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;
91 assert(V && "Marking constant with NULL");
94 assert(LatticeValue == forcedconstant &&
95 "Cannot move from overdefined to constant!");
96 // Stay at forcedconstant if the constant is the same.
97 if (V == ConstantVal) return false;
99 // Otherwise, we go to overdefined. Assumptions made based on the
100 // forced value are possibly wrong. Assuming this is another constant
101 // could expose a contradiction.
102 LatticeValue = overdefined;
106 assert(ConstantVal == V && "Marking constant with different value");
111 inline void markForcedConstant(Constant *V) {
112 assert(LatticeValue == undefined && "Can't force a defined value!");
113 LatticeValue = forcedconstant;
117 inline bool isUndefined() const { return LatticeValue == undefined; }
118 inline bool isConstant() const {
119 return LatticeValue == constant || LatticeValue == forcedconstant;
121 inline bool isOverdefined() const { return LatticeValue == overdefined; }
123 inline Constant *getConstant() const {
124 assert(isConstant() && "Cannot get the constant of a non-constant!");
129 } // end anonymous namespace
132 //===----------------------------------------------------------------------===//
134 /// SCCPSolver - This class is a general purpose solver for Sparse Conditional
135 /// Constant Propagation.
137 class SCCPSolver : public InstVisitor<SCCPSolver> {
138 std::set<BasicBlock*> BBExecutable;// The basic blocks that are executable
139 hash_map<Value*, LatticeVal> ValueState; // The state each value is in...
141 /// GlobalValue - If we are tracking any values for the contents of a global
142 /// variable, we keep a mapping from the constant accessor to the element of
143 /// the global, to the currently known value. If the value becomes
144 /// overdefined, it's entry is simply removed from this map.
145 hash_map<GlobalVariable*, LatticeVal> TrackedGlobals;
147 /// TrackedFunctionRetVals - If we are tracking arguments into and the return
148 /// value out of a function, it will have an entry in this map, indicating
149 /// what the known return value for the function is.
150 hash_map<Function*, LatticeVal> TrackedFunctionRetVals;
152 // The reason for two worklists is that overdefined is the lowest state
153 // on the lattice, and moving things to overdefined as fast as possible
154 // makes SCCP converge much faster.
155 // By having a separate worklist, we accomplish this because everything
156 // possibly overdefined will become overdefined at the soonest possible
158 std::vector<Value*> OverdefinedInstWorkList;
159 std::vector<Value*> InstWorkList;
162 std::vector<BasicBlock*> BBWorkList; // The BasicBlock work list
164 /// UsersOfOverdefinedPHIs - Keep track of any users of PHI nodes that are not
165 /// overdefined, despite the fact that the PHI node is overdefined.
166 std::multimap<PHINode*, Instruction*> UsersOfOverdefinedPHIs;
168 /// KnownFeasibleEdges - Entries in this set are edges which have already had
169 /// PHI nodes retriggered.
170 typedef std::pair<BasicBlock*,BasicBlock*> Edge;
171 std::set<Edge> KnownFeasibleEdges;
174 /// MarkBlockExecutable - This method can be used by clients to mark all of
175 /// the blocks that are known to be intrinsically live in the processed unit.
176 void MarkBlockExecutable(BasicBlock *BB) {
177 DOUT << "Marking Block Executable: " << BB->getName() << "\n";
178 BBExecutable.insert(BB); // Basic block is executable!
179 BBWorkList.push_back(BB); // Add the block to the work list!
182 /// TrackValueOfGlobalVariable - Clients can use this method to
183 /// inform the SCCPSolver that it should track loads and stores to the
184 /// specified global variable if it can. This is only legal to call if
185 /// performing Interprocedural SCCP.
186 void TrackValueOfGlobalVariable(GlobalVariable *GV) {
187 const Type *ElTy = GV->getType()->getElementType();
188 if (ElTy->isFirstClassType()) {
189 LatticeVal &IV = TrackedGlobals[GV];
190 if (!isa<UndefValue>(GV->getInitializer()))
191 IV.markConstant(GV->getInitializer());
195 /// AddTrackedFunction - If the SCCP solver is supposed to track calls into
196 /// and out of the specified function (which cannot have its address taken),
197 /// this method must be called.
198 void AddTrackedFunction(Function *F) {
199 assert(F->hasInternalLinkage() && "Can only track internal functions!");
200 // Add an entry, F -> undef.
201 TrackedFunctionRetVals[F];
204 /// Solve - Solve for constants and executable blocks.
208 /// ResolvedUndefsIn - While solving the dataflow for a function, we assume
209 /// that branches on undef values cannot reach any of their successors.
210 /// However, this is not a safe assumption. After we solve dataflow, this
211 /// method should be use to handle this. If this returns true, the solver
213 bool ResolvedUndefsIn(Function &F);
215 /// getExecutableBlocks - Once we have solved for constants, return the set of
216 /// blocks that is known to be executable.
217 std::set<BasicBlock*> &getExecutableBlocks() {
221 /// getValueMapping - Once we have solved for constants, return the mapping of
222 /// LLVM values to LatticeVals.
223 hash_map<Value*, LatticeVal> &getValueMapping() {
227 /// getTrackedFunctionRetVals - Get the inferred return value map.
229 const hash_map<Function*, LatticeVal> &getTrackedFunctionRetVals() {
230 return TrackedFunctionRetVals;
233 /// getTrackedGlobals - Get and return the set of inferred initializers for
234 /// global variables.
235 const hash_map<GlobalVariable*, LatticeVal> &getTrackedGlobals() {
236 return TrackedGlobals;
241 // markConstant - Make a value be marked as "constant". If the value
242 // is not already a constant, add it to the instruction work list so that
243 // the users of the instruction are updated later.
245 inline void markConstant(LatticeVal &IV, Value *V, Constant *C) {
246 if (IV.markConstant(C)) {
247 DOUT << "markConstant: " << *C << ": " << *V;
248 InstWorkList.push_back(V);
252 inline void markForcedConstant(LatticeVal &IV, Value *V, Constant *C) {
253 IV.markForcedConstant(C);
254 DOUT << "markForcedConstant: " << *C << ": " << *V;
255 InstWorkList.push_back(V);
258 inline void markConstant(Value *V, Constant *C) {
259 markConstant(ValueState[V], V, C);
262 // markOverdefined - Make a value be marked as "overdefined". If the
263 // value is not already overdefined, add it to the overdefined instruction
264 // work list so that the users of the instruction are updated later.
266 inline void markOverdefined(LatticeVal &IV, Value *V) {
267 if (IV.markOverdefined()) {
268 DEBUG(DOUT << "markOverdefined: ";
269 if (Function *F = dyn_cast<Function>(V))
270 DOUT << "Function '" << F->getName() << "'\n";
273 // Only instructions go on the work list
274 OverdefinedInstWorkList.push_back(V);
277 inline void markOverdefined(Value *V) {
278 markOverdefined(ValueState[V], V);
281 inline void mergeInValue(LatticeVal &IV, Value *V, LatticeVal &MergeWithV) {
282 if (IV.isOverdefined() || MergeWithV.isUndefined())
284 if (MergeWithV.isOverdefined())
285 markOverdefined(IV, V);
286 else if (IV.isUndefined())
287 markConstant(IV, V, MergeWithV.getConstant());
288 else if (IV.getConstant() != MergeWithV.getConstant())
289 markOverdefined(IV, V);
292 inline void mergeInValue(Value *V, LatticeVal &MergeWithV) {
293 return mergeInValue(ValueState[V], V, MergeWithV);
297 // getValueState - Return the LatticeVal object that corresponds to the value.
