Reapply [InlineCost] Enable the cost benefit analysis on FDO

This patch enables the cost-benefit-analysis-based inliner by default
if we have instrumentation profile.

- SPEC CPU 2017 shows a 0.4% improvement.

- An internal large benchmark shows a 0.9% reduction in the cycle
  count along with 14.6% reduction in the number of call instructions
  executed.

Differential Revision: https://reviews.llvm.org/D98213

llvm/lib/Analysis/InlineCost.cpp

@@ -675,15 +675,22 @@ class InlineCostCallAnalyzer final : public CallAnalyzer {
   }
 
   bool isCostBenefitAnalysisEnabled() {
-    if (!InlineEnableCostBenefitAnalysis)
-      return false;
-
     if (!PSI || !PSI->hasProfileSummary())
       return false;
 
     if (!GetBFI)
       return false;
 
+    if (InlineEnableCostBenefitAnalysis.getNumOccurrences()) {
+      // Honor the explicit request from the user.
+      if (!InlineEnableCostBenefitAnalysis)
+        return false;
+    } else {
+      // Otherwise, require instrumentation profile.
+      if (!PSI->hasInstrumentationProfile())
+        return false;
+    }
+
     auto *Caller = CandidateCall.getParent()->getParent();
     if (!Caller->getEntryCount())
       return false;