1 //===- SCCP.cpp - Sparse Conditional Constant Propagation -----------------===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by the LLVM research group and is distributed under
6 // the University of Illinois Open Source License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements sparse conditional constant propagation and merging:
12 // Specifically, this:
13 // * Assumes values are constant unless proven otherwise
14 // * Assumes BasicBlocks are dead unless proven otherwise
15 // * Proves values to be constant, and replaces them with constants
16 // * Proves conditional branches to be unconditional
19 // * This pass has a habit of making definitions be dead. It is a good idea
20 // to to run a DCE pass sometime after running this pass.
22 //===----------------------------------------------------------------------===//
24 #define DEBUG_TYPE "sccp"
25 #include "llvm/Transforms/Scalar.h"
26 #include "llvm/Transforms/IPO.h"
27 #include "llvm/Constants.h"
28 #include "llvm/DerivedTypes.h"
29 #include "llvm/Instructions.h"
30 #include "llvm/Pass.h"
31 #include "llvm/Support/InstVisitor.h"
32 #include "llvm/Transforms/Utils/Local.h"
33 #include "llvm/Support/CallSite.h"
34 #include "llvm/Support/Debug.h"
35 #include "llvm/ADT/hash_map"
36 #include "llvm/ADT/Statistic.h"
37 #include "llvm/ADT/STLExtras.h"
42 // LatticeVal class - This class represents the different lattice values that an
43 // instruction may occupy. It is a simple class with value semantics.
49 undefined, // This instruction has no known value
50 constant, // This instruction has a constant value
51 overdefined // This instruction has an unknown value
52 } LatticeValue; // The current lattice position
53 Constant *ConstantVal; // If Constant value, the current value
55 inline LatticeVal() : LatticeValue(undefined), ConstantVal(0) {}
57 // markOverdefined - Return true if this is a new status to be in...
58 inline bool markOverdefined() {
59 if (LatticeValue != overdefined) {
60 LatticeValue = overdefined;
66 // markConstant - Return true if this is a new status for us...
67 inline bool markConstant(Constant *V) {
68 if (LatticeValue != constant) {
69 LatticeValue = constant;
73 assert(ConstantVal == V && "Marking constant with different value");
78 inline bool isUndefined() const { return LatticeValue == undefined; }
79 inline bool isConstant() const { return LatticeValue == constant; }
80 inline bool isOverdefined() const { return LatticeValue == overdefined; }
82 inline Constant *getConstant() const {
83 assert(isConstant() && "Cannot get the constant of a non-constant!");
88 } // end anonymous namespace
91 //===----------------------------------------------------------------------===//
93 /// SCCPSolver - This class is a general purpose solver for Sparse Conditional
94 /// Constant Propagation.
96 class SCCPSolver : public InstVisitor<SCCPSolver> {
97 std::set<BasicBlock*> BBExecutable;// The basic blocks that are executable
98 hash_map<Value*, LatticeVal> ValueState; // The state each value is in...
100 /// GlobalValue - If we are tracking any values for the contents of a global
101 /// variable, we keep a mapping from the constant accessor to the element of
102 /// the global, to the currently known value. If the value becomes
103 /// overdefined, it's entry is simply removed from this map.
104 hash_map<GlobalVariable*, LatticeVal> TrackedGlobals;
106 /// TrackedFunctionRetVals - If we are tracking arguments into and the return
107 /// value out of a function, it will have an entry in this map, indicating
108 /// what the known return value for the function is.
109 hash_map<Function*, LatticeVal> TrackedFunctionRetVals;
111 // The reason for two worklists is that overdefined is the lowest state
112 // on the lattice, and moving things to overdefined as fast as possible
113 // makes SCCP converge much faster.
114 // By having a separate worklist, we accomplish this because everything
115 // possibly overdefined will become overdefined at the soonest possible
117 std::vector<Value*> OverdefinedInstWorkList;
118 std::vector<Value*> InstWorkList;
121 std::vector<BasicBlock*> BBWorkList; // The BasicBlock work list
123 /// UsersOfOverdefinedPHIs - Keep track of any users of PHI nodes that are not
124 /// overdefined, despite the fact that the PHI node is overdefined.
125 std::multimap<PHINode*, Instruction*> UsersOfOverdefinedPHIs;
127 /// KnownFeasibleEdges - Entries in this set are edges which have already had
128 /// PHI nodes retriggered.
129 typedef std::pair<BasicBlock*,BasicBlock*> Edge;
130 std::set<Edge> KnownFeasibleEdges;
133 /// MarkBlockExecutable - This method can be used by clients to mark all of
134 /// the blocks that are known to be intrinsically live in the processed unit.
135 void MarkBlockExecutable(BasicBlock *BB) {
136 DOUT << "Marking Block Executable: " << BB->getName() << "\n";
137 BBExecutable.insert(BB); // Basic block is executable!
138 BBWorkList.push_back(BB); // Add the block to the work list!
141 /// TrackValueOfGlobalVariable - Clients can use this method to
142 /// inform the SCCPSolver that it should track loads and stores to the
143 /// specified global variable if it can. This is only legal to call if
144 /// performing Interprocedural SCCP.
