1 //===- SCCP.cpp - Sparse Conditional Constant Propagation -----------------===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by the LLVM research group and is distributed under
6 // the University of Illinois Open Source License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements sparse conditional constant propagation and merging:
12 // Specifically, this:
13 // * Assumes values are constant unless proven otherwise
14 // * Assumes BasicBlocks are dead unless proven otherwise
15 // * Proves values to be constant, and replaces them with constants
16 // * Proves conditional branches to be unconditional
19 // * This pass has a habit of making definitions be dead. It is a good idea
20 // to to run a DCE pass sometime after running this pass.
22 //===----------------------------------------------------------------------===//
24 #define DEBUG_TYPE "sccp"
25 #include "llvm/Transforms/Scalar.h"
26 #include "llvm/Transforms/IPO.h"
27 #include "llvm/Constants.h"
28 #include "llvm/DerivedTypes.h"
29 #include "llvm/Instructions.h"
30 #include "llvm/Pass.h"
31 #include "llvm/Support/InstVisitor.h"
32 #include "llvm/Transforms/Utils/Local.h"
33 #include "llvm/Support/CallSite.h"
34 #include "llvm/Support/Debug.h"
35 #include "llvm/ADT/hash_map"
36 #include "llvm/ADT/Statistic.h"
37 #include "llvm/ADT/STLExtras.h"
43 // LatticeVal class - This class represents the different lattice values that an
44 // instruction may occupy. It is a simple class with value semantics.
50 undefined, // This instruction has no known value
51 constant, // This instruction has a constant value
52 overdefined // This instruction has an unknown value
53 } LatticeValue; // The current lattice position
54 Constant *ConstantVal; // If Constant value, the current value
56 inline LatticeVal() : LatticeValue(undefined), ConstantVal(0) {}
58 // markOverdefined - Return true if this is a new status to be in...
59 inline bool markOverdefined() {
60 if (LatticeValue != overdefined) {
61 LatticeValue = overdefined;
67 // markConstant - Return true if this is a new status for us...
68 inline bool markConstant(Constant *V) {
69 if (LatticeValue != constant) {
70 LatticeValue = constant;
74 assert(ConstantVal == V && "Marking constant with different value");
79 inline bool isUndefined() const { return LatticeValue == undefined; }
80 inline bool isConstant() const { return LatticeValue == constant; }
81 inline bool isOverdefined() const { return LatticeValue == overdefined; }
83 inline Constant *getConstant() const {
84 assert(isConstant() && "Cannot get the constant of a non-constant!");
89 } // end anonymous namespace
92 //===----------------------------------------------------------------------===//
94 /// SCCPSolver - This class is a general purpose solver for Sparse Conditional
95 /// Constant Propagation.
97 class SCCPSolver : public InstVisitor<SCCPSolver> {
98 std::set<BasicBlock*> BBExecutable;// The basic blocks that are executable
99 hash_map<Value*, LatticeVal> ValueState; // The state each value is in...
101 /// GlobalValue - If we are tracking any values for the contents of a global
102 /// variable, we keep a mapping from the constant accessor to the element of
103 /// the global, to the currently known value. If the value becomes
104 /// overdefined, it's entry is simply removed from this map.
105 hash_map<GlobalVariable*, LatticeVal> TrackedGlobals;
107 /// TrackedFunctionRetVals - If we are tracking arguments into and the return
108 /// value out of a function, it will have an entry in this map, indicating
109 /// what the known return value for the function is.
110 hash_map<Function*, LatticeVal> TrackedFunctionRetVals;
112 // The reason for two worklists is that overdefined is the lowest state
113 // on the lattice, and moving things to overdefined as fast as possible
114 // makes SCCP converge much faster.
115 // By having a separate worklist, we accomplish this because everything
116 // possibly overdefined will become overdefined at the soonest possible
118 std::vector<Value*> OverdefinedInstWorkList;
119 std::vector<Value*> InstWorkList;
122 std::vector<BasicBlock*> BBWorkList; // The BasicBlock work list
124 /// UsersOfOverdefinedPHIs - Keep track of any users of PHI nodes that are not
125 /// overdefined, despite the fact that the PHI node is overdefined.
126 std::multimap<PHINode*, Instruction*> UsersOfOverdefinedPHIs;
128 /// KnownFeasibleEdges - Entries in this set are edges which have already had
129 /// PHI nodes retriggered.
130 typedef std::pair<BasicBlock*,BasicBlock*> Edge;
131 std::set<Edge> KnownFeasibleEdges;
134 /// MarkBlockExecutable - This method can be used by clients to mark all of
135 /// the blocks that are known to be intrinsically live in the processed unit.
136 void MarkBlockExecutable(BasicBlock *BB) {
137 DEBUG(std::cerr << "Marking Block Executable: " << BB->getName() << "\n");
138 BBExecutable.insert(BB); // Basic block is executable!
139 BBWorkList.push_back(BB); // Add the block to the work list!
142 /// TrackValueOfGlobalVariable - Clients can use this method to
143 /// inform the SCCPSolver that it should track loads and stores to the
144 /// specified global variable if it can. This is only legal to call if
145 /// performing Interprocedural SCCP.
146 void TrackValueOfGlobalVariable(GlobalVariable *GV) {
147 const Type *ElTy = GV->getType()->getElementType();
148 if (ElTy->isFirstClassType()) {
149 LatticeVal &IV = TrackedGlobals[GV];
150 if (!isa<UndefValue>(GV->getInitializer()))
151 IV.markConstant(GV->getInitializer());
155 /// AddTrackedFunction - If the SCCP solver is supposed to track calls into
156 /// and out of the specified function (which cannot have its address taken),
157 /// this method must be called.
158 void AddTrackedFunction(Function *F) {
159 assert(F->hasInternalLinkage() && "Can only track internal functions!");
160 // Add an entry, F -> undef.
161 TrackedFunctionRetVals[F];
164 /// Solve - Solve for constants and executable blocks.
168 /// ResolveBranchesIn - While solving the dataflow for a function, we assume
169 /// that branches on undef values cannot reach any of their successors.
170 /// However, this is not a safe assumption. After we solve dataflow, this
171 /// method should be use to handle this. If this returns true, the solver
173 bool ResolveBranchesIn(Function &F);
175 /// getExecutableBlocks - Once we have solved for constants, return the set of
176 /// blocks that is known to be executable.
