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 (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 (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 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 typedef std::multimap<PHINode*, Instruction*>::iterator ItTy;
475 std::pair<ItTy, ItTy> Range = UsersOfOverdefinedPHIs.equal_range(PN);
476 for (ItTy It = Range.first, E = Range.second; It != E;) {
478 UsersOfOverdefinedPHIs.erase(It++);
484 /// InsertInOverdefinedPHIs - Insert an entry in the UsersOfOverdefinedPHIS
485 /// map for I and PN, but if one is there already, do not create another.
486 /// (Duplicate entries do not break anything directly, but can lead to
487 /// exponential growth of the table in rare cases.)
488 void InsertInOverdefinedPHIs(Instruction *I, PHINode *PN) {
489 typedef std::multimap<PHINode*, Instruction*>::iterator ItTy;
490 std::pair<ItTy, ItTy> Range = UsersOfOverdefinedPHIs.equal_range(PN);
491 for (ItTy J = Range.first, E = Range.second; J != E; ++J)
494 UsersOfOverdefinedPHIs.insert(std::make_pair(PN, I));
498 friend class InstVisitor<SCCPSolver>;
500 // visit implementations - Something changed in this instruction. Either an
501 // operand made a transition, or the instruction is newly executable. Change
502 // the value type of I to reflect these changes if appropriate.
503 void visitPHINode(PHINode &I);
506 void visitReturnInst(ReturnInst &I);
507 void visitTerminatorInst(TerminatorInst &TI);
509 void visitCastInst(CastInst &I);
510 void visitSelectInst(SelectInst &I);
511 void visitBinaryOperator(Instruction &I);
512 void visitCmpInst(CmpInst &I);
513 void visitExtractElementInst(ExtractElementInst &I);
514 void visitInsertElementInst(InsertElementInst &I);
515 void visitShuffleVectorInst(ShuffleVectorInst &I);
516 void visitExtractValueInst(ExtractValueInst &EVI);
517 void visitInsertValueInst(InsertValueInst &IVI);
519 // Instructions that cannot be folded away.
520 void visitStoreInst (StoreInst &I);
521 void visitLoadInst (LoadInst &I);
522 void visitGetElementPtrInst(GetElementPtrInst &I);
523 void visitCallInst (CallInst &I) {
526 void visitInvokeInst (InvokeInst &II) {
528 visitTerminatorInst(II);
530 void visitCallSite (CallSite CS);
531 void visitUnwindInst (TerminatorInst &I) { /*returns void*/ }
532 void visitUnreachableInst(TerminatorInst &I) { /*returns void*/ }
533 void visitAllocaInst (Instruction &I) { markOverdefined(&I); }
534 void visitVAArgInst (Instruction &I) { markAnythingOverdefined(&I); }
536 void visitInstruction(Instruction &I) {
537 // If a new instruction is added to LLVM that we don't handle.
538 dbgs() << "SCCP: Don't know how to handle: " << I;
539 markAnythingOverdefined(&I); // Just in case
543 } // end anonymous namespace
546 // getFeasibleSuccessors - Return a vector of booleans to indicate which
547 // successors are reachable from a given terminator instruction.
549 void SCCPSolver::getFeasibleSuccessors(TerminatorInst &TI,
550 SmallVector<bool, 16> &Succs) {
551 Succs.resize(TI.getNumSuccessors());
552 if (BranchInst *BI = dyn_cast<BranchInst>(&TI)) {
553 if (BI->isUnconditional()) {
558 LatticeVal BCValue = getValueState(BI->getCondition());
559 ConstantInt *CI = BCValue.getConstantInt();
561 // Overdefined condition variables, and branches on unfoldable constant
562 // conditions, mean the branch could go either way.
563 if (!BCValue.isUndefined())
564 Succs[0] = Succs[1] = true;
568 // Constant condition variables mean the branch can only go a single way.
569 Succs[CI->isZero()] = true;
573 if (isa<InvokeInst>(TI)) {
574 // Invoke instructions successors are always executable.
575 Succs[0] = Succs[1] = true;
579 if (SwitchInst *SI = dyn_cast<SwitchInst>(&TI)) {
580 LatticeVal SCValue = getValueState(SI->getCondition());
581 ConstantInt *CI = SCValue.getConstantInt();
583 if (CI == 0) { // Overdefined or undefined condition?
584 // All destinations are executable!
585 if (!SCValue.isUndefined())
586 Succs.assign(TI.getNumSuccessors(), true);
590 Succs[SI->findCaseValue(CI)] = true;
594 // TODO: This could be improved if the operand is a [cast of a] BlockAddress.
595 if (isa<IndirectBrInst>(&TI)) {
596 // Just mark all destinations executable!
597 Succs.assign(TI.getNumSuccessors(), true);
602 dbgs() << "Unknown terminator instruction: " << TI << '\n';
604 llvm_unreachable("SCCP: Don't know how to handle this terminator!");
608 // isEdgeFeasible - Return true if the control flow edge from the 'From' basic
609 // block to the 'To' basic block is currently feasible.
611 bool SCCPSolver::isEdgeFeasible(BasicBlock *From, BasicBlock *To) {
612 assert(BBExecutable.count(To) && "Dest should always be alive!");
614 // Make sure the source basic block is executable!!
615 if (!BBExecutable.count(From)) return false;
617 // Check to make sure this edge itself is actually feasible now.
618 TerminatorInst *TI = From->getTerminator();
619 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
620 if (BI->isUnconditional())
623 LatticeVal BCValue = getValueState(BI->getCondition());
625 // Overdefined condition variables mean the branch could go either way,
626 // undef conditions mean that neither edge is feasible yet.
627 ConstantInt *CI = BCValue.getConstantInt();
629 return !BCValue.isUndefined();
631 // Constant condition variables mean the branch can only go a single way.
632 return BI->getSuccessor(CI->isZero()) == To;
635 // Invoke instructions successors are always executable.
636 if (isa<InvokeInst>(TI))
639 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
640 LatticeVal SCValue = getValueState(SI->getCondition());
641 ConstantInt *CI = SCValue.getConstantInt();
644 return !SCValue.isUndefined();
646 // Make sure to skip the "default value" which isn't a value
647 for (unsigned i = 1, E = SI->getNumSuccessors(); i != E; ++i)
648 if (SI->getSuccessorValue(i) == CI) // Found the taken branch.
649 return SI->getSuccessor(i) == To;
651 // If the constant value is not equal to any of the branches, we must
652 // execute default branch.
653 return SI->getDefaultDest() == To;
656 // Just mark all destinations executable!
657 // TODO: This could be improved if the operand is a [cast of a] BlockAddress.
658 if (isa<IndirectBrInst>(TI))
662 dbgs() << "Unknown terminator instruction: " << *TI << '\n';
667 // visit Implementations - Something changed in this instruction, either an
668 // operand made a transition, or the instruction is newly executable. Change
669 // the value type of I to reflect these changes if appropriate. This method
670 // makes sure to do the following actions:
672 // 1. If a phi node merges two constants in, and has conflicting value coming
673 // from different branches, or if the PHI node merges in an overdefined
674 // value, then the PHI node becomes overdefined.
