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 LatticeVal &ValState = getValueState(I.getOperand(0));
753 LatticeVal &IdxState = getValueState(I.getOperand(1));
755 if (ValState.isOverdefined() || IdxState.isOverdefined())
757 else if(ValState.isConstant() && IdxState.isConstant())
758 markConstant(&I, ConstantExpr::getExtractElement(ValState.getConstant(),
759 IdxState.getConstant()));
762 void SCCPSolver::visitInsertElementInst(InsertElementInst &I) {
763 LatticeVal &ValState = getValueState(I.getOperand(0));
764 LatticeVal &EltState = getValueState(I.getOperand(1));
765 LatticeVal &IdxState = getValueState(I.getOperand(2));
767 if (ValState.isOverdefined() || EltState.isOverdefined() ||
768 IdxState.isOverdefined())
770 else if(ValState.isConstant() && EltState.isConstant() &&
771 IdxState.isConstant())
772 markConstant(&I, ConstantExpr::getInsertElement(ValState.getConstant(),
773 EltState.getConstant(),
774 IdxState.getConstant()));
775 else if (ValState.isUndefined() && EltState.isConstant() &&
776 IdxState.isConstant())
777 markConstant(&I, ConstantExpr::getInsertElement(UndefValue::get(I.getType()),
778 EltState.getConstant(),
779 IdxState.getConstant()));
782 void SCCPSolver::visitShuffleVectorInst(ShuffleVectorInst &I) {
783 LatticeVal &V1State = getValueState(I.getOperand(0));
784 LatticeVal &V2State = getValueState(I.getOperand(1));
785 LatticeVal &MaskState = getValueState(I.getOperand(2));
787 if (MaskState.isUndefined() ||
788 (V1State.isUndefined() && V2State.isUndefined()))
789 return; // Undefined output if mask or both inputs undefined.
791 if (V1State.isOverdefined() || V2State.isOverdefined() ||
792 MaskState.isOverdefined()) {
795 // A mix of constant/undef inputs.
796 Constant *V1 = V1State.isConstant() ?
797 V1State.getConstant() : UndefValue::get(I.getType());
798 Constant *V2 = V2State.isConstant() ?
799 V2State.getConstant() : UndefValue::get(I.getType());
800 Constant *Mask = MaskState.isConstant() ?
801 MaskState.getConstant() : UndefValue::get(I.getOperand(2)->getType());
802 markConstant(&I, ConstantExpr::getShuffleVector(V1, V2, Mask));
806 // Handle getelementptr instructions... if all operands are constants then we
807 // can turn this into a getelementptr ConstantExpr.
809 void SCCPSolver::visitGetElementPtrInst(GetElementPtrInst &I) {
810 LatticeVal &IV = ValueState[&I];
811 if (IV.isOverdefined()) return;
813 std::vector<Constant*> Operands;
814 Operands.reserve(I.getNumOperands());
816 for (unsigned i = 0, e = I.getNumOperands(); i != e; ++i) {
817 LatticeVal &State = getValueState(I.getOperand(i));
818 if (State.isUndefined())
819 return; // Operands are not resolved yet...
820 else if (State.isOverdefined()) {
821 markOverdefined(IV, &I);
824 assert(State.isConstant() && "Unknown state!");
825 Operands.push_back(State.getConstant());
828 Constant *Ptr = Operands[0];
829 Operands.erase(Operands.begin()); // Erase the pointer from idx list...
831 markConstant(IV, &I, ConstantExpr::getGetElementPtr(Ptr, Operands));
834 void SCCPSolver::visitStoreInst(Instruction &SI) {
835 if (TrackedGlobals.empty() || !isa<GlobalVariable>(SI.getOperand(1)))
837 GlobalVariable *GV = cast<GlobalVariable>(SI.getOperand(1));
838 hash_map<GlobalVariable*, LatticeVal>::iterator I = TrackedGlobals.find(GV);
839 if (I == TrackedGlobals.end() || I->second.isOverdefined()) return;
841 // Get the value we are storing into the global.
