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[analyzer] Faster hashing of subsequences in CompoundStmts. 

Summary: This patches improves the hashing subsequences in CompoundStmts by incrementally hashing all subsequences with the same starting position. This results in a reduction of the time for this constraint while running over SQLite from 1.10 seconds to 0.55 seconds (-50%).

Reviewers: NoQ

Reviewed By: NoQ

Subscribers: cfe-commits, xazax.hun, v.g.vassilev

Differential Revision: https://reviews.llvm.org/D34364

llvm-svn: 307509
This commit is contained in:
Raphael Isemann 2017-07-09 21:14:36 +00:00
parent c4b0ccd049
commit 4eac9f0545
1 changed files with 20 additions and 9 deletions
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27
clang/lib/Analysis/CloneDetection.cpp
View File

@ -239,16 +239,27 @@ size_t RecursiveCloneTypeIIConstraint::saveHash(
}
if (CS) {
for (unsigned Length = 2; Length <= CS->size(); ++Length) {
for (unsigned Pos = 0; Pos <= CS->size() - Length; ++Pos) {
// If we're in a CompoundStmt, we hash all possible combinations of child
// statements to find clones in those subsequences.
// We first go through every possible starting position of a subsequence.
for (unsigned Pos = 0; Pos < CS->size(); ++Pos) {
// Then we try all possible lengths this subsequence could have and
// reuse the same hash object to make sure we only hash every child
// hash exactly once.
llvm::MD5 Hash;
for (unsigned i = Pos; i < Pos + Length; ++i) {
size_t ChildHash = ChildHashes[i];
Hash.update(StringRef(reinterpret_cast<char *>(&ChildHash),
sizeof(ChildHash)));
}
for (unsigned Length = 1; Length <= CS->size() - Pos; ++Length) {
// Grab the current child hash and put it into our hash. We do
// -1 on the index because we start counting the length at 1.
size_t ChildHash = ChildHashes[Pos + Length - 1];
Hash.update(
StringRef(reinterpret_cast<char *>(&ChildHash), sizeof(ChildHash)));
// If we have at least two elements in our subsequence, we can start
// saving it.
if (Length > 1) {
llvm::MD5 SubHash = Hash;
StmtsByHash.push_back(std::make_pair(
createHash(Hash), StmtSequence(CS, D, Pos, Pos + Length)));
createHash(SubHash), StmtSequence(CS, D, Pos, Pos + Length)));
}
}
}
}