1 //===- SCCP.cpp - Sparse Conditional Constant Propagation -----------------===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by the LLVM research group and is distributed under
6 // the University of Illinois Open Source License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements sparse conditional constant propagation and merging:
12 // Specifically, this:
13 // * Assumes values are constant unless proven otherwise
14 // * Assumes BasicBlocks are dead unless proven otherwise
15 // * Proves values to be constant, and replaces them with constants
16 // * Proves conditional branches to be unconditional
19 // * This pass has a habit of making definitions be dead. It is a good idea
20 // to to run a DCE pass sometime after running this pass.
22 //===----------------------------------------------------------------------===//
24 #define DEBUG_TYPE "sccp"
25 #include "llvm/Transforms/Scalar.h"
26 #include "llvm/Transforms/IPO.h"
27 #include "llvm/Constants.h"
28 #include "llvm/DerivedTypes.h"
29 #include "llvm/Instructions.h"
30 #include "llvm/Pass.h"
31 #include "llvm/Support/InstVisitor.h"
32 #include "llvm/Transforms/Utils/Local.h"
33 #include "llvm/Support/CallSite.h"
34 #include "llvm/Support/Debug.h"
35 #include "llvm/ADT/hash_map"
36 #include "llvm/ADT/Statistic.h"
37 #include "llvm/ADT/STLExtras.h"
42 STATISTIC(NumInstRemoved, "Number of instructions removed");
43 STATISTIC(NumDeadBlocks , "Number of basic blocks unreachable");
45 STATISTIC(IPNumInstRemoved, "Number ofinstructions removed by IPSCCP");
46 STATISTIC(IPNumDeadBlocks , "Number of basic blocks unreachable by IPSCCP");
47 STATISTIC(IPNumArgsElimed ,"Number of arguments constant propagated by IPSCCP");
48 STATISTIC(IPNumGlobalConst, "Number of globals found to be constant by IPSCCP");
51 /// LatticeVal class - This class represents the different lattice values that
52 /// an LLVM value may occupy. It is a simple class with value semantics.
56 /// undefined - This LLVM Value has no known value yet.
59 /// constant - This LLVM Value has a specific constant value.
62 /// forcedconstant - This LLVM Value was thought to be undef until
63 /// ResolvedUndefsIn. This is treated just like 'constant', but if merged
64 /// with another (different) constant, it goes to overdefined, instead of
68 /// overdefined - This instruction is not known to be constant, and we know
71 } LatticeValue; // The current lattice position
73 Constant *ConstantVal; // If Constant value, the current value
75 inline LatticeVal() : LatticeValue(undefined), ConstantVal(0) {}
77 // markOverdefined - Return true if this is a new status to be in...
78 inline bool markOverdefined() {
79 if (LatticeValue != overdefined) {
80 LatticeValue = overdefined;
86 // markConstant - Return true if this is a new status for us.
87 inline bool markConstant(Constant *V) {
88 if (LatticeValue != constant) {
89 if (LatticeValue == undefined) {
90 LatticeValue = constant;
93 assert(LatticeValue == forcedconstant &&
94 "Cannot move from overdefined to constant!");
95 // Stay at forcedconstant if the constant is the same.
96 if (V == ConstantVal) return false;
98 // Otherwise, we go to overdefined. Assumptions made based on the
99 // forced value are possibly wrong. Assuming this is another constant
100 // could expose a contradiction.
101 LatticeValue = overdefined;
105 assert(ConstantVal == V && "Marking constant with different value");
110 inline void markForcedConstant(Constant *V) {
111 assert(LatticeValue == undefined && "Can't force a defined value!");
112 LatticeValue = forcedconstant;
116 inline bool isUndefined() const { return LatticeValue == undefined; }
117 inline bool isConstant() const {
118 return LatticeValue == constant || LatticeValue == forcedconstant;
120 inline bool isOverdefined() const { return LatticeValue == overdefined; }
122 inline Constant *getConstant() const {
123 assert(isConstant() && "Cannot get the constant of a non-constant!");
128 } // end anonymous namespace
131 //===----------------------------------------------------------------------===//
133 /// SCCPSolver - This class is a general purpose solver for Sparse Conditional
134 /// Constant Propagation.
136 class SCCPSolver : public InstVisitor<SCCPSolver> {
137 std::set<BasicBlock*> BBExecutable;// The basic blocks that are executable
138 hash_map<Value*, LatticeVal> ValueState; // The state each value is in...
140 /// GlobalValue - If we are tracking any values for the contents of a global
141 /// variable, we keep a mapping from the constant accessor to the element of
142 /// the global, to the currently known value. If the value becomes
143 /// overdefined, it's entry is simply removed from this map.
144 hash_map<GlobalVariable*, LatticeVal> TrackedGlobals;
146 /// TrackedFunctionRetVals - If we are tracking arguments into and the return
147 /// value out of a function, it will have an entry in this map, indicating
148 /// what the known return value for the function is.
149 hash_map<Function*, LatticeVal> TrackedFunctionRetVals;
151 // The reason for two worklists is that overdefined is the lowest state
152 // on the lattice, and moving things to overdefined as fast as possible
153 // makes SCCP converge much faster.
154 // By having a separate worklist, we accomplish this because everything
155 // possibly overdefined will become overdefined at the soonest possible
157 std::vector<Value*> OverdefinedInstWorkList;
158 std::vector<Value*> InstWorkList;
161 std::vector<BasicBlock*> BBWorkList; // The BasicBlock work list
163 /// UsersOfOverdefinedPHIs - Keep track of any users of PHI nodes that are not
164 /// overdefined, despite the fact that the PHI node is overdefined.
165 std::multimap<PHINode*, Instruction*> UsersOfOverdefinedPHIs;
167 /// KnownFeasibleEdges - Entries in this set are edges which have already had
168 /// PHI nodes retriggered.
169 typedef std::pair<BasicBlock*,BasicBlock*> Edge;
170 std::set<Edge> KnownFeasibleEdges;
173 /// MarkBlockExecutable - This method can be used by clients to mark all of
174 /// the blocks that are known to be intrinsically live in the processed unit.
175 void MarkBlockExecutable(BasicBlock *BB) {
176 DOUT << "Marking Block Executable: " << BB->getName() << "\n";
177 BBExecutable.insert(BB); // Basic block is executable!
178 BBWorkList.push_back(BB); // Add the block to the work list!
181 /// TrackValueOfGlobalVariable - Clients can use this method to
182 /// inform the SCCPSolver that it should track loads and stores to the
183 /// specified global variable if it can. This is only legal to call if
184 /// performing Interprocedural SCCP.
185 void TrackValueOfGlobalVariable(GlobalVariable *GV) {
186 const Type *ElTy = GV->getType()->getElementType();
187 if (ElTy->isFirstClassType()) {
188 LatticeVal &IV = TrackedGlobals[GV];
189 if (!isa<UndefValue>(GV->getInitializer()))
190 IV.markConstant(GV->getInitializer());
194 /// AddTrackedFunction - If the SCCP solver is supposed to track calls into
195 /// and out of the specified function (which cannot have its address taken),
196 /// this method must be called.
197 void AddTrackedFunction(Function *F) {
198 assert(F->hasInternalLinkage() && "Can only track internal functions!");
199 // Add an entry, F -> undef.
200 TrackedFunctionRetVals[F];
203 /// Solve - Solve for constants and executable blocks.
207 /// ResolvedUndefsIn - While solving the dataflow for a function, we assume
208 /// that branches on undef values cannot reach any of their successors.