298 // This function is necessary because not all values should start out in the
299 // underdefined state... Argument's should be overdefined, and
300 // constants should be marked as constants. If a value is not known to be an
301 // Instruction object, then use this accessor to get its value from the map.
303 inline LatticeVal &getValueState(Value *V) {
304 hash_map<Value*, LatticeVal>::iterator I = ValueState.find(V);
305 if (I != ValueState.end()) return I->second; // Common case, in the map
307 if (Constant *C = dyn_cast<Constant>(V)) {
308 if (isa<UndefValue>(V)) {
309 // Nothing to do, remain undefined.
311 ValueState[C].markConstant(C); // Constants are constant
314 // All others are underdefined by default...
315 return ValueState[V];
318 // markEdgeExecutable - Mark a basic block as executable, adding it to the BB
319 // work list if it is not already executable...
321 void markEdgeExecutable(BasicBlock *Source, BasicBlock *Dest) {
322 if (!KnownFeasibleEdges.insert(Edge(Source, Dest)).second)
323 return; // This edge is already known to be executable!
325 if (BBExecutable.count(Dest)) {
326 DOUT << "Marking Edge Executable: " << Source->getName()
327 << " -> " << Dest->getName() << "\n";
329 // The destination is already executable, but we just made an edge
330 // feasible that wasn't before. Revisit the PHI nodes in the block
331 // because they have potentially new operands.
332 for (BasicBlock::iterator I = Dest->begin(); isa<PHINode>(I); ++I)
333 visitPHINode(*cast<PHINode>(I));
336 MarkBlockExecutable(Dest);
340 // getFeasibleSuccessors - Return a vector of booleans to indicate which
341 // successors are reachable from a given terminator instruction.
343 void getFeasibleSuccessors(TerminatorInst &TI, std::vector<bool> &Succs);
345 // isEdgeFeasible - Return true if the control flow edge from the 'From' basic
346 // block to the 'To' basic block is currently feasible...
348 bool isEdgeFeasible(BasicBlock *From, BasicBlock *To);
350 // OperandChangedState - This method is invoked on all of the users of an
351 // instruction that was just changed state somehow.... Based on this
352 // information, we need to update the specified user of this instruction.
354 void OperandChangedState(User *U) {
355 // Only instructions use other variable values!
356 Instruction &I = cast<Instruction>(*U);
357 if (BBExecutable.count(I.getParent())) // Inst is executable?
362 friend class InstVisitor<SCCPSolver>;
364 // visit implementations - Something changed in this instruction... Either an
365 // operand made a transition, or the instruction is newly executable. Change
366 // the value type of I to reflect these changes if appropriate.
368 void visitPHINode(PHINode &I);
371 void visitReturnInst(ReturnInst &I);
372 void visitTerminatorInst(TerminatorInst &TI);
374 void visitCastInst(CastInst &I);
375 void visitSelectInst(SelectInst &I);
376 void visitBinaryOperator(Instruction &I);
377 void visitCmpInst(CmpInst &I);
378 void visitShiftInst(ShiftInst &I) { visitBinaryOperator(I); }
379 void visitExtractElementInst(ExtractElementInst &I);
380 void visitInsertElementInst(InsertElementInst &I);
381 void visitShuffleVectorInst(ShuffleVectorInst &I);
383 // Instructions that cannot be folded away...
384 void visitStoreInst (Instruction &I);
385 void visitLoadInst (LoadInst &I);
386 void visitGetElementPtrInst(GetElementPtrInst &I);
387 void visitCallInst (CallInst &I) { visitCallSite(CallSite::get(&I)); }
388 void visitInvokeInst (InvokeInst &II) {
389 visitCallSite(CallSite::get(&II));
390 visitTerminatorInst(II);
392 void visitCallSite (CallSite CS);
393 void visitUnwindInst (TerminatorInst &I) { /*returns void*/ }
394 void visitUnreachableInst(TerminatorInst &I) { /*returns void*/ }
395 void visitAllocationInst(Instruction &I) { markOverdefined(&I); }
396 void visitVANextInst (Instruction &I) { markOverdefined(&I); }
397 void visitVAArgInst (Instruction &I) { markOverdefined(&I); }
398 void visitFreeInst (Instruction &I) { /*returns void*/ }
400 void visitInstruction(Instruction &I) {
401 // If a new instruction is added to LLVM that we don't handle...
402 cerr << "SCCP: Don't know how to handle: " << I;
403 markOverdefined(&I); // Just in case
407 // getFeasibleSuccessors - Return a vector of booleans to indicate which
408 // successors are reachable from a given terminator instruction.
410 void SCCPSolver::getFeasibleSuccessors(TerminatorInst &TI,
411 std::vector<bool> &Succs) {
412 Succs.resize(TI.getNumSuccessors());
413 if (BranchInst *BI = dyn_cast<BranchInst>(&TI)) {
414 if (BI->isUnconditional()) {
417 LatticeVal &BCValue = getValueState(BI->getCondition());
418 if (BCValue.isOverdefined() ||
419 (BCValue.isConstant() &&
420 BCValue.getConstant()->getType() != Type::BoolTy)) {
421 // Overdefined condition variables, and branches on unfoldable constant
422 // conditions, mean the branch could go either way.
423 Succs[0] = Succs[1] = true;
424 } else if (BCValue.isConstant()) {
425 // Constant condition variables mean the branch can only go a single way
426 Succs[BCValue.getConstant() == ConstantInt::getFalse()] = true;
429 } else if (isa<InvokeInst>(&TI)) {
430 // Invoke instructions successors are always executable.
431 Succs[0] = Succs[1] = true;
432 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(&TI)) {
433 LatticeVal &SCValue = getValueState(SI->getCondition());
434 if (SCValue.isOverdefined() || // Overdefined condition?
435 (SCValue.isConstant() && !isa<ConstantInt>(SCValue.getConstant()))) {
436 // All destinations are executable!
437 Succs.assign(TI.getNumSuccessors(), true);
438 } else if (SCValue.isConstant()) {
439 Constant *CPV = SCValue.getConstant();
440 // Make sure to skip the "default value" which isn't a value
441 for (unsigned i = 1, E = SI->getNumSuccessors(); i != E; ++i) {
442 if (SI->getSuccessorValue(i) == CPV) {// Found the right branch...
448 // Constant value not equal to any of the branches... must execute
449 // default branch then...
453 cerr << "SCCP: Don't know how to handle: " << TI;
454 Succs.assign(TI.getNumSuccessors(), true);
459 // isEdgeFeasible - Return true if the control flow edge from the 'From' basic
460 // block to the 'To' basic block is currently feasible...
462 bool SCCPSolver::isEdgeFeasible(BasicBlock *From, BasicBlock *To) {
463 assert(BBExecutable.count(To) && "Dest should always be alive!");
465 // Make sure the source basic block is executable!!
466 if (!BBExecutable.count(From)) return false;
468 // Check to make sure this edge itself is actually feasible now...
469 TerminatorInst *TI = From->getTerminator();
470 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
471 if (BI->isUnconditional())
474 LatticeVal &BCValue = getValueState(BI->getCondition());
475 if (BCValue.isOverdefined()) {
476 // Overdefined condition variables mean the branch could go either way.
