1 //===------------------- SSI.cpp - Creates SSI Representation -------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This pass converts a list of variables to the Static Single Information
11 // form. This is a program representation described by Scott Ananian in his
12 // Master Thesis: "The Static Single Information Form (1999)".
13 // We are building an on-demand representation, that is, we do not convert
14 // every single variable in the target function to SSI form. Rather, we receive
15 // a list of target variables that must be converted. We also do not
16 // completely convert a target variable to the SSI format. Instead, we only
17 // change the variable in the points where new information can be attached
18 // to its live range, that is, at branch points.
20 //===----------------------------------------------------------------------===//
22 #define DEBUG_TYPE "ssi"
24 #include "llvm/Transforms/Scalar.h"
25 #include "llvm/Transforms/Utils/SSI.h"
26 #include "llvm/Analysis/Dominators.h"
30 static const std::string SSI_PHI = "SSI_phi";
31 static const std::string SSI_SIG = "SSI_sigma";
33 static const unsigned UNSIGNED_INFINITE = ~0U;
35 void SSI::getAnalysisUsage(AnalysisUsage &AU) const {
36 AU.addRequired<DominanceFrontier>();
37 AU.addRequired<DominatorTree>();
41 bool SSI::runOnFunction(Function &F) {
42 DT_ = &getAnalysis<DominatorTree>();
46 /// This methods creates the SSI representation for the list of values
47 /// received. It will only create SSI representation if a value is used
48 /// in a to decide a branch. Repeated values are created only once.
50 void SSI::createSSI(SmallVectorImpl<Instruction *> &value) {
53 for (unsigned i = 0; i < num_values; ++i) {
54 if (created.insert(value[i])) {
55 needConstruction[i] = true;
58 insertSigmaFunctions(value);
60 // Test if there is a need to transform to SSI
61 if (needConstruction.any()) {
62 insertPhiFunctions(value);
64 rename(DT_->getRoot());
71 /// Insert sigma functions (a sigma function is a phi function with one
74 void SSI::insertSigmaFunctions(SmallVectorImpl<Instruction *> &value) {
75 for (unsigned i = 0; i < num_values; ++i) {
76 if (!needConstruction[i])
80 for (Value::use_iterator begin = value[i]->use_begin(), end =
81 value[i]->use_end(); begin != end; ++begin) {
82 // Test if the Use of the Value is in a comparator
83 CmpInst *CI = dyn_cast<CmpInst>(begin);
84 if (CI && isUsedInTerminator(CI)) {
85 // Basic Block of the Instruction
86 BasicBlock *BB = CI->getParent();
87 // Last Instruction of the Basic Block
88 const TerminatorInst *TI = BB->getTerminator();
90 for (unsigned j = 0, e = TI->getNumSuccessors(); j < e; ++j) {
92 BasicBlock *BB_next = TI->getSuccessor(j);
94 BB_next->getUniquePredecessor() != NULL &&
95 dominateAny(BB_next, value[i])) {
96 PHINode *PN = PHINode::Create(
97 value[i]->getType(), SSI_SIG, BB_next->begin());
98 PN->addIncoming(value[i], BB);
99 sigmas.insert(std::make_pair(PN, i));
102 defsites[i].push_back(BB_next);
107 needConstruction[i] = need;
111 /// Insert phi functions when necessary
113 void SSI::insertPhiFunctions(SmallVectorImpl<Instruction *> &value) {
114 DominanceFrontier *DF = &getAnalysis<DominanceFrontier>();
115 for (unsigned i = 0; i < num_values; ++i) {
116 // Test if there were any sigmas for this variable
117 if (needConstruction[i]) {
119 SmallPtrSet<BasicBlock *, 1> BB_visited;
121 // Insert phi functions if there is any sigma function
122 while (!defsites[i].empty()) {
124 BasicBlock *BB = defsites[i].back();
126 defsites[i].pop_back();
127 DominanceFrontier::iterator DF_BB = DF->find(BB);
129 // Iterates through all the dominance frontier of BB
130 for (std::set<BasicBlock *>::iterator DF_BB_begin =
131 DF_BB->second.begin(), DF_BB_end = DF_BB->second.end();
132 DF_BB_begin != DF_BB_end; ++DF_BB_begin) {
133 BasicBlock *BB_dominated = *DF_BB_begin;
135 // Test if has not yet visited this node and if the
136 // original definition dominates this node
137 if (BB_visited.insert(BB_dominated) &&
138 DT_->properlyDominates(value_original[i], BB_dominated) &&
139 dominateAny(BB_dominated, value[i])) {
140 PHINode *PN = PHINode::Create(
141 value[i]->getType(), SSI_PHI, BB_dominated->begin());
142 phis.insert(std::make_pair(PN, i));
145 defsites[i].push_back(BB_dominated);
154 /// Some initialization for the rename part
156 void SSI::renameInit(SmallVectorImpl<Instruction *> &value) {
157 value_stack.resize(num_values);
158 for (unsigned i = 0; i < num_values; ++i) {
159 value_stack[i].push_back(value[i]);
163 /// Renames all variables in the specified BasicBlock.
