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* Copyright (C) 2013 The Android Open Source Project
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* See the License for the specific language governing permissions and
* limitations under the License.
#include <set>
#include <map>
#include "dex_file.h"
#include "dex_instruction.h"
#include "instruction_tools.h"
#include "instruction_nodes.h"
#include "utils/scoped_hashtable.h"
namespace sea_ir {
// Reverse post-order numbering constants
enum RegionNumbering {
class Region;
class InstructionNode;
class PhiInstructionNode;
class SignatureNode;
// A SignatureNode is a declaration of one parameter in the function signature.
// This class is used to provide place-holder definitions to which instructions
// can return from the GetSSAUses() calls, instead of having missing SSA edges.
class SignatureNode: public InstructionNode {
explicit SignatureNode(unsigned int parameter_register):
InstructionNode(NULL), defined_regs_() {
void ToDot(std::string& result) const {
result += StringId() +" [label=\"signature:";
std::stringstream vector_printer;
if (!defined_regs_.empty()) {
for (unsigned int crt_el = 0; crt_el < defined_regs_.size()-1; crt_el++) {
vector_printer << defined_regs_[crt_el] <<",";
vector_printer << defined_regs_[defined_regs_.size()-1] <<";";
result += "\"] // signature node\n";
std::vector<int> GetDefinitions() const {
return defined_regs_;
int GetResultRegister() const {
std::vector<int> GetUses() {
return std::vector<int>();
void Accept(IRVisitor* v) {
std::vector<int> defined_regs_;
class PhiInstructionNode: public InstructionNode {
explicit PhiInstructionNode(int register_no):
InstructionNode(NULL), register_no_(register_no), definition_edges_() {}
// Appends to @result the .dot string representation of the instruction.
void ToDot(std::string& result) const;
// Returns the register on which this phi-function is used.
int GetRegisterNumber() const {
return register_no_;
// Renames the use of @reg_no to refer to the instruction @definition.
// Phi-functions are different than normal instructions in that they
// have multiple predecessor regions; this is why RenameToSSA has
// the additional parameter specifying that @parameter_id is the incoming
// edge for @definition, essentially creating SSA form.
void RenameToSSA(int reg_no, InstructionNode* definition, unsigned int predecessor_id) {
DCHECK(NULL != definition) << "Tried to rename to SSA using a NULL definition for "
<< StringId() << " register " << reg_no;
if (definition_edges_.size() < predecessor_id+1) {
definition_edges_.resize(predecessor_id+1, NULL);
if (NULL == {
definition_edges_[predecessor_id] = new std::vector<InstructionNode*>();
// Returns the instruction that defines the phi register from predecessor
// on position @predecessor_pos. Note that the return value is vector<> just
// for consistency with the return value of GetSSAUses() on regular instructions,
// The returned vector should always have a single element because the IR is SSA.
std::vector<InstructionNode*>* GetSSAUses(int predecessor_pos) {
void Accept(IRVisitor* v) {
int register_no_;
std::vector<std::vector<InstructionNode*>*> definition_edges_;
// This class corresponds to a basic block in traditional compiler IRs.
// The dataflow analysis relies on this class both during execution and
// for storing its results.
class Region : public SeaNode {
explicit Region():
SeaNode(), successors_(), predecessors_(), reaching_defs_size_(0),
rpo_number_(NOT_VISITED), idom_(NULL), idominated_set_(), df_(), phi_set_() {}
// Adds @instruction as an instruction node child in the current region.
void AddChild(sea_ir::InstructionNode* instruction);
// Returns the last instruction node child of the current region.
// This child has the CFG successors pointing to the new regions.
SeaNode* GetLastChild() const;
// Returns all the child instructions of this region, in program order.
std::vector<InstructionNode*>* GetInstructions() {
return &instructions_;
// Appends to @result a dot language formatted string representing the node and
// (by convention) outgoing edges, so that the composition of theToDot() of all nodes
// builds a complete dot graph (without prolog and epilog though).
virtual void ToDot(std::string& result) const;
// Computes Downward Exposed Definitions for the current node.
void ComputeDownExposedDefs();
const std::map<int, sea_ir::InstructionNode*>* GetDownExposedDefs() const;
// Performs one iteration of the reaching definitions algorithm
// and returns true if the reaching definitions set changed.
bool UpdateReachingDefs();
// Returns the set of reaching definitions for the current region.
std::map<int, std::set<sea_ir::InstructionNode*>* >* GetReachingDefs();
void SetRPO(int rpo) {
rpo_number_ = rpo;
int GetRPO() {
return rpo_number_;
void SetIDominator(Region* dom) {
idom_ = dom;
Region* GetIDominator() const {
return idom_;
void AddToIDominatedSet(Region* dominated) {
const std::set<Region*>* GetIDominatedSet() {
return &idominated_set_;
// Adds @df_reg to the dominance frontier of the current region.
void AddToDominanceFrontier(Region* df_reg) {
// Returns the dominance frontier of the current region.
// Preconditions: SeaGraph.ComputeDominanceFrontier()
std::set<Region*>* GetDominanceFrontier() {
return &df_;
// Returns true if the region contains a phi function for @reg_no.
bool ContainsPhiFor(int reg_no) {
return (phi_set_.end() != phi_set_.find(reg_no));
// Returns the phi-functions from the region.
std::vector<PhiInstructionNode*>* GetPhiNodes() {
return &phi_instructions_;
// Adds a phi-function for @reg_no to this region.
