TSAN caught us racing in ScalarBench.cpp

bench/ScalarBench.cpp

 
 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 #include "SkBenchmark.h"
 #include "SkFloatBits.h"
 #include "SkRandom.h"
@@ skipping 23 matching lines @@
     virtual void onDraw(const int loops, SkCanvas* canvas) {
         for (int i = 0; i < loops; i++) {
             this->performTest();
         }
     }
 
 private:
     typedef SkBenchmark INHERITED;
 };
 
-// we want to stop the compiler from eliminating code that it thinks is a no-op
-// so we have a non-static global we increment, hoping that will convince the
-// compiler to execute everything
-int gScalarBench_NonStaticGlobal;
-
-#define always_do(pred)                     \
-    do {                                    \
-        if (pred) {                         \
-            ++gScalarBench_NonStaticGlobal; \
-        }                                   \
-    } while (0)
-
 // having unknown values in our arrays can throw off the timing a lot, perhaps
 // handling NaN values is a lot slower. Anyway, this guy is just meant to put
 // reasonable values in our arrays.
 template <typename T> void init9(T array[9]) {
     SkRandom rand;
     for (int i = 0; i < 9; i++) {
         array[i] = rand.nextSScalar1();
     }
 }
 
 class FloatComparisonBench : public ScalarBench {
 public:
     FloatComparisonBench() : INHERITED("compare_float") {
         init9(fArray);
     }
 protected:
     virtual int mulLoopCount() const { return 4; }
     virtual void performTest() {
-        always_do(fArray[6] != 0.0f || fArray[7] != 0.0f || fArray[8] != 1.0f);
-        always_do(fArray[2] != 0.0f || fArray[5] != 0.0f);
+        // xoring into a volatile prevents the compiler from optimizing these checks away.
+        volatile bool junk = false;
+        junk ^= (fArray[6] != 0.0f || fArray[7] != 0.0f || fArray[8] != 1.0f);
+        junk ^= (fArray[2] != 0.0f || fArray[5] != 0.0f);
     }
 private:
     float fArray[9];
     typedef ScalarBench INHERITED;
 };
 
 class ForcedIntComparisonBench : public ScalarBench {
 public:
     ForcedIntComparisonBench()
     : INHERITED("compare_forced_int") {
         init9(fArray);
     }
 protected:
     virtual int mulLoopCount() const { return 4; }
     virtual void performTest() {
-        always_do(SkScalarAs2sCompliment(fArray[6]) |
-                  SkScalarAs2sCompliment(fArray[7]) |
-                  (SkScalarAs2sCompliment(fArray[8]) - kPersp1Int));
-        always_do(SkScalarAs2sCompliment(fArray[2]) |
-                  SkScalarAs2sCompliment(fArray[5]));
+        // xoring into a volatile prevents the compiler from optimizing these checks away.
+        volatile int32_t junk = 0;
+        junk ^= (SkScalarAs2sCompliment(fArray[6]) |
+                 SkScalarAs2sCompliment(fArray[7]) |
+                (SkScalarAs2sCompliment(fArray[8]) - kPersp1Int));
+        junk ^= (SkScalarAs2sCompliment(fArray[2]) |
+                 SkScalarAs2sCompliment(fArray[5]));
     }
 private:
     static const int32_t kPersp1Int = 0x3f800000;
     SkScalar fArray[9];
     typedef ScalarBench INHERITED;
 };
 
 class IsFiniteScalarBench : public ScalarBench {
 public:
     IsFiniteScalarBench() : INHERITED("isfinite") {
@@ skipping 61 matching lines @@
 private:
     typedef SkBenchmark INHERITED;
 };
 
 ///////////////////////////////////////////////////////////////////////////////
 
 DEF_BENCH( return new FloatComparisonBench(); )
 DEF_BENCH( return new ForcedIntComparisonBench(); )
 DEF_BENCH( return new RectBoundsBench(); )
 DEF_BENCH( return new IsFiniteScalarBench(); )