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[cleanup] Tidy up and modernize comments and the definition order for

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the Use class.

More cleanups to come here. This class just needs some TLC.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@202798 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chandler Carruth 2014-03-04 08:51:00 +00:00
parent d186c936bb
commit 0a6057117e
2 changed files with 103 additions and 111 deletions
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90
include/llvm/IR/Use.h
View File

@ -6,20 +6,20 @@
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This defines the Use class. The Use class represents the operand of an
// 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
//
/// \file
///
/// This defines the Use class. The Use class represents the operand of an
/// 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_IR_USE_H
@ -51,15 +51,26 @@ public:
enum { NumLowBitsAvailable = 2 };
};
//===----------------------------------------------------------------------===//
// Use Class
//===----------------------------------------------------------------------===//
/// Use is here to make keeping the "use" list of a Value up-to-date really
/// easy.
/// \brief A Use represents the edge between a Value definition and its users.
///
/// This is notionally a two-dimensional linked list. It supports traversing
/// all of the uses for a particular value definition. It also supports jumping
/// directly to the used value when we arrive from the User's operands, and
/// jumping directly to the User when we arrive from the Value's uses.
///
/// The pointer to the used Value is explicit, and the pointer to the User is
/// implicit. The implicit pointer is found via a waymarking algorithm
/// described in the programmer's manual:
///
/// http://www.llvm.org/docs/ProgrammersManual.html#UserLayout
///
/// This is essentially the single most memory intensive object in LLVM because
/// of the number of uses in the system. At the same time, the constant time
/// operations it allows are essential to many optimizations having reasonable
/// time complexity.
class Use {
public:
/// swap - provide a fast substitute to std::swap<Use>
/// \brief Provide a fast substitute to std::swap<Use>
/// that also works with less standard-compliant compilers
void swap(Use &RHS);
@ -86,15 +97,13 @@ private:
}
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.
/// \brief 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);
@ -113,18 +122,19 @@ public:
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.
/// \brief Initializes the waymarking tags on an array of Uses.
///
/// This sets up the array of Uses such 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
/// \brief Destroys 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;
PointerIntPair<Use**, 2, PrevPtrTag> Prev;
@ -147,8 +157,8 @@ private:
friend class Value;
};
// simplify_type - Allow clients to treat uses just like values when using
// casting operators.
/// \brief Allow clients to treat uses just like values when using
/// casting operators.
template<> struct simplify_type<Use> {
typedef Value* SimpleType;
static SimpleType getSimplifiedValue(Use &Val) {
@ -186,7 +196,7 @@ public:
return !operator==(x);
}
/// atEnd - return true if this iterator is equal to use_end() on the value.
/// \brief Returns true if this iterator is equal to use_end() on the value.
bool atEnd() const { return U == 0; }
// Iterator traversal: forward iteration only
@ -208,16 +218,16 @@ public:
UserTy *operator->() const { return operator*(); }
Use &getUse() const { return *U; }
/// getOperandNo - Return the operand # of this use in its User. Defined in
/// User.h
/// \brief Return the operand # of this use in its User.
///
/// Defined in User.h
unsigned getOperandNo() const;
};
// Create wrappers for C Binding types (see CBindingWrapping.h).
DEFINE_SIMPLE_CONVERSION_FUNCTIONS(Use, LLVMUseRef)
} // End llvm namespace
}
#endif

124
lib/IR/Use.cpp
View File

@ -6,20 +6,13 @@
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the algorithm for finding the User of a Use.
//
//===----------------------------------------------------------------------===//
#include "llvm/IR/Use.h"
#include "llvm/IR/Value.h"
#include <new>
namespace llvm {
//===----------------------------------------------------------------------===//
// Use swap Implementation
//===----------------------------------------------------------------------===//
void Use::swap(Use &RHS) {
Value *V1(Val);
Value *V2(RHS.Val);
@ -45,9 +38,58 @@ void Use::swap(Use &RHS) {
}
}
//===----------------------------------------------------------------------===//
// Use getImpliedUser Implementation
//===----------------------------------------------------------------------===//
User *Use::getUser() const {
const Use *End = getImpliedUser();
const UserRef *ref = reinterpret_cast<const UserRef*>(End);
return ref->getInt()
? ref->getPointer()
: reinterpret_cast<User*>(const_cast<Use*>(End));
}
// Sets up the waymarking algoritm's tags for a series of Uses. See the
// algorithm details here:
//
// http://www.llvm.org/docs/ProgrammersManual.html#UserLayout
//
Use *Use::initTags(Use * const Start, Use *Stop) {
ptrdiff_t Done = 0;
while (Done < 20) {
if (Start == Stop--)
return Start;
static const PrevPtrTag tags[20] = { fullStopTag, oneDigitTag, stopTag,
oneDigitTag, oneDigitTag, stopTag,
zeroDigitTag, oneDigitTag, oneDigitTag,
stopTag, zeroDigitTag, oneDigitTag,
zeroDigitTag, oneDigitTag, stopTag,
oneDigitTag, oneDigitTag, oneDigitTag,
oneDigitTag, stopTag
};
new(Stop) Use(tags[Done++]);
}
ptrdiff_t Count = Done;
while (Start != Stop) {
--Stop;
if (!Count) {
new(Stop) Use(stopTag);
++Done;
Count = Done;
} else {
new(Stop) Use(PrevPtrTag(Count & 1));
Count >>= 1;
++Done;
}
}
return Start;
}
void Use::zap(Use *Start, const Use *Stop, bool del) {
while (Start != Stop)
(--Stop)->~Use();
if (del)
::operator delete(Start);
}
const Use *Use::getImpliedUser() const {
const Use *Current = this;
@ -82,64 +124,4 @@ const Use *Use::getImpliedUser() const {
}
}
//===----------------------------------------------------------------------===//
// Use initTags Implementation
//===----------------------------------------------------------------------===//
Use *Use::initTags(Use * const Start, Use *Stop) {
ptrdiff_t Done = 0;
while (Done < 20) {
if (Start == Stop--)
return Start;
static const PrevPtrTag tags[20] = { fullStopTag, oneDigitTag, stopTag,
oneDigitTag, oneDigitTag, stopTag,
zeroDigitTag, oneDigitTag, oneDigitTag,
stopTag, zeroDigitTag, oneDigitTag,
zeroDigitTag, oneDigitTag, stopTag,
oneDigitTag, oneDigitTag, oneDigitTag,
oneDigitTag, stopTag
};
new(Stop) Use(tags[Done++]);
}
ptrdiff_t Count = Done;
while (Start != Stop) {
--Stop;
if (!Count) {
new(Stop) Use(stopTag);
++Done;
Count = Done;
} else {
new(Stop) Use(PrevPtrTag(Count & 1));
Count >>= 1;
++Done;
}
}
return Start;
}
//===----------------------------------------------------------------------===//
// Use zap Implementation
//===----------------------------------------------------------------------===//
void Use::zap(Use *Start, const Use *Stop, bool del) {
while (Start != Stop)
(--Stop)->~Use();
if (del)
::operator delete(Start);
}
//===----------------------------------------------------------------------===//
// Use getUser Implementation
//===----------------------------------------------------------------------===//
User *Use::getUser() const {
const Use *End = getImpliedUser();
const UserRef *ref = reinterpret_cast<const UserRef*>(End);
return ref->getInt()
? ref->getPointer()
: reinterpret_cast<User*>(const_cast<Use*>(End));
}
} // End llvm namespace