Fix PR25838.

This is a quick fix to PR25838. The issue comes from the restriction that we
cannot normalize probabilities containing both known and unknown ones. A patch
that removes this restriction is under the review now:

http://reviews.llvm.org/D15548

llvm-svn: 255867

llvm/lib/CodeGen/IfConversion.cpp

@@ -1662,6 +1662,12 @@ void IfConverter::MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI, bool AddEdges) {
   ToBBI.BB->splice(ToBBI.BB->end(),
                    FromBBI.BB, FromBBI.BB->begin(), FromBBI.BB->end());
 
+  // Force normalizing the successors' probabilities of ToBBI.BB to convert all
+  // unknown probabilities into known ones.
+  // FIXME: This usage is too tricky and in the future we would like to
+  // eliminate all unknown probabilities in MBB.
+  ToBBI.BB->normalizeSuccProbs();
+
   SmallVector<MachineBasicBlock *, 4> FromSuccs(FromBBI.BB->succ_begin(),
                                                 FromBBI.BB->succ_end());
   MachineBasicBlock *NBB = getNextBlock(FromBBI.BB);

llvm/test/CodeGen/ARM/pr25838.ll

@@ -0,0 +1,34 @@
+; RUN: llc < %s
+; PR25838
+
+target triple = "armv7--linux-android"
+
+%0 = type { i32, i32 }
+
+define i32 @foo(%0* readonly) {
+  br i1 undef, label %12, label %2
+
+; <label>:2
+  %3 = trunc i64 undef to i32
+  %4 = icmp eq i32 undef, 0
+  br i1 %4, label %5, label %9
+
+; <label>:5
+  %6 = icmp slt i32 %3, 0
+  %7 = sub nsw i32 0, %3
+  %8 = select i1 %6, i32 %7, i32 %3
+  br label %12
+
+; <label>:9
+  br i1 undef, label %12, label %10
+
+; <label>:10
+  %11 = tail call i32 @bar(i32 undef)
+  unreachable
+
+; <label>:12
+  %13 = phi i32 [ %8, %5 ], [ 0, %1 ], [ undef, %9 ]
+  ret i32 %13
+}
+
+declare i32 @bar(i32)