Revert of TSAN caught us racing in ScalarBench.cpp (https://codereview.chromium.org/305033002/)

Reason for revert:
windows doesn't like it

Original issue's description:
> TSAN caught us racing in ScalarBench.cpp
>
> http://108.170.220.102:10117/builders/Test-Ubuntu13-ShuttleA-HD2000-x86_64-Debug-TSAN/builds/914/steps/RunDM/logs/stdio
>
> BUG=skia:
>
> Committed: http://code.google.com/p/skia/source/detail?r=14992

R=reed@google.com, mtklein@chromium.org
TBR=mtklein@chromium.org, reed@google.com
NOTREECHECKS=true
NOTRY=true
BUG=skia:

Author: mtklein@google.com

Review URL: https://codereview.chromium.org/308883003

git-svn-id: http://skia.googlecode.com/svn/trunk@14994 2bbb7eff-a529-9590-31e7-b0007b416f81

1 files changed, 19 insertions, 11 deletions

diff --git a/bench/ScalarBench.cpp b/bench/ScalarBench.cpp
index a023704fcd..54ee0fcd19 100644
--- a/bench/ScalarBench.cpp
+++ b/bench/ScalarBench.cpp
@@ -41,6 +41,18 @@ 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.
@@ -59,10 +71,8 @@ public:
 protected:
     virtual int mulLoopCount() const { return 4; }
     virtual void performTest() {
-        // 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);
+        always_do(fArray[6] != 0.0f || fArray[7] != 0.0f || fArray[8] != 1.0f);
+        always_do(fArray[2] != 0.0f || fArray[5] != 0.0f);
     }
 private:
     float fArray[9];
@@ -78,13 +88,11 @@ public:
 protected:
     virtual int mulLoopCount() const { return 4; }
     virtual void performTest() {
-        // xoring into a volatile prevents the compiler from optimizing these checks away.
-        volatile bool junk = false;
-        junk ^= (SkScalarAs2sCompliment(fArray[6]) |
-                 SkScalarAs2sCompliment(fArray[7]) |
-                (SkScalarAs2sCompliment(fArray[8]) - kPersp1Int));
-        junk ^= (SkScalarAs2sCompliment(fArray[2]) |
-                 SkScalarAs2sCompliment(fArray[5]));
+        always_do(SkScalarAs2sCompliment(fArray[6]) |
+                  SkScalarAs2sCompliment(fArray[7]) |
+                  (SkScalarAs2sCompliment(fArray[8]) - kPersp1Int));
+        always_do(SkScalarAs2sCompliment(fArray[2]) |
+                  SkScalarAs2sCompliment(fArray[5]));
     }
 private:
     static const int32_t kPersp1Int = 0x3f800000;