[LoopInfo] Use early return in branch weight update functions. NFC.

static void updateBranchWeights(BasicBlock *Header, BranchInst *LatchBR,

                                unsigned IterNumber, unsigned AvgIters,

                                uint64_t &PeeledHeaderWeight) {

  if (!PeeledHeaderWeight)

    return;

  // FIXME: Pick a more realistic distribution.

  // Currently the proportion of weight we assign to the fall-through

  // side of the branch drops linearly with the iteration number, and we use

  // a 0.9 fudge factor to make the drop-off less sharp...

  if (PeeledHeaderWeight) {

  uint64_t FallThruWeight =

      PeeledHeaderWeight * ((float)(AvgIters - IterNumber) / AvgIters * 0.9);

  uint64_t ExitWeight = PeeledHeaderWeight - FallThruWeight;

                : MDB.createBranchWeights(FallThruWeight, ExitWeight);

  LatchBR->setMetadata(LLVMContext::MD_prof, WeightNode);

}

}

/// Initialize the weights.

///

static void fixupBranchWeights(BasicBlock *Header, BranchInst *LatchBR,

                               uint64_t ExitWeight, uint64_t CurHeaderWeight) {

  // Adjust the branch weights on the loop exit.

  if (ExitWeight) {

  if (!ExitWeight)

    return;

  // The backedge count is the difference of current header weight and

  // current loop exit weight. If the current header weight is smaller than

  // the current loop exit weight, we mark the loop backedge weight as 1.

                : MDB.createBranchWeights(BackEdgeWeight, ExitWeight);

  LatchBR->setMetadata(LLVMContext::MD_prof, WeightNode);

}

}

/// Clones the body of the loop L, putting it between \p InsertTop and \p

/// InsertBot.