478 } else if (BCValue.isConstant()) {
479 // Not branching on an evaluatable constant?
480 if (BCValue.getConstant()->getType() != Type::BoolTy) return true;
482 // Constant condition variables mean the branch can only go a single way
483 return BI->getSuccessor(BCValue.getConstant() ==
484 ConstantInt::getFalse()) == To;
488 } else if (isa<InvokeInst>(TI)) {
489 // Invoke instructions successors are always executable.
491 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
492 LatticeVal &SCValue = getValueState(SI->getCondition());
493 if (SCValue.isOverdefined()) { // Overdefined condition?
494 // All destinations are executable!
496 } else if (SCValue.isConstant()) {
497 Constant *CPV = SCValue.getConstant();
498 if (!isa<ConstantInt>(CPV))
499 return true; // not a foldable constant?
501 // Make sure to skip the "default value" which isn't a value
502 for (unsigned i = 1, E = SI->getNumSuccessors(); i != E; ++i)
503 if (SI->getSuccessorValue(i) == CPV) // Found the taken branch...
504 return SI->getSuccessor(i) == To;
506 // Constant value not equal to any of the branches... must execute
507 // default branch then...
508 return SI->getDefaultDest() == To;
512 cerr << "Unknown terminator instruction: " << *TI;
517 // visit Implementations - Something changed in this instruction... Either an
518 // operand made a transition, or the instruction is newly executable. Change
519 // the value type of I to reflect these changes if appropriate. This method
520 // makes sure to do the following actions:
522 // 1. If a phi node merges two constants in, and has conflicting value coming
523 // from different branches, or if the PHI node merges in an overdefined
524 // value, then the PHI node becomes overdefined.
525 // 2. If a phi node merges only constants in, and they all agree on value, the
526 // PHI node becomes a constant value equal to that.
527 // 3. If V <- x (op) y && isConstant(x) && isConstant(y) V = Constant
528 // 4. If V <- x (op) y && (isOverdefined(x) || isOverdefined(y)) V = Overdefined
529 // 5. If V <- MEM or V <- CALL or V <- (unknown) then V = Overdefined
530 // 6. If a conditional branch has a value that is constant, make the selected
531 // destination executable
532 // 7. If a conditional branch has a value that is overdefined, make all
533 // successors executable.
535 void SCCPSolver::visitPHINode(PHINode &PN) {
536 LatticeVal &PNIV = getValueState(&PN);
537 if (PNIV.isOverdefined()) {
538 // There may be instructions using this PHI node that are not overdefined
539 // themselves. If so, make sure that they know that the PHI node operand
541 std::multimap<PHINode*, Instruction*>::iterator I, E;
542 tie(I, E) = UsersOfOverdefinedPHIs.equal_range(&PN);
544 std::vector<Instruction*> Users;
545 Users.reserve(std::distance(I, E));
546 for (; I != E; ++I) Users.push_back(I->second);
547 while (!Users.empty()) {
552 return; // Quick exit
555 // Super-extra-high-degree PHI nodes are unlikely to ever be marked constant,
556 // and slow us down a lot. Just mark them overdefined.
557 if (PN.getNumIncomingValues() > 64) {
558 markOverdefined(PNIV, &PN);
562 // Look at all of the executable operands of the PHI node. If any of them
563 // are overdefined, the PHI becomes overdefined as well. If they are all
564 // constant, and they agree with each other, the PHI becomes the identical
565 // constant. If they are constant and don't agree, the PHI is overdefined.
566 // If there are no executable operands, the PHI remains undefined.
568 Constant *OperandVal = 0;
569 for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) {
570 LatticeVal &IV = getValueState(PN.getIncomingValue(i));
571 if (IV.isUndefined()) continue; // Doesn't influence PHI node.
573 if (isEdgeFeasible(PN.getIncomingBlock(i), PN.getParent())) {
574 if (IV.isOverdefined()) { // PHI node becomes overdefined!
575 markOverdefined(PNIV, &PN);
579 if (OperandVal == 0) { // Grab the first value...
580 OperandVal = IV.getConstant();
581 } else { // Another value is being merged in!
582 // There is already a reachable operand. If we conflict with it,
583 // then the PHI node becomes overdefined. If we agree with it, we
586 // Check to see if there are two different constants merging...
587 if (IV.getConstant() != OperandVal) {
588 // Yes there is. This means the PHI node is not constant.
589 // You must be overdefined poor PHI.
591 markOverdefined(PNIV, &PN); // The PHI node now becomes overdefined
592 return; // I'm done analyzing you
598 // If we exited the loop, this means that the PHI node only has constant
599 // arguments that agree with each other(and OperandVal is the constant) or
600 // OperandVal is null because there are no defined incoming arguments. If
601 // this is the case, the PHI remains undefined.
604 markConstant(PNIV, &PN, OperandVal); // Acquire operand value
607 void SCCPSolver::visitReturnInst(ReturnInst &I) {
608 if (I.getNumOperands() == 0) return; // Ret void
610 // If we are tracking the return value of this function, merge it in.
611 Function *F = I.getParent()->getParent();
612 if (F->hasInternalLinkage() && !TrackedFunctionRetVals.empty()) {
613 hash_map<Function*, LatticeVal>::iterator TFRVI =
614 TrackedFunctionRetVals.find(F);
615 if (TFRVI != TrackedFunctionRetVals.end() &&
616 !TFRVI->second.isOverdefined()) {
617 LatticeVal &IV = getValueState(I.getOperand(0));
618 mergeInValue(TFRVI->second, F, IV);
624 void SCCPSolver::visitTerminatorInst(TerminatorInst &TI) {
625 std::vector<bool> SuccFeasible;
626 getFeasibleSuccessors(TI, SuccFeasible);
628 BasicBlock *BB = TI.getParent();
630 // Mark all feasible successors executable...
631 for (unsigned i = 0, e = SuccFeasible.size(); i != e; ++i)
633 markEdgeExecutable(BB, TI.getSuccessor(i));
636 void SCCPSolver::visitCastInst(CastInst &I) {
637 Value *V = I.getOperand(0);
638 LatticeVal &VState = getValueState(V);
639 if (VState.isOverdefined()) // Inherit overdefinedness of operand
641 else if (VState.isConstant()) // Propagate constant value
642 markConstant(&I, ConstantExpr::getCast(I.getOpcode(),
643 VState.getConstant(), I.getType()));
646 void SCCPSolver::visitSelectInst(SelectInst &I) {
647 LatticeVal &CondValue = getValueState(I.getCondition());
648 if (CondValue.isUndefined())
650 if (CondValue.isConstant() &&
651 CondValue.getConstant()->getType() == Type::BoolTy) {
652 if (ConstantInt *CondCB = dyn_cast<ConstantInt>(CondValue.getConstant())){
653 mergeInValue(&I, getValueState(CondCB->getBoolValue() ? I.getTrueValue()
654 : I.getFalseValue()));
659 // Otherwise, the condition is overdefined or a constant we can't evaluate.
660 // See if we can produce something better than overdefined based on the T/F
662 LatticeVal &TVal = getValueState(I.getTrueValue());
663 LatticeVal &FVal = getValueState(I.getFalseValue());
665 // select ?, C, C -> C.
