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 #include "llvm/Transforms/Scalar.h"
21 #include "llvm/ADT/DenseMap.h"
22 #include "llvm/ADT/DenseSet.h"
23 #include "llvm/ADT/PointerIntPair.h"
24 #include "llvm/ADT/SmallPtrSet.h"
25 #include "llvm/ADT/SmallVector.h"
26 #include "llvm/ADT/Statistic.h"
27 #include "llvm/Analysis/ConstantFolding.h"
28 #include "llvm/IR/CallSite.h"
29 #include "llvm/IR/Constants.h"
30 #include "llvm/IR/DataLayout.h"
31 #include "llvm/IR/DerivedTypes.h"
32 #include "llvm/IR/InstVisitor.h"
33 #include "llvm/IR/Instructions.h"
34 #include "llvm/Pass.h"
35 #include "llvm/Support/Debug.h"
36 #include "llvm/Support/ErrorHandling.h"
37 #include "llvm/Support/raw_ostream.h"
38 #include "llvm/Analysis/TargetLibraryInfo.h"
39 #include "llvm/Transforms/IPO.h"
40 #include "llvm/Transforms/Utils/Local.h"
44 #define DEBUG_TYPE "sccp"
46 STATISTIC(NumInstRemoved, "Number of instructions removed");
47 STATISTIC(NumDeadBlocks , "Number of basic blocks unreachable");
49 STATISTIC(IPNumInstRemoved, "Number of instructions removed by IPSCCP");
50 STATISTIC(IPNumArgsElimed ,"Number of arguments constant propagated by IPSCCP");
51 STATISTIC(IPNumGlobalConst, "Number of globals found to be constant by IPSCCP");
54 /// LatticeVal class - This class represents the different lattice values that
55 /// an LLVM value may occupy. It is a simple class with value semantics.
59 /// undefined - This LLVM Value has no known value yet.
62 /// constant - This LLVM Value has a specific constant value.
65 /// forcedconstant - This LLVM Value was thought to be undef until
66 /// ResolvedUndefsIn. This is treated just like 'constant', but if merged
67 /// with another (different) constant, it goes to overdefined, instead of
71 /// overdefined - This instruction is not known to be constant, and we know
76 /// Val: This stores the current lattice value along with the Constant* for
77 /// the constant if this is a 'constant' or 'forcedconstant' value.
78 PointerIntPair<Constant *, 2, LatticeValueTy> Val;
80 LatticeValueTy getLatticeValue() const {
85 LatticeVal() : Val(nullptr, undefined) {}
87 bool isUndefined() const { return getLatticeValue() == undefined; }
88 bool isConstant() const {
89 return getLatticeValue() == constant || getLatticeValue() == forcedconstant;
91 bool isOverdefined() const { return getLatticeValue() == overdefined; }
93 Constant *getConstant() const {
94 assert(isConstant() && "Cannot get the constant of a non-constant!");
95 return Val.getPointer();
98 /// markOverdefined - Return true if this is a change in status.
99 bool markOverdefined() {
103 Val.setInt(overdefined);
107 /// markConstant - Return true if this is a change in status.
108 bool markConstant(Constant *V) {
109 if (getLatticeValue() == constant) { // Constant but not forcedconstant.
110 assert(getConstant() == V && "Marking constant with different value");
115 Val.setInt(constant);
116 assert(V && "Marking constant with NULL");
119 assert(getLatticeValue() == forcedconstant &&
120 "Cannot move from overdefined to constant!");
121 // Stay at forcedconstant if the constant is the same.
122 if (V == getConstant()) return false;
124 // Otherwise, we go to overdefined. Assumptions made based on the
125 // forced value are possibly wrong. Assuming this is another constant
126 // could expose a contradiction.
127 Val.setInt(overdefined);
132 /// getConstantInt - If this is a constant with a ConstantInt value, return it
133 /// otherwise return null.
134 ConstantInt *getConstantInt() const {
136 return dyn_cast<ConstantInt>(getConstant());
140 void markForcedConstant(Constant *V) {
141 assert(isUndefined() && "Can't force a defined value!");
142 Val.setInt(forcedconstant);
146 } // end anonymous namespace.
151 //===----------------------------------------------------------------------===//
153 /// SCCPSolver - This class is a general purpose solver for Sparse Conditional
154 /// Constant Propagation.
156 class SCCPSolver : public InstVisitor<SCCPSolver> {
157 const DataLayout &DL;
158 const TargetLibraryInfo *TLI;
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 /// KnownFeasibleEdges - Entries in this set are edges which have already had
205 /// PHI nodes retriggered.
206 typedef std::pair<BasicBlock*, BasicBlock*> Edge;
207 DenseSet<Edge> KnownFeasibleEdges;
209 SCCPSolver(const DataLayout &DL, const TargetLibraryInfo *tli)
210 : DL(DL), TLI(tli) {}
212 /// MarkBlockExecutable - This method can be used by clients to mark all of
213 /// the blocks that are known to be intrinsically live in the processed unit.
215 /// This returns true if the block was not considered live before.
216 bool MarkBlockExecutable(BasicBlock *BB) {
217 if (!BBExecutable.insert(BB).second)
219 DEBUG(dbgs() << "Marking Block Executable: " << BB->getName() << '\n');
220 BBWorkList.push_back(BB); // Add the block to the work list!
224 /// TrackValueOfGlobalVariable - Clients can use this method to
225 /// inform the SCCPSolver that it should track loads and stores to the
226 /// specified global variable if it can. This is only legal to call if
227 /// performing Interprocedural SCCP.
228 void TrackValueOfGlobalVariable(GlobalVariable *GV) {
229 // We only track the contents of scalar globals.
230 if (GV->getType()->getElementType()->isSingleValueType()) {
231 LatticeVal &IV = TrackedGlobals[GV];
232 if (!isa<UndefValue>(GV->getInitializer()))
233 IV.markConstant(GV->getInitializer());
237 /// AddTrackedFunction - If the SCCP solver is supposed to track calls into
238 /// and out of the specified function (which cannot have its address taken),
239 /// this method must be called.
240 void AddTrackedFunction(Function *F) {
241 // Add an entry, F -> undef.