842 LatticeVal &PtrVal = getValueState(SI.getOperand(0));
844 mergeInValue(I->second, GV, PtrVal);
845 if (I->second.isOverdefined())
846 TrackedGlobals.erase(I); // No need to keep tracking this!
850 // Handle load instructions. If the operand is a constant pointer to a constant
851 // global, we can replace the load with the loaded constant value!
852 void SCCPSolver::visitLoadInst(LoadInst &I) {
853 LatticeVal &IV = ValueState[&I];
854 if (IV.isOverdefined()) return;
856 LatticeVal &PtrVal = getValueState(I.getOperand(0));
857 if (PtrVal.isUndefined()) return; // The pointer is not resolved yet!
858 if (PtrVal.isConstant() && !I.isVolatile()) {
859 Value *Ptr = PtrVal.getConstant();
860 if (isa<ConstantPointerNull>(Ptr)) {
862 markConstant(IV, &I, Constant::getNullValue(I.getType()));
866 // Transform load (constant global) into the value loaded.
867 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Ptr)) {
868 if (GV->isConstant()) {
869 if (!GV->isExternal()) {
870 markConstant(IV, &I, GV->getInitializer());
873 } else if (!TrackedGlobals.empty()) {
874 // If we are tracking this global, merge in the known value for it.
875 hash_map<GlobalVariable*, LatticeVal>::iterator It =
876 TrackedGlobals.find(GV);
877 if (It != TrackedGlobals.end()) {
878 mergeInValue(IV, &I, It->second);
884 // Transform load (constantexpr_GEP global, 0, ...) into the value loaded.
885 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr))
886 if (CE->getOpcode() == Instruction::GetElementPtr)
887 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(CE->getOperand(0)))
888 if (GV->isConstant() && !GV->isExternal())
890 ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE)) {
891 markConstant(IV, &I, V);
896 // Otherwise we cannot say for certain what value this load will produce.
898 markOverdefined(IV, &I);
901 void SCCPSolver::visitCallSite(CallSite CS) {
902 Function *F = CS.getCalledFunction();
904 // If we are tracking this function, we must make sure to bind arguments as
906 hash_map<Function*, LatticeVal>::iterator TFRVI =TrackedFunctionRetVals.end();
907 if (F && F->hasInternalLinkage())
908 TFRVI = TrackedFunctionRetVals.find(F);
910 if (TFRVI != TrackedFunctionRetVals.end()) {
911 // If this is the first call to the function hit, mark its entry block
913 if (!BBExecutable.count(F->begin()))
914 MarkBlockExecutable(F->begin());
916 CallSite::arg_iterator CAI = CS.arg_begin();
917 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
918 AI != E; ++AI, ++CAI) {
919 LatticeVal &IV = ValueState[AI];
920 if (!IV.isOverdefined())
921 mergeInValue(IV, AI, getValueState(*CAI));
924 Instruction *I = CS.getInstruction();
925 if (I->getType() == Type::VoidTy) return;
927 LatticeVal &IV = ValueState[I];
928 if (IV.isOverdefined()) return;
930 // Propagate the return value of the function to the value of the instruction.
931 if (TFRVI != TrackedFunctionRetVals.end()) {
932 mergeInValue(IV, I, TFRVI->second);
936 if (F == 0 || !F->isExternal() || !canConstantFoldCallTo(F)) {
937 markOverdefined(IV, I);
941 std::vector<Constant*> Operands;
942 Operands.reserve(I->getNumOperands()-1);
944 for (CallSite::arg_iterator AI = CS.arg_begin(), E = CS.arg_end();
946 LatticeVal &State = getValueState(*AI);
947 if (State.isUndefined())
948 return; // Operands are not resolved yet...
949 else if (State.isOverdefined()) {
950 markOverdefined(IV, I);
953 assert(State.isConstant() && "Unknown state!");
954 Operands.push_back(State.getConstant());
957 if (Constant *C = ConstantFoldCall(F, Operands))
958 markConstant(IV, I, C);
960 markOverdefined(IV, I);
964 void SCCPSolver::Solve() {
965 // Process the work lists until they are empty!