145 void TrackValueOfGlobalVariable(GlobalVariable *GV) {
146 const Type *ElTy = GV->getType()->getElementType();
147 if (ElTy->isFirstClassType()) {
148 LatticeVal &IV = TrackedGlobals[GV];
149 if (!isa<UndefValue>(GV->getInitializer()))
150 IV.markConstant(GV->getInitializer());
154 /// AddTrackedFunction - If the SCCP solver is supposed to track calls into
155 /// and out of the specified function (which cannot have its address taken),
156 /// this method must be called.
157 void AddTrackedFunction(Function *F) {
158 assert(F->hasInternalLinkage() && "Can only track internal functions!");
159 // Add an entry, F -> undef.
160 TrackedFunctionRetVals[F];
163 /// Solve - Solve for constants and executable blocks.
167 /// ResolveBranchesIn - While solving the dataflow for a function, we assume
168 /// that branches on undef values cannot reach any of their successors.
169 /// However, this is not a safe assumption. After we solve dataflow, this
170 /// method should be use to handle this. If this returns true, the solver
172 bool ResolveBranchesIn(Function &F);
174 /// getExecutableBlocks - Once we have solved for constants, return the set of
175 /// blocks that is known to be executable.
176 std::set<BasicBlock*> &getExecutableBlocks() {
180 /// getValueMapping - Once we have solved for constants, return the mapping of
181 /// LLVM values to LatticeVals.
182 hash_map<Value*, LatticeVal> &getValueMapping() {
186 /// getTrackedFunctionRetVals - Get the inferred return value map.
188 const hash_map<Function*, LatticeVal> &getTrackedFunctionRetVals() {
189 return TrackedFunctionRetVals;
192 /// getTrackedGlobals - Get and return the set of inferred initializers for
193 /// global variables.
194 const hash_map<GlobalVariable*, LatticeVal> &getTrackedGlobals() {
195 return TrackedGlobals;
200 // markConstant - Make a value be marked as "constant". If the value
201 // is not already a constant, add it to the instruction work list so that
202 // the users of the instruction are updated later.
204 inline void markConstant(LatticeVal &IV, Value *V, Constant *C) {
205 if (IV.markConstant(C)) {
206 DOUT << "markConstant: " << *C << ": " << *V;
207 InstWorkList.push_back(V);
210 inline void markConstant(Value *V, Constant *C) {
211 markConstant(ValueState[V], V, C);
214 // markOverdefined - Make a value be marked as "overdefined". If the
215 // value is not already overdefined, add it to the overdefined instruction
216 // work list so that the users of the instruction are updated later.
218 inline void markOverdefined(LatticeVal &IV, Value *V) {
219 if (IV.markOverdefined()) {
220 DEBUG(DOUT << "markOverdefined: ";
221 if (Function *F = dyn_cast<Function>(V))
222 DOUT << "Function '" << F->getName() << "'\n";
225 // Only instructions go on the work list
226 OverdefinedInstWorkList.push_back(V);
229 inline void markOverdefined(Value *V) {
230 markOverdefined(ValueState[V], V);
233 inline void mergeInValue(LatticeVal &IV, Value *V, LatticeVal &MergeWithV) {
234 if (IV.isOverdefined() || MergeWithV.isUndefined())
236 if (MergeWithV.isOverdefined())
237 markOverdefined(IV, V);
238 else if (IV.isUndefined())
239 markConstant(IV, V, MergeWithV.getConstant());
240 else if (IV.getConstant() != MergeWithV.getConstant())
241 markOverdefined(IV, V);
244 inline void mergeInValue(Value *V, LatticeVal &MergeWithV) {
245 return mergeInValue(ValueState[V], V, MergeWithV);
249 // getValueState - Return the LatticeVal object that corresponds to the value.
250 // This function is necessary because not all values should start out in the
251 // underdefined state... Argument's should be overdefined, and
252 // constants should be marked as constants. If a value is not known to be an
253 // Instruction object, then use this accessor to get its value from the map.
255 inline LatticeVal &getValueState(Value *V) {
256 hash_map<Value*, LatticeVal>::iterator I = ValueState.find(V);
257 if (I != ValueState.end()) return I->second; // Common case, in the map
259 if (Constant *CPV = dyn_cast<Constant>(V)) {
260 if (isa<UndefValue>(V)) {
261 // Nothing to do, remain undefined.
263 ValueState[CPV].markConstant(CPV); // Constants are constant
266 // All others are underdefined by default...
267 return ValueState[V];
270 // markEdgeExecutable - Mark a basic block as executable, adding it to the BB
271 // work list if it is not already executable...
273 void markEdgeExecutable(BasicBlock *Source, BasicBlock *Dest) {
274 if (!KnownFeasibleEdges.insert(Edge(Source, Dest)).second)
275 return; // This edge is already known to be executable!
277 if (BBExecutable.count(Dest)) {
278 DOUT << "Marking Edge Executable: " << Source->getName()
279 << " -> " << Dest->getName() << "\n";
281 // The destination is already executable, but we just made an edge
282 // feasible that wasn't before. Revisit the PHI nodes in the block
283 // because they have potentially new operands.
284 for (BasicBlock::iterator I = Dest->begin(); isa<PHINode>(I); ++I)
285 visitPHINode(*cast<PHINode>(I));
288 MarkBlockExecutable(Dest);
292 // getFeasibleSuccessors - Return a vector of booleans to indicate which
293 // successors are reachable from a given terminator instruction.
