src/pool-manager-impl.h - platform/external/vixl - Git at Google

 // Copyright 2017, VIXL authors
 // All rights reserved.
 //
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are met:
 //
 //   * Redistributions of source code must retain the above copyright notice,
 //     this list of conditions and the following disclaimer.
 //   * Redistributions in binary form must reproduce the above copyright notice,
 //     this list of conditions and the following disclaimer in the documentation
 //     and/or other materials provided with the distribution.
 //   * Neither the name of ARM Limited nor the names of its contributors may be
 //     used to endorse or promote products derived from this software without
 //     specific prior written permission.
 //
 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS CONTRIBUTORS "AS IS" AND
 // ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 // WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 // DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE
 // FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 // DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 // SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
 // CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 // OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

 #ifndef VIXL_POOL_MANAGER_IMPL_H_
 #define VIXL_POOL_MANAGER_IMPL_H_

 #include "pool-manager.h"

 #include <algorithm>
 #include "assembler-base-vixl.h"

 namespace vixl {


 template <typename T>
 T PoolManager<T>::Emit(MacroAssemblerInterface* masm,
                        T pc,
                        int num_bytes,
                        ForwardReference<T>* new_reference,
                        LocationBase<T>* new_object,
                        EmitOption option) {
   // Make sure that the buffer still has the alignment we think it does.
   VIXL_ASSERT(IsAligned(masm->AsAssemblerBase()
                             ->GetBuffer()
                             ->GetStartAddress<uintptr_t>(),
                         buffer_alignment_));

   // We should not call this method when the pools are blocked.
   VIXL_ASSERT(!IsBlocked());
   if (objects_.empty()) return pc;

   // Emit header.
   if (option == kBranchRequired) {
     masm->EmitPoolHeader();
     // TODO: The pc at this point might not actually be aligned according to
     // alignment_. This is to support the current AARCH32 MacroAssembler which
     // does not have a fixed size instruction set. In practice, the pc will be
     // aligned to the alignment instructions need for the current instruction
     // set, so we do not need to align it here. All other calculations do take
     // the alignment into account, which only makes the checkpoint calculations
     // more conservative when we use T32. Uncomment the following assertion if
     // the AARCH32 MacroAssembler is modified to only support one ISA at the
     // time.
     // VIXL_ASSERT(pc == AlignUp(pc, alignment_));
     pc += header_size_;
   } else {
     // If the header is optional, we might need to add some extra padding to
     // meet the minimum location of the first object.
     if (pc < objects_[0].min_location_) {
       int32_t padding = objects_[0].min_location_ - pc;
       masm->EmitNopBytes(padding);
       pc += padding;
     }
   }

   PoolObject<T>* existing_object = GetObjectIfTracked(new_object);

   // Go through all objects and emit one by one.
   for (objects_iter iter = objects_.begin(); iter != objects_.end();) {
     PoolObject<T>& current = *iter;
     if (ShouldSkipObject(&current,
                          pc,
                          num_bytes,
                          new_reference,
                          new_object,
                          existing_object)) {
       ++iter;
       continue;
     }
     LocationBase<T>* label_base = current.label_base_;
     T aligned_pc = AlignUp(pc, current.alignment_);
     masm->EmitPaddingBytes(aligned_pc - pc);
     pc = aligned_pc;
     VIXL_ASSERT(pc >= current.min_location_);
     VIXL_ASSERT(pc <= current.max_location_);
     // First call SetLocation, which will also resolve the references, and then
     // call EmitPoolObject, which might add a new reference.
     label_base->SetLocation(masm->AsAssemblerBase(), pc);
     label_base->EmitPoolObject(masm);
     int object_size = label_base->GetPoolObjectSizeInBytes();
     if (label_base->ShouldDeletePoolObjectOnPlacement()) {
       label_base->MarkBound();
       iter = RemoveAndDelete(iter);
     } else {
       VIXL_ASSERT(!current.label_base_->ShouldDeletePoolObjectOnPlacement());
       current.label_base_->UpdatePoolObject(&current);
       VIXL_ASSERT(current.alignment_ >= label_base->GetPoolObjectAlignment());
       ++iter;
     }
     pc += object_size;
   }

   // Recalculate the checkpoint before emitting the footer. The footer might
   // call Bind() which will check if we need to emit.
   RecalculateCheckpoint();

