[CodeGen] avoid broken successor probability in MBB dump

[inouehrs]

Summary

When printing successor probabilities for a MBB, a human readble value is somethimes shown as 200%.
The human readble output is based on getProbabilityIterator, which returns 0xFFFFFFFF for getNumerator() and 0x80000000 for getDenominator() for unknown BranchProbability.
By using getSuccProbability as we do for the non-human readable part, we can avoid this problem.

Example of broken probability

bb.1.if.then:
; predecessors: %bb.0
  successors: %bb.3(0x80000000); %bb.3(200.00%)

[thegameg]

LGTM. It would be nice to have a test too.

lib/CodeGen/MachineBasicBlock.cpp

for (auto I = succ_begin(), E = succ_end(); I != E; ++I) {
         OS << '('
            << format("0x%08" PRIx32, getSuccProbability(I).getNumerator())
            << ')';
     }
     if (!Probs.empty() && IsStandalone) {
       // Print human readable probabilities as comments.
       OS << "; ";
       for (auto I = succ_begin(), E = succ_end(); I != E; ++I) {
-        const BranchProbability &BP = *getProbabilityIterator(I);
+        const BranchProbability &BP = getSuccProbability(I);
         if (I != succ_begin())
           OS << ", ";
         OS << printMBBReference(**I) << '('
            << format("%.2f%%",
                      rint(((double)BP.getNumerator() / BP.getDenominator()) *
                           100.0 * 100.0) /
                          100.0)
            << ')';