242 if (StructType *STy = dyn_cast<StructType>(F->getReturnType())) {
243 MRVFunctionsTracked.insert(F);
244 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
245 TrackedMultipleRetVals.insert(std::make_pair(std::make_pair(F, i),
248 TrackedRetVals.insert(std::make_pair(F, LatticeVal()));
251 void AddArgumentTrackedFunction(Function *F) {
252 TrackingIncomingArguments.insert(F);
255 /// Solve - Solve for constants and executable blocks.
259 /// ResolvedUndefsIn - While solving the dataflow for a function, we assume
260 /// that branches on undef values cannot reach any of their successors.
261 /// However, this is not a safe assumption. After we solve dataflow, this
262 /// method should be use to handle this. If this returns true, the solver
264 bool ResolvedUndefsIn(Function &F);
266 bool isBlockExecutable(BasicBlock *BB) const {
267 return BBExecutable.count(BB);
270 LatticeVal getLatticeValueFor(Value *V) const {
271 DenseMap<Value*, LatticeVal>::const_iterator I = ValueState.find(V);
272 assert(I != ValueState.end() && "V is not in valuemap!");
276 /// getTrackedRetVals - Get the inferred return value map.
278 const DenseMap<Function*, LatticeVal> &getTrackedRetVals() {
279 return TrackedRetVals;
282 /// getTrackedGlobals - Get and return the set of inferred initializers for
283 /// global variables.
284 const DenseMap<GlobalVariable*, LatticeVal> &getTrackedGlobals() {
285 return TrackedGlobals;
288 void markOverdefined(Value *V) {
289 assert(!V->getType()->isStructTy() && "Should use other method");
290 markOverdefined(ValueState[V], V);
293 /// markAnythingOverdefined - Mark the specified value overdefined. This
294 /// works with both scalars and structs.
295 void markAnythingOverdefined(Value *V) {
296 if (StructType *STy = dyn_cast<StructType>(V->getType()))
297 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
298 markOverdefined(getStructValueState(V, i), V);
304 // markConstant - Make a value be marked as "constant". If the value
305 // is not already a constant, add it to the instruction work list so that
306 // the users of the instruction are updated later.
308 void markConstant(LatticeVal &IV, Value *V, Constant *C) {
309 if (!IV.markConstant(C)) return;
310 DEBUG(dbgs() << "markConstant: " << *C << ": " << *V << '\n');
311 if (IV.isOverdefined())
312 OverdefinedInstWorkList.push_back(V);
314 InstWorkList.push_back(V);
317 void markConstant(Value *V, Constant *C) {
318 assert(!V->getType()->isStructTy() && "Should use other method");
319 markConstant(ValueState[V], V, C);
322 void markForcedConstant(Value *V, Constant *C) {
323 assert(!V->getType()->isStructTy() && "Should use other method");
324 LatticeVal &IV = ValueState[V];
325 IV.markForcedConstant(C);
326 DEBUG(dbgs() << "markForcedConstant: " << *C << ": " << *V << '\n');
327 if (IV.isOverdefined())
328 OverdefinedInstWorkList.push_back(V);
330 InstWorkList.push_back(V);
334 // markOverdefined - Make a value be marked as "overdefined". If the
335 // value is not already overdefined, add it to the overdefined instruction
336 // work list so that the users of the instruction are updated later.
337 void markOverdefined(LatticeVal &IV, Value *V) {
338 if (!IV.markOverdefined()) return;
340 DEBUG(dbgs() << "markOverdefined: ";
341 if (Function *F = dyn_cast<Function>(V))
342 dbgs() << "Function '" << F->getName() << "'\n";
344 dbgs() << *V << '\n');
345 // Only instructions go on the work list
346 OverdefinedInstWorkList.push_back(V);
349 void mergeInValue(LatticeVal &IV, Value *V, LatticeVal MergeWithV) {
350 if (IV.isOverdefined() || MergeWithV.isUndefined())
352 if (MergeWithV.isOverdefined())
353 markOverdefined(IV, V);
354 else if (IV.isUndefined())
355 markConstant(IV, V, MergeWithV.getConstant());
356 else if (IV.getConstant() != MergeWithV.getConstant())
357 markOverdefined(IV, V);
360 void mergeInValue(Value *V, LatticeVal MergeWithV) {
361 assert(!V->getType()->isStructTy() && "Should use other method");
362 mergeInValue(ValueState[V], V, MergeWithV);
366 /// getValueState - Return the LatticeVal object that corresponds to the
367 /// value. This function handles the case when the value hasn't been seen yet
368 /// by properly seeding constants etc.
369 LatticeVal &getValueState(Value *V) {
370 assert(!V->getType()->isStructTy() && "Should use getStructValueState");
372 std::pair<DenseMap<Value*, LatticeVal>::iterator, bool> I =
373 ValueState.insert(std::make_pair(V, LatticeVal()));
374 LatticeVal &LV = I.first->second;
377 return LV; // Common case, already in the map.
379 if (Constant *C = dyn_cast<Constant>(V)) {
380 // Undef values remain undefined.
381 if (!isa<UndefValue>(V))
382 LV.markConstant(C); // Constants are constant
385 // All others are underdefined by default.
389 /// getStructValueState - Return the LatticeVal object that corresponds to the
390 /// value/field pair. This function handles the case when the value hasn't
391 /// been seen yet by properly seeding constants etc.
392 LatticeVal &getStructValueState(Value *V, unsigned i) {
393 assert(V->getType()->isStructTy() && "Should use getValueState");
394 assert(i < cast<StructType>(V->getType())->getNumElements() &&
395 "Invalid element #");
397 std::pair<DenseMap<std::pair<Value*, unsigned>, LatticeVal>::iterator,
398 bool> I = StructValueState.insert(
399 std::make_pair(std::make_pair(V, i), LatticeVal()));
400 LatticeVal &LV = I.first->second;
403 return LV; // Common case, already in the map.
405 if (Constant *C = dyn_cast<Constant>(V)) {
406 Constant *Elt = C->getAggregateElement(i);
409 LV.markOverdefined(); // Unknown sort of constant.
410 else if (isa<UndefValue>(Elt))
411 ; // Undef values remain undefined.
413 LV.markConstant(Elt); // Constants are constant.
416 // All others are underdefined by default.
421 /// markEdgeExecutable - Mark a basic block as executable, adding it to the BB
422 /// work list if it is not already executable.
