[BPI] Ignore remainder while distributing the remaining probability from unreachanble

This is a follow up patch for https://reviews.llvm.org/rL300440
to address a comment.

To make implementation to be consistent with other cases we just
ignore the remainder after distribution of remaining probability between
reachable edges.

If we reduced the probability of some edges coming to unreachable
blocks we should distribute the remaining part across other edges
coming to reachable blocks to satisfy the condition that sum of all
probabilities should be equal to one. If this remaining part is not
divided by number of "reachable" edges then we get this remainder.
This remainder probability should be pretty small. Other cases just ignore
if the sum of probabilities is not equal to one so we do the same.

Reviewers: chandlerc, sanjoy, vsk, junbuml, reames
Reviewed By: reames
Subscribers: reames, llvm-commits
Differential Revision: https://reviews.llvm.org/D32124

llvm-svn: 302883

1 files changed, 3 insertions, 8 deletions

diff --git a/llvm/lib/Analysis/BranchProbabilityInfo.cpp b/llvm/lib/Analysis/BranchProbabilityInfo.cpp
index 0dc4475ca0e..db87b17c156 100644
--- a/llvm/lib/Analysis/BranchProbabilityInfo.cpp
+++ b/llvm/lib/Analysis/BranchProbabilityInfo.cpp
@@ -301,6 +301,8 @@ bool BranchProbabilityInfo::calcMetadataWeights(const BasicBlock *BB) {
       WeightSum += Weights[i];
     }
   }
+  assert(WeightSum <= UINT32_MAX &&
+         "Expected weights to scale down to 32 bits");
 
   if (WeightSum == 0 || ReachableIdxs.size() == 0) {
     for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
@@ -328,21 +330,14 @@ bool BranchProbabilityInfo::calcMetadataWeights(const BasicBlock *BB) {
     // the difference between reachable blocks.
     if (ToDistribute > BranchProbability::getZero()) {
       BranchProbability PerEdge = ToDistribute / ReachableIdxs.size();
-      for (auto i : ReachableIdxs) {
+      for (auto i : ReachableIdxs)
         BP[i] += PerEdge;
-        ToDistribute -= PerEdge;
-      }
-      // Tail goes to the first reachable edge.
-      BP[ReachableIdxs[0]] += ToDistribute;
     }
   }
 
   for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
     setEdgeProbability(BB, i, BP[i]);
 
-  assert(WeightSum <= UINT32_MAX &&
-         "Expected weights to scale down to 32 bits");
-
   return true;
 }