third_party/v8/src/compiler/backend/gap-resolver.cc - cobalt - Git at Google

 // Copyright 2014 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/compiler/backend/gap-resolver.h"

 #include <algorithm>
 #include <set>

 #include "src/base/enum-set.h"
 #include "src/codegen/register-configuration.h"

 namespace v8 {
 namespace internal {
 namespace compiler {

 namespace {

 // Splits a FP move between two location operands into the equivalent series of
 // moves between smaller sub-operands, e.g. a double move to two single moves.
 // This helps reduce the number of cycles that would normally occur under FP
 // aliasing, and makes swaps much easier to implement.
 MoveOperands* Split(MoveOperands* move, MachineRepresentation smaller_rep,
                     ParallelMove* moves) {
   DCHECK(!kSimpleFPAliasing);
   // Splitting is only possible when the slot size is the same as float size.
   DCHECK_EQ(kSystemPointerSize, kFloatSize);
   const LocationOperand& src_loc = LocationOperand::cast(move->source());
   const LocationOperand& dst_loc = LocationOperand::cast(move->destination());
   MachineRepresentation dst_rep = dst_loc.representation();
   DCHECK_NE(smaller_rep, dst_rep);
   auto src_kind = src_loc.location_kind();
   auto dst_kind = dst_loc.location_kind();

   int aliases =
       1 << (ElementSizeLog2Of(dst_rep) - ElementSizeLog2Of(smaller_rep));
   int base = -1;
   USE(base);
   DCHECK_EQ(aliases, RegisterConfiguration::Default()->GetAliases(
                          dst_rep, 0, smaller_rep, &base));

   int src_index = -1;
   int slot_size = (1 << ElementSizeLog2Of(smaller_rep)) / kSystemPointerSize;
   int src_step = 1;
   if (src_kind == LocationOperand::REGISTER) {
     src_index = src_loc.register_code() * aliases;
   } else {
     src_index = src_loc.index();
     // For operands that occupy multiple slots, the index refers to the last
     // slot. On little-endian architectures, we start at the high slot and use a
     // negative step so that register-to-slot moves are in the correct order.
     src_step = -slot_size;
   }
   int dst_index = -1;
   int dst_step = 1;
   if (dst_kind == LocationOperand::REGISTER) {
     dst_index = dst_loc.register_code() * aliases;
   } else {
     dst_index = dst_loc.index();
     dst_step = -slot_size;
   }

   // Reuse 'move' for the first fragment. It is not pending.
   move->set_source(AllocatedOperand(src_kind, smaller_rep, src_index));
   move->set_destination(AllocatedOperand(dst_kind, smaller_rep, dst_index));
   // Add the remaining fragment moves.
   for (int i = 1; i < aliases; ++i) {
     src_index += src_step;
     dst_index += dst_step;
     moves->AddMove(AllocatedOperand(src_kind, smaller_rep, src_index),
                    AllocatedOperand(dst_kind, smaller_rep, dst_index));
   }
   // Return the first fragment.
   return move;
 }

 enum MoveOperandKind : uint8_t { kConstant, kGpReg, kFpReg, kStack };

 MoveOperandKind GetKind(const InstructionOperand& move) {
   if (move.IsConstant()) return kConstant;
   LocationOperand loc_op = LocationOperand::cast(move);
   if (loc_op.location_kind() != LocationOperand::REGISTER) return kStack;
   return IsFloatingPoint(loc_op.representation()) ? kFpReg : kGpReg;
 }

 }  // namespace

 void GapResolver::Resolve(ParallelMove* moves) {
   base::EnumSet<MoveOperandKind, uint8_t> source_kinds;
   base::EnumSet<MoveOperandKind, uint8_t> destination_kinds;