666 if (TVal.isConstant() && FVal.isConstant() &&
667 TVal.getConstant() == FVal.getConstant()) {
668 markConstant(&I, FVal.getConstant());
672 if (TVal.isUndefined()) { // select ?, undef, X -> X.
673 mergeInValue(&I, FVal);
674 } else if (FVal.isUndefined()) { // select ?, X, undef -> X.
675 mergeInValue(&I, TVal);
681 // Handle BinaryOperators and Shift Instructions...
682 void SCCPSolver::visitBinaryOperator(Instruction &I) {
683 LatticeVal &IV = ValueState[&I];
684 if (IV.isOverdefined()) return;
686 LatticeVal &V1State = getValueState(I.getOperand(0));
687 LatticeVal &V2State = getValueState(I.getOperand(1));
689 if (V1State.isOverdefined() || V2State.isOverdefined()) {
690 // If this is an AND or OR with 0 or -1, it doesn't matter that the other
691 // operand is overdefined.
692 if (I.getOpcode() == Instruction::And || I.getOpcode() == Instruction::Or) {
693 LatticeVal *NonOverdefVal = 0;
694 if (!V1State.isOverdefined()) {
695 NonOverdefVal = &V1State;
696 } else if (!V2State.isOverdefined()) {
697 NonOverdefVal = &V2State;
701 if (NonOverdefVal->isUndefined()) {
702 // Could annihilate value.
703 if (I.getOpcode() == Instruction::And)
704 markConstant(IV, &I, Constant::getNullValue(I.getType()));
705 else if (const PackedType *PT = dyn_cast<PackedType>(I.getType()))
706 markConstant(IV, &I, ConstantPacked::getAllOnesValue(PT));
708 markConstant(IV, &I, ConstantInt::getAllOnesValue(I.getType()));
711 if (I.getOpcode() == Instruction::And) {
712 if (NonOverdefVal->getConstant()->isNullValue()) {
713 markConstant(IV, &I, NonOverdefVal->getConstant());
714 return; // X and 0 = 0
717 if (ConstantInt *CI =
718 dyn_cast<ConstantInt>(NonOverdefVal->getConstant()))
719 if (CI->isAllOnesValue()) {
720 markConstant(IV, &I, NonOverdefVal->getConstant());
721 return; // X or -1 = -1
729 // If both operands are PHI nodes, it is possible that this instruction has
730 // a constant value, despite the fact that the PHI node doesn't. Check for
731 // this condition now.
732 if (PHINode *PN1 = dyn_cast<PHINode>(I.getOperand(0)))
733 if (PHINode *PN2 = dyn_cast<PHINode>(I.getOperand(1)))
734 if (PN1->getParent() == PN2->getParent()) {
735 // Since the two PHI nodes are in the same basic block, they must have
736 // entries for the same predecessors. Walk the predecessor list, and
737 // if all of the incoming values are constants, and the result of
738 // evaluating this expression with all incoming value pairs is the
739 // same, then this expression is a constant even though the PHI node
740 // is not a constant!
742 for (unsigned i = 0, e = PN1->getNumIncomingValues(); i != e; ++i) {
743 LatticeVal &In1 = getValueState(PN1->getIncomingValue(i));
744 BasicBlock *InBlock = PN1->getIncomingBlock(i);
746 getValueState(PN2->getIncomingValueForBlock(InBlock));
748 if (In1.isOverdefined() || In2.isOverdefined()) {
749 Result.markOverdefined();
750 break; // Cannot fold this operation over the PHI nodes!
751 } else if (In1.isConstant() && In2.isConstant()) {
752 Constant *V = ConstantExpr::get(I.getOpcode(), In1.getConstant(),
754 if (Result.isUndefined())
755 Result.markConstant(V);
756 else if (Result.isConstant() && Result.getConstant() != V) {
757 Result.markOverdefined();
763 // If we found a constant value here, then we know the instruction is
764 // constant despite the fact that the PHI nodes are overdefined.
765 if (Result.isConstant()) {
766 markConstant(IV, &I, Result.getConstant());
767 // Remember that this instruction is virtually using the PHI node
769 UsersOfOverdefinedPHIs.insert(std::make_pair(PN1, &I));
770 UsersOfOverdefinedPHIs.insert(std::make_pair(PN2, &I));
772 } else if (Result.isUndefined()) {
776 // Okay, this really is overdefined now. Since we might have
777 // speculatively thought that this was not overdefined before, and
778 // added ourselves to the UsersOfOverdefinedPHIs list for the PHIs,
779 // make sure to clean out any entries that we put there, for
781 std::multimap<PHINode*, Instruction*>::iterator It, E;
782 tie(It, E) = UsersOfOverdefinedPHIs.equal_range(PN1);
784 if (It->second == &I) {
785 UsersOfOverdefinedPHIs.erase(It++);
789 tie(It, E) = UsersOfOverdefinedPHIs.equal_range(PN2);
791 if (It->second == &I) {
792 UsersOfOverdefinedPHIs.erase(It++);
798 markOverdefined(IV, &I);
799 } else if (V1State.isConstant() && V2State.isConstant()) {
800 markConstant(IV, &I, ConstantExpr::get(I.getOpcode(), V1State.getConstant(),
801 V2State.getConstant()));
805 // Handle ICmpInst instruction...
806 void SCCPSolver::visitCmpInst(CmpInst &I) {
807 LatticeVal &IV = ValueState[&I];
808 if (IV.isOverdefined()) return;
810 LatticeVal &V1State = getValueState(I.getOperand(0));
811 LatticeVal &V2State = getValueState(I.getOperand(1));
813 if (V1State.isOverdefined() || V2State.isOverdefined()) {
814 // If both operands are PHI nodes, it is possible that this instruction has
815 // a constant value, despite the fact that the PHI node doesn't. Check for
816 // this condition now.
817 if (PHINode *PN1 = dyn_cast<PHINode>(I.getOperand(0)))
818 if (PHINode *PN2 = dyn_cast<PHINode>(I.getOperand(1)))
819 if (PN1->getParent() == PN2->getParent()) {
820 // Since the two PHI nodes are in the same basic block, they must have
821 // entries for the same predecessors. Walk the predecessor list, and
822 // if all of the incoming values are constants, and the result of
823 // evaluating this expression with all incoming value pairs is the
824 // same, then this expression is a constant even though the PHI node
825 // is not a constant!
827 for (unsigned i = 0, e = PN1->getNumIncomingValues(); i != e; ++i) {
828 LatticeVal &In1 = getValueState(PN1->getIncomingValue(i));
829 BasicBlock *InBlock = PN1->getIncomingBlock(i);
831 getValueState(PN2->getIncomingValueForBlock(InBlock));
833 if (In1.isOverdefined() || In2.isOverdefined()) {
834 Result.markOverdefined();
835 break; // Cannot fold this operation over the PHI nodes!
836 } else if (In1.isConstant() && In2.isConstant()) {
837 Constant *V = ConstantExpr::getCompare(I.getPredicate(),
840 if (Result.isUndefined())
841 Result.markConstant(V);
842 else if (Result.isConstant() && Result.getConstant() != V) {
843 Result.markOverdefined();
849 // If we found a constant value here, then we know the instruction is
850 // constant despite the fact that the PHI nodes are overdefined.