   // Always emit footer - this might add some padding.
   masm->EmitPoolFooter();
   pc = AlignUp(pc, alignment_);

   return pc;
 }

 template <typename T>
 bool PoolManager<T>::ShouldSkipObject(PoolObject<T>* pool_object,
                                       T pc,
                                       int num_bytes,
                                       ForwardReference<T>* new_reference,
                                       LocationBase<T>* new_object,
                                       PoolObject<T>* existing_object) const {
   // We assume that all objects before this have been skipped and all objects
   // after this will be emitted, therefore we will emit the whole pool. Add
   // the header size and alignment, as well as the number of bytes we are
   // planning to emit.
   T max_actual_location = pc + num_bytes + max_pool_size_;

   if (new_reference != NULL) {
     // If we're adding a new object, also assume that it will have to be emitted
     // before the object we are considering to skip.
     VIXL_ASSERT(new_object != NULL);
     T new_object_alignment = std::max(new_reference->object_alignment_,
                                       new_object->GetPoolObjectAlignment());
     if ((existing_object != NULL) &&
         (existing_object->alignment_ > new_object_alignment)) {
       new_object_alignment = existing_object->alignment_;
     }
     max_actual_location +=
         (new_object->GetPoolObjectSizeInBytes() + new_object_alignment - 1);
   }

   // Hard limit.
   if (max_actual_location >= pool_object->max_location_) return false;

   // Use heuristic.
   return (pc < pool_object->skip_until_location_hint_);
 }

 template <typename T>
 T PoolManager<T>::UpdateCheckpointForObject(T checkpoint,
                                             const PoolObject<T>* object) {
   checkpoint -= object->label_base_->GetPoolObjectSizeInBytes();
   if (checkpoint > object->max_location_) checkpoint = object->max_location_;
   checkpoint = AlignDown(checkpoint, object->alignment_);
   return checkpoint;
 }

 template <typename T>
 static T MaxCheckpoint() {
   return std::numeric_limits<T>::max();
 }

 template <typename T>
 static inline bool CheckCurrentPC(T pc, T checkpoint) {
   VIXL_ASSERT(pc <= checkpoint);
   // We must emit the pools if we are at the checkpoint now.
   return pc == checkpoint;
 }

 template <typename T>
 static inline bool CheckFuturePC(T pc, T checkpoint) {
   // We do not need to emit the pools now if the projected future PC will be
   // equal to the checkpoint (we will need to emit the pools then).
   return pc > checkpoint;
 }

 template <typename T>
 bool PoolManager<T>::MustEmit(T pc,
                               int num_bytes,
                               ForwardReference<T>* reference,
                               LocationBase<T>* label_base) const {
   // Check if we are at or past the checkpoint.
   if (CheckCurrentPC(pc, checkpoint_)) return true;

   // Check if the future PC will be past the checkpoint.
   pc += num_bytes;
   if (CheckFuturePC(pc, checkpoint_)) return true;

   // No new reference - nothing to do.
   if (reference == NULL) {
     VIXL_ASSERT(label_base == NULL);
     return false;
   }

   if (objects_.empty()) {
     // Basic assertions that restrictions on the new (and only) reference are
     // possible to satisfy.
     VIXL_ASSERT(AlignUp(pc + header_size_, alignment_) >=
                 reference->min_object_location_);
     VIXL_ASSERT(pc <= reference->max_object_location_);
     return false;
   }

   // Check if the object is already being tracked.
   const PoolObject<T>* existing_object = GetObjectIfTracked(label_base);
   if (existing_object != NULL) {
     // If the existing_object is already in existing_objects_ and its new
     // alignment and new location restrictions are not stricter, skip the more
     // expensive check.
     if ((reference->min_object_location_ <= existing_object->min_location_) &&
         (reference->max_object_location_ >= existing_object->max_location_) &&
         (reference->object_alignment_ <= existing_object->alignment_)) {
       return false;
     }
   }

   // Create a temporary object.
   PoolObject<T> temp(label_base);
   temp.RestrictRange(reference->min_object_location_,
                      reference->max_object_location_);
   temp.RestrictAlignment(reference->object_alignment_);
   if (existing_object != NULL) {
     temp.RestrictRange(existing_object->min_location_,
                        existing_object->max_location_);
     temp.RestrictAlignment(existing_object->alignment_);
   }

   // Check if the new reference can be added after the end of the current pool.
   // If yes, we don't need to emit.
   T last_reachable = AlignDown(temp.max_location_, temp.alignment_);
   const PoolObject<T>& last = objects_.back();
   T after_pool = AlignDown(last.max_location_, last.alignment_) +
                  last.label_base_->GetPoolObjectSizeInBytes();
   // The current object can be placed at the end of the pool, even if the last
   // object is placed at the last possible location.
   if (last_reachable >= after_pool) return false;
   // The current object can be placed after the code we are about to emit and
   // after the existing pool (with a pessimistic size estimate).
   if (last_reachable >= pc + num_bytes + max_pool_size_) return false;

   // We're not in a trivial case, so we need to recalculate the checkpoint.

   // Check (conservatively) if we can fit it into the objects_ array, without
   // breaking our assumptions. Here we want to recalculate the checkpoint as
   // if the new reference was added to the PoolManager but without actually
   // adding it (as removing it is non-trivial).