   // Remove redundant moves, collect source kinds and destination kinds to
   // detect simple non-overlapping moves, and collect FP move representations if
   // aliasing is non-simple.
   int fp_reps = 0;
   size_t nmoves = moves->size();
   for (size_t i = 0; i < nmoves;) {
     MoveOperands* move = (*moves)[i];
     if (move->IsRedundant()) {
       nmoves--;
       if (i < nmoves) (*moves)[i] = (*moves)[nmoves];
       continue;
     }
     i++;
     source_kinds.Add(GetKind(move->source()));
     destination_kinds.Add(GetKind(move->destination()));
     if (!kSimpleFPAliasing && move->destination().IsFPRegister()) {
       fp_reps |= RepresentationBit(
           LocationOperand::cast(move->destination()).representation());
     }
   }
   if (nmoves != moves->size()) moves->resize(nmoves);

   if ((source_kinds & destination_kinds).empty() || moves->size() < 2) {
     // Fast path for non-conflicting parallel moves.
     for (MoveOperands* move : *moves) {
       assembler_->AssembleMove(&move->source(), &move->destination());
     }
     return;
   }

   if (!kSimpleFPAliasing) {
     if (fp_reps && !base::bits::IsPowerOfTwo(fp_reps)) {
       // Start with the smallest FP moves, so we never encounter smaller moves
       // in the middle of a cycle of larger moves.
       if ((fp_reps & RepresentationBit(MachineRepresentation::kFloat32)) != 0) {
         split_rep_ = MachineRepresentation::kFloat32;
         for (size_t i = 0; i < moves->size(); ++i) {
           auto move = (*moves)[i];
           if (!move->IsEliminated() && move->destination().IsFloatRegister())
             PerformMove(moves, move);
         }
       }
       if ((fp_reps & RepresentationBit(MachineRepresentation::kFloat64)) != 0) {
         split_rep_ = MachineRepresentation::kFloat64;
         for (size_t i = 0; i < moves->size(); ++i) {
           auto move = (*moves)[i];
           if (!move->IsEliminated() && move->destination().IsDoubleRegister())
             PerformMove(moves, move);
         }
       }
     }
     split_rep_ = MachineRepresentation::kSimd128;
   }

   for (size_t i = 0; i < moves->size(); ++i) {
     auto move = (*moves)[i];
     if (!move->IsEliminated()) PerformMove(moves, move);
   }
 }

 void GapResolver::PerformMove(ParallelMove* moves, MoveOperands* move) {
   // Each call to this function performs a move and deletes it from the move
   // graph.  We first recursively perform any move blocking this one.  We mark a
   // move as "pending" on entry to PerformMove in order to detect cycles in the
   // move graph.  We use operand swaps to resolve cycles, which means that a
   // call to PerformMove could change any source operand in the move graph.
   DCHECK(!move->IsPending());
   DCHECK(!move->IsRedundant());

   // Clear this move's destination to indicate a pending move.  The actual
   // destination is saved on the side.
   InstructionOperand source = move->source();
   DCHECK(!source.IsInvalid());  // Or else it will look eliminated.
   InstructionOperand destination = move->destination();
   move->SetPending();

   // We may need to split moves between FP locations differently.
   const bool is_fp_loc_move =
       !kSimpleFPAliasing && destination.IsFPLocationOperand();

   // Perform a depth-first traversal of the move graph to resolve dependencies.
   // Any unperformed, unpending move with a source the same as this one's
   // destination blocks this one so recursively perform all such moves.
   for (size_t i = 0; i < moves->size(); ++i) {
     auto other = (*moves)[i];
     if (other->IsEliminated()) continue;
     if (other->IsPending()) continue;
     if (other->source().InterferesWith(destination)) {
       if (is_fp_loc_move &&
           LocationOperand::cast(other->source()).representation() >
               split_rep_) {
         // 'other' must also be an FP location move. Break it into fragments
         // of the same size as 'move'. 'other' is set to one of the fragments,
         // and the rest are appended to 'moves'.
         other = Split(other, split_rep_, moves);
         // 'other' may not block destination now.
         if (!other->source().InterferesWith(destination)) continue;
       }
       // Though PerformMove can change any source operand in the move graph,
       // this call cannot create a blocking move via a swap (this loop does not
       // miss any).  Assume there is a non-blocking move with source A and this
       // move is blocked on source B and there is a swap of A and B.  Then A and
       // B must be involved in the same cycle (or they would not be swapped).
       // Since this move's destination is B and there is only a single incoming
       // edge to an operand, this move must also be involved in the same cycle.
       // In that case, the blocking move will be created but will be "pending"
       // when we return from PerformMove.
       PerformMove(moves, other);
     }
   }

