1 //===- SCCP.cpp - Sparse Conditional Constant Propagation -----------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This 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
18 //===----------------------------------------------------------------------===//
20 #define DEBUG_TYPE "sccp"
21 #include "llvm/Transforms/Scalar.h"
22 #include "llvm/Transforms/IPO.h"
23 #include "llvm/Constants.h"
24 #include "llvm/DerivedTypes.h"
25 #include "llvm/Instructions.h"
26 #include "llvm/Pass.h"
27 #include "llvm/Analysis/ConstantFolding.h"
28 #include "llvm/Analysis/ValueTracking.h"
29 #include "llvm/Transforms/Utils/Local.h"
30 #include "llvm/Target/TargetData.h"
31 #include "llvm/Support/CallSite.h"
32 #include "llvm/Support/Debug.h"
33 #include "llvm/Support/ErrorHandling.h"
34 #include "llvm/Support/InstVisitor.h"
35 #include "llvm/Support/raw_ostream.h"
36 #include "llvm/ADT/DenseMap.h"
37 #include "llvm/ADT/DenseSet.h"
38 #include "llvm/ADT/PointerIntPair.h"
39 #include "llvm/ADT/SmallPtrSet.h"
40 #include "llvm/ADT/SmallVector.h"
41 #include "llvm/ADT/Statistic.h"
42 #include "llvm/ADT/STLExtras.h"
47 STATISTIC(NumInstRemoved, "Number of instructions removed");
48 STATISTIC(NumDeadBlocks , "Number of basic blocks unreachable");
50 STATISTIC(IPNumInstRemoved, "Number of instructions removed by IPSCCP");
51 STATISTIC(IPNumArgsElimed ,"Number of arguments constant propagated by IPSCCP");
52 STATISTIC(IPNumGlobalConst, "Number of globals found to be constant by IPSCCP");
55 /// LatticeVal class - This class represents the different lattice values that
56 /// an LLVM value may occupy. It is a simple class with value semantics.
60 /// undefined - This LLVM Value has no known value yet.
63 /// constant - This LLVM Value has a specific constant value.
66 /// forcedconstant - This LLVM Value was thought to be undef until
67 /// ResolvedUndefsIn. This is treated just like 'constant', but if merged
68 /// with another (different) constant, it goes to overdefined, instead of
72 /// overdefined - This instruction is not known to be constant, and we know
77 /// Val: This stores the current lattice value along with the Constant* for
78 /// the constant if this is a 'constant' or 'forcedconstant' value.
79 PointerIntPair<Constant *, 2, LatticeValueTy> Val;
81 LatticeValueTy getLatticeValue() const {
86 LatticeVal() : Val(0, undefined) {}
88 bool isUndefined() const { return getLatticeValue() == undefined; }
89 bool isConstant() const {
90 return getLatticeValue() == constant || getLatticeValue() == forcedconstant;
92 bool isOverdefined() const { return getLatticeValue() == overdefined; }
94 Constant *getConstant() const {
95 assert(isConstant() && "Cannot get the constant of a non-constant!");
96 return Val.getPointer();
99 /// markOverdefined - Return true if this is a change in status.
100 bool markOverdefined() {
104 Val.setInt(overdefined);
108 /// markConstant - Return true if this is a change in status.
109 bool markConstant(Constant *V) {
110 if (getLatticeValue() == constant) { // Constant but not forcedconstant.
111 assert(getConstant() == V && "Marking constant with different value");
116 Val.setInt(constant);
117 assert(V && "Marking constant with NULL");
120 assert(getLatticeValue() == forcedconstant &&
121 "Cannot move from overdefined to constant!");
122 // Stay at forcedconstant if the constant is the same.
123 if (V == getConstant()) return false;
125 // Otherwise, we go to overdefined. Assumptions made based on the
126 // forced value are possibly wrong. Assuming this is another constant
127 // could expose a contradiction.
128 Val.setInt(overdefined);
133 /// getConstantInt - If this is a constant with a ConstantInt value, return it
134 /// otherwise return null.
135 ConstantInt *getConstantInt() const {
137 return dyn_cast<ConstantInt>(getConstant());
141 void markForcedConstant(Constant *V) {
142 assert(isUndefined() && "Can't force a defined value!");
143 Val.setInt(forcedconstant);
147 } // end anonymous namespace.
152 //===----------------------------------------------------------------------===//
154 /// SCCPSolver - This class is a general purpose solver for Sparse Conditional
155 /// Constant Propagation.
157 class SCCPSolver : public InstVisitor<SCCPSolver> {
158 const TargetData *TD;
159 SmallPtrSet<BasicBlock*, 8> BBExecutable;// The BBs that are executable.
160 DenseMap<Value*, LatticeVal> ValueState; // The state each value is in.
162 /// StructValueState - This maintains ValueState for values that have
163 /// StructType, for example for formal arguments, calls, insertelement, etc.
165 DenseMap<std::pair<Value*, unsigned>, LatticeVal> StructValueState;
167 /// GlobalValue - If we are tracking any values for the contents of a global
168 /// variable, we keep a mapping from the constant accessor to the element of
169 /// the global, to the currently known value. If the value becomes
170 /// overdefined, it's entry is simply removed from this map.
171 DenseMap<GlobalVariable*, LatticeVal> TrackedGlobals;
173 /// TrackedRetVals - If we are tracking arguments into and the return
174 /// value out of a function, it will have an entry in this map, indicating
175 /// what the known return value for the function is.
176 DenseMap<Function*, LatticeVal> TrackedRetVals;
178 /// TrackedMultipleRetVals - Same as TrackedRetVals, but used for functions
179 /// that return multiple values.
180 DenseMap<std::pair<Function*, unsigned>, LatticeVal> TrackedMultipleRetVals;
182 /// MRVFunctionsTracked - Each function in TrackedMultipleRetVals is
183 /// represented here for efficient lookup.
184 SmallPtrSet<Function*, 16> MRVFunctionsTracked;
186 /// TrackingIncomingArguments - This is the set of functions for whose
187 /// arguments we make optimistic assumptions about and try to prove as
189 SmallPtrSet<Function*, 16> TrackingIncomingArguments;
191 /// The reason for two worklists is that overdefined is the lowest state
192 /// on the lattice, and moving things to overdefined as fast as possible
193 /// makes SCCP converge much faster.
195 /// By having a separate worklist, we accomplish this because everything
196 /// possibly overdefined will become overdefined at the soonest possible
198 SmallVector<Value*, 64> OverdefinedInstWorkList;
199 SmallVector<Value*, 64> InstWorkList;
202 SmallVector<BasicBlock*, 64> BBWorkList; // The BasicBlock work list
204 /// UsersOfOverdefinedPHIs - Keep track of any users of PHI nodes that are not
205 /// overdefined, despite the fact that the PHI node is overdefined.
206 std::multimap<PHINode*, Instruction*> UsersOfOverdefinedPHIs;
208 /// KnownFeasibleEdges - Entries in this set are edges which have already had
209 /// PHI nodes retriggered.
210 typedef std::pair<BasicBlock*, BasicBlock*> Edge;
211 DenseSet<Edge> KnownFeasibleEdges;
213 SCCPSolver(const TargetData *td) : TD(td) {}
215 /// MarkBlockExecutable - This method can be used by clients to mark all of
216 /// the blocks that are known to be intrinsically live in the processed unit.
218 /// This returns true if the block was not considered live before.
219 bool MarkBlockExecutable(BasicBlock *BB) {
220 if (!BBExecutable.insert(BB)) return false;
221 DEBUG(dbgs() << "Marking Block Executable: " << BB->getName() << "\n");
222 BBWorkList.push_back(BB); // Add the block to the work list!
226 /// TrackValueOfGlobalVariable - Clients can use this method to
227 /// inform the SCCPSolver that it should track loads and stores to the
228 /// specified global variable if it can. This is only legal to call if
229 /// performing Interprocedural SCCP.
230 void TrackValueOfGlobalVariable(GlobalVariable *GV) {
231 // We only track the contents of scalar globals.
232 if (GV->getType()->getElementType()->isSingleValueType()) {
233 LatticeVal &IV = TrackedGlobals[GV];
234 if (!isa<UndefValue>(GV->getInitializer()))
235 IV.markConstant(GV->getInitializer());
239 /// AddTrackedFunction - If the SCCP solver is supposed to track calls into
240 /// and out of the specified function (which cannot have its address taken),
241 /// this method must be called.
242 void AddTrackedFunction(Function *F) {
243 // Add an entry, F -> undef.
244 if (const StructType *STy = dyn_cast<StructType>(F->getReturnType())) {
245 MRVFunctionsTracked.insert(F);
246 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
247 TrackedMultipleRetVals.insert(std::make_pair(std::make_pair(F, i),
250 TrackedRetVals.insert(std::make_pair(F, LatticeVal()));
253 void AddArgumentTrackedFunction(Function *F) {
254 TrackingIncomingArguments.insert(F);
257 /// Solve - Solve for constants and executable blocks.
261 /// ResolvedUndefsIn - While solving the dataflow for a function, we assume
262 /// that branches on undef values cannot reach any of their successors.
