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SmallPtrSet: Avoid initializing Array in the small case.

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This patch avoids the initial memset at the cost of making iterators
slightly more complex. This should be beneficial as most SmallPtrSets
hold no or only a few elements, while iterating over them is less
common.

Differential Revision: http://reviews.llvm.org/D16672

llvm-svn: 260913
This commit is contained in:
Matthias Braun 2016-02-15 21:38:42 +00:00
parent b1bd9227a8
commit ad3e9d1469
2 changed files with 94 additions and 75 deletions
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64
include/llvm/ADT/SmallPtrSet.h
View File

@ -59,8 +59,11 @@ protected:
/// CurArraySize - The allocated size of CurArray, always a power of two.
unsigned CurArraySize;
// If small, this is # elts allocated consecutively
unsigned NumElements;
/// Number of elements in CurArray that contain a value or are a tombstone.
/// If small, all these elements are at the beginning of CurArray and the rest
/// is uninitialized.
unsigned NumNonEmpty;
/// Number of tombstones in CurArray.
unsigned NumTombstones;
// Helpers to copy and move construct a SmallPtrSet.
@ -68,11 +71,11 @@ protected:
const SmallPtrSetImplBase &that);
SmallPtrSetImplBase(const void **SmallStorage, unsigned SmallSize,
SmallPtrSetImplBase &&that);
explicit SmallPtrSetImplBase(const void **SmallStorage, unsigned SmallSize) :
SmallArray(SmallStorage), CurArray(SmallStorage), CurArraySize(SmallSize) {
explicit SmallPtrSetImplBase(const void **SmallStorage, unsigned SmallSize)
: SmallArray(SmallStorage), CurArray(SmallStorage),
CurArraySize(SmallSize), NumNonEmpty(0), NumTombstones(0) {
assert(SmallSize && (SmallSize & (SmallSize-1)) == 0 &&
"Initial size must be a power of two!");
clear();
}
~SmallPtrSetImplBase() {
if (!isSmall())
@ -82,17 +85,19 @@ protected:
public:
typedef unsigned size_type;
bool LLVM_ATTRIBUTE_UNUSED_RESULT empty() const { return size() == 0; }
size_type size() const { return NumElements; }
size_type size() const { return NumNonEmpty - NumTombstones; }
void clear() {
// If the capacity of the array is huge, and the # elements used is small,
// shrink the array.
if (!isSmall() && NumElements*4 < CurArraySize && CurArraySize > 32)
return shrink_and_clear();
if (!isSmall()) {
if (size() * 4 < CurArraySize && CurArraySize > 32)
return shrink_and_clear();
// Fill the array with empty markers.
memset(CurArray, -1, CurArraySize * sizeof(void *));
}
// Fill the array with empty markers.
memset(CurArray, -1, CurArraySize*sizeof(void*));
NumElements = 0;
NumNonEmpty = 0;
NumTombstones = 0;
}
@ -104,21 +109,37 @@ protected:
return reinterpret_cast<void*>(-1);
}
const void **EndPointer() const {
return isSmall() ? CurArray + NumNonEmpty : CurArray + CurArraySize;
}
/// insert_imp - This returns true if the pointer was new to the set, false if
/// it was already in the set. This is hidden from the client so that the
/// derived class can check that the right type of pointer is passed in.
std::pair<const void *const *, bool> insert_imp(const void *Ptr) {
if (isSmall()) {
// Check to see if it is already in the set.
for (const void **APtr = SmallArray, **E = SmallArray+NumElements;
APtr != E; ++APtr)
if (*APtr == Ptr)
const void **LastTombstone = nullptr;
for (const void **APtr = SmallArray, **E = SmallArray + NumNonEmpty;
APtr != E; ++APtr) {
const void *Value = *APtr;
if (Value == Ptr)
return std::make_pair(APtr, false);
if (Value == getTombstoneMarker())
LastTombstone = APtr;
}
// Did we find any tombstone marker?
if (LastTombstone != nullptr) {
*LastTombstone = Ptr;
--NumTombstones;
return std::make_pair(LastTombstone, true);
}
// Nope, there isn't. If we stay small, just 'pushback' now.
if (NumElements < CurArraySize) {
SmallArray[NumElements++] = Ptr;
return std::make_pair(SmallArray + (NumElements - 1), true);
if (NumNonEmpty < CurArraySize) {
SmallArray[NumNonEmpty++] = Ptr;
return std::make_pair(SmallArray + (NumNonEmpty - 1), true);
}
// Otherwise, hit the big set case, which will call grow.