   // This move's source may have changed due to swaps to resolve cycles and so
   // it may now be the last move in the cycle.  If so remove it.
   source = move->source();
   if (source.EqualsCanonicalized(destination)) {
     move->Eliminate();
     return;
   }

   // We are about to resolve this move and don't need it marked as pending, so
   // restore its destination.
   move->set_destination(destination);

   // The move may be blocked on a (at most one) pending move, in which case we
   // have a cycle.  Search for such a blocking move and perform a swap to
   // resolve it.
   auto blocker =
       std::find_if(moves->begin(), moves->end(), [&](MoveOperands* move) {
         return !move->IsEliminated() &&
                move->source().InterferesWith(destination);
       });
   if (blocker == moves->end()) {
     // The easy case: This move is not blocked.
     assembler_->AssembleMove(&source, &destination);
     move->Eliminate();
     return;
   }

   // Ensure source is a register or both are stack slots, to limit swap cases.
   if (source.IsStackSlot() || source.IsFPStackSlot()) {
     std::swap(source, destination);
   }
   assembler_->AssembleSwap(&source, &destination);
   move->Eliminate();

   // Update outstanding moves whose source may now have been moved.
   if (is_fp_loc_move) {
     // We may have to split larger moves.
     for (size_t i = 0; i < moves->size(); ++i) {
       auto other = (*moves)[i];
       if (other->IsEliminated()) continue;
       if (source.InterferesWith(other->source())) {
         if (LocationOperand::cast(other->source()).representation() >
             split_rep_) {
           other = Split(other, split_rep_, moves);
           if (!source.InterferesWith(other->source())) continue;
         }
         other->set_source(destination);
       } else if (destination.InterferesWith(other->source())) {
         if (LocationOperand::cast(other->source()).representation() >
             split_rep_) {
           other = Split(other, split_rep_, moves);
           if (!destination.InterferesWith(other->source())) continue;
         }
         other->set_source(source);
       }
     }
   } else {
     for (auto other : *moves) {
       if (other->IsEliminated()) continue;
       if (source.EqualsCanonicalized(other->source())) {
         other->set_source(destination);
       } else if (destination.EqualsCanonicalized(other->source())) {
         other->set_source(source);
       }
     }
   }
 }
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
	// Copyright 2014 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/compiler/backend/gap-resolver.h"

	#include <algorithm>
	#include <set>

	#include "src/base/enum-set.h"
	#include "src/codegen/register-configuration.h"

	namespace v8 {
	namespace internal {
	namespace compiler {

	namespace {

	// Splits a FP move between two location operands into the equivalent series of
	// moves between smaller sub-operands, e.g. a double move to two single moves.
	// This helps reduce the number of cycles that would normally occur under FP
	// aliasing, and makes swaps much easier to implement.
	MoveOperands* Split(MoveOperands* move, MachineRepresentation smaller_rep,
	ParallelMove* moves) {
	DCHECK(!kSimpleFPAliasing);
	// Splitting is only possible when the slot size is the same as float size.
	DCHECK_EQ(kSystemPointerSize, kFloatSize);
	const LocationOperand& src_loc = LocationOperand::cast(move->source());
	const LocationOperand& dst_loc = LocationOperand::cast(move->destination());
	MachineRepresentation dst_rep = dst_loc.representation();
	DCHECK_NE(smaller_rep, dst_rep);
	auto src_kind = src_loc.location_kind();
	auto dst_kind = dst_loc.location_kind();

	int aliases =
	1 << (ElementSizeLog2Of(dst_rep) - ElementSizeLog2Of(smaller_rep));
	int base = -1;
	USE(base);
	DCHECK_EQ(aliases, RegisterConfiguration::Default()->GetAliases(
	dst_rep, 0, smaller_rep, &base));

	int src_index = -1;
	int slot_size = (1 << ElementSizeLog2Of(smaller_rep)) / kSystemPointerSize;
	int src_step = 1;
	if (src_kind == LocationOperand::REGISTER) {
	src_index = src_loc.register_code() * aliases;
	} else {
	src_index = src_loc.index();
	// For operands that occupy multiple slots, the index refers to the last
	// slot. On little-endian architectures, we start at the high slot and use a
	// negative step so that register-to-slot moves are in the correct order.
	src_step = -slot_size;
	}
	int dst_index = -1;
	int dst_step = 1;
	if (dst_kind == LocationOperand::REGISTER) {
	dst_index = dst_loc.register_code() * aliases;
	} else {
	dst_index = dst_loc.index();
	dst_step = -slot_size;
	}