263 /// However, this is not a safe assumption. After we solve dataflow, this
264 /// method should be use to handle this. If this returns true, the solver
266 bool ResolvedUndefsIn(Function &F);
268 bool isBlockExecutable(BasicBlock *BB) const {
269 return BBExecutable.count(BB);
272 LatticeVal getLatticeValueFor(Value *V) const {
273 DenseMap<Value*, LatticeVal>::const_iterator I = ValueState.find(V);
274 assert(I != ValueState.end() && "V is not in valuemap!");
278 /*LatticeVal getStructLatticeValueFor(Value *V, unsigned i) const {
279 DenseMap<std::pair<Value*, unsigned>, LatticeVal>::const_iterator I =
280 StructValueState.find(std::make_pair(V, i));
281 assert(I != StructValueState.end() && "V is not in valuemap!");
285 /// getTrackedRetVals - Get the inferred return value map.
287 const DenseMap<Function*, LatticeVal> &getTrackedRetVals() {
288 return TrackedRetVals;
291 /// getTrackedGlobals - Get and return the set of inferred initializers for
292 /// global variables.
293 const DenseMap<GlobalVariable*, LatticeVal> &getTrackedGlobals() {
294 return TrackedGlobals;
297 void markOverdefined(Value *V) {
298 assert(!V->getType()->isStructTy() && "Should use other method");
299 markOverdefined(ValueState[V], V);
302 /// markAnythingOverdefined - Mark the specified value overdefined. This
303 /// works with both scalars and structs.
304 void markAnythingOverdefined(Value *V) {
305 if (const StructType *STy = dyn_cast<StructType>(V->getType()))
306 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
307 markOverdefined(getStructValueState(V, i), V);
313 // markConstant - Make a value be marked as "constant". If the value
314 // is not already a constant, add it to the instruction work list so that
315 // the users of the instruction are updated later.
317 void markConstant(LatticeVal &IV, Value *V, Constant *C) {
318 if (!IV.markConstant(C)) return;
319 DEBUG(dbgs() << "markConstant: " << *C << ": " << *V << '\n');
320 if (IV.isOverdefined())
321 OverdefinedInstWorkList.push_back(V);
323 InstWorkList.push_back(V);
326 void markConstant(Value *V, Constant *C) {
327 assert(!V->getType()->isStructTy() && "Should use other method");
328 markConstant(ValueState[V], V, C);
331 void markForcedConstant(Value *V, Constant *C) {
332 assert(!V->getType()->isStructTy() && "Should use other method");
333 LatticeVal &IV = ValueState[V];
334 IV.markForcedConstant(C);
335 DEBUG(dbgs() << "markForcedConstant: " << *C << ": " << *V << '\n');
336 if (IV.isOverdefined())
337 OverdefinedInstWorkList.push_back(V);
339 InstWorkList.push_back(V);
343 // markOverdefined - Make a value be marked as "overdefined". If the
344 // value is not already overdefined, add it to the overdefined instruction
345 // work list so that the users of the instruction are updated later.
346 void markOverdefined(LatticeVal &IV, Value *V) {
347 if (!IV.markOverdefined()) return;
349 DEBUG(dbgs() << "markOverdefined: ";
350 if (Function *F = dyn_cast<Function>(V))
351 dbgs() << "Function '" << F->getName() << "'\n";
353 dbgs() << *V << '\n');
354 // Only instructions go on the work list
355 OverdefinedInstWorkList.push_back(V);
358 void mergeInValue(LatticeVal &IV, Value *V, LatticeVal MergeWithV) {
359 if (IV.isOverdefined() || MergeWithV.isUndefined())
361 if (MergeWithV.isOverdefined())
362 markOverdefined(IV, V);
363 else if (IV.isUndefined())
364 markConstant(IV, V, MergeWithV.getConstant());
365 else if (IV.getConstant() != MergeWithV.getConstant())
366 markOverdefined(IV, V);
369 void mergeInValue(Value *V, LatticeVal MergeWithV) {
370 assert(!V->getType()->isStructTy() && "Should use other method");
371 mergeInValue(ValueState[V], V, MergeWithV);
375 /// getValueState - Return the LatticeVal object that corresponds to the
376 /// value. This function handles the case when the value hasn't been seen yet
377 /// by properly seeding constants etc.
378 LatticeVal &getValueState(Value *V) {
379 assert(!V->getType()->isStructTy() && "Should use getStructValueState");
381 std::pair<DenseMap<Value*, LatticeVal>::iterator, bool> I =
382 ValueState.insert(std::make_pair(V, LatticeVal()));
383 LatticeVal &LV = I.first->second;
386 return LV; // Common case, already in the map.
388 if (Constant *C = dyn_cast<Constant>(V)) {
389 // Undef values remain undefined.
390 if (!isa<UndefValue>(V))
391 LV.markConstant(C); // Constants are constant
394 // All others are underdefined by default.
398 /// getStructValueState - Return the LatticeVal object that corresponds to the
399 /// value/field pair. This function handles the case when the value hasn't
400 /// been seen yet by properly seeding constants etc.
401 LatticeVal &getStructValueState(Value *V, unsigned i) {
402 assert(V->getType()->isStructTy() && "Should use getValueState");
403 assert(i < cast<StructType>(V->getType())->getNumElements() &&
404 "Invalid element #");
406 std::pair<DenseMap<std::pair<Value*, unsigned>, LatticeVal>::iterator,
407 bool> I = StructValueState.insert(
408 std::make_pair(std::make_pair(V, i), LatticeVal()));
409 LatticeVal &LV = I.first->second;
412 return LV; // Common case, already in the map.
414 if (Constant *C = dyn_cast<Constant>(V)) {
415 if (isa<UndefValue>(C))
416 ; // Undef values remain undefined.
417 else if (ConstantStruct *CS = dyn_cast<ConstantStruct>(C))
418 LV.markConstant(CS->getOperand(i)); // Constants are constant.
419 else if (isa<ConstantAggregateZero>(C)) {
420 const Type *FieldTy = cast<StructType>(V->getType())->getElementType(i);
421 LV.markConstant(Constant::getNullValue(FieldTy));
423 LV.markOverdefined(); // Unknown sort of constant.
426 // All others are underdefined by default.
431 /// markEdgeExecutable - Mark a basic block as executable, adding it to the BB
432 /// work list if it is not already executable.
433 void markEdgeExecutable(BasicBlock *Source, BasicBlock *Dest) {
434 if (!KnownFeasibleEdges.insert(Edge(Source, Dest)).second)
435 return; // This edge is already known to be executable!
437 if (!MarkBlockExecutable(Dest)) {
438 // If the destination is already executable, we just made an *edge*
439 // feasible that wasn't before. Revisit the PHI nodes in the block
440 // because they have potentially new operands.
441 DEBUG(dbgs() << "Marking Edge Executable: " << Source->getName()
442 << " -> " << Dest->getName() << "\n");
445 for (BasicBlock::iterator I = Dest->begin();
446 (PN = dyn_cast<PHINode>(I)); ++I)
451 // getFeasibleSuccessors - Return a vector of booleans to indicate which
452 // successors are reachable from a given terminator instruction.
454 void getFeasibleSuccessors(TerminatorInst &TI, SmallVector<bool, 16> &Succs);
456 // isEdgeFeasible - Return true if the control flow edge from the 'From' basic
457 // block to the 'To' basic block is currently feasible.
459 bool isEdgeFeasible(BasicBlock *From, BasicBlock *To);
461 // OperandChangedState - This method is invoked on all of the users of an
462 // instruction that was just changed state somehow. Based on this
463 // information, we need to update the specified user of this instruction.
465 void OperandChangedState(Instruction *I) {
466 if (BBExecutable.count(I->getParent())) // Inst is executable?
470 /// RemoveFromOverdefinedPHIs - If I has any entries in the
471 /// UsersOfOverdefinedPHIs map for PN, remove them now.
472 void RemoveFromOverdefinedPHIs(Instruction *I, PHINode *PN) {
473 if (UsersOfOverdefinedPHIs.empty()) return;
474 std::multimap<PHINode*, Instruction*>::iterator It, E;
475 tie(It, E) = UsersOfOverdefinedPHIs.equal_range(PN);
478 UsersOfOverdefinedPHIs.erase(It++);
485 friend class InstVisitor<SCCPSolver>;
487 // visit implementations - Something changed in this instruction. Either an
488 // operand made a transition, or the instruction is newly executable. Change
489 // the value type of I to reflect these changes if appropriate.
490 void visitPHINode(PHINode &I);
493 void visitReturnInst(ReturnInst &I);
494 void visitTerminatorInst(TerminatorInst &TI);
496 void visitCastInst(CastInst &I);
497 void visitSelectInst(SelectInst &I);
498 void visitBinaryOperator(Instruction &I);
499 void visitCmpInst(CmpInst &I);
500 void visitExtractElementInst(ExtractElementInst &I);
501 void visitInsertElementInst(InsertElementInst &I);
502 void visitShuffleVectorInst(ShuffleVectorInst &I);
503 void visitExtractValueInst(ExtractValueInst &EVI);
504 void visitInsertValueInst(InsertValueInst &IVI);
506 // Instructions that cannot be folded away.