}
@ -135,7 +156,7 @@ protected:
if (isSmall()) {
// Linear search for the item.
for (const void *const *APtr = SmallArray,
*const *E = SmallArray+NumElements; APtr != E; ++APtr)
*const *E = SmallArray + NumNonEmpty; APtr != E; ++APtr)
if (*APtr == Ptr)
return true;
return false;
@ -295,7 +316,7 @@ public:
/// the element equal to Ptr.
std::pair<iterator, bool> insert(PtrType Ptr) {
auto p = insert_imp(PtrTraits::getAsVoidPointer(Ptr));
return std::make_pair(iterator(p.first, CurArray + CurArraySize), p.second);
return std::make_pair(iterator(p.first, EndPointer()), p.second);
}
/// erase - If the set contains the specified pointer, remove it and return
@ -316,10 +337,11 @@ public:
}
inline iterator begin() const {
return iterator(CurArray, CurArray+CurArraySize);
return iterator(CurArray, EndPointer());
}
inline iterator end() const {
return iterator(CurArray+CurArraySize, CurArray+CurArraySize);
const void *const *End = EndPointer();
return iterator(End, End);
}
};

105
lib/Support/SmallPtrSet.cpp
View File

@ -25,8 +25,9 @@ void SmallPtrSetImplBase::shrink_and_clear() {
free(CurArray);
// Reduce the number of buckets.
CurArraySize = NumElements > 16 ? 1 << (Log2_32_Ceil(NumElements) + 1) : 32;
NumElements = NumTombstones = 0;
unsigned Size = size();
CurArraySize = Size > 16 ? 1 << (Log2_32_Ceil(Size) + 1) : 32;
NumNonEmpty = NumTombstones = 0;
// Install the new array. Clear all the buckets to empty.
CurArray = (const void**)malloc(sizeof(void*) * CurArraySize);
@ -36,11 +37,10 @@ void SmallPtrSetImplBase::shrink_and_clear() {
std::pair<const void *const *, bool>
SmallPtrSetImplBase::insert_imp_big(const void *Ptr) {
if (LLVM_UNLIKELY(NumElements * 4 >= CurArraySize * 3)) {
if (LLVM_UNLIKELY(size() * 4 >= CurArraySize * 3)) {
// If more than 3/4 of the array is full, grow.
Grow(CurArraySize < 64 ? 128 : CurArraySize*2);
} else if (LLVM_UNLIKELY(CurArraySize - (NumElements + NumTombstones) <
CurArraySize / 8)) {
Grow(CurArraySize < 64 ? 128 : CurArraySize * 2);
} else if (LLVM_UNLIKELY(CurArraySize - NumNonEmpty < CurArraySize / 8)) {
// If fewer of 1/8 of the array is empty (meaning that many are filled with
// tombstones), rehash.
Grow(CurArraySize);
@ -54,21 +54,21 @@ SmallPtrSetImplBase::insert_imp_big(const void *Ptr) {
// Otherwise, insert it!
if (*Bucket == getTombstoneMarker())
--NumTombstones;
else
++NumNonEmpty; // Track density.
*Bucket = Ptr;
++NumElements; // Track density.
return std::make_pair(Bucket, true);
}
bool SmallPtrSetImplBase::erase_imp(const void * Ptr) {
if (isSmall()) {
// Check to see if it is in the set.
for (const void **APtr = SmallArray, **E = SmallArray+NumElements;
APtr != E; ++APtr)
for (const void **APtr = CurArray, **E = CurArray + NumNonEmpty; APtr != E;
++APtr)
if (*APtr == Ptr) {
// If it is in the set, replace this element.
