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);
333 void visitShuffleVectorInst(ShuffleVectorInst &I);
335 // Instructions that cannot be folded away...
336 void visitStoreInst (Instruction &I);
337 void visitLoadInst (LoadInst &I);
338 void visitGetElementPtrInst(GetElementPtrInst &I);
339 void visitCallInst (CallInst &I) { visitCallSite(CallSite::get(&I)); }
340 void visitInvokeInst (InvokeInst &II) {
341 visitCallSite(CallSite::get(&II));
342 visitTerminatorInst(II);
344 void visitCallSite (CallSite CS);
345 void visitUnwindInst (TerminatorInst &I) { /*returns void*/ }
346 void visitUnreachableInst(TerminatorInst &I) { /*returns void*/ }
347 void visitAllocationInst(Instruction &I) { markOverdefined(&I); }
348 void visitVANextInst (Instruction &I) { markOverdefined(&I); }
349 void visitVAArgInst (Instruction &I) { markOverdefined(&I); }
350 void visitFreeInst (Instruction &I) { /*returns void*/ }
352 void visitInstruction(Instruction &I) {
353 // If a new instruction is added to LLVM that we don't handle...
354 std::cerr << "SCCP: Don't know how to handle: " << I;
355 markOverdefined(&I); // Just in case
359 // getFeasibleSuccessors - Return a vector of booleans to indicate which
360 // successors are reachable from a given terminator instruction.
362 void SCCPSolver::getFeasibleSuccessors(TerminatorInst &TI,
363 std::vector<bool> &Succs) {
364 Succs.resize(TI.getNumSuccessors());
365 if (BranchInst *BI = dyn_cast<BranchInst>(&TI)) {
366 if (BI->isUnconditional()) {
369 LatticeVal &BCValue = getValueState(BI->getCondition());
370 if (BCValue.isOverdefined() ||
371 (BCValue.isConstant() && !isa<ConstantBool>(BCValue.getConstant()))) {
372 // Overdefined condition variables, and branches on unfoldable constant
373 // conditions, mean the branch could go either way.
374 Succs[0] = Succs[1] = true;
375 } else if (BCValue.isConstant()) {
376 // Constant condition variables mean the branch can only go a single way
377 Succs[BCValue.getConstant() == ConstantBool::getFalse()] = true;
380 } else if (InvokeInst *II = dyn_cast<InvokeInst>(&TI)) {
381 // Invoke instructions successors are always executable.
382 Succs[0] = Succs[1] = true;
383 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(&TI)) {
384 LatticeVal &SCValue = getValueState(SI->getCondition());
385 if (SCValue.isOverdefined() || // Overdefined condition?
386 (SCValue.isConstant() && !isa<ConstantInt>(SCValue.getConstant()))) {
387 // All destinations are executable!
388 Succs.assign(TI.getNumSuccessors(), true);
389 } else if (SCValue.isConstant()) {
390 Constant *CPV = SCValue.getConstant();
391 // Make sure to skip the "default value" which isn't a value
392 for (unsigned i = 1, E = SI->getNumSuccessors(); i != E; ++i) {
393 if (SI->getSuccessorValue(i) == CPV) {// Found the right branch...
399 // Constant value not equal to any of the branches... must execute
400 // default branch then...
404 std::cerr << "SCCP: Don't know how to handle: " << TI;
405 Succs.assign(TI.getNumSuccessors(), true);
410 // isEdgeFeasible - Return true if the control flow edge from the 'From' basic
411 // block to the 'To' basic block is currently feasible...
413 bool SCCPSolver::isEdgeFeasible(BasicBlock *From, BasicBlock *To) {
414 assert(BBExecutable.count(To) && "Dest should always be alive!");
416 // Make sure the source basic block is executable!!
417 if (!BBExecutable.count(From)) return false;
419 // Check to make sure this edge itself is actually feasible now...
420 TerminatorInst *TI = From->getTerminator();
421 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
422 if (BI->isUnconditional())
425 LatticeVal &BCValue = getValueState(BI->getCondition());
426 if (BCValue.isOverdefined()) {
427 // Overdefined condition variables mean the branch could go either way.
429 } else if (BCValue.isConstant()) {
430 // Not branching on an evaluatable constant?
431 if (!isa<ConstantBool>(BCValue.getConstant())) return true;
433 // Constant condition variables mean the branch can only go a single way
434 return BI->getSuccessor(BCValue.getConstant() ==
435 ConstantBool::getFalse()) == To;
439 } else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) {
440 // Invoke instructions successors are always executable.
442 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
443 LatticeVal &SCValue = getValueState(SI->getCondition());
444 if (SCValue.isOverdefined()) { // Overdefined condition?
445 // All destinations are executable!
447 } else if (SCValue.isConstant()) {
448 Constant *CPV = SCValue.getConstant();
449 if (!isa<ConstantInt>(CPV))
450 return true; // not a foldable constant?
452 // Make sure to skip the "default value" which isn't a value
453 for (unsigned i = 1, E = SI->getNumSuccessors(); i != E; ++i)
454 if (SI->getSuccessorValue(i) == CPV) // Found the taken branch...