507 void visitStoreInst (StoreInst &I);
508 void visitLoadInst (LoadInst &I);
509 void visitGetElementPtrInst(GetElementPtrInst &I);
510 void visitCallInst (CallInst &I) {
513 void visitInvokeInst (InvokeInst &II) {
515 visitTerminatorInst(II);
517 void visitCallSite (CallSite CS);
518 void visitUnwindInst (TerminatorInst &I) { /*returns void*/ }
519 void visitUnreachableInst(TerminatorInst &I) { /*returns void*/ }
520 void visitAllocaInst (Instruction &I) { markOverdefined(&I); }
521 void visitVAArgInst (Instruction &I) { markAnythingOverdefined(&I); }
523 void visitInstruction(Instruction &I) {
524 // If a new instruction is added to LLVM that we don't handle.
525 dbgs() << "SCCP: Don't know how to handle: " << I;
526 markAnythingOverdefined(&I); // Just in case
530 } // end anonymous namespace
533 // getFeasibleSuccessors - Return a vector of booleans to indicate which
534 // successors are reachable from a given terminator instruction.
536 void SCCPSolver::getFeasibleSuccessors(TerminatorInst &TI,
537 SmallVector<bool, 16> &Succs) {
538 Succs.resize(TI.getNumSuccessors());
539 if (BranchInst *BI = dyn_cast<BranchInst>(&TI)) {
540 if (BI->isUnconditional()) {
545 LatticeVal BCValue = getValueState(BI->getCondition());
546 ConstantInt *CI = BCValue.getConstantInt();
548 // Overdefined condition variables, and branches on unfoldable constant
549 // conditions, mean the branch could go either way.
550 if (!BCValue.isUndefined())
551 Succs[0] = Succs[1] = true;
555 // Constant condition variables mean the branch can only go a single way.
556 Succs[CI->isZero()] = true;
560 if (isa<InvokeInst>(TI)) {
561 // Invoke instructions successors are always executable.
562 Succs[0] = Succs[1] = true;
566 if (SwitchInst *SI = dyn_cast<SwitchInst>(&TI)) {
567 LatticeVal SCValue = getValueState(SI->getCondition());
568 ConstantInt *CI = SCValue.getConstantInt();
570 if (CI == 0) { // Overdefined or undefined condition?
571 // All destinations are executable!
572 if (!SCValue.isUndefined())
573 Succs.assign(TI.getNumSuccessors(), true);
577 Succs[SI->findCaseValue(CI)] = true;
581 // TODO: This could be improved if the operand is a [cast of a] BlockAddress.
582 if (isa<IndirectBrInst>(&TI)) {
583 // Just mark all destinations executable!
584 Succs.assign(TI.getNumSuccessors(), true);
589 dbgs() << "Unknown terminator instruction: " << TI << '\n';
591 llvm_unreachable("SCCP: Don't know how to handle this terminator!");
595 // isEdgeFeasible - Return true if the control flow edge from the 'From' basic
596 // block to the 'To' basic block is currently feasible.
598 bool SCCPSolver::isEdgeFeasible(BasicBlock *From, BasicBlock *To) {
599 assert(BBExecutable.count(To) && "Dest should always be alive!");
601 // Make sure the source basic block is executable!!
602 if (!BBExecutable.count(From)) return false;
604 // Check to make sure this edge itself is actually feasible now.
605 TerminatorInst *TI = From->getTerminator();
606 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
607 if (BI->isUnconditional())
610 LatticeVal BCValue = getValueState(BI->getCondition());
612 // Overdefined condition variables mean the branch could go either way,
613 // undef conditions mean that neither edge is feasible yet.
614 ConstantInt *CI = BCValue.getConstantInt();
616 return !BCValue.isUndefined();
618 // Constant condition variables mean the branch can only go a single way.
619 return BI->getSuccessor(CI->isZero()) == To;
622 // Invoke instructions successors are always executable.
623 if (isa<InvokeInst>(TI))
626 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
627 LatticeVal SCValue = getValueState(SI->getCondition());
628 ConstantInt *CI = SCValue.getConstantInt();
631 return !SCValue.isUndefined();
633 // Make sure to skip the "default value" which isn't a value
634 for (unsigned i = 1, E = SI->getNumSuccessors(); i != E; ++i)
635 if (SI->getSuccessorValue(i) == CI) // Found the taken branch.
636 return SI->getSuccessor(i) == To;
638 // If the constant value is not equal to any of the branches, we must
639 // execute default branch.
640 return SI->getDefaultDest() == To;
643 // Just mark all destinations executable!
644 // TODO: This could be improved if the operand is a [cast of a] BlockAddress.
645 if (isa<IndirectBrInst>(&TI))
649 dbgs() << "Unknown terminator instruction: " << *TI << '\n';
654 // visit Implementations - Something changed in this instruction, either an
655 // operand made a transition, or the instruction is newly executable. Change
656 // the value type of I to reflect these changes if appropriate. This method
657 // makes sure to do the following actions:
659 // 1. If a phi node merges two constants in, and has conflicting value coming
660 // from different branches, or if the PHI node merges in an overdefined
661 // value, then the PHI node becomes overdefined.
662 // 2. If a phi node merges only constants in, and they all agree on value, the
663 // PHI node becomes a constant value equal to that.
664 // 3. If V <- x (op) y && isConstant(x) && isConstant(y) V = Constant
665 // 4. If V <- x (op) y && (isOverdefined(x) || isOverdefined(y)) V = Overdefined
666 // 5. If V <- MEM or V <- CALL or V <- (unknown) then V = Overdefined
667 // 6. If a conditional branch has a value that is constant, make the selected
668 // destination executable
669 // 7. If a conditional branch has a value that is overdefined, make all
670 // successors executable.
672 void SCCPSolver::visitPHINode(PHINode &PN) {
673 // If this PN returns a struct, just mark the result overdefined.
674 // TODO: We could do a lot better than this if code actually uses this.
675 if (PN.getType()->isStructTy())
676 return markAnythingOverdefined(&PN);
678 if (getValueState(&PN).isOverdefined()) {
679 // There may be instructions using this PHI node that are not overdefined
680 // themselves. If so, make sure that they know that the PHI node operand
682 std::multimap<PHINode*, Instruction*>::iterator I, E;
683 tie(I, E) = UsersOfOverdefinedPHIs.equal_range(&PN);
687 SmallVector<Instruction*, 16> Users;
689 Users.push_back(I->second);
690 while (!Users.empty())
691 visit(Users.pop_back_val());
692 return; // Quick exit
695 // Super-extra-high-degree PHI nodes are unlikely to ever be marked constant,
696 // and slow us down a lot. Just mark them overdefined.
697 if (PN.getNumIncomingValues() > 64)
698 return markOverdefined(&PN);
700 // Look at all of the executable operands of the PHI node. If any of them
701 // are overdefined, the PHI becomes overdefined as well. If they are all
702 // constant, and they agree with each other, the PHI becomes the identical
703 // constant. If they are constant and don't agree, the PHI is overdefined.
704 // If there are no executable operands, the PHI remains undefined.
706 Constant *OperandVal = 0;
707 for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) {
708 LatticeVal IV = getValueState(PN.getIncomingValue(i));
709 if (IV.isUndefined()) continue; // Doesn't influence PHI node.
711 if (!isEdgeFeasible(PN.getIncomingBlock(i), PN.getParent()))
714 if (IV.isOverdefined()) // PHI node becomes overdefined!
715 return markOverdefined(&PN);
717 if (OperandVal == 0) { // Grab the first value.
718 OperandVal = IV.getConstant();
722 // There is already a reachable operand. If we conflict with it,
723 // then the PHI node becomes overdefined. If we agree with it, we
726 // Check to see if there are two different constants merging, if so, the PHI
727 // node is overdefined.
728 if (IV.getConstant() != OperandVal)
729 return markOverdefined(&PN);
732 // If we exited the loop, this means that the PHI node only has constant
733 // arguments that agree with each other(and OperandVal is the constant) or
734 // OperandVal is null because there are no defined incoming arguments. If
735 // this is the case, the PHI remains undefined.
738 markConstant(&PN, OperandVal); // Acquire operand value
744 void SCCPSolver::visitReturnInst(ReturnInst &I) {
745 if (I.getNumOperands() == 0) return; // ret void
747 Function *F = I.getParent()->getParent();
748 Value *ResultOp = I.getOperand(0);
750 // If we are tracking the return value of this function, merge it in.
751 if (!TrackedRetVals.empty() && !ResultOp->getType()->isStructTy()) {
752 DenseMap<Function*, LatticeVal>::iterator TFRVI =
753 TrackedRetVals.find(F);
754 if (TFRVI != TrackedRetVals.end()) {
755 mergeInValue(TFRVI->second, F, getValueState(ResultOp));
760 // Handle functions that return multiple values.
