Record whether the weights on out-edges from a MBB are normalized.

1. Create a utility function normalizeEdgeWeights() in MachineBranchProbabilityInfo that normalizes a list of edge weights so that the sum of then can fit in uint32_t.
2. Provide an interface in MachineBasicBlock to normalize its successors' weights.
3. Add a flag in MachineBasicBlock that tracks whether its successors' weights are normalized.
4. Provide an overload of getSumForBlock that accepts a non-const pointer to a MBB so that it can force normalizing this MBB's successors' weights.
5. Update several uses of getSumForBlock() by eliminating the once needed weight scale.

Differential Revision: http://reviews.llvm.org/D11442

llvm-svn: 244154

1 files changed, 4 insertions, 6 deletions

diff --git a/llvm/lib/CodeGen/MachineBlockPlacement.cpp b/llvm/lib/CodeGen/MachineBlockPlacement.cpp
index b77c803f77f..ecc093e97f5 100644
--- a/llvm/lib/CodeGen/MachineBlockPlacement.cpp
+++ b/llvm/lib/CodeGen/MachineBlockPlacement.cpp
@@ -361,8 +361,7 @@ MachineBlockPlacement::selectBestSuccessor(MachineBasicBlock *BB,
   // improve the MBPI interface to efficiently support query patterns such as
   // this.
   uint32_t BestWeight = 0;
-  uint32_t WeightScale = 0;
-  uint32_t SumWeight = MBPI->getSumForBlock(BB, WeightScale);
+  uint32_t SumWeight = MBPI->getSumForBlock(BB);
   DEBUG(dbgs() << "Attempting merge from: " << getBlockName(BB) << "\n");
   for (MachineBasicBlock *Succ : BB->successors()) {
     if (BlockFilter && !BlockFilter->count(Succ))
@@ -378,7 +377,7 @@ MachineBlockPlacement::selectBestSuccessor(MachineBasicBlock *BB,
     }
 
     uint32_t SuccWeight = MBPI->getEdgeWeight(BB, Succ);
-    BranchProbability SuccProb(SuccWeight / WeightScale, SumWeight);
+    BranchProbability SuccProb(SuccWeight, SumWeight);
 
     // If we outline optional branches, look whether Succ is unavoidable, i.e.
     // dominates all terminators of the MachineFunction. If it does, other
@@ -675,8 +674,7 @@ MachineBlockPlacement::findBestLoopExit(MachineFunction &F, MachineLoop &L,
     // FIXME: Due to the performance of the probability and weight routines in
     // the MBPI analysis, we use the internal weights and manually compute the
     // probabilities to avoid quadratic behavior.
-    uint32_t WeightScale = 0;
-    uint32_t SumWeight = MBPI->getSumForBlock(MBB, WeightScale);
+    uint32_t SumWeight = MBPI->getSumForBlock(MBB);
     for (MachineBasicBlock *Succ : MBB->successors()) {
       if (Succ->isLandingPad())
         continue;
@@ -705,7 +703,7 @@ MachineBlockPlacement::findBestLoopExit(MachineFunction &F, MachineLoop &L,
           BlocksExitingToOuterLoop.insert(MBB);
       }
 
-      BranchProbability SuccProb(SuccWeight / WeightScale, SumWeight);
+      BranchProbability SuccProb(SuccWeight, SumWeight);
       BlockFrequency ExitEdgeFreq = MBFI->getBlockFreq(MBB) * SuccProb;
       DEBUG(dbgs() << "    exiting: " << getBlockName(MBB) << " -> "
                    << getBlockName(Succ) << " [L:" << SuccLoopDepth << "] (";