455 return SI->getSuccessor(i) == To;
457 // Constant value not equal to any of the branches... must execute
458 // default branch then...
459 return SI->getDefaultDest() == To;
463 std::cerr << "Unknown terminator instruction: " << *TI;
468 // visit Implementations - Something changed in this instruction... Either an
469 // operand made a transition, or the instruction is newly executable. Change
470 // the value type of I to reflect these changes if appropriate. This method
471 // makes sure to do the following actions:
473 // 1. If a phi node merges two constants in, and has conflicting value coming
474 // from different branches, or if the PHI node merges in an overdefined
475 // value, then the PHI node becomes overdefined.
476 // 2. If a phi node merges only constants in, and they all agree on value, the
477 // PHI node becomes a constant value equal to that.
478 // 3. If V <- x (op) y && isConstant(x) && isConstant(y) V = Constant
479 // 4. If V <- x (op) y && (isOverdefined(x) || isOverdefined(y)) V = Overdefined
480 // 5. If V <- MEM or V <- CALL or V <- (unknown) then V = Overdefined
481 // 6. If a conditional branch has a value that is constant, make the selected
482 // destination executable
483 // 7. If a conditional branch has a value that is overdefined, make all
484 // successors executable.
486 void SCCPSolver::visitPHINode(PHINode &PN) {
487 LatticeVal &PNIV = getValueState(&PN);
488 if (PNIV.isOverdefined()) {
489 // There may be instructions using this PHI node that are not overdefined
490 // themselves. If so, make sure that they know that the PHI node operand
492 std::multimap<PHINode*, Instruction*>::iterator I, E;
493 tie(I, E) = UsersOfOverdefinedPHIs.equal_range(&PN);
495 std::vector<Instruction*> Users;
496 Users.reserve(std::distance(I, E));
497 for (; I != E; ++I) Users.push_back(I->second);
498 while (!Users.empty()) {
503 return; // Quick exit
506 // Super-extra-high-degree PHI nodes are unlikely to ever be marked constant,
507 // and slow us down a lot. Just mark them overdefined.
508 if (PN.getNumIncomingValues() > 64) {
509 markOverdefined(PNIV, &PN);
513 // Look at all of the executable operands of the PHI node. If any of them
514 // are overdefined, the PHI becomes overdefined as well. If they are all
515 // constant, and they agree with each other, the PHI becomes the identical
516 // constant. If they are constant and don't agree, the PHI is overdefined.
517 // If there are no executable operands, the PHI remains undefined.
519 Constant *OperandVal = 0;
520 for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) {
521 LatticeVal &IV = getValueState(PN.getIncomingValue(i));
522 if (IV.isUndefined()) continue; // Doesn't influence PHI node.
524 if (isEdgeFeasible(PN.getIncomingBlock(i), PN.getParent())) {
525 if (IV.isOverdefined()) { // PHI node becomes overdefined!
526 markOverdefined(PNIV, &PN);
530 if (OperandVal == 0) { // Grab the first value...
531 OperandVal = IV.getConstant();
532 } else { // Another value is being merged in!
533 // There is already a reachable operand. If we conflict with it,
534 // then the PHI node becomes overdefined. If we agree with it, we
537 // Check to see if there are two different constants merging...
538 if (IV.getConstant() != OperandVal) {
539 // Yes there is. This means the PHI node is not constant.
540 // You must be overdefined poor PHI.
542 markOverdefined(PNIV, &PN); // The PHI node now becomes overdefined
543 return; // I'm done analyzing you
549 // If we exited the loop, this means that the PHI node only has constant
550 // arguments that agree with each other(and OperandVal is the constant) or
551 // OperandVal is null because there are no defined incoming arguments. If
552 // this is the case, the PHI remains undefined.
555 markConstant(PNIV, &PN, OperandVal); // Acquire operand value
558 void SCCPSolver::visitReturnInst(ReturnInst &I) {
559 if (I.getNumOperands() == 0) return; // Ret void
561 // If we are tracking the return value of this function, merge it in.
562 Function *F = I.getParent()->getParent();
563 if (F->hasInternalLinkage() && !TrackedFunctionRetVals.empty()) {
564 hash_map<Function*, LatticeVal>::iterator TFRVI =
565 TrackedFunctionRetVals.find(F);
566 if (TFRVI != TrackedFunctionRetVals.end() &&
567 !TFRVI->second.isOverdefined()) {
568 LatticeVal &IV = getValueState(I.getOperand(0));
569 mergeInValue(TFRVI->second, F, IV);
575 void SCCPSolver::visitTerminatorInst(TerminatorInst &TI) {
576 std::vector<bool> SuccFeasible;
577 getFeasibleSuccessors(TI, SuccFeasible);
579 BasicBlock *BB = TI.getParent();
581 // Mark all feasible successors executable...