423 void markEdgeExecutable(BasicBlock *Source, BasicBlock *Dest) {
424 if (!KnownFeasibleEdges.insert(Edge(Source, Dest)).second)
425 return; // This edge is already known to be executable!
427 if (!MarkBlockExecutable(Dest)) {
428 // If the destination is already executable, we just made an *edge*
429 // feasible that wasn't before. Revisit the PHI nodes in the block
430 // because they have potentially new operands.
431 DEBUG(dbgs() << "Marking Edge Executable: " << Source->getName()
432 << " -> " << Dest->getName() << '\n');
435 for (BasicBlock::iterator I = Dest->begin();
436 (PN = dyn_cast<PHINode>(I)); ++I)
441 // getFeasibleSuccessors - Return a vector of booleans to indicate which
442 // successors are reachable from a given terminator instruction.
444 void getFeasibleSuccessors(TerminatorInst &TI, SmallVectorImpl<bool> &Succs);
446 // isEdgeFeasible - Return true if the control flow edge from the 'From' basic
447 // block to the 'To' basic block is currently feasible.
449 bool isEdgeFeasible(BasicBlock *From, BasicBlock *To);
451 // OperandChangedState - This method is invoked on all of the users of an
452 // instruction that was just changed state somehow. Based on this
453 // information, we need to update the specified user of this instruction.
455 void OperandChangedState(Instruction *I) {
456 if (BBExecutable.count(I->getParent())) // Inst is executable?
461 friend class InstVisitor<SCCPSolver>;
463 // visit implementations - Something changed in this instruction. Either an
464 // operand made a transition, or the instruction is newly executable. Change
465 // the value type of I to reflect these changes if appropriate.
466 void visitPHINode(PHINode &I);
469 void visitReturnInst(ReturnInst &I);
470 void visitTerminatorInst(TerminatorInst &TI);
472 void visitCastInst(CastInst &I);
473 void visitSelectInst(SelectInst &I);
474 void visitBinaryOperator(Instruction &I);
475 void visitCmpInst(CmpInst &I);
476 void visitExtractElementInst(ExtractElementInst &I);
477 void visitInsertElementInst(InsertElementInst &I);
478 void visitShuffleVectorInst(ShuffleVectorInst &I);
479 void visitExtractValueInst(ExtractValueInst &EVI);
480 void visitInsertValueInst(InsertValueInst &IVI);
481 void visitLandingPadInst(LandingPadInst &I) { markAnythingOverdefined(&I); }
483 // Instructions that cannot be folded away.
484 void visitStoreInst (StoreInst &I);
485 void visitLoadInst (LoadInst &I);
486 void visitGetElementPtrInst(GetElementPtrInst &I);
487 void visitCallInst (CallInst &I) {
490 void visitInvokeInst (InvokeInst &II) {
492 visitTerminatorInst(II);
494 void visitCallSite (CallSite CS);
495 void visitResumeInst (TerminatorInst &I) { /*returns void*/ }
496 void visitUnreachableInst(TerminatorInst &I) { /*returns void*/ }
497 void visitFenceInst (FenceInst &I) { /*returns void*/ }
498 void visitAtomicCmpXchgInst(AtomicCmpXchgInst &I) {
499 markAnythingOverdefined(&I);
501 void visitAtomicRMWInst (AtomicRMWInst &I) { markOverdefined(&I); }
502 void visitAllocaInst (Instruction &I) { markOverdefined(&I); }
503 void visitVAArgInst (Instruction &I) { markAnythingOverdefined(&I); }
505 void visitInstruction(Instruction &I) {
506 // If a new instruction is added to LLVM that we don't handle.
507 dbgs() << "SCCP: Don't know how to handle: " << I << '\n';
508 markAnythingOverdefined(&I); // Just in case
512 } // end anonymous namespace
515 // getFeasibleSuccessors - Return a vector of booleans to indicate which
516 // successors are reachable from a given terminator instruction.
518 void SCCPSolver::getFeasibleSuccessors(TerminatorInst &TI,
519 SmallVectorImpl<bool> &Succs) {
520 Succs.resize(TI.getNumSuccessors());
521 if (BranchInst *BI = dyn_cast<BranchInst>(&TI)) {
522 if (BI->isUnconditional()) {
527 LatticeVal BCValue = getValueState(BI->getCondition());
528 ConstantInt *CI = BCValue.getConstantInt();
530 // Overdefined condition variables, and branches on unfoldable constant
531 // conditions, mean the branch could go either way.
532 if (!BCValue.isUndefined())
533 Succs[0] = Succs[1] = true;
537 // Constant condition variables mean the branch can only go a single way.
538 Succs[CI->isZero()] = true;
542 if (isa<InvokeInst>(TI)) {
543 // Invoke instructions successors are always executable.
544 Succs[0] = Succs[1] = true;
548 if (SwitchInst *SI = dyn_cast<SwitchInst>(&TI)) {
549 if (!SI->getNumCases()) {
553 LatticeVal SCValue = getValueState(SI->getCondition());
554 ConstantInt *CI = SCValue.getConstantInt();
556 if (!CI) { // Overdefined or undefined condition?
557 // All destinations are executable!
558 if (!SCValue.isUndefined())
559 Succs.assign(TI.getNumSuccessors(), true);
563 Succs[SI->findCaseValue(CI).getSuccessorIndex()] = true;
567 // TODO: This could be improved if the operand is a [cast of a] BlockAddress.
568 if (isa<IndirectBrInst>(&TI)) {
569 // Just mark all destinations executable!
570 Succs.assign(TI.getNumSuccessors(), true);
575 dbgs() << "Unknown terminator instruction: " << TI << '\n';
577 llvm_unreachable("SCCP: Don't know how to handle this terminator!");
581 // isEdgeFeasible - Return true if the control flow edge from the 'From' basic
582 // block to the 'To' basic block is currently feasible.
584 bool SCCPSolver::isEdgeFeasible(BasicBlock *From, BasicBlock *To) {
585 assert(BBExecutable.count(To) && "Dest should always be alive!");
587 // Make sure the source basic block is executable!!
588 if (!BBExecutable.count(From)) return false;
590 // Check to make sure this edge itself is actually feasible now.
