llvm-6502/lib/Transforms/Utils/SSI.cpp

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//===------------------- SSI.cpp - Creates SSI Representation -------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This pass converts a list of variables to the Static Single Information
// form. This is a program representation described by Scott Ananian in his
// Master Thesis: "The Static Single Information Form (1999)".
// We are building an on-demand representation, that is, we do not convert
// every single variable in the target function to SSI form. Rather, we receive
// a list of target variables that must be converted. We also do not
// completely convert a target variable to the SSI format. Instead, we only
// change the variable in the points where new information can be attached
// to its live range, that is, at branch points.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "ssi"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/Utils/SSI.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/Dominators.h"
using namespace llvm;
static const std::string SSI_PHI = "SSI_phi";
static const std::string SSI_SIG = "SSI_sigma";
static const unsigned UNSIGNED_INFINITE = ~0U;
STATISTIC(NumSigmaInserted, "Number of sigma functions inserted");
STATISTIC(NumPhiInserted, "Number of phi functions inserted");
void SSI::getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<DominanceFrontier>();
AU.addRequired<DominatorTree>();
AU.setPreservesCFG();
}
bool SSI::runOnFunction(Function &F) {
DT_ = &getAnalysis<DominatorTree>();
return false;
}
/// This methods creates the SSI representation for the list of values
/// received. It will only create SSI representation if a value is used
/// in a to decide a branch. Repeated values are created only once.
///
void SSI::createSSI(SmallVectorImpl<Instruction *> &value) {
init(value);
for (unsigned i = 0; i < num_values; ++i) {
if (created.insert(value[i])) {
needConstruction[i] = true;
}
}
insertSigmaFunctions(value);
// Test if there is a need to transform to SSI
if (needConstruction.any()) {
insertPhiFunctions(value);
renameInit(value);
rename(DT_->getRoot());
fixPhis();
}
clean();
}
/// Insert sigma functions (a sigma function is a phi function with one
/// operator)
///
void SSI::insertSigmaFunctions(SmallVectorImpl<Instruction *> &value) {
for (unsigned i = 0; i < num_values; ++i) {
if (!needConstruction[i])
continue;
for (Value::use_iterator begin = value[i]->use_begin(), end =
value[i]->use_end(); begin != end; ++begin) {
// Test if the Use of the Value is in a comparator
if (CmpInst *CI = dyn_cast<CmpInst>(begin)) {
// Iterates through all uses of CmpInst
for (Value::use_iterator begin_ci = CI->use_begin(), end_ci =
CI->use_end(); begin_ci != end_ci; ++begin_ci) {
// Test if any use of CmpInst is in a Terminator
if (TerminatorInst *TI = dyn_cast<TerminatorInst>(begin_ci)) {
insertSigma(TI, value[i], i);
}
}
}
}
}
}
/// Inserts Sigma Functions in every BasicBlock successor to Terminator
/// Instruction TI. All inserted Sigma Function are related to Instruction I.
///
void SSI::insertSigma(TerminatorInst *TI, Instruction *I, unsigned pos) {
// Basic Block of the Terminator Instruction
BasicBlock *BB = TI->getParent();
for (unsigned i = 0, e = TI->getNumSuccessors(); i < e; ++i) {
// Next Basic Block
BasicBlock *BB_next = TI->getSuccessor(i);
if (BB_next != BB &&
BB_next->getSinglePredecessor() != NULL &&
dominateAny(BB_next, I)) {
PHINode *PN = PHINode::Create(I->getType(), SSI_SIG, BB_next->begin());
PN->addIncoming(I, BB);
sigmas.insert(std::make_pair(PN, pos));
created.insert(PN);
needConstruction[pos] = true;
defsites[pos].push_back(BB_next);
++NumSigmaInserted;
}
}
}
/// Insert phi functions when necessary
///
void SSI::insertPhiFunctions(SmallVectorImpl<Instruction *> &value) {
DominanceFrontier *DF = &getAnalysis<DominanceFrontier>();
for (unsigned i = 0; i < num_values; ++i) {
// Test if there were any sigmas for this variable
if (needConstruction[i]) {
SmallPtrSet<BasicBlock *, 16> BB_visited;
// Insert phi functions if there is any sigma function
while (!defsites[i].empty()) {
BasicBlock *BB = defsites[i].back();
defsites[i].pop_back();
DominanceFrontier::iterator DF_BB = DF->find(BB);
// The BB is unreachable. Skip it.