582 for (unsigned i = 0, e = SuccFeasible.size(); i != e; ++i)
584 markEdgeExecutable(BB, TI.getSuccessor(i));
587 void SCCPSolver::visitCastInst(CastInst &I) {
588 Value *V = I.getOperand(0);
589 LatticeVal &VState = getValueState(V);
590 if (VState.isOverdefined()) // Inherit overdefinedness of operand
592 else if (VState.isConstant()) // Propagate constant value
593 markConstant(&I, ConstantExpr::getCast(VState.getConstant(), I.getType()));
596 void SCCPSolver::visitSelectInst(SelectInst &I) {
597 LatticeVal &CondValue = getValueState(I.getCondition());
598 if (CondValue.isUndefined())
600 if (CondValue.isConstant()) {
601 if (ConstantBool *CondCB = dyn_cast<ConstantBool>(CondValue.getConstant())){
602 mergeInValue(&I, getValueState(CondCB->getValue() ? I.getTrueValue()
603 : I.getFalseValue()));
608 // Otherwise, the condition is overdefined or a constant we can't evaluate.
609 // See if we can produce something better than overdefined based on the T/F
611 LatticeVal &TVal = getValueState(I.getTrueValue());
612 LatticeVal &FVal = getValueState(I.getFalseValue());
614 // select ?, C, C -> C.
615 if (TVal.isConstant() && FVal.isConstant() &&
616 TVal.getConstant() == FVal.getConstant()) {
617 markConstant(&I, FVal.getConstant());
621 if (TVal.isUndefined()) { // select ?, undef, X -> X.
622 mergeInValue(&I, FVal);
623 } else if (FVal.isUndefined()) { // select ?, X, undef -> X.
624 mergeInValue(&I, TVal);
630 // Handle BinaryOperators and Shift Instructions...
631 void SCCPSolver::visitBinaryOperator(Instruction &I) {
632 LatticeVal &IV = ValueState[&I];
633 if (IV.isOverdefined()) return;
635 LatticeVal &V1State = getValueState(I.getOperand(0));
636 LatticeVal &V2State = getValueState(I.getOperand(1));
638 if (V1State.isOverdefined() || V2State.isOverdefined()) {
639 // If this is an AND or OR with 0 or -1, it doesn't matter that the other
640 // operand is overdefined.
641 if (I.getOpcode() == Instruction::And || I.getOpcode() == Instruction::Or) {
642 LatticeVal *NonOverdefVal = 0;
643 if (!V1State.isOverdefined()) {
644 NonOverdefVal = &V1State;
645 } else if (!V2State.isOverdefined()) {
646 NonOverdefVal = &V2State;
650 if (NonOverdefVal->isUndefined()) {
651 // Could annihilate value.
652 if (I.getOpcode() == Instruction::And)
653 markConstant(IV, &I, Constant::getNullValue(I.getType()));
655 markConstant(IV, &I, ConstantInt::getAllOnesValue(I.getType()));
658 if (I.getOpcode() == Instruction::And) {
659 if (NonOverdefVal->getConstant()->isNullValue()) {
660 markConstant(IV, &I, NonOverdefVal->getConstant());
661 return; // X or 0 = -1
664 if (ConstantIntegral *CI =
665 dyn_cast<ConstantIntegral>(NonOverdefVal->getConstant()))
666 if (CI->isAllOnesValue()) {
667 markConstant(IV, &I, NonOverdefVal->getConstant());
668 return; // X or -1 = -1
676 // If both operands are PHI nodes, it is possible that this instruction has
677 // a constant value, despite the fact that the PHI node doesn't. Check for
678 // this condition now.
679 if (PHINode *PN1 = dyn_cast<PHINode>(I.getOperand(0)))
680 if (PHINode *PN2 = dyn_cast<PHINode>(I.getOperand(1)))
681 if (PN1->getParent() == PN2->getParent()) {
682 // Since the two PHI nodes are in the same basic block, they must have
683 // entries for the same predecessors. Walk the predecessor list, and
684 // if all of the incoming values are constants, and the result of
685 // evaluating this expression with all incoming value pairs is the
686 // same, then this expression is a constant even though the PHI node
687 // is not a constant!
689 for (unsigned i = 0, e = PN1->getNumIncomingValues(); i != e; ++i) {
690 LatticeVal &In1 = getValueState(PN1->getIncomingValue(i));
691 BasicBlock *InBlock = PN1->getIncomingBlock(i);
693 getValueState(PN2->getIncomingValueForBlock(InBlock));
695 if (In1.isOverdefined() || In2.isOverdefined()) {
696 Result.markOverdefined();
697 break; // Cannot fold this operation over the PHI nodes!
698 } else if (In1.isConstant() && In2.isConstant()) {
699 Constant *V = ConstantExpr::get(I.getOpcode(), In1.getConstant(),
701 if (Result.isUndefined())
702 Result.markConstant(V);
703 else if (Result.isConstant() && Result.getConstant() != V) {
704 Result.markOverdefined();
710 // If we found a constant value here, then we know the instruction is
711 // constant despite the fact that the PHI nodes are overdefined.
