path: root/js/src/jit/shared/Lowering-shared.cpp

/* -*- 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/shared/Lowering-shared-inl.h"

#include "jit/LIR.h"
#include "jit/Lowering.h"
#include "jit/MIR.h"
#include "jit/ScalarTypeUtils.h"

#include "vm/SymbolType.h"

using namespace js;
using namespace jit;

using mozilla::Maybe;
using mozilla::Nothing;
using mozilla::Some;

bool LIRGeneratorShared::ShouldReorderCommutative(MDefinition* lhs,
                                                  MDefinition* rhs,
                                                  MInstruction* ins) {
  // lhs and rhs are used by the commutative operator.
  MOZ_ASSERT(lhs->hasDefUses());
  MOZ_ASSERT(rhs->hasDefUses());

  // Ensure that if there is a constant, then it is in rhs.
  if (rhs->isConstant()) {
    return false;
  }
  if (lhs->isConstant()) {
    return true;
  }

  // Since clobbering binary operations clobber the left operand, prefer a
  // non-constant lhs operand with no further uses. To be fully precise, we
  // should check whether this is the *last* use, but checking hasOneDefUse()
  // is a decent approximation which doesn't require any extra analysis.
  bool rhsSingleUse = rhs->hasOneDefUse();
  bool lhsSingleUse = lhs->hasOneDefUse();
  if (rhsSingleUse) {
    if (!lhsSingleUse) {
      return true;
    }
  } else {
    if (lhsSingleUse) {
      return false;
    }
  }

  // If this is a reduction-style computation, such as
  //
  //   sum = 0;
  //   for (...)
  //      sum += ...;
  //
  // put the phi on the left to promote coalescing. This is fairly specific.
  if (rhsSingleUse && rhs->isPhi() && rhs->block()->isLoopHeader() &&
      ins == rhs->toPhi()->getLoopBackedgeOperand()) {
    return true;
  }

  return false;
}

void LIRGeneratorShared::ReorderCommutative(MDefinition** lhsp,
                                            MDefinition** rhsp,
                                            MInstruction* ins) {
  MDefinition* lhs = *lhsp;
  MDefinition* rhs = *rhsp;

  if (ShouldReorderCommutative(lhs, rhs, ins)) {
    *rhsp = lhs;
    *lhsp = rhs;
  }
}

void LIRGeneratorShared::definePhiOneRegister(MPhi* phi, size_t lirIndex) {
  LPhi* lir = current->getPhi(lirIndex);

  uint32_t vreg = getVirtualRegister();

  phi->setVirtualRegister(vreg);
  lir->setDef(0, LDefinition(vreg, LDefinition::TypeFrom(phi->type())));
  annotate(lir);
}

#ifdef JS_NUNBOX32
void LIRGeneratorShared::definePhiTwoRegisters(MPhi* phi, size_t lirIndex) {
  LPhi* type = current->getPhi(lirIndex + VREG_TYPE_OFFSET);
  LPhi* payload = current->getPhi(lirIndex + VREG_DATA_OFFSET);

  uint32_t typeVreg = getVirtualRegister();
  phi->setVirtualRegister(typeVreg);

  uint32_t payloadVreg = getVirtualRegister();
  MOZ_ASSERT_IF(!errored(), typeVreg + 1 == payloadVreg);

  type->setDef(0, LDefinition(typeVreg, LDefinition::TYPE));
  payload->setDef(0, LDefinition(payloadVreg, LDefinition::PAYLOAD));
  annotate(type);
  annotate(payload);
}
#endif

void LIRGeneratorShared::lowerTypedPhiInput(MPhi* phi, uint32_t inputPosition,
                                            LBlock* block, size_t lirIndex) {
  MDefinition* operand = phi->getOperand(inputPosition);
  LPhi* lir = block->getPhi(lirIndex);
  lir->setOperand(inputPosition, LUse(operand->virtualRegister(), LUse::ANY));
}

LRecoverInfo* LIRGeneratorShared::getRecoverInfo(MResumePoint* rp) {
  if (cachedRecoverInfo_ && cachedRecoverInfo_->mir() == rp) {
    return cachedRecoverInfo_;
  }

  LRecoverInfo* recoverInfo = LRecoverInfo::New(gen, rp);
  if (!recoverInfo) {
    return nullptr;
  }

  cachedRecoverInfo_ = recoverInfo;
  return recoverInfo;
}

#ifdef DEBUG
bool LRecoverInfo::OperandIter::canOptimizeOutIfUnused() {
  MDefinition* ins = **this;

  // We check ins->type() in addition to ins->isUnused() because
  // EliminateDeadResumePointOperands may replace nodes with the constant
  // MagicValue(JS_OPTIMIZED_OUT).
  if ((ins->isUnused() || ins->type() == MIRType::MagicOptimizedOut) &&
      (*it_)->isResumePoint()) {
    return !(*it_)->toResumePoint()->isObservableOperand(op_);
  }

  return true;
}
#endif

LAllocation LIRGeneratorShared::useRegisterOrIndexConstant(
    MDefinition* mir, Scalar::Type type, int32_t offsetAdjustment) {
  if (CanUseInt32Constant(mir)) {
    MConstant* cst = mir->toConstant();
    int32_t val =
        cst->type() == MIRType::Int32 ? cst->toInt32() : cst->toIntPtr();
    int32_t offset;
    if (ArrayOffsetFitsInInt32(val, type, offsetAdjustment, &offset)) {
      return LAllocation(mir->toConstant());
    }
  }
  return useRegister(mir);
}

