constant-pool.cc

// Copyright 2018 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "src/constant-pool.h"
#include "src/assembler-inl.h"

namespace v8 {
namespace internal {

#if defined(V8_TARGET_ARCH_PPC)

ConstantPoolBuilder::ConstantPoolBuilder(int ptr_reach_bits,
                                         int double_reach_bits) {
  info_[ConstantPoolEntry::INTPTR].entries.reserve(64);
  info_[ConstantPoolEntry::INTPTR].regular_reach_bits = ptr_reach_bits;
  info_[ConstantPoolEntry::DOUBLE].regular_reach_bits = double_reach_bits;
}

ConstantPoolEntry::Access ConstantPoolBuilder::NextAccess(
    ConstantPoolEntry::Type type) const {
  const PerTypeEntryInfo& info = info_[type];

  if (info.overflow()) return ConstantPoolEntry::OVERFLOWED;

  int dbl_count = info_[ConstantPoolEntry::DOUBLE].regular_count;
  int dbl_offset = dbl_count * kDoubleSize;
  int ptr_count = info_[ConstantPoolEntry::INTPTR].regular_count;
  int ptr_offset = ptr_count * kPointerSize + dbl_offset;

  if (type == ConstantPoolEntry::DOUBLE) {
    // Double overflow detection must take into account the reach for both types
    int ptr_reach_bits = info_[ConstantPoolEntry::INTPTR].regular_reach_bits;
    if (!is_uintn(dbl_offset, info.regular_reach_bits) ||
        (ptr_count > 0 &&
         !is_uintn(ptr_offset + kDoubleSize - kPointerSize, ptr_reach_bits))) {
      return ConstantPoolEntry::OVERFLOWED;
    }
  } else {
    DCHECK(type == ConstantPoolEntry::INTPTR);
    if (!is_uintn(ptr_offset, info.regular_reach_bits)) {
      return ConstantPoolEntry::OVERFLOWED;
    }
  }

  return ConstantPoolEntry::REGULAR;
}

ConstantPoolEntry::Access ConstantPoolBuilder::AddEntry(
    ConstantPoolEntry& entry, ConstantPoolEntry::Type type) {
  DCHECK(!emitted_label_.is_bound());
  PerTypeEntryInfo& info = info_[type];
  const int entry_size = ConstantPoolEntry::size(type);
  bool merged = false;

  if (entry.sharing_ok()) {
    // Try to merge entries
    std::vector<ConstantPoolEntry>::iterator it = info.shared_entries.begin();
    int end = static_cast<int>(info.shared_entries.size());
    for (int i = 0; i < end; i++, it++) {
      if ((entry_size == kPointerSize) ? entry.value() == it->value()
                                       : entry.value64() == it->value64()) {
        // Merge with found entry.
        entry.set_merged_index(i);
        merged = true;
        break;
      }
    }
  }

  // By definition, merged entries have regular access.
  DCHECK(!merged || entry.merged_index() < info.regular_count);
  ConstantPoolEntry::Access access =
      (merged ? ConstantPoolEntry::REGULAR : NextAccess(type));

  // Enforce an upper bound on search time by limiting the search to
  // unique sharable entries which fit in the regular section.
  if (entry.sharing_ok() && !merged && access == ConstantPoolEntry::REGULAR) {
    info.shared_entries.push_back(entry);
  } else {
    info.entries.push_back(entry);
  }

  // We're done if we found a match or have already triggered the
  // overflow state.
  if (merged || info.overflow()) return access;

  if (access == ConstantPoolEntry::REGULAR) {
    info.regular_count++;
  } else {
    info.overflow_start = static_cast<int>(info.entries.size()) - 1;
  }

  return access;
}

void ConstantPoolBuilder::EmitSharedEntries(Assembler* assm,
                                            ConstantPoolEntry::Type type) {
  PerTypeEntryInfo& info = info_[type];
  std::vector<ConstantPoolEntry>& shared_entries = info.shared_entries;
  const int entry_size = ConstantPoolEntry::size(type);
  int base = emitted_label_.pos();
  DCHECK_GT(base, 0);
  int shared_end = static_cast<int>(shared_entries.size());
  std::vector<ConstantPoolEntry>::iterator shared_it = shared_entries.begin();
  for (int i = 0; i < shared_end; i++, shared_it++) {
    int offset = assm->pc_offset() - base;
    shared_it->set_offset(offset);  // Save offset for merged entries.
    if (entry_size == kPointerSize) {
      assm->dp(shared_it->value());
    } else {
      assm->dq(shared_it->value64());
    }
    DCHECK(is_uintn(offset, info.regular_reach_bits));