966 while (!BBWorkList.empty() || !InstWorkList.empty() ||
967 !OverdefinedInstWorkList.empty()) {
968 // Process the instruction work list...
969 while (!OverdefinedInstWorkList.empty()) {
970 Value *I = OverdefinedInstWorkList.back();
971 OverdefinedInstWorkList.pop_back();
973 DOUT << "\nPopped off OI-WL: " << *I;
975 // "I" got into the work list because it either made the transition from
976 // bottom to constant
978 // Anything on this worklist that is overdefined need not be visited
979 // since all of its users will have already been marked as overdefined
980 // Update all of the users of this instruction's value...
982 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
984 OperandChangedState(*UI);
986 // Process the instruction work list...
987 while (!InstWorkList.empty()) {
988 Value *I = InstWorkList.back();
989 InstWorkList.pop_back();
991 DOUT << "\nPopped off I-WL: " << *I;
993 // "I" got into the work list because it either made the transition from
994 // bottom to constant
996 // Anything on this worklist that is overdefined need not be visited
997 // since all of its users will have already been marked as overdefined.
998 // Update all of the users of this instruction's value...
1000 if (!getValueState(I).isOverdefined())
1001 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
1003 OperandChangedState(*UI);
1006 // Process the basic block work list...
1007 while (!BBWorkList.empty()) {
1008 BasicBlock *BB = BBWorkList.back();
1009 BBWorkList.pop_back();
1011 DOUT << "\nPopped off BBWL: " << *BB;
1013 // Notify all instructions in this basic block that they are newly
1020 /// ResolveBranchesIn - While solving the dataflow for a function, we assume
1021 /// that branches on undef values cannot reach any of their successors.
1022 /// However, this is not a safe assumption. After we solve dataflow, this
1023 /// method should be use to handle this. If this returns true, the solver
1024 /// should be rerun.
1026 /// This method handles this by finding an unresolved branch and marking it one
1027 /// of the edges from the block as being feasible, even though the condition
1028 /// doesn't say it would otherwise be. This allows SCCP to find the rest of the
1029 /// CFG and only slightly pessimizes the analysis results (by marking one,
1030 /// potentially unfeasible, edge feasible). This cannot usefully modify the
1031 /// constraints on the condition of the branch, as that would impact other users
1033 bool SCCPSolver::ResolveBranchesIn(Function &F) {
1034 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
1035 if (!BBExecutable.count(BB))
1038 TerminatorInst *TI = BB->getTerminator();
1039 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
1040 if (!BI->isConditional()) continue;
1041 if (!getValueState(BI->getCondition()).isUndefined())
1043 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
1044 if (!getValueState(SI->getCondition()).isUndefined())
1050 // If the edge to the first successor isn't thought to be feasible yet, mark
1052 if (KnownFeasibleEdges.count(Edge(BB, TI->getSuccessor(0))))
1055 // Otherwise, it isn't already thought to be feasible. Mark it as such now
1056 // and return. This will make other blocks reachable, which will allow new
1057 // values to be discovered and existing ones to be moved in the lattice.
1058 markEdgeExecutable(BB, TI->getSuccessor(0));
1067 Statistic<> NumInstRemoved("sccp", "Number of instructions removed");
1068 Statistic<> NumDeadBlocks ("sccp", "Number of basic blocks unreachable");
1070 //===--------------------------------------------------------------------===//
1072 /// SCCP Class - This class uses the SCCPSolver to implement a per-function
1073 /// Sparse Conditional COnstant Propagator.
1075 struct SCCP : public FunctionPass {
1076 // runOnFunction - Run the Sparse Conditional Constant Propagation
1077 // algorithm, and return true if the function was modified.
1079 bool runOnFunction(Function &F);
1081 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
1082 AU.setPreservesCFG();
1086 RegisterPass<SCCP> X("sccp", "Sparse Conditional Constant Propagation");
1087 } // end anonymous namespace
1090 // createSCCPPass - This is the public interface to this file...
1091 FunctionPass *llvm::createSCCPPass() {
1096 // runOnFunction() - Run the Sparse Conditional Constant Propagation algorithm,
1097 // and return true if the function was modified.
