1 //===- SCCP.cpp - Sparse Conditional Constant Propagation -----------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements sparse conditional constant propagation and merging:
12 // Specifically, this:
13 // * Assumes values are constant unless proven otherwise
14 // * Assumes BasicBlocks are dead unless proven otherwise
15 // * Proves values to be constant, and replaces them with constants
16 // * Proves conditional branches to be unconditional
18 //===----------------------------------------------------------------------===//
20 #define DEBUG_TYPE "sccp"
21 #include "llvm/Transforms/Scalar.h"
22 #include "llvm/Transforms/IPO.h"
23 #include "llvm/Constants.h"
24 #include "llvm/DerivedTypes.h"
25 #include "llvm/Instructions.h"
26 #include "llvm/Pass.h"
27 #include "llvm/Analysis/ConstantFolding.h"
28 #include "llvm/Analysis/ValueTracking.h"
29 #include "llvm/Transforms/Utils/Local.h"
30 #include "llvm/Target/TargetData.h"
31 #include "llvm/Support/CallSite.h"
32 #include "llvm/Support/Debug.h"
33 #include "llvm/Support/ErrorHandling.h"
34 #include "llvm/Support/InstVisitor.h"
35 #include "llvm/Support/raw_ostream.h"
36 #include "llvm/ADT/DenseMap.h"
37 #include "llvm/ADT/DenseSet.h"
38 #include "llvm/ADT/PointerIntPair.h"
39 #include "llvm/ADT/SmallPtrSet.h"
40 #include "llvm/ADT/SmallVector.h"
41 #include "llvm/ADT/Statistic.h"
42 #include "llvm/ADT/STLExtras.h"
47 STATISTIC(NumInstRemoved, "Number of instructions removed");
48 STATISTIC(NumDeadBlocks , "Number of basic blocks unreachable");
50 STATISTIC(IPNumInstRemoved, "Number of instructions removed by IPSCCP");
51 STATISTIC(IPNumArgsElimed ,"Number of arguments constant propagated by IPSCCP");
52 STATISTIC(IPNumGlobalConst, "Number of globals found to be constant by IPSCCP");
55 /// LatticeVal class - This class represents the different lattice values that
56 /// an LLVM value may occupy. It is a simple class with value semantics.
60 /// undefined - This LLVM Value has no known value yet.
63 /// constant - This LLVM Value has a specific constant value.
66 /// forcedconstant - This LLVM Value was thought to be undef until
67 /// ResolvedUndefsIn. This is treated just like 'constant', but if merged
68 /// with another (different) constant, it goes to overdefined, instead of
72 /// overdefined - This instruction is not known to be constant, and we know
77 /// Val: This stores the current lattice value along with the Constant* for
78 /// the constant if this is a 'constant' or 'forcedconstant' value.
79 PointerIntPair<Constant *, 2, LatticeValueTy> Val;
81 LatticeValueTy getLatticeValue() const {
86 LatticeVal() : Val(0, undefined) {}
88 bool isUndefined() const { return getLatticeValue() == undefined; }
89 bool isConstant() const {
90 return getLatticeValue() == constant || getLatticeValue() == forcedconstant;
92 bool isOverdefined() const { return getLatticeValue() == overdefined; }
94 Constant *getConstant() const {
95 assert(isConstant() && "Cannot get the constant of a non-constant!");
96 return Val.getPointer();
99 /// markOverdefined - Return true if this is a change in status.
100 bool markOverdefined() {
104 Val.setInt(overdefined);
108 /// markConstant - Return true if this is a change in status.
109 bool markConstant(Constant *V) {
110 if (getLatticeValue() == constant) { // Constant but not forcedconstant.
111 assert(getConstant() == V && "Marking constant with different value");
116 Val.setInt(constant);
117 assert(V && "Marking constant with NULL");
120 assert(getLatticeValue() == forcedconstant &&
121 "Cannot move from overdefined to constant!");
122 // Stay at forcedconstant if the constant is the same.
123 if (V == getConstant()) return false;
125 // Otherwise, we go to overdefined. Assumptions made based on the
126 // forced value are possibly wrong. Assuming this is another constant
127 // could expose a contradiction.
128 Val.setInt(overdefined);
133 /// getConstantInt - If this is a constant with a ConstantInt value, return it
134 /// otherwise return null.
135 ConstantInt *getConstantInt() const {
137 return dyn_cast<ConstantInt>(getConstant());
141 void markForcedConstant(Constant *V) {
142 assert(isUndefined() && "Can't force a defined value!");
143 Val.setInt(forcedconstant);
147 } // end anonymous namespace.
152 //===----------------------------------------------------------------------===//
154 /// SCCPSolver - This class is a general purpose solver for Sparse Conditional
155 /// Constant Propagation.
157 class SCCPSolver : public InstVisitor<SCCPSolver> {
158 const TargetData *TD;
159 SmallPtrSet<BasicBlock*, 8> BBExecutable;// The BBs that are executable.
160 DenseMap<Value*, LatticeVal> ValueState; // The state each value is in.
162 /// StructValueState - This maintains ValueState for values that have
163 /// StructType, for example for formal arguments, calls, insertelement, etc.
165 DenseMap<std::pair<Value*, unsigned>, LatticeVal> StructValueState;
167 /// GlobalValue - If we are tracking any values for the contents of a global
168 /// variable, we keep a mapping from the constant accessor to the element of
169 /// the global, to the currently known value. If the value becomes
170 /// overdefined, it's entry is simply removed from this map.
171 DenseMap<GlobalVariable*, LatticeVal> TrackedGlobals;
173 /// TrackedRetVals - If we are tracking arguments into and the return
174 /// value out of a function, it will have an entry in this map, indicating
175 /// what the known return value for the function is.
176 DenseMap<Function*, LatticeVal> TrackedRetVals;
178 /// TrackedMultipleRetVals - Same as TrackedRetVals, but used for functions
179 /// that return multiple values.
180 DenseMap<std::pair<Function*, unsigned>, LatticeVal> TrackedMultipleRetVals;
182 /// MRVFunctionsTracked - Each function in TrackedMultipleRetVals is
183 /// represented here for efficient lookup.
184 SmallPtrSet<Function*, 16> MRVFunctionsTracked;
186 /// TrackingIncomingArguments - This is the set of functions for whose
187 /// arguments we make optimistic assumptions about and try to prove as
189 SmallPtrSet<Function*, 16> TrackingIncomingArguments;
191 /// The reason for two worklists is that overdefined is the lowest state
192 /// on the lattice, and moving things to overdefined as fast as possible
193 /// makes SCCP converge much faster.
195 /// By having a separate worklist, we accomplish this because everything
196 /// possibly overdefined will become overdefined at the soonest possible
198 SmallVector<Value*, 64> OverdefinedInstWorkList;
199 SmallVector<Value*, 64> InstWorkList;
202 SmallVector<BasicBlock*, 64> BBWorkList; // The BasicBlock work list
204 /// UsersOfOverdefinedPHIs - Keep track of any users of PHI nodes that are not
205 /// overdefined, despite the fact that the PHI node is overdefined.
206 std::multimap<PHINode*, Instruction*> UsersOfOverdefinedPHIs;
208 /// KnownFeasibleEdges - Entries in this set are edges which have already had
209 /// PHI nodes retriggered.
210 typedef std::pair<BasicBlock*, BasicBlock*> Edge;
211 DenseSet<Edge> KnownFeasibleEdges;
213 SCCPSolver(const TargetData *td) : TD(td) {}
215 /// MarkBlockExecutable - This method can be used by clients to mark all of
216 /// the blocks that are known to be intrinsically live in the processed unit.
218 /// This returns true if the block was not considered live before.
219 bool MarkBlockExecutable(BasicBlock *BB) {
220 if (!BBExecutable.insert(BB)) return false;
221 DEBUG(errs() << "Marking Block Executable: " << BB->getName() << "\n");
222 BBWorkList.push_back(BB); // Add the block to the work list!
226 /// TrackValueOfGlobalVariable - Clients can use this method to
227 /// inform the SCCPSolver that it should track loads and stores to the
228 /// specified global variable if it can. This is only legal to call if
229 /// performing Interprocedural SCCP.
230 void TrackValueOfGlobalVariable(GlobalVariable *GV) {
231 // We only track the contents of scalar globals.
232 if (GV->getType()->getElementType()->isSingleValueType()) {
233 LatticeVal &IV = TrackedGlobals[GV];
234 if (!isa<UndefValue>(GV->getInitializer()))
235 IV.markConstant(GV->getInitializer());
239 /// AddTrackedFunction - If the SCCP solver is supposed to track calls into
240 /// and out of the specified function (which cannot have its address taken),
241 /// this method must be called.
242 void AddTrackedFunction(Function *F) {
243 // Add an entry, F -> undef.