    // Patch load sequence with correct offset.
    assm->PatchConstantPoolAccessInstruction(shared_it->position(), offset,
                                             ConstantPoolEntry::REGULAR, type);
  }
}

void ConstantPoolBuilder::EmitGroup(Assembler* assm,
                                    ConstantPoolEntry::Access access,
                                    ConstantPoolEntry::Type type) {
  PerTypeEntryInfo& info = info_[type];
  const bool overflow = info.overflow();
  std::vector<ConstantPoolEntry>& entries = info.entries;
  std::vector<ConstantPoolEntry>& shared_entries = info.shared_entries;
  const int entry_size = ConstantPoolEntry::size(type);
  int base = emitted_label_.pos();
  DCHECK_GT(base, 0);
  int begin;
  int end;

  if (access == ConstantPoolEntry::REGULAR) {
    // Emit any shared entries first
    EmitSharedEntries(assm, type);
  }

  if (access == ConstantPoolEntry::REGULAR) {
    begin = 0;
    end = overflow ? info.overflow_start : static_cast<int>(entries.size());
  } else {
    DCHECK(access == ConstantPoolEntry::OVERFLOWED);
    if (!overflow) return;
    begin = info.overflow_start;
    end = static_cast<int>(entries.size());
  }

  std::vector<ConstantPoolEntry>::iterator it = entries.begin();
  if (begin > 0) std::advance(it, begin);
  for (int i = begin; i < end; i++, it++) {
    // Update constant pool if necessary and get the entry's offset.
    int offset;
    ConstantPoolEntry::Access entry_access;
    if (!it->is_merged()) {
      // Emit new entry
      offset = assm->pc_offset() - base;
      entry_access = access;
      if (entry_size == kPointerSize) {
        assm->dp(it->value());
      } else {
        assm->dq(it->value64());
      }
    } else {
      // Retrieve offset from shared entry.
      offset = shared_entries[it->merged_index()].offset();
      entry_access = ConstantPoolEntry::REGULAR;
    }

    DCHECK(entry_access == ConstantPoolEntry::OVERFLOWED ||
           is_uintn(offset, info.regular_reach_bits));

    // Patch load sequence with correct offset.
    assm->PatchConstantPoolAccessInstruction(it->position(), offset,
                                             entry_access, type);
  }
}

// Emit and return position of pool.  Zero implies no constant pool.
int ConstantPoolBuilder::Emit(Assembler* assm) {
  bool emitted = emitted_label_.is_bound();
  bool empty = IsEmpty();

  if (!emitted) {
    // Mark start of constant pool.  Align if necessary.
    if (!empty) assm->DataAlign(kDoubleSize);
    assm->bind(&emitted_label_);
    if (!empty) {
      // Emit in groups based on access and type.
      // Emit doubles first for alignment purposes.
      EmitGroup(assm, ConstantPoolEntry::REGULAR, ConstantPoolEntry::DOUBLE);
      EmitGroup(assm, ConstantPoolEntry::REGULAR, ConstantPoolEntry::INTPTR);
      if (info_[ConstantPoolEntry::DOUBLE].overflow()) {
        assm->DataAlign(kDoubleSize);
        EmitGroup(assm, ConstantPoolEntry::OVERFLOWED,
                  ConstantPoolEntry::DOUBLE);
      }
      if (info_[ConstantPoolEntry::INTPTR].overflow()) {
        EmitGroup(assm, ConstantPoolEntry::OVERFLOWED,
                  ConstantPoolEntry::INTPTR);
      }
    }
  }

  return !empty ? emitted_label_.pos() : 0;
}

#endif  // defined(V8_TARGET_ARCH_PPC)

}  // namespace internal
}  // namespace v8