	// Reuse 'move' for the first fragment. It is not pending.
	move->set_source(AllocatedOperand(src_kind, smaller_rep, src_index));
	move->set_destination(AllocatedOperand(dst_kind, smaller_rep, dst_index));
	// Add the remaining fragment moves.
	for (int i = 1; i < aliases; ++i) {
	src_index += src_step;
	dst_index += dst_step;
	moves->AddMove(AllocatedOperand(src_kind, smaller_rep, src_index),
	AllocatedOperand(dst_kind, smaller_rep, dst_index));
	}
	// Return the first fragment.
	return move;
	}

	enum MoveOperandKind : uint8_t { kConstant, kGpReg, kFpReg, kStack };

	MoveOperandKind GetKind(const InstructionOperand& move) {
	if (move.IsConstant()) return kConstant;
	LocationOperand loc_op = LocationOperand::cast(move);
	if (loc_op.location_kind() != LocationOperand::REGISTER) return kStack;
	return IsFloatingPoint(loc_op.representation()) ? kFpReg : kGpReg;
	}

	} // namespace

	void GapResolver::Resolve(ParallelMove* moves) {
	base::EnumSet<MoveOperandKind, uint8_t> source_kinds;
	base::EnumSet<MoveOperandKind, uint8_t> destination_kinds;

	// Remove redundant moves, collect source kinds and destination kinds to
	// detect simple non-overlapping moves, and collect FP move representations if
	// aliasing is non-simple.
	int fp_reps = 0;
	size_t nmoves = moves->size();
	for (size_t i = 0; i < nmoves;) {
	MoveOperands* move = (*moves)[i];
	if (move->IsRedundant()) {
	nmoves--;
	if (i < nmoves) (moves)[i] = (moves)[nmoves];
	continue;
	}
	i++;
	source_kinds.Add(GetKind(move->source()));
	destination_kinds.Add(GetKind(move->destination()));
	if (!kSimpleFPAliasing && move->destination().IsFPRegister()) {
	fp_reps \|= RepresentationBit(
	LocationOperand::cast(move->destination()).representation());
	}
	}
	if (nmoves != moves->size()) moves->resize(nmoves);

	if ((source_kinds & destination_kinds).empty() \|\| moves->size() < 2) {
	// Fast path for non-conflicting parallel moves.
	for (MoveOperands* move : *moves) {
	assembler_->AssembleMove(&move->source(), &move->destination());
	}
	return;
	}

	if (!kSimpleFPAliasing) {
	if (fp_reps && !base::bits::IsPowerOfTwo(fp_reps)) {
	// Start with the smallest FP moves, so we never encounter smaller moves
	// in the middle of a cycle of larger moves.
	if ((fp_reps & RepresentationBit(MachineRepresentation::kFloat32)) != 0) {
	split_rep_ = MachineRepresentation::kFloat32;
	for (size_t i = 0; i < moves->size(); ++i) {
	auto move = (*moves)[i];
	if (!move->IsEliminated() && move->destination().IsFloatRegister())
	PerformMove(moves, move);
	}
	}
	if ((fp_reps & RepresentationBit(MachineRepresentation::kFloat64)) != 0) {
	split_rep_ = MachineRepresentation::kFloat64;
	for (size_t i = 0; i < moves->size(); ++i) {
	auto move = (*moves)[i];
	if (!move->IsEliminated() && move->destination().IsDoubleRegister())
	PerformMove(moves, move);
	}
	}
	}
	split_rep_ = MachineRepresentation::kSimd128;
	}

	for (size_t i = 0; i < moves->size(); ++i) {
	auto move = (*moves)[i];
	if (!move->IsEliminated()) PerformMove(moves, move);
	}
	}

	void GapResolver::PerformMove(ParallelMove* moves, MoveOperands* move) {
	// Each call to this function performs a move and deletes it from the move
	// graph. We first recursively perform any move blocking this one. We mark a
	// move as "pending" on entry to PerformMove in order to detect cycles in the
	// move graph. We use operand swaps to resolve cycles, which means that a
	// call to PerformMove could change any source operand in the move graph.
	DCHECK(!move->IsPending());
	DCHECK(!move->IsRedundant());