209 /// However, this is not a safe assumption. After we solve dataflow, this
210 /// method should be use to handle this. If this returns true, the solver
212 bool ResolvedUndefsIn(Function &F);
214 /// getExecutableBlocks - Once we have solved for constants, return the set of
215 /// blocks that is known to be executable.
216 std::set<BasicBlock*> &getExecutableBlocks() {
220 /// getValueMapping - Once we have solved for constants, return the mapping of
221 /// LLVM values to LatticeVals.
222 hash_map<Value*, LatticeVal> &getValueMapping() {
226 /// getTrackedFunctionRetVals - Get the inferred return value map.
228 const hash_map<Function*, LatticeVal> &getTrackedFunctionRetVals() {
229 return TrackedFunctionRetVals;
232 /// getTrackedGlobals - Get and return the set of inferred initializers for
233 /// global variables.
234 const hash_map<GlobalVariable*, LatticeVal> &getTrackedGlobals() {
235 return TrackedGlobals;
240 // markConstant - Make a value be marked as "constant". If the value
241 // is not already a constant, add it to the instruction work list so that
242 // the users of the instruction are updated later.
244 inline void markConstant(LatticeVal &IV, Value *V, Constant *C) {
245 if (IV.markConstant(C)) {
246 DOUT << "markConstant: " << *C << ": " << *V;
247 InstWorkList.push_back(V);
251 inline void markForcedConstant(LatticeVal &IV, Value *V, Constant *C) {
252 IV.markForcedConstant(C);
253 DOUT << "markForcedConstant: " << *C << ": " << *V;
254 InstWorkList.push_back(V);
257 inline void markConstant(Value *V, Constant *C) {
258 markConstant(ValueState[V], V, C);
261 // markOverdefined - Make a value be marked as "overdefined". If the
262 // value is not already overdefined, add it to the overdefined instruction
263 // work list so that the users of the instruction are updated later.
265 inline void markOverdefined(LatticeVal &IV, Value *V) {
266 if (IV.markOverdefined()) {
267 DEBUG(DOUT << "markOverdefined: ";
268 if (Function *F = dyn_cast<Function>(V))
269 DOUT << "Function '" << F->getName() << "'\n";
272 // Only instructions go on the work list
273 OverdefinedInstWorkList.push_back(V);
276 inline void markOverdefined(Value *V) {
277 markOverdefined(ValueState[V], V);
280 inline void mergeInValue(LatticeVal &IV, Value *V, LatticeVal &MergeWithV) {
281 if (IV.isOverdefined() || MergeWithV.isUndefined())
283 if (MergeWithV.isOverdefined())
284 markOverdefined(IV, V);
285 else if (IV.isUndefined())
286 markConstant(IV, V, MergeWithV.getConstant());
287 else if (IV.getConstant() != MergeWithV.getConstant())
288 markOverdefined(IV, V);
291 inline void mergeInValue(Value *V, LatticeVal &MergeWithV) {
292 return mergeInValue(ValueState[V], V, MergeWithV);
296 // getValueState - Return the LatticeVal object that corresponds to the value.
297 // This function is necessary because not all values should start out in the
298 // underdefined state... Argument's should be overdefined, and
299 // constants should be marked as constants. If a value is not known to be an
300 // Instruction object, then use this accessor to get its value from the map.
302 inline LatticeVal &getValueState(Value *V) {
303 hash_map<Value*, LatticeVal>::iterator I = ValueState.find(V);
304 if (I != ValueState.end()) return I->second; // Common case, in the map
306 if (Constant *C = dyn_cast<Constant>(V)) {
307 if (isa<UndefValue>(V)) {
308 // Nothing to do, remain undefined.
310 ValueState[C].markConstant(C); // Constants are constant
313 // All others are underdefined by default...
314 return ValueState[V];
317 // markEdgeExecutable - Mark a basic block as executable, adding it to the BB
318 // work list if it is not already executable...
320 void markEdgeExecutable(BasicBlock *Source, BasicBlock *Dest) {
321 if (!KnownFeasibleEdges.insert(Edge(Source, Dest)).second)
322 return; // This edge is already known to be executable!
324 if (BBExecutable.count(Dest)) {
325 DOUT << "Marking Edge Executable: " << Source->getName()
326 << " -> " << Dest->getName() << "\n";
328 // The destination is already executable, but we just made an edge
329 // feasible that wasn't before. Revisit the PHI nodes in the block
330 // because they have potentially new operands.
331 for (BasicBlock::iterator I = Dest->begin(); isa<PHINode>(I); ++I)
332 visitPHINode(*cast<PHINode>(I));
335 MarkBlockExecutable(Dest);
339 // getFeasibleSuccessors - Return a vector of booleans to indicate which
340 // successors are reachable from a given terminator instruction.
342 void getFeasibleSuccessors(TerminatorInst &TI, std::vector<bool> &Succs);
344 // isEdgeFeasible - Return true if the control flow edge from the 'From' basic
345 // block to the 'To' basic block is currently feasible...
347 bool isEdgeFeasible(BasicBlock *From, BasicBlock *To);
349 // OperandChangedState - This method is invoked on all of the users of an
350 // instruction that was just changed state somehow.... Based on this
351 // information, we need to update the specified user of this instruction.
353 void OperandChangedState(User *U) {
354 // Only instructions use other variable values!
355 Instruction &I = cast<Instruction>(*U);
356 if (BBExecutable.count(I.getParent())) // Inst is executable?
361 friend class InstVisitor<SCCPSolver>;
363 // visit implementations - Something changed in this instruction... Either an
364 // operand made a transition, or the instruction is newly executable. Change
365 // the value type of I to reflect these changes if appropriate.
367 void visitPHINode(PHINode &I);
370 void visitReturnInst(ReturnInst &I);
371 void visitTerminatorInst(TerminatorInst &TI);
373 void visitCastInst(CastInst &I);
374 void visitSelectInst(SelectInst &I);
375 void visitBinaryOperator(Instruction &I);
376 void visitCmpInst(CmpInst &I);
377 void visitShiftInst(ShiftInst &I) { visitBinaryOperator(I); }
378 void visitExtractElementInst(ExtractElementInst &I);
379 void visitInsertElementInst(InsertElementInst &I);
380 void visitShuffleVectorInst(ShuffleVectorInst &I);
382 // Instructions that cannot be folded away...
383 void visitStoreInst (Instruction &I);
384 void visitLoadInst (LoadInst &I);
385 void visitGetElementPtrInst(GetElementPtrInst &I);
386 void visitCallInst (CallInst &I) { visitCallSite(CallSite::get(&I)); }
387 void visitInvokeInst (InvokeInst &II) {
388 visitCallSite(CallSite::get(&II));
389 visitTerminatorInst(II);
391 void visitCallSite (CallSite CS);
392 void visitUnwindInst (TerminatorInst &I) { /*returns void*/ }
393 void visitUnreachableInst(TerminatorInst &I) { /*returns void*/ }
394 void visitAllocationInst(Instruction &I) { markOverdefined(&I); }
395 void visitVANextInst (Instruction &I) { markOverdefined(&I); }
396 void visitVAArgInst (Instruction &I) { markOverdefined(&I); }
397 void visitFreeInst (Instruction &I) { /*returns void*/ }
399 void visitInstruction(Instruction &I) {
400 // If a new instruction is added to LLVM that we don't handle...
401 cerr << "SCCP: Don't know how to handle: " << I;
402 markOverdefined(&I); // Just in case
406 // getFeasibleSuccessors - Return a vector of booleans to indicate which
407 // successors are reachable from a given terminator instruction.