   T checkpoint = MaxCheckpoint<T>();
   // Will temp be the last object in objects_?
   if (PoolObjectLessThan(last, temp)) {
     checkpoint = UpdateCheckpointForObject(checkpoint, &temp);
     if (checkpoint < temp.min_location_) return true;
   }

   bool tempNotPlacedYet = true;
   for (int i = static_cast<int>(objects_.size()) - 1; i >= 0; --i) {
     const PoolObject<T>& current = objects_[i];
     if (tempNotPlacedYet && PoolObjectLessThan(current, temp)) {
       checkpoint = UpdateCheckpointForObject(checkpoint, &temp);
       if (checkpoint < temp.min_location_) return true;
       if (CheckFuturePC(pc, checkpoint)) return true;
       tempNotPlacedYet = false;
     }
     if (current.label_base_ == label_base) continue;
     checkpoint = UpdateCheckpointForObject(checkpoint, &current);
     if (checkpoint < current.min_location_) return true;
     if (CheckFuturePC(pc, checkpoint)) return true;
   }
   // temp is the object with the smallest max_location_.
   if (tempNotPlacedYet) {
     checkpoint = UpdateCheckpointForObject(checkpoint, &temp);
     if (checkpoint < temp.min_location_) return true;
   }

   // Take the header into account.
   checkpoint -= header_size_;
   checkpoint = AlignDown(checkpoint, alignment_);

   return CheckFuturePC(pc, checkpoint);
 }

 template <typename T>
 void PoolManager<T>::RecalculateCheckpoint(SortOption sort_option) {
   // TODO: Improve the max_pool_size_ estimate by starting from the
   // min_location_ of the first object, calculating the end of the pool as if
   // all objects were placed starting from there, and in the end adding the
   // maximum object alignment found minus one (which is the maximum extra
   // padding we would need if we were to relocate the pool to a different
   // address).
   max_pool_size_ = 0;

   if (objects_.empty()) {
     checkpoint_ = MaxCheckpoint<T>();
     return;
   }

   // Sort objects by their max_location_.
   if (sort_option == kSortRequired) {
     std::sort(objects_.begin(), objects_.end(), PoolObjectLessThan);
   }

   // Add the header size and header and footer max alignment to the maximum
   // pool size.
   max_pool_size_ += header_size_ + 2 * (alignment_ - 1);

   T checkpoint = MaxCheckpoint<T>();
   int last_object_index = static_cast<int>(objects_.size()) - 1;
   for (int i = last_object_index; i >= 0; --i) {
     // Bring back the checkpoint by the size of the current object, unless
     // we need to bring it back more, then align.
     PoolObject<T>& current = objects_[i];
     checkpoint = UpdateCheckpointForObject(checkpoint, &current);
     VIXL_ASSERT(checkpoint >= current.min_location_);
     max_pool_size_ += (current.alignment_ - 1 +
                        current.label_base_->GetPoolObjectSizeInBytes());
   }
   // Take the header into account.
   checkpoint -= header_size_;
   checkpoint = AlignDown(checkpoint, alignment_);

   // Update the checkpoint of the pool manager.
   checkpoint_ = checkpoint;

   // NOTE: To handle min_location_ in the generic case, we could make a second
   // pass of the objects_ vector, increasing the checkpoint as needed, while
   // maintaining the alignment requirements.
   // It should not be possible to have any issues with min_location_ with actual
   // code, since there should always be some kind of branch over the pool,
   // whether introduced by the pool emission or by the user, which will make
   // sure the min_location_ requirement is satisfied. It's possible that the
   // user could emit code in the literal pool and intentionally load the first
   // value and then fall-through into the pool, but that is not a supported use
   // of VIXL and we will assert in that case.
 }

 template <typename T>
 bool PoolManager<T>::PoolObjectLessThan(const PoolObject<T>& a,
                                         const PoolObject<T>& b) {
   if (a.max_location_ != b.max_location_)
     return (a.max_location_ < b.max_location_);
   int a_size = a.label_base_->GetPoolObjectSizeInBytes();
   int b_size = b.label_base_->GetPoolObjectSizeInBytes();
   if (a_size != b_size) return (a_size < b_size);
   if (a.alignment_ != b.alignment_) return (a.alignment_ < b.alignment_);
   if (a.min_location_ != b.min_location_)
     return (a.min_location_ < b.min_location_);
   return false;
 }

 template <typename T>
 void PoolManager<T>::AddObjectReference(const ForwardReference<T>* reference,
                                         LocationBase<T>* label_base) {
   VIXL_ASSERT(reference->object_alignment_ <= buffer_alignment_);
   VIXL_ASSERT(label_base->GetPoolObjectAlignment() <= buffer_alignment_);

   PoolObject<T>* object = GetObjectIfTracked(label_base);

   if (object == NULL) {
     PoolObject<T> new_object(label_base);
     new_object.RestrictRange(reference->min_object_location_,
                              reference->max_object_location_);
     new_object.RestrictAlignment(reference->object_alignment_);
     Insert(new_object);
   } else {
     object->RestrictRange(reference->min_object_location_,
                           reference->max_object_location_);
     object->RestrictAlignment(reference->object_alignment_);

