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// 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/instruction.h"
#include "src/zone/zone-containers.h"
namespace v8 {
namespace internal {
namespace compiler {
class InstructionBlock;
class InstructionSequence;
// The register allocator validator traverses instructions in the instruction
// sequence, and verifies the correctness of machine operand substitutions of
// virtual registers. It collects the virtual register instruction signatures
// before register allocation. Then, after the register allocation pipeline
// completes, it compares the operand substitutions against the pre-allocation
// data.
// At a high level, validation works as follows: we iterate through each block,
// and, in a block, through each instruction; then:
// - when an operand is the output of an instruction, we associate it to the
// virtual register that the instruction sequence declares as its output. We
// use the concept of "FinalAssessment" to model this.
// - when an operand is used in an instruction, we check that the assessment
// matches the expectation of the instruction
// - moves simply copy the assessment over to the new operand
// - blocks with more than one predecessor associate to each operand a "Pending"
// assessment. The pending assessment remembers the operand and block where it
// was created. Then, when the value is used (which may be as a different
// operand, because of moves), we check that the virtual register at the use
// site matches the definition of this pending operand: either the phi inputs
// match, or, if it's not a phi, all the predecessors at the point the pending
// assessment was defined have that operand assigned to the given virtual
// register. If all checks out, we record in the assessment that the virtual
// register is aliased by the specific operand.
// If a block is a loop header - so one or more of its predecessors are it or
// below - we still treat uses of operands as above, but we record which operand
// assessments haven't been made yet, and what virtual register they must
// correspond to, and verify that when we are done with the respective
// predecessor blocks.
// This way, the algorithm always makes a final decision about the operands
// in an instruction, ensuring convergence.
// Operand assessments are recorded per block, as the result at the exit from
// the block. When moving to a new block, we copy assessments from its single
// predecessor, or, if the block has multiple predecessors, the mechanism was
// described already.
enum AssessmentKind { Final, Pending };
class Assessment : public ZoneObject {
AssessmentKind kind() const { return kind_; }
explicit Assessment(AssessmentKind kind) : kind_(kind) {}
AssessmentKind kind_;
// PendingAssessments are associated to operands coming from the multiple
// predecessors of a block. We only record the operand and the block, and
// will determine if the way the operand is defined (from the predecessors)
// matches a particular use. We allow more than one vreg association with
// an operand - this handles scenarios where multiple phis are
// defined with identical operands, and the move optimizer moved down the moves
// separating the 2 phis in the block defining them.
class PendingAssessment final : public Assessment {
explicit PendingAssessment(Zone* zone, const InstructionBlock* origin,
InstructionOperand operand)
: Assessment(Pending),
aliases_(zone) {}
static const PendingAssessment* cast(const Assessment* assessment) {
CHECK(assessment->kind() == Pending);
return static_cast<const PendingAssessment*>(assessment);
static PendingAssessment* cast(Assessment* assessment) {
CHECK(assessment->kind() == Pending);
return static_cast<PendingAssessment*>(assessment);
const InstructionBlock* origin() const { return origin_; }
InstructionOperand operand() const { return operand_; }
bool IsAliasOf(int vreg) const { return aliases_.count(vreg) > 0; }
void AddAlias(int vreg) { aliases_.insert(vreg); }
const InstructionBlock* const origin_;
InstructionOperand operand_;
ZoneSet<int> aliases_;
// FinalAssessments are associated to operands that we know to be a certain
// virtual register.
class FinalAssessment final : public Assessment {
explicit FinalAssessment(int virtual_register)
: Assessment(Final), virtual_register_(virtual_register) {}
int virtual_register() const { return virtual_register_; }
static const FinalAssessment* cast(const Assessment* assessment) {
CHECK(assessment->kind() == Final);
return static_cast<const FinalAssessment*>(assessment);
int virtual_register_;
struct OperandAsKeyLess {
bool operator()(const InstructionOperand& a,
const InstructionOperand& b) const {
return a.CompareCanonicalized(b);
// Assessments associated with a basic block.
class BlockAssessments : public ZoneObject {
using OperandMap = ZoneMap<InstructionOperand, Assessment*, OperandAsKeyLess>;
explicit BlockAssessments(Zone* zone)
: map_(zone), map_for_moves_(zone), zone_(zone) {}
void Drop(InstructionOperand operand) { map_.erase(operand); }
void DropRegisters();
void AddDefinition(InstructionOperand operand, int virtual_register) {
auto existent = map_.find(operand);
if (existent != map_.end()) {
// Drop the assignment
std::make_pair(operand, new (zone_) FinalAssessment(virtual_register)));
void PerformMoves(const Instruction* instruction);
void PerformParallelMoves(const ParallelMove* moves);
void CopyFrom(const BlockAssessments* other) {
map_.insert(other->map_.begin(), other->map_.end());
OperandMap& map() { return map_; }
const OperandMap& map() const { return map_; }
void Print() const;
OperandMap map_;
OperandMap map_for_moves_;
Zone* zone_;
class RegisterAllocatorVerifier final : public ZoneObject {
RegisterAllocatorVerifier(Zone* zone, const RegisterConfiguration* config,
const InstructionSequence* sequence);
void VerifyAssignment(const char* caller_info);
void VerifyGapMoves();
enum ConstraintType {
struct OperandConstraint {
ConstraintType type_;
// Constant or immediate value, register code, slot index, or slot size
// when relevant.
int value_;
int spilled_slot_;
int virtual_register_;
struct InstructionConstraint {
const Instruction* instruction_;
size_t operand_constaints_size_;
OperandConstraint* operand_constraints_;
using Constraints = ZoneVector<InstructionConstraint>;
class DelayedAssessments : public ZoneObject {
explicit DelayedAssessments(Zone* zone) : map_(zone) {}
const ZoneMap<InstructionOperand, int, OperandAsKeyLess>& map() const {
return map_;
void AddDelayedAssessment(InstructionOperand op, int vreg) {
auto it = map_.find(op);
if (it == map_.end()) {
map_.insert(std::make_pair(op, vreg));
} else {
CHECK_EQ(it->second, vreg);
ZoneMap<InstructionOperand, int, OperandAsKeyLess> map_;
Zone* zone() const { return zone_; }
const RegisterConfiguration* config() { return config_; }
const InstructionSequence* sequence() const { return sequence_; }
Constraints* constraints() { return &constraints_; }
static void VerifyInput(const OperandConstraint& constraint);
static void VerifyTemp(const OperandConstraint& constraint);
static void VerifyOutput(const OperandConstraint& constraint);
void BuildConstraint(const InstructionOperand* op,
OperandConstraint* constraint);
void CheckConstraint(const InstructionOperand* op,
const OperandConstraint* constraint);
BlockAssessments* CreateForBlock(const InstructionBlock* block);
// Prove that this operand is an alias of this virtual register in the given
// block. Update the assessment if that's the case.
void ValidatePendingAssessment(RpoNumber block_id, InstructionOperand op,
const BlockAssessments* current_assessments,
PendingAssessment* const assessment,
int virtual_register);
void ValidateUse(RpoNumber block_id, BlockAssessments* current_assessments,
InstructionOperand op, int virtual_register);
Zone* const zone_;
const RegisterConfiguration* config_;
const InstructionSequence* const sequence_;
Constraints constraints_;
ZoneMap<RpoNumber, BlockAssessments*> assessments_;
ZoneMap<RpoNumber, DelayedAssessments*> outstanding_assessments_;
// TODO(chromium:725559): remove after we understand this bug's root cause.
const char* caller_info_ = nullptr;
} // namespace compiler
} // namespace internal
} // namespace v8