177 std::set<BasicBlock*> &getExecutableBlocks() {
181 /// getValueMapping - Once we have solved for constants, return the mapping of
182 /// LLVM values to LatticeVals.
183 hash_map<Value*, LatticeVal> &getValueMapping() {
187 /// getTrackedFunctionRetVals - Get the inferred return value map.
189 const hash_map<Function*, LatticeVal> &getTrackedFunctionRetVals() {
190 return TrackedFunctionRetVals;
193 /// getTrackedGlobals - Get and return the set of inferred initializers for
194 /// global variables.
195 const hash_map<GlobalVariable*, LatticeVal> &getTrackedGlobals() {
196 return TrackedGlobals;
201 // markConstant - Make a value be marked as "constant". If the value
202 // is not already a constant, add it to the instruction work list so that
203 // the users of the instruction are updated later.
205 inline void markConstant(LatticeVal &IV, Value *V, Constant *C) {
206 if (IV.markConstant(C)) {
207 DEBUG(std::cerr << "markConstant: " << *C << ": " << *V);
208 InstWorkList.push_back(V);
211 inline void markConstant(Value *V, Constant *C) {
212 markConstant(ValueState[V], V, C);
215 // markOverdefined - Make a value be marked as "overdefined". If the
216 // value is not already overdefined, add it to the overdefined instruction
217 // work list so that the users of the instruction are updated later.
219 inline void markOverdefined(LatticeVal &IV, Value *V) {
220 if (IV.markOverdefined()) {
221 DEBUG(std::cerr << "markOverdefined: ";
222 if (Function *F = dyn_cast<Function>(V))
223 std::cerr << "Function '" << F->getName() << "'\n";
226 // Only instructions go on the work list
227 OverdefinedInstWorkList.push_back(V);
230 inline void markOverdefined(Value *V) {
231 markOverdefined(ValueState[V], V);
234 inline void mergeInValue(LatticeVal &IV, Value *V, LatticeVal &MergeWithV) {
235 if (IV.isOverdefined() || MergeWithV.isUndefined())
237 if (MergeWithV.isOverdefined())
238 markOverdefined(IV, V);
239 else if (IV.isUndefined())
240 markConstant(IV, V, MergeWithV.getConstant());
241 else if (IV.getConstant() != MergeWithV.getConstant())
242 markOverdefined(IV, V);
245 inline void mergeInValue(Value *V, LatticeVal &MergeWithV) {
246 return mergeInValue(ValueState[V], V, MergeWithV);
250 // getValueState - Return the LatticeVal object that corresponds to the value.
251 // This function is necessary because not all values should start out in the
252 // underdefined state... Argument's should be overdefined, and
253 // constants should be marked as constants. If a value is not known to be an
254 // Instruction object, then use this accessor to get its value from the map.
256 inline LatticeVal &getValueState(Value *V) {
257 hash_map<Value*, LatticeVal>::iterator I = ValueState.find(V);
258 if (I != ValueState.end()) return I->second; // Common case, in the map
260 if (Constant *CPV = dyn_cast<Constant>(V)) {
261 if (isa<UndefValue>(V)) {
262 // Nothing to do, remain undefined.
264 ValueState[CPV].markConstant(CPV); // Constants are constant
267 // All others are underdefined by default...
268 return ValueState[V];
271 // markEdgeExecutable - Mark a basic block as executable, adding it to the BB
272 // work list if it is not already executable...
274 void markEdgeExecutable(BasicBlock *Source, BasicBlock *Dest) {
275 if (!KnownFeasibleEdges.insert(Edge(Source, Dest)).second)
276 return; // This edge is already known to be executable!
278 if (BBExecutable.count(Dest)) {
279 DEBUG(std::cerr << "Marking Edge Executable: " << Source->getName()
280 << " -> " << Dest->getName() << "\n");
282 // The destination is already executable, but we just made an edge
283 // feasible that wasn't before. Revisit the PHI nodes in the block
284 // because they have potentially new operands.
285 for (BasicBlock::iterator I = Dest->begin(); isa<PHINode>(I); ++I)
286 visitPHINode(*cast<PHINode>(I));
289 MarkBlockExecutable(Dest);
293 // getFeasibleSuccessors - Return a vector of booleans to indicate which
294 // successors are reachable from a given terminator instruction.
296 void getFeasibleSuccessors(TerminatorInst &TI, std::vector<bool> &Succs);
298 // isEdgeFeasible - Return true if the control flow edge from the 'From' basic
299 // block to the 'To' basic block is currently feasible...
301 bool isEdgeFeasible(BasicBlock *From, BasicBlock *To);
303 // OperandChangedState - This method is invoked on all of the users of an
304 // instruction that was just changed state somehow.... Based on this
305 // information, we need to update the specified user of this instruction.
307 void OperandChangedState(User *U) {
308 // Only instructions use other variable values!
309 Instruction &I = cast<Instruction>(*U);
310 if (BBExecutable.count(I.getParent())) // Inst is executable?
315 friend class InstVisitor<SCCPSolver>;
317 // visit implementations - Something changed in this instruction... Either an
318 // operand made a transition, or the instruction is newly executable. Change
319 // the value type of I to reflect these changes if appropriate.
321 void visitPHINode(PHINode &I);
324 void visitReturnInst(ReturnInst &I);
325 void visitTerminatorInst(TerminatorInst &TI);
327 void visitCastInst(CastInst &I);
328 void visitSelectInst(SelectInst &I);
329 void visitBinaryOperator(Instruction &I);
330 void visitShiftInst(ShiftInst &I) { visitBinaryOperator(I); }
331 void visitExtractElementInst(ExtractElementInst &I);
332 void visitInsertElementInst(InsertElementInst &I);
334 // Instructions that cannot be folded away...