591 TerminatorInst *TI = From->getTerminator();
592 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
593 if (BI->isUnconditional())
596 LatticeVal BCValue = getValueState(BI->getCondition());
598 // Overdefined condition variables mean the branch could go either way,
599 // undef conditions mean that neither edge is feasible yet.
600 ConstantInt *CI = BCValue.getConstantInt();
602 return !BCValue.isUndefined();
604 // Constant condition variables mean the branch can only go a single way.
605 return BI->getSuccessor(CI->isZero()) == To;
608 // Invoke instructions successors are always executable.
609 if (isa<InvokeInst>(TI))
612 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
613 if (SI->getNumCases() < 1)
616 LatticeVal SCValue = getValueState(SI->getCondition());
617 ConstantInt *CI = SCValue.getConstantInt();
620 return !SCValue.isUndefined();
622 return SI->findCaseValue(CI).getCaseSuccessor() == To;
625 // Just mark all destinations executable!
626 // TODO: This could be improved if the operand is a [cast of a] BlockAddress.
627 if (isa<IndirectBrInst>(TI))
631 dbgs() << "Unknown terminator instruction: " << *TI << '\n';
633 llvm_unreachable(nullptr);
636 // visit Implementations - Something changed in this instruction, either an
637 // operand made a transition, or the instruction is newly executable. Change
638 // the value type of I to reflect these changes if appropriate. This method
639 // makes sure to do the following actions:
641 // 1. If a phi node merges two constants in, and has conflicting value coming
642 // from different branches, or if the PHI node merges in an overdefined
643 // value, then the PHI node becomes overdefined.
644 // 2. If a phi node merges only constants in, and they all agree on value, the
645 // PHI node becomes a constant value equal to that.
646 // 3. If V <- x (op) y && isConstant(x) && isConstant(y) V = Constant
647 // 4. If V <- x (op) y && (isOverdefined(x) || isOverdefined(y)) V = Overdefined
648 // 5. If V <- MEM or V <- CALL or V <- (unknown) then V = Overdefined
649 // 6. If a conditional branch has a value that is constant, make the selected
650 // destination executable
651 // 7. If a conditional branch has a value that is overdefined, make all
652 // successors executable.
654 void SCCPSolver::visitPHINode(PHINode &PN) {
655 // If this PN returns a struct, just mark the result overdefined.
656 // TODO: We could do a lot better than this if code actually uses this.
657 if (PN.getType()->isStructTy())
658 return markAnythingOverdefined(&PN);
660 if (getValueState(&PN).isOverdefined())
661 return; // Quick exit
663 // Super-extra-high-degree PHI nodes are unlikely to ever be marked constant,
664 // and slow us down a lot. Just mark them overdefined.
665 if (PN.getNumIncomingValues() > 64)
666 return markOverdefined(&PN);
668 // Look at all of the executable operands of the PHI node. If any of them
669 // are overdefined, the PHI becomes overdefined as well. If they are all
670 // constant, and they agree with each other, the PHI becomes the identical
671 // constant. If they are constant and don't agree, the PHI is overdefined.
672 // If there are no executable operands, the PHI remains undefined.
674 Constant *OperandVal = nullptr;
675 for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) {
676 LatticeVal IV = getValueState(PN.getIncomingValue(i));
677 if (IV.isUndefined()) continue; // Doesn't influence PHI node.
679 if (!isEdgeFeasible(PN.getIncomingBlock(i), PN.getParent()))
682 if (IV.isOverdefined()) // PHI node becomes overdefined!
683 return markOverdefined(&PN);
685 if (!OperandVal) { // Grab the first value.
686 OperandVal = IV.getConstant();
690 // There is already a reachable operand. If we conflict with it,
691 // then the PHI node becomes overdefined. If we agree with it, we
694 // Check to see if there are two different constants merging, if so, the PHI
695 // node is overdefined.
696 if (IV.getConstant() != OperandVal)
697 return markOverdefined(&PN);
700 // If we exited the loop, this means that the PHI node only has constant
701 // arguments that agree with each other(and OperandVal is the constant) or
702 // OperandVal is null because there are no defined incoming arguments. If
703 // this is the case, the PHI remains undefined.
706 markConstant(&PN, OperandVal); // Acquire operand value
709 void SCCPSolver::visitReturnInst(ReturnInst &I) {
710 if (I.getNumOperands() == 0) return; // ret void
712 Function *F = I.getParent()->getParent();
713 Value *ResultOp = I.getOperand(0);
715 // If we are tracking the return value of this function, merge it in.
716 if (!TrackedRetVals.empty() && !ResultOp->getType()->isStructTy()) {
717 DenseMap<Function*, LatticeVal>::iterator TFRVI =
718 TrackedRetVals.find(F);
719 if (TFRVI != TrackedRetVals.end()) {
720 mergeInValue(TFRVI->second, F, getValueState(ResultOp));
725 // Handle functions that return multiple values.
726 if (!TrackedMultipleRetVals.empty()) {
727 if (StructType *STy = dyn_cast<StructType>(ResultOp->getType()))
728 if (MRVFunctionsTracked.count(F))
729 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
730 mergeInValue(TrackedMultipleRetVals[std::make_pair(F, i)], F,
731 getStructValueState(ResultOp, i));
736 void SCCPSolver::visitTerminatorInst(TerminatorInst &TI) {
737 SmallVector<bool, 16> SuccFeasible;
738 getFeasibleSuccessors(TI, SuccFeasible);
740 BasicBlock *BB = TI.getParent();
742 // Mark all feasible successors executable.
743 for (unsigned i = 0, e = SuccFeasible.size(); i != e; ++i)
745 markEdgeExecutable(BB, TI.getSuccessor(i));
748 void SCCPSolver::visitCastInst(CastInst &I) {
749 LatticeVal OpSt = getValueState(I.getOperand(0));
750 if (OpSt.isOverdefined()) // Inherit overdefinedness of operand
752 else if (OpSt.isConstant()) // Propagate constant value
753 markConstant(&I, ConstantExpr::getCast(I.getOpcode(),
754 OpSt.getConstant(), I.getType()));
758 void SCCPSolver::visitExtractValueInst(ExtractValueInst &EVI) {
759 // If this returns a struct, mark all elements over defined, we don't track
760 // structs in structs.
761 if (EVI.getType()->isStructTy())
762 return markAnythingOverdefined(&EVI);
764 // If this is extracting from more than one level of struct, we don't know.