409 void SCCPSolver::getFeasibleSuccessors(TerminatorInst &TI,
410 std::vector<bool> &Succs) {
411 Succs.resize(TI.getNumSuccessors());
412 if (BranchInst *BI = dyn_cast<BranchInst>(&TI)) {
413 if (BI->isUnconditional()) {
416 LatticeVal &BCValue = getValueState(BI->getCondition());
417 if (BCValue.isOverdefined() ||
418 (BCValue.isConstant() && !isa<ConstantBool>(BCValue.getConstant()))) {
419 // Overdefined condition variables, and branches on unfoldable constant
420 // conditions, mean the branch could go either way.
421 Succs[0] = Succs[1] = true;
422 } else if (BCValue.isConstant()) {
423 // Constant condition variables mean the branch can only go a single way
424 Succs[BCValue.getConstant() == ConstantBool::getFalse()] = true;
427 } else if (isa<InvokeInst>(&TI)) {
428 // Invoke instructions successors are always executable.
429 Succs[0] = Succs[1] = true;
430 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(&TI)) {
431 LatticeVal &SCValue = getValueState(SI->getCondition());
432 if (SCValue.isOverdefined() || // Overdefined condition?
433 (SCValue.isConstant() && !isa<ConstantInt>(SCValue.getConstant()))) {
434 // All destinations are executable!
435 Succs.assign(TI.getNumSuccessors(), true);
436 } else if (SCValue.isConstant()) {
437 Constant *CPV = SCValue.getConstant();
438 // Make sure to skip the "default value" which isn't a value
439 for (unsigned i = 1, E = SI->getNumSuccessors(); i != E; ++i) {
440 if (SI->getSuccessorValue(i) == CPV) {// Found the right branch...
446 // Constant value not equal to any of the branches... must execute
447 // default branch then...
451 cerr << "SCCP: Don't know how to handle: " << TI;
452 Succs.assign(TI.getNumSuccessors(), true);
457 // isEdgeFeasible - Return true if the control flow edge from the 'From' basic
458 // block to the 'To' basic block is currently feasible...
460 bool SCCPSolver::isEdgeFeasible(BasicBlock *From, BasicBlock *To) {
461 assert(BBExecutable.count(To) && "Dest should always be alive!");
463 // Make sure the source basic block is executable!!
464 if (!BBExecutable.count(From)) return false;
466 // Check to make sure this edge itself is actually feasible now...
467 TerminatorInst *TI = From->getTerminator();
468 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
469 if (BI->isUnconditional())
472 LatticeVal &BCValue = getValueState(BI->getCondition());
473 if (BCValue.isOverdefined()) {
474 // Overdefined condition variables mean the branch could go either way.
476 } else if (BCValue.isConstant()) {
477 // Not branching on an evaluatable constant?
478 if (!isa<ConstantBool>(BCValue.getConstant())) return true;
480 // Constant condition variables mean the branch can only go a single way
481 return BI->getSuccessor(BCValue.getConstant() ==
482 ConstantBool::getFalse()) == To;
486 } else if (isa<InvokeInst>(TI)) {
487 // Invoke instructions successors are always executable.
489 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
490 LatticeVal &SCValue = getValueState(SI->getCondition());
491 if (SCValue.isOverdefined()) { // Overdefined condition?
492 // All destinations are executable!
494 } else if (SCValue.isConstant()) {
495 Constant *CPV = SCValue.getConstant();
496 if (!isa<ConstantInt>(CPV))
497 return true; // not a foldable constant?
499 // Make sure to skip the "default value" which isn't a value
500 for (unsigned i = 1, E = SI->getNumSuccessors(); i != E; ++i)
501 if (SI->getSuccessorValue(i) == CPV) // Found the taken branch...
502 return SI->getSuccessor(i) == To;
504 // Constant value not equal to any of the branches... must execute
505 // default branch then...
506 return SI->getDefaultDest() == To;
510 cerr << "Unknown terminator instruction: " << *TI;
515 // visit Implementations - Something changed in this instruction... Either an
516 // operand made a transition, or the instruction is newly executable. Change
517 // the value type of I to reflect these changes if appropriate. This method
518 // makes sure to do the following actions:
520 // 1. If a phi node merges two constants in, and has conflicting value coming
521 // from different branches, or if the PHI node merges in an overdefined
522 // value, then the PHI node becomes overdefined.
523 // 2. If a phi node merges only constants in, and they all agree on value, the
524 // PHI node becomes a constant value equal to that.
525 // 3. If V <- x (op) y && isConstant(x) && isConstant(y) V = Constant
526 // 4. If V <- x (op) y && (isOverdefined(x) || isOverdefined(y)) V = Overdefined
527 // 5. If V <- MEM or V <- CALL or V <- (unknown) then V = Overdefined
528 // 6. If a conditional branch has a value that is constant, make the selected
529 // destination executable
530 // 7. If a conditional branch has a value that is overdefined, make all
531 // successors executable.
533 void SCCPSolver::visitPHINode(PHINode &PN) {
534 LatticeVal &PNIV = getValueState(&PN);
535 if (PNIV.isOverdefined()) {
536 // There may be instructions using this PHI node that are not overdefined
537 // themselves. If so, make sure that they know that the PHI node operand
539 std::multimap<PHINode*, Instruction*>::iterator I, E;
540 tie(I, E) = UsersOfOverdefinedPHIs.equal_range(&PN);
542 std::vector<Instruction*> Users;
543 Users.reserve(std::distance(I, E));
544 for (; I != E; ++I) Users.push_back(I->second);
545 while (!Users.empty()) {
550 return; // Quick exit
553 // Super-extra-high-degree PHI nodes are unlikely to ever be marked constant,
554 // and slow us down a lot. Just mark them overdefined.
555 if (PN.getNumIncomingValues() > 64) {
556 markOverdefined(PNIV, &PN);
560 // Look at all of the executable operands of the PHI node. If any of them
561 // are overdefined, the PHI becomes overdefined as well. If they are all
562 // constant, and they agree with each other, the PHI becomes the identical
563 // constant. If they are constant and don't agree, the PHI is overdefined.
564 // If there are no executable operands, the PHI remains undefined.
566 Constant *OperandVal = 0;
567 for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) {
568 LatticeVal &IV = getValueState(PN.getIncomingValue(i));
569 if (IV.isUndefined()) continue; // Doesn't influence PHI node.
571 if (isEdgeFeasible(PN.getIncomingBlock(i), PN.getParent())) {
572 if (IV.isOverdefined()) { // PHI node becomes overdefined!
573 markOverdefined(PNIV, &PN);
577 if (OperandVal == 0) { // Grab the first value...
578 OperandVal = IV.getConstant();
579 } else { // Another value is being merged in!
580 // There is already a reachable operand. If we conflict with it,
581 // then the PHI node becomes overdefined. If we agree with it, we
584 // Check to see if there are two different constants merging...
585 if (IV.getConstant() != OperandVal) {
586 // Yes there is. This means the PHI node is not constant.
587 // You must be overdefined poor PHI.
589 markOverdefined(PNIV, &PN); // The PHI node now becomes overdefined
590 return; // I'm done analyzing you
596 // If we exited the loop, this means that the PHI node only has constant
597 // arguments that agree with each other(and OperandVal is the constant) or
598 // OperandVal is null because there are no defined incoming arguments. If
599 // this is the case, the PHI remains undefined.
602 markConstant(PNIV, &PN, OperandVal); // Acquire operand value
605 void SCCPSolver::visitReturnInst(ReturnInst &I) {
606 if (I.getNumOperands() == 0) return; // Ret void
608 // If we are tracking the return value of this function, merge it in.