244 if (const StructType *STy = dyn_cast<StructType>(F->getReturnType())) {
245 MRVFunctionsTracked.insert(F);
246 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
247 TrackedMultipleRetVals.insert(std::make_pair(std::make_pair(F, i),
250 TrackedRetVals.insert(std::make_pair(F, LatticeVal()));
253 void AddArgumentTrackedFunction(Function *F) {
254 TrackingIncomingArguments.insert(F);
257 /// Solve - Solve for constants and executable blocks.
261 /// ResolvedUndefsIn - While solving the dataflow for a function, we assume
262 /// that branches on undef values cannot reach any of their successors.
263 /// However, this is not a safe assumption. After we solve dataflow, this
264 /// method should be use to handle this. If this returns true, the solver
266 bool ResolvedUndefsIn(Function &F);
268 bool isBlockExecutable(BasicBlock *BB) const {
269 return BBExecutable.count(BB);
272 LatticeVal getLatticeValueFor(Value *V) const {
273 DenseMap<Value*, LatticeVal>::const_iterator I = ValueState.find(V);
274 assert(I != ValueState.end() && "V is not in valuemap!");
278 LatticeVal getStructLatticeValueFor(Value *V, unsigned i) const {
279 DenseMap<std::pair<Value*, unsigned>, LatticeVal>::const_iterator I =
280 StructValueState.find(std::make_pair(V, i));
281 assert(I != StructValueState.end() && "V is not in valuemap!");
285 /// getTrackedRetVals - Get the inferred return value map.
287 const DenseMap<Function*, LatticeVal> &getTrackedRetVals() {
288 return TrackedRetVals;
291 /// getTrackedGlobals - Get and return the set of inferred initializers for
292 /// global variables.
293 const DenseMap<GlobalVariable*, LatticeVal> &getTrackedGlobals() {
294 return TrackedGlobals;
297 void markOverdefined(Value *V) {
298 assert(!isa<StructType>(V->getType()) && "Should use other method");
299 markOverdefined(ValueState[V], V);
302 /// markAnythingOverdefined - Mark the specified value overdefined. This
303 /// works with both scalars and structs.
304 void markAnythingOverdefined(Value *V) {
305 if (const StructType *STy = dyn_cast<StructType>(V->getType()))
306 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
307 markOverdefined(getStructValueState(V, i), V);
313 // markConstant - Make a value be marked as "constant". If the value
314 // is not already a constant, add it to the instruction work list so that
315 // the users of the instruction are updated later.
317 void markConstant(LatticeVal &IV, Value *V, Constant *C) {
318 if (!IV.markConstant(C)) return;
319 DEBUG(errs() << "markConstant: " << *C << ": " << *V << '\n');
320 InstWorkList.push_back(V);
323 void markConstant(Value *V, Constant *C) {
324 assert(!isa<StructType>(V->getType()) && "Should use other method");
325 markConstant(ValueState[V], V, C);
328 void markForcedConstant(Value *V, Constant *C) {
329 assert(!isa<StructType>(V->getType()) && "Should use other method");
330 ValueState[V].markForcedConstant(C);
331 DEBUG(errs() << "markForcedConstant: " << *C << ": " << *V << '\n');
332 InstWorkList.push_back(V);
336 // markOverdefined - Make a value be marked as "overdefined". If the
337 // value is not already overdefined, add it to the overdefined instruction
338 // work list so that the users of the instruction are updated later.
339 void markOverdefined(LatticeVal &IV, Value *V) {
340 if (!IV.markOverdefined()) return;
342 DEBUG(errs() << "markOverdefined: ";
343 if (Function *F = dyn_cast<Function>(V))
344 errs() << "Function '" << F->getName() << "'\n";
346 errs() << *V << '\n');
347 // Only instructions go on the work list
348 OverdefinedInstWorkList.push_back(V);
351 void mergeInValue(LatticeVal &IV, Value *V, LatticeVal MergeWithV) {
352 if (IV.isOverdefined() || MergeWithV.isUndefined())
354 if (MergeWithV.isOverdefined())
355 markOverdefined(IV, V);
356 else if (IV.isUndefined())
357 markConstant(IV, V, MergeWithV.getConstant());
358 else if (IV.getConstant() != MergeWithV.getConstant())
359 markOverdefined(IV, V);
362 void mergeInValue(Value *V, LatticeVal MergeWithV) {
363 assert(!isa<StructType>(V->getType()) && "Should use other method");
364 mergeInValue(ValueState[V], V, MergeWithV);
368 /// getValueState - Return the LatticeVal object that corresponds to the
369 /// value. This function handles the case when the value hasn't been seen yet
370 /// by properly seeding constants etc.
371 LatticeVal &getValueState(Value *V) {
372 assert(!isa<StructType>(V->getType()) && "Should use getStructValueState");
374 std::pair<DenseMap<Value*, LatticeVal>::iterator, bool> I =
375 ValueState.insert(std::make_pair(V, LatticeVal()));
376 LatticeVal &LV = I.first->second;
379 return LV; // Common case, already in the map.
381 if (Constant *C = dyn_cast<Constant>(V)) {
382 // Undef values remain undefined.
383 if (!isa<UndefValue>(V))
384 LV.markConstant(C); // Constants are constant
387 // All others are underdefined by default.
391 /// getStructValueState - Return the LatticeVal object that corresponds to the
392 /// value/field pair. This function handles the case when the value hasn't
393 /// been seen yet by properly seeding constants etc.
394 LatticeVal &getStructValueState(Value *V, unsigned i) {
395 assert(isa<StructType>(V->getType()) && "Should use getValueState");
396 assert(i < cast<StructType>(V->getType())->getNumElements() &&
397 "Invalid element #");
399 std::pair<DenseMap<std::pair<Value*, unsigned>, LatticeVal>::iterator,
400 bool> I = StructValueState.insert(
401 std::make_pair(std::make_pair(V, i), LatticeVal()));
402 LatticeVal &LV = I.first->second;
405 return LV; // Common case, already in the map.
407 if (Constant *C = dyn_cast<Constant>(V)) {
408 if (isa<UndefValue>(C))
409 ; // Undef values remain undefined.
410 else if (ConstantStruct *CS = dyn_cast<ConstantStruct>(C))
411 LV.markConstant(CS->getOperand(i)); // Constants are constant.
412 else if (isa<ConstantAggregateZero>(C)) {
413 const Type *FieldTy = cast<StructType>(V->getType())->getElementType(i);
414 LV.markConstant(Constant::getNullValue(FieldTy));
416 LV.markOverdefined(); // Unknown sort of constant.
419 // All others are underdefined by default.
424 /// markEdgeExecutable - Mark a basic block as executable, adding it to the BB
425 /// work list if it is not already executable.
426 void markEdgeExecutable(BasicBlock *Source, BasicBlock *Dest) {
427 if (!KnownFeasibleEdges.insert(Edge(Source, Dest)).second)
428 return; // This edge is already known to be executable!
430 if (!MarkBlockExecutable(Dest)) {
431 // If the destination is already executable, we just made an *edge*
432 // feasible that wasn't before. Revisit the PHI nodes in the block
433 // because they have potentially new operands.
434 DEBUG(errs() << "Marking Edge Executable: " << Source->getName()
435 << " -> " << Dest->getName() << "\n");
438 for (BasicBlock::iterator I = Dest->begin();
439 (PN = dyn_cast<PHINode>(I)); ++I)
444 // getFeasibleSuccessors - Return a vector of booleans to indicate which
445 // successors are reachable from a given terminator instruction.
447 void getFeasibleSuccessors(TerminatorInst &TI, SmallVector<bool, 16> &Succs);
449 // isEdgeFeasible - Return true if the control flow edge from the 'From' basic
450 // block to the 'To' basic block is currently feasible.
452 bool isEdgeFeasible(BasicBlock *From, BasicBlock *To);
454 // OperandChangedState - This method is invoked on all of the users of an
455 // instruction that was just changed state somehow. Based on this
456 // information, we need to update the specified user of this instruction.
458 void OperandChangedState(Instruction *I) {
459 if (BBExecutable.count(I->getParent())) // Inst is executable?
463 /// RemoveFromOverdefinedPHIs - If I has any entries in the
464 /// UsersOfOverdefinedPHIs map for PN, remove them now.
465 void RemoveFromOverdefinedPHIs(Instruction *I, PHINode *PN) {
466 if (UsersOfOverdefinedPHIs.empty()) return;
467 std::multimap<PHINode*, Instruction*>::iterator It, E;
468 tie(It, E) = UsersOfOverdefinedPHIs.equal_range(PN);
471 UsersOfOverdefinedPHIs.erase(It++);
478 friend class InstVisitor<SCCPSolver>;
480 // visit implementations - Something changed in this instruction. Either an
481 // operand made a transition, or the instruction is newly executable. Change
482 // the value type of I to reflect these changes if appropriate.