765 if (EVI.getNumIndices() != 1)
766 return markOverdefined(&EVI);
768 Value *AggVal = EVI.getAggregateOperand();
769 if (AggVal->getType()->isStructTy()) {
770 unsigned i = *EVI.idx_begin();
771 LatticeVal EltVal = getStructValueState(AggVal, i);
772 mergeInValue(getValueState(&EVI), &EVI, EltVal);
774 // Otherwise, must be extracting from an array.
775 return markOverdefined(&EVI);
779 void SCCPSolver::visitInsertValueInst(InsertValueInst &IVI) {
780 StructType *STy = dyn_cast<StructType>(IVI.getType());
782 return markOverdefined(&IVI);
784 // If this has more than one index, we can't handle it, drive all results to
786 if (IVI.getNumIndices() != 1)
787 return markAnythingOverdefined(&IVI);
789 Value *Aggr = IVI.getAggregateOperand();
790 unsigned Idx = *IVI.idx_begin();
792 // Compute the result based on what we're inserting.
793 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
794 // This passes through all values that aren't the inserted element.
796 LatticeVal EltVal = getStructValueState(Aggr, i);
797 mergeInValue(getStructValueState(&IVI, i), &IVI, EltVal);
801 Value *Val = IVI.getInsertedValueOperand();
802 if (Val->getType()->isStructTy())
803 // We don't track structs in structs.
804 markOverdefined(getStructValueState(&IVI, i), &IVI);
806 LatticeVal InVal = getValueState(Val);
807 mergeInValue(getStructValueState(&IVI, i), &IVI, InVal);
812 void SCCPSolver::visitSelectInst(SelectInst &I) {
813 // If this select returns a struct, just mark the result overdefined.
814 // TODO: We could do a lot better than this if code actually uses this.
815 if (I.getType()->isStructTy())
816 return markAnythingOverdefined(&I);
818 LatticeVal CondValue = getValueState(I.getCondition());
819 if (CondValue.isUndefined())
822 if (ConstantInt *CondCB = CondValue.getConstantInt()) {
823 Value *OpVal = CondCB->isZero() ? I.getFalseValue() : I.getTrueValue();
824 mergeInValue(&I, getValueState(OpVal));
828 // Otherwise, the condition is overdefined or a constant we can't evaluate.
829 // See if we can produce something better than overdefined based on the T/F
831 LatticeVal TVal = getValueState(I.getTrueValue());
832 LatticeVal FVal = getValueState(I.getFalseValue());
834 // select ?, C, C -> C.
835 if (TVal.isConstant() && FVal.isConstant() &&
836 TVal.getConstant() == FVal.getConstant())
837 return markConstant(&I, FVal.getConstant());
839 if (TVal.isUndefined()) // select ?, undef, X -> X.
840 return mergeInValue(&I, FVal);
841 if (FVal.isUndefined()) // select ?, X, undef -> X.
842 return mergeInValue(&I, TVal);
846 // Handle Binary Operators.
847 void SCCPSolver::visitBinaryOperator(Instruction &I) {
848 LatticeVal V1State = getValueState(I.getOperand(0));
849 LatticeVal V2State = getValueState(I.getOperand(1));
851 LatticeVal &IV = ValueState[&I];
852 if (IV.isOverdefined()) return;
854 if (V1State.isConstant() && V2State.isConstant())
855 return markConstant(IV, &I,
856 ConstantExpr::get(I.getOpcode(), V1State.getConstant(),
857 V2State.getConstant()));
859 // If something is undef, wait for it to resolve.
860 if (!V1State.isOverdefined() && !V2State.isOverdefined())
863 // Otherwise, one of our operands is overdefined. Try to produce something
864 // better than overdefined with some tricks.
866 // If this is an AND or OR with 0 or -1, it doesn't matter that the other
867 // operand is overdefined.
868 if (I.getOpcode() == Instruction::And || I.getOpcode() == Instruction::Or) {
869 LatticeVal *NonOverdefVal = nullptr;
870 if (!V1State.isOverdefined())
871 NonOverdefVal = &V1State;
872 else if (!V2State.isOverdefined())
873 NonOverdefVal = &V2State;
876 if (NonOverdefVal->isUndefined()) {
877 // Could annihilate value.
878 if (I.getOpcode() == Instruction::And)
879 markConstant(IV, &I, Constant::getNullValue(I.getType()));
880 else if (VectorType *PT = dyn_cast<VectorType>(I.getType()))
881 markConstant(IV, &I, Constant::getAllOnesValue(PT));
884 Constant::getAllOnesValue(I.getType()));
888 if (I.getOpcode() == Instruction::And) {
890 if (NonOverdefVal->getConstant()->isNullValue())
891 return markConstant(IV, &I, NonOverdefVal->getConstant());
893 if (ConstantInt *CI = NonOverdefVal->getConstantInt())
894 if (CI->isAllOnesValue()) // X or -1 = -1
895 return markConstant(IV, &I, NonOverdefVal->getConstant());
904 // Handle ICmpInst instruction.
905 void SCCPSolver::visitCmpInst(CmpInst &I) {
906 LatticeVal V1State = getValueState(I.getOperand(0));
907 LatticeVal V2State = getValueState(I.getOperand(1));
909 LatticeVal &IV = ValueState[&I];
910 if (IV.isOverdefined()) return;
912 if (V1State.isConstant() && V2State.isConstant())
913 return markConstant(IV, &I, ConstantExpr::getCompare(I.getPredicate(),
914 V1State.getConstant(),
915 V2State.getConstant()));
917 // If operands are still undefined, wait for it to resolve.
918 if (!V1State.isOverdefined() && !V2State.isOverdefined())
924 void SCCPSolver::visitExtractElementInst(ExtractElementInst &I) {
925 // TODO : SCCP does not handle vectors properly.
926 return markOverdefined(&I);
929 LatticeVal &ValState = getValueState(I.getOperand(0));
930 LatticeVal &IdxState = getValueState(I.getOperand(1));
932 if (ValState.isOverdefined() || IdxState.isOverdefined())
934 else if(ValState.isConstant() && IdxState.isConstant())
935 markConstant(&I, ConstantExpr::getExtractElement(ValState.getConstant(),
936 IdxState.getConstant()));
940 void SCCPSolver::visitInsertElementInst(InsertElementInst &I) {
941 // TODO : SCCP does not handle vectors properly.