675 // 2. If a phi node merges only constants in, and they all agree on value, the
676 // PHI node becomes a constant value equal to that.
677 // 3. If V <- x (op) y && isConstant(x) && isConstant(y) V = Constant
678 // 4. If V <- x (op) y && (isOverdefined(x) || isOverdefined(y)) V = Overdefined
679 // 5. If V <- MEM or V <- CALL or V <- (unknown) then V = Overdefined
680 // 6. If a conditional branch has a value that is constant, make the selected
681 // destination executable
682 // 7. If a conditional branch has a value that is overdefined, make all
683 // successors executable.
685 void SCCPSolver::visitPHINode(PHINode &PN) {
686 // If this PN returns a struct, just mark the result overdefined.
687 // TODO: We could do a lot better than this if code actually uses this.
688 if (PN.getType()->isStructTy())
689 return markAnythingOverdefined(&PN);
691 if (getValueState(&PN).isOverdefined()) {
692 // There may be instructions using this PHI node that are not overdefined
693 // themselves. If so, make sure that they know that the PHI node operand
695 typedef std::multimap<PHINode*, Instruction*>::iterator ItTy;
696 std::pair<ItTy, ItTy> Range = UsersOfOverdefinedPHIs.equal_range(&PN);
698 if (Range.first == Range.second)
701 SmallVector<Instruction*, 16> Users;
702 for (ItTy I = Range.first, E = Range.second; I != E; ++I)
703 Users.push_back(I->second);
704 while (!Users.empty())
705 visit(Users.pop_back_val());
706 return; // Quick exit
709 // Super-extra-high-degree PHI nodes are unlikely to ever be marked constant,
710 // and slow us down a lot. Just mark them overdefined.
711 if (PN.getNumIncomingValues() > 64)
712 return markOverdefined(&PN);
714 // Look at all of the executable operands of the PHI node. If any of them
715 // are overdefined, the PHI becomes overdefined as well. If they are all
716 // constant, and they agree with each other, the PHI becomes the identical
717 // constant. If they are constant and don't agree, the PHI is overdefined.
718 // If there are no executable operands, the PHI remains undefined.
720 Constant *OperandVal = 0;
721 for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) {
722 LatticeVal IV = getValueState(PN.getIncomingValue(i));
723 if (IV.isUndefined()) continue; // Doesn't influence PHI node.
725 if (!isEdgeFeasible(PN.getIncomingBlock(i), PN.getParent()))
728 if (IV.isOverdefined()) // PHI node becomes overdefined!
729 return markOverdefined(&PN);
731 if (OperandVal == 0) { // Grab the first value.
732 OperandVal = IV.getConstant();
736 // There is already a reachable operand. If we conflict with it,
737 // then the PHI node becomes overdefined. If we agree with it, we
740 // Check to see if there are two different constants merging, if so, the PHI
741 // node is overdefined.
742 if (IV.getConstant() != OperandVal)
743 return markOverdefined(&PN);
746 // If we exited the loop, this means that the PHI node only has constant
747 // arguments that agree with each other(and OperandVal is the constant) or
748 // OperandVal is null because there are no defined incoming arguments. If
749 // this is the case, the PHI remains undefined.
752 markConstant(&PN, OperandVal); // Acquire operand value
758 void SCCPSolver::visitReturnInst(ReturnInst &I) {
759 if (I.getNumOperands() == 0) return; // ret void
761 Function *F = I.getParent()->getParent();
762 Value *ResultOp = I.getOperand(0);
764 // If we are tracking the return value of this function, merge it in.
765 if (!TrackedRetVals.empty() && !ResultOp->getType()->isStructTy()) {
766 DenseMap<Function*, LatticeVal>::iterator TFRVI =
767 TrackedRetVals.find(F);
768 if (TFRVI != TrackedRetVals.end()) {
769 mergeInValue(TFRVI->second, F, getValueState(ResultOp));
774 // Handle functions that return multiple values.
775 if (!TrackedMultipleRetVals.empty()) {
776 if (StructType *STy = dyn_cast<StructType>(ResultOp->getType()))
777 if (MRVFunctionsTracked.count(F))
778 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
779 mergeInValue(TrackedMultipleRetVals[std::make_pair(F, i)], F,
780 getStructValueState(ResultOp, i));
785 void SCCPSolver::visitTerminatorInst(TerminatorInst &TI) {
786 SmallVector<bool, 16> SuccFeasible;
787 getFeasibleSuccessors(TI, SuccFeasible);
789 BasicBlock *BB = TI.getParent();
791 // Mark all feasible successors executable.
792 for (unsigned i = 0, e = SuccFeasible.size(); i != e; ++i)
794 markEdgeExecutable(BB, TI.getSuccessor(i));
797 void SCCPSolver::visitCastInst(CastInst &I) {
798 LatticeVal OpSt = getValueState(I.getOperand(0));
799 if (OpSt.isOverdefined()) // Inherit overdefinedness of operand
801 else if (OpSt.isConstant()) // Propagate constant value
802 markConstant(&I, ConstantExpr::getCast(I.getOpcode(),
803 OpSt.getConstant(), I.getType()));
807 void SCCPSolver::visitExtractValueInst(ExtractValueInst &EVI) {
808 // If this returns a struct, mark all elements over defined, we don't track
809 // structs in structs.
810 if (EVI.getType()->isStructTy())
811 return markAnythingOverdefined(&EVI);
813 // If this is extracting from more than one level of struct, we don't know.
814 if (EVI.getNumIndices() != 1)
815 return markOverdefined(&EVI);
817 Value *AggVal = EVI.getAggregateOperand();
818 if (AggVal->getType()->isStructTy()) {
819 unsigned i = *EVI.idx_begin();
820 LatticeVal EltVal = getStructValueState(AggVal, i);
821 mergeInValue(getValueState(&EVI), &EVI, EltVal);
823 // Otherwise, must be extracting from an array.
824 return markOverdefined(&EVI);
828 void SCCPSolver::visitInsertValueInst(InsertValueInst &IVI) {
829 StructType *STy = dyn_cast<StructType>(IVI.getType());
831 return markOverdefined(&IVI);
833 // If this has more than one index, we can't handle it, drive all results to
835 if (IVI.getNumIndices() != 1)
836 return markAnythingOverdefined(&IVI);
838 Value *Aggr = IVI.getAggregateOperand();
839 unsigned Idx = *IVI.idx_begin();
841 // Compute the result based on what we're inserting.
842 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
843 // This passes through all values that aren't the inserted element.
845 LatticeVal EltVal = getStructValueState(Aggr, i);
846 mergeInValue(getStructValueState(&IVI, i), &IVI, EltVal);
850 Value *Val = IVI.getInsertedValueOperand();
851 if (Val->getType()->isStructTy())
852 // We don't track structs in structs.
853 markOverdefined(getStructValueState(&IVI, i), &IVI);
855 LatticeVal InVal = getValueState(Val);
856 mergeInValue(getStructValueState(&IVI, i), &IVI, InVal);
861 void SCCPSolver::visitSelectInst(SelectInst &I) {
862 // If this select returns a struct, just mark the result overdefined.