     // Move the object, if needed.
     if (objects_.size() != 1) {
       PoolObject<T> new_object(*object);
       ptrdiff_t distance = std::distance(objects_.data(), object);
       objects_.erase(objects_.begin() + distance);
       Insert(new_object);
     }
   }
   // No need to sort, we inserted the object in an already sorted array.
   RecalculateCheckpoint(kNoSortRequired);
 }

 template <typename T>
 void PoolManager<T>::Insert(const PoolObject<T>& new_object) {
   bool inserted = false;
   // Place the object in the right position.
   for (objects_iter iter = objects_.begin(); iter != objects_.end(); ++iter) {
     PoolObject<T>& current = *iter;
     if (!PoolObjectLessThan(current, new_object)) {
       objects_.insert(iter, new_object);
       inserted = true;
       break;
     }
   }
   if (!inserted) {
     objects_.push_back(new_object);
   }
 }

 template <typename T>
 void PoolManager<T>::RemoveAndDelete(PoolObject<T>* object) {
   for (objects_iter iter = objects_.begin(); iter != objects_.end(); ++iter) {
     PoolObject<T>& current = *iter;
     if (current.label_base_ == object->label_base_) {
       (void)RemoveAndDelete(iter);
       return;
     }
   }
   VIXL_UNREACHABLE();
 }

 template <typename T>
 typename PoolManager<T>::objects_iter PoolManager<T>::RemoveAndDelete(
     objects_iter iter) {
   PoolObject<T>& object = *iter;
   LocationBase<T>* label_base = object.label_base_;

   // Check if we also need to delete the LocationBase object.
   if (label_base->ShouldBeDeletedOnPoolManagerDestruction()) {
     delete_on_destruction_.push_back(label_base);
   }
   if (label_base->ShouldBeDeletedOnPlacementByPoolManager()) {
     VIXL_ASSERT(!label_base->ShouldBeDeletedOnPoolManagerDestruction());
     delete label_base;
   }

   return objects_.erase(iter);
 }

 template <typename T>
 T PoolManager<T>::Bind(MacroAssemblerInterface* masm,
                        LocationBase<T>* object,
                        T location) {
   PoolObject<T>* existing_object = GetObjectIfTracked(object);
   int alignment;
   T min_location;
   if (existing_object == NULL) {
     alignment = object->GetMaxAlignment();
     min_location = object->GetMinLocation();
   } else {
     alignment = existing_object->alignment_;
     min_location = existing_object->min_location_;
   }

   // Align if needed, and add necessary padding to reach the min_location_.
   T aligned_location = AlignUp(location, alignment);
   masm->EmitNopBytes(aligned_location - location);
   location = aligned_location;
   while (location < min_location) {
     masm->EmitNopBytes(alignment);
     location += alignment;
   }

   object->SetLocation(masm->AsAssemblerBase(), location);
   object->MarkBound();

   if (existing_object != NULL) {
     RemoveAndDelete(existing_object);
     // No need to sort, we removed the object from a sorted array.
     RecalculateCheckpoint(kNoSortRequired);
   }

   // We assume that the maximum padding we can possibly add here is less
   // than the header alignment - hence that we're not going to go past our
   // checkpoint.
   VIXL_ASSERT(!CheckFuturePC(location, checkpoint_));
   return location;
 }

 template <typename T>
 void PoolManager<T>::Release(T pc) {
   USE(pc);
   if (--monitor_ == 0) {
     // Ensure the pool has not been blocked for too long.
     VIXL_ASSERT(pc <= checkpoint_);
   }
 }

 template <typename T>
 PoolManager<T>::~PoolManager<T>() VIXL_NEGATIVE_TESTING_ALLOW_EXCEPTION {
 #ifdef VIXL_DEBUG
   // Check for unbound objects.
   for (objects_iter iter = objects_.begin(); iter != objects_.end(); ++iter) {
     // There should not be any bound objects left in the pool. For unbound
     // objects, we will check in the destructor of the object itself.
     VIXL_ASSERT(!(*iter).label_base_->IsBound());
   }
 #endif
   // Delete objects the pool manager owns.
   for (typename std::vector<LocationBase<T> *>::iterator
            iter = delete_on_destruction_.begin(),
            end = delete_on_destruction_.end();
        iter != end;
        ++iter) {
     delete *iter;
   }
 }

 template <typename T>
 int PoolManager<T>::GetPoolSizeForTest() const {
   // Iterate over objects and return their cumulative size. This does not take
   // any padding into account, just the size of the objects themselves.
   int size = 0;
   for (const_objects_iter iter = objects_.begin(); iter != objects_.end();
        ++iter) {
     size += (*iter).label_base_->GetPoolObjectSizeInBytes();
   }
   return size;
 }
 }