164 /// Only variables that need to be rename will be.
166 void SSI::rename(BasicBlock *BB) {
167 BitVector *defined = new BitVector(num_values, false);
169 // Iterate through instructions and make appropriate renaming.
170 // For SSI_PHI (b = PHI()), store b at value_stack as a new
171 // definition of the variable it represents.
172 // For SSI_SIG (b = PHI(a)), substitute a with the current
173 // value of a, present in the value_stack.
174 // Then store bin the value_stack as the new definition of a.
175 // For all other instructions (b = OP(a, c, d, ...)), we need to substitute
176 // all operands with its current value, present in value_stack.
177 for (BasicBlock::iterator begin = BB->begin(), end = BB->end();
178 begin != end; ++begin) {
179 Instruction *I = begin;
180 if (PHINode *PN = dyn_cast<PHINode>(I)) { // Treat PHI functions
184 if ((position = getPositionPhi(PN)) != -1) {
185 value_stack[position].push_back(PN);
186 (*defined)[position] = true;
190 else if ((position = getPositionSigma(PN)) != -1) {
192 value_stack[position].push_back(PN);
193 (*defined)[position] = true;
196 // Treat all other PHI functions
202 // Treat all other functions
208 // This loop iterates in all BasicBlocks that are successors of the current
209 // BasicBlock. For each SSI_PHI instruction found, insert an operand.
210 // This operand is the current operand in value_stack for the variable
211 // in "position". And the BasicBlock this operand represents is the current
213 for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI) {
214 BasicBlock *BB_succ = *SI;
216 for (BasicBlock::iterator begin = BB_succ->begin(),
217 notPhi = BB_succ->getFirstNonPHI(); begin != *notPhi; ++begin) {
218 Instruction *I = begin;
221 if ((PN = dyn_cast<PHINode>(I)) && ((position
222 = getPositionPhi(PN)) != -1)) {
223 PN->addIncoming(value_stack[position].back(), BB);
228 // This loop calls rename on all children from this block. This time children
229 // refers to a successor block in the dominance tree.
230 DomTreeNode *DTN = DT_->getNode(BB);
231 for (DomTreeNode::iterator begin = DTN->begin(), end = DTN->end();
232 begin != end; ++begin) {
233 DomTreeNodeBase<BasicBlock> *DTN_children = *begin;
234 BasicBlock *BB_children = DTN_children->getBlock();
238 // Now we remove all inserted definitions of a variable from the top of
239 // the stack leaving the previous one as the top.