if (DF_BB == DF->end())
continue;
// Iterates through all the dominance frontier of BB
for (std::set<BasicBlock *>::iterator DF_BB_begin =
DF_BB->second.begin(), DF_BB_end = DF_BB->second.end();
DF_BB_begin != DF_BB_end; ++DF_BB_begin) {
BasicBlock *BB_dominated = *DF_BB_begin;
// Test if has not yet visited this node and if the
// original definition dominates this node
if (BB_visited.insert(BB_dominated) &&
DT_->properlyDominates(value_original[i], BB_dominated) &&
dominateAny(BB_dominated, value[i])) {
PHINode *PN = PHINode::Create(
value[i]->getType(), SSI_PHI, BB_dominated->begin());
phis.insert(std::make_pair(PN, i));
created.insert(PN);
defsites[i].push_back(BB_dominated);
++NumPhiInserted;
}
}
}
BB_visited.clear();
}
}
}
/// Some initialization for the rename part
///
void SSI::renameInit(SmallVectorImpl<Instruction *> &value) {
value_stack.resize(num_values);
for (unsigned i = 0; i < num_values; ++i) {
value_stack[i].push_back(value[i]);
}
}
/// Renames all variables in the specified BasicBlock.
/// Only variables that need to be rename will be.
///
void SSI::rename(BasicBlock *BB) {
BitVector *defined = new BitVector(num_values, false);
// Iterate through instructions and make appropriate renaming.
// For SSI_PHI (b = PHI()), store b at value_stack as a new
// definition of the variable it represents.
// For SSI_SIG (b = PHI(a)), substitute a with the current
// value of a, present in the value_stack.
// Then store bin the value_stack as the new definition of a.
// For all other instructions (b = OP(a, c, d, ...)), we need to substitute
// all operands with its current value, present in value_stack.
for (BasicBlock::iterator begin = BB->begin(), end = BB->end();
begin != end; ++begin) {
Instruction *I = begin;
if (PHINode *PN = dyn_cast<PHINode>(I)) { // Treat PHI functions
int position;
// Treat SSI_PHI
if ((position = getPositionPhi(PN)) != -1) {
value_stack[position].push_back(PN);
(*defined)[position] = true;
}
// Treat SSI_SIG
else if ((position = getPositionSigma(PN)) != -1) {
substituteUse(I);
value_stack[position].push_back(PN);
(*defined)[position] = true;
}
// Treat all other PHI functions
else {
substituteUse(I);
}
}
// Treat all other functions
else {
substituteUse(I);
}
}
// This loop iterates in all BasicBlocks that are successors of the current
// BasicBlock. For each SSI_PHI instruction found, insert an operand.
// This operand is the current operand in value_stack for the variable
// in "position". And the BasicBlock this operand represents is the current
// BasicBlock.
for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI) {
BasicBlock *BB_succ = *SI;
for (BasicBlock::iterator begin = BB_succ->begin(),
notPhi = BB_succ->getFirstNonPHI(); begin != *notPhi; ++begin) {
Instruction *I = begin;
PHINode *PN = dyn_cast<PHINode>(I);
int position;
if (PN && ((position = getPositionPhi(PN)) != -1)) {
PN->addIncoming(value_stack[position].back(), BB);
}
}
}
// This loop calls rename on all children from this block. This time children
// refers to a successor block in the dominance tree.
DomTreeNode *DTN = DT_->getNode(BB);
for (DomTreeNode::iterator begin = DTN->begin(), end = DTN->end();
begin != end; ++begin) {
DomTreeNodeBase<BasicBlock> *DTN_children = *begin;
BasicBlock *BB_children = DTN_children->getBlock();
rename(BB_children);
}
// Now we remove all inserted definitions of a variable from the top of
// the stack leaving the previous one as the top.
if (defined->any()) {
for (unsigned i = 0; i < num_values; ++i) {
if ((*defined)[i]) {
value_stack[i].pop_back();
}
}
}
delete defined;
}
/// Substitute any use in this instruction for the last definition of
/// the variable
///
void SSI::substituteUse(Instruction *I) {
for (unsigned i = 0, e = I->getNumOperands(); i < e; ++i) {
Value *operand = I->getOperand(i);
for (unsigned j = 0; j < num_values; ++j) {
if (operand == value_stack[j].front() &&
I != value_stack[j].back()) {
PHINode *PN_I = dyn_cast<PHINode>(I);
PHINode *PN_vs = dyn_cast<PHINode>(value_stack[j].back());
// If a phi created in a BasicBlock is used as an operand of another
// created in the same BasicBlock, this step marks this second phi,
// to fix this issue later. It cannot be fixed now, because the
// operands of the first phi are not final yet.
if (PN_I && PN_vs &&
value_stack[j].back()->getParent() == I->getParent()) {
phisToFix.insert(PN_I);
}
I->setOperand(i, value_stack[j].back());
break;
}
}
}
}
/// Test if the BasicBlock BB dominates any use or definition of value.
/// If it dominates a phi instruction that is on the same BasicBlock,
/// that does not count.
