[polly] scop detection: could we stop iterating over uses?

[Sebastian Pop]

Hi,

I see that we call hasScalarDependency over every instruction in a region, and
that iterates over all the uses of the instruction.  Here is the code of that
function, with a nice "dirty hack" comment in it:

bool ScopDetection::hasScalarDependency(Instruction &Inst,
                                        Region &RefRegion) const {
  for (Instruction::use_iterator UI = Inst.use_begin(), UE = Inst.use_end();
       UI != UE; ++UI)
    if (Instruction *Use = dyn_cast<Instruction>(*UI))
      if (!RefRegion.contains(Use->getParent())) {
        // DirtyHack 1: PHINode user outside the Scop is not allow, if this
        // PHINode is induction variable, the scalar to array transform may
        // break it and introduce a non-indvar PHINode, which is not allow in
        // Scop.
        // This can be fix by:
        // Introduce a IndependentBlockPrepare pass, which translate all
        // PHINodes not in Scop to array.
        // The IndependentBlockPrepare pass can also split the entry block of
        // the function to hold the alloca instruction created by scalar to
        // array.  and split the exit block of the Scop so the new create load
        // instruction for escape users will not break other Scops.
        if (isa<PHINode>(Use))
          return true;
      }

  return false;
}

My question is how do we remove all this code: it is very expensive!

Thanks,
Sebastian
-- 
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
hosted by The Linux Foundation