 #endif  // VIXL_POOL_MANAGER_IMPL_H_
	// Copyright 2017, VIXL authors
	// All rights reserved.
	//
	// Redistribution and use in source and binary forms, with or without
	// modification, are permitted provided that the following conditions are met:
	//
	// * Redistributions of source code must retain the above copyright notice,
	// this list of conditions and the following disclaimer.
	// * Redistributions in binary form must reproduce the above copyright notice,
	// this list of conditions and the following disclaimer in the documentation
	// and/or other materials provided with the distribution.
	// * Neither the name of ARM Limited nor the names of its contributors may be
	// used to endorse or promote products derived from this software without
	// specific prior written permission.
	//
	// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS CONTRIBUTORS "AS IS" AND
	// ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
	// WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
	// DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE
	// FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
	// DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
	// SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
	// CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
	// OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
	// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

	#ifndef VIXL_POOL_MANAGER_IMPL_H_
	#define VIXL_POOL_MANAGER_IMPL_H_

	#include "pool-manager.h"

	#include <algorithm>
	#include "assembler-base-vixl.h"

	namespace vixl {


	template <typename T>
	T PoolManager<T>::Emit(MacroAssemblerInterface* masm,
	T pc,
	int num_bytes,
	ForwardReference<T>* new_reference,
	LocationBase<T>* new_object,
	EmitOption option) {
	// Make sure that the buffer still has the alignment we think it does.
	VIXL_ASSERT(IsAligned(masm->AsAssemblerBase()
	->GetBuffer()
	->GetStartAddress<uintptr_t>(),
	buffer_alignment_));

	// We should not call this method when the pools are blocked.
	VIXL_ASSERT(!IsBlocked());
	if (objects_.empty()) return pc;

	// Emit header.
	if (option == kBranchRequired) {
	masm->EmitPoolHeader();
	// TODO: The pc at this point might not actually be aligned according to
	// alignment_. This is to support the current AARCH32 MacroAssembler which
	// does not have a fixed size instruction set. In practice, the pc will be
	// aligned to the alignment instructions need for the current instruction
	// set, so we do not need to align it here. All other calculations do take
	// the alignment into account, which only makes the checkpoint calculations
	// more conservative when we use T32. Uncomment the following assertion if
	// the AARCH32 MacroAssembler is modified to only support one ISA at the
	// time.
	// VIXL_ASSERT(pc == AlignUp(pc, alignment_));
	pc += header_size_;
	} else {
	// If the header is optional, we might need to add some extra padding to
	// meet the minimum location of the first object.
	if (pc < objects_[0].min_location_) {
	int32_t padding = objects_[0].min_location_ - pc;
	masm->EmitNopBytes(padding);
	pc += padding;
	}
	}

	PoolObject<T>* existing_object = GetObjectIfTracked(new_object);

	// Go through all objects and emit one by one.
	for (objects_iter iter = objects_.begin(); iter != objects_.end();) {
	PoolObject<T>& current = *iter;
	if (ShouldSkipObject(&current,
	pc,
	num_bytes,
	new_reference,
	new_object,
	existing_object)) {
	++iter;
	continue;
	}
	LocationBase<T>* label_base = current.label_base_;
	T aligned_pc = AlignUp(pc, current.alignment_);
	masm->EmitPaddingBytes(aligned_pc - pc);
	pc = aligned_pc;
	VIXL_ASSERT(pc >= current.min_location_);
	VIXL_ASSERT(pc <= current.max_location_);
	// First call SetLocation, which will also resolve the references, and then
	// call EmitPoolObject, which might add a new reference.
	label_base->SetLocation(masm->AsAssemblerBase(), pc);
	label_base->EmitPoolObject(masm);
	int object_size = label_base->GetPoolObjectSizeInBytes();
	if (label_base->ShouldDeletePoolObjectOnPlacement()) {
	label_base->MarkBound();
	iter = RemoveAndDelete(iter);
	} else {
	VIXL_ASSERT(!current.label_base_->ShouldDeletePoolObjectOnPlacement());
	current.label_base_->UpdatePoolObject(&current);
	VIXL_ASSERT(current.alignment_ >= label_base->GetPoolObjectAlignment());
	++iter;
	}
	pc += object_size;
	}

	// Recalculate the checkpoint before emitting the footer. The footer might
	// call Bind() which will check if we need to emit.
	RecalculateCheckpoint();