483 void visitPHINode(PHINode &I);
486 void visitReturnInst(ReturnInst &I);
487 void visitTerminatorInst(TerminatorInst &TI);
489 void visitCastInst(CastInst &I);
490 void visitSelectInst(SelectInst &I);
491 void visitBinaryOperator(Instruction &I);
492 void visitCmpInst(CmpInst &I);
493 void visitExtractElementInst(ExtractElementInst &I);
494 void visitInsertElementInst(InsertElementInst &I);
495 void visitShuffleVectorInst(ShuffleVectorInst &I);
496 void visitExtractValueInst(ExtractValueInst &EVI);
497 void visitInsertValueInst(InsertValueInst &IVI);
499 // Instructions that cannot be folded away.
500 void visitStoreInst (StoreInst &I);
501 void visitLoadInst (LoadInst &I);
502 void visitGetElementPtrInst(GetElementPtrInst &I);
503 void visitCallInst (CallInst &I) {
504 visitCallSite(CallSite::get(&I));
506 void visitInvokeInst (InvokeInst &II) {
507 visitCallSite(CallSite::get(&II));
508 visitTerminatorInst(II);
510 void visitCallSite (CallSite CS);
511 void visitUnwindInst (TerminatorInst &I) { /*returns void*/ }
512 void visitUnreachableInst(TerminatorInst &I) { /*returns void*/ }
513 void visitAllocaInst (Instruction &I) { markOverdefined(&I); }
514 void visitVANextInst (Instruction &I) { markOverdefined(&I); }
515 void visitVAArgInst (Instruction &I) { markAnythingOverdefined(&I); }
517 void visitInstruction(Instruction &I) {
518 // If a new instruction is added to LLVM that we don't handle.
519 errs() << "SCCP: Don't know how to handle: " << I;
520 markAnythingOverdefined(&I); // Just in case
524 } // end anonymous namespace
527 // getFeasibleSuccessors - Return a vector of booleans to indicate which
528 // successors are reachable from a given terminator instruction.
530 void SCCPSolver::getFeasibleSuccessors(TerminatorInst &TI,
531 SmallVector<bool, 16> &Succs) {
532 Succs.resize(TI.getNumSuccessors());
533 if (BranchInst *BI = dyn_cast<BranchInst>(&TI)) {
534 if (BI->isUnconditional()) {
539 LatticeVal BCValue = getValueState(BI->getCondition());
540 ConstantInt *CI = BCValue.getConstantInt();
542 // Overdefined condition variables, and branches on unfoldable constant
543 // conditions, mean the branch could go either way.
544 if (!BCValue.isUndefined())
545 Succs[0] = Succs[1] = true;
549 // Constant condition variables mean the branch can only go a single way.
550 Succs[CI->isZero()] = true;
554 if (isa<InvokeInst>(TI)) {
555 // Invoke instructions successors are always executable.
556 Succs[0] = Succs[1] = true;
560 if (SwitchInst *SI = dyn_cast<SwitchInst>(&TI)) {
561 LatticeVal SCValue = getValueState(SI->getCondition());
562 ConstantInt *CI = SCValue.getConstantInt();
564 if (CI == 0) { // Overdefined or undefined condition?
565 // All destinations are executable!
566 if (!SCValue.isUndefined())
567 Succs.assign(TI.getNumSuccessors(), true);
571 Succs[SI->findCaseValue(CI)] = true;
575 // TODO: This could be improved if the operand is a [cast of a] BlockAddress.
576 if (isa<IndirectBrInst>(&TI)) {
577 // Just mark all destinations executable!
578 Succs.assign(TI.getNumSuccessors(), true);
583 errs() << "Unknown terminator instruction: " << TI << '\n';
585 llvm_unreachable("SCCP: Don't know how to handle this terminator!");
589 // isEdgeFeasible - Return true if the control flow edge from the 'From' basic
590 // block to the 'To' basic block is currently feasible.
592 bool SCCPSolver::isEdgeFeasible(BasicBlock *From, BasicBlock *To) {
593 assert(BBExecutable.count(To) && "Dest should always be alive!");
595 // Make sure the source basic block is executable!!
596 if (!BBExecutable.count(From)) return false;
598 // Check to make sure this edge itself is actually feasible now.
599 TerminatorInst *TI = From->getTerminator();
600 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
601 if (BI->isUnconditional())
604 LatticeVal BCValue = getValueState(BI->getCondition());
606 // Overdefined condition variables mean the branch could go either way,
607 // undef conditions mean that neither edge is feasible yet.
608 ConstantInt *CI = BCValue.getConstantInt();
610 return !BCValue.isUndefined();
612 // Constant condition variables mean the branch can only go a single way.
613 return BI->getSuccessor(CI->isZero()) == To;
616 // Invoke instructions successors are always executable.
617 if (isa<InvokeInst>(TI))
620 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
621 LatticeVal SCValue = getValueState(SI->getCondition());
622 ConstantInt *CI = SCValue.getConstantInt();
625 return !SCValue.isUndefined();
627 // Make sure to skip the "default value" which isn't a value
628 for (unsigned i = 1, E = SI->getNumSuccessors(); i != E; ++i)
629 if (SI->getSuccessorValue(i) == CI) // Found the taken branch.
630 return SI->getSuccessor(i) == To;
632 // If the constant value is not equal to any of the branches, we must
633 // execute default branch.
634 return SI->getDefaultDest() == To;
637 // Just mark all destinations executable!
638 // TODO: This could be improved if the operand is a [cast of a] BlockAddress.
639 if (isa<IndirectBrInst>(&TI))
643 errs() << "Unknown terminator instruction: " << *TI << '\n';
648 // visit Implementations - Something changed in this instruction, either an
649 // operand made a transition, or the instruction is newly executable. Change
650 // the value type of I to reflect these changes if appropriate. This method
651 // makes sure to do the following actions:
653 // 1. If a phi node merges two constants in, and has conflicting value coming
654 // from different branches, or if the PHI node merges in an overdefined
655 // value, then the PHI node becomes overdefined.
656 // 2. If a phi node merges only constants in, and they all agree on value, the
657 // PHI node becomes a constant value equal to that.
658 // 3. If V <- x (op) y && isConstant(x) && isConstant(y) V = Constant
659 // 4. If V <- x (op) y && (isOverdefined(x) || isOverdefined(y)) V = Overdefined
660 // 5. If V <- MEM or V <- CALL or V <- (unknown) then V = Overdefined
661 // 6. If a conditional branch has a value that is constant, make the selected
662 // destination executable
663 // 7. If a conditional branch has a value that is overdefined, make all
664 // successors executable.
666 void SCCPSolver::visitPHINode(PHINode &PN) {
667 // If this PN returns a struct, just mark the result overdefined.
668 // TODO: We could do a lot better than this if code actually uses this.
669 if (isa<StructType>(PN.getType()))
670 return markAnythingOverdefined(&PN);
672 if (getValueState(&PN).isOverdefined()) {
673 // There may be instructions using this PHI node that are not overdefined
674 // themselves. If so, make sure that they know that the PHI node operand
676 std::multimap<PHINode*, Instruction*>::iterator I, E;
677 tie(I, E) = UsersOfOverdefinedPHIs.equal_range(&PN);
681 SmallVector<Instruction*, 16> Users;
683 Users.push_back(I->second);
684 while (!Users.empty())
685 visit(Users.pop_back_val());
686 return; // Quick exit
689 // Super-extra-high-degree PHI nodes are unlikely to ever be marked constant,
690 // and slow us down a lot. Just mark them overdefined.
691 if (PN.getNumIncomingValues() > 64)
692 return markOverdefined(&PN);
694 // Look at all of the executable operands of the PHI node. If any of them
695 // are overdefined, the PHI becomes overdefined as well. If they are all
696 // constant, and they agree with each other, the PHI becomes the identical
697 // constant. If they are constant and don't agree, the PHI is overdefined.
698 // If there are no executable operands, the PHI remains undefined.
700 Constant *OperandVal = 0;
701 for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) {
702 LatticeVal IV = getValueState(PN.getIncomingValue(i));
703 if (IV.isUndefined()) continue; // Doesn't influence PHI node.
705 if (!isEdgeFeasible(PN.getIncomingBlock(i), PN.getParent()))
708 if (IV.isOverdefined()) // PHI node becomes overdefined!
709 return markOverdefined(&PN);
711 if (OperandVal == 0) { // Grab the first value.
712 OperandVal = IV.getConstant();
716 // There is already a reachable operand. If we conflict with it,
717 // then the PHI node becomes overdefined. If we agree with it, we
720 // Check to see if there are two different constants merging, if so, the PHI
721 // node is overdefined.
722 if (IV.getConstant() != OperandVal)
723 return markOverdefined(&PN);
726 // If we exited the loop, this means that the PHI node only has constant
727 // arguments that agree with each other(and OperandVal is the constant) or
728 // OperandVal is null because there are no defined incoming arguments. If
729 // this is the case, the PHI remains undefined.