863 // TODO: We could do a lot better than this if code actually uses this.
864 if (I.getType()->isStructTy())
865 return markAnythingOverdefined(&I);
867 LatticeVal CondValue = getValueState(I.getCondition());
868 if (CondValue.isUndefined())
871 if (ConstantInt *CondCB = CondValue.getConstantInt()) {
872 Value *OpVal = CondCB->isZero() ? I.getFalseValue() : I.getTrueValue();
873 mergeInValue(&I, getValueState(OpVal));
877 // Otherwise, the condition is overdefined or a constant we can't evaluate.
878 // See if we can produce something better than overdefined based on the T/F
880 LatticeVal TVal = getValueState(I.getTrueValue());
881 LatticeVal FVal = getValueState(I.getFalseValue());
883 // select ?, C, C -> C.
884 if (TVal.isConstant() && FVal.isConstant() &&
885 TVal.getConstant() == FVal.getConstant())
886 return markConstant(&I, FVal.getConstant());
888 if (TVal.isUndefined()) // select ?, undef, X -> X.
889 return mergeInValue(&I, FVal);
890 if (FVal.isUndefined()) // select ?, X, undef -> X.
891 return mergeInValue(&I, TVal);
895 // Handle Binary Operators.
896 void SCCPSolver::visitBinaryOperator(Instruction &I) {
897 LatticeVal V1State = getValueState(I.getOperand(0));
898 LatticeVal V2State = getValueState(I.getOperand(1));
900 LatticeVal &IV = ValueState[&I];
901 if (IV.isOverdefined()) return;
903 if (V1State.isConstant() && V2State.isConstant())
904 return markConstant(IV, &I,
905 ConstantExpr::get(I.getOpcode(), V1State.getConstant(),
906 V2State.getConstant()));
908 // If something is undef, wait for it to resolve.
909 if (!V1State.isOverdefined() && !V2State.isOverdefined())
912 // Otherwise, one of our operands is overdefined. Try to produce something
913 // better than overdefined with some tricks.
915 // If this is an AND or OR with 0 or -1, it doesn't matter that the other
916 // operand is overdefined.
917 if (I.getOpcode() == Instruction::And || I.getOpcode() == Instruction::Or) {
918 LatticeVal *NonOverdefVal = 0;
919 if (!V1State.isOverdefined())
920 NonOverdefVal = &V1State;
921 else if (!V2State.isOverdefined())
922 NonOverdefVal = &V2State;
925 if (NonOverdefVal->isUndefined()) {
926 // Could annihilate value.
927 if (I.getOpcode() == Instruction::And)
928 markConstant(IV, &I, Constant::getNullValue(I.getType()));
929 else if (VectorType *PT = dyn_cast<VectorType>(I.getType()))
930 markConstant(IV, &I, Constant::getAllOnesValue(PT));
933 Constant::getAllOnesValue(I.getType()));
937 if (I.getOpcode() == Instruction::And) {
939 if (NonOverdefVal->getConstant()->isNullValue())
940 return markConstant(IV, &I, NonOverdefVal->getConstant());
942 if (ConstantInt *CI = NonOverdefVal->getConstantInt())
943 if (CI->isAllOnesValue()) // X or -1 = -1
944 return markConstant(IV, &I, NonOverdefVal->getConstant());
950 // If both operands are PHI nodes, it is possible that this instruction has
951 // a constant value, despite the fact that the PHI node doesn't. Check for
952 // this condition now.
953 if (PHINode *PN1 = dyn_cast<PHINode>(I.getOperand(0)))
954 if (PHINode *PN2 = dyn_cast<PHINode>(I.getOperand(1)))
955 if (PN1->getParent() == PN2->getParent()) {
956 // Since the two PHI nodes are in the same basic block, they must have
957 // entries for the same predecessors. Walk the predecessor list, and
958 // if all of the incoming values are constants, and the result of
959 // evaluating this expression with all incoming value pairs is the
960 // same, then this expression is a constant even though the PHI node
961 // is not a constant!
963 for (unsigned i = 0, e = PN1->getNumIncomingValues(); i != e; ++i) {
964 LatticeVal In1 = getValueState(PN1->getIncomingValue(i));
965 BasicBlock *InBlock = PN1->getIncomingBlock(i);
966 LatticeVal In2 =getValueState(PN2->getIncomingValueForBlock(InBlock));
968 if (In1.isOverdefined() || In2.isOverdefined()) {
969 Result.markOverdefined();
970 break; // Cannot fold this operation over the PHI nodes!
973 if (In1.isConstant() && In2.isConstant()) {
974 Constant *V = ConstantExpr::get(I.getOpcode(), In1.getConstant(),
976 if (Result.isUndefined())
977 Result.markConstant(V);
978 else if (Result.isConstant() && Result.getConstant() != V) {
979 Result.markOverdefined();
985 // If we found a constant value here, then we know the instruction is
986 // constant despite the fact that the PHI nodes are overdefined.
987 if (Result.isConstant()) {
988 markConstant(IV, &I, Result.getConstant());
989 // Remember that this instruction is virtually using the PHI node
991 InsertInOverdefinedPHIs(&I, PN1);
992 InsertInOverdefinedPHIs(&I, PN2);
996 if (Result.isUndefined())
999 // Okay, this really is overdefined now. Since we might have
1000 // speculatively thought that this was not overdefined before, and
1001 // added ourselves to the UsersOfOverdefinedPHIs list for the PHIs,
1002 // make sure to clean out any entries that we put there, for
1004 RemoveFromOverdefinedPHIs(&I, PN1);
1005 RemoveFromOverdefinedPHIs(&I, PN2);
1008 markOverdefined(&I);
1011 // Handle ICmpInst instruction.
1012 void SCCPSolver::visitCmpInst(CmpInst &I) {
1013 LatticeVal V1State = getValueState(I.getOperand(0));
1014 LatticeVal V2State = getValueState(I.getOperand(1));
1016 LatticeVal &IV = ValueState[&I];
1017 if (IV.isOverdefined()) return;
1019 if (V1State.isConstant() && V2State.isConstant())
1020 return markConstant(IV, &I, ConstantExpr::getCompare(I.getPredicate(),
1021 V1State.getConstant(),
1022 V2State.getConstant()));
1024 // If operands are still undefined, wait for it to resolve.
1025 if (!V1State.isOverdefined() && !V2State.isOverdefined())
1028 // If something is overdefined, use some tricks to avoid ending up and over
1029 // defined if we can.
1031 // If both operands are PHI nodes, it is possible that this instruction has
1032 // a constant value, despite the fact that the PHI node doesn't. Check for
1033 // this condition now.
1034 if (PHINode *PN1 = dyn_cast<PHINode>(I.getOperand(0)))
1035 if (PHINode *PN2 = dyn_cast<PHINode>(I.getOperand(1)))
1036 if (PN1->getParent() == PN2->getParent()) {
1037 // Since the two PHI nodes are in the same basic block, they must have
1038 // entries for the same predecessors. Walk the predecessor list, and
1039 // if all of the incoming values are constants, and the result of
1040 // evaluating this expression with all incoming value pairs is the
1041 // same, then this expression is a constant even though the PHI node
1042 // is not a constant!
