// 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.h"
+#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:
/// 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);
/// Destructor - Only for zap()
- inline ~Use() {
+ ~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);
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;
*List = this;
}
void removeFromList() {
- Use **StrippedPrev = stripTag<fullStopTag>(Prev);
+ Use **StrippedPrev = Prev.getPointer();
*StrippedPrev = Next;
if (Next) Next->setPrev(StrippedPrev);
}
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;
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