	// Always emit footer - this might add some padding.
	masm->EmitPoolFooter();
	pc = AlignUp(pc, alignment_);

	return pc;
	}

	template <typename T>
	bool PoolManager<T>::ShouldSkipObject(PoolObject<T>* pool_object,
	T pc,
	int num_bytes,
	ForwardReference<T>* new_reference,
	LocationBase<T>* new_object,
	PoolObject<T>* existing_object) const {
	// We assume that all objects before this have been skipped and all objects
	// after this will be emitted, therefore we will emit the whole pool. Add
	// the header size and alignment, as well as the number of bytes we are
	// planning to emit.
	T max_actual_location = pc + num_bytes + max_pool_size_;

	if (new_reference != NULL) {
	// If we're adding a new object, also assume that it will have to be emitted
	// before the object we are considering to skip.
	VIXL_ASSERT(new_object != NULL);
	T new_object_alignment = std::max(new_reference->object_alignment_,
	new_object->GetPoolObjectAlignment());
	if ((existing_object != NULL) &&
	(existing_object->alignment_ > new_object_alignment)) {
	new_object_alignment = existing_object->alignment_;
	}
	max_actual_location +=
	(new_object->GetPoolObjectSizeInBytes() + new_object_alignment - 1);
	}

	// Hard limit.
	if (max_actual_location >= pool_object->max_location_) return false;

	// Use heuristic.
	return (pc < pool_object->skip_until_location_hint_);
	}

	template <typename T>
	T PoolManager<T>::UpdateCheckpointForObject(T checkpoint,
	const PoolObject<T>* object) {
	checkpoint -= object->label_base_->GetPoolObjectSizeInBytes();
	if (checkpoint > object->max_location_) checkpoint = object->max_location_;
	checkpoint = AlignDown(checkpoint, object->alignment_);
	return checkpoint;
	}

	template <typename T>
	static T MaxCheckpoint() {
	return std::numeric_limits<T>::max();
	}

	template <typename T>
	static inline bool CheckCurrentPC(T pc, T checkpoint) {
	VIXL_ASSERT(pc <= checkpoint);
	// We must emit the pools if we are at the checkpoint now.
	return pc == checkpoint;
	}

	template <typename T>
	static inline bool CheckFuturePC(T pc, T checkpoint) {
	// We do not need to emit the pools now if the projected future PC will be
	// equal to the checkpoint (we will need to emit the pools then).
	return pc > checkpoint;
	}

	template <typename T>
	bool PoolManager<T>::MustEmit(T pc,
	int num_bytes,
	ForwardReference<T>* reference,
	LocationBase<T>* label_base) const {
	// Check if we are at or past the checkpoint.
	if (CheckCurrentPC(pc, checkpoint_)) return true;

	// Check if the future PC will be past the checkpoint.
	pc += num_bytes;
	if (CheckFuturePC(pc, checkpoint_)) return true;

	// No new reference - nothing to do.
	if (reference == NULL) {
	VIXL_ASSERT(label_base == NULL);
	return false;
	}

	if (objects_.empty()) {
	// Basic assertions that restrictions on the new (and only) reference are
	// possible to satisfy.
	VIXL_ASSERT(AlignUp(pc + header_size_, alignment_) >=
	reference->min_object_location_);
	VIXL_ASSERT(pc <= reference->max_object_location_);
	return false;
	}

	// Check if the object is already being tracked.
	const PoolObject<T>* existing_object = GetObjectIfTracked(label_base);
	if (existing_object != NULL) {
	// If the existing_object is already in existing_objects_ and its new
	// alignment and new location restrictions are not stricter, skip the more
	// expensive check.
	if ((reference->min_object_location_ <= existing_object->min_location_) &&
	(reference->max_object_location_ >= existing_object->max_location_) &&
	(reference->object_alignment_ <= existing_object->alignment_)) {
	return false;
	}
	}

	// Create a temporary object.
	PoolObject<T> temp(label_base);
	temp.RestrictRange(reference->min_object_location_,
	reference->max_object_location_);
	temp.RestrictAlignment(reference->object_alignment_);
	if (existing_object != NULL) {
	temp.RestrictRange(existing_object->min_location_,
	existing_object->max_location_);
	temp.RestrictAlignment(existing_object->alignment_);
	}

	// Check if the new reference can be added after the end of the current pool.
	// If yes, we don't need to emit.
	T last_reachable = AlignDown(temp.max_location_, temp.alignment_);
	const PoolObject<T>& last = objects_.back();
	T after_pool = AlignDown(last.max_location_, last.alignment_) +
	last.label_base_->GetPoolObjectSizeInBytes();
	// The current object can be placed at the end of the pool, even if the last
	// object is placed at the last possible location.
	if (last_reachable >= after_pool) return false;
	// The current object can be placed after the code we are about to emit and
	// after the existing pool (with a pessimistic size estimate).
	if (last_reachable >= pc + num_bytes + max_pool_size_) return false;

	// We're not in a trivial case, so we need to recalculate the checkpoint.

	// Check (conservatively) if we can fit it into the objects_ array, without
	// breaking our assumptions. Here we want to recalculate the checkpoint as
	// if the new reference was added to the PoolManager but without actually
	// adding it (as removing it is non-trivial).

