[CSSPGO][Preinliner] Set default value of sample-profile-inline-limit-max to 50000.

[hoy]

Summary

The previous threshold 3000 is too small to enable any inlining for giant functions which come in with bigger size than that. In real world, I've seen a big hot function with 34000 dissasembly size. Motivated by that I'm changing the value to 50000.

With the new value the allowance size growth should still be reasonable, as it is also bounded by another threshold, i.e, --sample-profile-inline-growth-limit , which defaults to 12. The new value should mostly only affect giant functions.

I've seen for serveral internal services, the new threshold boosts performance, and it has neutral impact for other services without hot giant functions. So far I haven't seen any performance regression with that.

[wenlei]

lgtm, thanks.

llvm/tools/llvm-profgen/CSPreInliner.cpp

: UseContextCost(UseContextCostForPreInliner),
       ContextTracker(Tracker), Binary(Binary), Summary(Summary) {
   // Set default preinliner hot/cold call site threshold tuned with CSSPGO.
   // for good performance with reasonable profile size.
   if (!SampleHotCallSiteThreshold.getNumOccurrences())
     SampleHotCallSiteThreshold = 1500;
   if (!SampleColdCallSiteThreshold.getNumOccurrences())
     SampleColdCallSiteThreshold = 0;
   if (!ProfileInlineLimitMax.getNumOccurrences())
-    ProfileInlineLimitMax = 3000;
+    ProfileInlineLimitMax = 50000;
 }
 
 std::vector<StringRef> CSPreInliner::buildTopDownOrder() {
   std::vector<StringRef> Order;
   ProfiledCallGraph ProfiledCG(ContextTracker);
 
   // Now that we have a profiled call graph, construct top-down order
   // by building up SCC and reversing SCC order.