[BFI] Use rounding while computing profile counts.

Summary:
Profile count of a block is computed by multiplying its block frequency
by entry count and dividing the result by entry block frequency. Do
rounded division in the last step and update test cases appropriately.

Reviewers: davidxl

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D50822

llvm-svn: 339835

1 files changed, 3 insertions, 1 deletions

diff --git a/llvm/lib/Analysis/BlockFrequencyInfoImpl.cpp b/llvm/lib/Analysis/BlockFrequencyInfoImpl.cpp
index 3d095068e7f..98209888f8a 100644
--- a/llvm/lib/Analysis/BlockFrequencyInfoImpl.cpp
+++ b/llvm/lib/Analysis/BlockFrequencyInfoImpl.cpp
@@ -573,7 +573,9 @@ BlockFrequencyInfoImplBase::getProfileCountFromFreq(const Function &F,
   APInt BlockFreq(128, Freq);
   APInt EntryFreq(128, getEntryFreq());
   BlockCount *= BlockFreq;
-  BlockCount = BlockCount.udiv(EntryFreq);
+  // Rounded division of BlockCount by EntryFreq. Since EntryFreq is unsigned
+  // lshr by 1 gives EntryFreq/2.
+  BlockCount = (BlockCount + EntryFreq.lshr(1)).udiv(EntryFreq);
   return BlockCount.getLimitedValue();
 }