#ifdef JS_NUNBOX32
LSnapshot* LIRGeneratorShared::buildSnapshot(MResumePoint* rp,
                                             BailoutKind kind) {
  LRecoverInfo* recoverInfo = getRecoverInfo(rp);
  if (!recoverInfo) {
    return nullptr;
  }

  LSnapshot* snapshot = LSnapshot::New(gen, recoverInfo, kind);
  if (!snapshot) {
    return nullptr;
  }

  size_t index = 0;
  for (LRecoverInfo::OperandIter it(recoverInfo); !it; ++it) {
    // Check that optimized out operands are in eliminable slots.
    MOZ_ASSERT(it.canOptimizeOutIfUnused());

    MDefinition* ins = *it;

    if (ins->isRecoveredOnBailout()) {
      continue;
    }

    LAllocation* type = snapshot->typeOfSlot(index);
    LAllocation* payload = snapshot->payloadOfSlot(index);
    ++index;

    if (ins->isBox()) {
      ins = ins->toBox()->getOperand(0);
    }

    // Guards should never be eliminated.
    MOZ_ASSERT_IF(ins->isUnused(), !ins->isGuard());

    // Snapshot operands other than constants should never be
    // emitted-at-uses. Try-catch support depends on there being no
    // code between an instruction and the LOsiPoint that follows it.
    MOZ_ASSERT_IF(!ins->isConstant(), !ins->isEmittedAtUses());

    // The register allocation will fill these fields in with actual
    // register/stack assignments. During code generation, we can restore
    // interpreter state with the given information. Note that for
    // constants, including known types, we record a dummy placeholder,
    // since we can recover the same information, much cleaner, from MIR.
    if (ins->isConstant() || ins->isUnused()) {
      *type = LAllocation();
      *payload = LAllocation();
    } else if (ins->type() != MIRType::Value) {
      *type = LAllocation();
      *payload = use(ins, LUse(LUse::KEEPALIVE));
    } else {
      *type = useType(ins, LUse::KEEPALIVE);
      *payload = usePayload(ins, LUse::KEEPALIVE);
    }
  }

  return snapshot;
}

#elif JS_PUNBOX64

LSnapshot* LIRGeneratorShared::buildSnapshot(MResumePoint* rp,
                                             BailoutKind kind) {
  LRecoverInfo* recoverInfo = getRecoverInfo(rp);
  if (!recoverInfo) {
    return nullptr;
  }

  LSnapshot* snapshot = LSnapshot::New(gen, recoverInfo, kind);
  if (!snapshot) {
    return nullptr;
  }

  size_t index = 0;
  for (LRecoverInfo::OperandIter it(recoverInfo); !it; ++it) {
    // Check that optimized out operands are in eliminable slots.
    MOZ_ASSERT(it.canOptimizeOutIfUnused());

    MDefinition* def = *it;

    if (def->isRecoveredOnBailout()) {
      continue;
    }

    if (def->isBox()) {
      def = def->toBox()->getOperand(0);
    }

    // Guards should never be eliminated.
    MOZ_ASSERT_IF(def->isUnused(), !def->isGuard());

    // Snapshot operands other than constants should never be
    // emitted-at-uses. Try-catch support depends on there being no
    // code between an instruction and the LOsiPoint that follows it.
    MOZ_ASSERT_IF(!def->isConstant(), !def->isEmittedAtUses());

    LAllocation* a = snapshot->getEntry(index++);

    if (def->isUnused()) {
      *a = LAllocation();
      continue;
    }

    *a = useKeepaliveOrConstant(def);
  }

  return snapshot;
}
#endif

void LIRGeneratorShared::assignSnapshot(LInstruction* ins, BailoutKind kind) {
  // assignSnapshot must be called before define/add, since
  // it may add new instructions for emitted-at-use operands.
  MOZ_ASSERT(ins->id() == 0);
  MOZ_ASSERT(kind != BailoutKind::Unknown);

  LSnapshot* snapshot = buildSnapshot(lastResumePoint_, kind);
  if (!snapshot) {
    abort(AbortReason::Alloc, "buildSnapshot failed");
    return;
  }

  ins->assignSnapshot(snapshot);
}

void LIRGeneratorShared::assignSafepoint(LInstruction* ins, MInstruction* mir,
                                         BailoutKind kind) {
  MOZ_ASSERT(!osiPoint_);
  MOZ_ASSERT(!ins->safepoint());

  ins->initSafepoint(alloc());

  MResumePoint* mrp =
      mir->resumePoint() ? mir->resumePoint() : lastResumePoint_;
  LSnapshot* postSnapshot = buildSnapshot(mrp, kind);
  if (!postSnapshot) {
    abort(AbortReason::Alloc, "buildSnapshot failed");
    return;
  }

  osiPoint_ = new (alloc()) LOsiPoint(ins->safepoint(), postSnapshot);

  if (!lirGraph_.noteNeedsSafepoint(ins)) {
    abort(AbortReason::Alloc, "noteNeedsSafepoint failed");
    return;
  }
}

void LIRGeneratorShared::assignWasmSafepoint(LInstruction* ins) {
  MOZ_ASSERT(!osiPoint_);
  MOZ_ASSERT(!ins->safepoint());

  ins->initSafepoint(alloc());

  if (!lirGraph_.noteNeedsSafepoint(ins)) {
    abort(AbortReason::Alloc, "noteNeedsSafepoint failed");
    return;
  }
}