732 markConstant(&PN, OperandVal); // Acquire operand value
738 void SCCPSolver::visitReturnInst(ReturnInst &I) {
739 if (I.getNumOperands() == 0) return; // ret void
741 Function *F = I.getParent()->getParent();
742 Value *ResultOp = I.getOperand(0);
744 // If we are tracking the return value of this function, merge it in.
745 if (!TrackedRetVals.empty() && !isa<StructType>(ResultOp->getType())) {
746 DenseMap<Function*, LatticeVal>::iterator TFRVI =
747 TrackedRetVals.find(F);
748 if (TFRVI != TrackedRetVals.end()) {
749 mergeInValue(TFRVI->second, F, getValueState(ResultOp));
754 // Handle functions that return multiple values.
755 if (!TrackedMultipleRetVals.empty()) {
756 if (const StructType *STy = dyn_cast<StructType>(ResultOp->getType()))
757 if (MRVFunctionsTracked.count(F))
758 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
759 mergeInValue(TrackedMultipleRetVals[std::make_pair(F, i)], F,
760 getStructValueState(ResultOp, i));
765 void SCCPSolver::visitTerminatorInst(TerminatorInst &TI) {
766 SmallVector<bool, 16> SuccFeasible;
767 getFeasibleSuccessors(TI, SuccFeasible);
769 BasicBlock *BB = TI.getParent();
771 // Mark all feasible successors executable.
772 for (unsigned i = 0, e = SuccFeasible.size(); i != e; ++i)
774 markEdgeExecutable(BB, TI.getSuccessor(i));
777 void SCCPSolver::visitCastInst(CastInst &I) {
778 LatticeVal OpSt = getValueState(I.getOperand(0));
779 if (OpSt.isOverdefined()) // Inherit overdefinedness of operand
781 else if (OpSt.isConstant()) // Propagate constant value
782 markConstant(&I, ConstantExpr::getCast(I.getOpcode(),
783 OpSt.getConstant(), I.getType()));
787 void SCCPSolver::visitExtractValueInst(ExtractValueInst &EVI) {
788 // If this returns a struct, mark all elements over defined, we don't track
789 // structs in structs.
790 if (isa<StructType>(EVI.getType()))
791 return markAnythingOverdefined(&EVI);
793 // If this is extracting from more than one level of struct, we don't know.
794 if (EVI.getNumIndices() != 1)
795 return markOverdefined(&EVI);
797 Value *AggVal = EVI.getAggregateOperand();
798 unsigned i = *EVI.idx_begin();
799 LatticeVal EltVal = getStructValueState(AggVal, i);
800 mergeInValue(getValueState(&EVI), &EVI, EltVal);
803 void SCCPSolver::visitInsertValueInst(InsertValueInst &IVI) {
804 const StructType *STy = dyn_cast<StructType>(IVI.getType());
806 return markOverdefined(&IVI);
808 // If this has more than one index, we can't handle it, drive all results to
810 if (IVI.getNumIndices() != 1)
811 return markAnythingOverdefined(&IVI);
813 Value *Aggr = IVI.getAggregateOperand();
814 unsigned Idx = *IVI.idx_begin();
816 // Compute the result based on what we're inserting.
817 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
818 // This passes through all values that aren't the inserted element.
820 LatticeVal EltVal = getStructValueState(Aggr, i);
821 mergeInValue(getStructValueState(&IVI, i), &IVI, EltVal);
825 Value *Val = IVI.getInsertedValueOperand();
826 if (isa<StructType>(Val->getType()))
827 // We don't track structs in structs.
828 markOverdefined(getStructValueState(&IVI, i), &IVI);
830 LatticeVal InVal = getValueState(Val);
831 mergeInValue(getStructValueState(&IVI, i), &IVI, InVal);
836 void SCCPSolver::visitSelectInst(SelectInst &I) {
837 // If this select returns a struct, just mark the result overdefined.
838 // TODO: We could do a lot better than this if code actually uses this.
839 if (isa<StructType>(I.getType()))
840 return markAnythingOverdefined(&I);
842 LatticeVal CondValue = getValueState(I.getCondition());
843 if (CondValue.isUndefined())
846 if (ConstantInt *CondCB = CondValue.getConstantInt()) {
847 Value *OpVal = CondCB->isZero() ? I.getFalseValue() : I.getTrueValue();
848 mergeInValue(&I, getValueState(OpVal));
852 // Otherwise, the condition is overdefined or a constant we can't evaluate.
853 // See if we can produce something better than overdefined based on the T/F
855 LatticeVal TVal = getValueState(I.getTrueValue());
856 LatticeVal FVal = getValueState(I.getFalseValue());
858 // select ?, C, C -> C.
859 if (TVal.isConstant() && FVal.isConstant() &&
860 TVal.getConstant() == FVal.getConstant())
861 return markConstant(&I, FVal.getConstant());
863 if (TVal.isUndefined()) // select ?, undef, X -> X.
864 return mergeInValue(&I, FVal);
865 if (FVal.isUndefined()) // select ?, X, undef -> X.
866 return mergeInValue(&I, TVal);
870 // Handle Binary Operators.
871 void SCCPSolver::visitBinaryOperator(Instruction &I) {
872 LatticeVal V1State = getValueState(I.getOperand(0));
873 LatticeVal V2State = getValueState(I.getOperand(1));
875 LatticeVal &IV = ValueState[&I];
876 if (IV.isOverdefined()) return;
878 if (V1State.isConstant() && V2State.isConstant())
879 return markConstant(IV, &I,
880 ConstantExpr::get(I.getOpcode(), V1State.getConstant(),
881 V2State.getConstant()));
883 // If something is undef, wait for it to resolve.
884 if (!V1State.isOverdefined() && !V2State.isOverdefined())
887 // Otherwise, one of our operands is overdefined. Try to produce something
888 // better than overdefined with some tricks.
890 // If this is an AND or OR with 0 or -1, it doesn't matter that the other
891 // operand is overdefined.
892 if (I.getOpcode() == Instruction::And || I.getOpcode() == Instruction::Or) {
893 LatticeVal *NonOverdefVal = 0;
894 if (!V1State.isOverdefined())
895 NonOverdefVal = &V1State;
896 else if (!V2State.isOverdefined())
897 NonOverdefVal = &V2State;
900 if (NonOverdefVal->isUndefined()) {
901 // Could annihilate value.
902 if (I.getOpcode() == Instruction::And)
903 markConstant(IV, &I, Constant::getNullValue(I.getType()));
904 else if (const VectorType *PT = dyn_cast<VectorType>(I.getType()))
905 markConstant(IV, &I, Constant::getAllOnesValue(PT));
908 Constant::getAllOnesValue(I.getType()));
912 if (I.getOpcode() == Instruction::And) {
914 if (NonOverdefVal->getConstant()->isNullValue())
915 return markConstant(IV, &I, NonOverdefVal->getConstant());
917 if (ConstantInt *CI = NonOverdefVal->getConstantInt())
918 if (CI->isAllOnesValue()) // X or -1 = -1
919 return markConstant(IV, &I, NonOverdefVal->getConstant());
925 // If both operands are PHI nodes, it is possible that this instruction has
926 // a constant value, despite the fact that the PHI node doesn't. Check for
927 // this condition now.
928 if (PHINode *PN1 = dyn_cast<PHINode>(I.getOperand(0)))
929 if (PHINode *PN2 = dyn_cast<PHINode>(I.getOperand(1)))
930 if (PN1->getParent() == PN2->getParent()) {
931 // Since the two PHI nodes are in the same basic block, they must have
932 // entries for the same predecessors. Walk the predecessor list, and
933 // if all of the incoming values are constants, and the result of
934 // evaluating this expression with all incoming value pairs is the
935 // same, then this expression is a constant even though the PHI node
936 // is not a constant!
938 for (unsigned i = 0, e = PN1->getNumIncomingValues(); i != e; ++i) {
939 LatticeVal In1 = getValueState(PN1->getIncomingValue(i));
940 BasicBlock *InBlock = PN1->getIncomingBlock(i);
941 LatticeVal In2 =getValueState(PN2->getIncomingValueForBlock(InBlock));
943 if (In1.isOverdefined() || In2.isOverdefined()) {
944 Result.markOverdefined();
945 break; // Cannot fold this operation over the PHI nodes!
948 if (In1.isConstant() && In2.isConstant()) {
949 Constant *V = ConstantExpr::get(I.getOpcode(), In1.getConstant(),
951 if (Result.isUndefined())
952 Result.markConstant(V);
953 else if (Result.isConstant() && Result.getConstant() != V) {
954 Result.markOverdefined();
960 // If we found a constant value here, then we know the instruction is
961 // constant despite the fact that the PHI nodes are overdefined.