851 if (Result.isConstant()) {
852 markConstant(IV, &I, Result.getConstant());
853 // Remember that this instruction is virtually using the PHI node
855 UsersOfOverdefinedPHIs.insert(std::make_pair(PN1, &I));
856 UsersOfOverdefinedPHIs.insert(std::make_pair(PN2, &I));
858 } else if (Result.isUndefined()) {
862 // Okay, this really is overdefined now. Since we might have
863 // speculatively thought that this was not overdefined before, and
864 // added ourselves to the UsersOfOverdefinedPHIs list for the PHIs,
865 // make sure to clean out any entries that we put there, for
867 std::multimap<PHINode*, Instruction*>::iterator It, E;
868 tie(It, E) = UsersOfOverdefinedPHIs.equal_range(PN1);
870 if (It->second == &I) {
871 UsersOfOverdefinedPHIs.erase(It++);
875 tie(It, E) = UsersOfOverdefinedPHIs.equal_range(PN2);
877 if (It->second == &I) {
878 UsersOfOverdefinedPHIs.erase(It++);
884 markOverdefined(IV, &I);
885 } else if (V1State.isConstant() && V2State.isConstant()) {
886 markConstant(IV, &I, ConstantExpr::getCompare(I.getPredicate(),
887 V1State.getConstant(),
888 V2State.getConstant()));
892 void SCCPSolver::visitExtractElementInst(ExtractElementInst &I) {
893 // FIXME : SCCP does not handle vectors properly.
898 LatticeVal &ValState = getValueState(I.getOperand(0));
899 LatticeVal &IdxState = getValueState(I.getOperand(1));
901 if (ValState.isOverdefined() || IdxState.isOverdefined())
903 else if(ValState.isConstant() && IdxState.isConstant())
904 markConstant(&I, ConstantExpr::getExtractElement(ValState.getConstant(),
905 IdxState.getConstant()));
909 void SCCPSolver::visitInsertElementInst(InsertElementInst &I) {
910 // FIXME : SCCP does not handle vectors properly.
914 LatticeVal &ValState = getValueState(I.getOperand(0));
915 LatticeVal &EltState = getValueState(I.getOperand(1));
916 LatticeVal &IdxState = getValueState(I.getOperand(2));
918 if (ValState.isOverdefined() || EltState.isOverdefined() ||
919 IdxState.isOverdefined())
921 else if(ValState.isConstant() && EltState.isConstant() &&
922 IdxState.isConstant())
923 markConstant(&I, ConstantExpr::getInsertElement(ValState.getConstant(),
924 EltState.getConstant(),
925 IdxState.getConstant()));
926 else if (ValState.isUndefined() && EltState.isConstant() &&
927 IdxState.isConstant())
928 markConstant(&I, ConstantExpr::getInsertElement(UndefValue::get(I.getType()),
929 EltState.getConstant(),
930 IdxState.getConstant()));
934 void SCCPSolver::visitShuffleVectorInst(ShuffleVectorInst &I) {
935 // FIXME : SCCP does not handle vectors properly.
939 LatticeVal &V1State = getValueState(I.getOperand(0));
940 LatticeVal &V2State = getValueState(I.getOperand(1));
941 LatticeVal &MaskState = getValueState(I.getOperand(2));
943 if (MaskState.isUndefined() ||
944 (V1State.isUndefined() && V2State.isUndefined()))
945 return; // Undefined output if mask or both inputs undefined.
947 if (V1State.isOverdefined() || V2State.isOverdefined() ||
948 MaskState.isOverdefined()) {
951 // A mix of constant/undef inputs.
952 Constant *V1 = V1State.isConstant() ?
953 V1State.getConstant() : UndefValue::get(I.getType());
954 Constant *V2 = V2State.isConstant() ?
955 V2State.getConstant() : UndefValue::get(I.getType());
956 Constant *Mask = MaskState.isConstant() ?
957 MaskState.getConstant() : UndefValue::get(I.getOperand(2)->getType());
958 markConstant(&I, ConstantExpr::getShuffleVector(V1, V2, Mask));
963 // Handle getelementptr instructions... if all operands are constants then we
964 // can turn this into a getelementptr ConstantExpr.
966 void SCCPSolver::visitGetElementPtrInst(GetElementPtrInst &I) {
967 LatticeVal &IV = ValueState[&I];
968 if (IV.isOverdefined()) return;
970 std::vector<Constant*> Operands;
971 Operands.reserve(I.getNumOperands());
973 for (unsigned i = 0, e = I.getNumOperands(); i != e; ++i) {
974 LatticeVal &State = getValueState(I.getOperand(i));
975 if (State.isUndefined())
976 return; // Operands are not resolved yet...
977 else if (State.isOverdefined()) {
978 markOverdefined(IV, &I);
981 assert(State.isConstant() && "Unknown state!");
982 Operands.push_back(State.getConstant());
985 Constant *Ptr = Operands[0];
986 Operands.erase(Operands.begin()); // Erase the pointer from idx list...
988 markConstant(IV, &I, ConstantExpr::getGetElementPtr(Ptr, Operands));
991 void SCCPSolver::visitStoreInst(Instruction &SI) {
992 if (TrackedGlobals.empty() || !isa<GlobalVariable>(SI.getOperand(1)))
994 GlobalVariable *GV = cast<GlobalVariable>(SI.getOperand(1));
995 hash_map<GlobalVariable*, LatticeVal>::iterator I = TrackedGlobals.find(GV);
996 if (I == TrackedGlobals.end() || I->second.isOverdefined()) return;
998 // Get the value we are storing into the global.
999 LatticeVal &PtrVal = getValueState(SI.getOperand(0));
1001 mergeInValue(I->second, GV, PtrVal);
1002 if (I->second.isOverdefined())
1003 TrackedGlobals.erase(I); // No need to keep tracking this!
1007 // Handle load instructions. If the operand is a constant pointer to a constant
1008 // global, we can replace the load with the loaded constant value!
1009 void SCCPSolver::visitLoadInst(LoadInst &I) {
1010 LatticeVal &IV = ValueState[&I];
1011 if (IV.isOverdefined()) return;
1013 LatticeVal &PtrVal = getValueState(I.getOperand(0));
1014 if (PtrVal.isUndefined()) return; // The pointer is not resolved yet!
1015 if (PtrVal.isConstant() && !I.isVolatile()) {
1016 Value *Ptr = PtrVal.getConstant();
1017 if (isa<ConstantPointerNull>(Ptr)) {
1018 // load null -> null
1019 markConstant(IV, &I, Constant::getNullValue(I.getType()));
1023 // Transform load (constant global) into the value loaded.
1024 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Ptr)) {
1025 if (GV->isConstant()) {
1026 if (!GV->isExternal()) {
1027 markConstant(IV, &I, GV->getInitializer());
1030 } else if (!TrackedGlobals.empty()) {
1031 // If we are tracking this global, merge in the known value for it.
1032 hash_map<GlobalVariable*, LatticeVal>::iterator It =
1033 TrackedGlobals.find(GV);
1034 if (It != TrackedGlobals.end()) {
1035 mergeInValue(IV, &I, It->second);
1041 // Transform load (constantexpr_GEP global, 0, ...) into the value loaded.
1042 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr))
1043 if (CE->getOpcode() == Instruction::GetElementPtr)
1044 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(CE->getOperand(0)))
1045 if (GV->isConstant() && !GV->isExternal())
1047 ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE)) {
1048 markConstant(IV, &I, V);
1053 // Otherwise we cannot say for certain what value this load will produce.