*APtr = E[-1];
E[-1] = getEmptyMarker();
--NumElements;
*APtr = getTombstoneMarker();
++NumTombstones;
return true;
}
@ -81,7 +81,6 @@ bool SmallPtrSetImplBase::erase_imp(const void * Ptr) {
// Set this as a tombstone.
*Bucket = getTombstoneMarker();
--NumElements;
++NumTombstones;
return true;
}
@ -116,10 +115,8 @@ const void * const *SmallPtrSetImplBase::FindBucketFor(const void *Ptr) const {
/// Grow - Allocate a larger backing store for the buckets and move it over.
///
void SmallPtrSetImplBase::Grow(unsigned NewSize) {
// Allocate at twice as many buckets, but at least 128.
unsigned OldSize = CurArraySize;
const void **OldBuckets = CurArray;
const void **OldEnd = EndPointer();
bool WasSmall = isSmall();
// Install the new array. Clear all the buckets to empty.
@ -128,27 +125,18 @@ void SmallPtrSetImplBase::Grow(unsigned NewSize) {
CurArraySize = NewSize;
memset(CurArray, -1, NewSize*sizeof(void*));
// Copy over all the elements.
if (WasSmall) {
// Small sets store their elements in order.
for (const void **BucketPtr = OldBuckets, **E = OldBuckets+NumElements;
BucketPtr != E; ++BucketPtr) {
const void *Elt = *BucketPtr;
// Copy over all valid entries.
for (const void **BucketPtr = OldBuckets; BucketPtr != OldEnd; ++BucketPtr) {
// Copy over the element if it is valid.
const void *Elt = *BucketPtr;
if (Elt != getTombstoneMarker() && Elt != getEmptyMarker())
*const_cast<void**>(FindBucketFor(Elt)) = const_cast<void*>(Elt);
}
} else {
// Copy over all valid entries.
for (const void **BucketPtr = OldBuckets, **E = OldBuckets+OldSize;
BucketPtr != E; ++BucketPtr) {
// Copy over the element if it is valid.
const void *Elt = *BucketPtr;
if (Elt != getTombstoneMarker() && Elt != getEmptyMarker())
*const_cast<void**>(FindBucketFor(Elt)) = const_cast<void*>(Elt);
}
free(OldBuckets);
NumTombstones = 0;
}
if (!WasSmall)
free(OldBuckets);
NumNonEmpty -= NumTombstones;
NumTombstones = 0;
}
SmallPtrSetImplBase::SmallPtrSetImplBase(const void **SmallStorage,
@ -209,9 +197,9 @@ void SmallPtrSetImplBase::CopyHelper(const SmallPtrSetImplBase &RHS) {
CurArraySize = RHS.CurArraySize;
// Copy over the contents from the other set
memcpy(CurArray, RHS.CurArray, sizeof(void*)*CurArraySize);
std::copy(RHS.CurArray, RHS.EndPointer(), CurArray);
NumElements = RHS.NumElements;
NumNonEmpty = RHS.NumNonEmpty;
NumTombstones = RHS.NumTombstones;
}
@ -229,7 +217,7 @@ void SmallPtrSetImplBase::MoveHelper(unsigned SmallSize,
if (RHS.isSmall()) {
// Copy a small RHS rather than moving.
CurArray = SmallArray;
memcpy(CurArray, RHS.CurArray, sizeof(void*)*RHS.CurArraySize);
std::copy(RHS.CurArray, RHS.CurArray + RHS.NumNonEmpty, CurArray);
} else {
CurArray = RHS.CurArray;
RHS.CurArray = RHS.SmallArray;
@ -237,13 +225,13 @@ void SmallPtrSetImplBase::MoveHelper(unsigned SmallSize,
// Copy the rest of the trivial members.