295 void getFeasibleSuccessors(TerminatorInst &TI, std::vector<bool> &Succs);
297 // isEdgeFeasible - Return true if the control flow edge from the 'From' basic
298 // block to the 'To' basic block is currently feasible...
300 bool isEdgeFeasible(BasicBlock *From, BasicBlock *To);
302 // OperandChangedState - This method is invoked on all of the users of an
303 // instruction that was just changed state somehow.... Based on this
304 // information, we need to update the specified user of this instruction.
306 void OperandChangedState(User *U) {
307 // Only instructions use other variable values!
308 Instruction &I = cast<Instruction>(*U);
309 if (BBExecutable.count(I.getParent())) // Inst is executable?
314 friend class InstVisitor<SCCPSolver>;
316 // visit implementations - Something changed in this instruction... Either an
317 // operand made a transition, or the instruction is newly executable. Change
318 // the value type of I to reflect these changes if appropriate.
320 void visitPHINode(PHINode &I);
323 void visitReturnInst(ReturnInst &I);
324 void visitTerminatorInst(TerminatorInst &TI);
326 void visitCastInst(CastInst &I);
327 void visitSelectInst(SelectInst &I);
328 void visitBinaryOperator(Instruction &I);
329 void visitShiftInst(ShiftInst &I) { visitBinaryOperator(I); }
330 void visitExtractElementInst(ExtractElementInst &I);
331 void visitInsertElementInst(InsertElementInst &I);
332 void visitShuffleVectorInst(ShuffleVectorInst &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 llvm_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::getFalse()] = true;
379 } else if (isa<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 llvm_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::getFalse()) == To;
438 } else if (isa<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 llvm_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()) {
600 if (ConstantBool *CondCB = dyn_cast<ConstantBool>(CondValue.getConstant())){
601 mergeInValue(&I, getValueState(CondCB->getValue() ? I.getTrueValue()
602 : I.getFalseValue()));
607 // Otherwise, the condition is overdefined or a constant we can't evaluate.
608 // See if we can produce something better than overdefined based on the T/F
610 LatticeVal &TVal = getValueState(I.getTrueValue());
611 LatticeVal &FVal = getValueState(I.getFalseValue());
613 // select ?, C, C -> C.
614 if (TVal.isConstant() && FVal.isConstant() &&
615 TVal.getConstant() == FVal.getConstant()) {
616 markConstant(&I, FVal.getConstant());
620 if (TVal.isUndefined()) { // select ?, undef, X -> X.
621 mergeInValue(&I, FVal);
622 } else if (FVal.isUndefined()) { // select ?, X, undef -> X.
623 mergeInValue(&I, TVal);
629 // Handle BinaryOperators and Shift Instructions...
630 void SCCPSolver::visitBinaryOperator(Instruction &I) {
631 LatticeVal &IV = ValueState[&I];
632 if (IV.isOverdefined()) return;
634 LatticeVal &V1State = getValueState(I.getOperand(0));
635 LatticeVal &V2State = getValueState(I.getOperand(1));
637 if (V1State.isOverdefined() || V2State.isOverdefined()) {
638 // If this is an AND or OR with 0 or -1, it doesn't matter that the other
639 // operand is overdefined.
640 if (I.getOpcode() == Instruction::And || I.getOpcode() == Instruction::Or) {
641 LatticeVal *NonOverdefVal = 0;
642 if (!V1State.isOverdefined()) {
643 NonOverdefVal = &V1State;
644 } else if (!V2State.isOverdefined()) {
645 NonOverdefVal = &V2State;
649 if (NonOverdefVal->isUndefined()) {
650 // Could annihilate value.
651 if (I.getOpcode() == Instruction::And)
652 markConstant(IV, &I, Constant::getNullValue(I.getType()));
654 markConstant(IV, &I, ConstantInt::getAllOnesValue(I.getType()));
657 if (I.getOpcode() == Instruction::And) {
658 if (NonOverdefVal->getConstant()->isNullValue()) {
659 markConstant(IV, &I, NonOverdefVal->getConstant());
660 return; // X or 0 = -1
663 if (ConstantIntegral *CI =
664 dyn_cast<ConstantIntegral>(NonOverdefVal->getConstant()))
665 if (CI->isAllOnesValue()) {
666 markConstant(IV, &I, NonOverdefVal->getConstant());
667 return; // X or -1 = -1
675 // If both operands are PHI nodes, it is possible that this instruction has
676 // a constant value, despite the fact that the PHI node doesn't. Check for
677 // this condition now.
678 if (PHINode *PN1 = dyn_cast<PHINode>(I.getOperand(0)))
679 if (PHINode *PN2 = dyn_cast<PHINode>(I.getOperand(1)))
680 if (PN1->getParent() == PN2->getParent()) {
681 // Since the two PHI nodes are in the same basic block, they must have
682 // entries for the same predecessors. Walk the predecessor list, and
683 // if all of the incoming values are constants, and the result of
684 // evaluating this expression with all incoming value pairs is the
685 // same, then this expression is a constant even though the PHI node
686 // is not a constant!
688 for (unsigned i = 0, e = PN1->getNumIncomingValues(); i != e; ++i) {
689 LatticeVal &In1 = getValueState(PN1->getIncomingValue(i));
690 BasicBlock *InBlock = PN1->getIncomingBlock(i);
692 getValueState(PN2->getIncomingValueForBlock(InBlock));
694 if (In1.isOverdefined() || In2.isOverdefined()) {
695 Result.markOverdefined();
696 break; // Cannot fold this operation over the PHI nodes!