1044 for (unsigned i = 0, e = PN1->getNumIncomingValues(); i != e; ++i) {
1045 LatticeVal In1 = getValueState(PN1->getIncomingValue(i));
1046 BasicBlock *InBlock = PN1->getIncomingBlock(i);
1047 LatticeVal In2 =getValueState(PN2->getIncomingValueForBlock(InBlock));
1049 if (In1.isOverdefined() || In2.isOverdefined()) {
1050 Result.markOverdefined();
1051 break; // Cannot fold this operation over the PHI nodes!
1054 if (In1.isConstant() && In2.isConstant()) {
1055 Constant *V = ConstantExpr::getCompare(I.getPredicate(),
1058 if (Result.isUndefined())
1059 Result.markConstant(V);
1060 else if (Result.isConstant() && Result.getConstant() != V) {
1061 Result.markOverdefined();
1067 // If we found a constant value here, then we know the instruction is
1068 // constant despite the fact that the PHI nodes are overdefined.
1069 if (Result.isConstant()) {
1070 markConstant(&I, Result.getConstant());
1071 // Remember that this instruction is virtually using the PHI node
1073 InsertInOverdefinedPHIs(&I, PN1);
1074 InsertInOverdefinedPHIs(&I, PN2);
1078 if (Result.isUndefined())
1081 // Okay, this really is overdefined now. Since we might have
1082 // speculatively thought that this was not overdefined before, and
1083 // added ourselves to the UsersOfOverdefinedPHIs list for the PHIs,
1084 // make sure to clean out any entries that we put there, for
1086 RemoveFromOverdefinedPHIs(&I, PN1);
1087 RemoveFromOverdefinedPHIs(&I, PN2);
1090 markOverdefined(&I);
1093 void SCCPSolver::visitExtractElementInst(ExtractElementInst &I) {
1094 // TODO : SCCP does not handle vectors properly.
1095 return markOverdefined(&I);
1098 LatticeVal &ValState = getValueState(I.getOperand(0));
1099 LatticeVal &IdxState = getValueState(I.getOperand(1));
1101 if (ValState.isOverdefined() || IdxState.isOverdefined())
1102 markOverdefined(&I);
1103 else if(ValState.isConstant() && IdxState.isConstant())
1104 markConstant(&I, ConstantExpr::getExtractElement(ValState.getConstant(),
1105 IdxState.getConstant()));
1109 void SCCPSolver::visitInsertElementInst(InsertElementInst &I) {
1110 // TODO : SCCP does not handle vectors properly.
1111 return markOverdefined(&I);
1113 LatticeVal &ValState = getValueState(I.getOperand(0));
1114 LatticeVal &EltState = getValueState(I.getOperand(1));
1115 LatticeVal &IdxState = getValueState(I.getOperand(2));
1117 if (ValState.isOverdefined() || EltState.isOverdefined() ||
1118 IdxState.isOverdefined())
1119 markOverdefined(&I);
1120 else if(ValState.isConstant() && EltState.isConstant() &&
1121 IdxState.isConstant())
1122 markConstant(&I, ConstantExpr::getInsertElement(ValState.getConstant(),
1123 EltState.getConstant(),
1124 IdxState.getConstant()));
1125 else if (ValState.isUndefined() && EltState.isConstant() &&
1126 IdxState.isConstant())
1127 markConstant(&I,ConstantExpr::getInsertElement(UndefValue::get(I.getType()),
1128 EltState.getConstant(),
1129 IdxState.getConstant()));
1133 void SCCPSolver::visitShuffleVectorInst(ShuffleVectorInst &I) {
1134 // TODO : SCCP does not handle vectors properly.
1135 return markOverdefined(&I);
1137 LatticeVal &V1State = getValueState(I.getOperand(0));
1138 LatticeVal &V2State = getValueState(I.getOperand(1));
1139 LatticeVal &MaskState = getValueState(I.getOperand(2));
1141 if (MaskState.isUndefined() ||
1142 (V1State.isUndefined() && V2State.isUndefined()))
1143 return; // Undefined output if mask or both inputs undefined.
1145 if (V1State.isOverdefined() || V2State.isOverdefined() ||
1146 MaskState.isOverdefined()) {
1147 markOverdefined(&I);
1149 // A mix of constant/undef inputs.
1150 Constant *V1 = V1State.isConstant() ?
1151 V1State.getConstant() : UndefValue::get(I.getType());
1152 Constant *V2 = V2State.isConstant() ?
1153 V2State.getConstant() : UndefValue::get(I.getType());
1154 Constant *Mask = MaskState.isConstant() ?
1155 MaskState.getConstant() : UndefValue::get(I.getOperand(2)->getType());
1156 markConstant(&I, ConstantExpr::getShuffleVector(V1, V2, Mask));
1161 // Handle getelementptr instructions. If all operands are constants then we
1162 // can turn this into a getelementptr ConstantExpr.
1164 void SCCPSolver::visitGetElementPtrInst(GetElementPtrInst &I) {
1165 if (ValueState[&I].isOverdefined()) return;
1167 SmallVector<Constant*, 8> Operands;
1168 Operands.reserve(I.getNumOperands());
1170 for (unsigned i = 0, e = I.getNumOperands(); i != e; ++i) {
1171 LatticeVal State = getValueState(I.getOperand(i));
1172 if (State.isUndefined())
1173 return; // Operands are not resolved yet.
1175 if (State.isOverdefined())
1176 return markOverdefined(&I);
1178 assert(State.isConstant() && "Unknown state!");
1179 Operands.push_back(State.getConstant());
1182 Constant *Ptr = Operands[0];
1183 ArrayRef<Constant *> Indices(Operands.begin() + 1, Operands.end());
1184 markConstant(&I, ConstantExpr::getGetElementPtr(Ptr, Indices));
1187 void SCCPSolver::visitStoreInst(StoreInst &SI) {
1188 // If this store is of a struct, ignore it.
1189 if (SI.getOperand(0)->getType()->isStructTy())
1192 if (TrackedGlobals.empty() || !isa<GlobalVariable>(SI.getOperand(1)))
1195 GlobalVariable *GV = cast<GlobalVariable>(SI.getOperand(1));
1196 DenseMap<GlobalVariable*, LatticeVal>::iterator I = TrackedGlobals.find(GV);
1197 if (I == TrackedGlobals.end() || I->second.isOverdefined()) return;
1199 // Get the value we are storing into the global, then merge it.
1200 mergeInValue(I->second, GV, getValueState(SI.getOperand(0)));
1201 if (I->second.isOverdefined())
1202 TrackedGlobals.erase(I); // No need to keep tracking this!
1206 // Handle load instructions. If the operand is a constant pointer to a constant
1207 // global, we can replace the load with the loaded constant value!
1208 void SCCPSolver::visitLoadInst(LoadInst &I) {
1209 // If this load is of a struct, just mark the result overdefined.
1210 if (I.getType()->isStructTy())
1211 return markAnythingOverdefined(&I);
1213 LatticeVal PtrVal = getValueState(I.getOperand(0));
1214 if (PtrVal.isUndefined()) return; // The pointer is not resolved yet!