761 if (!TrackedMultipleRetVals.empty()) {
762 if (const StructType *STy = dyn_cast<StructType>(ResultOp->getType()))
763 if (MRVFunctionsTracked.count(F))
764 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
765 mergeInValue(TrackedMultipleRetVals[std::make_pair(F, i)], F,
766 getStructValueState(ResultOp, i));
771 void SCCPSolver::visitTerminatorInst(TerminatorInst &TI) {
772 SmallVector<bool, 16> SuccFeasible;
773 getFeasibleSuccessors(TI, SuccFeasible);
775 BasicBlock *BB = TI.getParent();
777 // Mark all feasible successors executable.
778 for (unsigned i = 0, e = SuccFeasible.size(); i != e; ++i)
780 markEdgeExecutable(BB, TI.getSuccessor(i));
783 void SCCPSolver::visitCastInst(CastInst &I) {
784 LatticeVal OpSt = getValueState(I.getOperand(0));
785 if (OpSt.isOverdefined()) // Inherit overdefinedness of operand
787 else if (OpSt.isConstant()) // Propagate constant value
788 markConstant(&I, ConstantExpr::getCast(I.getOpcode(),
789 OpSt.getConstant(), I.getType()));
793 void SCCPSolver::visitExtractValueInst(ExtractValueInst &EVI) {
794 // If this returns a struct, mark all elements over defined, we don't track
795 // structs in structs.
796 if (EVI.getType()->isStructTy())
797 return markAnythingOverdefined(&EVI);
799 // If this is extracting from more than one level of struct, we don't know.
800 if (EVI.getNumIndices() != 1)
801 return markOverdefined(&EVI);
803 Value *AggVal = EVI.getAggregateOperand();
804 if (AggVal->getType()->isStructTy()) {
805 unsigned i = *EVI.idx_begin();
806 LatticeVal EltVal = getStructValueState(AggVal, i);
807 mergeInValue(getValueState(&EVI), &EVI, EltVal);
809 // Otherwise, must be extracting from an array.
810 return markOverdefined(&EVI);
814 void SCCPSolver::visitInsertValueInst(InsertValueInst &IVI) {
815 const StructType *STy = dyn_cast<StructType>(IVI.getType());
817 return markOverdefined(&IVI);
819 // If this has more than one index, we can't handle it, drive all results to
821 if (IVI.getNumIndices() != 1)
822 return markAnythingOverdefined(&IVI);
824 Value *Aggr = IVI.getAggregateOperand();
825 unsigned Idx = *IVI.idx_begin();
827 // Compute the result based on what we're inserting.
828 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
829 // This passes through all values that aren't the inserted element.
831 LatticeVal EltVal = getStructValueState(Aggr, i);
832 mergeInValue(getStructValueState(&IVI, i), &IVI, EltVal);
836 Value *Val = IVI.getInsertedValueOperand();
837 if (Val->getType()->isStructTy())
838 // We don't track structs in structs.
839 markOverdefined(getStructValueState(&IVI, i), &IVI);
841 LatticeVal InVal = getValueState(Val);
842 mergeInValue(getStructValueState(&IVI, i), &IVI, InVal);
847 void SCCPSolver::visitSelectInst(SelectInst &I) {
848 // If this select returns a struct, just mark the result overdefined.
849 // TODO: We could do a lot better than this if code actually uses this.
850 if (I.getType()->isStructTy())
851 return markAnythingOverdefined(&I);
853 LatticeVal CondValue = getValueState(I.getCondition());
854 if (CondValue.isUndefined())
857 if (ConstantInt *CondCB = CondValue.getConstantInt()) {
858 Value *OpVal = CondCB->isZero() ? I.getFalseValue() : I.getTrueValue();
859 mergeInValue(&I, getValueState(OpVal));
863 // Otherwise, the condition is overdefined or a constant we can't evaluate.
864 // See if we can produce something better than overdefined based on the T/F
866 LatticeVal TVal = getValueState(I.getTrueValue());
867 LatticeVal FVal = getValueState(I.getFalseValue());
869 // select ?, C, C -> C.
870 if (TVal.isConstant() && FVal.isConstant() &&
871 TVal.getConstant() == FVal.getConstant())
872 return markConstant(&I, FVal.getConstant());
874 if (TVal.isUndefined()) // select ?, undef, X -> X.
875 return mergeInValue(&I, FVal);
876 if (FVal.isUndefined()) // select ?, X, undef -> X.
877 return mergeInValue(&I, TVal);
881 // Handle Binary Operators.
882 void SCCPSolver::visitBinaryOperator(Instruction &I) {
883 LatticeVal V1State = getValueState(I.getOperand(0));
884 LatticeVal V2State = getValueState(I.getOperand(1));
886 LatticeVal &IV = ValueState[&I];
887 if (IV.isOverdefined()) return;
889 if (V1State.isConstant() && V2State.isConstant())
890 return markConstant(IV, &I,
891 ConstantExpr::get(I.getOpcode(), V1State.getConstant(),
892 V2State.getConstant()));
894 // If something is undef, wait for it to resolve.
895 if (!V1State.isOverdefined() && !V2State.isOverdefined())
898 // Otherwise, one of our operands is overdefined. Try to produce something
899 // better than overdefined with some tricks.
901 // If this is an AND or OR with 0 or -1, it doesn't matter that the other
902 // operand is overdefined.
903 if (I.getOpcode() == Instruction::And || I.getOpcode() == Instruction::Or) {
904 LatticeVal *NonOverdefVal = 0;
905 if (!V1State.isOverdefined())
906 NonOverdefVal = &V1State;
907 else if (!V2State.isOverdefined())
908 NonOverdefVal = &V2State;
911 if (NonOverdefVal->isUndefined()) {
912 // Could annihilate value.
913 if (I.getOpcode() == Instruction::And)
914 markConstant(IV, &I, Constant::getNullValue(I.getType()));
915 else if (const VectorType *PT = dyn_cast<VectorType>(I.getType()))
916 markConstant(IV, &I, Constant::getAllOnesValue(PT));
919 Constant::getAllOnesValue(I.getType()));
923 if (I.getOpcode() == Instruction::And) {
925 if (NonOverdefVal->getConstant()->isNullValue())
926 return markConstant(IV, &I, NonOverdefVal->getConstant());
928 if (ConstantInt *CI = NonOverdefVal->getConstantInt())
929 if (CI->isAllOnesValue()) // X or -1 = -1
930 return markConstant(IV, &I, NonOverdefVal->getConstant());
936 // If both operands are PHI nodes, it is possible that this instruction has
937 // a constant value, despite the fact that the PHI node doesn't. Check for
938 // this condition now.
939 if (PHINode *PN1 = dyn_cast<PHINode>(I.getOperand(0)))
940 if (PHINode *PN2 = dyn_cast<PHINode>(I.getOperand(1)))
941 if (PN1->getParent() == PN2->getParent()) {
942 // Since the two PHI nodes are in the same basic block, they must have
943 // entries for the same predecessors. Walk the predecessor list, and
944 // if all of the incoming values are constants, and the result of
945 // evaluating this expression with all incoming value pairs is the
946 // same, then this expression is a constant even though the PHI node
947 // is not a constant!
949 for (unsigned i = 0, e = PN1->getNumIncomingValues(); i != e; ++i) {
950 LatticeVal In1 = getValueState(PN1->getIncomingValue(i));
951 BasicBlock *InBlock = PN1->getIncomingBlock(i);
952 LatticeVal In2 =getValueState(PN2->getIncomingValueForBlock(InBlock));
954 if (In1.isOverdefined() || In2.isOverdefined()) {
955 Result.markOverdefined();
956 break; // Cannot fold this operation over the PHI nodes!
959 if (In1.isConstant() && In2.isConstant()) {
960 Constant *V = ConstantExpr::get(I.getOpcode(), In1.getConstant(),
962 if (Result.isUndefined())
963 Result.markConstant(V);
964 else if (Result.isConstant() && Result.getConstant() != V) {
965 Result.markOverdefined();
971 // If we found a constant value here, then we know the instruction is
972 // constant despite the fact that the PHI nodes are overdefined.
973 if (Result.isConstant()) {
974 markConstant(IV, &I, Result.getConstant());
975 // Remember that this instruction is virtually using the PHI node
977 UsersOfOverdefinedPHIs.insert(std::make_pair(PN1, &I));
978 UsersOfOverdefinedPHIs.insert(std::make_pair(PN2, &I));
982 if (Result.isUndefined())
985 // Okay, this really is overdefined now. Since we might have
986 // speculatively thought that this was not overdefined before, and
987 // added ourselves to the UsersOfOverdefinedPHIs list for the PHIs,
988 // make sure to clean out any entries that we put there, for
990 RemoveFromOverdefinedPHIs(&I, PN1);
991 RemoveFromOverdefinedPHIs(&I, PN2);
997 // Handle ICmpInst instruction.
998 void SCCPSolver::visitCmpInst(CmpInst &I) {
999 LatticeVal V1State = getValueState(I.getOperand(0));
1000 LatticeVal V2State = getValueState(I.getOperand(1));
1002 LatticeVal &IV = ValueState[&I];
1003 if (IV.isOverdefined()) return;
1005 if (V1State.isConstant() && V2State.isConstant())
1006 return markConstant(IV, &I, ConstantExpr::getCompare(I.getPredicate(),
1007 V1State.getConstant(),
1008 V2State.getConstant()));
1010 // If operands are still undefined, wait for it to resolve.