962 if (Result.isConstant()) {
963 markConstant(IV, &I, Result.getConstant());
964 // Remember that this instruction is virtually using the PHI node
966 UsersOfOverdefinedPHIs.insert(std::make_pair(PN1, &I));
967 UsersOfOverdefinedPHIs.insert(std::make_pair(PN2, &I));
971 if (Result.isUndefined())
974 // Okay, this really is overdefined now. Since we might have
975 // speculatively thought that this was not overdefined before, and
976 // added ourselves to the UsersOfOverdefinedPHIs list for the PHIs,
977 // make sure to clean out any entries that we put there, for
979 RemoveFromOverdefinedPHIs(&I, PN1);
980 RemoveFromOverdefinedPHIs(&I, PN2);
986 // Handle ICmpInst instruction.
987 void SCCPSolver::visitCmpInst(CmpInst &I) {
988 LatticeVal V1State = getValueState(I.getOperand(0));
989 LatticeVal V2State = getValueState(I.getOperand(1));
991 LatticeVal &IV = ValueState[&I];
992 if (IV.isOverdefined()) return;
994 if (V1State.isConstant() && V2State.isConstant())
995 return markConstant(IV, &I, ConstantExpr::getCompare(I.getPredicate(),
996 V1State.getConstant(),
997 V2State.getConstant()));
999 // If operands are still undefined, wait for it to resolve.
1000 if (!V1State.isOverdefined() && !V2State.isOverdefined())
1003 // If something is overdefined, use some tricks to avoid ending up and over
1004 // defined if we can.
1006 // If both operands are PHI nodes, it is possible that this instruction has
1007 // a constant value, despite the fact that the PHI node doesn't. Check for
1008 // this condition now.
1009 if (PHINode *PN1 = dyn_cast<PHINode>(I.getOperand(0)))
1010 if (PHINode *PN2 = dyn_cast<PHINode>(I.getOperand(1)))
1011 if (PN1->getParent() == PN2->getParent()) {
1012 // Since the two PHI nodes are in the same basic block, they must have
1013 // entries for the same predecessors. Walk the predecessor list, and
1014 // if all of the incoming values are constants, and the result of
1015 // evaluating this expression with all incoming value pairs is the
1016 // same, then this expression is a constant even though the PHI node
1017 // is not a constant!
1019 for (unsigned i = 0, e = PN1->getNumIncomingValues(); i != e; ++i) {
1020 LatticeVal In1 = getValueState(PN1->getIncomingValue(i));
1021 BasicBlock *InBlock = PN1->getIncomingBlock(i);
1022 LatticeVal In2 =getValueState(PN2->getIncomingValueForBlock(InBlock));
1024 if (In1.isOverdefined() || In2.isOverdefined()) {
1025 Result.markOverdefined();
1026 break; // Cannot fold this operation over the PHI nodes!
1029 if (In1.isConstant() && In2.isConstant()) {
1030 Constant *V = ConstantExpr::getCompare(I.getPredicate(),
1033 if (Result.isUndefined())
1034 Result.markConstant(V);
1035 else if (Result.isConstant() && Result.getConstant() != V) {
1036 Result.markOverdefined();
1042 // If we found a constant value here, then we know the instruction is
1043 // constant despite the fact that the PHI nodes are overdefined.
1044 if (Result.isConstant()) {
1045 markConstant(&I, Result.getConstant());
1046 // Remember that this instruction is virtually using the PHI node
1048 UsersOfOverdefinedPHIs.insert(std::make_pair(PN1, &I));
1049 UsersOfOverdefinedPHIs.insert(std::make_pair(PN2, &I));
1053 if (Result.isUndefined())
1056 // Okay, this really is overdefined now. Since we might have
1057 // speculatively thought that this was not overdefined before, and
1058 // added ourselves to the UsersOfOverdefinedPHIs list for the PHIs,
1059 // make sure to clean out any entries that we put there, for
1061 RemoveFromOverdefinedPHIs(&I, PN1);
1062 RemoveFromOverdefinedPHIs(&I, PN2);
1065 markOverdefined(&I);
1068 void SCCPSolver::visitExtractElementInst(ExtractElementInst &I) {
1069 // TODO : SCCP does not handle vectors properly.
1070 return markOverdefined(&I);
1073 LatticeVal &ValState = getValueState(I.getOperand(0));
1074 LatticeVal &IdxState = getValueState(I.getOperand(1));
1076 if (ValState.isOverdefined() || IdxState.isOverdefined())
1077 markOverdefined(&I);
1078 else if(ValState.isConstant() && IdxState.isConstant())
1079 markConstant(&I, ConstantExpr::getExtractElement(ValState.getConstant(),
1080 IdxState.getConstant()));
1084 void SCCPSolver::visitInsertElementInst(InsertElementInst &I) {
1085 // TODO : SCCP does not handle vectors properly.
1086 return markOverdefined(&I);
1088 LatticeVal &ValState = getValueState(I.getOperand(0));
1089 LatticeVal &EltState = getValueState(I.getOperand(1));
1090 LatticeVal &IdxState = getValueState(I.getOperand(2));
1092 if (ValState.isOverdefined() || EltState.isOverdefined() ||
1093 IdxState.isOverdefined())
1094 markOverdefined(&I);
1095 else if(ValState.isConstant() && EltState.isConstant() &&
1096 IdxState.isConstant())
1097 markConstant(&I, ConstantExpr::getInsertElement(ValState.getConstant(),
1098 EltState.getConstant(),
1099 IdxState.getConstant()));
1100 else if (ValState.isUndefined() && EltState.isConstant() &&
1101 IdxState.isConstant())
1102 markConstant(&I,ConstantExpr::getInsertElement(UndefValue::get(I.getType()),
1103 EltState.getConstant(),
1104 IdxState.getConstant()));
1108 void SCCPSolver::visitShuffleVectorInst(ShuffleVectorInst &I) {
1109 // TODO : SCCP does not handle vectors properly.
1110 return markOverdefined(&I);
1112 LatticeVal &V1State = getValueState(I.getOperand(0));
1113 LatticeVal &V2State = getValueState(I.getOperand(1));
1114 LatticeVal &MaskState = getValueState(I.getOperand(2));
1116 if (MaskState.isUndefined() ||
1117 (V1State.isUndefined() && V2State.isUndefined()))
1118 return; // Undefined output if mask or both inputs undefined.
1120 if (V1State.isOverdefined() || V2State.isOverdefined() ||
1121 MaskState.isOverdefined()) {
1122 markOverdefined(&I);
1124 // A mix of constant/undef inputs.
1125 Constant *V1 = V1State.isConstant() ?
1126 V1State.getConstant() : UndefValue::get(I.getType());
1127 Constant *V2 = V2State.isConstant() ?
1128 V2State.getConstant() : UndefValue::get(I.getType());
1129 Constant *Mask = MaskState.isConstant() ?
1130 MaskState.getConstant() : UndefValue::get(I.getOperand(2)->getType());
1131 markConstant(&I, ConstantExpr::getShuffleVector(V1, V2, Mask));
1136 // Handle getelementptr instructions. If all operands are constants then we
1137 // can turn this into a getelementptr ConstantExpr.
1139 void SCCPSolver::visitGetElementPtrInst(GetElementPtrInst &I) {
1140 if (ValueState[&I].isOverdefined()) return;
1142 SmallVector<Constant*, 8> Operands;
1143 Operands.reserve(I.getNumOperands());
1145 for (unsigned i = 0, e = I.getNumOperands(); i != e; ++i) {
1146 LatticeVal State = getValueState(I.getOperand(i));
1147 if (State.isUndefined())
1148 return; // Operands are not resolved yet.
1150 if (State.isOverdefined())
1151 return markOverdefined(&I);
1153 assert(State.isConstant() && "Unknown state!");
1154 Operands.push_back(State.getConstant());
1157 Constant *Ptr = Operands[0];
1158 markConstant(&I, ConstantExpr::getGetElementPtr(Ptr, &Operands[0]+1,
1159 Operands.size()-1));
1162 void SCCPSolver::visitStoreInst(StoreInst &SI) {
1163 // If this store is of a struct, ignore it.
1164 if (isa<StructType>(SI.getOperand(0)->getType()))
1167 if (TrackedGlobals.empty() || !isa<GlobalVariable>(SI.getOperand(1)))
1170 GlobalVariable *GV = cast<GlobalVariable>(SI.getOperand(1));
1171 DenseMap<GlobalVariable*, LatticeVal>::iterator I = TrackedGlobals.find(GV);
1172 if (I == TrackedGlobals.end() || I->second.isOverdefined()) return;
1174 // Get the value we are storing into the global, then merge it.
1175 mergeInValue(I->second, GV, getValueState(SI.getOperand(0)));
1176 if (I->second.isOverdefined())
1177 TrackedGlobals.erase(I); // No need to keep tracking this!
1181 // Handle load instructions. If the operand is a constant pointer to a constant
1182 // global, we can replace the load with the loaded constant value!
1183 void SCCPSolver::visitLoadInst(LoadInst &I) {
1184 // If this load is of a struct, just mark the result overdefined.