712 if (Result.isConstant()) {
713 markConstant(IV, &I, Result.getConstant());
714 // Remember that this instruction is virtually using the PHI node
716 UsersOfOverdefinedPHIs.insert(std::make_pair(PN1, &I));
717 UsersOfOverdefinedPHIs.insert(std::make_pair(PN2, &I));
719 } else if (Result.isUndefined()) {
723 // Okay, this really is overdefined now. Since we might have
724 // speculatively thought that this was not overdefined before, and
725 // added ourselves to the UsersOfOverdefinedPHIs list for the PHIs,
726 // make sure to clean out any entries that we put there, for
728 std::multimap<PHINode*, Instruction*>::iterator It, E;
729 tie(It, E) = UsersOfOverdefinedPHIs.equal_range(PN1);
731 if (It->second == &I) {
732 UsersOfOverdefinedPHIs.erase(It++);
736 tie(It, E) = UsersOfOverdefinedPHIs.equal_range(PN2);
738 if (It->second == &I) {
739 UsersOfOverdefinedPHIs.erase(It++);
745 markOverdefined(IV, &I);
746 } else if (V1State.isConstant() && V2State.isConstant()) {
747 markConstant(IV, &I, ConstantExpr::get(I.getOpcode(), V1State.getConstant(),
748 V2State.getConstant()));
752 void SCCPSolver::visitExtractElementInst(ExtractElementInst &I) {
753 LatticeVal &ValState = getValueState(I.getOperand(0));
754 LatticeVal &IdxState = getValueState(I.getOperand(1));
756 if (ValState.isOverdefined() || IdxState.isOverdefined())
758 else if(ValState.isConstant() && IdxState.isConstant())
759 markConstant(&I, ConstantExpr::getExtractElement(ValState.getConstant(),
760 IdxState.getConstant()));
763 void SCCPSolver::visitInsertElementInst(InsertElementInst &I) {
764 LatticeVal &ValState = getValueState(I.getOperand(0));
765 LatticeVal &EltState = getValueState(I.getOperand(1));
766 LatticeVal &IdxState = getValueState(I.getOperand(2));
768 if (ValState.isOverdefined() || EltState.isOverdefined() ||
769 IdxState.isOverdefined())
771 else if(ValState.isConstant() && EltState.isConstant() &&
772 IdxState.isConstant())
773 markConstant(&I, ConstantExpr::getInsertElement(ValState.getConstant(),
774 EltState.getConstant(),
775 IdxState.getConstant()));
776 else if (ValState.isUndefined() && EltState.isConstant() &&
777 IdxState.isConstant())
778 markConstant(&I, ConstantExpr::getInsertElement(UndefValue::get(I.getType()),
779 EltState.getConstant(),
780 IdxState.getConstant()));
783 void SCCPSolver::visitShuffleVectorInst(ShuffleVectorInst &I) {
784 LatticeVal &V1State = getValueState(I.getOperand(0));
785 LatticeVal &V2State = getValueState(I.getOperand(1));
786 LatticeVal &MaskState = getValueState(I.getOperand(2));
788 if (MaskState.isUndefined() ||
789 (V1State.isUndefined() && V2State.isUndefined()))
790 return; // Undefined output if mask or both inputs undefined.
792 if (V1State.isOverdefined() || V2State.isOverdefined() ||
793 MaskState.isOverdefined()) {
796 // A mix of constant/undef inputs.
797 Constant *V1 = V1State.isConstant() ?
798 V1State.getConstant() : UndefValue::get(I.getType());
799 Constant *V2 = V2State.isConstant() ?
800 V2State.getConstant() : UndefValue::get(I.getType());
801 Constant *Mask = MaskState.isConstant() ?
802 MaskState.getConstant() : UndefValue::get(I.getOperand(2)->getType());
803 markConstant(&I, ConstantExpr::getShuffleVector(V1, V2, Mask));
807 // Handle getelementptr instructions... if all operands are constants then we
808 // can turn this into a getelementptr ConstantExpr.
810 void SCCPSolver::visitGetElementPtrInst(GetElementPtrInst &I) {
811 LatticeVal &IV = ValueState[&I];
812 if (IV.isOverdefined()) return;
814 std::vector<Constant*> Operands;
815 Operands.reserve(I.getNumOperands());
817 for (unsigned i = 0, e = I.getNumOperands(); i != e; ++i) {
818 LatticeVal &State = getValueState(I.getOperand(i));
819 if (State.isUndefined())
820 return; // Operands are not resolved yet...
821 else if (State.isOverdefined()) {
822 markOverdefined(IV, &I);
825 assert(State.isConstant() && "Unknown state!");
826 Operands.push_back(State.getConstant());
829 Constant *Ptr = Operands[0];
830 Operands.erase(Operands.begin()); // Erase the pointer from idx list...
832 markConstant(IV, &I, ConstantExpr::getGetElementPtr(Ptr, Operands));
835 void SCCPSolver::visitStoreInst(Instruction &SI) {
836 if (TrackedGlobals.empty() || !isa<GlobalVariable>(SI.getOperand(1)))
838 GlobalVariable *GV = cast<GlobalVariable>(SI.getOperand(1));
839 hash_map<GlobalVariable*, LatticeVal>::iterator I = TrackedGlobals.find(GV);
840 if (I == TrackedGlobals.end() || I->second.isOverdefined()) return;
842 // Get the value we are storing into the global.