335 void visitStoreInst (Instruction &I);
336 void visitLoadInst (LoadInst &I);
337 void visitGetElementPtrInst(GetElementPtrInst &I);
338 void visitCallInst (CallInst &I) { visitCallSite(CallSite::get(&I)); }
339 void visitInvokeInst (InvokeInst &II) {
340 visitCallSite(CallSite::get(&II));
341 visitTerminatorInst(II);
343 void visitCallSite (CallSite CS);
344 void visitUnwindInst (TerminatorInst &I) { /*returns void*/ }
345 void visitUnreachableInst(TerminatorInst &I) { /*returns void*/ }
346 void visitAllocationInst(Instruction &I) { markOverdefined(&I); }
347 void visitVANextInst (Instruction &I) { markOverdefined(&I); }
348 void visitVAArgInst (Instruction &I) { markOverdefined(&I); }
349 void visitFreeInst (Instruction &I) { /*returns void*/ }
351 void visitInstruction(Instruction &I) {
352 // If a new instruction is added to LLVM that we don't handle...
353 std::cerr << "SCCP: Don't know how to handle: " << I;
354 markOverdefined(&I); // Just in case
358 // getFeasibleSuccessors - Return a vector of booleans to indicate which
359 // successors are reachable from a given terminator instruction.
361 void SCCPSolver::getFeasibleSuccessors(TerminatorInst &TI,
362 std::vector<bool> &Succs) {
363 Succs.resize(TI.getNumSuccessors());
364 if (BranchInst *BI = dyn_cast<BranchInst>(&TI)) {
365 if (BI->isUnconditional()) {
368 LatticeVal &BCValue = getValueState(BI->getCondition());
369 if (BCValue.isOverdefined() ||
370 (BCValue.isConstant() && !isa<ConstantBool>(BCValue.getConstant()))) {
371 // Overdefined condition variables, and branches on unfoldable constant
372 // conditions, mean the branch could go either way.
373 Succs[0] = Succs[1] = true;
374 } else if (BCValue.isConstant()) {
375 // Constant condition variables mean the branch can only go a single way
376 Succs[BCValue.getConstant() == ConstantBool::False] = true;
379 } else if (InvokeInst *II = dyn_cast<InvokeInst>(&TI)) {
380 // Invoke instructions successors are always executable.
381 Succs[0] = Succs[1] = true;
382 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(&TI)) {
383 LatticeVal &SCValue = getValueState(SI->getCondition());
384 if (SCValue.isOverdefined() || // Overdefined condition?
385 (SCValue.isConstant() && !isa<ConstantInt>(SCValue.getConstant()))) {
386 // All destinations are executable!
387 Succs.assign(TI.getNumSuccessors(), true);
388 } else if (SCValue.isConstant()) {
389 Constant *CPV = SCValue.getConstant();
390 // Make sure to skip the "default value" which isn't a value
391 for (unsigned i = 1, E = SI->getNumSuccessors(); i != E; ++i) {
392 if (SI->getSuccessorValue(i) == CPV) {// Found the right branch...
398 // Constant value not equal to any of the branches... must execute
399 // default branch then...
403 std::cerr << "SCCP: Don't know how to handle: " << TI;
404 Succs.assign(TI.getNumSuccessors(), true);
409 // isEdgeFeasible - Return true if the control flow edge from the 'From' basic
410 // block to the 'To' basic block is currently feasible...
412 bool SCCPSolver::isEdgeFeasible(BasicBlock *From, BasicBlock *To) {
413 assert(BBExecutable.count(To) && "Dest should always be alive!");
415 // Make sure the source basic block is executable!!
416 if (!BBExecutable.count(From)) return false;
418 // Check to make sure this edge itself is actually feasible now...
419 TerminatorInst *TI = From->getTerminator();
420 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
421 if (BI->isUnconditional())
424 LatticeVal &BCValue = getValueState(BI->getCondition());
425 if (BCValue.isOverdefined()) {
426 // Overdefined condition variables mean the branch could go either way.
428 } else if (BCValue.isConstant()) {
429 // Not branching on an evaluatable constant?
430 if (!isa<ConstantBool>(BCValue.getConstant())) return true;
432 // Constant condition variables mean the branch can only go a single way
433 return BI->getSuccessor(BCValue.getConstant() ==
434 ConstantBool::False) == To;
438 } else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) {
439 // Invoke instructions successors are always executable.
441 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
442 LatticeVal &SCValue = getValueState(SI->getCondition());
443 if (SCValue.isOverdefined()) { // Overdefined condition?
444 // All destinations are executable!
446 } else if (SCValue.isConstant()) {
447 Constant *CPV = SCValue.getConstant();
448 if (!isa<ConstantInt>(CPV))
449 return true; // not a foldable constant?
451 // Make sure to skip the "default value" which isn't a value
452 for (unsigned i = 1, E = SI->getNumSuccessors(); i != E; ++i)
453 if (SI->getSuccessorValue(i) == CPV) // Found the taken branch...
454 return SI->getSuccessor(i) == To;
456 // Constant value not equal to any of the branches... must execute
457 // default branch then...
458 return SI->getDefaultDest() == To;
462 std::cerr << "Unknown terminator instruction: " << *TI;
467 // visit Implementations - Something changed in this instruction... Either an
468 // operand made a transition, or the instruction is newly executable. Change
469 // the value type of I to reflect these changes if appropriate. This method
470 // makes sure to do the following actions:
472 // 1. If a phi node merges two constants in, and has conflicting value coming
473 // from different branches, or if the PHI node merges in an overdefined
474 // value, then the PHI node becomes overdefined.
475 // 2. If a phi node merges only constants in, and they all agree on value, the
476 // PHI node becomes a constant value equal to that.
477 // 3. If V <- x (op) y && isConstant(x) && isConstant(y) V = Constant
478 // 4. If V <- x (op) y && (isOverdefined(x) || isOverdefined(y)) V = Overdefined
479 // 5. If V <- MEM or V <- CALL or V <- (unknown) then V = Overdefined
480 // 6. If a conditional branch has a value that is constant, make the selected
481 // destination executable
482 // 7. If a conditional branch has a value that is overdefined, make all
483 // successors executable.
485 void SCCPSolver::visitPHINode(PHINode &PN) {
486 LatticeVal &PNIV = getValueState(&PN);
487 if (PNIV.isOverdefined()) {
488 // There may be instructions using this PHI node that are not overdefined
489 // themselves. If so, make sure that they know that the PHI node operand
491 std::multimap<PHINode*, Instruction*>::iterator I, E;
492 tie(I, E) = UsersOfOverdefinedPHIs.equal_range(&PN);
494 std::vector<Instruction*> Users;
495 Users.reserve(std::distance(I, E));
496 for (; I != E; ++I) Users.push_back(I->second);
497 while (!Users.empty()) {
502 return; // Quick exit
505 // Super-extra-high-degree PHI nodes are unlikely to ever be marked constant,
506 // and slow us down a lot. Just mark them overdefined.