1011 if (!V1State.isOverdefined() && !V2State.isOverdefined())
1014 // If something is overdefined, use some tricks to avoid ending up and over
1015 // defined if we can.
1017 // If both operands are PHI nodes, it is possible that this instruction has
1018 // a constant value, despite the fact that the PHI node doesn't. Check for
1019 // this condition now.
1020 if (PHINode *PN1 = dyn_cast<PHINode>(I.getOperand(0)))
1021 if (PHINode *PN2 = dyn_cast<PHINode>(I.getOperand(1)))
1022 if (PN1->getParent() == PN2->getParent()) {
1023 // Since the two PHI nodes are in the same basic block, they must have
1024 // entries for the same predecessors. Walk the predecessor list, and
1025 // if all of the incoming values are constants, and the result of
1026 // evaluating this expression with all incoming value pairs is the
1027 // same, then this expression is a constant even though the PHI node
1028 // is not a constant!
1030 for (unsigned i = 0, e = PN1->getNumIncomingValues(); i != e; ++i) {
1031 LatticeVal In1 = getValueState(PN1->getIncomingValue(i));
1032 BasicBlock *InBlock = PN1->getIncomingBlock(i);
1033 LatticeVal In2 =getValueState(PN2->getIncomingValueForBlock(InBlock));
1035 if (In1.isOverdefined() || In2.isOverdefined()) {
1036 Result.markOverdefined();
1037 break; // Cannot fold this operation over the PHI nodes!
1040 if (In1.isConstant() && In2.isConstant()) {
1041 Constant *V = ConstantExpr::getCompare(I.getPredicate(),
1044 if (Result.isUndefined())
1045 Result.markConstant(V);
1046 else if (Result.isConstant() && Result.getConstant() != V) {
1047 Result.markOverdefined();
1053 // If we found a constant value here, then we know the instruction is
1054 // constant despite the fact that the PHI nodes are overdefined.
1055 if (Result.isConstant()) {
1056 markConstant(&I, Result.getConstant());
1057 // Remember that this instruction is virtually using the PHI node
1059 UsersOfOverdefinedPHIs.insert(std::make_pair(PN1, &I));
1060 UsersOfOverdefinedPHIs.insert(std::make_pair(PN2, &I));
1064 if (Result.isUndefined())
1067 // Okay, this really is overdefined now. Since we might have
1068 // speculatively thought that this was not overdefined before, and
1069 // added ourselves to the UsersOfOverdefinedPHIs list for the PHIs,
1070 // make sure to clean out any entries that we put there, for
1072 RemoveFromOverdefinedPHIs(&I, PN1);
1073 RemoveFromOverdefinedPHIs(&I, PN2);
1076 markOverdefined(&I);
1079 void SCCPSolver::visitExtractElementInst(ExtractElementInst &I) {
1080 // TODO : SCCP does not handle vectors properly.
1081 return markOverdefined(&I);
1084 LatticeVal &ValState = getValueState(I.getOperand(0));
1085 LatticeVal &IdxState = getValueState(I.getOperand(1));
1087 if (ValState.isOverdefined() || IdxState.isOverdefined())
1088 markOverdefined(&I);
1089 else if(ValState.isConstant() && IdxState.isConstant())
1090 markConstant(&I, ConstantExpr::getExtractElement(ValState.getConstant(),
1091 IdxState.getConstant()));
1095 void SCCPSolver::visitInsertElementInst(InsertElementInst &I) {
1096 // TODO : SCCP does not handle vectors properly.
1097 return markOverdefined(&I);
1099 LatticeVal &ValState = getValueState(I.getOperand(0));
1100 LatticeVal &EltState = getValueState(I.getOperand(1));
1101 LatticeVal &IdxState = getValueState(I.getOperand(2));
1103 if (ValState.isOverdefined() || EltState.isOverdefined() ||
1104 IdxState.isOverdefined())
1105 markOverdefined(&I);
1106 else if(ValState.isConstant() && EltState.isConstant() &&
1107 IdxState.isConstant())
1108 markConstant(&I, ConstantExpr::getInsertElement(ValState.getConstant(),
1109 EltState.getConstant(),
1110 IdxState.getConstant()));
1111 else if (ValState.isUndefined() && EltState.isConstant() &&
1112 IdxState.isConstant())
1113 markConstant(&I,ConstantExpr::getInsertElement(UndefValue::get(I.getType()),
1114 EltState.getConstant(),
1115 IdxState.getConstant()));
1119 void SCCPSolver::visitShuffleVectorInst(ShuffleVectorInst &I) {
1120 // TODO : SCCP does not handle vectors properly.
1121 return markOverdefined(&I);
1123 LatticeVal &V1State = getValueState(I.getOperand(0));
1124 LatticeVal &V2State = getValueState(I.getOperand(1));
1125 LatticeVal &MaskState = getValueState(I.getOperand(2));
1127 if (MaskState.isUndefined() ||
1128 (V1State.isUndefined() && V2State.isUndefined()))
1129 return; // Undefined output if mask or both inputs undefined.
1131 if (V1State.isOverdefined() || V2State.isOverdefined() ||
1132 MaskState.isOverdefined()) {
1133 markOverdefined(&I);
1135 // A mix of constant/undef inputs.
1136 Constant *V1 = V1State.isConstant() ?
1137 V1State.getConstant() : UndefValue::get(I.getType());
1138 Constant *V2 = V2State.isConstant() ?
1139 V2State.getConstant() : UndefValue::get(I.getType());
1140 Constant *Mask = MaskState.isConstant() ?
1141 MaskState.getConstant() : UndefValue::get(I.getOperand(2)->getType());
1142 markConstant(&I, ConstantExpr::getShuffleVector(V1, V2, Mask));
1147 // Handle getelementptr instructions. If all operands are constants then we
1148 // can turn this into a getelementptr ConstantExpr.
1150 void SCCPSolver::visitGetElementPtrInst(GetElementPtrInst &I) {
1151 if (ValueState[&I].isOverdefined()) return;
1153 SmallVector<Constant*, 8> Operands;
1154 Operands.reserve(I.getNumOperands());
1156 for (unsigned i = 0, e = I.getNumOperands(); i != e; ++i) {
1157 LatticeVal State = getValueState(I.getOperand(i));
1158 if (State.isUndefined())
1159 return; // Operands are not resolved yet.
1161 if (State.isOverdefined())
1162 return markOverdefined(&I);
1164 assert(State.isConstant() && "Unknown state!");
1165 Operands.push_back(State.getConstant());
1168 Constant *Ptr = Operands[0];
1169 markConstant(&I, ConstantExpr::getGetElementPtr(Ptr, &Operands[0]+1,
1170 Operands.size()-1));
1173 void SCCPSolver::visitStoreInst(StoreInst &SI) {
1174 // If this store is of a struct, ignore it.
1175 if (SI.getOperand(0)->getType()->isStructTy())
1178 if (TrackedGlobals.empty() || !isa<GlobalVariable>(SI.getOperand(1)))
1181 GlobalVariable *GV = cast<GlobalVariable>(SI.getOperand(1));
1182 DenseMap<GlobalVariable*, LatticeVal>::iterator I = TrackedGlobals.find(GV);
1183 if (I == TrackedGlobals.end() || I->second.isOverdefined()) return;
1185 // Get the value we are storing into the global, then merge it.
1186 mergeInValue(I->second, GV, getValueState(SI.getOperand(0)));
1187 if (I->second.isOverdefined())
1188 TrackedGlobals.erase(I); // No need to keep tracking this!
1192 // Handle load instructions. If the operand is a constant pointer to a constant
1193 // global, we can replace the load with the loaded constant value!
1194 void SCCPSolver::visitLoadInst(LoadInst &I) {
1195 // If this load is of a struct, just mark the result overdefined.
1196 if (I.getType()->isStructTy())
1197 return markAnythingOverdefined(&I);
1199 LatticeVal PtrVal = getValueState(I.getOperand(0));
1200 if (PtrVal.isUndefined()) return; // The pointer is not resolved yet!
1202 LatticeVal &IV = ValueState[&I];
1203 if (IV.isOverdefined()) return;
1205 if (!PtrVal.isConstant() || I.isVolatile())
1206 return markOverdefined(IV, &I);
1208 Constant *Ptr = PtrVal.getConstant();
1210 // load null -> null
1211 if (isa<ConstantPointerNull>(Ptr) && I.getPointerAddressSpace() == 0)
1212 return markConstant(IV, &I, Constant::getNullValue(I.getType()));
1214 // Transform load (constant global) into the value loaded.
1215 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Ptr)) {
1216 if (!TrackedGlobals.empty()) {
1217 // If we are tracking this global, merge in the known value for it.
1218 DenseMap<GlobalVariable*, LatticeVal>::iterator It =
1219 TrackedGlobals.find(GV);
1220 if (It != TrackedGlobals.end()) {
1221 mergeInValue(IV, &I, It->second);
1227 // Transform load from a constant into a constant if possible.