843 LatticeVal &PtrVal = getValueState(SI.getOperand(0));
845 mergeInValue(I->second, GV, PtrVal);
846 if (I->second.isOverdefined())
847 TrackedGlobals.erase(I); // No need to keep tracking this!
851 // Handle load instructions. If the operand is a constant pointer to a constant
852 // global, we can replace the load with the loaded constant value!
853 void SCCPSolver::visitLoadInst(LoadInst &I) {
854 LatticeVal &IV = ValueState[&I];
855 if (IV.isOverdefined()) return;
857 LatticeVal &PtrVal = getValueState(I.getOperand(0));
858 if (PtrVal.isUndefined()) return; // The pointer is not resolved yet!
859 if (PtrVal.isConstant() && !I.isVolatile()) {
860 Value *Ptr = PtrVal.getConstant();
861 if (isa<ConstantPointerNull>(Ptr)) {
863 markConstant(IV, &I, Constant::getNullValue(I.getType()));
867 // Transform load (constant global) into the value loaded.
868 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Ptr)) {
869 if (GV->isConstant()) {
870 if (!GV->isExternal()) {
871 markConstant(IV, &I, GV->getInitializer());
874 } else if (!TrackedGlobals.empty()) {
875 // If we are tracking this global, merge in the known value for it.
876 hash_map<GlobalVariable*, LatticeVal>::iterator It =
877 TrackedGlobals.find(GV);
878 if (It != TrackedGlobals.end()) {
879 mergeInValue(IV, &I, It->second);
885 // Transform load (constantexpr_GEP global, 0, ...) into the value loaded.
886 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr))
887 if (CE->getOpcode() == Instruction::GetElementPtr)
888 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(CE->getOperand(0)))
889 if (GV->isConstant() && !GV->isExternal())
891 ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE)) {
892 markConstant(IV, &I, V);
897 // Otherwise we cannot say for certain what value this load will produce.
899 markOverdefined(IV, &I);
902 void SCCPSolver::visitCallSite(CallSite CS) {
903 Function *F = CS.getCalledFunction();
905 // If we are tracking this function, we must make sure to bind arguments as
907 hash_map<Function*, LatticeVal>::iterator TFRVI =TrackedFunctionRetVals.end();
908 if (F && F->hasInternalLinkage())
909 TFRVI = TrackedFunctionRetVals.find(F);
911 if (TFRVI != TrackedFunctionRetVals.end()) {
912 // If this is the first call to the function hit, mark its entry block
914 if (!BBExecutable.count(F->begin()))
915 MarkBlockExecutable(F->begin());
917 CallSite::arg_iterator CAI = CS.arg_begin();
918 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
919 AI != E; ++AI, ++CAI) {
920 LatticeVal &IV = ValueState[AI];
921 if (!IV.isOverdefined())
922 mergeInValue(IV, AI, getValueState(*CAI));
925 Instruction *I = CS.getInstruction();
926 if (I->getType() == Type::VoidTy) return;
928 LatticeVal &IV = ValueState[I];
929 if (IV.isOverdefined()) return;
931 // Propagate the return value of the function to the value of the instruction.
932 if (TFRVI != TrackedFunctionRetVals.end()) {
933 mergeInValue(IV, I, TFRVI->second);
937 if (F == 0 || !F->isExternal() || !canConstantFoldCallTo(F)) {
938 markOverdefined(IV, I);
942 std::vector<Constant*> Operands;
943 Operands.reserve(I->getNumOperands()-1);
945 for (CallSite::arg_iterator AI = CS.arg_begin(), E = CS.arg_end();
947 LatticeVal &State = getValueState(*AI);
948 if (State.isUndefined())
949 return; // Operands are not resolved yet...
950 else if (State.isOverdefined()) {
951 markOverdefined(IV, I);
954 assert(State.isConstant() && "Unknown state!");
955 Operands.push_back(State.getConstant());
958 if (Constant *C = ConstantFoldCall(F, Operands))
959 markConstant(IV, I, C);
961 markOverdefined(IV, I);
965 void SCCPSolver::Solve() {
966 // Process the work lists until they are empty!
967 while (!BBWorkList.empty() || !InstWorkList.empty() ||
968 !OverdefinedInstWorkList.empty()) {
969 // Process the instruction work list...
970 while (!OverdefinedInstWorkList.empty()) {
971 Value *I = OverdefinedInstWorkList.back();
972 OverdefinedInstWorkList.pop_back();
974 DEBUG(std::cerr << "\nPopped off OI-WL: " << *I);
976 // "I" got into the work list because it either made the transition from
977 // bottom to constant
979 // Anything on this worklist that is overdefined need not be visited
980 // since all of its users will have already been marked as overdefined
981 // Update all of the users of this instruction's value...
983 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
985 OperandChangedState(*UI);
987 // Process the instruction work list...
988 while (!InstWorkList.empty()) {
989 Value *I = InstWorkList.back();
990 InstWorkList.pop_back();
992 DEBUG(std::cerr << "\nPopped off I-WL: " << *I);
994 // "I" got into the work list because it either made the transition from
995 // bottom to constant
997 // Anything on this worklist that is overdefined need not be visited
998 // since all of its users will have already been marked as overdefined.