1099 bool SCCP::runOnFunction(Function &F) {
1100 DOUT << "SCCP on function '" << F.getName() << "'\n";
1103 // Mark the first block of the function as being executable.
1104 Solver.MarkBlockExecutable(F.begin());
1106 // Mark all arguments to the function as being overdefined.
1107 hash_map<Value*, LatticeVal> &Values = Solver.getValueMapping();
1108 for (Function::arg_iterator AI = F.arg_begin(), E = F.arg_end(); AI != E; ++AI)
1109 Values[AI].markOverdefined();
1111 // Solve for constants.
1112 bool ResolvedBranches = true;
1113 while (ResolvedBranches) {
1115 DOUT << "RESOLVING UNDEF BRANCHES\n";
1116 ResolvedBranches = Solver.ResolveBranchesIn(F);
1119 bool MadeChanges = false;
1121 // If we decided that there are basic blocks that are dead in this function,
1122 // delete their contents now. Note that we cannot actually delete the blocks,
1123 // as we cannot modify the CFG of the function.
1125 std::set<BasicBlock*> &ExecutableBBs = Solver.getExecutableBlocks();
1126 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
1127 if (!ExecutableBBs.count(BB)) {
1128 DOUT << " BasicBlock Dead:" << *BB;
1131 // Delete the instructions backwards, as it has a reduced likelihood of
1132 // having to update as many def-use and use-def chains.
1133 std::vector<Instruction*> Insts;
1134 for (BasicBlock::iterator I = BB->begin(), E = BB->getTerminator();
1137 while (!Insts.empty()) {
1138 Instruction *I = Insts.back();
1140 if (!I->use_empty())
1141 I->replaceAllUsesWith(UndefValue::get(I->getType()));
1142 BB->getInstList().erase(I);
1147 // Iterate over all of the instructions in a function, replacing them with
1148 // constants if we have found them to be of constant values.
1150 for (BasicBlock::iterator BI = BB->begin(), E = BB->end(); BI != E; ) {
1151 Instruction *Inst = BI++;
1152 if (Inst->getType() != Type::VoidTy) {
1153 LatticeVal &IV = Values[Inst];
1154 if (IV.isConstant() || IV.isUndefined() &&
1155 !isa<TerminatorInst>(Inst)) {
1156 Constant *Const = IV.isConstant()
1157 ? IV.getConstant() : UndefValue::get(Inst->getType());
1158 DOUT << " Constant: " << *Const << " = " << *Inst;
1160 // Replaces all of the uses of a variable with uses of the constant.
1161 Inst->replaceAllUsesWith(Const);
1163 // Delete the instruction.
1164 BB->getInstList().erase(Inst);
1166 // Hey, we just changed something!
1178 Statistic<> IPNumInstRemoved("ipsccp", "Number of instructions removed");
1179 Statistic<> IPNumDeadBlocks ("ipsccp", "Number of basic blocks unreachable");
1180 Statistic<> IPNumArgsElimed ("ipsccp",
1181 "Number of arguments constant propagated");
1182 Statistic<> IPNumGlobalConst("ipsccp",
1183 "Number of globals found to be constant");
1185 //===--------------------------------------------------------------------===//
1187 /// IPSCCP Class - This class implements interprocedural Sparse Conditional
1188 /// Constant Propagation.
1190 struct IPSCCP : public ModulePass {
1191 bool runOnModule(Module &M);
1194 RegisterPass<IPSCCP>
1195 Y("ipsccp", "Interprocedural Sparse Conditional Constant Propagation");
1196 } // end anonymous namespace
1198 // createIPSCCPPass - This is the public interface to this file...
1199 ModulePass *llvm::createIPSCCPPass() {
1200 return new IPSCCP();
1204 static bool AddressIsTaken(GlobalValue *GV) {
1205 // Delete any dead constantexpr klingons.
1206 GV->removeDeadConstantUsers();
1208 for (Value::use_iterator UI = GV->use_begin(), E = GV->use_end();
1210 if (StoreInst *SI = dyn_cast<StoreInst>(*UI)) {
1211 if (SI->getOperand(0) == GV || SI->isVolatile())
1212 return true; // Storing addr of GV.