1216 LatticeVal &IV = ValueState[&I];
1217 if (IV.isOverdefined()) return;
1219 if (!PtrVal.isConstant() || I.isVolatile())
1220 return markOverdefined(IV, &I);
1222 Constant *Ptr = PtrVal.getConstant();
1224 // load null -> null
1225 if (isa<ConstantPointerNull>(Ptr) && I.getPointerAddressSpace() == 0)
1226 return markConstant(IV, &I, Constant::getNullValue(I.getType()));
1228 // Transform load (constant global) into the value loaded.
1229 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Ptr)) {
1230 if (!TrackedGlobals.empty()) {
1231 // If we are tracking this global, merge in the known value for it.
1232 DenseMap<GlobalVariable*, LatticeVal>::iterator It =
1233 TrackedGlobals.find(GV);
1234 if (It != TrackedGlobals.end()) {
1235 mergeInValue(IV, &I, It->second);
1241 // Transform load from a constant into a constant if possible.
1242 if (Constant *C = ConstantFoldLoadFromConstPtr(Ptr, TD))
1243 return markConstant(IV, &I, C);
1245 // Otherwise we cannot say for certain what value this load will produce.
1247 markOverdefined(IV, &I);
1250 void SCCPSolver::visitCallSite(CallSite CS) {
1251 Function *F = CS.getCalledFunction();
1252 Instruction *I = CS.getInstruction();
1254 // The common case is that we aren't tracking the callee, either because we
1255 // are not doing interprocedural analysis or the callee is indirect, or is
1256 // external. Handle these cases first.
1257 if (F == 0 || F->isDeclaration()) {
1259 // Void return and not tracking callee, just bail.
1260 if (I->getType()->isVoidTy()) return;
1262 // Otherwise, if we have a single return value case, and if the function is
1263 // a declaration, maybe we can constant fold it.
1264 if (F && F->isDeclaration() && !I->getType()->isStructTy() &&
1265 canConstantFoldCallTo(F)) {
1267 SmallVector<Constant*, 8> Operands;
1268 for (CallSite::arg_iterator AI = CS.arg_begin(), E = CS.arg_end();
1270 LatticeVal State = getValueState(*AI);
1272 if (State.isUndefined())
1273 return; // Operands are not resolved yet.
1274 if (State.isOverdefined())
1275 return markOverdefined(I);
1276 assert(State.isConstant() && "Unknown state!");
1277 Operands.push_back(State.getConstant());
1280 // If we can constant fold this, mark the result of the call as a
1282 if (Constant *C = ConstantFoldCall(F, Operands))
1283 return markConstant(I, C);
1286 // Otherwise, we don't know anything about this call, mark it overdefined.
1287 return markAnythingOverdefined(I);
1290 // If this is a local function that doesn't have its address taken, mark its
1291 // entry block executable and merge in the actual arguments to the call into
1292 // the formal arguments of the function.
1293 if (!TrackingIncomingArguments.empty() && TrackingIncomingArguments.count(F)){
1294 MarkBlockExecutable(F->begin());
1296 // Propagate information from this call site into the callee.
1297 CallSite::arg_iterator CAI = CS.arg_begin();
1298 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
1299 AI != E; ++AI, ++CAI) {
1300 // If this argument is byval, and if the function is not readonly, there
1301 // will be an implicit copy formed of the input aggregate.
1302 if (AI->hasByValAttr() && !F->onlyReadsMemory()) {
1303 markOverdefined(AI);
1307 if (StructType *STy = dyn_cast<StructType>(AI->getType())) {
1308 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
1309 LatticeVal CallArg = getStructValueState(*CAI, i);
1310 mergeInValue(getStructValueState(AI, i), AI, CallArg);
1313 mergeInValue(AI, getValueState(*CAI));
1318 // If this is a single/zero retval case, see if we're tracking the function.
1319 if (StructType *STy = dyn_cast<StructType>(F->getReturnType())) {
1320 if (!MRVFunctionsTracked.count(F))
1321 goto CallOverdefined; // Not tracking this callee.
1323 // If we are tracking this callee, propagate the result of the function
1324 // into this call site.
1325 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
1326 mergeInValue(getStructValueState(I, i), I,
1327 TrackedMultipleRetVals[std::make_pair(F, i)]);
1329 DenseMap<Function*, LatticeVal>::iterator TFRVI = TrackedRetVals.find(F);
1330 if (TFRVI == TrackedRetVals.end())
1331 goto CallOverdefined; // Not tracking this callee.
1333 // If so, propagate the return value of the callee into this call result.
1334 mergeInValue(I, TFRVI->second);
1338 void SCCPSolver::Solve() {
1339 // Process the work lists until they are empty!
1340 while (!BBWorkList.empty() || !InstWorkList.empty() ||
1341 !OverdefinedInstWorkList.empty()) {
1342 // Process the overdefined instruction's work list first, which drives other
1343 // things to overdefined more quickly.
1344 while (!OverdefinedInstWorkList.empty()) {
1345 Value *I = OverdefinedInstWorkList.pop_back_val();
1347 DEBUG(dbgs() << "\nPopped off OI-WL: " << *I << '\n');
1349 // "I" got into the work list because it either made the transition from
1350 // bottom to constant
1352 // Anything on this worklist that is overdefined need not be visited
1353 // since all of its users will have already been marked as overdefined
1354 // Update all of the users of this instruction's value.
1356 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
1358 if (Instruction *I = dyn_cast<Instruction>(*UI))
1359 OperandChangedState(I);
1362 // Process the instruction work list.
1363 while (!InstWorkList.empty()) {
1364 Value *I = InstWorkList.pop_back_val();
1366 DEBUG(dbgs() << "\nPopped off I-WL: " << *I << '\n');
1368 // "I" got into the work list because it made the transition from undef to
1371 // Anything on this worklist that is overdefined need not be visited
1372 // since all of its users will have already been marked as overdefined.
1373 // Update all of the users of this instruction's value.
1375 if (I->getType()->isStructTy() || !getValueState(I).isOverdefined())
1376 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
1378 if (Instruction *I = dyn_cast<Instruction>(*UI))
1379 OperandChangedState(I);
1382 // Process the basic block work list.
1383 while (!BBWorkList.empty()) {
1384 BasicBlock *BB = BBWorkList.back();
1385 BBWorkList.pop_back();
1387 DEBUG(dbgs() << "\nPopped off BBWL: " << *BB << '\n');
1389 // Notify all instructions in this basic block that they are newly
1396 /// ResolvedUndefsIn - While solving the dataflow for a function, we assume
1397 /// that branches on undef values cannot reach any of their successors.
1398 /// However, this is not a safe assumption. After we solve dataflow, this
1399 /// method should be use to handle this. If this returns true, the solver
1400 /// should be rerun.