999 // Update all of the users of this instruction's value...
1001 if (!getValueState(I).isOverdefined())
1002 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
1004 OperandChangedState(*UI);
1007 // Process the basic block work list...
1008 while (!BBWorkList.empty()) {
1009 BasicBlock *BB = BBWorkList.back();
1010 BBWorkList.pop_back();
1012 DEBUG(std::cerr << "\nPopped off BBWL: " << *BB);
1014 // Notify all instructions in this basic block that they are newly
1021 /// ResolveBranchesIn - While solving the dataflow for a function, we assume
1022 /// that branches on undef values cannot reach any of their successors.
1023 /// However, this is not a safe assumption. After we solve dataflow, this
1024 /// method should be use to handle this. If this returns true, the solver
1025 /// should be rerun.
1027 /// This method handles this by finding an unresolved branch and marking it one
1028 /// of the edges from the block as being feasible, even though the condition
1029 /// doesn't say it would otherwise be. This allows SCCP to find the rest of the
1030 /// CFG and only slightly pessimizes the analysis results (by marking one,
1031 /// potentially unfeasible, edge feasible). This cannot usefully modify the
1032 /// constraints on the condition of the branch, as that would impact other users
1034 bool SCCPSolver::ResolveBranchesIn(Function &F) {
1035 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
1036 if (!BBExecutable.count(BB))
1039 TerminatorInst *TI = BB->getTerminator();
1040 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
1041 if (!BI->isConditional()) continue;
1042 if (!getValueState(BI->getCondition()).isUndefined())
1044 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
1045 if (!getValueState(SI->getCondition()).isUndefined())
1051 // If the edge to the first successor isn't thought to be feasible yet, mark
1053 if (KnownFeasibleEdges.count(Edge(BB, TI->getSuccessor(0))))
1056 // Otherwise, it isn't already thought to be feasible. Mark it as such now
1057 // and return. This will make other blocks reachable, which will allow new
1058 // values to be discovered and existing ones to be moved in the lattice.
1059 markEdgeExecutable(BB, TI->getSuccessor(0));
1068 Statistic<> NumInstRemoved("sccp", "Number of instructions removed");
1069 Statistic<> NumDeadBlocks ("sccp", "Number of basic blocks unreachable");
1071 //===--------------------------------------------------------------------===//
1073 /// SCCP Class - This class uses the SCCPSolver to implement a per-function
1074 /// Sparse Conditional COnstant Propagator.
1076 struct SCCP : public FunctionPass {
1077 // runOnFunction - Run the Sparse Conditional Constant Propagation
1078 // algorithm, and return true if the function was modified.
1080 bool runOnFunction(Function &F);
1082 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
1083 AU.setPreservesCFG();
1087 RegisterPass<SCCP> X("sccp", "Sparse Conditional Constant Propagation");
1088 } // end anonymous namespace
1091 // createSCCPPass - This is the public interface to this file...
1092 FunctionPass *llvm::createSCCPPass() {
1097 // runOnFunction() - Run the Sparse Conditional Constant Propagation algorithm,
1098 // and return true if the function was modified.
1100 bool SCCP::runOnFunction(Function &F) {
1101 DEBUG(std::cerr << "SCCP on function '" << F.getName() << "'\n");
1104 // Mark the first block of the function as being executable.
1105 Solver.MarkBlockExecutable(F.begin());
1107 // Mark all arguments to the function as being overdefined.
1108 hash_map<Value*, LatticeVal> &Values = Solver.getValueMapping();
1109 for (Function::arg_iterator AI = F.arg_begin(), E = F.arg_end(); AI != E; ++AI)
1110 Values[AI].markOverdefined();
1112 // Solve for constants.
1113 bool ResolvedBranches = true;
1114 while (ResolvedBranches) {
1116 DEBUG(std::cerr << "RESOLVING UNDEF BRANCHES\n");
1117 ResolvedBranches = Solver.ResolveBranchesIn(F);
1120 bool MadeChanges = false;
1122 // If we decided that there are basic blocks that are dead in this function,
1123 // delete their contents now. Note that we cannot actually delete the blocks,
1124 // as we cannot modify the CFG of the function.
1126 std::set<BasicBlock*> &ExecutableBBs = Solver.getExecutableBlocks();
1127 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
1128 if (!ExecutableBBs.count(BB)) {
1129 DEBUG(std::cerr << " BasicBlock Dead:" << *BB);
1132 // Delete the instructions backwards, as it has a reduced likelihood of
1133 // having to update as many def-use and use-def chains.
1134 std::vector<Instruction*> Insts;
1135 for (BasicBlock::iterator I = BB->begin(), E = BB->getTerminator();
1138 while (!Insts.empty()) {
1139 Instruction *I = Insts.back();
1141 if (!I->use_empty())
1142 I->replaceAllUsesWith(UndefValue::get(I->getType()));
1143 BB->getInstList().erase(I);
1148 // Iterate over all of the instructions in a function, replacing them with
1149 // constants if we have found them to be of constant values.