507 if (PN.getNumIncomingValues() > 64) {
508 markOverdefined(PNIV, &PN);
512 // Look at all of the executable operands of the PHI node. If any of them
513 // are overdefined, the PHI becomes overdefined as well. If they are all
514 // constant, and they agree with each other, the PHI becomes the identical
515 // constant. If they are constant and don't agree, the PHI is overdefined.
516 // If there are no executable operands, the PHI remains undefined.
518 Constant *OperandVal = 0;
519 for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) {
520 LatticeVal &IV = getValueState(PN.getIncomingValue(i));
521 if (IV.isUndefined()) continue; // Doesn't influence PHI node.
523 if (isEdgeFeasible(PN.getIncomingBlock(i), PN.getParent())) {
524 if (IV.isOverdefined()) { // PHI node becomes overdefined!
525 markOverdefined(PNIV, &PN);
529 if (OperandVal == 0) { // Grab the first value...
530 OperandVal = IV.getConstant();
531 } else { // Another value is being merged in!
532 // There is already a reachable operand. If we conflict with it,
533 // then the PHI node becomes overdefined. If we agree with it, we
536 // Check to see if there are two different constants merging...
537 if (IV.getConstant() != OperandVal) {
538 // Yes there is. This means the PHI node is not constant.
539 // You must be overdefined poor PHI.
541 markOverdefined(PNIV, &PN); // The PHI node now becomes overdefined
542 return; // I'm done analyzing you
548 // If we exited the loop, this means that the PHI node only has constant
549 // arguments that agree with each other(and OperandVal is the constant) or
550 // OperandVal is null because there are no defined incoming arguments. If
551 // this is the case, the PHI remains undefined.
554 markConstant(PNIV, &PN, OperandVal); // Acquire operand value
557 void SCCPSolver::visitReturnInst(ReturnInst &I) {
558 if (I.getNumOperands() == 0) return; // Ret void
560 // If we are tracking the return value of this function, merge it in.
561 Function *F = I.getParent()->getParent();
562 if (F->hasInternalLinkage() && !TrackedFunctionRetVals.empty()) {
563 hash_map<Function*, LatticeVal>::iterator TFRVI =
564 TrackedFunctionRetVals.find(F);
565 if (TFRVI != TrackedFunctionRetVals.end() &&
566 !TFRVI->second.isOverdefined()) {
567 LatticeVal &IV = getValueState(I.getOperand(0));
568 mergeInValue(TFRVI->second, F, IV);
574 void SCCPSolver::visitTerminatorInst(TerminatorInst &TI) {
575 std::vector<bool> SuccFeasible;
576 getFeasibleSuccessors(TI, SuccFeasible);
578 BasicBlock *BB = TI.getParent();
580 // Mark all feasible successors executable...
581 for (unsigned i = 0, e = SuccFeasible.size(); i != e; ++i)
583 markEdgeExecutable(BB, TI.getSuccessor(i));
586 void SCCPSolver::visitCastInst(CastInst &I) {
587 Value *V = I.getOperand(0);
588 LatticeVal &VState = getValueState(V);
589 if (VState.isOverdefined()) // Inherit overdefinedness of operand
591 else if (VState.isConstant()) // Propagate constant value
592 markConstant(&I, ConstantExpr::getCast(VState.getConstant(), I.getType()));
595 void SCCPSolver::visitSelectInst(SelectInst &I) {
596 LatticeVal &CondValue = getValueState(I.getCondition());
597 if (CondValue.isUndefined())
599 if (CondValue.isConstant()) {
601 if (CondValue.getConstant() == ConstantBool::True) {
602 mergeInValue(&I, getValueState(I.getTrueValue()));
604 } else if (CondValue.getConstant() == ConstantBool::False) {
605 mergeInValue(&I, getValueState(I.getFalseValue()));
610 // Otherwise, the condition is overdefined or a constant we can't evaluate.
611 // See if we can produce something better than overdefined based on the T/F
613 LatticeVal &TVal = getValueState(I.getTrueValue());
614 LatticeVal &FVal = getValueState(I.getFalseValue());
616 // select ?, C, C -> C.
617 if (TVal.isConstant() && FVal.isConstant() &&
618 TVal.getConstant() == FVal.getConstant()) {
619 markConstant(&I, FVal.getConstant());
623 if (TVal.isUndefined()) { // select ?, undef, X -> X.
624 mergeInValue(&I, FVal);
625 } else if (FVal.isUndefined()) { // select ?, X, undef -> X.
626 mergeInValue(&I, TVal);
632 // Handle BinaryOperators and Shift Instructions...
633 void SCCPSolver::visitBinaryOperator(Instruction &I) {
634 LatticeVal &IV = ValueState[&I];
635 if (IV.isOverdefined()) return;
637 LatticeVal &V1State = getValueState(I.getOperand(0));
638 LatticeVal &V2State = getValueState(I.getOperand(1));
640 if (V1State.isOverdefined() || V2State.isOverdefined()) {
641 // If this is an AND or OR with 0 or -1, it doesn't matter that the other
642 // operand is overdefined.
643 if (I.getOpcode() == Instruction::And || I.getOpcode() == Instruction::Or) {
644 LatticeVal *NonOverdefVal = 0;
645 if (!V1State.isOverdefined()) {
646 NonOverdefVal = &V1State;
647 } else if (!V2State.isOverdefined()) {
648 NonOverdefVal = &V2State;
652 if (NonOverdefVal->isUndefined()) {
653 // Could annihilate value.
654 if (I.getOpcode() == Instruction::And)
655 markConstant(IV, &I, Constant::getNullValue(I.getType()));
657 markConstant(IV, &I, ConstantInt::getAllOnesValue(I.getType()));
660 if (I.getOpcode() == Instruction::And) {
661 if (NonOverdefVal->getConstant()->isNullValue()) {
662 markConstant(IV, &I, NonOverdefVal->getConstant());
663 return; // X or 0 = -1
666 if (ConstantIntegral *CI =
667 dyn_cast<ConstantIntegral>(NonOverdefVal->getConstant()))
668 if (CI->isAllOnesValue()) {
669 markConstant(IV, &I, NonOverdefVal->getConstant());
670 return; // X or -1 = -1
678 // If both operands are PHI nodes, it is possible that this instruction has
679 // a constant value, despite the fact that the PHI node doesn't. Check for
680 // this condition now.