1055 markOverdefined(IV, &I);
1058 void SCCPSolver::visitCallSite(CallSite CS) {
1059 Function *F = CS.getCalledFunction();
1061 // If we are tracking this function, we must make sure to bind arguments as
1063 hash_map<Function*, LatticeVal>::iterator TFRVI =TrackedFunctionRetVals.end();
1064 if (F && F->hasInternalLinkage())
1065 TFRVI = TrackedFunctionRetVals.find(F);
1067 if (TFRVI != TrackedFunctionRetVals.end()) {
1068 // If this is the first call to the function hit, mark its entry block
1070 if (!BBExecutable.count(F->begin()))
1071 MarkBlockExecutable(F->begin());
1073 CallSite::arg_iterator CAI = CS.arg_begin();
1074 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
1075 AI != E; ++AI, ++CAI) {
1076 LatticeVal &IV = ValueState[AI];
1077 if (!IV.isOverdefined())
1078 mergeInValue(IV, AI, getValueState(*CAI));
1081 Instruction *I = CS.getInstruction();
1082 if (I->getType() == Type::VoidTy) return;
1084 LatticeVal &IV = ValueState[I];
1085 if (IV.isOverdefined()) return;
1087 // Propagate the return value of the function to the value of the instruction.
1088 if (TFRVI != TrackedFunctionRetVals.end()) {
1089 mergeInValue(IV, I, TFRVI->second);
1093 if (F == 0 || !F->isExternal() || !canConstantFoldCallTo(F)) {
1094 markOverdefined(IV, I);
1098 std::vector<Constant*> Operands;
1099 Operands.reserve(I->getNumOperands()-1);
1101 for (CallSite::arg_iterator AI = CS.arg_begin(), E = CS.arg_end();
1103 LatticeVal &State = getValueState(*AI);
1104 if (State.isUndefined())
1105 return; // Operands are not resolved yet...
1106 else if (State.isOverdefined()) {
1107 markOverdefined(IV, I);
1110 assert(State.isConstant() && "Unknown state!");
1111 Operands.push_back(State.getConstant());
1114 if (Constant *C = ConstantFoldCall(F, Operands))
1115 markConstant(IV, I, C);
1117 markOverdefined(IV, I);
1121 void SCCPSolver::Solve() {
1122 // Process the work lists until they are empty!
1123 while (!BBWorkList.empty() || !InstWorkList.empty() ||
1124 !OverdefinedInstWorkList.empty()) {
1125 // Process the instruction work list...
1126 while (!OverdefinedInstWorkList.empty()) {
1127 Value *I = OverdefinedInstWorkList.back();
1128 OverdefinedInstWorkList.pop_back();
1130 DOUT << "\nPopped off OI-WL: " << *I;
1132 // "I" got into the work list because it either made the transition from
1133 // bottom to constant
1135 // Anything on this worklist that is overdefined need not be visited
1136 // since all of its users will have already been marked as overdefined
1137 // Update all of the users of this instruction's value...
1139 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
1141 OperandChangedState(*UI);
1143 // Process the instruction work list...
1144 while (!InstWorkList.empty()) {
1145 Value *I = InstWorkList.back();
1146 InstWorkList.pop_back();
1148 DOUT << "\nPopped off I-WL: " << *I;
1150 // "I" got into the work list because it either made the transition from
1151 // bottom to constant
1153 // Anything on this worklist that is overdefined need not be visited
1154 // since all of its users will have already been marked as overdefined.
1155 // Update all of the users of this instruction's value...
1157 if (!getValueState(I).isOverdefined())
1158 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
1160 OperandChangedState(*UI);
1163 // Process the basic block work list...
1164 while (!BBWorkList.empty()) {
1165 BasicBlock *BB = BBWorkList.back();
1166 BBWorkList.pop_back();
1168 DOUT << "\nPopped off BBWL: " << *BB;
1170 // Notify all instructions in this basic block that they are newly
1177 /// ResolvedUndefsIn - While solving the dataflow for a function, we assume
1178 /// that branches on undef values cannot reach any of their successors.
1179 /// However, this is not a safe assumption. After we solve dataflow, this
1180 /// method should be use to handle this. If this returns true, the solver
1181 /// should be rerun.
1183 /// This method handles this by finding an unresolved branch and marking it one
1184 /// of the edges from the block as being feasible, even though the condition
1185 /// doesn't say it would otherwise be. This allows SCCP to find the rest of the
1186 /// CFG and only slightly pessimizes the analysis results (by marking one,
1187 /// potentially infeasible, edge feasible). This cannot usefully modify the
1188 /// constraints on the condition of the branch, as that would impact other users
1191 /// This scan also checks for values that use undefs, whose results are actually
1192 /// defined. For example, 'zext i8 undef to i32' should produce all zeros
1193 /// conservatively, as "(zext i8 X -> i32) & 0xFF00" must always return zero,
1194 /// even if X isn't defined.
1195 bool SCCPSolver::ResolvedUndefsIn(Function &F) {
1196 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
1197 if (!BBExecutable.count(BB))
1200 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
1201 // Look for instructions which produce undef values.
1202 if (I->getType() == Type::VoidTy) continue;
1204 LatticeVal &LV = getValueState(I);
1205 if (!LV.isUndefined()) continue;
1207 // Get the lattice values of the first two operands for use below.
1208 LatticeVal &Op0LV = getValueState(I->getOperand(0));
1210 if (I->getNumOperands() == 2) {
1211 // If this is a two-operand instruction, and if both operands are
1212 // undefs, the result stays undef.
1213 Op1LV = getValueState(I->getOperand(1));
1214 if (Op0LV.isUndefined() && Op1LV.isUndefined())
1218 // If this is an instructions whose result is defined even if the input is
1219 // not fully defined, propagate the information.
1220 const Type *ITy = I->getType();
1221 switch (I->getOpcode()) {
1222 default: break; // Leave the instruction as an undef.
1223 case Instruction::ZExt:
1224 // After a zero extend, we know the top part is zero. SExt doesn't have
1225 // to be handled here, because we don't know whether the top part is 1's
1227 assert(Op0LV.isUndefined());
1228 markForcedConstant(LV, I, Constant::getNullValue(ITy));
1230 case Instruction::Mul:
1231 case Instruction::And:
1232 // undef * X -> 0. X could be zero.
1233 // undef & X -> 0. X could be zero.
1234 markForcedConstant(LV, I, Constant::getNullValue(ITy));
1237 case Instruction::Or:
1238 // undef | X -> -1. X could be -1.
1239 if (const PackedType *PTy = dyn_cast<PackedType>(ITy))
1240 markForcedConstant(LV, I, ConstantPacked::getAllOnesValue(PTy));
1242 markForcedConstant(LV, I, ConstantInt::getAllOnesValue(ITy));
1245 case Instruction::SDiv:
1246 case Instruction::UDiv:
1247 case Instruction::SRem:
1248 case Instruction::URem:
1249 // X / undef -> undef. No change.
1250 // X % undef -> undef. No change.
1251 if (Op1LV.isUndefined()) break;
1253 // undef / X -> 0. X could be maxint.
1254 // undef % X -> 0. X could be 1.
1255 markForcedConstant(LV, I, Constant::getNullValue(ITy));
1258 case Instruction::AShr:
1259 // undef >>s X -> undef. No change.