1213 } else if (isa<InvokeInst>(*UI) || isa<CallInst>(*UI)) {
1214 // Make sure we are calling the function, not passing the address.
1215 CallSite CS = CallSite::get(cast<Instruction>(*UI));
1216 for (CallSite::arg_iterator AI = CS.arg_begin(),
1217 E = CS.arg_end(); AI != E; ++AI)
1220 } else if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) {
1221 if (LI->isVolatile())
1229 bool IPSCCP::runOnModule(Module &M) {
1232 // Loop over all functions, marking arguments to those with their addresses
1233 // taken or that are external as overdefined.
1235 hash_map<Value*, LatticeVal> &Values = Solver.getValueMapping();
1236 for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F)
1237 if (!F->hasInternalLinkage() || AddressIsTaken(F)) {
1238 if (!F->isExternal())
1239 Solver.MarkBlockExecutable(F->begin());
1240 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
1242 Values[AI].markOverdefined();
1244 Solver.AddTrackedFunction(F);
1247 // Loop over global variables. We inform the solver about any internal global
1248 // variables that do not have their 'addresses taken'. If they don't have
1249 // their addresses taken, we can propagate constants through them.
1250 for (Module::global_iterator G = M.global_begin(), E = M.global_end();
1252 if (!G->isConstant() && G->hasInternalLinkage() && !AddressIsTaken(G))
1253 Solver.TrackValueOfGlobalVariable(G);
1255 // Solve for constants.
1256 bool ResolvedBranches = true;
1257 while (ResolvedBranches) {
1260 DOUT << "RESOLVING UNDEF BRANCHES\n";
1261 ResolvedBranches = false;
1262 for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F)
1263 ResolvedBranches |= Solver.ResolveBranchesIn(*F);
1266 bool MadeChanges = false;
1268 // Iterate over all of the instructions in the module, replacing them with
1269 // constants if we have found them to be of constant values.
1271 std::set<BasicBlock*> &ExecutableBBs = Solver.getExecutableBlocks();
1272 for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) {
1273 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
1275 if (!AI->use_empty()) {
1276 LatticeVal &IV = Values[AI];
1277 if (IV.isConstant() || IV.isUndefined()) {
1278 Constant *CST = IV.isConstant() ?
1279 IV.getConstant() : UndefValue::get(AI->getType());
1280 DOUT << "*** Arg " << *AI << " = " << *CST <<"\n";
1282 // Replaces all of the uses of a variable with uses of the
1284 AI->replaceAllUsesWith(CST);
1289 std::vector<BasicBlock*> BlocksToErase;
1290 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
1291 if (!ExecutableBBs.count(BB)) {
1292 DOUT << " BasicBlock Dead:" << *BB;
1295 // Delete the instructions backwards, as it has a reduced likelihood of
1296 // having to update as many def-use and use-def chains.
1297 std::vector<Instruction*> Insts;
1298 TerminatorInst *TI = BB->getTerminator();
1299 for (BasicBlock::iterator I = BB->begin(), E = TI; I != E; ++I)
1302 while (!Insts.empty()) {
1303 Instruction *I = Insts.back();
1305 if (!I->use_empty())
1306 I->replaceAllUsesWith(UndefValue::get(I->getType()));
1307 BB->getInstList().erase(I);
1312 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) {
1313 BasicBlock *Succ = TI->getSuccessor(i);
1314 if (Succ->begin() != Succ->end() && isa<PHINode>(Succ->begin()))
1315 TI->getSuccessor(i)->removePredecessor(BB);
1317 if (!TI->use_empty())
1318 TI->replaceAllUsesWith(UndefValue::get(TI->getType()));
1319 BB->getInstList().erase(TI);
1321 if (&*BB != &F->front())
1322 BlocksToErase.push_back(BB);
1324 new UnreachableInst(BB);
1327 for (BasicBlock::iterator BI = BB->begin(), E = BB->end(); BI != E; ) {
1328 Instruction *Inst = BI++;
1329 if (Inst->getType() != Type::VoidTy) {
1330 LatticeVal &IV = Values[Inst];
1331 if (IV.isConstant() || IV.isUndefined() &&
1332 !isa<TerminatorInst>(Inst)) {
1333 Constant *Const = IV.isConstant()
1334 ? IV.getConstant() : UndefValue::get(Inst->getType());
1335 DOUT << " Constant: " << *Const << " = " << *Inst;
1337 // Replaces all of the uses of a variable with uses of the
1339 Inst->replaceAllUsesWith(Const);
1341 // Delete the instruction.