CurArraySize = RHS.CurArraySize;
NumElements = RHS.NumElements;
NumNonEmpty = RHS.NumNonEmpty;
NumTombstones = RHS.NumTombstones;
// Make the RHS small and empty.
RHS.CurArraySize = SmallSize;
assert(RHS.CurArray == RHS.SmallArray);
RHS.NumElements = 0;
RHS.NumNonEmpty = 0;
RHS.NumTombstones = 0;
}
@ -254,7 +242,7 @@ void SmallPtrSetImplBase::swap(SmallPtrSetImplBase &RHS) {
if (!this->isSmall() && !RHS.isSmall()) {
std::swap(this->CurArray, RHS.CurArray);
std::swap(this->CurArraySize, RHS.CurArraySize);
std::swap(this->NumElements, RHS.NumElements);
std::swap(this->NumNonEmpty, RHS.NumNonEmpty);
std::swap(this->NumTombstones, RHS.NumTombstones);
return;
}
@ -264,35 +252,44 @@ void SmallPtrSetImplBase::swap(SmallPtrSetImplBase &RHS) {
// If only RHS is small, copy the small elements into LHS and move the pointer
// from LHS to RHS.
if (!this->isSmall() && RHS.isSmall()) {
std::copy(RHS.SmallArray, RHS.SmallArray+RHS.CurArraySize,
this->SmallArray);
std::swap(this->NumElements, RHS.NumElements);
std::swap(this->CurArraySize, RHS.CurArraySize);
assert(RHS.CurArray == RHS.SmallArray);
std::copy(RHS.CurArray, RHS.CurArray + RHS.NumNonEmpty, this->SmallArray);
std::swap(RHS.CurArraySize, this->CurArraySize);
std::swap(this->NumNonEmpty, RHS.NumNonEmpty);
std::swap(this->NumTombstones, RHS.NumTombstones);
RHS.CurArray = this->CurArray;
RHS.NumTombstones = this->NumTombstones;
this->CurArray = this->SmallArray;
this->NumTombstones = 0;
return;
}
// If only LHS is small, copy the small elements into RHS and move the pointer
// from RHS to LHS.
if (this->isSmall() && !RHS.isSmall()) {
std::copy(this->SmallArray, this->SmallArray+this->CurArraySize,
assert(this->CurArray == this->SmallArray);
std::copy(this->CurArray, this->CurArray + this->NumNonEmpty,
RHS.SmallArray);
std::swap(RHS.NumElements, this->NumElements);
std::swap(RHS.CurArraySize, this->CurArraySize);
std::swap(RHS.NumNonEmpty, this->NumNonEmpty);
std::swap(RHS.NumTombstones, this->NumTombstones);
this->CurArray = RHS.CurArray;
this->NumTombstones = RHS.NumTombstones;
RHS.CurArray = RHS.SmallArray;
RHS.NumTombstones = 0;
return;
}
// Both a small, just swap the small elements.
assert(this->isSmall() && RHS.isSmall());
assert(this->CurArraySize == RHS.CurArraySize);
std::swap_ranges(this->SmallArray, this->SmallArray+this->CurArraySize,
unsigned MinNonEmpty = std::min(this->NumNonEmpty, RHS.NumNonEmpty);
std::swap_ranges(this->SmallArray, this->SmallArray + MinNonEmpty,
RHS.SmallArray);
std::swap(this->NumElements, RHS.NumElements);
if (this->NumNonEmpty > MinNonEmpty) {
std::copy(this->SmallArray + MinNonEmpty,
this->SmallArray + this->NumNonEmpty,
RHS.SmallArray + MinNonEmpty);
} else {
std::copy(RHS.SmallArray + MinNonEmpty, RHS.SmallArray + RHS.NumNonEmpty,
this->SmallArray + MinNonEmpty);
}
assert(this->CurArraySize == RHS.CurArraySize);
std::swap(this->NumNonEmpty, RHS.NumNonEmpty);
std::swap(this->NumTombstones, RHS.NumTombstones);
}