Irreducible loop metadata for more accurate block frequency under PGO.

Summary:
Currently the block frequency analysis is an approximation for irreducible
loops.

The new irreducible loop metadata is used to annotate the irreducible loop
headers with their header weights based on the PGO profile (currently this is
approximated to be evenly weighted) and to help improve the accuracy of the
block frequency analysis for irreducible loops.

This patch is a basic support for this.

Reviewers: davidxl

Reviewed By: davidxl

Subscribers: mehdi_amini, llvm-commits, eraman

Differential Revision: https://reviews.llvm.org/D39028

llvm-svn: 317278

1 files changed, 6 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/MachineBlockFrequencyInfo.cpp b/llvm/lib/CodeGen/MachineBlockFrequencyInfo.cpp
index 14cd91206d8..2c336e45056 100644
--- a/llvm/lib/CodeGen/MachineBlockFrequencyInfo.cpp
+++ b/llvm/lib/CodeGen/MachineBlockFrequencyInfo.cpp
@@ -234,6 +234,12 @@ MachineBlockFrequencyInfo::getProfileCountFromFreq(uint64_t Freq) const {
   return MBFI ? MBFI->getProfileCountFromFreq(*F, Freq) : None;
 }
 
+bool
+MachineBlockFrequencyInfo::isIrrLoopHeader(const MachineBasicBlock *MBB) {
+  assert(MBFI && "Expected analysis to be available");
+  return MBFI->isIrrLoopHeader(MBB);
+}
+
 const MachineFunction *MachineBlockFrequencyInfo::getFunction() const {
   return MBFI ? MBFI->getFunction() : nullptr;
 }