609 Function *F = I.getParent()->getParent();
610 if (F->hasInternalLinkage() && !TrackedFunctionRetVals.empty()) {
611 hash_map<Function*, LatticeVal>::iterator TFRVI =
612 TrackedFunctionRetVals.find(F);
613 if (TFRVI != TrackedFunctionRetVals.end() &&
614 !TFRVI->second.isOverdefined()) {
615 LatticeVal &IV = getValueState(I.getOperand(0));
616 mergeInValue(TFRVI->second, F, IV);
622 void SCCPSolver::visitTerminatorInst(TerminatorInst &TI) {
623 std::vector<bool> SuccFeasible;
624 getFeasibleSuccessors(TI, SuccFeasible);
626 BasicBlock *BB = TI.getParent();
628 // Mark all feasible successors executable...
629 for (unsigned i = 0, e = SuccFeasible.size(); i != e; ++i)
631 markEdgeExecutable(BB, TI.getSuccessor(i));
634 void SCCPSolver::visitCastInst(CastInst &I) {
635 Value *V = I.getOperand(0);
636 LatticeVal &VState = getValueState(V);
637 if (VState.isOverdefined()) // Inherit overdefinedness of operand
639 else if (VState.isConstant()) // Propagate constant value
640 markConstant(&I, ConstantExpr::getCast(I.getOpcode(),
641 VState.getConstant(), I.getType()));
644 void SCCPSolver::visitSelectInst(SelectInst &I) {
645 LatticeVal &CondValue = getValueState(I.getCondition());
646 if (CondValue.isUndefined())
648 if (CondValue.isConstant()) {
649 if (ConstantBool *CondCB = dyn_cast<ConstantBool>(CondValue.getConstant())){
650 mergeInValue(&I, getValueState(CondCB->getValue() ? I.getTrueValue()
651 : I.getFalseValue()));
656 // Otherwise, the condition is overdefined or a constant we can't evaluate.
657 // See if we can produce something better than overdefined based on the T/F
659 LatticeVal &TVal = getValueState(I.getTrueValue());
660 LatticeVal &FVal = getValueState(I.getFalseValue());
662 // select ?, C, C -> C.
663 if (TVal.isConstant() && FVal.isConstant() &&
664 TVal.getConstant() == FVal.getConstant()) {
665 markConstant(&I, FVal.getConstant());
669 if (TVal.isUndefined()) { // select ?, undef, X -> X.
670 mergeInValue(&I, FVal);
671 } else if (FVal.isUndefined()) { // select ?, X, undef -> X.
672 mergeInValue(&I, TVal);
678 // Handle BinaryOperators and Shift Instructions...
679 void SCCPSolver::visitBinaryOperator(Instruction &I) {
680 LatticeVal &IV = ValueState[&I];
681 if (IV.isOverdefined()) return;
683 LatticeVal &V1State = getValueState(I.getOperand(0));
684 LatticeVal &V2State = getValueState(I.getOperand(1));
686 if (V1State.isOverdefined() || V2State.isOverdefined()) {
687 // If this is an AND or OR with 0 or -1, it doesn't matter that the other
688 // operand is overdefined.
689 if (I.getOpcode() == Instruction::And || I.getOpcode() == Instruction::Or) {
690 LatticeVal *NonOverdefVal = 0;
691 if (!V1State.isOverdefined()) {
692 NonOverdefVal = &V1State;
693 } else if (!V2State.isOverdefined()) {
694 NonOverdefVal = &V2State;
698 if (NonOverdefVal->isUndefined()) {
699 // Could annihilate value.
700 if (I.getOpcode() == Instruction::And)
701 markConstant(IV, &I, Constant::getNullValue(I.getType()));
703 markConstant(IV, &I, ConstantInt::getAllOnesValue(I.getType()));
706 if (I.getOpcode() == Instruction::And) {
707 if (NonOverdefVal->getConstant()->isNullValue()) {
708 markConstant(IV, &I, NonOverdefVal->getConstant());
709 return; // X or 0 = -1
712 if (ConstantIntegral *CI =
713 dyn_cast<ConstantIntegral>(NonOverdefVal->getConstant()))
714 if (CI->isAllOnesValue()) {
715 markConstant(IV, &I, NonOverdefVal->getConstant());
716 return; // X or -1 = -1
724 // If both operands are PHI nodes, it is possible that this instruction has
725 // a constant value, despite the fact that the PHI node doesn't. Check for
726 // this condition now.
727 if (PHINode *PN1 = dyn_cast<PHINode>(I.getOperand(0)))
728 if (PHINode *PN2 = dyn_cast<PHINode>(I.getOperand(1)))
729 if (PN1->getParent() == PN2->getParent()) {
730 // Since the two PHI nodes are in the same basic block, they must have
731 // entries for the same predecessors. Walk the predecessor list, and
732 // if all of the incoming values are constants, and the result of
733 // evaluating this expression with all incoming value pairs is the
734 // same, then this expression is a constant even though the PHI node
735 // is not a constant!
737 for (unsigned i = 0, e = PN1->getNumIncomingValues(); i != e; ++i) {
738 LatticeVal &In1 = getValueState(PN1->getIncomingValue(i));
739 BasicBlock *InBlock = PN1->getIncomingBlock(i);
741 getValueState(PN2->getIncomingValueForBlock(InBlock));
743 if (In1.isOverdefined() || In2.isOverdefined()) {
744 Result.markOverdefined();
745 break; // Cannot fold this operation over the PHI nodes!
746 } else if (In1.isConstant() && In2.isConstant()) {
747 Constant *V = ConstantExpr::get(I.getOpcode(), In1.getConstant(),
749 if (Result.isUndefined())
750 Result.markConstant(V);
751 else if (Result.isConstant() && Result.getConstant() != V) {
752 Result.markOverdefined();
758 // If we found a constant value here, then we know the instruction is
759 // constant despite the fact that the PHI nodes are overdefined.
760 if (Result.isConstant()) {
761 markConstant(IV, &I, Result.getConstant());
762 // Remember that this instruction is virtually using the PHI node
764 UsersOfOverdefinedPHIs.insert(std::make_pair(PN1, &I));
765 UsersOfOverdefinedPHIs.insert(std::make_pair(PN2, &I));
767 } else if (Result.isUndefined()) {
771 // Okay, this really is overdefined now. Since we might have
772 // speculatively thought that this was not overdefined before, and
773 // added ourselves to the UsersOfOverdefinedPHIs list for the PHIs,
774 // make sure to clean out any entries that we put there, for
776 std::multimap<PHINode*, Instruction*>::iterator It, E;
777 tie(It, E) = UsersOfOverdefinedPHIs.equal_range(PN1);
779 if (It->second == &I) {
780 UsersOfOverdefinedPHIs.erase(It++);
784 tie(It, E) = UsersOfOverdefinedPHIs.equal_range(PN2);
786 if (It->second == &I) {
787 UsersOfOverdefinedPHIs.erase(It++);
793 markOverdefined(IV, &I);
794 } else if (V1State.isConstant() && V2State.isConstant()) {
795 markConstant(IV, &I, ConstantExpr::get(I.getOpcode(), V1State.getConstant(),
796 V2State.getConstant()));
800 // Handle ICmpInst instruction...
801 void SCCPSolver::visitCmpInst(CmpInst &I) {
802 LatticeVal &IV = ValueState[&I];
803 if (IV.isOverdefined()) return;
805 LatticeVal &V1State = getValueState(I.getOperand(0));
806 LatticeVal &V2State = getValueState(I.getOperand(1));
808 if (V1State.isOverdefined() || V2State.isOverdefined()) {
809 // If both operands are PHI nodes, it is possible that this instruction has
810 // a constant value, despite the fact that the PHI node doesn't. Check for
811 // this condition now.
