From: Cong Hou <congh@google.com>
Date: Tue, 1 Dec 2015 00:55:42 +0000 (+0000)
Subject: Fix a bug in MachineBlockPlacement that may cause assertion failure during BranchProb... 
X-Git-Url: http://plrg.eecs.uci.edu/git/?p=oota-llvm.git;a=commitdiff_plain;h=08802fa03338ebbe7f759586ef039d53f0d53194

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

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 ddddd483e80..fcddf346cf6 100644
--- 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