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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";
+
+STATISTIC(NumSigmaInserted, "Number of sigma functions inserted");
+STATISTIC(NumPhiInserted, "Number of phi functions inserted");
+
+void SSI::getAnalysisUsage(AnalysisUsage &AU) const {
+ AU.addRequiredTransitive<DominanceFrontier>();
+ AU.addRequiredTransitive<DominatorTree>();
+ AU.setPreservesAll();
+}
+
+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
+/// to decide a branch. Repeated values are created only once.
+///
+void SSI::createSSI(SmallVectorImpl<Instruction *> &value) {
+ init(value);
+
+ SmallPtrSet<Instruction*, 4> needConstruction;
+ for (SmallVectorImpl<Instruction*>::iterator I = value.begin(),
+ E = value.end(); I != E; ++I)
+ if (created.insert(*I))
+ needConstruction.insert(*I);
+
+ insertSigmaFunctions(needConstruction);
+
+ // Test if there is a need to transform to SSI
+ if (!needConstruction.empty()) {
+ insertPhiFunctions(needConstruction);
+ renameInit(needConstruction);
+ rename(DT_->getRoot());
+ fixPhis();
+ }
+
+ clean();
+}
+
+/// Insert sigma functions (a sigma function is a phi function with one
+/// operator)
+///
+void SSI::insertSigmaFunctions(SmallPtrSet<Instruction*, 4> &value) {
+ for (SmallPtrSet<Instruction*, 4>::iterator I = value.begin(),
+ E = value.end(); I != E; ++I) {
+ for (Value::use_iterator begin = (*I)->use_begin(),
+ end = (*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, *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) {
+ // 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[PN] = I;
+ created.insert(PN);
+ defsites[I].push_back(BB_next);
+ ++NumSigmaInserted;
+ }
+ }
+}
+
+/// Insert phi functions when necessary
+///
+void SSI::insertPhiFunctions(SmallPtrSet<Instruction*, 4> &value) {
+ DominanceFrontier *DF = &getAnalysis<DominanceFrontier>();
+ for (SmallPtrSet<Instruction*, 4>::iterator I = value.begin(),
+ E = value.end(); I != E; ++I) {
+ // Test if there were any sigmas for this variable
+ 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, *I)) {
+ PHINode *PN = PHINode::Create(
+ (*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(SmallPtrSet<Instruction*, 4> &value) {
+ for (SmallPtrSet<Instruction*, 4>::iterator I = value.begin(),
+ E = value.end(); I != E; ++I)
+ value_stack[*I].push_back(*I);
+}
+
+/// Renames all variables in the specified BasicBlock.
+/// Only variables that need to be rename will be.
+///
+void SSI::rename(BasicBlock *BB) {
+ SmallPtrSet<Instruction*, 8> defined;
+
+ // 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
+ Instruction* position;
+
+ // Treat SSI_PHI
+ if ((position = getPositionPhi(PN))) {
+ value_stack[position].push_back(PN);
+ defined.insert(position);
+ // Treat SSI_SIG
+ } else if ((position = getPositionSigma(PN))) {
+ substituteUse(I);
+ value_stack[position].push_back(PN);
+ defined.insert(position);
+ }
+
+ // 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);
+ Instruction* position;
+ if (PN && ((position = getPositionPhi(PN)))) {
+ 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.
+ for (SmallPtrSet<Instruction*, 8>::iterator DI = defined.begin(),
+ DE = defined.end(); DI != DE; ++DI)
+ value_stack[*DI].pop_back();
+}
+
+/// 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 (DenseMap<Instruction*, SmallVector<Instruction*, 1> >::iterator
+ VI = value_stack.begin(), VE = value_stack.end(); VI != VE; ++VI) {
+ if (operand == VI->second.front() &&
+ I != VI->second.back()) {
+ PHINode *PN_I = dyn_cast<PHINode>(I);
+ PHINode *PN_vs = dyn_cast<PHINode>(VI->second.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 &&
+ VI->second.back()->getParent() == I->getParent()) {
+
+ phisToFix.insert(PN_I);
+ }
+
+ I->setOperand(i, VI->second.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 *, Instruction*> 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.
+///
+Instruction* SSI::getPositionPhi(PHINode *PN) {
+ DenseMap<PHINode *, Instruction*>::iterator val = phis.find(PN);
+ if (val == phis.end())
+ return 0;
+ else
+ return val->second;
+}
+
+/// Return which variable (position on the vector of variables) this phi
+/// represents on the sigmas list.
+///
+Instruction* SSI::getPositionSigma(PHINode *PN) {
+ DenseMap<PHINode *, Instruction*>::iterator val = sigmas.find(PN);
+ if (val == sigmas.end())
+ return 0;
+ else
+ return val->second;
+}
+
+/// Initializes
+///
+void SSI::init(SmallVectorImpl<Instruction *> &value) {
+ for (SmallVectorImpl<Instruction *>::iterator I = value.begin(),
+ E = value.end(); I != E; ++I) {
+ value_original[*I] = (*I)->getParent();
+ defsites[*I].push_back((*I)->getParent());
+ }
+}
+
+/// Clean all used resources in this creation of SSI
+///
+void SSI::clean() {
+ phis.clear();
+ sigmas.clear();
+ phisToFix.clear();
+
+ defsites.clear();
+ value_stack.clear();
+ value_original.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 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()->isVoidTy())
+ 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");
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