[Statistics] Use Statistic::operator+= instead of adding and assigning separately.

I believe this technically fixes a multithreaded race condition in this code. But my primary concern was as part of looking at removing the ability to treat Statistics like a plain unsigned. There are many weird operations on Statistics in the codebase.

llvm-svn: 303314
diff --git a/llvm/lib/Transforms/Scalar/EarlyCSE.cpp b/llvm/lib/Transforms/Scalar/EarlyCSE.cpp
index d8f8a58..c4f4509 100644
--- a/llvm/lib/Transforms/Scalar/EarlyCSE.cpp
+++ b/llvm/lib/Transforms/Scalar/EarlyCSE.cpp
@@ -606,7 +606,7 @@
         if (unsigned Count = replaceDominatedUsesWith(
                 CondInst, TorF, DT, BasicBlockEdge(Pred, BB))) {
           Changed = true;
-          NumCSECVP = NumCSECVP + Count;
+          NumCSECVP += Count;
         }
       }
     }
diff --git a/llvm/lib/Transforms/Scalar/LoadCombine.cpp b/llvm/lib/Transforms/Scalar/LoadCombine.cpp
index 02215d3..494cbc6 100644
--- a/llvm/lib/Transforms/Scalar/LoadCombine.cpp
+++ b/llvm/lib/Transforms/Scalar/LoadCombine.cpp
@@ -228,7 +228,7 @@
     L.Load->replaceAllUsesWith(V);
   }
 
-  NumLoadsCombined = NumLoadsCombined + Loads.size();
+  NumLoadsCombined += Loads.size();
   return true;
 }