942 return markOverdefined(&I);
944 LatticeVal &ValState = getValueState(I.getOperand(0));
945 LatticeVal &EltState = getValueState(I.getOperand(1));
946 LatticeVal &IdxState = getValueState(I.getOperand(2));
948 if (ValState.isOverdefined() || EltState.isOverdefined() ||
949 IdxState.isOverdefined())
951 else if(ValState.isConstant() && EltState.isConstant() &&
952 IdxState.isConstant())
953 markConstant(&I, ConstantExpr::getInsertElement(ValState.getConstant(),
954 EltState.getConstant(),
955 IdxState.getConstant()));
956 else if (ValState.isUndefined() && EltState.isConstant() &&
957 IdxState.isConstant())
958 markConstant(&I,ConstantExpr::getInsertElement(UndefValue::get(I.getType()),
959 EltState.getConstant(),
960 IdxState.getConstant()));
964 void SCCPSolver::visitShuffleVectorInst(ShuffleVectorInst &I) {
965 // TODO : SCCP does not handle vectors properly.
966 return markOverdefined(&I);
968 LatticeVal &V1State = getValueState(I.getOperand(0));
969 LatticeVal &V2State = getValueState(I.getOperand(1));
970 LatticeVal &MaskState = getValueState(I.getOperand(2));
972 if (MaskState.isUndefined() ||
973 (V1State.isUndefined() && V2State.isUndefined()))
974 return; // Undefined output if mask or both inputs undefined.
976 if (V1State.isOverdefined() || V2State.isOverdefined() ||
977 MaskState.isOverdefined()) {
980 // A mix of constant/undef inputs.
981 Constant *V1 = V1State.isConstant() ?
982 V1State.getConstant() : UndefValue::get(I.getType());
983 Constant *V2 = V2State.isConstant() ?
984 V2State.getConstant() : UndefValue::get(I.getType());
985 Constant *Mask = MaskState.isConstant() ?
986 MaskState.getConstant() : UndefValue::get(I.getOperand(2)->getType());
987 markConstant(&I, ConstantExpr::getShuffleVector(V1, V2, Mask));
992 // Handle getelementptr instructions. If all operands are constants then we
993 // can turn this into a getelementptr ConstantExpr.
995 void SCCPSolver::visitGetElementPtrInst(GetElementPtrInst &I) {
996 if (ValueState[&I].isOverdefined()) return;
998 SmallVector<Constant*, 8> Operands;
999 Operands.reserve(I.getNumOperands());
1001 for (unsigned i = 0, e = I.getNumOperands(); i != e; ++i) {
1002 LatticeVal State = getValueState(I.getOperand(i));
1003 if (State.isUndefined())
1004 return; // Operands are not resolved yet.
1006 if (State.isOverdefined())
1007 return markOverdefined(&I);
1009 assert(State.isConstant() && "Unknown state!");
1010 Operands.push_back(State.getConstant());
1013 Constant *Ptr = Operands[0];
1014 auto Indices = makeArrayRef(Operands.begin() + 1, Operands.end());
1015 markConstant(&I, ConstantExpr::getGetElementPtr(Ptr, Indices));
1018 void SCCPSolver::visitStoreInst(StoreInst &SI) {
1019 // If this store is of a struct, ignore it.
1020 if (SI.getOperand(0)->getType()->isStructTy())
1023 if (TrackedGlobals.empty() || !isa<GlobalVariable>(SI.getOperand(1)))
1026 GlobalVariable *GV = cast<GlobalVariable>(SI.getOperand(1));
1027 DenseMap<GlobalVariable*, LatticeVal>::iterator I = TrackedGlobals.find(GV);
1028 if (I == TrackedGlobals.end() || I->second.isOverdefined()) return;
1030 // Get the value we are storing into the global, then merge it.
1031 mergeInValue(I->second, GV, getValueState(SI.getOperand(0)));
1032 if (I->second.isOverdefined())
1033 TrackedGlobals.erase(I); // No need to keep tracking this!
1037 // Handle load instructions. If the operand is a constant pointer to a constant
1038 // global, we can replace the load with the loaded constant value!
1039 void SCCPSolver::visitLoadInst(LoadInst &I) {
1040 // If this load is of a struct, just mark the result overdefined.
1041 if (I.getType()->isStructTy())
1042 return markAnythingOverdefined(&I);
1044 LatticeVal PtrVal = getValueState(I.getOperand(0));
1045 if (PtrVal.isUndefined()) return; // The pointer is not resolved yet!
1047 LatticeVal &IV = ValueState[&I];
1048 if (IV.isOverdefined()) return;
1050 if (!PtrVal.isConstant() || I.isVolatile())
1051 return markOverdefined(IV, &I);
1053 Constant *Ptr = PtrVal.getConstant();
1055 // load null -> null
1056 if (isa<ConstantPointerNull>(Ptr) && I.getPointerAddressSpace() == 0)
1057 return markConstant(IV, &I, Constant::getNullValue(I.getType()));
1059 // Transform load (constant global) into the value loaded.
1060 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Ptr)) {
1061 if (!TrackedGlobals.empty()) {
1062 // If we are tracking this global, merge in the known value for it.
1063 DenseMap<GlobalVariable*, LatticeVal>::iterator It =
1064 TrackedGlobals.find(GV);
1065 if (It != TrackedGlobals.end()) {
1066 mergeInValue(IV, &I, It->second);
1072 // Transform load from a constant into a constant if possible.
1073 if (Constant *C = ConstantFoldLoadFromConstPtr(Ptr, DL))
1074 return markConstant(IV, &I, C);
1076 // Otherwise we cannot say for certain what value this load will produce.
1078 markOverdefined(IV, &I);
1081 void SCCPSolver::visitCallSite(CallSite CS) {
1082 Function *F = CS.getCalledFunction();
1083 Instruction *I = CS.getInstruction();
1085 // The common case is that we aren't tracking the callee, either because we
1086 // are not doing interprocedural analysis or the callee is indirect, or is
1087 // external. Handle these cases first.
1088 if (!F || F->isDeclaration()) {
1090 // Void return and not tracking callee, just bail.
1091 if (I->getType()->isVoidTy()) return;
1093 // Otherwise, if we have a single return value case, and if the function is
1094 // a declaration, maybe we can constant fold it.
