Changing the default MaxNumPromotions from 2 to 3.

[danielcdh]

Summary

In performance tuning, we see performance benefits when enlarge the maximum num promotion targets to 3. This is safe as soon as we have total percentage threshold properly setup (https://reviews.llvm.org/D35962)

[tejohnson]

LGTM

lib/Analysis/IndirectCallPromotionAnalysis.cpp

 static cl::opt<unsigned>
     ICPPercentThreshold("icp-percent-threshold", cl::init(30), cl::Hidden,
                         cl::ZeroOrMore,
                         cl::desc("The percentage threshold for the promotion"));
 
 // Set the maximum number of targets to promote for a single indirect-call
 // callsite.
 static cl::opt<unsigned>
-    MaxNumPromotions("icp-max-prom", cl::init(2), cl::Hidden, cl::ZeroOrMore,
+    MaxNumPromotions("icp-max-prom", cl::init(3), cl::Hidden, cl::ZeroOrMore,
                      cl::desc("Max number of promotions for a single indirect "
                               "call callsite"));
 
 ICallPromotionAnalysis::ICallPromotionAnalysis() {
   ValueDataArray = llvm::make_unique<InstrProfValueData[]>(MaxNumPromotions);
 }
 
 bool ICallPromotionAnalysis::isPromotionProfitable(uint64_t Count,