	T checkpoint = MaxCheckpoint<T>();
	// Will temp be the last object in objects_?
	if (PoolObjectLessThan(last, temp)) {
	checkpoint = UpdateCheckpointForObject(checkpoint, &temp);
	if (checkpoint < temp.min_location_) return true;
	}

	bool tempNotPlacedYet = true;
	for (int i = static_cast<int>(objects_.size()) - 1; i >= 0; --i) {
	const PoolObject<T>& current = objects_[i];
	if (tempNotPlacedYet && PoolObjectLessThan(current, temp)) {
	checkpoint = UpdateCheckpointForObject(checkpoint, &temp);
	if (checkpoint < temp.min_location_) return true;
	if (CheckFuturePC(pc, checkpoint)) return true;
	tempNotPlacedYet = false;
	}
	if (current.label_base_ == label_base) continue;
	checkpoint = UpdateCheckpointForObject(checkpoint, &current);
	if (checkpoint < current.min_location_) return true;
	if (CheckFuturePC(pc, checkpoint)) return true;
	}
	// temp is the object with the smallest max_location_.
	if (tempNotPlacedYet) {
	checkpoint = UpdateCheckpointForObject(checkpoint, &temp);
	if (checkpoint < temp.min_location_) return true;
	}

	// Take the header into account.
	checkpoint -= header_size_;
	checkpoint = AlignDown(checkpoint, alignment_);

	return CheckFuturePC(pc, checkpoint);
	}

	template <typename T>
	void PoolManager<T>::RecalculateCheckpoint(SortOption sort_option) {
	// TODO: Improve the max_pool_size_ estimate by starting from the
	// min_location_ of the first object, calculating the end of the pool as if
	// all objects were placed starting from there, and in the end adding the
	// maximum object alignment found minus one (which is the maximum extra
	// padding we would need if we were to relocate the pool to a different
	// address).
	max_pool_size_ = 0;

	if (objects_.empty()) {
	checkpoint_ = MaxCheckpoint<T>();
	return;
	}

	// Sort objects by their max_location_.
	if (sort_option == kSortRequired) {
	std::sort(objects_.begin(), objects_.end(), PoolObjectLessThan);
	}

	// Add the header size and header and footer max alignment to the maximum
	// pool size.
	max_pool_size_ += header_size_ + 2 * (alignment_ - 1);

	T checkpoint = MaxCheckpoint<T>();
	int last_object_index = static_cast<int>(objects_.size()) - 1;
	for (int i = last_object_index; i >= 0; --i) {
	// Bring back the checkpoint by the size of the current object, unless
	// we need to bring it back more, then align.
	PoolObject<T>& current = objects_[i];
	checkpoint = UpdateCheckpointForObject(checkpoint, &current);
	VIXL_ASSERT(checkpoint >= current.min_location_);
	max_pool_size_ += (current.alignment_ - 1 +
	current.label_base_->GetPoolObjectSizeInBytes());
	}
	// Take the header into account.
	checkpoint -= header_size_;
	checkpoint = AlignDown(checkpoint, alignment_);

	// Update the checkpoint of the pool manager.
	checkpoint_ = checkpoint;

	// NOTE: To handle min_location_ in the generic case, we could make a second
	// pass of the objects_ vector, increasing the checkpoint as needed, while
	// maintaining the alignment requirements.
	// It should not be possible to have any issues with min_location_ with actual
	// code, since there should always be some kind of branch over the pool,
	// whether introduced by the pool emission or by the user, which will make
	// sure the min_location_ requirement is satisfied. It's possible that the
	// user could emit code in the literal pool and intentionally load the first
	// value and then fall-through into the pool, but that is not a supported use
	// of VIXL and we will assert in that case.
	}

	template <typename T>
	bool PoolManager<T>::PoolObjectLessThan(const PoolObject<T>& a,
	const PoolObject<T>& b) {
	if (a.max_location_ != b.max_location_)
	return (a.max_location_ < b.max_location_);
	int a_size = a.label_base_->GetPoolObjectSizeInBytes();
	int b_size = b.label_base_->GetPoolObjectSizeInBytes();
	if (a_size != b_size) return (a_size < b_size);
	if (a.alignment_ != b.alignment_) return (a.alignment_ < b.alignment_);
	if (a.min_location_ != b.min_location_)
	return (a.min_location_ < b.min_location_);
	return false;
	}

	template <typename T>
	void PoolManager<T>::AddObjectReference(const ForwardReference<T>* reference,
	LocationBase<T>* label_base) {
	VIXL_ASSERT(reference->object_alignment_ <= buffer_alignment_);
	VIXL_ASSERT(label_base->GetPoolObjectAlignment() <= buffer_alignment_);

	PoolObject<T>* object = GetObjectIfTracked(label_base);

	if (object == NULL) {
	PoolObject<T> new_object(label_base);
	new_object.RestrictRange(reference->min_object_location_,
	reference->max_object_location_);
	new_object.RestrictAlignment(reference->object_alignment_);
	Insert(new_object);
	} else {
	object->RestrictRange(reference->min_object_location_,
	reference->max_object_location_);
	object->RestrictAlignment(reference->object_alignment_);