812 if (PHINode *PN1 = dyn_cast<PHINode>(I.getOperand(0)))
813 if (PHINode *PN2 = dyn_cast<PHINode>(I.getOperand(1)))
814 if (PN1->getParent() == PN2->getParent()) {
815 // Since the two PHI nodes are in the same basic block, they must have
816 // entries for the same predecessors. Walk the predecessor list, and
817 // if all of the incoming values are constants, and the result of
818 // evaluating this expression with all incoming value pairs is the
819 // same, then this expression is a constant even though the PHI node
820 // is not a constant!
822 for (unsigned i = 0, e = PN1->getNumIncomingValues(); i != e; ++i) {
823 LatticeVal &In1 = getValueState(PN1->getIncomingValue(i));
824 BasicBlock *InBlock = PN1->getIncomingBlock(i);
826 getValueState(PN2->getIncomingValueForBlock(InBlock));
828 if (In1.isOverdefined() || In2.isOverdefined()) {
829 Result.markOverdefined();
830 break; // Cannot fold this operation over the PHI nodes!
831 } else if (In1.isConstant() && In2.isConstant()) {
832 Constant *V = ConstantExpr::getCompare(I.getPredicate(),
835 if (Result.isUndefined())
836 Result.markConstant(V);
837 else if (Result.isConstant() && Result.getConstant() != V) {
838 Result.markOverdefined();
844 // If we found a constant value here, then we know the instruction is
845 // constant despite the fact that the PHI nodes are overdefined.
846 if (Result.isConstant()) {
847 markConstant(IV, &I, Result.getConstant());
848 // Remember that this instruction is virtually using the PHI node
850 UsersOfOverdefinedPHIs.insert(std::make_pair(PN1, &I));
851 UsersOfOverdefinedPHIs.insert(std::make_pair(PN2, &I));
853 } else if (Result.isUndefined()) {
857 // Okay, this really is overdefined now. Since we might have
858 // speculatively thought that this was not overdefined before, and
859 // added ourselves to the UsersOfOverdefinedPHIs list for the PHIs,
860 // make sure to clean out any entries that we put there, for
862 std::multimap<PHINode*, Instruction*>::iterator It, E;
863 tie(It, E) = UsersOfOverdefinedPHIs.equal_range(PN1);
865 if (It->second == &I) {
866 UsersOfOverdefinedPHIs.erase(It++);
870 tie(It, E) = UsersOfOverdefinedPHIs.equal_range(PN2);
872 if (It->second == &I) {
873 UsersOfOverdefinedPHIs.erase(It++);
879 markOverdefined(IV, &I);
880 } else if (V1State.isConstant() && V2State.isConstant()) {
881 markConstant(IV, &I, ConstantExpr::getCompare(I.getPredicate(),
882 V1State.getConstant(),
883 V2State.getConstant()));
887 void SCCPSolver::visitExtractElementInst(ExtractElementInst &I) {
888 // FIXME : SCCP does not handle vectors properly.
893 LatticeVal &ValState = getValueState(I.getOperand(0));
894 LatticeVal &IdxState = getValueState(I.getOperand(1));
896 if (ValState.isOverdefined() || IdxState.isOverdefined())
898 else if(ValState.isConstant() && IdxState.isConstant())
899 markConstant(&I, ConstantExpr::getExtractElement(ValState.getConstant(),
900 IdxState.getConstant()));
904 void SCCPSolver::visitInsertElementInst(InsertElementInst &I) {
905 // FIXME : SCCP does not handle vectors properly.
909 LatticeVal &ValState = getValueState(I.getOperand(0));
910 LatticeVal &EltState = getValueState(I.getOperand(1));
911 LatticeVal &IdxState = getValueState(I.getOperand(2));
913 if (ValState.isOverdefined() || EltState.isOverdefined() ||
914 IdxState.isOverdefined())
916 else if(ValState.isConstant() && EltState.isConstant() &&
917 IdxState.isConstant())
918 markConstant(&I, ConstantExpr::getInsertElement(ValState.getConstant(),
919 EltState.getConstant(),
920 IdxState.getConstant()));
921 else if (ValState.isUndefined() && EltState.isConstant() &&
922 IdxState.isConstant())
923 markConstant(&I, ConstantExpr::getInsertElement(UndefValue::get(I.getType()),
924 EltState.getConstant(),
925 IdxState.getConstant()));
929 void SCCPSolver::visitShuffleVectorInst(ShuffleVectorInst &I) {
930 // FIXME : SCCP does not handle vectors properly.
934 LatticeVal &V1State = getValueState(I.getOperand(0));
935 LatticeVal &V2State = getValueState(I.getOperand(1));
936 LatticeVal &MaskState = getValueState(I.getOperand(2));
938 if (MaskState.isUndefined() ||
939 (V1State.isUndefined() && V2State.isUndefined()))
940 return; // Undefined output if mask or both inputs undefined.
942 if (V1State.isOverdefined() || V2State.isOverdefined() ||
943 MaskState.isOverdefined()) {
946 // A mix of constant/undef inputs.
947 Constant *V1 = V1State.isConstant() ?
948 V1State.getConstant() : UndefValue::get(I.getType());
949 Constant *V2 = V2State.isConstant() ?
950 V2State.getConstant() : UndefValue::get(I.getType());
951 Constant *Mask = MaskState.isConstant() ?
952 MaskState.getConstant() : UndefValue::get(I.getOperand(2)->getType());
953 markConstant(&I, ConstantExpr::getShuffleVector(V1, V2, Mask));
958 // Handle getelementptr instructions... if all operands are constants then we
959 // can turn this into a getelementptr ConstantExpr.
961 void SCCPSolver::visitGetElementPtrInst(GetElementPtrInst &I) {
962 LatticeVal &IV = ValueState[&I];
963 if (IV.isOverdefined()) return;
965 std::vector<Constant*> Operands;
966 Operands.reserve(I.getNumOperands());
968 for (unsigned i = 0, e = I.getNumOperands(); i != e; ++i) {
969 LatticeVal &State = getValueState(I.getOperand(i));
970 if (State.isUndefined())
971 return; // Operands are not resolved yet...
972 else if (State.isOverdefined()) {
973 markOverdefined(IV, &I);
976 assert(State.isConstant() && "Unknown state!");
977 Operands.push_back(State.getConstant());
980 Constant *Ptr = Operands[0];
981 Operands.erase(Operands.begin()); // Erase the pointer from idx list...
983 markConstant(IV, &I, ConstantExpr::getGetElementPtr(Ptr, Operands));
986 void SCCPSolver::visitStoreInst(Instruction &SI) {
987 if (TrackedGlobals.empty() || !isa<GlobalVariable>(SI.getOperand(1)))
989 GlobalVariable *GV = cast<GlobalVariable>(SI.getOperand(1));
990 hash_map<GlobalVariable*, LatticeVal>::iterator I = TrackedGlobals.find(GV);
991 if (I == TrackedGlobals.end() || I->second.isOverdefined()) return;
993 // Get the value we are storing into the global.
994 LatticeVal &PtrVal = getValueState(SI.getOperand(0));
996 mergeInValue(I->second, GV, PtrVal);
997 if (I->second.isOverdefined())
998 TrackedGlobals.erase(I); // No need to keep tracking this!
1002 // Handle load instructions. If the operand is a constant pointer to a constant
1003 // global, we can replace the load with the loaded constant value!
1004 void SCCPSolver::visitLoadInst(LoadInst &I) {
1005 LatticeVal &IV = ValueState[&I];
1006 if (IV.isOverdefined()) return;
1008 LatticeVal &PtrVal = getValueState(I.getOperand(0));
1009 if (PtrVal.isUndefined()) return; // The pointer is not resolved yet!