///
bool SSI::dominateAny(BasicBlock *BB, Instruction *value) {
for (Value::use_iterator begin = value->use_begin(),
end = value->use_end(); begin != end; ++begin) {
Instruction *I = cast<Instruction>(*begin);
BasicBlock *BB_father = I->getParent();
if (BB == BB_father && isa<PHINode>(I))
continue;
if (DT_->dominates(BB, BB_father)) {
return true;
}
}
return false;
}
/// When there is a phi node that is created in a BasicBlock and it is used
/// as an operand of another phi function used in the same BasicBlock,
/// LLVM looks this as an error. So on the second phi, the first phi is called
/// P and the BasicBlock it incomes is B. This P will be replaced by the value
/// it has for BasicBlock B. It also includes undef values for predecessors
/// that were not included in the phi.
///
void SSI::fixPhis() {
for (SmallPtrSet<PHINode *, 1>::iterator begin = phisToFix.begin(),
end = phisToFix.end(); begin != end; ++begin) {
PHINode *PN = *begin;
for (unsigned i = 0, e = PN->getNumIncomingValues(); i < e; ++i) {
PHINode *PN_father = dyn_cast<PHINode>(PN->getIncomingValue(i));
if (PN_father && PN->getParent() == PN_father->getParent() &&
!DT_->dominates(PN->getParent(), PN->getIncomingBlock(i))) {
BasicBlock *BB = PN->getIncomingBlock(i);
int pos = PN_father->getBasicBlockIndex(BB);
PN->setIncomingValue(i, PN_father->getIncomingValue(pos));
}
}
}
for (DenseMapIterator<PHINode *, unsigned> begin = phis.begin(),
end = phis.end(); begin != end; ++begin) {
PHINode *PN = begin->first;
BasicBlock *BB = PN->getParent();
pred_iterator PI = pred_begin(BB), PE = pred_end(BB);
SmallVector<BasicBlock*, 8> Preds(PI, PE);
for (unsigned size = Preds.size();
PI != PE && PN->getNumIncomingValues() != size; ++PI) {
bool found = false;
for (unsigned i = 0, pn_end = PN->getNumIncomingValues();
i < pn_end; ++i) {
if (PN->getIncomingBlock(i) == *PI) {
found = true;
break;
}
}
if (!found) {
PN->addIncoming(UndefValue::get(PN->getType()), *PI);
}
}
}
}
/// Return which variable (position on the vector of variables) this phi
/// represents on the phis list.
///
unsigned SSI::getPositionPhi(PHINode *PN) {
DenseMap<PHINode *, unsigned>::iterator val = phis.find(PN);
if (val == phis.end())
return UNSIGNED_INFINITE;
else
return val->second;
}
/// Return which variable (position on the vector of variables) this phi
/// represents on the sigmas list.
///
unsigned SSI::getPositionSigma(PHINode *PN) {
DenseMap<PHINode *, unsigned>::iterator val = sigmas.find(PN);
if (val == sigmas.end())
return UNSIGNED_INFINITE;
else
return val->second;
}
/// Initializes
///
void SSI::init(SmallVectorImpl<Instruction *> &value) {
num_values = value.size();
needConstruction.resize(num_values, false);
value_original.resize(num_values);
defsites.resize(num_values);
for (unsigned i = 0; i < num_values; ++i) {
value_original[i] = value[i]->getParent();
defsites[i].push_back(value_original[i]);
}
}
/// Clean all used resources in this creation of SSI
///
void SSI::clean() {
for (unsigned i = 0; i < num_values; ++i) {
defsites[i].clear();
if (i < value_stack.size())
value_stack[i].clear();
}
phis.clear();
sigmas.clear();
phisToFix.clear();
defsites.clear();
value_stack.clear();
value_original.clear();
needConstruction.clear();
}
/// createSSIPass - The public interface to this file...
///
FunctionPass *llvm::createSSIPass() { return new SSI(); }
char SSI::ID = 0;
static RegisterPass<SSI> X("ssi", "Static Single Information Construction");
/// SSIEverything - A pass that runs createSSI on every non-void variable,
/// intended for debugging.
namespace {
struct VISIBILITY_HIDDEN SSIEverything : public FunctionPass {
static char ID; // Pass identification, replacement for typeid
SSIEverything() : FunctionPass(&ID) {}
bool runOnFunction(Function &F);
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<SSI>();
}
};
}
bool SSIEverything::runOnFunction(Function &F) {
SmallVector<Instruction *, 16> Insts;
SSI &ssi = getAnalysis<SSI>();
if (F.isDeclaration() || F.isIntrinsic()) return false;
for (Function::iterator B = F.begin(), BE = F.end(); B != BE; ++B)
for (BasicBlock::iterator I = B->begin(), E = B->end(); I != E; ++I)
if (I->getType() != Type::getVoidTy(F.getContext()))
Insts.push_back(I);
ssi.createSSI(Insts);
return true;
}
/// createSSIEverythingPass - The public interface to this file...
///
FunctionPass *llvm::createSSIEverythingPass() { return new SSIEverything(); }
char SSIEverything::ID = 0;
static RegisterPass<SSIEverything>
Y("ssi-everything", "Static Single Information Construction");