1260 if (Op0LV.isUndefined()) break;
1262 // X >>s undef -> X. X could be 0, X could have the high-bit known set.
1263 if (Op0LV.isConstant())
1264 markForcedConstant(LV, I, Op0LV.getConstant());
1266 markOverdefined(LV, I);
1268 case Instruction::LShr:
1269 case Instruction::Shl:
1270 // undef >> X -> undef. No change.
1271 // undef << X -> undef. No change.
1272 if (Op0LV.isUndefined()) break;
1274 // X >> undef -> 0. X could be 0.
1275 // X << undef -> 0. X could be 0.
1276 markForcedConstant(LV, I, Constant::getNullValue(ITy));
1278 case Instruction::Select:
1279 // undef ? X : Y -> X or Y. There could be commonality between X/Y.
1280 if (Op0LV.isUndefined()) {
1281 if (!Op1LV.isConstant()) // Pick the constant one if there is any.
1282 Op1LV = getValueState(I->getOperand(2));
1283 } else if (Op1LV.isUndefined()) {
1284 // c ? undef : undef -> undef. No change.
1285 Op1LV = getValueState(I->getOperand(2));
1286 if (Op1LV.isUndefined())
1288 // Otherwise, c ? undef : x -> x.
1290 // Leave Op1LV as Operand(1)'s LatticeValue.
1293 if (Op1LV.isConstant())
1294 markForcedConstant(LV, I, Op1LV.getConstant());
1296 markOverdefined(LV, I);
1301 TerminatorInst *TI = BB->getTerminator();
1302 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
1303 if (!BI->isConditional()) continue;
1304 if (!getValueState(BI->getCondition()).isUndefined())
1306 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
1307 if (!getValueState(SI->getCondition()).isUndefined())
1313 // If the edge to the first successor isn't thought to be feasible yet, mark
1315 if (KnownFeasibleEdges.count(Edge(BB, TI->getSuccessor(0))))
1318 // Otherwise, it isn't already thought to be feasible. Mark it as such now
1319 // and return. This will make other blocks reachable, which will allow new
1320 // values to be discovered and existing ones to be moved in the lattice.
1321 markEdgeExecutable(BB, TI->getSuccessor(0));
1330 //===--------------------------------------------------------------------===//
1332 /// SCCP Class - This class uses the SCCPSolver to implement a per-function
1333 /// Sparse Conditional Constant Propagator.
1335 struct SCCP : public FunctionPass {
1336 // runOnFunction - Run the Sparse Conditional Constant Propagation
1337 // algorithm, and return true if the function was modified.
1339 bool runOnFunction(Function &F);
1341 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
1342 AU.setPreservesCFG();
1346 RegisterPass<SCCP> X("sccp", "Sparse Conditional Constant Propagation");
1347 } // end anonymous namespace
1350 // createSCCPPass - This is the public interface to this file...
1351 FunctionPass *llvm::createSCCPPass() {
1356 // runOnFunction() - Run the Sparse Conditional Constant Propagation algorithm,
1357 // and return true if the function was modified.
1359 bool SCCP::runOnFunction(Function &F) {
1360 DOUT << "SCCP on function '" << F.getName() << "'\n";
1363 // Mark the first block of the function as being executable.
1364 Solver.MarkBlockExecutable(F.begin());
1366 // Mark all arguments to the function as being overdefined.
1367 hash_map<Value*, LatticeVal> &Values = Solver.getValueMapping();
1368 for (Function::arg_iterator AI = F.arg_begin(), E = F.arg_end(); AI != E; ++AI)
1369 Values[AI].markOverdefined();
1371 // Solve for constants.
1372 bool ResolvedUndefs = true;
1373 while (ResolvedUndefs) {
1375 DOUT << "RESOLVING UNDEFs\n";
1376 ResolvedUndefs = Solver.ResolvedUndefsIn(F);
1379 bool MadeChanges = false;
1381 // If we decided that there are basic blocks that are dead in this function,
1382 // delete their contents now. Note that we cannot actually delete the blocks,
1383 // as we cannot modify the CFG of the function.
1385 std::set<BasicBlock*> &ExecutableBBs = Solver.getExecutableBlocks();
1386 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
1387 if (!ExecutableBBs.count(BB)) {
1388 DOUT << " BasicBlock Dead:" << *BB;
1391 // Delete the instructions backwards, as it has a reduced likelihood of
1392 // having to update as many def-use and use-def chains.
1393 std::vector<Instruction*> Insts;
1394 for (BasicBlock::iterator I = BB->begin(), E = BB->getTerminator();
1397 while (!Insts.empty()) {
1398 Instruction *I = Insts.back();
1400 if (!I->use_empty())
1401 I->replaceAllUsesWith(UndefValue::get(I->getType()));
1402 BB->getInstList().erase(I);
1407 // Iterate over all of the instructions in a function, replacing them with
1408 // constants if we have found them to be of constant values.
1410 for (BasicBlock::iterator BI = BB->begin(), E = BB->end(); BI != E; ) {
1411 Instruction *Inst = BI++;
1412 if (Inst->getType() != Type::VoidTy) {
1413 LatticeVal &IV = Values[Inst];
1414 if (IV.isConstant() || IV.isUndefined() &&
1415 !isa<TerminatorInst>(Inst)) {
1416 Constant *Const = IV.isConstant()
1417 ? IV.getConstant() : UndefValue::get(Inst->getType());
1418 DOUT << " Constant: " << *Const << " = " << *Inst;
1420 // Replaces all of the uses of a variable with uses of the constant.
1421 Inst->replaceAllUsesWith(Const);
1423 // Delete the instruction.
1424 BB->getInstList().erase(Inst);
1426 // Hey, we just changed something!
1438 //===--------------------------------------------------------------------===//
1440 /// IPSCCP Class - This class implements interprocedural Sparse Conditional
1441 /// Constant Propagation.
1443 struct IPSCCP : public ModulePass {
1444 bool runOnModule(Module &M);
1447 RegisterPass<IPSCCP>
1448 Y("ipsccp", "Interprocedural Sparse Conditional Constant Propagation");
1449 } // end anonymous namespace
1451 // createIPSCCPPass - This is the public interface to this file...
1452 ModulePass *llvm::createIPSCCPPass() {
1453 return new IPSCCP();
1457 static bool AddressIsTaken(GlobalValue *GV) {
1458 // Delete any dead constantexpr klingons.
1459 GV->removeDeadConstantUsers();
1461 for (Value::use_iterator UI = GV->use_begin(), E = GV->use_end();
1463 if (StoreInst *SI = dyn_cast<StoreInst>(*UI)) {
1464 if (SI->getOperand(0) == GV || SI->isVolatile())
1465 return true; // Storing addr of GV.
1466 } else if (isa<InvokeInst>(*UI) || isa<CallInst>(*UI)) {
1467 // Make sure we are calling the function, not passing the address.
1468 CallSite CS = CallSite::get(cast<Instruction>(*UI));
1469 for (CallSite::arg_iterator AI = CS.arg_begin(),
1470 E = CS.arg_end(); AI != E; ++AI)
1473 } else if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) {
1474 if (LI->isVolatile())
1482 bool IPSCCP::runOnModule(Module &M) {
1485 // Loop over all functions, marking arguments to those with their addresses
1486 // taken or that are external as overdefined.