1151 for (BasicBlock::iterator BI = BB->begin(), E = BB->end(); BI != E; ) {
1152 Instruction *Inst = BI++;
1153 if (Inst->getType() != Type::VoidTy) {
1154 LatticeVal &IV = Values[Inst];
1155 if (IV.isConstant() || IV.isUndefined() &&
1156 !isa<TerminatorInst>(Inst)) {
1157 Constant *Const = IV.isConstant()
1158 ? IV.getConstant() : UndefValue::get(Inst->getType());
1159 DEBUG(std::cerr << " Constant: " << *Const << " = " << *Inst);
1161 // Replaces all of the uses of a variable with uses of the constant.
1162 Inst->replaceAllUsesWith(Const);
1164 // Delete the instruction.
1165 BB->getInstList().erase(Inst);
1167 // Hey, we just changed something!
1179 Statistic<> IPNumInstRemoved("ipsccp", "Number of instructions removed");
1180 Statistic<> IPNumDeadBlocks ("ipsccp", "Number of basic blocks unreachable");
1181 Statistic<> IPNumArgsElimed ("ipsccp",
1182 "Number of arguments constant propagated");
1183 Statistic<> IPNumGlobalConst("ipsccp",
1184 "Number of globals found to be constant");
1186 //===--------------------------------------------------------------------===//
1188 /// IPSCCP Class - This class implements interprocedural Sparse Conditional
1189 /// Constant Propagation.
1191 struct IPSCCP : public ModulePass {
1192 bool runOnModule(Module &M);
1195 RegisterPass<IPSCCP>
1196 Y("ipsccp", "Interprocedural Sparse Conditional Constant Propagation");
1197 } // end anonymous namespace
1199 // createIPSCCPPass - This is the public interface to this file...
1200 ModulePass *llvm::createIPSCCPPass() {
1201 return new IPSCCP();
1205 static bool AddressIsTaken(GlobalValue *GV) {
1206 // Delete any dead constantexpr klingons.
1207 GV->removeDeadConstantUsers();
1209 for (Value::use_iterator UI = GV->use_begin(), E = GV->use_end();
1211 if (StoreInst *SI = dyn_cast<StoreInst>(*UI)) {
1212 if (SI->getOperand(0) == GV || SI->isVolatile())
1213 return true; // Storing addr of GV.
1214 } else if (isa<InvokeInst>(*UI) || isa<CallInst>(*UI)) {
1215 // Make sure we are calling the function, not passing the address.
1216 CallSite CS = CallSite::get(cast<Instruction>(*UI));
1217 for (CallSite::arg_iterator AI = CS.arg_begin(),
1218 E = CS.arg_end(); AI != E; ++AI)
1221 } else if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) {
1222 if (LI->isVolatile())
1230 bool IPSCCP::runOnModule(Module &M) {
1233 // Loop over all functions, marking arguments to those with their addresses
1234 // taken or that are external as overdefined.
1236 hash_map<Value*, LatticeVal> &Values = Solver.getValueMapping();
1237 for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F)
1238 if (!F->hasInternalLinkage() || AddressIsTaken(F)) {
1239 if (!F->isExternal())
1240 Solver.MarkBlockExecutable(F->begin());
1241 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
1243 Values[AI].markOverdefined();
1245 Solver.AddTrackedFunction(F);
1248 // Loop over global variables. We inform the solver about any internal global
1249 // variables that do not have their 'addresses taken'. If they don't have
1250 // their addresses taken, we can propagate constants through them.
1251 for (Module::global_iterator G = M.global_begin(), E = M.global_end();
1253 if (!G->isConstant() && G->hasInternalLinkage() && !AddressIsTaken(G))
1254 Solver.TrackValueOfGlobalVariable(G);
1256 // Solve for constants.
1257 bool ResolvedBranches = true;
1258 while (ResolvedBranches) {
1261 DEBUG(std::cerr << "RESOLVING UNDEF BRANCHES\n");
1262 ResolvedBranches = false;
1263 for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F)
1264 ResolvedBranches |= Solver.ResolveBranchesIn(*F);
1267 bool MadeChanges = false;
1269 // Iterate over all of the instructions in the module, replacing them with
1270 // constants if we have found them to be of constant values.
1272 std::set<BasicBlock*> &ExecutableBBs = Solver.getExecutableBlocks();
1273 for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) {
1274 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
1276 if (!AI->use_empty()) {
1277 LatticeVal &IV = Values[AI];
1278 if (IV.isConstant() || IV.isUndefined()) {
1279 Constant *CST = IV.isConstant() ?
1280 IV.getConstant() : UndefValue::get(AI->getType());
1281 DEBUG(std::cerr << "*** Arg " << *AI << " = " << *CST <<"\n");
1283 // Replaces all of the uses of a variable with uses of the
1285 AI->replaceAllUsesWith(CST);
1290 std::vector<BasicBlock*> BlocksToErase;
1291 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
1292 if (!ExecutableBBs.count(BB)) {
1293 DEBUG(std::cerr << " BasicBlock Dead:" << *BB);
1296 // Delete the instructions backwards, as it has a reduced likelihood of
1297 // having to update as many def-use and use-def chains.