681 if (PHINode *PN1 = dyn_cast<PHINode>(I.getOperand(0)))
682 if (PHINode *PN2 = dyn_cast<PHINode>(I.getOperand(1)))
683 if (PN1->getParent() == PN2->getParent()) {
684 // Since the two PHI nodes are in the same basic block, they must have
685 // entries for the same predecessors. Walk the predecessor list, and
686 // if all of the incoming values are constants, and the result of
687 // evaluating this expression with all incoming value pairs is the
688 // same, then this expression is a constant even though the PHI node
689 // is not a constant!
691 for (unsigned i = 0, e = PN1->getNumIncomingValues(); i != e; ++i) {
692 LatticeVal &In1 = getValueState(PN1->getIncomingValue(i));
693 BasicBlock *InBlock = PN1->getIncomingBlock(i);
695 getValueState(PN2->getIncomingValueForBlock(InBlock));
697 if (In1.isOverdefined() || In2.isOverdefined()) {
698 Result.markOverdefined();
699 break; // Cannot fold this operation over the PHI nodes!
700 } else if (In1.isConstant() && In2.isConstant()) {
701 Constant *V = ConstantExpr::get(I.getOpcode(), In1.getConstant(),
703 if (Result.isUndefined())
704 Result.markConstant(V);
705 else if (Result.isConstant() && Result.getConstant() != V) {
706 Result.markOverdefined();
712 // If we found a constant value here, then we know the instruction is
713 // constant despite the fact that the PHI nodes are overdefined.
714 if (Result.isConstant()) {
715 markConstant(IV, &I, Result.getConstant());
716 // Remember that this instruction is virtually using the PHI node
718 UsersOfOverdefinedPHIs.insert(std::make_pair(PN1, &I));
719 UsersOfOverdefinedPHIs.insert(std::make_pair(PN2, &I));
721 } else if (Result.isUndefined()) {
725 // Okay, this really is overdefined now. Since we might have
726 // speculatively thought that this was not overdefined before, and
727 // added ourselves to the UsersOfOverdefinedPHIs list for the PHIs,
728 // make sure to clean out any entries that we put there, for
730 std::multimap<PHINode*, Instruction*>::iterator It, E;
731 tie(It, E) = UsersOfOverdefinedPHIs.equal_range(PN1);
733 if (It->second == &I) {
734 UsersOfOverdefinedPHIs.erase(It++);
738 tie(It, E) = UsersOfOverdefinedPHIs.equal_range(PN2);
740 if (It->second == &I) {
741 UsersOfOverdefinedPHIs.erase(It++);
747 markOverdefined(IV, &I);
748 } else if (V1State.isConstant() && V2State.isConstant()) {
749 markConstant(IV, &I, ConstantExpr::get(I.getOpcode(), V1State.getConstant(),
750 V2State.getConstant()));
754 void SCCPSolver::visitExtractElementInst(ExtractElementInst &I) {
755 LatticeVal &ValState = getValueState(I.getOperand(0));
756 LatticeVal &IdxState = getValueState(I.getOperand(1));
758 if (ValState.isOverdefined() || IdxState.isOverdefined())
760 else if(ValState.isConstant() && IdxState.isConstant())
761 markConstant(&I, ConstantExpr::getExtractElement(ValState.getConstant(),
762 IdxState.getConstant()));
765 void SCCPSolver::visitInsertElementInst(InsertElementInst &I) {
766 LatticeVal &ValState = getValueState(I.getOperand(0));
767 LatticeVal &EltState = getValueState(I.getOperand(1));
768 LatticeVal &IdxState = getValueState(I.getOperand(2));
770 if (ValState.isOverdefined() || EltState.isOverdefined() ||
771 IdxState.isOverdefined())
773 else if(ValState.isConstant() && EltState.isConstant() &&
774 IdxState.isConstant())
775 markConstant(&I, ConstantExpr::getInsertElement(ValState.getConstant(),
776 EltState.getConstant(),
777 IdxState.getConstant()));
778 else if (ValState.isUndefined() && EltState.isConstant() &&
779 IdxState.isConstant())
780 markConstant(&I, ConstantExpr::getInsertElement(UndefValue::get(I.getType()),
781 EltState.getConstant(),
782 IdxState.getConstant()));
785 // Handle getelementptr instructions... if all operands are constants then we
786 // can turn this into a getelementptr ConstantExpr.
788 void SCCPSolver::visitGetElementPtrInst(GetElementPtrInst &I) {
789 LatticeVal &IV = ValueState[&I];
790 if (IV.isOverdefined()) return;
792 std::vector<Constant*> Operands;
793 Operands.reserve(I.getNumOperands());
795 for (unsigned i = 0, e = I.getNumOperands(); i != e; ++i) {
796 LatticeVal &State = getValueState(I.getOperand(i));
797 if (State.isUndefined())
798 return; // Operands are not resolved yet...
799 else if (State.isOverdefined()) {
800 markOverdefined(IV, &I);
803 assert(State.isConstant() && "Unknown state!");
804 Operands.push_back(State.getConstant());
807 Constant *Ptr = Operands[0];
808 Operands.erase(Operands.begin()); // Erase the pointer from idx list...
810 markConstant(IV, &I, ConstantExpr::getGetElementPtr(Ptr, Operands));
813 void SCCPSolver::visitStoreInst(Instruction &SI) {
814 if (TrackedGlobals.empty() || !isa<GlobalVariable>(SI.getOperand(1)))
816 GlobalVariable *GV = cast<GlobalVariable>(SI.getOperand(1));
817 hash_map<GlobalVariable*, LatticeVal>::iterator I = TrackedGlobals.find(GV);
818 if (I == TrackedGlobals.end() || I->second.isOverdefined()) return;
820 // Get the value we are storing into the global.
821 LatticeVal &PtrVal = getValueState(SI.getOperand(0));
823 mergeInValue(I->second, GV, PtrVal);
824 if (I->second.isOverdefined())
825 TrackedGlobals.erase(I); // No need to keep tracking this!
829 // Handle load instructions. If the operand is a constant pointer to a constant
830 // global, we can replace the load with the loaded constant value!