1402 /// This method handles this by finding an unresolved branch and marking it one
1403 /// of the edges from the block as being feasible, even though the condition
1404 /// doesn't say it would otherwise be. This allows SCCP to find the rest of the
1405 /// CFG and only slightly pessimizes the analysis results (by marking one,
1406 /// potentially infeasible, edge feasible). This cannot usefully modify the
1407 /// constraints on the condition of the branch, as that would impact other users
1410 /// This scan also checks for values that use undefs, whose results are actually
1411 /// defined. For example, 'zext i8 undef to i32' should produce all zeros
1412 /// conservatively, as "(zext i8 X -> i32) & 0xFF00" must always return zero,
1413 /// even if X isn't defined.
1414 bool SCCPSolver::ResolvedUndefsIn(Function &F) {
1415 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
1416 if (!BBExecutable.count(BB))
1419 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
1420 // Look for instructions which produce undef values.
1421 if (I->getType()->isVoidTy()) continue;
1423 if (StructType *STy = dyn_cast<StructType>(I->getType())) {
1424 // Only a few things that can be structs matter for undef. Just send
1425 // all their results to overdefined. We could be more precise than this
1426 // but it isn't worth bothering.
1427 if (isa<CallInst>(I) || isa<SelectInst>(I)) {
1428 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
1429 LatticeVal &LV = getStructValueState(I, i);
1430 if (LV.isUndefined())
1431 markOverdefined(LV, I);
1437 LatticeVal &LV = getValueState(I);
1438 if (!LV.isUndefined()) continue;
1440 // No instructions using structs need disambiguation.
1441 if (I->getOperand(0)->getType()->isStructTy())
1444 // Get the lattice values of the first two operands for use below.
1445 LatticeVal Op0LV = getValueState(I->getOperand(0));
1447 if (I->getNumOperands() == 2) {
1448 // No instructions using structs need disambiguation.
1449 if (I->getOperand(1)->getType()->isStructTy())
1452 // If this is a two-operand instruction, and if both operands are
1453 // undefs, the result stays undef.
1454 Op1LV = getValueState(I->getOperand(1));
1455 if (Op0LV.isUndefined() && Op1LV.isUndefined())
1459 // If this is an instructions whose result is defined even if the input is
1460 // not fully defined, propagate the information.
1461 Type *ITy = I->getType();
1462 switch (I->getOpcode()) {
1463 default: break; // Leave the instruction as an undef.
1464 case Instruction::ZExt:
1465 // After a zero extend, we know the top part is zero. SExt doesn't have
1466 // to be handled here, because we don't know whether the top part is 1's
1468 case Instruction::SIToFP: // some FP values are not possible, just use 0.
1469 case Instruction::UIToFP: // some FP values are not possible, just use 0.
1470 markForcedConstant(I, Constant::getNullValue(ITy));
1472 case Instruction::Mul:
1473 case Instruction::And:
1474 // undef * X -> 0. X could be zero.
1475 // undef & X -> 0. X could be zero.
1476 markForcedConstant(I, Constant::getNullValue(ITy));
1479 case Instruction::Or:
1480 // undef | X -> -1. X could be -1.
1481 markForcedConstant(I, Constant::getAllOnesValue(ITy));
1484 case Instruction::SDiv:
1485 case Instruction::UDiv:
1486 case Instruction::SRem:
1487 case Instruction::URem:
1488 // X / undef -> undef. No change.
1489 // X % undef -> undef. No change.
1490 if (Op1LV.isUndefined()) break;
1492 // undef / X -> 0. X could be maxint.
1493 // undef % X -> 0. X could be 1.
1494 markForcedConstant(I, Constant::getNullValue(ITy));
1497 case Instruction::AShr:
1498 // undef >>s X -> undef. No change.
1499 if (Op0LV.isUndefined()) break;
1501 // X >>s undef -> X. X could be 0, X could have the high-bit known set.
1502 if (Op0LV.isConstant())
1503 markForcedConstant(I, Op0LV.getConstant());
1507 case Instruction::LShr:
1508 case Instruction::Shl:
1509 // undef >> X -> undef. No change.
1510 // undef << X -> undef. No change.
1511 if (Op0LV.isUndefined()) break;
1513 // X >> undef -> 0. X could be 0.
1514 // X << undef -> 0. X could be 0.
1515 markForcedConstant(I, Constant::getNullValue(ITy));
1517 case Instruction::Select:
1518 // undef ? X : Y -> X or Y. There could be commonality between X/Y.
1519 if (Op0LV.isUndefined()) {
1520 if (!Op1LV.isConstant()) // Pick the constant one if there is any.
1521 Op1LV = getValueState(I->getOperand(2));
1522 } else if (Op1LV.isUndefined()) {
1523 // c ? undef : undef -> undef. No change.
1524 Op1LV = getValueState(I->getOperand(2));
1525 if (Op1LV.isUndefined())
1527 // Otherwise, c ? undef : x -> x.
1529 // Leave Op1LV as Operand(1)'s LatticeValue.
1532 if (Op1LV.isConstant())
1533 markForcedConstant(I, Op1LV.getConstant());
1537 case Instruction::Call:
1538 // If a call has an undef result, it is because it is constant foldable
1539 // but one of the inputs was undef. Just force the result to
1546 // Check to see if we have a branch or switch on an undefined value. If so
1547 // we force the branch to go one way or the other to make the successor
1548 // values live. It doesn't really matter which way we force it.
1549 TerminatorInst *TI = BB->getTerminator();
1550 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
1551 if (!BI->isConditional()) continue;
1552 if (!getValueState(BI->getCondition()).isUndefined())
1555 // If the input to SCCP is actually branch on undef, fix the undef to
1557 if (isa<UndefValue>(BI->getCondition())) {
1558 BI->setCondition(ConstantInt::getFalse(BI->getContext()));
1559 markEdgeExecutable(BB, TI->getSuccessor(1));
1563 // Otherwise, it is a branch on a symbolic value which is currently
1564 // considered to be undef. Handle this by forcing the input value to the
1566 markForcedConstant(BI->getCondition(),
1567 ConstantInt::getFalse(TI->getContext()));
1571 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
1572 if (SI->getNumSuccessors() < 2) // no cases
1574 if (!getValueState(SI->getCondition()).isUndefined())
1577 // If the input to SCCP is actually switch on undef, fix the undef to
1578 // the first constant.
1579 if (isa<UndefValue>(SI->getCondition())) {
1580 SI->setCondition(SI->getCaseValue(1));
1581 markEdgeExecutable(BB, TI->getSuccessor(1));
1585 markForcedConstant(SI->getCondition(), SI->getCaseValue(1));
1595 //===--------------------------------------------------------------------===//
1597 /// SCCP Class - This class uses the SCCPSolver to implement a per-function
1598 /// Sparse Conditional Constant Propagator.
1600 struct SCCP : public FunctionPass {
1601 static char ID; // Pass identification, replacement for typeid
1602 SCCP() : FunctionPass(ID) {
1603 initializeSCCPPass(*PassRegistry::getPassRegistry());
1606 // runOnFunction - Run the Sparse Conditional Constant Propagation
1607 // algorithm, and return true if the function was modified.
1609 bool runOnFunction(Function &F);
1611 } // end anonymous namespace
1614 INITIALIZE_PASS(SCCP, "sccp",
1615 "Sparse Conditional Constant Propagation", false, false)
1617 // createSCCPPass - This is the public interface to this file.