1095 if (F && F->isDeclaration() && !I->getType()->isStructTy() &&
1096 canConstantFoldCallTo(F)) {
1098 SmallVector<Constant*, 8> Operands;
1099 for (CallSite::arg_iterator AI = CS.arg_begin(), E = CS.arg_end();
1101 LatticeVal State = getValueState(*AI);
1103 if (State.isUndefined())
1104 return; // Operands are not resolved yet.
1105 if (State.isOverdefined())
1106 return markOverdefined(I);
1107 assert(State.isConstant() && "Unknown state!");
1108 Operands.push_back(State.getConstant());
1111 if (getValueState(I).isOverdefined())
1114 // If we can constant fold this, mark the result of the call as a
1116 if (Constant *C = ConstantFoldCall(F, Operands, TLI))
1117 return markConstant(I, C);
1120 // Otherwise, we don't know anything about this call, mark it overdefined.
1121 return markAnythingOverdefined(I);
1124 // If this is a local function that doesn't have its address taken, mark its
1125 // entry block executable and merge in the actual arguments to the call into
1126 // the formal arguments of the function.
1127 if (!TrackingIncomingArguments.empty() && TrackingIncomingArguments.count(F)){
1128 MarkBlockExecutable(F->begin());
1130 // Propagate information from this call site into the callee.
1131 CallSite::arg_iterator CAI = CS.arg_begin();
1132 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
1133 AI != E; ++AI, ++CAI) {
1134 // If this argument is byval, and if the function is not readonly, there
1135 // will be an implicit copy formed of the input aggregate.
1136 if (AI->hasByValAttr() && !F->onlyReadsMemory()) {
1137 markOverdefined(AI);
1141 if (StructType *STy = dyn_cast<StructType>(AI->getType())) {
1142 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
1143 LatticeVal CallArg = getStructValueState(*CAI, i);
1144 mergeInValue(getStructValueState(AI, i), AI, CallArg);
1147 mergeInValue(AI, getValueState(*CAI));
1152 // If this is a single/zero retval case, see if we're tracking the function.
1153 if (StructType *STy = dyn_cast<StructType>(F->getReturnType())) {
1154 if (!MRVFunctionsTracked.count(F))
1155 goto CallOverdefined; // Not tracking this callee.
1157 // If we are tracking this callee, propagate the result of the function
1158 // into this call site.
1159 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
1160 mergeInValue(getStructValueState(I, i), I,
1161 TrackedMultipleRetVals[std::make_pair(F, i)]);
1163 DenseMap<Function*, LatticeVal>::iterator TFRVI = TrackedRetVals.find(F);
1164 if (TFRVI == TrackedRetVals.end())
1165 goto CallOverdefined; // Not tracking this callee.
1167 // If so, propagate the return value of the callee into this call result.
1168 mergeInValue(I, TFRVI->second);
1172 void SCCPSolver::Solve() {
1173 // Process the work lists until they are empty!
1174 while (!BBWorkList.empty() || !InstWorkList.empty() ||
1175 !OverdefinedInstWorkList.empty()) {
1176 // Process the overdefined instruction's work list first, which drives other
1177 // things to overdefined more quickly.
1178 while (!OverdefinedInstWorkList.empty()) {
1179 Value *I = OverdefinedInstWorkList.pop_back_val();
1181 DEBUG(dbgs() << "\nPopped off OI-WL: " << *I << '\n');
1183 // "I" got into the work list because it either made the transition from
1184 // bottom to constant, or to overdefined.
1186 // Anything on this worklist that is overdefined need not be visited
1187 // since all of its users will have already been marked as overdefined
1188 // Update all of the users of this instruction's value.
1190 for (User *U : I->users())
1191 if (Instruction *UI = dyn_cast<Instruction>(U))
1192 OperandChangedState(UI);
1195 // Process the instruction work list.
1196 while (!InstWorkList.empty()) {
1197 Value *I = InstWorkList.pop_back_val();
1199 DEBUG(dbgs() << "\nPopped off I-WL: " << *I << '\n');
1201 // "I" got into the work list because it made the transition from undef to
1204 // Anything on this worklist that is overdefined need not be visited
1205 // since all of its users will have already been marked as overdefined.
1206 // Update all of the users of this instruction's value.
1208 if (I->getType()->isStructTy() || !getValueState(I).isOverdefined())
1209 for (User *U : I->users())
1210 if (Instruction *UI = dyn_cast<Instruction>(U))
1211 OperandChangedState(UI);
1214 // Process the basic block work list.
1215 while (!BBWorkList.empty()) {
1216 BasicBlock *BB = BBWorkList.back();
1217 BBWorkList.pop_back();
1219 DEBUG(dbgs() << "\nPopped off BBWL: " << *BB << '\n');
1221 // Notify all instructions in this basic block that they are newly
1228 /// ResolvedUndefsIn - While solving the dataflow for a function, we assume
1229 /// that branches on undef values cannot reach any of their successors.
1230 /// However, this is not a safe assumption. After we solve dataflow, this
1231 /// method should be use to handle this. If this returns true, the solver
1232 /// should be rerun.
1234 /// This method handles this by finding an unresolved branch and marking it one
1235 /// of the edges from the block as being feasible, even though the condition
1236 /// doesn't say it would otherwise be. This allows SCCP to find the rest of the
1237 /// CFG and only slightly pessimizes the analysis results (by marking one,
1238 /// potentially infeasible, edge feasible). This cannot usefully modify the
1239 /// constraints on the condition of the branch, as that would impact other users
1242 /// This scan also checks for values that use undefs, whose results are actually
1243 /// defined. For example, 'zext i8 undef to i32' should produce all zeros
1244 /// conservatively, as "(zext i8 X -> i32) & 0xFF00" must always return zero,
1245 /// even if X isn't defined.
1246 bool SCCPSolver::ResolvedUndefsIn(Function &F) {
1247 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
1248 if (!BBExecutable.count(BB))
1251 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
1252 // Look for instructions which produce undef values.
1253 if (I->getType()->isVoidTy()) continue;
1255 if (StructType *STy = dyn_cast<StructType>(I->getType())) {
1256 // Only a few things that can be structs matter for undef.
1258 // Tracked calls must never be marked overdefined in ResolvedUndefsIn.