697 } else if (In1.isConstant() && In2.isConstant()) {
698 Constant *V = ConstantExpr::get(I.getOpcode(), In1.getConstant(),
700 if (Result.isUndefined())
701 Result.markConstant(V);
702 else if (Result.isConstant() && Result.getConstant() != V) {
703 Result.markOverdefined();
709 // If we found a constant value here, then we know the instruction is
710 // constant despite the fact that the PHI nodes are overdefined.
711 if (Result.isConstant()) {
712 markConstant(IV, &I, Result.getConstant());
713 // Remember that this instruction is virtually using the PHI node
715 UsersOfOverdefinedPHIs.insert(std::make_pair(PN1, &I));
716 UsersOfOverdefinedPHIs.insert(std::make_pair(PN2, &I));
718 } else if (Result.isUndefined()) {
722 // Okay, this really is overdefined now. Since we might have
723 // speculatively thought that this was not overdefined before, and
724 // added ourselves to the UsersOfOverdefinedPHIs list for the PHIs,
725 // make sure to clean out any entries that we put there, for
727 std::multimap<PHINode*, Instruction*>::iterator It, E;
728 tie(It, E) = UsersOfOverdefinedPHIs.equal_range(PN1);
730 if (It->second == &I) {
731 UsersOfOverdefinedPHIs.erase(It++);
735 tie(It, E) = UsersOfOverdefinedPHIs.equal_range(PN2);
737 if (It->second == &I) {
738 UsersOfOverdefinedPHIs.erase(It++);
744 markOverdefined(IV, &I);
745 } else if (V1State.isConstant() && V2State.isConstant()) {
746 markConstant(IV, &I, ConstantExpr::get(I.getOpcode(), V1State.getConstant(),
747 V2State.getConstant()));
751 void SCCPSolver::visitExtractElementInst(ExtractElementInst &I) {
752 // FIXME : SCCP does not handle vectors properly.
757 LatticeVal &ValState = getValueState(I.getOperand(0));
758 LatticeVal &IdxState = getValueState(I.getOperand(1));
760 if (ValState.isOverdefined() || IdxState.isOverdefined())
762 else if(ValState.isConstant() && IdxState.isConstant())
763 markConstant(&I, ConstantExpr::getExtractElement(ValState.getConstant(),
764 IdxState.getConstant()));
768 void SCCPSolver::visitInsertElementInst(InsertElementInst &I) {
769 // FIXME : SCCP does not handle vectors properly.
773 LatticeVal &ValState = getValueState(I.getOperand(0));
774 LatticeVal &EltState = getValueState(I.getOperand(1));
775 LatticeVal &IdxState = getValueState(I.getOperand(2));
777 if (ValState.isOverdefined() || EltState.isOverdefined() ||
778 IdxState.isOverdefined())
780 else if(ValState.isConstant() && EltState.isConstant() &&
781 IdxState.isConstant())
782 markConstant(&I, ConstantExpr::getInsertElement(ValState.getConstant(),
783 EltState.getConstant(),
784 IdxState.getConstant()));
785 else if (ValState.isUndefined() && EltState.isConstant() &&
786 IdxState.isConstant())
787 markConstant(&I, ConstantExpr::getInsertElement(UndefValue::get(I.getType()),
788 EltState.getConstant(),
789 IdxState.getConstant()));
793 void SCCPSolver::visitShuffleVectorInst(ShuffleVectorInst &I) {
794 // FIXME : SCCP does not handle vectors properly.
798 LatticeVal &V1State = getValueState(I.getOperand(0));
799 LatticeVal &V2State = getValueState(I.getOperand(1));
800 LatticeVal &MaskState = getValueState(I.getOperand(2));
802 if (MaskState.isUndefined() ||
803 (V1State.isUndefined() && V2State.isUndefined()))
804 return; // Undefined output if mask or both inputs undefined.
806 if (V1State.isOverdefined() || V2State.isOverdefined() ||
807 MaskState.isOverdefined()) {
810 // A mix of constant/undef inputs.
811 Constant *V1 = V1State.isConstant() ?
812 V1State.getConstant() : UndefValue::get(I.getType());
813 Constant *V2 = V2State.isConstant() ?
814 V2State.getConstant() : UndefValue::get(I.getType());
815 Constant *Mask = MaskState.isConstant() ?
816 MaskState.getConstant() : UndefValue::get(I.getOperand(2)->getType());
817 markConstant(&I, ConstantExpr::getShuffleVector(V1, V2, Mask));
822 // Handle getelementptr instructions... if all operands are constants then we
823 // can turn this into a getelementptr ConstantExpr.
825 void SCCPSolver::visitGetElementPtrInst(GetElementPtrInst &I) {
826 LatticeVal &IV = ValueState[&I];
827 if (IV.isOverdefined()) return;
829 std::vector<Constant*> Operands;
830 Operands.reserve(I.getNumOperands());
832 for (unsigned i = 0, e = I.getNumOperands(); i != e; ++i) {
833 LatticeVal &State = getValueState(I.getOperand(i));
834 if (State.isUndefined())
835 return; // Operands are not resolved yet...
