Update the branch weight metadata in JumpThreading pass.

In JumpThreading pass, the branch weight metadata is not updated after CFG modification. Consider the jump threading on PredBB, BB, and SuccBB. After jump threading, the weight on BB->SuccBB should be adjusted as some of it is contributed by the edge PredBB->BB, which doesn't exist anymore. This patch tries to update the edge weight in metadata on BB->SuccBB by scaling it by 1 - Freq(PredBB->BB) / Freq(BB->SuccBB). 

Differential revision: http://reviews.llvm.org/D10979

llvm-svn: 250089

2 files changed, 13 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/BlockFrequencyInfo.cpp b/llvm/lib/Analysis/BlockFrequencyInfo.cpp
index ac4ee8f11e0..90b7a339a0f 100644
--- a/llvm/lib/Analysis/BlockFrequencyInfo.cpp
+++ b/llvm/lib/Analysis/BlockFrequencyInfo.cpp
@@ -129,6 +129,12 @@ BlockFrequency BlockFrequencyInfo::getBlockFreq(const BasicBlock *BB) const {
   return BFI ? BFI->getBlockFreq(BB) : 0;
 }
 
+void BlockFrequencyInfo::setBlockFreq(const BasicBlock *BB,
+                                      uint64_t Freq) {
+  assert(BFI && "Expected analysis to be available");
+  BFI->setBlockFreq(BB, Freq);
+}
+
 /// Pop up a ghostview window with the current block frequency propagation
 /// rendered using dot.
 void BlockFrequencyInfo::view() const {
diff --git a/llvm/lib/Analysis/BlockFrequencyInfoImpl.cpp b/llvm/lib/Analysis/BlockFrequencyInfoImpl.cpp
index 903a263a65f..48e23af2690 100644
--- a/llvm/lib/Analysis/BlockFrequencyInfoImpl.cpp
+++ b/llvm/lib/Analysis/BlockFrequencyInfoImpl.cpp
@@ -530,6 +530,13 @@ BlockFrequencyInfoImplBase::getFloatingBlockFreq(const BlockNode &Node) const {
   return Freqs[Node.Index].Scaled;
 }
 
+void BlockFrequencyInfoImplBase::setBlockFreq(const BlockNode &Node,
+                                              uint64_t Freq) {
+  assert(Node.isValid() && "Expected valid node");
+  assert(Node.Index < Freqs.size() && "Expected legal index");
+  Freqs[Node.Index].Integer = Freq;
+}
+
 std::string
 BlockFrequencyInfoImplBase::getBlockName(const BlockNode &Node) const {
   return std::string();