[llvm] r275357 - [SCCP] Generalize tryToReplaceInstWithConstant to work also with arguments.

[Matthew Simpson via llvm-commits]

Hi Davide,

We're seeing large compile-time regressions with this change and LTO when
compiling spec2000/2006. For example, the compile-time of spec2000/crafty
roughly doubles. Would you mind taking a look? We're compiling with "-Ofast
-flto -fuse-ld=gold -mcpu=kryo". Please let me know if you're unable to
reproduce. Thanks!

-- Matt



On Wed, Jul 13, 2016 at 10:34 PM, Davide Italiano via llvm-commits <
llvm-commits at lists.llvm.org> wrote:

> On Wed, Jul 13, 2016 at 6:51 PM, Eli Friedman <eli.friedman at gmail.com>
> wrote:
> > On Wed, Jul 13, 2016 at 6:27 PM, Davide Italiano via llvm-commits
> > <llvm-commits at lists.llvm.org> wrote:
> >>
> >> Author: davide
> >> Date: Wed Jul 13 20:27:29 2016
> >> New Revision: 275357
> >>
> >> URL: http://llvm.org/viewvc/llvm-project?rev=275357&view=rev
> >> Log:
> >> [SCCP] Generalize tryToReplaceInstWithConstant to work also with
> >> arguments.
> >>
> >> Modified:
> >>     llvm/trunk/lib/Transforms/Scalar/SCCP.cpp
> >>
> >> Modified: llvm/trunk/lib/Transforms/Scalar/SCCP.cpp
> >> URL:
> >>
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/SCCP.cpp?rev=275357&r1=275356&r2=275357&view=diff
> >>
> >>
> ==============================================================================
> >> --- llvm/trunk/lib/Transforms/Scalar/SCCP.cpp (original)
> >> +++ llvm/trunk/lib/Transforms/Scalar/SCCP.cpp Wed Jul 13 20:27:29 2016
> >> @@ -1510,16 +1510,16 @@ bool SCCPSolver::ResolvedUndefsIn(Functi
> >>    return false;
> >>  }
> >>
> >> -static bool tryToReplaceInstWithConstant(SCCPSolver Solver, Instruction
> >> *Inst,
> >> -                                         bool shouldEraseFromParent) {
> >> +template <typename ArgOrInst>
> >> +static bool tryToReplaceWithConstant(SCCPSolver Solver, ArgOrInst *AI)
> {
> >
> >
> > Can you just use a Value* here?
> >
>
> Sure, I'll change that.
>
> >>
> >>    Constant *Const = nullptr;
> >> -  if (Inst->getType()->isStructTy()) {
> >> -    std::vector<LatticeVal> IVs =
> Solver.getStructLatticeValueFor(Inst);
> >> +  if (AI->getType()->isStructTy()) {
> >> +    std::vector<LatticeVal> IVs = Solver.getStructLatticeValueFor(AI);
> >>      if (std::any_of(IVs.begin(), IVs.end(),
> >>                      [](LatticeVal &LV) { return LV.isOverdefined(); }))
> >>        return false;
> >>      std::vector<Constant *> ConstVals;
> >> -    StructType *ST = dyn_cast<StructType>(Inst->getType());
> >> +    StructType *ST = dyn_cast<StructType>(AI->getType());
> >>      for (unsigned i = 0, e = ST->getNumElements(); i != e; ++i) {
> >>        LatticeVal V = IVs[i];
> >>        ConstVals.push_back(V.isConstant()
> >> @@ -1528,18 +1528,23 @@ static bool tryToReplaceInstWithConstant
> >>      }
> >>      Const = ConstantStruct::get(ST, ConstVals);
> >>    } else {
> >> -    LatticeVal IV = Solver.getLatticeValueFor(Inst);
> >> +    LatticeVal IV = Solver.getLatticeValueFor(AI);
> >>      if (IV.isOverdefined())
> >>        return false;
> >> -
> >> -    Const =
> >> -        IV.isConstant() ? IV.getConstant() :
> >> UndefValue::get(Inst->getType());
> >> +    Const = IV.isConstant() ? IV.getConstant() :
> >> UndefValue::get(AI->getType());
> >>    }
> >>    assert(Const && "Constant is nullptr here!");
> >> -  DEBUG(dbgs() << "  Constant: " << *Const << " = " << *Inst << '\n');
> >> +  DEBUG(dbgs() << "  Constant: " << *Const << " = " << *AI << '\n');
> >>
> >>    // Replaces all of the uses of a variable with uses of the constant.
> >> -  Inst->replaceAllUsesWith(Const);
> >> +  AI->replaceAllUsesWith(Const);
> >> +  return true;
> >> +}
> >> +
> >> +static bool tryToReplaceInstWithConstant(SCCPSolver Solver, Instruction
> >> *Inst,
> >> +                                         bool shouldEraseFromParent) {
> >> +  if (!tryToReplaceWithConstant(Solver, Inst))
> >> +    return false;
> >>
> >>    // Delete the instruction.
> >>    if (shouldEraseFromParent)
> >> @@ -1766,17 +1771,8 @@ static bool runIPSCCP(Module &M, const D
> >>          // TODO: Could use getStructLatticeValueFor to find out if the
> >> entire
> >>          // result is a constant and replace it entirely if so.
> >>
> >> -        LatticeVal IV = Solver.getLatticeValueFor(&*AI);
> >> -        if (IV.isOverdefined()) continue;
> >> -
> >> -        Constant *CST = IV.isConstant() ?
> >> -        IV.getConstant() : UndefValue::get(AI->getType());
> >> -        DEBUG(dbgs() << "***  Arg " << *AI << " = " << *CST <<"\n");
> >> -
> >> -        // Replaces all of the uses of a variable with uses of the
> >> -        // constant.
> >> -        AI->replaceAllUsesWith(CST);
> >> -        ++IPNumArgsElimed;
> >> +        if (tryToReplaceWithConstant(Solver, &*AI))
> >> +          ++IPNumArgsElimed;
> >>        }
> >>      }
> >
> >
> > Testcase?
> >
>
> Sorry if I failed to mention on this commit, but this is NFC as we
> skip the replacement phase if the argument is of struct type (unless
> I'm missing something).
> My next patch, http://reviews.llvm.org/D22329 , changes the behaviour
> and add test cases.
>
>
> Thanks for your review!
>
> --
> Davide
>
> "There are no solved problems; there are only problems that are more
> or less solved" -- Henri Poincare
> _______________________________________________
> llvm-commits mailing list
> llvm-commits at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-commits
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20160714/e5900bfc/attachment.html>