[llvm] r280054 - [libFuzzer] use bits instead of bytes for memcmp/strcmp value profile -- the fuzzer reaches the goal much faster, at least on the simple puzzles

[Kostya Serebryany via llvm-commits]

Author: kcc
Date: Mon Aug 29 22:05:50 2016
New Revision: 280054

URL: http://llvm.org/viewvc/llvm-project?rev=280054&view=rev
Log:
[libFuzzer] use bits instead of bytes for memcmp/strcmp value profile -- the fuzzer reaches the goal much faster, at least on the simple puzzles

Modified:
    llvm/trunk/lib/Fuzzer/FuzzerTraceState.cpp
    llvm/trunk/lib/Fuzzer/test/value-profile-mem.test

Modified: llvm/trunk/lib/Fuzzer/FuzzerTraceState.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Fuzzer/FuzzerTraceState.cpp?rev=280054&r1=280053&r2=280054&view=diff
==============================================================================
--- llvm/trunk/lib/Fuzzer/FuzzerTraceState.cpp (original)
+++ llvm/trunk/lib/Fuzzer/FuzzerTraceState.cpp Mon Aug 29 22:05:50 2016
@@ -552,26 +552,34 @@ static void AddValueForMemcmp(void *call
                               size_t n) {
   if (!n) return;
   size_t Len = std::min(n, (size_t)32);
-  const char *A1 = reinterpret_cast<const char *>(s1);
-  const char *A2 = reinterpret_cast<const char *>(s2);
-  size_t LastSameByte = 0;
-  for (; LastSameByte < Len; LastSameByte++)
-    if (A1[LastSameByte] != A2[LastSameByte])
+  const uint8_t *A1 = reinterpret_cast<const uint8_t *>(s1);
+  const uint8_t *A2 = reinterpret_cast<const uint8_t *>(s2);
+  size_t I = 0;
+  for (; I < Len; I++)
+    if (A1[I] != A2[I])
       break;
   size_t PC = reinterpret_cast<size_t>(caller_pc);
-  VP.AddValue((PC & 4095) | (LastSameByte << 12));
+  size_t Idx = I * 8;
+  if (I < Len)
+    Idx += __builtin_popcountl((A1[I] ^ A2[I])) - 1;
+  VP.AddValue((PC & 4095) | (Idx << 12));
 }
 
 static void AddValueForStrcmp(void *caller_pc, const char *s1, const char *s2,
                               size_t n) {
   if (!n) return;
   size_t Len = std::min(n, (size_t)32);
-  size_t LastSameByte = 0;
-  for (; LastSameByte < Len; LastSameByte++)
-    if (s1[LastSameByte] != s2[LastSameByte] || s1[LastSameByte] == 0)
+  const uint8_t *A1 = reinterpret_cast<const uint8_t *>(s1);
+  const uint8_t *A2 = reinterpret_cast<const uint8_t *>(s2);
+  size_t I = 0;
+  for (; I < Len; I++)
+    if (A1[I] != A2[I] || A1[I] == 0)
       break;
   size_t PC = reinterpret_cast<size_t>(caller_pc);
-  VP.AddValue((PC & 4095) | (LastSameByte << 12));
+  size_t Idx = I * 8;
+  if (I < Len && A1[I])
+    Idx += __builtin_popcountl((A1[I] ^ A2[I])) - 1;
+  VP.AddValue((PC & 4095) | (Idx << 12));
 }
 
 ATTRIBUTE_TARGET_POPCNT

Modified: llvm/trunk/lib/Fuzzer/test/value-profile-mem.test
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Fuzzer/test/value-profile-mem.test?rev=280054&r1=280053&r2=280054&view=diff
==============================================================================
--- llvm/trunk/lib/Fuzzer/test/value-profile-mem.test (original)
+++ llvm/trunk/lib/Fuzzer/test/value-profile-mem.test Mon Aug 29 22:05:50 2016
@@ -1,4 +1,4 @@
 CHECK: BINGO
-RUN: not LLVMFuzzer-SingleMemcmpTest -seed=1 -use_memcmp=0 -use_value_profile=1 -runs=10000000 2>&1 | FileCheck %s
-RUN: not LLVMFuzzer-SingleStrcmpTest -seed=1 -use_memcmp=0 -use_value_profile=1 -runs=10000000 2>&1 | FileCheck %s
-RUN: not LLVMFuzzer-SingleStrncmpTest -seed=1 -use_memcmp=0 -use_value_profile=1 -runs=10000000 2>&1 | FileCheck %s
+RUN: not LLVMFuzzer-SingleMemcmpTest -seed=1 -use_memcmp=0 -use_value_profile=1 -runs=1000000 2>&1 | FileCheck %s
+RUN: not LLVMFuzzer-SingleStrcmpTest -seed=1 -use_memcmp=0 -use_value_profile=1 -runs=1000000 2>&1 | FileCheck %s
+RUN: not LLVMFuzzer-SingleStrncmpTest -seed=1 -use_memcmp=0 -use_value_profile=1 -runs=1000000 2>&1 | FileCheck %s