1010 if (PtrVal.isConstant() && !I.isVolatile()) {
1011 Value *Ptr = PtrVal.getConstant();
1012 if (isa<ConstantPointerNull>(Ptr)) {
1013 // load null -> null
1014 markConstant(IV, &I, Constant::getNullValue(I.getType()));
1018 // Transform load (constant global) into the value loaded.
1019 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Ptr)) {
1020 if (GV->isConstant()) {
1021 if (!GV->isExternal()) {
1022 markConstant(IV, &I, GV->getInitializer());
1025 } else if (!TrackedGlobals.empty()) {
1026 // If we are tracking this global, merge in the known value for it.
1027 hash_map<GlobalVariable*, LatticeVal>::iterator It =
1028 TrackedGlobals.find(GV);
1029 if (It != TrackedGlobals.end()) {
1030 mergeInValue(IV, &I, It->second);
1036 // Transform load (constantexpr_GEP global, 0, ...) into the value loaded.
1037 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr))
1038 if (CE->getOpcode() == Instruction::GetElementPtr)
1039 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(CE->getOperand(0)))
1040 if (GV->isConstant() && !GV->isExternal())
1042 ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE)) {
1043 markConstant(IV, &I, V);
1048 // Otherwise we cannot say for certain what value this load will produce.
1050 markOverdefined(IV, &I);
1053 void SCCPSolver::visitCallSite(CallSite CS) {
1054 Function *F = CS.getCalledFunction();
1056 // If we are tracking this function, we must make sure to bind arguments as
1058 hash_map<Function*, LatticeVal>::iterator TFRVI =TrackedFunctionRetVals.end();
1059 if (F && F->hasInternalLinkage())
1060 TFRVI = TrackedFunctionRetVals.find(F);
1062 if (TFRVI != TrackedFunctionRetVals.end()) {
1063 // If this is the first call to the function hit, mark its entry block
1065 if (!BBExecutable.count(F->begin()))
1066 MarkBlockExecutable(F->begin());
1068 CallSite::arg_iterator CAI = CS.arg_begin();
1069 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
1070 AI != E; ++AI, ++CAI) {
1071 LatticeVal &IV = ValueState[AI];
1072 if (!IV.isOverdefined())
1073 mergeInValue(IV, AI, getValueState(*CAI));
1076 Instruction *I = CS.getInstruction();
1077 if (I->getType() == Type::VoidTy) return;
1079 LatticeVal &IV = ValueState[I];
1080 if (IV.isOverdefined()) return;
1082 // Propagate the return value of the function to the value of the instruction.
1083 if (TFRVI != TrackedFunctionRetVals.end()) {
1084 mergeInValue(IV, I, TFRVI->second);
1088 if (F == 0 || !F->isExternal() || !canConstantFoldCallTo(F)) {
1089 markOverdefined(IV, I);
1093 std::vector<Constant*> Operands;
1094 Operands.reserve(I->getNumOperands()-1);
1096 for (CallSite::arg_iterator AI = CS.arg_begin(), E = CS.arg_end();
1098 LatticeVal &State = getValueState(*AI);
1099 if (State.isUndefined())
1100 return; // Operands are not resolved yet...
1101 else if (State.isOverdefined()) {
1102 markOverdefined(IV, I);
1105 assert(State.isConstant() && "Unknown state!");
1106 Operands.push_back(State.getConstant());
1109 if (Constant *C = ConstantFoldCall(F, Operands))
1110 markConstant(IV, I, C);
1112 markOverdefined(IV, I);
1116 void SCCPSolver::Solve() {
1117 // Process the work lists until they are empty!
1118 while (!BBWorkList.empty() || !InstWorkList.empty() ||
1119 !OverdefinedInstWorkList.empty()) {
1120 // Process the instruction work list...
1121 while (!OverdefinedInstWorkList.empty()) {
1122 Value *I = OverdefinedInstWorkList.back();
1123 OverdefinedInstWorkList.pop_back();
1125 DOUT << "\nPopped off OI-WL: " << *I;
1127 // "I" got into the work list because it either made the transition from
1128 // bottom to constant
1130 // Anything on this worklist that is overdefined need not be visited
1131 // since all of its users will have already been marked as overdefined
1132 // Update all of the users of this instruction's value...
1134 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
1136 OperandChangedState(*UI);
1138 // Process the instruction work list...
1139 while (!InstWorkList.empty()) {
1140 Value *I = InstWorkList.back();
1141 InstWorkList.pop_back();
1143 DOUT << "\nPopped off I-WL: " << *I;
1145 // "I" got into the work list because it either made the transition from
1146 // bottom to constant
1148 // Anything on this worklist that is overdefined need not be visited
1149 // since all of its users will have already been marked as overdefined.
1150 // Update all of the users of this instruction's value...
1152 if (!getValueState(I).isOverdefined())
1153 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
1155 OperandChangedState(*UI);
1158 // Process the basic block work list...
1159 while (!BBWorkList.empty()) {
1160 BasicBlock *BB = BBWorkList.back();
1161 BBWorkList.pop_back();
1163 DOUT << "\nPopped off BBWL: " << *BB;
1165 // Notify all instructions in this basic block that they are newly
1172 /// ResolvedUndefsIn - While solving the dataflow for a function, we assume
1173 /// that branches on undef values cannot reach any of their successors.
1174 /// However, this is not a safe assumption. After we solve dataflow, this
1175 /// method should be use to handle this. If this returns true, the solver
1176 /// should be rerun.
1178 /// This method handles this by finding an unresolved branch and marking it one
1179 /// of the edges from the block as being feasible, even though the condition
1180 /// doesn't say it would otherwise be. This allows SCCP to find the rest of the
1181 /// CFG and only slightly pessimizes the analysis results (by marking one,
1182 /// potentially infeasible, edge feasible). This cannot usefully modify the
1183 /// constraints on the condition of the branch, as that would impact other users
1186 /// This scan also checks for values that use undefs, whose results are actually
1187 /// defined. For example, 'zext i8 undef to i32' should produce all zeros
1188 /// conservatively, as "(zext i8 X -> i32) & 0xFF00" must always return zero,
1189 /// even if X isn't defined.
1190 bool SCCPSolver::ResolvedUndefsIn(Function &F) {
1191 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
1192 if (!BBExecutable.count(BB))
1195 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
1196 // Look for instructions which produce undef values.
1197 if (I->getType() == Type::VoidTy) continue;
1199 LatticeVal &LV = getValueState(I);
1200 if (!LV.isUndefined()) continue;
1202 // Get the lattice values of the first two operands for use below.
1203 LatticeVal &Op0LV = getValueState(I->getOperand(0));
1205 if (I->getNumOperands() == 2) {
1206 // If this is a two-operand instruction, and if both operands are
1207 // undefs, the result stays undef.
1208 Op1LV = getValueState(I->getOperand(1));
1209 if (Op0LV.isUndefined() && Op1LV.isUndefined())
1213 // If this is an instructions whose result is defined even if the input is
1214 // not fully defined, propagate the information.
1215 const Type *ITy = I->getType();
1216 switch (I->getOpcode()) {
1217 default: break; // Leave the instruction as an undef.
1218 case Instruction::ZExt:
1219 // After a zero extend, we know the top part is zero. SExt doesn't have
1220 // to be handled here, because we don't know whether the top part is 1's
1222 assert(Op0LV.isUndefined());
1223 markForcedConstant(LV, I, Constant::getNullValue(ITy));
1225 case Instruction::Mul:
1226 case Instruction::And:
1227 // undef * X -> 0. X could be zero.
1228 // undef & X -> 0. X could be zero.
1229 markForcedConstant(LV, I, Constant::getNullValue(ITy));
1232 case Instruction::Or:
1233 // undef | X -> -1. X could be -1.
