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Replaced (FoldingSet) profiling of ImutAVLTree with a hashing based scheme. The

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problem was that we previously hashed based on the pointers of the left and
right children, but this is bogus: we can easily have different trees that
represent the same set. Now we use a hashing based scheme that compares the
*contents* of the trees, but not without having to do a full scan of a tree. The
only caveat is that with hashing is that we may have collisions, which result in
two different trees being falsely labeled as equivalent. If this becomes a
problem, we can add extra data to the profile to hopefully resolve most
collisions.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@46224 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Ted Kremenek 2008-01-21 22:33:30 +00:00
parent 82137bd061
commit 6518f5fcbf
1 changed files with 23 additions and 6 deletions
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29
include/llvm/ADT/ImmutableSet.h
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@ -198,6 +198,7 @@ private:
ImutAVLTree* Right;
unsigned Height;
value_type Value;
unsigned Hash;
//===----------------------------------------------------===//
// Profiling or FoldingSet.
@ -205,22 +206,38 @@ private:
private:
static inline
unsigned ComputeHash(ImutAVLTree* L, ImutAVLTree* R, value_type_ref V) {
FoldingSetNodeID ID;
ID.AddInteger(L ? L->ComputeHash() : 0);
ImutInfo::Profile(ID,V);
ID.AddInteger(R ? R->ComputeHash() : 0);
return ID.ComputeHash();
}
inline unsigned ComputeHash() {
if (!isMutable() && Hash) return Hash;
Hash = ComputeHash(getSafeLeft(), getRight(), getValue());
return Hash;
}
/// Profile - Generates a FoldingSet profile for a tree node before it is
/// created. This is used by the ImutAVLFactory when creating
/// trees.
static inline
void Profile(FoldingSetNodeID& ID, ImutAVLTree* L, ImutAVLTree* R,
value_type_ref V) {
ID.AddPointer(L);
ID.AddPointer(R);
ImutInfo::Profile(ID,V);
value_type_ref V) {
ID.AddInteger(ComputeHash(L, R, V));
}
public:
/// Profile - Generates a FoldingSet profile for an existing tree node.
void Profile(FoldingSetNodeID& ID) {
Profile(ID,getSafeLeft(),getRight(),getValue());
ID.AddInteger(ComputeHash());
}
//===----------------------------------------------------===//
@ -235,7 +252,7 @@ private:
/// ImutAVLFactory.
ImutAVLTree(ImutAVLTree* l, ImutAVLTree* r, value_type_ref v, unsigned height)
: Left(reinterpret_cast<uintptr_t>(l) | Mutable),
Right(r), Height(height), Value(v) {}
Right(r), Height(height), Value(v), Hash(0) {}
/// isMutable - Returns true if the left and right subtree references