836 else if (State.isOverdefined()) {
837 markOverdefined(IV, &I);
840 assert(State.isConstant() && "Unknown state!");
841 Operands.push_back(State.getConstant());
844 Constant *Ptr = Operands[0];
845 Operands.erase(Operands.begin()); // Erase the pointer from idx list...
847 markConstant(IV, &I, ConstantExpr::getGetElementPtr(Ptr, Operands));
850 void SCCPSolver::visitStoreInst(Instruction &SI) {
851 if (TrackedGlobals.empty() || !isa<GlobalVariable>(SI.getOperand(1)))
853 GlobalVariable *GV = cast<GlobalVariable>(SI.getOperand(1));
854 hash_map<GlobalVariable*, LatticeVal>::iterator I = TrackedGlobals.find(GV);
855 if (I == TrackedGlobals.end() || I->second.isOverdefined()) return;
857 // Get the value we are storing into the global.
858 LatticeVal &PtrVal = getValueState(SI.getOperand(0));
860 mergeInValue(I->second, GV, PtrVal);
861 if (I->second.isOverdefined())
862 TrackedGlobals.erase(I); // No need to keep tracking this!
866 // Handle load instructions. If the operand is a constant pointer to a constant
867 // global, we can replace the load with the loaded constant value!
868 void SCCPSolver::visitLoadInst(LoadInst &I) {
869 LatticeVal &IV = ValueState[&I];
870 if (IV.isOverdefined()) return;
872 LatticeVal &PtrVal = getValueState(I.getOperand(0));
873 if (PtrVal.isUndefined()) return; // The pointer is not resolved yet!
874 if (PtrVal.isConstant() && !I.isVolatile()) {
875 Value *Ptr = PtrVal.getConstant();
876 if (isa<ConstantPointerNull>(Ptr)) {
878 markConstant(IV, &I, Constant::getNullValue(I.getType()));
882 // Transform load (constant global) into the value loaded.
883 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Ptr)) {
884 if (GV->isConstant()) {
885 if (!GV->isExternal()) {
886 markConstant(IV, &I, GV->getInitializer());
889 } else if (!TrackedGlobals.empty()) {
890 // If we are tracking this global, merge in the known value for it.
891 hash_map<GlobalVariable*, LatticeVal>::iterator It =
892 TrackedGlobals.find(GV);
893 if (It != TrackedGlobals.end()) {
894 mergeInValue(IV, &I, It->second);
900 // Transform load (constantexpr_GEP global, 0, ...) into the value loaded.
901 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr))
902 if (CE->getOpcode() == Instruction::GetElementPtr)
903 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(CE->getOperand(0)))
904 if (GV->isConstant() && !GV->isExternal())
906 ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE)) {
907 markConstant(IV, &I, V);
912 // Otherwise we cannot say for certain what value this load will produce.
914 markOverdefined(IV, &I);
917 void SCCPSolver::visitCallSite(CallSite CS) {
918 Function *F = CS.getCalledFunction();
920 // If we are tracking this function, we must make sure to bind arguments as
922 hash_map<Function*, LatticeVal>::iterator TFRVI =TrackedFunctionRetVals.end();
923 if (F && F->hasInternalLinkage())
924 TFRVI = TrackedFunctionRetVals.find(F);
926 if (TFRVI != TrackedFunctionRetVals.end()) {
927 // If this is the first call to the function hit, mark its entry block
929 if (!BBExecutable.count(F->begin()))
930 MarkBlockExecutable(F->begin());
932 CallSite::arg_iterator CAI = CS.arg_begin();
933 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
934 AI != E; ++AI, ++CAI) {
935 LatticeVal &IV = ValueState[AI];
936 if (!IV.isOverdefined())
937 mergeInValue(IV, AI, getValueState(*CAI));
940 Instruction *I = CS.getInstruction();
941 if (I->getType() == Type::VoidTy) return;
943 LatticeVal &IV = ValueState[I];
944 if (IV.isOverdefined()) return;
946 // Propagate the return value of the function to the value of the instruction.
947 if (TFRVI != TrackedFunctionRetVals.end()) {
948 mergeInValue(IV, I, TFRVI->second);
952 if (F == 0 || !F->isExternal() || !canConstantFoldCallTo(F)) {
953 markOverdefined(IV, I);
957 std::vector<Constant*> Operands;
958 Operands.reserve(I->getNumOperands()-1);
960 for (CallSite::arg_iterator AI = CS.arg_begin(), E = CS.arg_end();
962 LatticeVal &State = getValueState(*AI);
963 if (State.isUndefined())
964 return; // Operands are not resolved yet...
965 else if (State.isOverdefined()) {
966 markOverdefined(IV, I);
969 assert(State.isConstant() && "Unknown state!");
970 Operands.push_back(State.getConstant());
973 if (Constant *C = ConstantFoldCall(F, Operands))
974 markConstant(IV, I, C);
976 markOverdefined(IV, I);
980 void SCCPSolver::Solve() {
981 // Process the work lists until they are empty!
982 while (!BBWorkList.empty() || !InstWorkList.empty() ||
983 !OverdefinedInstWorkList.empty()) {
984 // Process the instruction work list...