1298 std::vector<Instruction*> Insts;
1299 TerminatorInst *TI = BB->getTerminator();
1300 for (BasicBlock::iterator I = BB->begin(), E = TI; I != E; ++I)
1303 while (!Insts.empty()) {
1304 Instruction *I = Insts.back();
1306 if (!I->use_empty())
1307 I->replaceAllUsesWith(UndefValue::get(I->getType()));
1308 BB->getInstList().erase(I);
1313 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) {
1314 BasicBlock *Succ = TI->getSuccessor(i);
1315 if (Succ->begin() != Succ->end() && isa<PHINode>(Succ->begin()))
1316 TI->getSuccessor(i)->removePredecessor(BB);
1318 if (!TI->use_empty())
1319 TI->replaceAllUsesWith(UndefValue::get(TI->getType()));
1320 BB->getInstList().erase(TI);
1322 if (&*BB != &F->front())
1323 BlocksToErase.push_back(BB);
1325 new UnreachableInst(BB);
1328 for (BasicBlock::iterator BI = BB->begin(), E = BB->end(); BI != E; ) {
1329 Instruction *Inst = BI++;
1330 if (Inst->getType() != Type::VoidTy) {
1331 LatticeVal &IV = Values[Inst];
1332 if (IV.isConstant() || IV.isUndefined() &&
1333 !isa<TerminatorInst>(Inst)) {
1334 Constant *Const = IV.isConstant()
1335 ? IV.getConstant() : UndefValue::get(Inst->getType());
1336 DEBUG(std::cerr << " Constant: " << *Const << " = " << *Inst);
1338 // Replaces all of the uses of a variable with uses of the
1340 Inst->replaceAllUsesWith(Const);
1342 // Delete the instruction.
1343 if (!isa<TerminatorInst>(Inst) && !isa<CallInst>(Inst))
1344 BB->getInstList().erase(Inst);
1346 // Hey, we just changed something!
1354 // Now that all instructions in the function are constant folded, erase dead
1355 // blocks, because we can now use ConstantFoldTerminator to get rid of
1357 for (unsigned i = 0, e = BlocksToErase.size(); i != e; ++i) {
1358 // If there are any PHI nodes in this successor, drop entries for BB now.
1359 BasicBlock *DeadBB = BlocksToErase[i];
1360 while (!DeadBB->use_empty()) {
1361 Instruction *I = cast<Instruction>(DeadBB->use_back());
1362 bool Folded = ConstantFoldTerminator(I->getParent());
1364 // The constant folder may not have been able to fold the termiantor
1365 // if this is a branch or switch on undef. Fold it manually as a
1366 // branch to the first successor.
1367 if (BranchInst *BI = dyn_cast<BranchInst>(I)) {
1368 assert(BI->isConditional() && isa<UndefValue>(BI->getCondition()) &&
1369 "Branch should be foldable!");
1370 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(I)) {
1371 assert(isa<UndefValue>(SI->getCondition()) && "Switch should fold");
1373 assert(0 && "Didn't fold away reference to block!");
1376 // Make this an uncond branch to the first successor.
1377 TerminatorInst *TI = I->getParent()->getTerminator();
1378 new BranchInst(TI->getSuccessor(0), TI);
1380 // Remove entries in successor phi nodes to remove edges.
1381 for (unsigned i = 1, e = TI->getNumSuccessors(); i != e; ++i)
1382 TI->getSuccessor(i)->removePredecessor(TI->getParent());
1384 // Remove the old terminator.
1385 TI->eraseFromParent();
1389 // Finally, delete the basic block.
1390 F->getBasicBlockList().erase(DeadBB);
1394 // If we inferred constant or undef return values for a function, we replaced
1395 // all call uses with the inferred value. This means we don't need to bother
1396 // actually returning anything from the function. Replace all return
1397 // instructions with return undef.
1398 const hash_map<Function*, LatticeVal> &RV =Solver.getTrackedFunctionRetVals();
1399 for (hash_map<Function*, LatticeVal>::const_iterator I = RV.begin(),
1400 E = RV.end(); I != E; ++I)
1401 if (!I->second.isOverdefined() &&
1402 I->first->getReturnType() != Type::VoidTy) {
1403 Function *F = I->first;
1404 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
1405 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator()))
1406 if (!isa<UndefValue>(RI->getOperand(0)))
1407 RI->setOperand(0, UndefValue::get(F->getReturnType()));
1410 // If we infered constant or undef values for globals variables, we can delete
1411 // the global and any stores that remain to it.
1412 const hash_map<GlobalVariable*, LatticeVal> &TG = Solver.getTrackedGlobals();
1413 for (hash_map<GlobalVariable*, LatticeVal>::const_iterator I = TG.begin(),
1414 E = TG.end(); I != E; ++I) {
1415 GlobalVariable *GV = I->first;
1416 assert(!I->second.isOverdefined() &&
1417 "Overdefined values should have been taken out of the map!");
1418 DEBUG(std::cerr << "Found that GV '" << GV->getName()<< "' is constant!\n");
1419 while (!GV->use_empty()) {
1420 StoreInst *SI = cast<StoreInst>(GV->use_back());
1421 SI->eraseFromParent();
1423 M.getGlobalList().erase(GV);