// Note: The insertion order does not matter, as phi-functions
// are conceptually executed at the same time.
bool InsertPhiFor(int reg_no);
// Sets the phi-function uses to be as defined in @scoped_table for predecessor @@predecessor.
void SetPhiDefinitionsForUses(const utils::ScopedHashtable<int, InstructionNode*>* scoped_table,
Region* predecessor);
void Accept(IRVisitor* v) {
void AddSuccessor(Region* successor) {
DCHECK(successor) << "Tried to add NULL successor to SEA node.";
void AddPredecessor(Region* predecessor) {
DCHECK(predecessor) << "Tried to add NULL predecessor to SEA node.";
std::vector<sea_ir::Region*>* GetSuccessors() {
return &successors_;
std::vector<sea_ir::Region*>* GetPredecessors() {
return &predecessors_;
std::vector<sea_ir::Region*> successors_; // CFG successor nodes (regions)
std::vector<sea_ir::Region*> predecessors_; // CFG predecessor nodes (instructions/regions)
std::vector<sea_ir::InstructionNode*> instructions_;
std::map<int, sea_ir::InstructionNode*> de_defs_;
std::map<int, std::set<sea_ir::InstructionNode*>* > reaching_defs_;
int reaching_defs_size_;
int rpo_number_; // reverse postorder number of the region
// Immediate dominator node.
Region* idom_;
// The set of nodes immediately dominated by the region.
std::set<Region*> idominated_set_;
// Records the dominance frontier.
std::set<Region*> df_;
// Records the set of register numbers that have phi nodes in this region.
std::set<int> phi_set_;
std::vector<PhiInstructionNode*> phi_instructions_;
// A SeaGraph instance corresponds to a source code function.
// Its main point is to encapsulate the SEA IR representation of it
// and acts as starting point for visitors (ex: during code generation).
class SeaGraph: IVisitable {
static SeaGraph* GetCurrentGraph();
void CompileMethod(const art::DexFile::CodeItem* code_item,
uint32_t class_def_idx, uint32_t method_idx, const art::DexFile& dex_file);
// Returns all regions corresponding to this SeaGraph.
std::vector<Region*>* GetRegions() {
return &regions_;
// Returns a string representation of the region and its Instruction children.
void DumpSea(std::string filename) const;
// Recursively computes the reverse postorder value for @crt_bb and successors.
static void ComputeRPO(Region* crt_bb, int& crt_rpo);
// Returns the "lowest common ancestor" of @i and @j in the dominator tree.
static Region* Intersect(Region* i, Region* j);
//Returns the vector of parameters of the function.
std::vector<SignatureNode*>* GetParameterNodes() {
return &parameters_;
uint32_t class_def_idx_;
uint32_t method_idx_;
SeaGraph(): class_def_idx_(0), method_idx_(0), regions_(), parameters_() {
// Registers @childReg as a region belonging to the SeaGraph instance.
void AddRegion(Region* childReg);
// Returns new region and registers it with the SeaGraph instance.
Region* GetNewRegion();
// Adds a (formal) parameter node to the vector of parameters of the function.
void AddParameterNode(SignatureNode* parameterNode) {
// Adds a CFG edge from @src node to @dst node.
void AddEdge(Region* src, Region* dst) const;
// Builds the non-SSA sea-ir representation of the function @code_item from @dex_file
// with class id @class_def_idx and method id @method_idx.
void BuildMethodSeaGraph(const art::DexFile::CodeItem* code_item,
const art::DexFile& dex_file, uint32_t class_def_idx, uint32_t method_idx);
// Computes immediate dominators for each region.
// Precondition: ComputeMethodSeaGraph()
void ComputeIDominators();
// Computes Downward Exposed Definitions for all regions in the graph.
void ComputeDownExposedDefs();
// Computes the reaching definitions set following the equations from
// Cooper & Torczon, "Engineering a Compiler", second edition, page 491.
// Precondition: ComputeDEDefs()
void ComputeReachingDefs();
// Computes the reverse-postorder numbering for the region nodes.
// Precondition: ComputeDEDefs()
void ComputeRPO();
// Computes the dominance frontier for all regions in the graph,
// following the algorithm from
// Cooper & Torczon, "Engineering a Compiler", second edition, page 499.
// Precondition: ComputeIDominators()
void ComputeDominanceFrontier();
// Converts the IR to semi-pruned SSA form.
void ConvertToSSA();
// Performs the renaming phase of the SSA transformation during ConvertToSSA() execution.
void RenameAsSSA();
// Identifies the definitions corresponding to uses for region @node
// by using the scoped hashtable of names @ scoped_table.
void RenameAsSSA(Region* node, utils::ScopedHashtable<int, InstructionNode*>* scoped_table);
virtual void Accept(IRVisitor* visitor) {
virtual ~SeaGraph() {}
// Generate LLVM IR for the method.
// Precondition: ConvertToSSA().
void GenerateLLVM();
static SeaGraph graph_;
std::vector<Region*> regions_;
std::vector<SignatureNode*> parameters_;
} // end namespace sea_ir