *this; ++*this; return tmp;
   }
 
-  // Retrieve a reference to the current SCC
+  // Retrieve a pointer to the current User.
   UserTy *operator*() const {
-    assert(U && "Cannot increment end iterator!");
+    assert(U && "Cannot dereference end iterator!");
     return U->getUser();
   }
 
@@ -152,30 +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