1185 if (isa<StructType>(I.getType()))
1186 return markAnythingOverdefined(&I);
1188 LatticeVal PtrVal = getValueState(I.getOperand(0));
1189 if (PtrVal.isUndefined()) return; // The pointer is not resolved yet!
1191 LatticeVal &IV = ValueState[&I];
1192 if (IV.isOverdefined()) return;
1194 if (!PtrVal.isConstant() || I.isVolatile())
1195 return markOverdefined(IV, &I);
1197 Constant *Ptr = PtrVal.getConstant();
1199 // load null -> null
1200 if (isa<ConstantPointerNull>(Ptr) && I.getPointerAddressSpace() == 0)
1201 return markConstant(IV, &I, Constant::getNullValue(I.getType()));
1203 // Transform load (constant global) into the value loaded.
1204 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Ptr)) {
1205 if (!TrackedGlobals.empty()) {
1206 // If we are tracking this global, merge in the known value for it.
1207 DenseMap<GlobalVariable*, LatticeVal>::iterator It =
1208 TrackedGlobals.find(GV);
1209 if (It != TrackedGlobals.end()) {
1210 mergeInValue(IV, &I, It->second);
1216 // Transform load from a constant into a constant if possible.
1217 if (Constant *C = ConstantFoldLoadFromConstPtr(Ptr, TD))
1218 return markConstant(IV, &I, C);
1220 // Otherwise we cannot say for certain what value this load will produce.
1222 markOverdefined(IV, &I);
1225 void SCCPSolver::visitCallSite(CallSite CS) {
1226 Function *F = CS.getCalledFunction();
1227 Instruction *I = CS.getInstruction();
1229 // The common case is that we aren't tracking the callee, either because we
1230 // are not doing interprocedural analysis or the callee is indirect, or is
1231 // external. Handle these cases first.
1232 if (F == 0 || F->isDeclaration()) {
1234 // Void return and not tracking callee, just bail.
1235 if (I->getType()->isVoidTy()) return;
1237 // Otherwise, if we have a single return value case, and if the function is
1238 // a declaration, maybe we can constant fold it.
1239 if (F && F->isDeclaration() && !isa<StructType>(I->getType()) &&
1240 canConstantFoldCallTo(F)) {
1242 SmallVector<Constant*, 8> Operands;
1243 for (CallSite::arg_iterator AI = CS.arg_begin(), E = CS.arg_end();
1245 LatticeVal State = getValueState(*AI);
1247 if (State.isUndefined())
1248 return; // Operands are not resolved yet.
1249 if (State.isOverdefined())
1250 return markOverdefined(I);
1251 assert(State.isConstant() && "Unknown state!");
1252 Operands.push_back(State.getConstant());
1255 // If we can constant fold this, mark the result of the call as a
1257 if (Constant *C = ConstantFoldCall(F, Operands.data(), Operands.size()))
1258 return markConstant(I, C);
1261 // Otherwise, we don't know anything about this call, mark it overdefined.
1262 return markAnythingOverdefined(I);
1265 // If this is a local function that doesn't have its address taken, mark its
1266 // entry block executable and merge in the actual arguments to the call into
1267 // the formal arguments of the function.
1268 if (!TrackingIncomingArguments.empty() && TrackingIncomingArguments.count(F)){
1269 MarkBlockExecutable(F->begin());
1271 // Propagate information from this call site into the callee.
1272 CallSite::arg_iterator CAI = CS.arg_begin();
1273 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
1274 AI != E; ++AI, ++CAI) {
1275 // If this argument is byval, and if the function is not readonly, there
1276 // will be an implicit copy formed of the input aggregate.
1277 if (AI->hasByValAttr() && !F->onlyReadsMemory()) {
1278 markOverdefined(AI);
1282 if (const StructType *STy = dyn_cast<StructType>(AI->getType())) {
1283 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
1284 LatticeVal CallArg = getStructValueState(*CAI, i);
1285 mergeInValue(getStructValueState(AI, i), AI, CallArg);
1288 mergeInValue(AI, getValueState(*CAI));
1293 // If this is a single/zero retval case, see if we're tracking the function.
1294 if (const StructType *STy = dyn_cast<StructType>(F->getReturnType())) {
1295 if (!MRVFunctionsTracked.count(F))
1296 goto CallOverdefined; // Not tracking this callee.
1298 // If we are tracking this callee, propagate the result of the function
1299 // into this call site.
1300 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
1301 mergeInValue(getStructValueState(I, i), I,
1302 TrackedMultipleRetVals[std::make_pair(F, i)]);
1304 DenseMap<Function*, LatticeVal>::iterator TFRVI = TrackedRetVals.find(F);
1305 if (TFRVI == TrackedRetVals.end())
1306 goto CallOverdefined; // Not tracking this callee.
1308 // If so, propagate the return value of the callee into this call result.
1309 mergeInValue(I, TFRVI->second);
1313 void SCCPSolver::Solve() {
1314 // Process the work lists until they are empty!
1315 while (!BBWorkList.empty() || !InstWorkList.empty() ||
1316 !OverdefinedInstWorkList.empty()) {
1317 // Process the overdefined instruction's work list first, which drives other
1318 // things to overdefined more quickly.
1319 while (!OverdefinedInstWorkList.empty()) {
1320 Value *I = OverdefinedInstWorkList.pop_back_val();
1322 DEBUG(errs() << "\nPopped off OI-WL: " << *I << '\n');
1324 // "I" got into the work list because it either made the transition from
1325 // bottom to constant
1327 // Anything on this worklist that is overdefined need not be visited
1328 // since all of its users will have already been marked as overdefined
1329 // Update all of the users of this instruction's value.
1331 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
1333 if (Instruction *I = dyn_cast<Instruction>(*UI))
1334 OperandChangedState(I);
1337 // Process the instruction work list.
1338 while (!InstWorkList.empty()) {
1339 Value *I = InstWorkList.pop_back_val();
1341 DEBUG(errs() << "\nPopped off I-WL: " << *I << '\n');
1343 // "I" got into the work list because it made the transition from undef to
1346 // Anything on this worklist that is overdefined need not be visited
1347 // since all of its users will have already been marked as overdefined.
1348 // Update all of the users of this instruction's value.
1350 if (isa<StructType>(I->getType()) || !getValueState(I).isOverdefined())
1351 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
1353 if (Instruction *I = dyn_cast<Instruction>(*UI))
1354 OperandChangedState(I);
1357 // Process the basic block work list.
1358 while (!BBWorkList.empty()) {
1359 BasicBlock *BB = BBWorkList.back();
1360 BBWorkList.pop_back();
1362 DEBUG(errs() << "\nPopped off BBWL: " << *BB << '\n');
1364 // Notify all instructions in this basic block that they are newly
1371 /// ResolvedUndefsIn - While solving the dataflow for a function, we assume
1372 /// that branches on undef values cannot reach any of their successors.
1373 /// However, this is not a safe assumption. After we solve dataflow, this
1374 /// method should be use to handle this. If this returns true, the solver
1375 /// should be rerun.
1377 /// This method handles this by finding an unresolved branch and marking it one
1378 /// of the edges from the block as being feasible, even though the condition
1379 /// doesn't say it would otherwise be. This allows SCCP to find the rest of the
1380 /// CFG and only slightly pessimizes the analysis results (by marking one,
1381 /// potentially infeasible, edge feasible). This cannot usefully modify the
1382 /// constraints on the condition of the branch, as that would impact other users
1385 /// This scan also checks for values that use undefs, whose results are actually
1386 /// defined. For example, 'zext i8 undef to i32' should produce all zeros
1387 /// conservatively, as "(zext i8 X -> i32) & 0xFF00" must always return zero,
1388 /// even if X isn't defined.
1389 bool SCCPSolver::ResolvedUndefsIn(Function &F) {
1390 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
1391 if (!BBExecutable.count(BB))
1394 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
1395 // Look for instructions which produce undef values.
1396 if (I->getType()->isVoidTy()) continue;
1398 if (const StructType *STy = dyn_cast<StructType>(I->getType())) {
1399 // Only a few things that can be structs matter for undef. Just send
1400 // all their results to overdefined. We could be more precise than this
1401 // but it isn't worth bothering.
1402 if (isa<CallInst>(I) || isa<SelectInst>(I)) {
1403 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
1404 LatticeVal &LV = getStructValueState(I, i);
1405 if (LV.isUndefined())
1406 markOverdefined(LV, I);
1412 LatticeVal &LV = getValueState(I);
1413 if (!LV.isUndefined()) continue;
1415 // No instructions using structs need disambiguation.
1416 if (isa<StructType>(I->getOperand(0)->getType()))
1419 // Get the lattice values of the first two operands for use below.
1420 LatticeVal Op0LV = getValueState(I->getOperand(0));
1422 if (I->getNumOperands() == 2) {
1423 // No instructions using structs need disambiguation.