831 void SCCPSolver::visitLoadInst(LoadInst &I) {
832 LatticeVal &IV = ValueState[&I];
833 if (IV.isOverdefined()) return;
835 LatticeVal &PtrVal = getValueState(I.getOperand(0));
836 if (PtrVal.isUndefined()) return; // The pointer is not resolved yet!
837 if (PtrVal.isConstant() && !I.isVolatile()) {
838 Value *Ptr = PtrVal.getConstant();
839 if (isa<ConstantPointerNull>(Ptr)) {
841 markConstant(IV, &I, Constant::getNullValue(I.getType()));
845 // Transform load (constant global) into the value loaded.
846 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Ptr)) {
847 if (GV->isConstant()) {
848 if (!GV->isExternal()) {
849 markConstant(IV, &I, GV->getInitializer());
852 } else if (!TrackedGlobals.empty()) {
853 // If we are tracking this global, merge in the known value for it.
854 hash_map<GlobalVariable*, LatticeVal>::iterator It =
855 TrackedGlobals.find(GV);
856 if (It != TrackedGlobals.end()) {
857 mergeInValue(IV, &I, It->second);
863 // Transform load (constantexpr_GEP global, 0, ...) into the value loaded.
864 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr))
865 if (CE->getOpcode() == Instruction::GetElementPtr)
866 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(CE->getOperand(0)))
867 if (GV->isConstant() && !GV->isExternal())
869 ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE)) {
870 markConstant(IV, &I, V);
875 // Otherwise we cannot say for certain what value this load will produce.
877 markOverdefined(IV, &I);
880 void SCCPSolver::visitCallSite(CallSite CS) {
881 Function *F = CS.getCalledFunction();
883 // If we are tracking this function, we must make sure to bind arguments as
885 hash_map<Function*, LatticeVal>::iterator TFRVI =TrackedFunctionRetVals.end();
886 if (F && F->hasInternalLinkage())
887 TFRVI = TrackedFunctionRetVals.find(F);
889 if (TFRVI != TrackedFunctionRetVals.end()) {
890 // If this is the first call to the function hit, mark its entry block
892 if (!BBExecutable.count(F->begin()))
893 MarkBlockExecutable(F->begin());
895 CallSite::arg_iterator CAI = CS.arg_begin();
896 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
897 AI != E; ++AI, ++CAI) {
898 LatticeVal &IV = ValueState[AI];
899 if (!IV.isOverdefined())
900 mergeInValue(IV, AI, getValueState(*CAI));
903 Instruction *I = CS.getInstruction();
904 if (I->getType() == Type::VoidTy) return;
906 LatticeVal &IV = ValueState[I];
907 if (IV.isOverdefined()) return;
909 // Propagate the return value of the function to the value of the instruction.
910 if (TFRVI != TrackedFunctionRetVals.end()) {
911 mergeInValue(IV, I, TFRVI->second);
915 if (F == 0 || !F->isExternal() || !canConstantFoldCallTo(F)) {
916 markOverdefined(IV, I);
920 std::vector<Constant*> Operands;
921 Operands.reserve(I->getNumOperands()-1);
923 for (CallSite::arg_iterator AI = CS.arg_begin(), E = CS.arg_end();
925 LatticeVal &State = getValueState(*AI);
926 if (State.isUndefined())
927 return; // Operands are not resolved yet...
928 else if (State.isOverdefined()) {
929 markOverdefined(IV, I);
932 assert(State.isConstant() && "Unknown state!");
933 Operands.push_back(State.getConstant());
936 if (Constant *C = ConstantFoldCall(F, Operands))
937 markConstant(IV, I, C);
939 markOverdefined(IV, I);
943 void SCCPSolver::Solve() {
944 // Process the work lists until they are empty!
945 while (!BBWorkList.empty() || !InstWorkList.empty() ||
946 !OverdefinedInstWorkList.empty()) {
947 // Process the instruction work list...
948 while (!OverdefinedInstWorkList.empty()) {
949 Value *I = OverdefinedInstWorkList.back();
950 OverdefinedInstWorkList.pop_back();
952 DEBUG(std::cerr << "\nPopped off OI-WL: " << *I);
954 // "I" got into the work list because it either made the transition from
955 // bottom to constant
957 // Anything on this worklist that is overdefined need not be visited
958 // since all of its users will have already been marked as overdefined
959 // Update all of the users of this instruction's value...
961 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
963 OperandChangedState(*UI);
965 // Process the instruction work list...
966 while (!InstWorkList.empty()) {
967 Value *I = InstWorkList.back();
968 InstWorkList.pop_back();
970 DEBUG(std::cerr << "\nPopped off I-WL: " << *I);
972 // "I" got into the work list because it either made the transition from
973 // bottom to constant
975 // Anything on this worklist that is overdefined need not be visited
976 // since all of its users will have already been marked as overdefined.
977 // Update all of the users of this instruction's value...
979 if (!getValueState(I).isOverdefined())
980 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
982 OperandChangedState(*UI);
985 // Process the basic block work list...
986 while (!BBWorkList.empty()) {
987 BasicBlock *BB = BBWorkList.back();
988 BBWorkList.pop_back();
990 DEBUG(std::cerr << "\nPopped off BBWL: " << *BB);
992 // Notify all instructions in this basic block that they are newly
999 /// ResolveBranchesIn - While solving the dataflow for a function, we assume
1000 /// that branches on undef values cannot reach any of their successors.
1001 /// However, this is not a safe assumption. After we solve dataflow, this
1002 /// method should be use to handle this. If this returns true, the solver
1003 /// should be rerun.