1228 if (Constant *C = ConstantFoldLoadFromConstPtr(Ptr, TD))
1229 return markConstant(IV, &I, C);
1231 // Otherwise we cannot say for certain what value this load will produce.
1233 markOverdefined(IV, &I);
1236 void SCCPSolver::visitCallSite(CallSite CS) {
1237 Function *F = CS.getCalledFunction();
1238 Instruction *I = CS.getInstruction();
1240 // The common case is that we aren't tracking the callee, either because we
1241 // are not doing interprocedural analysis or the callee is indirect, or is
1242 // external. Handle these cases first.
1243 if (F == 0 || F->isDeclaration()) {
1245 // Void return and not tracking callee, just bail.
1246 if (I->getType()->isVoidTy()) return;
1248 // Otherwise, if we have a single return value case, and if the function is
1249 // a declaration, maybe we can constant fold it.
1250 if (F && F->isDeclaration() && !I->getType()->isStructTy() &&
1251 canConstantFoldCallTo(F)) {
1253 SmallVector<Constant*, 8> Operands;
1254 for (CallSite::arg_iterator AI = CS.arg_begin(), E = CS.arg_end();
1256 LatticeVal State = getValueState(*AI);
1258 if (State.isUndefined())
1259 return; // Operands are not resolved yet.
1260 if (State.isOverdefined())
1261 return markOverdefined(I);
1262 assert(State.isConstant() && "Unknown state!");
1263 Operands.push_back(State.getConstant());
1266 // If we can constant fold this, mark the result of the call as a
1268 if (Constant *C = ConstantFoldCall(F, Operands.data(), Operands.size()))
1269 return markConstant(I, C);
1272 // Otherwise, we don't know anything about this call, mark it overdefined.
1273 return markAnythingOverdefined(I);
1276 // If this is a local function that doesn't have its address taken, mark its
1277 // entry block executable and merge in the actual arguments to the call into
1278 // the formal arguments of the function.
1279 if (!TrackingIncomingArguments.empty() && TrackingIncomingArguments.count(F)){
1280 MarkBlockExecutable(F->begin());
1282 // Propagate information from this call site into the callee.
1283 CallSite::arg_iterator CAI = CS.arg_begin();
1284 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
1285 AI != E; ++AI, ++CAI) {
1286 // If this argument is byval, and if the function is not readonly, there
1287 // will be an implicit copy formed of the input aggregate.
1288 if (AI->hasByValAttr() && !F->onlyReadsMemory()) {
1289 markOverdefined(AI);
1293 if (const StructType *STy = dyn_cast<StructType>(AI->getType())) {
1294 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
1295 LatticeVal CallArg = getStructValueState(*CAI, i);
1296 mergeInValue(getStructValueState(AI, i), AI, CallArg);
1299 mergeInValue(AI, getValueState(*CAI));
1304 // If this is a single/zero retval case, see if we're tracking the function.
1305 if (const StructType *STy = dyn_cast<StructType>(F->getReturnType())) {
1306 if (!MRVFunctionsTracked.count(F))
1307 goto CallOverdefined; // Not tracking this callee.
1309 // If we are tracking this callee, propagate the result of the function
1310 // into this call site.
1311 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
1312 mergeInValue(getStructValueState(I, i), I,
1313 TrackedMultipleRetVals[std::make_pair(F, i)]);
1315 DenseMap<Function*, LatticeVal>::iterator TFRVI = TrackedRetVals.find(F);
1316 if (TFRVI == TrackedRetVals.end())
1317 goto CallOverdefined; // Not tracking this callee.
1319 // If so, propagate the return value of the callee into this call result.
1320 mergeInValue(I, TFRVI->second);
1324 void SCCPSolver::Solve() {
1325 // Process the work lists until they are empty!
1326 while (!BBWorkList.empty() || !InstWorkList.empty() ||
1327 !OverdefinedInstWorkList.empty()) {
1328 // Process the overdefined instruction's work list first, which drives other
1329 // things to overdefined more quickly.
1330 while (!OverdefinedInstWorkList.empty()) {
1331 Value *I = OverdefinedInstWorkList.pop_back_val();
1333 DEBUG(dbgs() << "\nPopped off OI-WL: " << *I << '\n');
1335 // "I" got into the work list because it either made the transition from
1336 // bottom to constant
1338 // Anything on this worklist that is overdefined need not be visited
1339 // since all of its users will have already been marked as overdefined
1340 // Update all of the users of this instruction's value.
1342 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
1344 if (Instruction *I = dyn_cast<Instruction>(*UI))
1345 OperandChangedState(I);
1348 // Process the instruction work list.
1349 while (!InstWorkList.empty()) {
1350 Value *I = InstWorkList.pop_back_val();
1352 DEBUG(dbgs() << "\nPopped off I-WL: " << *I << '\n');
1354 // "I" got into the work list because it made the transition from undef to
1357 // Anything on this worklist that is overdefined need not be visited
1358 // since all of its users will have already been marked as overdefined.
1359 // Update all of the users of this instruction's value.
1361 if (I->getType()->isStructTy() || !getValueState(I).isOverdefined())
1362 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
1364 if (Instruction *I = dyn_cast<Instruction>(*UI))
1365 OperandChangedState(I);
1368 // Process the basic block work list.
1369 while (!BBWorkList.empty()) {
1370 BasicBlock *BB = BBWorkList.back();
1371 BBWorkList.pop_back();
1373 DEBUG(dbgs() << "\nPopped off BBWL: " << *BB << '\n');
1375 // Notify all instructions in this basic block that they are newly
1382 /// ResolvedUndefsIn - While solving the dataflow for a function, we assume
1383 /// that branches on undef values cannot reach any of their successors.
1384 /// However, this is not a safe assumption. After we solve dataflow, this
1385 /// method should be use to handle this. If this returns true, the solver
1386 /// should be rerun.
1388 /// This method handles this by finding an unresolved branch and marking it one
1389 /// of the edges from the block as being feasible, even though the condition
1390 /// doesn't say it would otherwise be. This allows SCCP to find the rest of the
1391 /// CFG and only slightly pessimizes the analysis results (by marking one,
1392 /// potentially infeasible, edge feasible). This cannot usefully modify the
1393 /// constraints on the condition of the branch, as that would impact other users
1396 /// This scan also checks for values that use undefs, whose results are actually
1397 /// defined. For example, 'zext i8 undef to i32' should produce all zeros
1398 /// conservatively, as "(zext i8 X -> i32) & 0xFF00" must always return zero,
1399 /// even if X isn't defined.
1400 bool SCCPSolver::ResolvedUndefsIn(Function &F) {
1401 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
1402 if (!BBExecutable.count(BB))
1405 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
1406 // Look for instructions which produce undef values.
1407 if (I->getType()->isVoidTy()) continue;
1409 if (const StructType *STy = dyn_cast<StructType>(I->getType())) {
1410 // Only a few things that can be structs matter for undef. Just send
1411 // all their results to overdefined. We could be more precise than this
1412 // but it isn't worth bothering.
1413 if (isa<CallInst>(I) || isa<SelectInst>(I)) {
1414 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
1415 LatticeVal &LV = getStructValueState(I, i);
1416 if (LV.isUndefined())
1417 markOverdefined(LV, I);
1423 LatticeVal &LV = getValueState(I);
1424 if (!LV.isUndefined()) continue;
1426 // No instructions using structs need disambiguation.
1427 if (I->getOperand(0)->getType()->isStructTy())
1430 // Get the lattice values of the first two operands for use below.
1431 LatticeVal Op0LV = getValueState(I->getOperand(0));
1433 if (I->getNumOperands() == 2) {
1434 // No instructions using structs need disambiguation.
1435 if (I->getOperand(1)->getType()->isStructTy())
1438 // If this is a two-operand instruction, and if both operands are
1439 // undefs, the result stays undef.
1440 Op1LV = getValueState(I->getOperand(1));
1441 if (Op0LV.isUndefined() && Op1LV.isUndefined())
1445 // If this is an instructions whose result is defined even if the input is
1446 // not fully defined, propagate the information.
1447 const Type *ITy = I->getType();
1448 switch (I->getOpcode()) {
1449 default: break; // Leave the instruction as an undef.
1450 case Instruction::ZExt:
1451 // After a zero extend, we know the top part is zero. SExt doesn't have
1452 // to be handled here, because we don't know whether the top part is 1's
1454 case Instruction::SIToFP: // some FP values are not possible, just use 0.
1455 case Instruction::UIToFP: // some FP values are not possible, just use 0.
1456 markForcedConstant(I, Constant::getNullValue(ITy));
1458 case Instruction::Mul:
1459 case Instruction::And:
1460 // undef * X -> 0. X could be zero.
1461 // undef & X -> 0. X could be zero.
1462 markForcedConstant(I, Constant::getNullValue(ITy));
1465 case Instruction::Or:
1466 // undef | X -> -1. X could be -1.
1467 markForcedConstant(I, Constant::getAllOnesValue(ITy));
1470 case Instruction::SDiv:
1471 case Instruction::UDiv:
1472 case Instruction::SRem:
1473 case Instruction::URem:
1474 // X / undef -> undef. No change.