1424 if (isa<StructType>(I->getOperand(1)->getType()))
1427 // If this is a two-operand instruction, and if both operands are
1428 // undefs, the result stays undef.
1429 Op1LV = getValueState(I->getOperand(1));
1430 if (Op0LV.isUndefined() && Op1LV.isUndefined())
1434 // If this is an instructions whose result is defined even if the input is
1435 // not fully defined, propagate the information.
1436 const Type *ITy = I->getType();
1437 switch (I->getOpcode()) {
1438 default: break; // Leave the instruction as an undef.
1439 case Instruction::ZExt:
1440 // After a zero extend, we know the top part is zero. SExt doesn't have
1441 // to be handled here, because we don't know whether the top part is 1's
1443 markForcedConstant(I, Constant::getNullValue(ITy));
1445 case Instruction::Mul:
1446 case Instruction::And:
1447 // undef * X -> 0. X could be zero.
1448 // undef & X -> 0. X could be zero.
1449 markForcedConstant(I, Constant::getNullValue(ITy));
1452 case Instruction::Or:
1453 // undef | X -> -1. X could be -1.
1454 markForcedConstant(I, Constant::getAllOnesValue(ITy));
1457 case Instruction::SDiv:
1458 case Instruction::UDiv:
1459 case Instruction::SRem:
1460 case Instruction::URem:
1461 // X / undef -> undef. No change.
1462 // X % undef -> undef. No change.
1463 if (Op1LV.isUndefined()) break;
1465 // undef / X -> 0. X could be maxint.
1466 // undef % X -> 0. X could be 1.
1467 markForcedConstant(I, Constant::getNullValue(ITy));
1470 case Instruction::AShr:
1471 // undef >>s X -> undef. No change.
1472 if (Op0LV.isUndefined()) break;
1474 // X >>s undef -> X. X could be 0, X could have the high-bit known set.
1475 if (Op0LV.isConstant())
1476 markForcedConstant(I, Op0LV.getConstant());
1480 case Instruction::LShr:
1481 case Instruction::Shl:
1482 // undef >> X -> undef. No change.
1483 // undef << X -> undef. No change.
1484 if (Op0LV.isUndefined()) break;
1486 // X >> undef -> 0. X could be 0.
1487 // X << undef -> 0. X could be 0.
1488 markForcedConstant(I, Constant::getNullValue(ITy));
1490 case Instruction::Select:
1491 // undef ? X : Y -> X or Y. There could be commonality between X/Y.
1492 if (Op0LV.isUndefined()) {
1493 if (!Op1LV.isConstant()) // Pick the constant one if there is any.
1494 Op1LV = getValueState(I->getOperand(2));
1495 } else if (Op1LV.isUndefined()) {
1496 // c ? undef : undef -> undef. No change.
1497 Op1LV = getValueState(I->getOperand(2));
1498 if (Op1LV.isUndefined())
1500 // Otherwise, c ? undef : x -> x.
1502 // Leave Op1LV as Operand(1)'s LatticeValue.
1505 if (Op1LV.isConstant())
1506 markForcedConstant(I, Op1LV.getConstant());
1510 case Instruction::Call:
1511 // If a call has an undef result, it is because it is constant foldable
1512 // but one of the inputs was undef. Just force the result to
1519 TerminatorInst *TI = BB->getTerminator();
1520 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
1521 if (!BI->isConditional()) continue;
1522 if (!getValueState(BI->getCondition()).isUndefined())
1524 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
1525 if (SI->getNumSuccessors() < 2) // no cases
1527 if (!getValueState(SI->getCondition()).isUndefined())
1533 // If the edge to the second successor isn't thought to be feasible yet,
1534 // mark it so now. We pick the second one so that this goes to some
1535 // enumerated value in a switch instead of going to the default destination.
1536 if (KnownFeasibleEdges.count(Edge(BB, TI->getSuccessor(1))))
1539 // Otherwise, it isn't already thought to be feasible. Mark it as such now
1540 // and return. This will make other blocks reachable, which will allow new
1541 // values to be discovered and existing ones to be moved in the lattice.
1542 markEdgeExecutable(BB, TI->getSuccessor(1));
1544 // This must be a conditional branch of switch on undef. At this point,
1545 // force the old terminator to branch to the first successor. This is
1546 // required because we are now influencing the dataflow of the function with
1547 // the assumption that this edge is taken. If we leave the branch condition
1548 // as undef, then further analysis could think the undef went another way
1549 // leading to an inconsistent set of conclusions.
1550 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
1551 BI->setCondition(ConstantInt::getFalse(BI->getContext()));
1553 SwitchInst *SI = cast<SwitchInst>(TI);
1554 SI->setCondition(SI->getCaseValue(1));
1565 //===--------------------------------------------------------------------===//
1567 /// SCCP Class - This class uses the SCCPSolver to implement a per-function
1568 /// Sparse Conditional Constant Propagator.
1570 struct SCCP : public FunctionPass {
1571 static char ID; // Pass identification, replacement for typeid
1572 SCCP() : FunctionPass(&ID) {}
1574 // runOnFunction - Run the Sparse Conditional Constant Propagation
1575 // algorithm, and return true if the function was modified.
1577 bool runOnFunction(Function &F);
1579 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
1580 AU.setPreservesCFG();
1583 } // end anonymous namespace
1586 static RegisterPass<SCCP>
1587 X("sccp", "Sparse Conditional Constant Propagation");
1589 // createSCCPPass - This is the public interface to this file.
1590 FunctionPass *llvm::createSCCPPass() {
1594 static void DeleteInstructionInBlock(BasicBlock *BB) {
1595 DEBUG(errs() << " BasicBlock Dead:" << *BB);
1598 // Delete the instructions backwards, as it has a reduced likelihood of
1599 // having to update as many def-use and use-def chains.
1600 while (!isa<TerminatorInst>(BB->begin())) {
1601 Instruction *I = --BasicBlock::iterator(BB->getTerminator());
1603 if (!I->use_empty())
1604 I->replaceAllUsesWith(UndefValue::get(I->getType()));
1605 BB->getInstList().erase(I);
1610 // runOnFunction() - Run the Sparse Conditional Constant Propagation algorithm,
1611 // and return true if the function was modified.
1613 bool SCCP::runOnFunction(Function &F) {
1614 DEBUG(errs() << "SCCP on function '" << F.getName() << "'\n");
1615 SCCPSolver Solver(getAnalysisIfAvailable<TargetData>());
1617 // Mark the first block of the function as being executable.
1618 Solver.MarkBlockExecutable(F.begin());
1620 // Mark all arguments to the function as being overdefined.
1621 for (Function::arg_iterator AI = F.arg_begin(), E = F.arg_end(); AI != E;++AI)
1622 Solver.markAnythingOverdefined(AI);
1624 // Solve for constants.
1625 bool ResolvedUndefs = true;
1626 while (ResolvedUndefs) {
1628 DEBUG(errs() << "RESOLVING UNDEFs\n");
1629 ResolvedUndefs = Solver.ResolvedUndefsIn(F);
1632 bool MadeChanges = false;
1634 // If we decided that there are basic blocks that are dead in this function,
1635 // delete their contents now. Note that we cannot actually delete the blocks,
1636 // as we cannot modify the CFG of the function.
1638 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
1639 if (!Solver.isBlockExecutable(BB)) {
1640 DeleteInstructionInBlock(BB);
1645 // Iterate over all of the instructions in a function, replacing them with
1646 // constants if we have found them to be of constant values.
1648 for (BasicBlock::iterator BI = BB->begin(), E = BB->end(); BI != E; ) {
1649 Instruction *Inst = BI++;
1650 if (Inst->getType()->isVoidTy() || isa<TerminatorInst>(Inst))
1653 // TODO: Reconstruct structs from their elements.
1654 if (isa<StructType>(Inst->getType()))
1657 LatticeVal IV = Solver.getLatticeValueFor(Inst);
1658 if (IV.isOverdefined())
1661 Constant *Const = IV.isConstant()
1662 ? IV.getConstant() : UndefValue::get(Inst->getType());
1663 DEBUG(errs() << " Constant: " << *Const << " = " << *Inst);
1665 // Replaces all of the uses of a variable with uses of the constant.
1666 Inst->replaceAllUsesWith(Const);
1668 // Delete the instruction.
1669 Inst->eraseFromParent();
1671 // Hey, we just changed something!
1681 //===--------------------------------------------------------------------===//
1683 /// IPSCCP Class - This class implements interprocedural Sparse Conditional
1684 /// Constant Propagation.
1686 struct IPSCCP : public ModulePass {
1688 IPSCCP() : ModulePass(&ID) {}
1689 bool runOnModule(Module &M);
1691 } // end anonymous namespace
1693 char IPSCCP::ID = 0;
1694 static RegisterPass<IPSCCP>
1695 Y("ipsccp", "Interprocedural Sparse Conditional Constant Propagation");
1697 // createIPSCCPPass - This is the public interface to this file.
