Fix a bug in MachineBlockPlacement that may cause assertion failure during BranchProb...

The root cause is the rounding behavior in BranchProbability construction. We may consider to use truncation instead in the future.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@254356 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/MachineBlockPlacement.cpp b/lib/CodeGen/MachineBlockPlacement.cpp
index ddddd483e8013ea9bcdfdf4ec056423005057825..fcddf346cf680cf2221e730a86f3b047425161d7 100644 (file)
--- a/lib/CodeGen/MachineBlockPlacement.cpp
+++ b/lib/CodeGen/MachineBlockPlacement.cpp
@@ -423,9 +423,13 @@ MachineBlockPlacement::selectBestSuccessor(MachineBasicBlock *BB,
 
   DEBUG(dbgs() << "Attempting merge from: " << getBlockName(BB) << "\n");
   for (MachineBasicBlock *Succ : Successors) {
-    BranchProbability SuccProb(
-        MBPI->getEdgeProbability(BB, Succ).getNumerator(),
-        AdjustedSumProb.getNumerator());
+    BranchProbability SuccProb;
+    uint32_t SuccProbN = MBPI->getEdgeProbability(BB, Succ).getNumerator();
+    uint32_t SuccProbD = AdjustedSumProb.getNumerator();
+    if (SuccProbN >= SuccProbD)
+      SuccProb = BranchProbability::getOne();
+    else
+      SuccProb = BranchProbability(SuccProbN, SuccProbD);
 
     // If we outline optional branches, look whether Succ is unavoidable, i.e.
     // dominates all terminators of the MachineFunction. If it does, other