TailDuplicator: Remove no-op analyzeBranch call

[arsenm]

Summary

This could fail, which looked concerning. However nothing was actually
using the results of this. I assume this was intended to use the
anti-feature of analyzeBranch of removing instructions, but wasn't
actually calling it with AllowModify = true.

Fixes bug 42162.

[sanjoy]

lgtm

[arsenm]

r362800

lib/CodeGen/TailDuplicator.cpp

for (MachineBasicBlock::iterator I = TailBB->begin(), E = TailBB->end();
       } else {
         // Replace def of virtual registers with new registers, and update
         // uses with PHI source register or the new registers.
         duplicateInstruction(MI, TailBB, PredBB, LocalVRMap, UsedByPhi);
       }
     }
     appendCopies(PredBB, CopyInfos, Copies);
 
-    // Simplify
-    MachineBasicBlock *PredTBB = nullptr, *PredFBB = nullptr;
-    SmallVector<MachineOperand, 4> PredCond;
-    TII->analyzeBranch(*PredBB, PredTBB, PredFBB, PredCond);
-
     NumTailDupAdded += TailBB->size() - 1; // subtract one for removed branch
 
     // Update the CFG.
     PredBB->removeSuccessor(PredBB->succ_begin());
     assert(PredBB->succ_empty() &&
            "TailDuplicate called on block with multiple successors!");
     for (MachineBasicBlock *Succ : TailBB->successors())
       PredBB->addSuccessor(Succ, MBPI->getEdgeProbability(TailBB, Succ));