1698 ModulePass *llvm::createIPSCCPPass() {
1699 return new IPSCCP();
1703 static bool AddressIsTaken(GlobalValue *GV) {
1704 // Delete any dead constantexpr klingons.
1705 GV->removeDeadConstantUsers();
1707 for (Value::use_iterator UI = GV->use_begin(), E = GV->use_end();
1709 if (StoreInst *SI = dyn_cast<StoreInst>(*UI)) {
1710 if (SI->getOperand(0) == GV || SI->isVolatile())
1711 return true; // Storing addr of GV.
1712 } else if (isa<InvokeInst>(*UI) || isa<CallInst>(*UI)) {
1713 // Make sure we are calling the function, not passing the address.
1714 if (UI.getOperandNo() != 0)
1716 } else if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) {
1717 if (LI->isVolatile())
1719 } else if (isa<BlockAddress>(*UI)) {
1720 // blockaddress doesn't take the address of the function, it takes addr
1728 bool IPSCCP::runOnModule(Module &M) {
1729 SCCPSolver Solver(getAnalysisIfAvailable<TargetData>());
1731 // Loop over all functions, marking arguments to those with their addresses
1732 // taken or that are external as overdefined.
1734 for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) {
1735 if (F->isDeclaration())
1738 // If this is a strong or ODR definition of this function, then we can
1739 // propagate information about its result into callsites of it.
1740 if (!F->mayBeOverridden())
1741 Solver.AddTrackedFunction(F);
1743 // If this function only has direct calls that we can see, we can track its
1744 // arguments and return value aggressively, and can assume it is not called
1745 // unless we see evidence to the contrary.
1746 if (F->hasLocalLinkage() && !AddressIsTaken(F)) {
1747 Solver.AddArgumentTrackedFunction(F);
1751 // Assume the function is called.
1752 Solver.MarkBlockExecutable(F->begin());
1754 // Assume nothing about the incoming arguments.
1755 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
1757 Solver.markAnythingOverdefined(AI);
1760 // Loop over global variables. We inform the solver about any internal global
1761 // variables that do not have their 'addresses taken'. If they don't have
1762 // their addresses taken, we can propagate constants through them.
1763 for (Module::global_iterator G = M.global_begin(), E = M.global_end();
1765 if (!G->isConstant() && G->hasLocalLinkage() && !AddressIsTaken(G))
1766 Solver.TrackValueOfGlobalVariable(G);
1768 // Solve for constants.
1769 bool ResolvedUndefs = true;
1770 while (ResolvedUndefs) {
1773 DEBUG(errs() << "RESOLVING UNDEFS\n");
1774 ResolvedUndefs = false;
1775 for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F)
1776 ResolvedUndefs |= Solver.ResolvedUndefsIn(*F);
1779 bool MadeChanges = false;
1781 // Iterate over all of the instructions in the module, replacing them with
1782 // constants if we have found them to be of constant values.
1784 SmallVector<BasicBlock*, 512> BlocksToErase;
1786 for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) {
1787 if (Solver.isBlockExecutable(F->begin())) {
1788 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
1790 if (AI->use_empty() || isa<StructType>(AI->getType())) continue;
1792 // TODO: Could use getStructLatticeValueFor to find out if the entire
1793 // result is a constant and replace it entirely if so.
1795 LatticeVal IV = Solver.getLatticeValueFor(AI);
1796 if (IV.isOverdefined()) continue;
1798 Constant *CST = IV.isConstant() ?
1799 IV.getConstant() : UndefValue::get(AI->getType());
1800 DEBUG(errs() << "*** Arg " << *AI << " = " << *CST <<"\n");
1802 // Replaces all of the uses of a variable with uses of the
1804 AI->replaceAllUsesWith(CST);
1809 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB) {
1810 if (!Solver.isBlockExecutable(BB)) {
1811 DeleteInstructionInBlock(BB);
1814 TerminatorInst *TI = BB->getTerminator();
1815 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) {
1816 BasicBlock *Succ = TI->getSuccessor(i);
1817 if (!Succ->empty() && isa<PHINode>(Succ->begin()))
1818 TI->getSuccessor(i)->removePredecessor(BB);
1820 if (!TI->use_empty())
1821 TI->replaceAllUsesWith(UndefValue::get(TI->getType()));
1822 TI->eraseFromParent();
1824 if (&*BB != &F->front())
1825 BlocksToErase.push_back(BB);
1827 new UnreachableInst(M.getContext(), BB);
1831 for (BasicBlock::iterator BI = BB->begin(), E = BB->end(); BI != E; ) {
1832 Instruction *Inst = BI++;
1833 if (Inst->getType()->isVoidTy() || isa<StructType>(Inst->getType()))
1836 // TODO: Could use getStructLatticeValueFor to find out if the entire
1837 // result is a constant and replace it entirely if so.
1839 LatticeVal IV = Solver.getLatticeValueFor(Inst);
1840 if (IV.isOverdefined())
1843 Constant *Const = IV.isConstant()
1844 ? IV.getConstant() : UndefValue::get(Inst->getType());
1845 DEBUG(errs() << " Constant: " << *Const << " = " << *Inst);
1847 // Replaces all of the uses of a variable with uses of the
1849 Inst->replaceAllUsesWith(Const);
1851 // Delete the instruction.
1852 if (!isa<CallInst>(Inst) && !isa<TerminatorInst>(Inst))
1853 Inst->eraseFromParent();
1855 // Hey, we just changed something!
1861 // Now that all instructions in the function are constant folded, erase dead
1862 // blocks, because we can now use ConstantFoldTerminator to get rid of
1864 for (unsigned i = 0, e = BlocksToErase.size(); i != e; ++i) {
1865 // If there are any PHI nodes in this successor, drop entries for BB now.
1866 BasicBlock *DeadBB = BlocksToErase[i];
1867 while (!DeadBB->use_empty()) {
1868 Instruction *I = cast<Instruction>(DeadBB->use_back());
1869 bool Folded = ConstantFoldTerminator(I->getParent());
1871 // The constant folder may not have been able to fold the terminator
1872 // if this is a branch or switch on undef. Fold it manually as a
1873 // branch to the first successor.
1875 if (BranchInst *BI = dyn_cast<BranchInst>(I)) {
1876 assert(BI->isConditional() && isa<UndefValue>(BI->getCondition()) &&
1877 "Branch should be foldable!");
1878 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(I)) {
1879 assert(isa<UndefValue>(SI->getCondition()) && "Switch should fold");
1881 llvm_unreachable("Didn't fold away reference to block!");
1885 // Make this an uncond branch to the first successor.
1886 TerminatorInst *TI = I->getParent()->getTerminator();
1887 BranchInst::Create(TI->getSuccessor(0), TI);
1889 // Remove entries in successor phi nodes to remove edges.
1890 for (unsigned i = 1, e = TI->getNumSuccessors(); i != e; ++i)
1891 TI->getSuccessor(i)->removePredecessor(TI->getParent());
1893 // Remove the old terminator.
1894 TI->eraseFromParent();
1898 // Finally, delete the basic block.
1899 F->getBasicBlockList().erase(DeadBB);
1901 BlocksToErase.clear();
1904 // If we inferred constant or undef return values for a function, we replaced
1905 // all call uses with the inferred value. This means we don't need to bother
1906 // actually returning anything from the function. Replace all return
1907 // instructions with return undef.
1908 // TODO: Process multiple value ret instructions also.
1909 const DenseMap<Function*, LatticeVal> &RV = Solver.getTrackedRetVals();
1910 for (DenseMap<Function*, LatticeVal>::const_iterator I = RV.begin(),
1911 E = RV.end(); I != E; ++I) {
1912 Function *F = I->first;
1913 if (I->second.isOverdefined() || F->getReturnType()->isVoidTy())
1916 // We can only do this if we know that nothing else can call the function.
1917 if (!F->hasLocalLinkage() || AddressIsTaken(F))
1920 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
1921 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator()))
1922 if (!isa<UndefValue>(RI->getOperand(0)))
1923 RI->setOperand(0, UndefValue::get(F->getReturnType()));
1926 // If we infered constant or undef values for globals variables, we can delete
1927 // the global and any stores that remain to it.
1928 const DenseMap<GlobalVariable*, LatticeVal> &TG = Solver.getTrackedGlobals();
1929 for (DenseMap<GlobalVariable*, LatticeVal>::const_iterator I = TG.begin(),
1930 E = TG.end(); I != E; ++I) {
1931 GlobalVariable *GV = I->first;
1932 assert(!I->second.isOverdefined() &&
1933 "Overdefined values should have been taken out of the map!");
1934 DEBUG(errs() << "Found that GV '" << GV->getName() << "' is constant!\n");
1935 while (!GV->use_empty()) {
1936 StoreInst *SI = cast<StoreInst>(GV->use_back());
1937 SI->eraseFromParent();
1939 M.getGlobalList().erase(GV);