1234 markForcedConstant(LV, I, ConstantInt::getAllOnesValue(ITy));
1237 case Instruction::SDiv:
1238 case Instruction::UDiv:
1239 case Instruction::SRem:
1240 case Instruction::URem:
1241 // X / undef -> undef. No change.
1242 // X % undef -> undef. No change.
1243 if (Op1LV.isUndefined()) break;
1245 // undef / X -> 0. X could be maxint.
1246 // undef % X -> 0. X could be 1.
1247 markForcedConstant(LV, I, Constant::getNullValue(ITy));
1250 case Instruction::AShr:
1251 // undef >>s X -> undef. No change.
1252 if (Op0LV.isUndefined()) break;
1254 // X >>s undef -> X. X could be 0, X could have the high-bit known set.
1255 if (Op0LV.isConstant())
1256 markForcedConstant(LV, I, Op0LV.getConstant());
1258 markOverdefined(LV, I);
1260 case Instruction::LShr:
1261 case Instruction::Shl:
1262 // undef >> X -> undef. No change.
1263 // undef << X -> undef. No change.
1264 if (Op0LV.isUndefined()) break;
1266 // X >> undef -> 0. X could be 0.
1267 // X << undef -> 0. X could be 0.
1268 markForcedConstant(LV, I, Constant::getNullValue(ITy));
1270 case Instruction::Select:
1271 // undef ? X : Y -> X or Y. There could be commonality between X/Y.
1272 if (Op0LV.isUndefined()) {
1273 if (!Op1LV.isConstant()) // Pick the constant one if there is any.
1274 Op1LV = getValueState(I->getOperand(2));
1275 } else if (Op1LV.isUndefined()) {
1276 // c ? undef : undef -> undef. No change.
1277 Op1LV = getValueState(I->getOperand(2));
1278 if (Op1LV.isUndefined())
1280 // Otherwise, c ? undef : x -> x.
1282 // Leave Op1LV as Operand(1)'s LatticeValue.
1285 if (Op1LV.isConstant())
1286 markForcedConstant(LV, I, Op1LV.getConstant());
1288 markOverdefined(LV, I);
1293 TerminatorInst *TI = BB->getTerminator();
1294 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
1295 if (!BI->isConditional()) continue;
1296 if (!getValueState(BI->getCondition()).isUndefined())
1298 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
1299 if (!getValueState(SI->getCondition()).isUndefined())
1305 // If the edge to the first successor isn't thought to be feasible yet, mark
1307 if (KnownFeasibleEdges.count(Edge(BB, TI->getSuccessor(0))))
1310 // Otherwise, it isn't already thought to be feasible. Mark it as such now
1311 // and return. This will make other blocks reachable, which will allow new
1312 // values to be discovered and existing ones to be moved in the lattice.
1313 markEdgeExecutable(BB, TI->getSuccessor(0));
1322 //===--------------------------------------------------------------------===//
1324 /// SCCP Class - This class uses the SCCPSolver to implement a per-function
1325 /// Sparse Conditional COnstant Propagator.
1327 struct SCCP : public FunctionPass {
1328 // runOnFunction - Run the Sparse Conditional Constant Propagation
1329 // algorithm, and return true if the function was modified.
1331 bool runOnFunction(Function &F);
1333 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
1334 AU.setPreservesCFG();
1338 RegisterPass<SCCP> X("sccp", "Sparse Conditional Constant Propagation");
1339 } // end anonymous namespace
1342 // createSCCPPass - This is the public interface to this file...
1343 FunctionPass *llvm::createSCCPPass() {
1348 // runOnFunction() - Run the Sparse Conditional Constant Propagation algorithm,
1349 // and return true if the function was modified.
1351 bool SCCP::runOnFunction(Function &F) {
1352 DOUT << "SCCP on function '" << F.getName() << "'\n";
1355 // Mark the first block of the function as being executable.
1356 Solver.MarkBlockExecutable(F.begin());
1358 // Mark all arguments to the function as being overdefined.
1359 hash_map<Value*, LatticeVal> &Values = Solver.getValueMapping();
1360 for (Function::arg_iterator AI = F.arg_begin(), E = F.arg_end(); AI != E; ++AI)
1361 Values[AI].markOverdefined();
1363 // Solve for constants.
1364 bool ResolvedUndefs = true;
1365 while (ResolvedUndefs) {
1367 DOUT << "RESOLVING UNDEFs\n";
1368 ResolvedUndefs = Solver.ResolvedUndefsIn(F);
1371 bool MadeChanges = false;
1373 // If we decided that there are basic blocks that are dead in this function,
1374 // delete their contents now. Note that we cannot actually delete the blocks,
1375 // as we cannot modify the CFG of the function.
1377 std::set<BasicBlock*> &ExecutableBBs = Solver.getExecutableBlocks();
1378 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
1379 if (!ExecutableBBs.count(BB)) {
1380 DOUT << " BasicBlock Dead:" << *BB;
1383 // Delete the instructions backwards, as it has a reduced likelihood of
1384 // having to update as many def-use and use-def chains.
1385 std::vector<Instruction*> Insts;
1386 for (BasicBlock::iterator I = BB->begin(), E = BB->getTerminator();
1389 while (!Insts.empty()) {
1390 Instruction *I = Insts.back();
1392 if (!I->use_empty())
1393 I->replaceAllUsesWith(UndefValue::get(I->getType()));
1394 BB->getInstList().erase(I);
1399 // Iterate over all of the instructions in a function, replacing them with
1400 // constants if we have found them to be of constant values.
1402 for (BasicBlock::iterator BI = BB->begin(), E = BB->end(); BI != E; ) {
1403 Instruction *Inst = BI++;
1404 if (Inst->getType() != Type::VoidTy) {
1405 LatticeVal &IV = Values[Inst];
1406 if (IV.isConstant() || IV.isUndefined() &&
1407 !isa<TerminatorInst>(Inst)) {
1408 Constant *Const = IV.isConstant()
1409 ? IV.getConstant() : UndefValue::get(Inst->getType());
1410 DOUT << " Constant: " << *Const << " = " << *Inst;
1412 // Replaces all of the uses of a variable with uses of the constant.
1413 Inst->replaceAllUsesWith(Const);
1415 // Delete the instruction.
1416 BB->getInstList().erase(Inst);
1418 // Hey, we just changed something!
1430 //===--------------------------------------------------------------------===//
1432 /// IPSCCP Class - This class implements interprocedural Sparse Conditional
1433 /// Constant Propagation.
1435 struct IPSCCP : public ModulePass {
1436 bool runOnModule(Module &M);
1439 RegisterPass<IPSCCP>
1440 Y("ipsccp", "Interprocedural Sparse Conditional Constant Propagation");
1441 } // end anonymous namespace
1443 // createIPSCCPPass - This is the public interface to this file...
1444 ModulePass *llvm::createIPSCCPPass() {
1445 return new IPSCCP();
1449 static bool AddressIsTaken(GlobalValue *GV) {
1450 // Delete any dead constantexpr klingons.
1451 GV->removeDeadConstantUsers();
1453 for (Value::use_iterator UI = GV->use_begin(), E = GV->use_end();
1455 if (StoreInst *SI = dyn_cast<StoreInst>(*UI)) {
1456 if (SI->getOperand(0) == GV || SI->isVolatile())
1457 return true; // Storing addr of GV.
1458 } else if (isa<InvokeInst>(*UI) || isa<CallInst>(*UI)) {
1459 // Make sure we are calling the function, not passing the address.