1488 hash_map<Value*, LatticeVal> &Values = Solver.getValueMapping();
1489 for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F)
1490 if (!F->hasInternalLinkage() || AddressIsTaken(F)) {
1491 if (!F->isExternal())
1492 Solver.MarkBlockExecutable(F->begin());
1493 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
1495 Values[AI].markOverdefined();
1497 Solver.AddTrackedFunction(F);
1500 // Loop over global variables. We inform the solver about any internal global
1501 // variables that do not have their 'addresses taken'. If they don't have
1502 // their addresses taken, we can propagate constants through them.
1503 for (Module::global_iterator G = M.global_begin(), E = M.global_end();
1505 if (!G->isConstant() && G->hasInternalLinkage() && !AddressIsTaken(G))
1506 Solver.TrackValueOfGlobalVariable(G);
1508 // Solve for constants.
1509 bool ResolvedUndefs = true;
1510 while (ResolvedUndefs) {
1513 DOUT << "RESOLVING UNDEFS\n";
1514 ResolvedUndefs = false;
1515 for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F)
1516 ResolvedUndefs |= Solver.ResolvedUndefsIn(*F);
1519 bool MadeChanges = false;
1521 // Iterate over all of the instructions in the module, replacing them with
1522 // constants if we have found them to be of constant values.
1524 std::set<BasicBlock*> &ExecutableBBs = Solver.getExecutableBlocks();
1525 for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) {
1526 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
1528 if (!AI->use_empty()) {
1529 LatticeVal &IV = Values[AI];
1530 if (IV.isConstant() || IV.isUndefined()) {
1531 Constant *CST = IV.isConstant() ?
1532 IV.getConstant() : UndefValue::get(AI->getType());
1533 DOUT << "*** Arg " << *AI << " = " << *CST <<"\n";
1535 // Replaces all of the uses of a variable with uses of the
1537 AI->replaceAllUsesWith(CST);
1542 std::vector<BasicBlock*> BlocksToErase;
1543 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
1544 if (!ExecutableBBs.count(BB)) {
1545 DOUT << " BasicBlock Dead:" << *BB;
1548 // Delete the instructions backwards, as it has a reduced likelihood of
1549 // having to update as many def-use and use-def chains.
1550 std::vector<Instruction*> Insts;
1551 TerminatorInst *TI = BB->getTerminator();
1552 for (BasicBlock::iterator I = BB->begin(), E = TI; I != E; ++I)
1555 while (!Insts.empty()) {
1556 Instruction *I = Insts.back();
1558 if (!I->use_empty())
1559 I->replaceAllUsesWith(UndefValue::get(I->getType()));
1560 BB->getInstList().erase(I);
1565 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) {
1566 BasicBlock *Succ = TI->getSuccessor(i);
1567 if (Succ->begin() != Succ->end() && isa<PHINode>(Succ->begin()))
1568 TI->getSuccessor(i)->removePredecessor(BB);
1570 if (!TI->use_empty())
1571 TI->replaceAllUsesWith(UndefValue::get(TI->getType()));
1572 BB->getInstList().erase(TI);
1574 if (&*BB != &F->front())
1575 BlocksToErase.push_back(BB);
1577 new UnreachableInst(BB);
1580 for (BasicBlock::iterator BI = BB->begin(), E = BB->end(); BI != E; ) {
1581 Instruction *Inst = BI++;
1582 if (Inst->getType() != Type::VoidTy) {
1583 LatticeVal &IV = Values[Inst];
1584 if (IV.isConstant() || IV.isUndefined() &&
1585 !isa<TerminatorInst>(Inst)) {
1586 Constant *Const = IV.isConstant()
1587 ? IV.getConstant() : UndefValue::get(Inst->getType());
1588 DOUT << " Constant: " << *Const << " = " << *Inst;
1590 // Replaces all of the uses of a variable with uses of the
1592 Inst->replaceAllUsesWith(Const);
1594 // Delete the instruction.
1595 if (!isa<TerminatorInst>(Inst) && !isa<CallInst>(Inst))
1596 BB->getInstList().erase(Inst);
1598 // Hey, we just changed something!
1606 // Now that all instructions in the function are constant folded, erase dead
1607 // blocks, because we can now use ConstantFoldTerminator to get rid of
1609 for (unsigned i = 0, e = BlocksToErase.size(); i != e; ++i) {
1610 // If there are any PHI nodes in this successor, drop entries for BB now.
1611 BasicBlock *DeadBB = BlocksToErase[i];
1612 while (!DeadBB->use_empty()) {
1613 Instruction *I = cast<Instruction>(DeadBB->use_back());
1614 bool Folded = ConstantFoldTerminator(I->getParent());
1616 // The constant folder may not have been able to fold the termiantor
1617 // if this is a branch or switch on undef. Fold it manually as a
1618 // branch to the first successor.
1619 if (BranchInst *BI = dyn_cast<BranchInst>(I)) {
1620 assert(BI->isConditional() && isa<UndefValue>(BI->getCondition()) &&
1621 "Branch should be foldable!");
1622 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(I)) {
1623 assert(isa<UndefValue>(SI->getCondition()) && "Switch should fold");
1625 assert(0 && "Didn't fold away reference to block!");
1628 // Make this an uncond branch to the first successor.
1629 TerminatorInst *TI = I->getParent()->getTerminator();
1630 new BranchInst(TI->getSuccessor(0), TI);
1632 // Remove entries in successor phi nodes to remove edges.
1633 for (unsigned i = 1, e = TI->getNumSuccessors(); i != e; ++i)
1634 TI->getSuccessor(i)->removePredecessor(TI->getParent());
1636 // Remove the old terminator.
1637 TI->eraseFromParent();
1641 // Finally, delete the basic block.
1642 F->getBasicBlockList().erase(DeadBB);
1646 // If we inferred constant or undef return values for a function, we replaced
1647 // all call uses with the inferred value. This means we don't need to bother
1648 // actually returning anything from the function. Replace all return
1649 // instructions with return undef.
1650 const hash_map<Function*, LatticeVal> &RV =Solver.getTrackedFunctionRetVals();
1651 for (hash_map<Function*, LatticeVal>::const_iterator I = RV.begin(),
1652 E = RV.end(); I != E; ++I)
1653 if (!I->second.isOverdefined() &&
1654 I->first->getReturnType() != Type::VoidTy) {
1655 Function *F = I->first;
1656 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
1657 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator()))
1658 if (!isa<UndefValue>(RI->getOperand(0)))
1659 RI->setOperand(0, UndefValue::get(F->getReturnType()));
1662 // If we infered constant or undef values for globals variables, we can delete
1663 // the global and any stores that remain to it.
1664 const hash_map<GlobalVariable*, LatticeVal> &TG = Solver.getTrackedGlobals();
1665 for (hash_map<GlobalVariable*, LatticeVal>::const_iterator I = TG.begin(),
1666 E = TG.end(); I != E; ++I) {
1667 GlobalVariable *GV = I->first;
1668 assert(!I->second.isOverdefined() &&
1669 "Overdefined values should have been taken out of the map!");
1670 DOUT << "Found that GV '" << GV->getName()<< "' is constant!\n";
1671 while (!GV->use_empty()) {
1672 StoreInst *SI = cast<StoreInst>(GV->use_back());
1673 SI->eraseFromParent();
1675 M.getGlobalList().erase(GV);