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[libFuzzer] don't create too many trace-based mutations as it may be too slow

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llvm-svn: 259600
This commit is contained in:
Kostya Serebryany 2016-02-02 23:17:45 +00:00
parent 5301a2e16c
commit aa6ade3737
1 changed files with 18 additions and 2 deletions
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20
lib/Fuzzer/FuzzerTraceState.cpp
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@ -259,6 +259,22 @@ class TraceState {
Signed >>= 16;
return Signed == 0 || Signed == -1L;
}
// We don't want to create too many trace-based mutations as it is both
// expensive and useless. So after some number of mutations is collected,
// start rejecting some of them. The more there are mutations the more we
// reject.
bool WantToHandleOneMoreMutation() {
const size_t FirstN = 64;
// Gladly handle first N mutations.
if (NumMutations <= FirstN) return true;
size_t Diff = NumMutations - FirstN;
size_t DiffLog = sizeof(long) * 8 - __builtin_clzl((long)Diff);
assert(DiffLog > 0 && DiffLog < 64);
bool WantThisOne = USF.GetRand()(1 << DiffLog) == 0; // 1 out of DiffLog.
return WantThisOne;
}
static const size_t kMaxMutations = 1 << 16;
size_t NumMutations;
TraceBasedMutation Mutations[kMaxMutations];
@ -362,7 +378,7 @@ void TraceState::DFSanSwitchCallback(uint64_t PC, size_t ValSizeInBits,
int TraceState::TryToAddDesiredData(uint64_t PresentData, uint64_t DesiredData,
size_t DataSize) {
if (NumMutations >= kMaxMutations) return 0;
if (NumMutations >= kMaxMutations || !WantToHandleOneMoreMutation()) return 0;
int Res = 0;
const uint8_t *Beg = *CurrentUnitData;
const uint8_t *End = Beg + *CurrentUnitSize;
@ -383,7 +399,7 @@ int TraceState::TryToAddDesiredData(uint64_t PresentData, uint64_t DesiredData,
int TraceState::TryToAddDesiredData(const uint8_t *PresentData,
const uint8_t *DesiredData,
size_t DataSize) {
if (NumMutations >= kMaxMutations) return 0;
if (NumMutations >= kMaxMutations || !WantToHandleOneMoreMutation()) return 0;
int Res = 0;
const uint8_t *Beg = *CurrentUnitData;
const uint8_t *End = Beg + *CurrentUnitSize;