1460 CallSite CS = CallSite::get(cast<Instruction>(*UI));
1461 for (CallSite::arg_iterator AI = CS.arg_begin(),
1462 E = CS.arg_end(); AI != E; ++AI)
1465 } else if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) {
1466 if (LI->isVolatile())
1474 bool IPSCCP::runOnModule(Module &M) {
1477 // Loop over all functions, marking arguments to those with their addresses
1478 // taken or that are external as overdefined.
1480 hash_map<Value*, LatticeVal> &Values = Solver.getValueMapping();
1481 for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F)
1482 if (!F->hasInternalLinkage() || AddressIsTaken(F)) {
1483 if (!F->isExternal())
1484 Solver.MarkBlockExecutable(F->begin());
1485 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
1487 Values[AI].markOverdefined();
1489 Solver.AddTrackedFunction(F);
1492 // Loop over global variables. We inform the solver about any internal global
1493 // variables that do not have their 'addresses taken'. If they don't have
1494 // their addresses taken, we can propagate constants through them.
1495 for (Module::global_iterator G = M.global_begin(), E = M.global_end();
1497 if (!G->isConstant() && G->hasInternalLinkage() && !AddressIsTaken(G))
1498 Solver.TrackValueOfGlobalVariable(G);
1500 // Solve for constants.
1501 bool ResolvedUndefs = true;
1502 while (ResolvedUndefs) {
1505 DOUT << "RESOLVING UNDEFS\n";
1506 ResolvedUndefs = false;
1507 for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F)
1508 ResolvedUndefs |= Solver.ResolvedUndefsIn(*F);
1511 bool MadeChanges = false;
1513 // Iterate over all of the instructions in the module, replacing them with
1514 // constants if we have found them to be of constant values.
1516 std::set<BasicBlock*> &ExecutableBBs = Solver.getExecutableBlocks();
1517 for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) {
1518 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
1520 if (!AI->use_empty()) {
1521 LatticeVal &IV = Values[AI];
1522 if (IV.isConstant() || IV.isUndefined()) {
1523 Constant *CST = IV.isConstant() ?
1524 IV.getConstant() : UndefValue::get(AI->getType());
1525 DOUT << "*** Arg " << *AI << " = " << *CST <<"\n";
1527 // Replaces all of the uses of a variable with uses of the
1529 AI->replaceAllUsesWith(CST);
1534 std::vector<BasicBlock*> BlocksToErase;
1535 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
1536 if (!ExecutableBBs.count(BB)) {
1537 DOUT << " BasicBlock Dead:" << *BB;
1540 // Delete the instructions backwards, as it has a reduced likelihood of
1541 // having to update as many def-use and use-def chains.
1542 std::vector<Instruction*> Insts;
1543 TerminatorInst *TI = BB->getTerminator();
1544 for (BasicBlock::iterator I = BB->begin(), E = TI; I != E; ++I)
1547 while (!Insts.empty()) {
1548 Instruction *I = Insts.back();
1550 if (!I->use_empty())
1551 I->replaceAllUsesWith(UndefValue::get(I->getType()));
1552 BB->getInstList().erase(I);
1557 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) {
1558 BasicBlock *Succ = TI->getSuccessor(i);
1559 if (Succ->begin() != Succ->end() && isa<PHINode>(Succ->begin()))
1560 TI->getSuccessor(i)->removePredecessor(BB);
1562 if (!TI->use_empty())
1563 TI->replaceAllUsesWith(UndefValue::get(TI->getType()));
1564 BB->getInstList().erase(TI);
1566 if (&*BB != &F->front())
1567 BlocksToErase.push_back(BB);
1569 new UnreachableInst(BB);
1572 for (BasicBlock::iterator BI = BB->begin(), E = BB->end(); BI != E; ) {
1573 Instruction *Inst = BI++;
1574 if (Inst->getType() != Type::VoidTy) {
1575 LatticeVal &IV = Values[Inst];
1576 if (IV.isConstant() || IV.isUndefined() &&
1577 !isa<TerminatorInst>(Inst)) {
1578 Constant *Const = IV.isConstant()
1579 ? IV.getConstant() : UndefValue::get(Inst->getType());
1580 DOUT << " Constant: " << *Const << " = " << *Inst;
1582 // Replaces all of the uses of a variable with uses of the
1584 Inst->replaceAllUsesWith(Const);
1586 // Delete the instruction.
1587 if (!isa<TerminatorInst>(Inst) && !isa<CallInst>(Inst))
1588 BB->getInstList().erase(Inst);
1590 // Hey, we just changed something!
1598 // Now that all instructions in the function are constant folded, erase dead
1599 // blocks, because we can now use ConstantFoldTerminator to get rid of
1601 for (unsigned i = 0, e = BlocksToErase.size(); i != e; ++i) {
1602 // If there are any PHI nodes in this successor, drop entries for BB now.
1603 BasicBlock *DeadBB = BlocksToErase[i];
1604 while (!DeadBB->use_empty()) {
1605 Instruction *I = cast<Instruction>(DeadBB->use_back());
1606 bool Folded = ConstantFoldTerminator(I->getParent());
1608 // The constant folder may not have been able to fold the termiantor
1609 // if this is a branch or switch on undef. Fold it manually as a
1610 // branch to the first successor.
1611 if (BranchInst *BI = dyn_cast<BranchInst>(I)) {
1612 assert(BI->isConditional() && isa<UndefValue>(BI->getCondition()) &&
1613 "Branch should be foldable!");
1614 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(I)) {
1615 assert(isa<UndefValue>(SI->getCondition()) && "Switch should fold");
1617 assert(0 && "Didn't fold away reference to block!");
1620 // Make this an uncond branch to the first successor.
1621 TerminatorInst *TI = I->getParent()->getTerminator();
1622 new BranchInst(TI->getSuccessor(0), TI);
1624 // Remove entries in successor phi nodes to remove edges.
1625 for (unsigned i = 1, e = TI->getNumSuccessors(); i != e; ++i)
1626 TI->getSuccessor(i)->removePredecessor(TI->getParent());
1628 // Remove the old terminator.
1629 TI->eraseFromParent();
1633 // Finally, delete the basic block.
1634 F->getBasicBlockList().erase(DeadBB);
1638 // If we inferred constant or undef return values for a function, we replaced
1639 // all call uses with the inferred value. This means we don't need to bother
1640 // actually returning anything from the function. Replace all return
1641 // instructions with return undef.
1642 const hash_map<Function*, LatticeVal> &RV =Solver.getTrackedFunctionRetVals();
1643 for (hash_map<Function*, LatticeVal>::const_iterator I = RV.begin(),
1644 E = RV.end(); I != E; ++I)
1645 if (!I->second.isOverdefined() &&
1646 I->first->getReturnType() != Type::VoidTy) {
1647 Function *F = I->first;
1648 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
1649 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator()))
1650 if (!isa<UndefValue>(RI->getOperand(0)))
1651 RI->setOperand(0, UndefValue::get(F->getReturnType()));
1654 // If we infered constant or undef values for globals variables, we can delete
1655 // the global and any stores that remain to it.
1656 const hash_map<GlobalVariable*, LatticeVal> &TG = Solver.getTrackedGlobals();
1657 for (hash_map<GlobalVariable*, LatticeVal>::const_iterator I = TG.begin(),
1658 E = TG.end(); I != E; ++I) {
1659 GlobalVariable *GV = I->first;
1660 assert(!I->second.isOverdefined() &&
1661 "Overdefined values should have been taken out of the map!");
1662 DOUT << "Found that GV '" << GV->getName()<< "' is constant!\n";
1663 while (!GV->use_empty()) {
1664 StoreInst *SI = cast<StoreInst>(GV->use_back());
1665 SI->eraseFromParent();
1667 M.getGlobalList().erase(GV);