1342 if (!isa<TerminatorInst>(Inst) && !isa<CallInst>(Inst))
1343 BB->getInstList().erase(Inst);
1345 // Hey, we just changed something!
1353 // Now that all instructions in the function are constant folded, erase dead
1354 // blocks, because we can now use ConstantFoldTerminator to get rid of
1356 for (unsigned i = 0, e = BlocksToErase.size(); i != e; ++i) {
1357 // If there are any PHI nodes in this successor, drop entries for BB now.
1358 BasicBlock *DeadBB = BlocksToErase[i];
1359 while (!DeadBB->use_empty()) {
1360 Instruction *I = cast<Instruction>(DeadBB->use_back());
1361 bool Folded = ConstantFoldTerminator(I->getParent());
1363 // The constant folder may not have been able to fold the termiantor
1364 // if this is a branch or switch on undef. Fold it manually as a
1365 // branch to the first successor.
1366 if (BranchInst *BI = dyn_cast<BranchInst>(I)) {
1367 assert(BI->isConditional() && isa<UndefValue>(BI->getCondition()) &&
1368 "Branch should be foldable!");
1369 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(I)) {
1370 assert(isa<UndefValue>(SI->getCondition()) && "Switch should fold");
1372 assert(0 && "Didn't fold away reference to block!");
1375 // Make this an uncond branch to the first successor.
1376 TerminatorInst *TI = I->getParent()->getTerminator();
1377 new BranchInst(TI->getSuccessor(0), TI);
1379 // Remove entries in successor phi nodes to remove edges.
1380 for (unsigned i = 1, e = TI->getNumSuccessors(); i != e; ++i)
1381 TI->getSuccessor(i)->removePredecessor(TI->getParent());
1383 // Remove the old terminator.
1384 TI->eraseFromParent();
1388 // Finally, delete the basic block.
1389 F->getBasicBlockList().erase(DeadBB);
1393 // If we inferred constant or undef return values for a function, we replaced
1394 // all call uses with the inferred value. This means we don't need to bother
1395 // actually returning anything from the function. Replace all return
1396 // instructions with return undef.
1397 const hash_map<Function*, LatticeVal> &RV =Solver.getTrackedFunctionRetVals();
1398 for (hash_map<Function*, LatticeVal>::const_iterator I = RV.begin(),
1399 E = RV.end(); I != E; ++I)
1400 if (!I->second.isOverdefined() &&
1401 I->first->getReturnType() != Type::VoidTy) {
1402 Function *F = I->first;
1403 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
1404 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator()))
1405 if (!isa<UndefValue>(RI->getOperand(0)))
1406 RI->setOperand(0, UndefValue::get(F->getReturnType()));
1409 // If we infered constant or undef values for globals variables, we can delete
1410 // the global and any stores that remain to it.
1411 const hash_map<GlobalVariable*, LatticeVal> &TG = Solver.getTrackedGlobals();
1412 for (hash_map<GlobalVariable*, LatticeVal>::const_iterator I = TG.begin(),
1413 E = TG.end(); I != E; ++I) {
1414 GlobalVariable *GV = I->first;
1415 assert(!I->second.isOverdefined() &&
1416 "Overdefined values should have been taken out of the map!");
1417 DOUT << "Found that GV '" << GV->getName()<< "' is constant!\n";
1418 while (!GV->use_empty()) {
1419 StoreInst *SI = cast<StoreInst>(GV->use_back());
1420 SI->eraseFromParent();
1422 M.getGlobalList().erase(GV);