[LoopSimplify] Use BB::instructionsWithoutDebug to skip DbgInfo (NFC).

[fhahn]

Summary

This patch updates some code responsible the skip debug info to use
BasicBlock::instructionsWithoutDebug. I think this makes things slightly
simpler and more direct.

[aprantl]

thanks!

llvm/trunk/lib/Transforms/Utils/LoopSimplify.cpp

for (unsigned i = 0, e = ExitingBlocks.size(); i != e; ++i) {
       if (!BI || !BI->isConditional()) continue;
       CmpInst *CI = dyn_cast<CmpInst>(BI->getCondition());
       if (!CI || CI->getParent() != ExitingBlock) continue;
 
       // Attempt to hoist out all instructions except for the
       // comparison and the branch.
       bool AllInvariant = true;
       bool AnyInvariant = false;
-      for (BasicBlock::iterator I = ExitingBlock->begin(); &*I != BI; ) {
+      for (auto I = ExitingBlock->instructionsWithoutDebug().begin(); &*I != BI; ) {
         Instruction *Inst = &*I++;
-        // Skip debug info intrinsics.
-        if (isa<DbgInfoIntrinsic>(Inst))
-          continue;
         if (Inst == CI)
           continue;
         if (!L->makeLoopInvariant(Inst, AnyInvariant,
                                   Preheader ? Preheader->getTerminator()
                                             : nullptr)) {
           AllInvariant = false;
           break;
         }