240 if (defined->any()) {
241 for (unsigned i = 0; i < num_values; ++i) {
243 value_stack[i].pop_back();
249 /// Substitute any use in this instruction for the last definition of
252 void SSI::substituteUse(Instruction *I) {
253 for (unsigned i = 0, e = I->getNumOperands(); i < e; ++i) {
254 Value *operand = I->getOperand(i);
255 for (unsigned j = 0; j < num_values; ++j) {
256 if (operand == value_stack[j].front() &&
257 I != value_stack[j].back()) {
258 PHINode *PN_I = dyn_cast<PHINode>(I);
259 PHINode *PN_vs = dyn_cast<PHINode>(value_stack[j].back());
261 // If a phi created in a BasicBlock is used as an operand of another
262 // created in the same BasicBlock, this step marks this second phi,
263 // to fix this issue later. It cannot be fixed now, because the
264 // operands of the first phi are not final yet.
266 value_stack[j].back()->getParent() == I->getParent()) {
268 phisToFix.insert(PN_I);
271 I->setOperand(i, value_stack[j].back());
278 /// Test if the BasicBlock BB dominates any use or definition of value.
280 bool SSI::dominateAny(BasicBlock *BB, Instruction *value) {
281 for (Value::use_iterator begin = value->use_begin(),
282 end = value->use_end(); begin != end; ++begin) {
283 Instruction *I = cast<Instruction>(*begin);
284 BasicBlock *BB_father = I->getParent();
285 if (DT_->dominates(BB, BB_father)) {
292 /// When there is a phi node that is created in a BasicBlock and it is used
293 /// as an operand of another phi function used in the same BasicBlock,
294 /// LLVM looks this as an error. So on the second phi, the first phi is called
295 /// P and the BasicBlock it incomes is B. This P will be replaced by the value
296 /// it has for BasicBlock B.
298 void SSI::fixPhis() {
299 for (SmallPtrSet<PHINode *, 1>::iterator begin = phisToFix.begin(),
300 end = phisToFix.end(); begin != end; ++begin) {
301 PHINode *PN = *begin;
302 for (unsigned i = 0, e = PN->getNumIncomingValues(); i < e; ++i) {
304 if ((PN_father = dyn_cast<PHINode>(PN->getIncomingValue(i))) &&
305 PN->getParent() == PN_father->getParent()) {
306 BasicBlock *BB = PN->getIncomingBlock(i);
307 int pos = PN_father->getBasicBlockIndex(BB);
308 PN->setIncomingValue(i, PN_father->getIncomingValue(pos));
314 /// Return which variable (position on the vector of variables) this phi
315 /// represents on the phis list.
317 unsigned SSI::getPositionPhi(PHINode *PN) {
318 DenseMap<PHINode *, unsigned>::iterator val = phis.find(PN);
319 if (val == phis.end())
320 return UNSIGNED_INFINITE;
325 /// Return which variable (position on the vector of variables) this phi
326 /// represents on the sigmas list.
328 unsigned SSI::getPositionSigma(PHINode *PN) {
329 DenseMap<PHINode *, unsigned>::iterator val = sigmas.find(PN);
330 if (val == sigmas.end())
331 return UNSIGNED_INFINITE;
336 /// Return true if the the Comparison Instruction is an operator
337 /// of the Terminator instruction of its Basic Block.
339 unsigned SSI::isUsedInTerminator(CmpInst *CI) {
340 TerminatorInst *TI = CI->getParent()->getTerminator();
341 if (TI->getNumOperands() == 0) {
343 } else if (CI == TI->getOperand(0)) {
352 void SSI::init(SmallVectorImpl<Instruction *> &value) {
353 num_values = value.size();
354 needConstruction.resize(num_values, false);
356 value_original.resize(num_values);
357 defsites.resize(num_values);
359 for (unsigned i = 0; i < num_values; ++i) {
360 value_original[i] = value[i]->getParent();
361 defsites[i].push_back(value_original[i]);
365 /// Clean all used resources in this creation of SSI
368 for (unsigned i = 0; i < num_values; ++i) {
370 if (i < value_stack.size())
371 value_stack[i].clear();
380 value_original.clear();
381 needConstruction.clear();
384 /// createSSIPass - The public interface to this file...
386 FunctionPass *llvm::createSSIPass() { return new SSI(); }
389 static RegisterPass<SSI> X("ssi", "Static Single Information Construction");