[libfuzzer] prune_corpus option for disabling pruning during the load.

Summary:
The option is very useful for testing, plus I intend to measure
its effect on fuzzer effectiveness.

Differential Revision: http://reviews.llvm.org/D21084

llvm-svn: 272035

5 files changed, 19 insertions, 1 deletions

diff --git a/llvm/lib/Fuzzer/FuzzerDriver.cpp b/llvm/lib/Fuzzer/FuzzerDriver.cpp
index de5e461eda5..9807d605aeb 100644
--- a/llvm/lib/Fuzzer/FuzzerDriver.cpp
+++ b/llvm/lib/Fuzzer/FuzzerDriver.cpp
@@ -336,6 +336,7 @@ int FuzzerDriver(int *argc, char ***argv, UserCallback Callback) {
   Options.PrintNewCovPcs = Flags.print_new_cov_pcs;
   Options.PrintFinalStats = Flags.print_final_stats;
   Options.TruncateUnits = Flags.truncate_units;
+  Options.PruneCorpus = Flags.prune_corpus;
 
   unsigned Seed = Flags.seed;
   // Initialize Seed.
diff --git a/llvm/lib/Fuzzer/FuzzerFlags.def b/llvm/lib/Fuzzer/FuzzerFlags.def
index 1f27fe8902f..2945152ae70 100644
--- a/llvm/lib/Fuzzer/FuzzerFlags.def
+++ b/llvm/lib/Fuzzer/FuzzerFlags.def
@@ -85,6 +85,8 @@ FUZZER_FLAG_INT(detect_leaks, 1, "If 1, and if LeakSanitizer is enabled "
 FUZZER_FLAG_INT(rss_limit_mb, 2048, "If non-zero, the fuzzer will exit upon"
     "reaching this limit of RSS memory usage.")
 FUZZER_FLAG_INT(truncate_units, 0, "Try truncated units when loading corpus.")
+FUZZER_FLAG_INT(prune_corpus, 1, "Prune corpus items without new coverage when "
+                                 "loading corpus.")
 
 FUZZER_DEPRECATED_FLAG(exit_on_first)
 FUZZER_DEPRECATED_FLAG(save_minimized_corpus)
diff --git a/llvm/lib/Fuzzer/FuzzerInternal.h b/llvm/lib/Fuzzer/FuzzerInternal.h
index 637d2b4b375..ba4ced5b608 100644
--- a/llvm/lib/Fuzzer/FuzzerInternal.h
+++ b/llvm/lib/Fuzzer/FuzzerInternal.h
@@ -331,6 +331,7 @@ public:
     bool PrintFinalStats = false;
     bool DetectLeaks = true;
     bool TruncateUnits = false;
+    bool PruneCorpus = true;
   };
 
   // Aggregates all available coverage measurements.
diff --git a/llvm/lib/Fuzzer/FuzzerLoop.cpp b/llvm/lib/Fuzzer/FuzzerLoop.cpp
index 378178e064d..b7422329e05 100644
--- a/llvm/lib/Fuzzer/FuzzerLoop.cpp
+++ b/llvm/lib/Fuzzer/FuzzerLoop.cpp
@@ -400,7 +400,8 @@ void Fuzzer::ShuffleAndMinimize() {
   }
 
   for (const auto &U : Corpus) {
-    if (RunOne(U)) {
+    bool NewCoverage = RunOne(U);
+    if (!Options.PruneCorpus || NewCoverage) {
       NewCorpus.push_back(U);
       if (Options.Verbosity >= 2)
         Printf("NEW0: %zd L %zd\n", MaxCoverage.BlockCoverage, U.size());
diff --git a/llvm/lib/Fuzzer/test/fuzzer-prunecorpus.test b/llvm/lib/Fuzzer/test/fuzzer-prunecorpus.test
new file mode 100644
index 00000000000..a8a660e91b9
--- /dev/null
+++ b/llvm/lib/Fuzzer/test/fuzzer-prunecorpus.test
@@ -0,0 +1,13 @@
+RUN: rm -rf %t/PruneCorpus
+RUN: mkdir -p %t/PruneCorpus
+RUN: echo a > %t/PruneCorpus/a
+RUN: echo b > %t/PruneCorpus/b
+RUN: LLVMFuzzer-EmptyTest %t/PruneCorpus -prune_corpus=1 -runs=0 2>&1 | FileCheck %s --check-prefix=PRUNE
+RUN: LLVMFuzzer-EmptyTest %t/PruneCorpus -prune_corpus=0 -runs=0 2>&1 | FileCheck %s --check-prefix=NOPRUNE
+RUN: rm -rf %t/PruneCorpus
+
+PRUNE: READ units: 2
+PRUNE: INITED{{.*}}units: 1
+NOPRUNE: READ units: 2
+NOPRUNE: INITED{{.*}}units: 2
+