985 while (!OverdefinedInstWorkList.empty()) {
986 Value *I = OverdefinedInstWorkList.back();
987 OverdefinedInstWorkList.pop_back();
989 DOUT << "\nPopped off OI-WL: " << *I;
991 // "I" got into the work list because it either made the transition from
992 // bottom to constant
994 // Anything on this worklist that is overdefined need not be visited
995 // since all of its users will have already been marked as overdefined
996 // Update all of the users of this instruction's value...
998 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
1000 OperandChangedState(*UI);
1002 // Process the instruction work list...
1003 while (!InstWorkList.empty()) {
1004 Value *I = InstWorkList.back();
1005 InstWorkList.pop_back();
1007 DOUT << "\nPopped off I-WL: " << *I;
1009 // "I" got into the work list because it either made the transition from
1010 // bottom to constant
1012 // Anything on this worklist that is overdefined need not be visited
1013 // since all of its users will have already been marked as overdefined.
1014 // Update all of the users of this instruction's value...
1016 if (!getValueState(I).isOverdefined())
1017 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
1019 OperandChangedState(*UI);
1022 // Process the basic block work list...
1023 while (!BBWorkList.empty()) {
1024 BasicBlock *BB = BBWorkList.back();
1025 BBWorkList.pop_back();
1027 DOUT << "\nPopped off BBWL: " << *BB;
1029 // Notify all instructions in this basic block that they are newly
1036 /// ResolveBranchesIn - While solving the dataflow for a function, we assume
1037 /// that branches on undef values cannot reach any of their successors.
1038 /// However, this is not a safe assumption. After we solve dataflow, this
1039 /// method should be use to handle this. If this returns true, the solver
1040 /// should be rerun.
1042 /// This method handles this by finding an unresolved branch and marking it one
1043 /// of the edges from the block as being feasible, even though the condition
1044 /// doesn't say it would otherwise be. This allows SCCP to find the rest of the
1045 /// CFG and only slightly pessimizes the analysis results (by marking one,
1046 /// potentially unfeasible, edge feasible). This cannot usefully modify the
1047 /// constraints on the condition of the branch, as that would impact other users
1049 bool SCCPSolver::ResolveBranchesIn(Function &F) {
1050 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
1051 if (!BBExecutable.count(BB))
1054 TerminatorInst *TI = BB->getTerminator();
1055 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
1056 if (!BI->isConditional()) continue;
1057 if (!getValueState(BI->getCondition()).isUndefined())
1059 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
1060 if (!getValueState(SI->getCondition()).isUndefined())
1066 // If the edge to the first successor isn't thought to be feasible yet, mark
1068 if (KnownFeasibleEdges.count(Edge(BB, TI->getSuccessor(0))))
1071 // Otherwise, it isn't already thought to be feasible. Mark it as such now
1072 // and return. This will make other blocks reachable, which will allow new
1073 // values to be discovered and existing ones to be moved in the lattice.
1074 markEdgeExecutable(BB, TI->getSuccessor(0));
1083 Statistic NumInstRemoved("sccp", "Number of instructions removed");
1084 Statistic NumDeadBlocks ("sccp", "Number of basic blocks unreachable");
1086 //===--------------------------------------------------------------------===//
1088 /// SCCP Class - This class uses the SCCPSolver to implement a per-function
1089 /// Sparse Conditional COnstant Propagator.
1091 struct SCCP : public FunctionPass {
1092 // runOnFunction - Run the Sparse Conditional Constant Propagation
1093 // algorithm, and return true if the function was modified.
1095 bool runOnFunction(Function &F);
1097 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
1098 AU.setPreservesCFG();
1102 RegisterPass<SCCP> X("sccp", "Sparse Conditional Constant Propagation");
1103 } // end anonymous namespace
1106 // createSCCPPass - This is the public interface to this file...
1107 FunctionPass *llvm::createSCCPPass() {
1112 // runOnFunction() - Run the Sparse Conditional Constant Propagation algorithm,
1113 // and return true if the function was modified.
1115 bool SCCP::runOnFunction(Function &F) {
1116 DOUT << "SCCP on function '" << F.getName() << "'\n";
1119 // Mark the first block of the function as being executable.
1120 Solver.MarkBlockExecutable(F.begin());
1122 // Mark all arguments to the function as being overdefined.
1123 hash_map<Value*, LatticeVal> &Values = Solver.getValueMapping();
1124 for (Function::arg_iterator AI = F.arg_begin(), E = F.arg_end(); AI != E; ++AI)
1125 Values[AI].markOverdefined();
1127 // Solve for constants.
1128 bool ResolvedBranches = true;
1129 while (ResolvedBranches) {
1131 DOUT << "RESOLVING UNDEF BRANCHES\n";
1132 ResolvedBranches = Solver.ResolveBranchesIn(F);
1135 bool MadeChanges = false;
1137 // If we decided that there are basic blocks that are dead in this function,
1138 // delete their contents now. Note that we cannot actually delete the blocks,
1139 // as we cannot modify the CFG of the function.
1141 std::set<BasicBlock*> &ExecutableBBs = Solver.getExecutableBlocks();
1142 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
1143 if (!ExecutableBBs.count(BB)) {
1144 DOUT << " BasicBlock Dead:" << *BB;
1147 // Delete the instructions backwards, as it has a reduced likelihood of
1148 // having to update as many def-use and use-def chains.