	// Move the object, if needed.
	if (objects_.size() != 1) {
	PoolObject<T> new_object(*object);
	ptrdiff_t distance = std::distance(objects_.data(), object);
	objects_.erase(objects_.begin() + distance);
	Insert(new_object);
	}
	}
	// No need to sort, we inserted the object in an already sorted array.
	RecalculateCheckpoint(kNoSortRequired);
	}

	template <typename T>
	void PoolManager<T>::Insert(const PoolObject<T>& new_object) {
	bool inserted = false;
	// Place the object in the right position.
	for (objects_iter iter = objects_.begin(); iter != objects_.end(); ++iter) {
	PoolObject<T>& current = *iter;
	if (!PoolObjectLessThan(current, new_object)) {
	objects_.insert(iter, new_object);
	inserted = true;
	break;
	}
	}
	if (!inserted) {
	objects_.push_back(new_object);
	}
	}

	template <typename T>
	void PoolManager<T>::RemoveAndDelete(PoolObject<T>* object) {
	for (objects_iter iter = objects_.begin(); iter != objects_.end(); ++iter) {
	PoolObject<T>& current = *iter;
	if (current.label_base_ == object->label_base_) {
	(void)RemoveAndDelete(iter);
	return;
	}
	}
	VIXL_UNREACHABLE();
	}

	template <typename T>
	typename PoolManager<T>::objects_iter PoolManager<T>::RemoveAndDelete(
	objects_iter iter) {
	PoolObject<T>& object = *iter;
	LocationBase<T>* label_base = object.label_base_;

	// Check if we also need to delete the LocationBase object.
	if (label_base->ShouldBeDeletedOnPoolManagerDestruction()) {
	delete_on_destruction_.push_back(label_base);
	}
	if (label_base->ShouldBeDeletedOnPlacementByPoolManager()) {
	VIXL_ASSERT(!label_base->ShouldBeDeletedOnPoolManagerDestruction());
	delete label_base;
	}

	return objects_.erase(iter);
	}

	template <typename T>
	T PoolManager<T>::Bind(MacroAssemblerInterface* masm,
	LocationBase<T>* object,
	T location) {
	PoolObject<T>* existing_object = GetObjectIfTracked(object);
	int alignment;
	T min_location;
	if (existing_object == NULL) {
	alignment = object->GetMaxAlignment();
	min_location = object->GetMinLocation();
	} else {
	alignment = existing_object->alignment_;
	min_location = existing_object->min_location_;
	}

	// Align if needed, and add necessary padding to reach the min_location_.
	T aligned_location = AlignUp(location, alignment);
	masm->EmitNopBytes(aligned_location - location);
	location = aligned_location;
	while (location < min_location) {
	masm->EmitNopBytes(alignment);
	location += alignment;
	}

	object->SetLocation(masm->AsAssemblerBase(), location);
	object->MarkBound();

	if (existing_object != NULL) {
	RemoveAndDelete(existing_object);
	// No need to sort, we removed the object from a sorted array.
	RecalculateCheckpoint(kNoSortRequired);
	}

	// We assume that the maximum padding we can possibly add here is less
	// than the header alignment - hence that we're not going to go past our
	// checkpoint.
	VIXL_ASSERT(!CheckFuturePC(location, checkpoint_));
	return location;
	}

	template <typename T>
	void PoolManager<T>::Release(T pc) {
	USE(pc);
	if (--monitor_ == 0) {
	// Ensure the pool has not been blocked for too long.
	VIXL_ASSERT(pc <= checkpoint_);
	}
	}

	template <typename T>
	PoolManager<T>::~PoolManager<T>() VIXL_NEGATIVE_TESTING_ALLOW_EXCEPTION {
	#ifdef VIXL_DEBUG
	// Check for unbound objects.
	for (objects_iter iter = objects_.begin(); iter != objects_.end(); ++iter) {
	// There should not be any bound objects left in the pool. For unbound
	// objects, we will check in the destructor of the object itself.
	VIXL_ASSERT(!(*iter).label_base_->IsBound());
	}
	#endif
	// Delete objects the pool manager owns.
	for (typename std::vector<LocationBase<T> *>::iterator
	iter = delete_on_destruction_.begin(),
	end = delete_on_destruction_.end();
	iter != end;
	++iter) {
	delete *iter;
	}
	}

	template <typename T>
	int PoolManager<T>::GetPoolSizeForTest() const {
	// Iterate over objects and return their cumulative size. This does not take
	// any padding into account, just the size of the objects themselves.
	int size = 0;
	for (const_objects_iter iter = objects_.begin(); iter != objects_.end();
	++iter) {
	size += (*iter).label_base_->GetPoolObjectSizeInBytes();
	}
	return size;
	}
	}

	#endif // VIXL_POOL_MANAGER_IMPL_H_