[BPI] Use a safer constructor to calculate branch probabilities

BPI may trigger signed overflow UB while computing branch probabilities
for cold calls or to unreachables. For example, with our current choice
of weights, we'll crash if there are >= 2^12 branches to an unreachable.

Use a safer BranchProbability constructor which is better at handling
fractions with large denominators.

rdar://problem/29368161

Differential Revision: https://reviews.llvm.org/D27862

llvm-svn: 290016

1 files changed, 12 insertions, 12 deletions

diff --git a/llvm/lib/Analysis/BranchProbabilityInfo.cpp b/llvm/lib/Analysis/BranchProbabilityInfo.cpp
index a91ac8d06fa..185e11fa266 100644
--- a/llvm/lib/Analysis/BranchProbabilityInfo.cpp
+++ b/llvm/lib/Analysis/BranchProbabilityInfo.cpp
@@ -162,12 +162,12 @@ bool BranchProbabilityInfo::calcUnreachableHeuristics(const BasicBlock *BB) {
     return true;
   }
 
-  BranchProbability UnreachableProb(UR_TAKEN_WEIGHT,
-                                    (UR_TAKEN_WEIGHT + UR_NONTAKEN_WEIGHT) *
-                                        UnreachableEdges.size());
-  BranchProbability ReachableProb(UR_NONTAKEN_WEIGHT,
-                                  (UR_TAKEN_WEIGHT + UR_NONTAKEN_WEIGHT) *
-                                      ReachableEdges.size());
+  auto UnreachableProb = BranchProbability::getBranchProbability(
+      UR_TAKEN_WEIGHT,
+      (UR_TAKEN_WEIGHT + UR_NONTAKEN_WEIGHT) * UnreachableEdges.size());
+  auto ReachableProb = BranchProbability::getBranchProbability(
+      UR_NONTAKEN_WEIGHT,
+      (UR_TAKEN_WEIGHT + UR_NONTAKEN_WEIGHT) * ReachableEdges.size());
 
   for (unsigned SuccIdx : UnreachableEdges)
     setEdgeProbability(BB, SuccIdx, UnreachableProb);
@@ -300,12 +300,12 @@ bool BranchProbabilityInfo::calcColdCallHeuristics(const BasicBlock *BB) {
     return true;
   }
 
-  BranchProbability ColdProb(CC_TAKEN_WEIGHT,
-                             (CC_TAKEN_WEIGHT + CC_NONTAKEN_WEIGHT) *
-                                 ColdEdges.size());
-  BranchProbability NormalProb(CC_NONTAKEN_WEIGHT,
-                               (CC_TAKEN_WEIGHT + CC_NONTAKEN_WEIGHT) *
-                                   NormalEdges.size());
+  auto ColdProb = BranchProbability::getBranchProbability(
+      CC_TAKEN_WEIGHT,
+      (CC_TAKEN_WEIGHT + CC_NONTAKEN_WEIGHT) * ColdEdges.size());
+  auto NormalProb = BranchProbability::getBranchProbability(
+      CC_NONTAKEN_WEIGHT,
+      (CC_TAKEN_WEIGHT + CC_NONTAKEN_WEIGHT) * NormalEdges.size());
 
   for (unsigned SuccIdx : ColdEdges)
     setEdgeProbability(BB, SuccIdx, ColdProb);