1149 std::vector<Instruction*> Insts;
1150 for (BasicBlock::iterator I = BB->begin(), E = BB->getTerminator();
1153 while (!Insts.empty()) {
1154 Instruction *I = Insts.back();
1156 if (!I->use_empty())
1157 I->replaceAllUsesWith(UndefValue::get(I->getType()));
1158 BB->getInstList().erase(I);
1163 // Iterate over all of the instructions in a function, replacing them with
1164 // constants if we have found them to be of constant values.
1166 for (BasicBlock::iterator BI = BB->begin(), E = BB->end(); BI != E; ) {
1167 Instruction *Inst = BI++;
1168 if (Inst->getType() != Type::VoidTy) {
1169 LatticeVal &IV = Values[Inst];
1170 if (IV.isConstant() || IV.isUndefined() &&
1171 !isa<TerminatorInst>(Inst)) {
1172 Constant *Const = IV.isConstant()
1173 ? IV.getConstant() : UndefValue::get(Inst->getType());
1174 DOUT << " Constant: " << *Const << " = " << *Inst;
1176 // Replaces all of the uses of a variable with uses of the constant.
1177 Inst->replaceAllUsesWith(Const);
1179 // Delete the instruction.
1180 BB->getInstList().erase(Inst);
1182 // Hey, we just changed something!
1194 Statistic IPNumInstRemoved("ipsccp", "Number of instructions removed");
1195 Statistic IPNumDeadBlocks ("ipsccp", "Number of basic blocks unreachable");
1196 Statistic IPNumArgsElimed ("ipsccp",
1197 "Number of arguments constant propagated");
1198 Statistic IPNumGlobalConst("ipsccp",
1199 "Number of globals found to be constant");
1201 //===--------------------------------------------------------------------===//
1203 /// IPSCCP Class - This class implements interprocedural Sparse Conditional
1204 /// Constant Propagation.
1206 struct IPSCCP : public ModulePass {
1207 bool runOnModule(Module &M);
1210 RegisterPass<IPSCCP>
1211 Y("ipsccp", "Interprocedural Sparse Conditional Constant Propagation");
1212 } // end anonymous namespace
1214 // createIPSCCPPass - This is the public interface to this file...
1215 ModulePass *llvm::createIPSCCPPass() {
1216 return new IPSCCP();
1220 static bool AddressIsTaken(GlobalValue *GV) {
1221 // Delete any dead constantexpr klingons.
1222 GV->removeDeadConstantUsers();
1224 for (Value::use_iterator UI = GV->use_begin(), E = GV->use_end();
1226 if (StoreInst *SI = dyn_cast<StoreInst>(*UI)) {
1227 if (SI->getOperand(0) == GV || SI->isVolatile())
1228 return true; // Storing addr of GV.
1229 } else if (isa<InvokeInst>(*UI) || isa<CallInst>(*UI)) {
1230 // Make sure we are calling the function, not passing the address.
1231 CallSite CS = CallSite::get(cast<Instruction>(*UI));
1232 for (CallSite::arg_iterator AI = CS.arg_begin(),
1233 E = CS.arg_end(); AI != E; ++AI)
1236 } else if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) {
1237 if (LI->isVolatile())
1245 bool IPSCCP::runOnModule(Module &M) {
1248 // Loop over all functions, marking arguments to those with their addresses
1249 // taken or that are external as overdefined.
1251 hash_map<Value*, LatticeVal> &Values = Solver.getValueMapping();
1252 for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F)
1253 if (!F->hasInternalLinkage() || AddressIsTaken(F)) {
1254 if (!F->isExternal())
1255 Solver.MarkBlockExecutable(F->begin());
1256 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
1258 Values[AI].markOverdefined();
1260 Solver.AddTrackedFunction(F);
1263 // Loop over global variables. We inform the solver about any internal global
1264 // variables that do not have their 'addresses taken'. If they don't have
1265 // their addresses taken, we can propagate constants through them.
1266 for (Module::global_iterator G = M.global_begin(), E = M.global_end();
1268 if (!G->isConstant() && G->hasInternalLinkage() && !AddressIsTaken(G))
1269 Solver.TrackValueOfGlobalVariable(G);
1271 // Solve for constants.
1272 bool ResolvedBranches = true;
1273 while (ResolvedBranches) {
1276 DOUT << "RESOLVING UNDEF BRANCHES\n";
1277 ResolvedBranches = false;
1278 for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F)
1279 ResolvedBranches |= Solver.ResolveBranchesIn(*F);
1282 bool MadeChanges = false;
1284 // Iterate over all of the instructions in the module, replacing them with
1285 // constants if we have found them to be of constant values.
1287 std::set<BasicBlock*> &ExecutableBBs = Solver.getExecutableBlocks();
1288 for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) {
1289 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
1291 if (!AI->use_empty()) {
1292 LatticeVal &IV = Values[AI];
1293 if (IV.isConstant() || IV.isUndefined()) {
1294 Constant *CST = IV.isConstant() ?
1295 IV.getConstant() : UndefValue::get(AI->getType());
1296 DOUT << "*** Arg " << *AI << " = " << *CST <<"\n";
1298 // Replaces all of the uses of a variable with uses of the
1300 AI->replaceAllUsesWith(CST);
1305 std::vector<BasicBlock*> BlocksToErase;
1306 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
1307 if (!ExecutableBBs.count(BB)) {
1308 DOUT << " BasicBlock Dead:" << *BB;
1311 // Delete the instructions backwards, as it has a reduced likelihood of
1312 // having to update as many def-use and use-def chains.
