Adjust the hotness threshold from 99.9% to 99%.

Summary: We originally set the hotness threshold as 99.9% to be consistent with gcc FDO. But because the inline heuristic is different between 2 compilers: llvm uses bottom-up algorithm while gcc uses priority based. The LLVM algorithm tends to inline too much early that prevents hot callsites from further inlined into its caller. Due to this restriction, we think it is reasonable to lower the hotness threshold to give priority to those that are really hot. Our experiments show that this change would improve performance on large applications. Note that the inline heuristic has great room for further tuning. Once the inline heuristics are refined, we could adjust this threshold to allow inlining for less hot callsites.

Reviewers: davidxl, tejohnson, eraman

Reviewed By: tejohnson

Subscribers: sanjoy, llvm-commits

Differential Revision: https://reviews.llvm.org/D36317

llvm-svn: 310065

diff --git a/llvm/lib/Analysis/ProfileSummaryInfo.cpp b/llvm/lib/Analysis/ProfileSummaryInfo.cpp
index 48bd54f..4bad196 100644 (file)
--- a/llvm/lib/Analysis/ProfileSummaryInfo.cpp
+++ b/llvm/lib/Analysis/ProfileSummaryInfo.cpp
@@ -30,7 +30,7 @@ using namespace llvm;
 // considered cold).
 
 static cl::opt<int> ProfileSummaryCutoffHot(
-    "profile-summary-cutoff-hot", cl::Hidden, cl::init(999000), cl::ZeroOrMore,
+    "profile-summary-cutoff-hot", cl::Hidden, cl::init(990000), cl::ZeroOrMore,
     cl::desc("A count is hot if it exceeds the minimum count to"
              " reach this percentile of total counts."));