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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
 * vim: set ts=8 sts=2 et sw=2 tw=80:
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#include "jit/FoldLinearArithConstants.h"

#include "jit/IonAnalysis.h"
#include "jit/MIR.h"
#include "jit/MIRGenerator.h"
#include "jit/MIRGraph.h"

using namespace js;
using namespace jit;

namespace js {
namespace jit {

// Mark this node and its children as RecoveredOnBailout when they are not used.
// The marked nodes will be removed during DCE. Marking as RecoveredOnBailout is
// necessary because the Sink pass is ran before this pass.
static void markNodesAsRecoveredOnBailout(MDefinition* def) {
  if (def->hasLiveDefUses() || !DeadIfUnused(def) ||
      !def->canRecoverOnBailout()) {
    return;
  }

  JitSpew(JitSpew_FLAC, "mark as recovered on bailout: %s%u", def->opName(),
          def->id());
  def->setRecoveredOnBailoutUnchecked();

  // Recursively mark nodes that do not have multiple uses. This loop is
  // necessary because a node could be an unused right shift zero or an
  // unused add, and both need to be marked as RecoveredOnBailout.
  for (size_t i = 0; i < def->numOperands(); i++) {
    markNodesAsRecoveredOnBailout(def->getOperand(i));
  }
}

// Fold AddIs with one variable and two or more constants into one AddI.
static void AnalyzeAdd(TempAllocator& alloc, MAdd* add) {
  if (add->specialization() != MIRType::Int32 || add->isRecoveredOnBailout()) {
    return;
  }

  if (!add->hasUses()) {
    return;
  }

  JitSpew(JitSpew_FLAC, "analyze add: %s%u", add->opName(), add->id());

  SimpleLinearSum sum = ExtractLinearSum(add);
  if (sum.constant == 0 || !sum.term) {
    return;
  }

  // Determine which operand is the constant.
  int idx = add->getOperand(0)->isConstant() ? 0 : 1;
  if (add->getOperand(idx)->isConstant()) {
    // Do not replace an add where the outcome is the same add instruction.
    MOZ_ASSERT(add->getOperand(idx)->toConstant()->type() == MIRType::Int32);
    if (sum.term == add->getOperand(1 - idx) ||
        sum.constant == add->getOperand(idx)->toConstant()->toInt32()) {
      return;
    }
  }

  MInstruction* rhs = MConstant::New(alloc, Int32Value(sum.constant));
  add->block()->insertBefore(add, rhs);

  MAdd* addNew =
      MAdd::New(alloc, sum.term, rhs, MIRType::Int32, add->truncateKind());

  add->replaceAllLiveUsesWith(addNew);
  add->block()->insertBefore(add, addNew);
  JitSpew(JitSpew_FLAC, "replaced with: %s%u", addNew->opName(), addNew->id());
  JitSpew(JitSpew_FLAC, "and constant: %s%u (%d)", rhs->opName(), rhs->id(),
          sum.constant);

  // Mark the stale nodes as RecoveredOnBailout since the Sink pass has
  // been run before this pass. DCE will then remove the unused nodes.
  markNodesAsRecoveredOnBailout(add);
}

bool FoldLinearArithConstants(MIRGenerator* mir, MIRGraph& graph) {
  for (PostorderIterator block(graph.poBegin()); block != graph.poEnd();
       block++) {
    if (mir->shouldCancel("Fold Linear Arithmetic Constants (main loop)")) {
      return false;
    }

    for (MInstructionIterator i = block->begin(); i != block->end(); i++) {
      if (!graph.alloc().ensureBallast()) {
        return false;
      }

      if (mir->shouldCancel("Fold Linear Arithmetic Constants (inner loop)")) {
        return false;
      }

      if (i->isAdd()) {
        AnalyzeAdd(graph.alloc(), i->toAdd());
      }
    }
  }
  return true;
}

} /* namespace jit */
} /* namespace js */