	// Clear this move's destination to indicate a pending move. The actual
	// destination is saved on the side.
	InstructionOperand source = move->source();
	DCHECK(!source.IsInvalid()); // Or else it will look eliminated.
	InstructionOperand destination = move->destination();
	move->SetPending();

	// We may need to split moves between FP locations differently.
	const bool is_fp_loc_move =
	!kSimpleFPAliasing && destination.IsFPLocationOperand();

	// Perform a depth-first traversal of the move graph to resolve dependencies.
	// Any unperformed, unpending move with a source the same as this one's
	// destination blocks this one so recursively perform all such moves.
	for (size_t i = 0; i < moves->size(); ++i) {
	auto other = (*moves)[i];
	if (other->IsEliminated()) continue;
	if (other->IsPending()) continue;
	if (other->source().InterferesWith(destination)) {
	if (is_fp_loc_move &&
	LocationOperand::cast(other->source()).representation() >
	split_rep_) {
	// 'other' must also be an FP location move. Break it into fragments
	// of the same size as 'move'. 'other' is set to one of the fragments,
	// and the rest are appended to 'moves'.
	other = Split(other, split_rep_, moves);
	// 'other' may not block destination now.
	if (!other->source().InterferesWith(destination)) continue;
	}
	// Though PerformMove can change any source operand in the move graph,
	// this call cannot create a blocking move via a swap (this loop does not
	// miss any). Assume there is a non-blocking move with source A and this
	// move is blocked on source B and there is a swap of A and B. Then A and
	// B must be involved in the same cycle (or they would not be swapped).
	// Since this move's destination is B and there is only a single incoming
	// edge to an operand, this move must also be involved in the same cycle.
	// In that case, the blocking move will be created but will be "pending"
	// when we return from PerformMove.
	PerformMove(moves, other);
	}
	}

	// This move's source may have changed due to swaps to resolve cycles and so
	// it may now be the last move in the cycle. If so remove it.
	source = move->source();
	if (source.EqualsCanonicalized(destination)) {
	move->Eliminate();
	return;
	}

	// We are about to resolve this move and don't need it marked as pending, so
	// restore its destination.
	move->set_destination(destination);

	// The move may be blocked on a (at most one) pending move, in which case we
	// have a cycle. Search for such a blocking move and perform a swap to
	// resolve it.
	auto blocker =
	std::find_if(moves->begin(), moves->end(), [&](MoveOperands* move) {
	return !move->IsEliminated() &&
	move->source().InterferesWith(destination);
	});
	if (blocker == moves->end()) {
	// The easy case: This move is not blocked.
	assembler_->AssembleMove(&source, &destination);
	move->Eliminate();
	return;
	}

	// Ensure source is a register or both are stack slots, to limit swap cases.
	if (source.IsStackSlot() \|\| source.IsFPStackSlot()) {
	std::swap(source, destination);
	}
	assembler_->AssembleSwap(&source, &destination);
	move->Eliminate();

	// Update outstanding moves whose source may now have been moved.
	if (is_fp_loc_move) {
	// We may have to split larger moves.
	for (size_t i = 0; i < moves->size(); ++i) {
	auto other = (*moves)[i];
	if (other->IsEliminated()) continue;
	if (source.InterferesWith(other->source())) {
	if (LocationOperand::cast(other->source()).representation() >
	split_rep_) {
	other = Split(other, split_rep_, moves);
	if (!source.InterferesWith(other->source())) continue;
	}
	other->set_source(destination);
	} else if (destination.InterferesWith(other->source())) {
	if (LocationOperand::cast(other->source()).representation() >
	split_rep_) {
	other = Split(other, split_rep_, moves);
	if (!destination.InterferesWith(other->source())) continue;
	}
	other->set_source(source);
	}
	}
	} else {
	for (auto other : *moves) {
	if (other->IsEliminated()) continue;
	if (source.EqualsCanonicalized(other->source())) {
	other->set_source(destination);
	} else if (destination.EqualsCanonicalized(other->source())) {
	other->set_source(source);
	}
	}
	}
	}
	} // namespace compiler
	} // namespace internal
	} // namespace v8