[LLVMdev] ScalarEvolution Patch

[Wojciech Matyjewicz]

Hi,

> Is the following patch to ScalarEvolution correct?  It seems that
> without it, the enclosing for loop could skip over SCEVAddRecExpr's in
> the Ops[] array.

The patch is correct, but doesn't seem to be necessary. Please note that
if a loop-invariant is found it is not only erased from the Ops[] array,
but also inserted into the LIOps[] one:

  for (; Idx < Ops.size() && isa<SCEVAddRecExpr>(Ops[Idx]); ++Idx) {
    std::vector<SCEVHandle> LIOps;
    SCEVAddRecExpr *AddRec = cast<SCEVAddRecExpr>(Ops[Idx]);
    for (unsigned i = 0, e = Ops.size(); i != e; ++i)
      if (Ops[i]->isLoopInvariant(AddRec->getLoop())) {
        LIOps.push_back(Ops[i]);
        Ops.erase(Ops.begin()+i);
        --i; --e;
      }

and just after this code there is an dead-end 'if':

    if (!LIOps.empty()) {
      [...]
      return getAddExpr(Ops);
    }
   [...]
  }

that will never allow the outer 'for' loop to continue, if some loop
invariant was found.

But I admit it's a little bit obscure.

Wojtek