[llvm] r282562 - [libFuzzer] speedup TracePC::FinalizeTrace

[Kostya Serebryany via llvm-commits]

Author: kcc
Date: Tue Sep 27 20:16:24 2016
New Revision: 282562

URL: http://llvm.org/viewvc/llvm-project?rev=282562&view=rev
Log:
[libFuzzer] speedup TracePC::FinalizeTrace

Modified:
    llvm/trunk/lib/Fuzzer/FuzzerTracePC.cpp
    llvm/trunk/lib/Fuzzer/FuzzerTracePC.h

Modified: llvm/trunk/lib/Fuzzer/FuzzerTracePC.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Fuzzer/FuzzerTracePC.cpp?rev=282562&r1=282561&r2=282562&view=diff
==============================================================================
--- llvm/trunk/lib/Fuzzer/FuzzerTracePC.cpp (original)
+++ llvm/trunk/lib/Fuzzer/FuzzerTracePC.cpp Tue Sep 27 20:16:24 2016
@@ -70,20 +70,27 @@ void TracePC::ResetGuards() {
 
 void TracePC::FinalizeTrace() {
   if (TotalPCCoverage) {
-    for (size_t Idx = 1, N = Min(kNumCounters, NumGuards + 1); Idx < N;
-         Idx++) {
-      uint8_t Counter = Counters[Idx];
-      if (!Counter) continue;
-      Counters[Idx] = 0;
-      unsigned Bit = 0;
-      /**/ if (Counter >= 128) Bit = 7;
-      else if (Counter >= 32) Bit = 6;
-      else if (Counter >= 16) Bit = 5;
-      else if (Counter >= 8) Bit = 4;
-      else if (Counter >= 4) Bit = 3;
-      else if (Counter >= 3) Bit = 2;
-      else if (Counter >= 2) Bit = 1;
-      CounterMap.AddValue(Idx * 8 + Bit);
+    const size_t Step = 8;
+    assert(reinterpret_cast<uintptr_t>(Counters) % Step == 0);
+    size_t N = Min(kNumCounters, NumGuards + 1);
+    N = (N + Step - 1) & ~(Step - 1);  // Round up.
+    for (size_t Idx = 0; Idx < N; Idx += Step) {
+      uint64_t Bundle = *reinterpret_cast<uint64_t*>(&Counters[Idx]);
+      if (!Bundle) continue;
+      for (size_t i = Idx; i < Idx + Step; i++) {
+        uint8_t Counter = (Bundle >> (i * 8)) & 0xff;
+        if (!Counter) continue;
+        Counters[i] = 0;
+        unsigned Bit = 0;
+        /**/ if (Counter >= 128) Bit = 7;
+        else if (Counter >= 32) Bit = 6;
+        else if (Counter >= 16) Bit = 5;
+        else if (Counter >= 8) Bit = 4;
+        else if (Counter >= 4) Bit = 3;
+        else if (Counter >= 3) Bit = 2;
+        else if (Counter >= 2) Bit = 1;
+        CounterMap.AddValue(i * 8 + Bit);
+      }
     }
   }
 }

Modified: llvm/trunk/lib/Fuzzer/FuzzerTracePC.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Fuzzer/FuzzerTracePC.h?rev=282562&r1=282561&r2=282562&view=diff
==============================================================================
--- llvm/trunk/lib/Fuzzer/FuzzerTracePC.h (original)
+++ llvm/trunk/lib/Fuzzer/FuzzerTracePC.h Tue Sep 27 20:16:24 2016
@@ -79,7 +79,7 @@ private:
   size_t NumGuards = 0;
 
   static const size_t kNumCounters = 1 << 14;
-  uint8_t Counters[kNumCounters];
+  alignas(8) uint8_t Counters[kNumCounters];
 
   static const size_t kNumPCs = 1 << 20;
   uintptr_t PCs[kNumPCs];