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SmallPtrSet: Provide a more efficient implementation of swap than the default triple-copy std::swap.

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This currently assumes that both sets have the same SmallSize to keep the implementation simple,
a limitation that can be lifted if someone cares.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@152143 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Benjamin Kramer
2012-03-06 20:40:02 +00:00
parent 54427e5219
commit 2945a32ffd
3 changed files with 138 additions and 0 deletions
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50
lib/Support/SmallPtrSet.cpp
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@ -14,6 +14,7 @@
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/Support/MathExtras.h"
#include <algorithm>
#include <cstdlib>
using namespace llvm;
@ -223,6 +224,55 @@ void SmallPtrSetImpl::CopyFrom(const SmallPtrSetImpl &RHS) {
NumTombstones = RHS.NumTombstones;
}
void SmallPtrSetImpl::swap(SmallPtrSetImpl &RHS) {
if (this == &RHS) return;
// We can only avoid copying elements if neither set is small.
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->NumTombstones, RHS.NumTombstones);
return;
}
// FIXME: From here on we assume that both sets have the same small size.
// 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.NumElements, this->SmallArray);
std::swap(this->NumElements, RHS.NumElements);
std::swap(this->CurArraySize, RHS.CurArraySize);
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->NumElements,
RHS.SmallArray);
std::swap(RHS.NumElements, this->NumElements);
std::swap(RHS.CurArraySize, this->CurArraySize);
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);
unsigned MaxElems = std::max(this->NumElements, RHS.NumElements);
std::swap_ranges(this->SmallArray, this->SmallArray+MaxElems, RHS.SmallArray);
std::swap(this->NumElements, RHS.NumElements);
}
SmallPtrSetImpl::~SmallPtrSetImpl() {
if (!isSmall())
free(CurArray);