[JumpThreading] Fix opcode bonus in getJumpThreadDuplicationCost()

[oota-llvm.git] / lib / Transforms / Scalar / JumpThreading.cpp

diff --git a/lib/Transforms/Scalar/JumpThreading.cpp b/lib/Transforms/Scalar/JumpThreading.cpp
index d30c336be2125e6bdf73167f4b26b93d3218959c..087ce8ac50d4e7d3371d367547737c6a8e24e339 100644 (file)
--- a/lib/Transforms/Scalar/JumpThreading.cpp
+++ b/lib/Transforms/Scalar/JumpThreading.cpp
@@ -286,6 +286,21 @@ static unsigned getJumpThreadDuplicationCost(const BasicBlock *BB,
   // FIXME: THREADING will delete values that are just used to compute the
   // branch, so they shouldn't count against the duplication cost.
 
+  unsigned Bonus = 0;
+  const TerminatorInst *BBTerm = BB->getTerminator();
+  // Threading through a switch statement is particularly profitable.  If this
+  // block ends in a switch, decrease its cost to make it more likely to happen.
+  if (isa<SwitchInst>(BBTerm))
+    Bonus = 6;
+
+  // The same holds for indirect branches, but slightly more so.
+  if (isa<IndirectBrInst>(BBTerm))
+    Bonus = 8;
+
+  // Bump the threshold up so the early exit from the loop doesn't skip the
+  // terminator-based Size adjustment at the end.
+  Threshold += Bonus;
+
   // Sum up the cost of each instruction until we get to the terminator.  Don't
   // include the terminator because the copy won't include it.
   unsigned Size = 0;
@@ -326,16 +341,7 @@ static unsigned getJumpThreadDuplicationCost(const BasicBlock *BB,
     }
   }
 
-  // Threading through a switch statement is particularly profitable.  If this
-  // block ends in a switch, decrease its cost to make it more likely to happen.
-  if (isa<SwitchInst>(I))
-    Size = Size > 6 ? Size-6 : 0;
-
-  // The same holds for indirect branches, but slightly more so.
-  if (isa<IndirectBrInst>(I))
-    Size = Size > 8 ? Size-8 : 0;
-
-  return Size;
+  return Size > Bonus ? Size - Bonus : 0;
 }
 
 /// FindLoopHeaders - We do not want jump threading to turn proper loop
@@ -1647,14 +1653,19 @@ void JumpThreading::UpdateBlockFreqAndEdgeWeight(BasicBlock *PredBB,
 
   uint64_t MaxBBSuccFreq =
       *std::max_element(BBSuccFreq.begin(), BBSuccFreq.end());
-  SmallVector<BranchProbability, 4> BBSuccProbs;
-  for (uint64_t Freq : BBSuccFreq)
-    BBSuccProbs.push_back(
-        BranchProbability::getBranchProbability(Freq, MaxBBSuccFreq));
 
-  // Normalize edge probabilities so that they sum up to one.
-  BranchProbability::normalizeProbabilities(BBSuccProbs.begin(),
-                                            BBSuccProbs.end());
+  SmallVector<BranchProbability, 4> BBSuccProbs;
+  if (MaxBBSuccFreq == 0)
+    BBSuccProbs.assign(BBSuccFreq.size(),
+                       {1, static_cast<unsigned>(BBSuccFreq.size())});
+  else {
+    for (uint64_t Freq : BBSuccFreq)
+      BBSuccProbs.push_back(
+          BranchProbability::getBranchProbability(Freq, MaxBBSuccFreq));
+    // Normalize edge probabilities so that they sum up to one.
+    BranchProbability::normalizeProbabilities(BBSuccProbs.begin(),
+                                              BBSuccProbs.end());
+  }
 
   // Update edge probabilities in BPI.
   for (int I = 0, E = BBSuccProbs.size(); I < E; I++)