1475 // X % undef -> undef. No change.
1476 if (Op1LV.isUndefined()) break;
1478 // undef / X -> 0. X could be maxint.
1479 // undef % X -> 0. X could be 1.
1480 markForcedConstant(I, Constant::getNullValue(ITy));
1483 case Instruction::AShr:
1484 // undef >>s X -> undef. No change.
1485 if (Op0LV.isUndefined()) break;
1487 // X >>s undef -> X. X could be 0, X could have the high-bit known set.
1488 if (Op0LV.isConstant())
1489 markForcedConstant(I, Op0LV.getConstant());
1493 case Instruction::LShr:
1494 case Instruction::Shl:
1495 // undef >> X -> undef. No change.
1496 // undef << X -> undef. No change.
1497 if (Op0LV.isUndefined()) break;
1499 // X >> undef -> 0. X could be 0.
1500 // X << undef -> 0. X could be 0.
1501 markForcedConstant(I, Constant::getNullValue(ITy));
1503 case Instruction::Select:
1504 // undef ? X : Y -> X or Y. There could be commonality between X/Y.
1505 if (Op0LV.isUndefined()) {
1506 if (!Op1LV.isConstant()) // Pick the constant one if there is any.
1507 Op1LV = getValueState(I->getOperand(2));
1508 } else if (Op1LV.isUndefined()) {
1509 // c ? undef : undef -> undef. No change.
1510 Op1LV = getValueState(I->getOperand(2));
1511 if (Op1LV.isUndefined())
1513 // Otherwise, c ? undef : x -> x.
1515 // Leave Op1LV as Operand(1)'s LatticeValue.
1518 if (Op1LV.isConstant())
1519 markForcedConstant(I, Op1LV.getConstant());
1523 case Instruction::Call:
1524 // If a call has an undef result, it is because it is constant foldable
1525 // but one of the inputs was undef. Just force the result to
1532 // Check to see if we have a branch or switch on an undefined value. If so
1533 // we force the branch to go one way or the other to make the successor
1534 // values live. It doesn't really matter which way we force it.
1535 TerminatorInst *TI = BB->getTerminator();
1536 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
1537 if (!BI->isConditional()) continue;
1538 if (!getValueState(BI->getCondition()).isUndefined())
1541 // If the input to SCCP is actually branch on undef, fix the undef to
1543 if (isa<UndefValue>(BI->getCondition())) {
1544 BI->setCondition(ConstantInt::getFalse(BI->getContext()));
1545 markEdgeExecutable(BB, TI->getSuccessor(1));
1549 // Otherwise, it is a branch on a symbolic value which is currently
1550 // considered to be undef. Handle this by forcing the input value to the
1552 markForcedConstant(BI->getCondition(),
1553 ConstantInt::getFalse(TI->getContext()));
1557 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
1558 if (SI->getNumSuccessors() < 2) // no cases
1560 if (!getValueState(SI->getCondition()).isUndefined())
1563 // If the input to SCCP is actually switch on undef, fix the undef to
1564 // the first constant.
1565 if (isa<UndefValue>(SI->getCondition())) {
1566 SI->setCondition(SI->getCaseValue(1));
1567 markEdgeExecutable(BB, TI->getSuccessor(1));
1571 markForcedConstant(SI->getCondition(), SI->getCaseValue(1));
1581 //===--------------------------------------------------------------------===//
1583 /// SCCP Class - This class uses the SCCPSolver to implement a per-function
1584 /// Sparse Conditional Constant Propagator.
1586 struct SCCP : public FunctionPass {
1587 static char ID; // Pass identification, replacement for typeid
1588 SCCP() : FunctionPass(ID) {
1589 initializeSCCPPass(*PassRegistry::getPassRegistry());
1592 // runOnFunction - Run the Sparse Conditional Constant Propagation
1593 // algorithm, and return true if the function was modified.
1595 bool runOnFunction(Function &F);
1597 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
1598 AU.setPreservesCFG();
1601 } // end anonymous namespace
1604 INITIALIZE_PASS(SCCP, "sccp",
1605 "Sparse Conditional Constant Propagation", false, false)
1607 // createSCCPPass - This is the public interface to this file.
1608 FunctionPass *llvm::createSCCPPass() {
1612 static void DeleteInstructionInBlock(BasicBlock *BB) {
1613 DEBUG(dbgs() << " BasicBlock Dead:" << *BB);
1616 // Delete the instructions backwards, as it has a reduced likelihood of
1617 // having to update as many def-use and use-def chains.
1618 while (!isa<TerminatorInst>(BB->begin())) {
1619 Instruction *I = --BasicBlock::iterator(BB->getTerminator());
1621 if (!I->use_empty())
1622 I->replaceAllUsesWith(UndefValue::get(I->getType()));
1623 BB->getInstList().erase(I);
1628 // runOnFunction() - Run the Sparse Conditional Constant Propagation algorithm,
1629 // and return true if the function was modified.
1631 bool SCCP::runOnFunction(Function &F) {
1632 DEBUG(dbgs() << "SCCP on function '" << F.getName() << "'\n");
1633 SCCPSolver Solver(getAnalysisIfAvailable<TargetData>());
1635 // Mark the first block of the function as being executable.
1636 Solver.MarkBlockExecutable(F.begin());
1638 // Mark all arguments to the function as being overdefined.
1639 for (Function::arg_iterator AI = F.arg_begin(), E = F.arg_end(); AI != E;++AI)
1640 Solver.markAnythingOverdefined(AI);
1642 // Solve for constants.
1643 bool ResolvedUndefs = true;
1644 while (ResolvedUndefs) {
1646 DEBUG(dbgs() << "RESOLVING UNDEFs\n");
1647 ResolvedUndefs = Solver.ResolvedUndefsIn(F);
1650 bool MadeChanges = false;
1652 // If we decided that there are basic blocks that are dead in this function,
1653 // delete their contents now. Note that we cannot actually delete the blocks,
1654 // as we cannot modify the CFG of the function.
1656 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
1657 if (!Solver.isBlockExecutable(BB)) {
1658 DeleteInstructionInBlock(BB);
1663 // Iterate over all of the instructions in a function, replacing them with
1664 // constants if we have found them to be of constant values.
1666 for (BasicBlock::iterator BI = BB->begin(), E = BB->end(); BI != E; ) {
1667 Instruction *Inst = BI++;
1668 if (Inst->getType()->isVoidTy() || isa<TerminatorInst>(Inst))
1671 // TODO: Reconstruct structs from their elements.
1672 if (Inst->getType()->isStructTy())
1675 LatticeVal IV = Solver.getLatticeValueFor(Inst);
1676 if (IV.isOverdefined())
1679 Constant *Const = IV.isConstant()
1680 ? IV.getConstant() : UndefValue::get(Inst->getType());
1681 DEBUG(dbgs() << " Constant: " << *Const << " = " << *Inst);
1683 // Replaces all of the uses of a variable with uses of the constant.
1684 Inst->replaceAllUsesWith(Const);
1686 // Delete the instruction.
1687 Inst->eraseFromParent();
1689 // Hey, we just changed something!
1699 //===--------------------------------------------------------------------===//
1701 /// IPSCCP Class - This class implements interprocedural Sparse Conditional
1702 /// Constant Propagation.
1704 struct IPSCCP : public ModulePass {
1706 IPSCCP() : ModulePass(ID) {
1707 initializeIPSCCPPass(*PassRegistry::getPassRegistry());
1709 bool runOnModule(Module &M);
1711 } // end anonymous namespace
1713 char IPSCCP::ID = 0;
1714 INITIALIZE_PASS(IPSCCP, "ipsccp",
1715 "Interprocedural Sparse Conditional Constant Propagation",
1718 // createIPSCCPPass - This is the public interface to this file.
1719 ModulePass *llvm::createIPSCCPPass() {
1720 return new IPSCCP();
1724 static bool AddressIsTaken(const GlobalValue *GV) {
1725 // Delete any dead constantexpr klingons.
1726 GV->removeDeadConstantUsers();
1728 for (Value::const_use_iterator UI = GV->use_begin(), E = GV->use_end();
1730 const User *U = *UI;
1731 if (const StoreInst *SI = dyn_cast<StoreInst>(U)) {
1732 if (SI->getOperand(0) == GV || SI->isVolatile())
1733 return true; // Storing addr of GV.
1734 } else if (isa<InvokeInst>(U) || isa<CallInst>(U)) {
1735 // Make sure we are calling the function, not passing the address.
1736 ImmutableCallSite CS(cast<Instruction>(U));
1737 if (!CS.isCallee(UI))
1739 } else if (const LoadInst *LI = dyn_cast<LoadInst>(U)) {
1740 if (LI->isVolatile())
1742 } else if (isa<BlockAddress>(U)) {
1743 // blockaddress doesn't take the address of the function, it takes addr
1752 bool IPSCCP::runOnModule(Module &M) {
1753 SCCPSolver Solver(getAnalysisIfAvailable<TargetData>());
1755 // AddressTakenFunctions - This set keeps track of the address-taken functions
1756 // that are in the input. As IPSCCP runs through and simplifies code,
1757 // functions that were address taken can end up losing their
1758 // address-taken-ness. Because of this, we keep track of their addresses from
1759 // the first pass so we can use them for the later simplification pass.