1618 FunctionPass *llvm::createSCCPPass() {
1622 static void DeleteInstructionInBlock(BasicBlock *BB) {
1623 DEBUG(dbgs() << " BasicBlock Dead:" << *BB);
1626 // Delete the instructions backwards, as it has a reduced likelihood of
1627 // having to update as many def-use and use-def chains.
1628 while (!isa<TerminatorInst>(BB->begin())) {
1629 Instruction *I = --BasicBlock::iterator(BB->getTerminator());
1631 if (!I->use_empty())
1632 I->replaceAllUsesWith(UndefValue::get(I->getType()));
1633 BB->getInstList().erase(I);
1638 // runOnFunction() - Run the Sparse Conditional Constant Propagation algorithm,
1639 // and return true if the function was modified.
1641 bool SCCP::runOnFunction(Function &F) {
1642 DEBUG(dbgs() << "SCCP on function '" << F.getName() << "'\n");
1643 SCCPSolver Solver(getAnalysisIfAvailable<TargetData>());
1645 // Mark the first block of the function as being executable.
1646 Solver.MarkBlockExecutable(F.begin());
1648 // Mark all arguments to the function as being overdefined.
1649 for (Function::arg_iterator AI = F.arg_begin(), E = F.arg_end(); AI != E;++AI)
1650 Solver.markAnythingOverdefined(AI);
1652 // Solve for constants.
1653 bool ResolvedUndefs = true;
1654 while (ResolvedUndefs) {
1656 DEBUG(dbgs() << "RESOLVING UNDEFs\n");
1657 ResolvedUndefs = Solver.ResolvedUndefsIn(F);
1660 bool MadeChanges = false;
1662 // If we decided that there are basic blocks that are dead in this function,
1663 // delete their contents now. Note that we cannot actually delete the blocks,
1664 // as we cannot modify the CFG of the function.
1666 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
1667 if (!Solver.isBlockExecutable(BB)) {
1668 DeleteInstructionInBlock(BB);
1673 // Iterate over all of the instructions in a function, replacing them with
1674 // constants if we have found them to be of constant values.
1676 for (BasicBlock::iterator BI = BB->begin(), E = BB->end(); BI != E; ) {
1677 Instruction *Inst = BI++;
1678 if (Inst->getType()->isVoidTy() || isa<TerminatorInst>(Inst))
1681 // TODO: Reconstruct structs from their elements.
1682 if (Inst->getType()->isStructTy())
1685 LatticeVal IV = Solver.getLatticeValueFor(Inst);
1686 if (IV.isOverdefined())
1689 Constant *Const = IV.isConstant()
1690 ? IV.getConstant() : UndefValue::get(Inst->getType());
1691 DEBUG(dbgs() << " Constant: " << *Const << " = " << *Inst);
1693 // Replaces all of the uses of a variable with uses of the constant.
1694 Inst->replaceAllUsesWith(Const);
1696 // Delete the instruction.
1697 Inst->eraseFromParent();
1699 // Hey, we just changed something!
1709 //===--------------------------------------------------------------------===//
1711 /// IPSCCP Class - This class implements interprocedural Sparse Conditional
1712 /// Constant Propagation.
1714 struct IPSCCP : public ModulePass {
1716 IPSCCP() : ModulePass(ID) {
1717 initializeIPSCCPPass(*PassRegistry::getPassRegistry());
1719 bool runOnModule(Module &M);
1721 } // end anonymous namespace
1723 char IPSCCP::ID = 0;
1724 INITIALIZE_PASS(IPSCCP, "ipsccp",
1725 "Interprocedural Sparse Conditional Constant Propagation",
1728 // createIPSCCPPass - This is the public interface to this file.
1729 ModulePass *llvm::createIPSCCPPass() {
1730 return new IPSCCP();
1734 static bool AddressIsTaken(const GlobalValue *GV) {
1735 // Delete any dead constantexpr klingons.
1736 GV->removeDeadConstantUsers();
1738 for (Value::const_use_iterator UI = GV->use_begin(), E = GV->use_end();
1740 const User *U = *UI;
1741 if (const StoreInst *SI = dyn_cast<StoreInst>(U)) {
1742 if (SI->getOperand(0) == GV || SI->isVolatile())
1743 return true; // Storing addr of GV.
1744 } else if (isa<InvokeInst>(U) || isa<CallInst>(U)) {
1745 // Make sure we are calling the function, not passing the address.
1746 ImmutableCallSite CS(cast<Instruction>(U));
1747 if (!CS.isCallee(UI))
1749 } else if (const LoadInst *LI = dyn_cast<LoadInst>(U)) {
1750 if (LI->isVolatile())
1752 } else if (isa<BlockAddress>(U)) {
1753 // blockaddress doesn't take the address of the function, it takes addr
1762 bool IPSCCP::runOnModule(Module &M) {
1763 SCCPSolver Solver(getAnalysisIfAvailable<TargetData>());
1765 // AddressTakenFunctions - This set keeps track of the address-taken functions
1766 // that are in the input. As IPSCCP runs through and simplifies code,
1767 // functions that were address taken can end up losing their
1768 // address-taken-ness. Because of this, we keep track of their addresses from
1769 // the first pass so we can use them for the later simplification pass.
1770 SmallPtrSet<Function*, 32> AddressTakenFunctions;
1772 // Loop over all functions, marking arguments to those with their addresses
1773 // taken or that are external as overdefined.
1775 for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) {
1776 if (F->isDeclaration())
1779 // If this is a strong or ODR definition of this function, then we can
1780 // propagate information about its result into callsites of it.
1781 if (!F->mayBeOverridden())
1782 Solver.AddTrackedFunction(F);
1784 // If this function only has direct calls that we can see, we can track its
1785 // arguments and return value aggressively, and can assume it is not called
1786 // unless we see evidence to the contrary.
1787 if (F->hasLocalLinkage()) {
1788 if (AddressIsTaken(F))
1789 AddressTakenFunctions.insert(F);
1791 Solver.AddArgumentTrackedFunction(F);
1796 // Assume the function is called.
1797 Solver.MarkBlockExecutable(F->begin());
1799 // Assume nothing about the incoming arguments.
1800 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
1802 Solver.markAnythingOverdefined(AI);
1805 // Loop over global variables. We inform the solver about any internal global
1806 // variables that do not have their 'addresses taken'. If they don't have
1807 // their addresses taken, we can propagate constants through them.
1808 for (Module::global_iterator G = M.global_begin(), E = M.global_end();
1810 if (!G->isConstant() && G->hasLocalLinkage() && !AddressIsTaken(G))
1811 Solver.TrackValueOfGlobalVariable(G);
1813 // Solve for constants.
1814 bool ResolvedUndefs = true;
1815 while (ResolvedUndefs) {
1818 DEBUG(dbgs() << "RESOLVING UNDEFS\n");
1819 ResolvedUndefs = false;
1820 for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F)
1821 ResolvedUndefs |= Solver.ResolvedUndefsIn(*F);
1824 bool MadeChanges = false;
1826 // Iterate over all of the instructions in the module, replacing them with
1827 // constants if we have found them to be of constant values.
