diff --git a/llvm/include/llvm/CodeGen/MachineBlockFrequencyInfo.h b/llvm/include/llvm/CodeGen/MachineBlockFrequencyInfo.h
--- a/llvm/include/llvm/CodeGen/MachineBlockFrequencyInfo.h
+++ b/llvm/include/llvm/CodeGen/MachineBlockFrequencyInfo.h
@@ -74,7 +74,11 @@
 
   bool isIrrLoopHeader(const MachineBasicBlock *MBB) const;
 
-  void setBlockFreq(const MachineBasicBlock *MBB, uint64_t Freq);
+  /// incrementally calculate block frequencies when we split edges, to avoid
+  /// full CFG traversal.
+  void onEdgeSplit(const MachineBasicBlock &NewPredecessor,
+                   const MachineBasicBlock &NewSuccessor,
+                   const MachineBranchProbabilityInfo &MBPI);
 
   const MachineFunction *getFunction() const;
   const MachineBranchProbabilityInfo *getMBPI() const;
diff --git a/llvm/lib/CodeGen/MachineBlockFrequencyInfo.cpp b/llvm/lib/CodeGen/MachineBlockFrequencyInfo.cpp
--- a/llvm/lib/CodeGen/MachineBlockFrequencyInfo.cpp
+++ b/llvm/lib/CodeGen/MachineBlockFrequencyInfo.cpp
@@ -247,10 +247,15 @@
   return MBFI->isIrrLoopHeader(MBB);
 }
 
-void MachineBlockFrequencyInfo::setBlockFreq(const MachineBasicBlock *MBB,
-                                             uint64_t Freq) {
+void MachineBlockFrequencyInfo::onEdgeSplit(
+    const MachineBasicBlock &NewPredecessor,
+    const MachineBasicBlock &NewSuccessor,
+    const MachineBranchProbabilityInfo &MBPI) {
   assert(MBFI && "Expected analysis to be available");
-  MBFI->setBlockFreq(MBB, Freq);
+  auto NewSuccFreq = MBFI->getBlockFreq(&NewPredecessor) *
+                     MBPI.getEdgeProbability(&NewPredecessor, &NewSuccessor);
+
+  MBFI->setBlockFreq(&NewSuccessor, NewSuccFreq.getFrequency());
 }
 
 const MachineFunction *MachineBlockFrequencyInfo::getFunction() const {
diff --git a/llvm/lib/CodeGen/MachineSink.cpp b/llvm/lib/CodeGen/MachineSink.cpp
--- a/llvm/lib/CodeGen/MachineSink.cpp
+++ b/llvm/lib/CodeGen/MachineSink.cpp
@@ -347,11 +347,9 @@
                           << printMBBReference(*Pair.first) << " -- "
                           << printMBBReference(*NewSucc) << " -- "
                           << printMBBReference(*Pair.second) << '\n');
-        if (MBFI) {
-          auto NewSuccFreq = MBFI->getBlockFreq(Pair.first) *
-                             MBPI->getEdgeProbability(Pair.first, NewSucc);
-          MBFI->setBlockFreq(NewSucc, NewSuccFreq.getFrequency());
-        }
+        if (MBFI)
+          MBFI->onEdgeSplit(*Pair.first, *NewSucc, *MBPI);
+
         MadeChange = true;
         ++NumSplit;
       } else