1004 bool SCCPSolver::ResolveBranchesIn(Function &F) {
1005 bool BranchesResolved = false;
1006 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
1007 if (BBExecutable.count(BB)) {
1008 TerminatorInst *TI = BB->getTerminator();
1009 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
1010 if (BI->isConditional()) {
1011 LatticeVal &BCValue = getValueState(BI->getCondition());
1012 if (BCValue.isUndefined()) {
1013 BI->setCondition(ConstantBool::True);
1014 BranchesResolved = true;
1018 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
1019 LatticeVal &SCValue = getValueState(SI->getCondition());
1020 if (SCValue.isUndefined()) {
1021 const Type *CondTy = SI->getCondition()->getType();
1022 SI->setCondition(Constant::getNullValue(CondTy));
1023 BranchesResolved = true;
1029 return BranchesResolved;
1034 Statistic<> NumInstRemoved("sccp", "Number of instructions removed");
1035 Statistic<> NumDeadBlocks ("sccp", "Number of basic blocks unreachable");
1037 //===--------------------------------------------------------------------===//
1039 /// SCCP Class - This class uses the SCCPSolver to implement a per-function
1040 /// Sparse Conditional COnstant Propagator.
1042 struct SCCP : public FunctionPass {
1043 // runOnFunction - Run the Sparse Conditional Constant Propagation
1044 // algorithm, and return true if the function was modified.
1046 bool runOnFunction(Function &F);
1048 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
1049 AU.setPreservesCFG();
1053 RegisterOpt<SCCP> X("sccp", "Sparse Conditional Constant Propagation");
1054 } // end anonymous namespace
1057 // createSCCPPass - This is the public interface to this file...
1058 FunctionPass *llvm::createSCCPPass() {
1063 // runOnFunction() - Run the Sparse Conditional Constant Propagation algorithm,
1064 // and return true if the function was modified.
1066 bool SCCP::runOnFunction(Function &F) {
1067 DEBUG(std::cerr << "SCCP on function '" << F.getName() << "'\n");
1070 // Mark the first block of the function as being executable.
1071 Solver.MarkBlockExecutable(F.begin());
1073 // Mark all arguments to the function as being overdefined.
1074 hash_map<Value*, LatticeVal> &Values = Solver.getValueMapping();
1075 for (Function::arg_iterator AI = F.arg_begin(), E = F.arg_end(); AI != E; ++AI)
1076 Values[AI].markOverdefined();
1078 // Solve for constants.
1079 bool ResolvedBranches = true;
1080 while (ResolvedBranches) {
1082 DEBUG(std::cerr << "RESOLVING UNDEF BRANCHES\n");
1083 ResolvedBranches = Solver.ResolveBranchesIn(F);
1086 bool MadeChanges = false;
1088 // If we decided that there are basic blocks that are dead in this function,
1089 // delete their contents now. Note that we cannot actually delete the blocks,
1090 // as we cannot modify the CFG of the function.
1092 std::set<BasicBlock*> &ExecutableBBs = Solver.getExecutableBlocks();
1093 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
1094 if (!ExecutableBBs.count(BB)) {
1095 DEBUG(std::cerr << " BasicBlock Dead:" << *BB);
1098 // Delete the instructions backwards, as it has a reduced likelihood of
1099 // having to update as many def-use and use-def chains.
1100 std::vector<Instruction*> Insts;
1101 for (BasicBlock::iterator I = BB->begin(), E = BB->getTerminator();
1104 while (!Insts.empty()) {
1105 Instruction *I = Insts.back();
1107 if (!I->use_empty())
1108 I->replaceAllUsesWith(UndefValue::get(I->getType()));
1109 BB->getInstList().erase(I);
1114 // Iterate over all of the instructions in a function, replacing them with
1115 // constants if we have found them to be of constant values.
1117 for (BasicBlock::iterator BI = BB->begin(), E = BB->end(); BI != E; ) {
1118 Instruction *Inst = BI++;
1119 if (Inst->getType() != Type::VoidTy) {
1120 LatticeVal &IV = Values[Inst];
1121 if (IV.isConstant() || IV.isUndefined() &&
1122 !isa<TerminatorInst>(Inst)) {
1123 Constant *Const = IV.isConstant()
1124 ? IV.getConstant() : UndefValue::get(Inst->getType());
1125 DEBUG(std::cerr << " Constant: " << *Const << " = " << *Inst);
1127 // Replaces all of the uses of a variable with uses of the constant.
1128 Inst->replaceAllUsesWith(Const);
1130 // Delete the instruction.
1131 BB->getInstList().erase(Inst);
1133 // Hey, we just changed something!
1145 Statistic<> IPNumInstRemoved("ipsccp", "Number of instructions removed");
1146 Statistic<> IPNumDeadBlocks ("ipsccp", "Number of basic blocks unreachable");
1147 Statistic<> IPNumArgsElimed ("ipsccp",
1148 "Number of arguments constant propagated");
1149 Statistic<> IPNumGlobalConst("ipsccp",
1150 "Number of globals found to be constant");
1152 //===--------------------------------------------------------------------===//
1154 /// IPSCCP Class - This class implements interprocedural Sparse Conditional
1155 /// Constant Propagation.
1157 struct IPSCCP : public ModulePass {
1158 bool runOnModule(Module &M);
1162 Y("ipsccp", "Interprocedural Sparse Conditional Constant Propagation");
1163 } // end anonymous namespace
1165 // createIPSCCPPass - This is the public interface to this file...
1166 ModulePass *llvm::createIPSCCPPass() {
1167 return new IPSCCP();
1171 static bool AddressIsTaken(GlobalValue *GV) {
1172 // Delete any dead constantexpr klingons.
1173 GV->removeDeadConstantUsers();
1175 for (Value::use_iterator UI = GV->use_begin(), E = GV->use_end();
1177 if (StoreInst *SI = dyn_cast<StoreInst>(*UI)) {
1178 if (SI->getOperand(0) == GV || SI->isVolatile())
1179 return true; // Storing addr of GV.
1180 } else if (isa<InvokeInst>(*UI) || isa<CallInst>(*UI)) {
1181 // Make sure we are calling the function, not passing the address.
1182 CallSite CS = CallSite::get(cast<Instruction>(*UI));
1183 for (CallSite::arg_iterator AI = CS.arg_begin(),
1184 E = CS.arg_end(); AI != E; ++AI)
1187 } else if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) {
1188 if (LI->isVolatile())
1196 bool IPSCCP::runOnModule(Module &M) {
1199 // Loop over all functions, marking arguments to those with their addresses
1200 // taken or that are external as overdefined.