1313 std::vector<Instruction*> Insts;
1314 TerminatorInst *TI = BB->getTerminator();
1315 for (BasicBlock::iterator I = BB->begin(), E = TI; I != E; ++I)
1318 while (!Insts.empty()) {
1319 Instruction *I = Insts.back();
1321 if (!I->use_empty())
1322 I->replaceAllUsesWith(UndefValue::get(I->getType()));
1323 BB->getInstList().erase(I);
1328 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) {
1329 BasicBlock *Succ = TI->getSuccessor(i);
1330 if (Succ->begin() != Succ->end() && isa<PHINode>(Succ->begin()))
1331 TI->getSuccessor(i)->removePredecessor(BB);
1333 if (!TI->use_empty())
1334 TI->replaceAllUsesWith(UndefValue::get(TI->getType()));
1335 BB->getInstList().erase(TI);
1337 if (&*BB != &F->front())
1338 BlocksToErase.push_back(BB);
1340 new UnreachableInst(BB);
1343 for (BasicBlock::iterator BI = BB->begin(), E = BB->end(); BI != E; ) {
1344 Instruction *Inst = BI++;
1345 if (Inst->getType() != Type::VoidTy) {
1346 LatticeVal &IV = Values[Inst];
1347 if (IV.isConstant() || IV.isUndefined() &&
1348 !isa<TerminatorInst>(Inst)) {
1349 Constant *Const = IV.isConstant()
1350 ? IV.getConstant() : UndefValue::get(Inst->getType());
1351 DOUT << " Constant: " << *Const << " = " << *Inst;
1353 // Replaces all of the uses of a variable with uses of the
1355 Inst->replaceAllUsesWith(Const);
1357 // Delete the instruction.
1358 if (!isa<TerminatorInst>(Inst) && !isa<CallInst>(Inst))
1359 BB->getInstList().erase(Inst);
1361 // Hey, we just changed something!
1369 // Now that all instructions in the function are constant folded, erase dead
1370 // blocks, because we can now use ConstantFoldTerminator to get rid of
1372 for (unsigned i = 0, e = BlocksToErase.size(); i != e; ++i) {
1373 // If there are any PHI nodes in this successor, drop entries for BB now.
1374 BasicBlock *DeadBB = BlocksToErase[i];
1375 while (!DeadBB->use_empty()) {
1376 Instruction *I = cast<Instruction>(DeadBB->use_back());
1377 bool Folded = ConstantFoldTerminator(I->getParent());
1379 // The constant folder may not have been able to fold the termiantor
1380 // if this is a branch or switch on undef. Fold it manually as a
1381 // branch to the first successor.
1382 if (BranchInst *BI = dyn_cast<BranchInst>(I)) {
1383 assert(BI->isConditional() && isa<UndefValue>(BI->getCondition()) &&
1384 "Branch should be foldable!");
1385 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(I)) {
1386 assert(isa<UndefValue>(SI->getCondition()) && "Switch should fold");
1388 assert(0 && "Didn't fold away reference to block!");
1391 // Make this an uncond branch to the first successor.
1392 TerminatorInst *TI = I->getParent()->getTerminator();
1393 new BranchInst(TI->getSuccessor(0), TI);
1395 // Remove entries in successor phi nodes to remove edges.
1396 for (unsigned i = 1, e = TI->getNumSuccessors(); i != e; ++i)
1397 TI->getSuccessor(i)->removePredecessor(TI->getParent());
1399 // Remove the old terminator.
1400 TI->eraseFromParent();
1404 // Finally, delete the basic block.
1405 F->getBasicBlockList().erase(DeadBB);
1409 // If we inferred constant or undef return values for a function, we replaced
1410 // all call uses with the inferred value. This means we don't need to bother
1411 // actually returning anything from the function. Replace all return
1412 // instructions with return undef.
1413 const hash_map<Function*, LatticeVal> &RV =Solver.getTrackedFunctionRetVals();
1414 for (hash_map<Function*, LatticeVal>::const_iterator I = RV.begin(),
1415 E = RV.end(); I != E; ++I)
1416 if (!I->second.isOverdefined() &&
1417 I->first->getReturnType() != Type::VoidTy) {
1418 Function *F = I->first;
1419 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
1420 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator()))
1421 if (!isa<UndefValue>(RI->getOperand(0)))
1422 RI->setOperand(0, UndefValue::get(F->getReturnType()));
1425 // If we infered constant or undef values for globals variables, we can delete
1426 // the global and any stores that remain to it.
1427 const hash_map<GlobalVariable*, LatticeVal> &TG = Solver.getTrackedGlobals();
1428 for (hash_map<GlobalVariable*, LatticeVal>::const_iterator I = TG.begin(),
1429 E = TG.end(); I != E; ++I) {
1430 GlobalVariable *GV = I->first;
1431 assert(!I->second.isOverdefined() &&
1432 "Overdefined values should have been taken out of the map!");
1433 DOUT << "Found that GV '" << GV->getName()<< "' is constant!\n";
1434 while (!GV->use_empty()) {
1435 StoreInst *SI = cast<StoreInst>(GV->use_back());
1436 SI->eraseFromParent();
1438 M.getGlobalList().erase(GV);