// LLVM loop pass that adds required barriers to loops.
//
// Copyright (c) 2011 Universidad Rey Juan Carlos
//               2012-2019 Pekka Jääskeläinen
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.

#include <iostream>

#include "CompilerWarnings.h"
IGNORE_COMPILER_WARNING("-Wunused-parameter")

#include "pocl.h"

#include "llvm/IR/Constants.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/Dominators.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"

#include "LoopBarriers.h"
#include "Barrier.h"
#include "Workgroup.h"

POP_COMPILER_DIAGS

//#define DEBUG_LOOP_BARRIERS

using namespace llvm;
using namespace pocl;

namespace {
  static
  RegisterPass<LoopBarriers> X("loop-barriers",
                               "Add needed barriers to loops");
}

char LoopBarriers::ID = 0;

void
LoopBarriers::getAnalysisUsage(AnalysisUsage &AU) const {
  AU.addRequired<DominatorTreeWrapperPass>();
}

bool
LoopBarriers::runOnLoop(Loop *L, LPPassManager &LPM) {
  if (!Workgroup::isKernelToProcess(*L->getHeader()->getParent()))
    return false;

  if (!Workgroup::hasWorkgroupBarriers(*L->getHeader()->getParent()))
    return false;

  return ProcessLoop(L, LPM);;
}

bool
LoopBarriers::ProcessLoop(Loop *L, LPPassManager &) {
  bool isBLoop = false;
  bool changed = false;

  DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();

  for (Loop::block_iterator i = L->block_begin(), e = L->block_end();
       i != e && !isBLoop; ++i) {
    for (BasicBlock::iterator j = (*i)->begin(), e = (*i)->end();
         j != e; ++j) {
      if (isa<Barrier>(j)) {
          isBLoop = true;
          break;
      }
    }
  }

  for (Loop::block_iterator i = L->block_begin(), e = L->block_end();
       i != e && isBLoop; ++i) {
    for (BasicBlock::iterator j = (*i)->begin(), e = (*i)->end();
         j != e; ++j) {
      if (isa<Barrier>(j)) {

        // Found a barrier in this loop:
        // 1) add a barrier in the loop header.
        // 2) add a barrier in the latches

        // Add a barrier on the preheader to ensure all WIs reach
        // the loop header with all the previous code already
        // executed.
        BasicBlock *preheader = L->getLoopPreheader();
        assert((preheader != NULL) && "Non-canonicalized loop found!\n");
#ifdef DEBUG_LOOP_BARRIERS
        std::cerr << "### adding to preheader BB" << std::endl;
        preheader->dump();
        std::cerr << "### before instr" << std::endl;
        preheader->getTerminator()->dump();
#endif
        Barrier::Create(preheader->getTerminator());
        preheader->setName(preheader->getName() + ".loopbarrier");

        // Add a barrier after the PHI nodes on the header (the replicated
        // headers will be merged afterwards).
        BasicBlock *header = L->getHeader();
        if (header->getFirstNonPHI() != &header->front()) {
          Barrier::Create(header->getFirstNonPHI());
          header->setName(header->getName() + ".phibarrier");
          // Split the block to  create a replicable region of
          // the loop contents in case the phi node contains a
          // branch (that can be to inside the region).
          //          if (header->getTerminator()->getNumSuccessors() > 1)
          //    SplitBlock(header, header->getTerminator(), this);
        }

        // Add the barriers on the exiting block and the latches,
        // which might not always be the same if there is computation
        // after the exit decision.
        BasicBlock *brexit = L->getExitingBlock();
        if (brexit != NULL) {
          Barrier::Create(brexit->getTerminator());
          brexit->setName(brexit->getName() + ".brexitbarrier");
        }

        BasicBlock *latch = L->getLoopLatch();
        if (latch != NULL && brexit != latch) {
          // This loop has only one latch. Do not check for dominance, we
          // are probably running before BTR.
          Barrier::Create(latch->getTerminator());
          latch->setName(latch->getName() + ".latchbarrier");
          return changed;
        }

        // Modified code from llvm::LoopBase::getLoopLatch to
        // go trough all the latches.
        BasicBlock *Header = L->getHeader();
        typedef GraphTraits<Inverse<BasicBlock *> > InvBlockTraits;
        InvBlockTraits::ChildIteratorType PI =
          InvBlockTraits::child_begin(Header);
        InvBlockTraits::ChildIteratorType PE =
          InvBlockTraits::child_end(Header);

        BasicBlock *Latch = NULL;
        for (; PI != PE; ++PI) {
          BasicBlock *N = *PI;
          if (L->contains(N)) {
            Latch = N;
            // Latch found in the loop, see if the barrier dominates it
            // (otherwise if might no even belong to this "tail", see
            // forifbarrier1 graph test).
            if (DT->dominates(j->getParent(), Latch)) {
              Barrier::Create(Latch->getTerminator());
              Latch->setName(Latch->getName() + ".latchbarrier");
            }
          }
        }
        return true;
      }
    }
  }

  /* This is a loop without a barrier. Ensure we have a non-barrier
     block as a preheader so we can replicate the loop as a whole.

     If the block has proper instructions after the barrier, it
     will be split in CanonicalizeBarriers. */
  BasicBlock *preheader = L->getLoopPreheader();
  assert((preheader != NULL) && "Non-canonicalized loop found!\n");

  Instruction *t = preheader->getTerminator();
  Instruction *prev = NULL;
  if (&preheader->front() != t)
    prev = t->getPrevNode();
  if (prev && isa<Barrier>(prev)) {
#ifdef LLVM_OLDER_THAN_3_7
      BasicBlock *new_b = SplitBlock(preheader, t, this);
#else
      BasicBlock *new_b = SplitBlock(preheader, t);
#endif
      new_b->setName(preheader->getName() + ".postbarrier_dummy");
      return true;
  }

  return changed;
}