1202 hash_map<Value*, LatticeVal> &Values = Solver.getValueMapping();
1203 for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F)
1204 if (!F->hasInternalLinkage() || AddressIsTaken(F)) {
1205 if (!F->isExternal())
1206 Solver.MarkBlockExecutable(F->begin());
1207 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
1209 Values[AI].markOverdefined();
1211 Solver.AddTrackedFunction(F);
1214 // Loop over global variables. We inform the solver about any internal global
1215 // variables that do not have their 'addresses taken'. If they don't have
1216 // their addresses taken, we can propagate constants through them.
1217 for (Module::global_iterator G = M.global_begin(), E = M.global_end();
1219 if (!G->isConstant() && G->hasInternalLinkage() && !AddressIsTaken(G))
1220 Solver.TrackValueOfGlobalVariable(G);
1222 // Solve for constants.
1223 bool ResolvedBranches = true;
1224 while (ResolvedBranches) {
1227 DEBUG(std::cerr << "RESOLVING UNDEF BRANCHES\n");
1228 ResolvedBranches = false;
1229 for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F)
1230 ResolvedBranches |= Solver.ResolveBranchesIn(*F);
1233 bool MadeChanges = false;
1235 // Iterate over all of the instructions in the module, replacing them with
1236 // constants if we have found them to be of constant values.
1238 std::set<BasicBlock*> &ExecutableBBs = Solver.getExecutableBlocks();
1239 for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) {
1240 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
1242 if (!AI->use_empty()) {
1243 LatticeVal &IV = Values[AI];
1244 if (IV.isConstant() || IV.isUndefined()) {
1245 Constant *CST = IV.isConstant() ?
1246 IV.getConstant() : UndefValue::get(AI->getType());
1247 DEBUG(std::cerr << "*** Arg " << *AI << " = " << *CST <<"\n");
1249 // Replaces all of the uses of a variable with uses of the
1251 AI->replaceAllUsesWith(CST);
1256 std::vector<BasicBlock*> BlocksToErase;
1257 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
1258 if (!ExecutableBBs.count(BB)) {
1259 DEBUG(std::cerr << " BasicBlock Dead:" << *BB);
1262 // Delete the instructions backwards, as it has a reduced likelihood of
1263 // having to update as many def-use and use-def chains.
1264 std::vector<Instruction*> Insts;
1265 TerminatorInst *TI = BB->getTerminator();
1266 for (BasicBlock::iterator I = BB->begin(), E = TI; I != E; ++I)
1269 while (!Insts.empty()) {
1270 Instruction *I = Insts.back();
1272 if (!I->use_empty())
1273 I->replaceAllUsesWith(UndefValue::get(I->getType()));
1274 BB->getInstList().erase(I);
1279 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) {
1280 BasicBlock *Succ = TI->getSuccessor(i);
1281 if (Succ->begin() != Succ->end() && isa<PHINode>(Succ->begin()))
1282 TI->getSuccessor(i)->removePredecessor(BB);
1284 if (!TI->use_empty())
1285 TI->replaceAllUsesWith(UndefValue::get(TI->getType()));
1286 BB->getInstList().erase(TI);
1288 if (&*BB != &F->front())
1289 BlocksToErase.push_back(BB);
1291 new UnreachableInst(BB);
1294 for (BasicBlock::iterator BI = BB->begin(), E = BB->end(); BI != E; ) {
1295 Instruction *Inst = BI++;
1296 if (Inst->getType() != Type::VoidTy) {
1297 LatticeVal &IV = Values[Inst];
1298 if (IV.isConstant() || IV.isUndefined() &&
1299 !isa<TerminatorInst>(Inst)) {
1300 Constant *Const = IV.isConstant()
1301 ? IV.getConstant() : UndefValue::get(Inst->getType());
1302 DEBUG(std::cerr << " Constant: " << *Const << " = " << *Inst);
1304 // Replaces all of the uses of a variable with uses of the
1306 Inst->replaceAllUsesWith(Const);
1308 // Delete the instruction.
1309 if (!isa<TerminatorInst>(Inst) && !isa<CallInst>(Inst))
1310 BB->getInstList().erase(Inst);
1312 // Hey, we just changed something!
1320 // Now that all instructions in the function are constant folded, erase dead
1321 // blocks, because we can now use ConstantFoldTerminator to get rid of
1323 for (unsigned i = 0, e = BlocksToErase.size(); i != e; ++i) {
1324 // If there are any PHI nodes in this successor, drop entries for BB now.
1325 BasicBlock *DeadBB = BlocksToErase[i];
1326 while (!DeadBB->use_empty()) {
1327 Instruction *I = cast<Instruction>(DeadBB->use_back());
1328 bool Folded = ConstantFoldTerminator(I->getParent());
1329 assert(Folded && "Didn't fold away reference to block!");
1332 // Finally, delete the basic block.
1333 F->getBasicBlockList().erase(DeadBB);
1337 // If we inferred constant or undef return values for a function, we replaced
1338 // all call uses with the inferred value. This means we don't need to bother
1339 // actually returning anything from the function. Replace all return
1340 // instructions with return undef.
1341 const hash_map<Function*, LatticeVal> &RV =Solver.getTrackedFunctionRetVals();
1342 for (hash_map<Function*, LatticeVal>::const_iterator I = RV.begin(),
1343 E = RV.end(); I != E; ++I)
1344 if (!I->second.isOverdefined() &&
1345 I->first->getReturnType() != Type::VoidTy) {
1346 Function *F = I->first;
1347 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
1348 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator()))
1349 if (!isa<UndefValue>(RI->getOperand(0)))
1350 RI->setOperand(0, UndefValue::get(F->getReturnType()));
1353 // If we infered constant or undef values for globals variables, we can delete
1354 // the global and any stores that remain to it.
1355 const hash_map<GlobalVariable*, LatticeVal> &TG = Solver.getTrackedGlobals();
1356 for (hash_map<GlobalVariable*, LatticeVal>::const_iterator I = TG.begin(),
1357 E = TG.end(); I != E; ++I) {
1358 GlobalVariable *GV = I->first;
1359 assert(!I->second.isOverdefined() &&
1360 "Overdefined values should have been taken out of the map!");
1361 DEBUG(std::cerr << "Found that GV '" << GV->getName()<< "' is constant!\n");
1362 while (!GV->use_empty()) {
1363 StoreInst *SI = cast<StoreInst>(GV->use_back());
1364 SI->eraseFromParent();
1366 M.getGlobalList().erase(GV);