1760 SmallPtrSet<Function*, 32> AddressTakenFunctions;
1762 // Loop over all functions, marking arguments to those with their addresses
1763 // taken or that are external as overdefined.
1765 for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) {
1766 if (F->isDeclaration())
1769 // If this is a strong or ODR definition of this function, then we can
1770 // propagate information about its result into callsites of it.
1771 if (!F->mayBeOverridden())
1772 Solver.AddTrackedFunction(F);
1774 // If this function only has direct calls that we can see, we can track its
1775 // arguments and return value aggressively, and can assume it is not called
1776 // unless we see evidence to the contrary.
1777 if (F->hasLocalLinkage()) {
1778 if (AddressIsTaken(F))
1779 AddressTakenFunctions.insert(F);
1781 Solver.AddArgumentTrackedFunction(F);
1786 // Assume the function is called.
1787 Solver.MarkBlockExecutable(F->begin());
1789 // Assume nothing about the incoming arguments.
1790 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
1792 Solver.markAnythingOverdefined(AI);
1795 // Loop over global variables. We inform the solver about any internal global
1796 // variables that do not have their 'addresses taken'. If they don't have
1797 // their addresses taken, we can propagate constants through them.
1798 for (Module::global_iterator G = M.global_begin(), E = M.global_end();
1800 if (!G->isConstant() && G->hasLocalLinkage() && !AddressIsTaken(G))
1801 Solver.TrackValueOfGlobalVariable(G);
1803 // Solve for constants.
1804 bool ResolvedUndefs = true;
1805 while (ResolvedUndefs) {
1808 DEBUG(dbgs() << "RESOLVING UNDEFS\n");
1809 ResolvedUndefs = false;
1810 for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F)
1811 ResolvedUndefs |= Solver.ResolvedUndefsIn(*F);
1814 bool MadeChanges = false;
1816 // Iterate over all of the instructions in the module, replacing them with
1817 // constants if we have found them to be of constant values.
1819 SmallVector<BasicBlock*, 512> BlocksToErase;
1821 for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) {
1822 if (Solver.isBlockExecutable(F->begin())) {
1823 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
1825 if (AI->use_empty() || AI->getType()->isStructTy()) continue;
1827 // TODO: Could use getStructLatticeValueFor to find out if the entire
1828 // result is a constant and replace it entirely if so.
1830 LatticeVal IV = Solver.getLatticeValueFor(AI);
1831 if (IV.isOverdefined()) continue;
1833 Constant *CST = IV.isConstant() ?
1834 IV.getConstant() : UndefValue::get(AI->getType());
1835 DEBUG(dbgs() << "*** Arg " << *AI << " = " << *CST <<"\n");
1837 // Replaces all of the uses of a variable with uses of the
1839 AI->replaceAllUsesWith(CST);
1844 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB) {
1845 if (!Solver.isBlockExecutable(BB)) {
1846 DeleteInstructionInBlock(BB);
1849 TerminatorInst *TI = BB->getTerminator();
1850 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) {
1851 BasicBlock *Succ = TI->getSuccessor(i);
1852 if (!Succ->empty() && isa<PHINode>(Succ->begin()))
1853 TI->getSuccessor(i)->removePredecessor(BB);
1855 if (!TI->use_empty())
1856 TI->replaceAllUsesWith(UndefValue::get(TI->getType()));
1857 TI->eraseFromParent();
1859 if (&*BB != &F->front())
1860 BlocksToErase.push_back(BB);
1862 new UnreachableInst(M.getContext(), BB);
1866 for (BasicBlock::iterator BI = BB->begin(), E = BB->end(); BI != E; ) {
1867 Instruction *Inst = BI++;
1868 if (Inst->getType()->isVoidTy() || Inst->getType()->isStructTy())
1871 // TODO: Could use getStructLatticeValueFor to find out if the entire
1872 // result is a constant and replace it entirely if so.
1874 LatticeVal IV = Solver.getLatticeValueFor(Inst);
1875 if (IV.isOverdefined())
1878 Constant *Const = IV.isConstant()
1879 ? IV.getConstant() : UndefValue::get(Inst->getType());
1880 DEBUG(dbgs() << " Constant: " << *Const << " = " << *Inst);
1882 // Replaces all of the uses of a variable with uses of the
1884 Inst->replaceAllUsesWith(Const);
1886 // Delete the instruction.
1887 if (!isa<CallInst>(Inst) && !isa<TerminatorInst>(Inst))
1888 Inst->eraseFromParent();
1890 // Hey, we just changed something!
1896 // Now that all instructions in the function are constant folded, erase dead
1897 // blocks, because we can now use ConstantFoldTerminator to get rid of
1899 for (unsigned i = 0, e = BlocksToErase.size(); i != e; ++i) {
1900 // If there are any PHI nodes in this successor, drop entries for BB now.
1901 BasicBlock *DeadBB = BlocksToErase[i];
1902 for (Value::use_iterator UI = DeadBB->use_begin(), UE = DeadBB->use_end();
1904 // Grab the user and then increment the iterator early, as the user
1905 // will be deleted. Step past all adjacent uses from the same user.
1906 Instruction *I = dyn_cast<Instruction>(*UI);
1907 do { ++UI; } while (UI != UE && *UI == I);
1909 // Ignore blockaddress users; BasicBlock's dtor will handle them.
1912 bool Folded = ConstantFoldTerminator(I->getParent());
1914 // The constant folder may not have been able to fold the terminator
1915 // if this is a branch or switch on undef. Fold it manually as a
1916 // branch to the first successor.
1918 if (BranchInst *BI = dyn_cast<BranchInst>(I)) {
1919 assert(BI->isConditional() && isa<UndefValue>(BI->getCondition()) &&
1920 "Branch should be foldable!");
1921 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(I)) {
1922 assert(isa<UndefValue>(SI->getCondition()) && "Switch should fold");
1924 llvm_unreachable("Didn't fold away reference to block!");
1928 // Make this an uncond branch to the first successor.
1929 TerminatorInst *TI = I->getParent()->getTerminator();
1930 BranchInst::Create(TI->getSuccessor(0), TI);
1932 // Remove entries in successor phi nodes to remove edges.
1933 for (unsigned i = 1, e = TI->getNumSuccessors(); i != e; ++i)
1934 TI->getSuccessor(i)->removePredecessor(TI->getParent());
1936 // Remove the old terminator.
1937 TI->eraseFromParent();
1941 // Finally, delete the basic block.
1942 F->getBasicBlockList().erase(DeadBB);
1944 BlocksToErase.clear();
1947 // If we inferred constant or undef return values for a function, we replaced
1948 // all call uses with the inferred value. This means we don't need to bother
1949 // actually returning anything from the function. Replace all return
1950 // instructions with return undef.
1952 // Do this in two stages: first identify the functions we should process, then
1953 // actually zap their returns. This is important because we can only do this
1954 // if the address of the function isn't taken. In cases where a return is the
1955 // last use of a function, the order of processing functions would affect
1956 // whether other functions are optimizable.
1957 SmallVector<ReturnInst*, 8> ReturnsToZap;
1959 // TODO: Process multiple value ret instructions also.
1960 const DenseMap<Function*, LatticeVal> &RV = Solver.getTrackedRetVals();
1961 for (DenseMap<Function*, LatticeVal>::const_iterator I = RV.begin(),
1962 E = RV.end(); I != E; ++I) {
1963 Function *F = I->first;
1964 if (I->second.isOverdefined() || F->getReturnType()->isVoidTy())
1967 // We can only do this if we know that nothing else can call the function.
1968 if (!F->hasLocalLinkage() || AddressTakenFunctions.count(F))
1971 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
1972 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator()))
1973 if (!isa<UndefValue>(RI->getOperand(0)))
1974 ReturnsToZap.push_back(RI);
1977 // Zap all returns which we've identified as zap to change.
1978 for (unsigned i = 0, e = ReturnsToZap.size(); i != e; ++i) {
1979 Function *F = ReturnsToZap[i]->getParent()->getParent();
1980 ReturnsToZap[i]->setOperand(0, UndefValue::get(F->getReturnType()));
1983 // If we infered constant or undef values for globals variables, we can delete
1984 // the global and any stores that remain to it.
1985 const DenseMap<GlobalVariable*, LatticeVal> &TG = Solver.getTrackedGlobals();
1986 for (DenseMap<GlobalVariable*, LatticeVal>::const_iterator I = TG.begin(),
1987 E = TG.end(); I != E; ++I) {
1988 GlobalVariable *GV = I->first;
1989 assert(!I->second.isOverdefined() &&
1990 "Overdefined values should have been taken out of the map!");
1991 DEBUG(dbgs() << "Found that GV '" << GV->getName() << "' is constant!\n");
1992 while (!GV->use_empty()) {
1993 StoreInst *SI = cast<StoreInst>(GV->use_back());
1994 SI->eraseFromParent();
1996 M.getGlobalList().erase(GV);