[libfuzzer] Trying random unit prefixes during corpus load.

Differential Revision: http://reviews.llvm.org/D20301

llvm-svn: 270632

1 files changed, 22 insertions, 0 deletions

diff --git a/llvm/lib/Fuzzer/test/FuzzerUnittest.cpp b/llvm/lib/Fuzzer/test/FuzzerUnittest.cpp
index 7b49f2f08e4..66e9285eb05 100644
--- a/llvm/lib/Fuzzer/test/FuzzerUnittest.cpp
+++ b/llvm/lib/Fuzzer/test/FuzzerUnittest.cpp
@@ -13,6 +13,10 @@ extern "C" int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
   abort();
 }
 
+static int EmptyLLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
+  return 0;
+}
+
 TEST(Fuzzer, CrossOver) {
   Random Rand(0);
   MutationDispatcher MD(Rand);
@@ -423,3 +427,21 @@ TEST(Corpus, Distribution) {
     EXPECT_GT(Hist[i], TriesPerUnit / N / 3);
   }
 }
+
+TEST(Corpus, TruncateUnits) {
+  Random Rand(0);
+  MutationDispatcher MD(Rand);
+  Fuzzer::FuzzingOptions Options;
+  Options.OutputCorpus = ""; // stops from writing new units.
+  Fuzzer Fuzz(EmptyLLVMFuzzerTestOneInput, MD, Options);
+
+  Fuzz.AddToCorpus(Unit(1024, static_cast<uint8_t>(1)));
+  Fuzz.ResetCoverage();
+
+  std::vector<Unit> NewCorpus;
+  Fuzz.TruncateUnits(&NewCorpus);
+
+  // New corpus should have a shorter unit.
+  EXPECT_EQ(1ul, NewCorpus.size());
+  EXPECT_EQ(1ul, NewCorpus[0].size());
+}