1829 SmallVector<BasicBlock*, 512> BlocksToErase;
1831 for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) {
1832 if (Solver.isBlockExecutable(F->begin())) {
1833 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
1835 if (AI->use_empty() || AI->getType()->isStructTy()) continue;
1837 // TODO: Could use getStructLatticeValueFor to find out if the entire
1838 // result is a constant and replace it entirely if so.
1840 LatticeVal IV = Solver.getLatticeValueFor(AI);
1841 if (IV.isOverdefined()) continue;
1843 Constant *CST = IV.isConstant() ?
1844 IV.getConstant() : UndefValue::get(AI->getType());
1845 DEBUG(dbgs() << "*** Arg " << *AI << " = " << *CST <<"\n");
1847 // Replaces all of the uses of a variable with uses of the
1849 AI->replaceAllUsesWith(CST);
1854 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB) {
1855 if (!Solver.isBlockExecutable(BB)) {
1856 DeleteInstructionInBlock(BB);
1859 TerminatorInst *TI = BB->getTerminator();
1860 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) {
1861 BasicBlock *Succ = TI->getSuccessor(i);
1862 if (!Succ->empty() && isa<PHINode>(Succ->begin()))
1863 TI->getSuccessor(i)->removePredecessor(BB);
1865 if (!TI->use_empty())
1866 TI->replaceAllUsesWith(UndefValue::get(TI->getType()));
1867 TI->eraseFromParent();
1869 if (&*BB != &F->front())
1870 BlocksToErase.push_back(BB);
1872 new UnreachableInst(M.getContext(), BB);
1876 for (BasicBlock::iterator BI = BB->begin(), E = BB->end(); BI != E; ) {
1877 Instruction *Inst = BI++;
1878 if (Inst->getType()->isVoidTy() || Inst->getType()->isStructTy())
1881 // TODO: Could use getStructLatticeValueFor to find out if the entire
1882 // result is a constant and replace it entirely if so.
1884 LatticeVal IV = Solver.getLatticeValueFor(Inst);
1885 if (IV.isOverdefined())
1888 Constant *Const = IV.isConstant()
1889 ? IV.getConstant() : UndefValue::get(Inst->getType());
1890 DEBUG(dbgs() << " Constant: " << *Const << " = " << *Inst);
1892 // Replaces all of the uses of a variable with uses of the
1894 Inst->replaceAllUsesWith(Const);
1896 // Delete the instruction.
1897 if (!isa<CallInst>(Inst) && !isa<TerminatorInst>(Inst))
1898 Inst->eraseFromParent();
1900 // Hey, we just changed something!
1906 // Now that all instructions in the function are constant folded, erase dead
1907 // blocks, because we can now use ConstantFoldTerminator to get rid of
1909 for (unsigned i = 0, e = BlocksToErase.size(); i != e; ++i) {
1910 // If there are any PHI nodes in this successor, drop entries for BB now.
1911 BasicBlock *DeadBB = BlocksToErase[i];
1912 for (Value::use_iterator UI = DeadBB->use_begin(), UE = DeadBB->use_end();
1914 // Grab the user and then increment the iterator early, as the user
1915 // will be deleted. Step past all adjacent uses from the same user.
1916 Instruction *I = dyn_cast<Instruction>(*UI);
1917 do { ++UI; } while (UI != UE && *UI == I);
1919 // Ignore blockaddress users; BasicBlock's dtor will handle them.
1922 bool Folded = ConstantFoldTerminator(I->getParent());
1924 // The constant folder may not have been able to fold the terminator
1925 // if this is a branch or switch on undef. Fold it manually as a
1926 // branch to the first successor.
1928 if (BranchInst *BI = dyn_cast<BranchInst>(I)) {
1929 assert(BI->isConditional() && isa<UndefValue>(BI->getCondition()) &&
1930 "Branch should be foldable!");
1931 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(I)) {
1932 assert(isa<UndefValue>(SI->getCondition()) && "Switch should fold");
1934 llvm_unreachable("Didn't fold away reference to block!");
1938 // Make this an uncond branch to the first successor.
1939 TerminatorInst *TI = I->getParent()->getTerminator();
1940 BranchInst::Create(TI->getSuccessor(0), TI);
1942 // Remove entries in successor phi nodes to remove edges.
1943 for (unsigned i = 1, e = TI->getNumSuccessors(); i != e; ++i)
1944 TI->getSuccessor(i)->removePredecessor(TI->getParent());
1946 // Remove the old terminator.
1947 TI->eraseFromParent();
1951 // Finally, delete the basic block.
1952 F->getBasicBlockList().erase(DeadBB);
1954 BlocksToErase.clear();
1957 // If we inferred constant or undef return values for a function, we replaced
1958 // all call uses with the inferred value. This means we don't need to bother
1959 // actually returning anything from the function. Replace all return
1960 // instructions with return undef.
1962 // Do this in two stages: first identify the functions we should process, then
1963 // actually zap their returns. This is important because we can only do this
1964 // if the address of the function isn't taken. In cases where a return is the
1965 // last use of a function, the order of processing functions would affect
1966 // whether other functions are optimizable.
1967 SmallVector<ReturnInst*, 8> ReturnsToZap;
1969 // TODO: Process multiple value ret instructions also.
1970 const DenseMap<Function*, LatticeVal> &RV = Solver.getTrackedRetVals();
1971 for (DenseMap<Function*, LatticeVal>::const_iterator I = RV.begin(),
1972 E = RV.end(); I != E; ++I) {
1973 Function *F = I->first;
1974 if (I->second.isOverdefined() || F->getReturnType()->isVoidTy())
1977 // We can only do this if we know that nothing else can call the function.
1978 if (!F->hasLocalLinkage() || AddressTakenFunctions.count(F))
1981 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
1982 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator()))
1983 if (!isa<UndefValue>(RI->getOperand(0)))
1984 ReturnsToZap.push_back(RI);
1987 // Zap all returns which we've identified as zap to change.
1988 for (unsigned i = 0, e = ReturnsToZap.size(); i != e; ++i) {
1989 Function *F = ReturnsToZap[i]->getParent()->getParent();
1990 ReturnsToZap[i]->setOperand(0, UndefValue::get(F->getReturnType()));
1993 // If we inferred constant or undef values for globals variables, we can delete
1994 // the global and any stores that remain to it.
1995 const DenseMap<GlobalVariable*, LatticeVal> &TG = Solver.getTrackedGlobals();
1996 for (DenseMap<GlobalVariable*, LatticeVal>::const_iterator I = TG.begin(),
1997 E = TG.end(); I != E; ++I) {
1998 GlobalVariable *GV = I->first;
1999 assert(!I->second.isOverdefined() &&
2000 "Overdefined values should have been taken out of the map!");
2001 DEBUG(dbgs() << "Found that GV '" << GV->getName() << "' is constant!\n");
2002 while (!GV->use_empty()) {
2003 StoreInst *SI = cast<StoreInst>(GV->use_back());
2004 SI->eraseFromParent();
2006 M.getGlobalList().erase(GV);