1259 if (CallSite CS = CallSite(I))
1260 if (Function *F = CS.getCalledFunction())
1261 if (MRVFunctionsTracked.count(F))
1264 // extractvalue and insertvalue don't need to be marked; they are
1265 // tracked as precisely as their operands.
1266 if (isa<ExtractValueInst>(I) || isa<InsertValueInst>(I))
1269 // Send the results of everything else to overdefined. We could be
1270 // more precise than this but it isn't worth bothering.
1271 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
1272 LatticeVal &LV = getStructValueState(I, i);
1273 if (LV.isUndefined())
1274 markOverdefined(LV, I);
1279 LatticeVal &LV = getValueState(I);
1280 if (!LV.isUndefined()) continue;
1282 // extractvalue is safe; check here because the argument is a struct.
1283 if (isa<ExtractValueInst>(I))
1286 // Compute the operand LatticeVals, for convenience below.
1287 // Anything taking a struct is conservatively assumed to require
1288 // overdefined markings.
1289 if (I->getOperand(0)->getType()->isStructTy()) {
1293 LatticeVal Op0LV = getValueState(I->getOperand(0));
1295 if (I->getNumOperands() == 2) {
1296 if (I->getOperand(1)->getType()->isStructTy()) {
1301 Op1LV = getValueState(I->getOperand(1));
1303 // If this is an instructions whose result is defined even if the input is
1304 // not fully defined, propagate the information.
1305 Type *ITy = I->getType();
1306 switch (I->getOpcode()) {
1307 case Instruction::Add:
1308 case Instruction::Sub:
1309 case Instruction::Trunc:
1310 case Instruction::FPTrunc:
1311 case Instruction::BitCast:
1312 break; // Any undef -> undef
1313 case Instruction::FSub:
1314 case Instruction::FAdd:
1315 case Instruction::FMul:
1316 case Instruction::FDiv:
1317 case Instruction::FRem:
1318 // Floating-point binary operation: be conservative.
1319 if (Op0LV.isUndefined() && Op1LV.isUndefined())
1320 markForcedConstant(I, Constant::getNullValue(ITy));
1324 case Instruction::ZExt:
1325 case Instruction::SExt:
1326 case Instruction::FPToUI:
1327 case Instruction::FPToSI:
1328 case Instruction::FPExt:
1329 case Instruction::PtrToInt:
1330 case Instruction::IntToPtr:
1331 case Instruction::SIToFP:
1332 case Instruction::UIToFP:
1333 // undef -> 0; some outputs are impossible
1334 markForcedConstant(I, Constant::getNullValue(ITy));
1336 case Instruction::Mul:
1337 case Instruction::And:
1338 // Both operands undef -> undef
1339 if (Op0LV.isUndefined() && Op1LV.isUndefined())
1341 // undef * X -> 0. X could be zero.
1342 // undef & X -> 0. X could be zero.
1343 markForcedConstant(I, Constant::getNullValue(ITy));
1346 case Instruction::Or:
1347 // Both operands undef -> undef
1348 if (Op0LV.isUndefined() && Op1LV.isUndefined())
1350 // undef | X -> -1. X could be -1.
1351 markForcedConstant(I, Constant::getAllOnesValue(ITy));
1354 case Instruction::Xor:
1355 // undef ^ undef -> 0; strictly speaking, this is not strictly
1356 // necessary, but we try to be nice to people who expect this
1357 // behavior in simple cases
1358 if (Op0LV.isUndefined() && Op1LV.isUndefined()) {
1359 markForcedConstant(I, Constant::getNullValue(ITy));
1362 // undef ^ X -> undef
1365 case Instruction::SDiv:
1366 case Instruction::UDiv:
1367 case Instruction::SRem:
1368 case Instruction::URem:
1369 // X / undef -> undef. No change.
1370 // X % undef -> undef. No change.
1371 if (Op1LV.isUndefined()) break;
1373 // undef / X -> 0. X could be maxint.
1374 // undef % X -> 0. X could be 1.
1375 markForcedConstant(I, Constant::getNullValue(ITy));
1378 case Instruction::AShr:
1379 // X >>a undef -> undef.
1380 if (Op1LV.isUndefined()) break;
1382 // undef >>a X -> all ones
1383 markForcedConstant(I, Constant::getAllOnesValue(ITy));
1385 case Instruction::LShr:
1386 case Instruction::Shl:
1387 // X << undef -> undef.
1388 // X >> undef -> undef.
1389 if (Op1LV.isUndefined()) break;
1393 markForcedConstant(I, Constant::getNullValue(ITy));
1395 case Instruction::Select:
1396 Op1LV = getValueState(I->getOperand(1));
1397 // undef ? X : Y -> X or Y. There could be commonality between X/Y.
1398 if (Op0LV.isUndefined()) {
1399 if (!Op1LV.isConstant()) // Pick the constant one if there is any.
1400 Op1LV = getValueState(I->getOperand(2));
1401 } else if (Op1LV.isUndefined()) {
1402 // c ? undef : undef -> undef. No change.
1403 Op1LV = getValueState(I->getOperand(2));
1404 if (Op1LV.isUndefined())
1406 // Otherwise, c ? undef : x -> x.
1408 // Leave Op1LV as Operand(1)'s LatticeValue.
1411 if (Op1LV.isConstant())
1412 markForcedConstant(I, Op1LV.getConstant());
1416 case Instruction::Load:
1417 // A load here means one of two things: a load of undef from a global,
1418 // a load from an unknown pointer. Either way, having it return undef
1421 case Instruction::ICmp:
1422 // X == undef -> undef. Other comparisons get more complicated.
1423 if (cast<ICmpInst>(I)->isEquality())
1427 case Instruction::Call:
1428 case Instruction::Invoke: {
1429 // There are two reasons a call can have an undef result
1430 // 1. It could be tracked.
1431 // 2. It could be constant-foldable.
1432 // Because of the way we solve return values, tracked calls must
1433 // never be marked overdefined in ResolvedUndefsIn.
1434 if (Function *F = CallSite(I).getCalledFunction())
1435 if (TrackedRetVals.count(F))
1438 // If the call is constant-foldable, we mark it overdefined because
1439 // we do not know what return values are valid.
1444 // If we don't know what should happen here, conservatively mark it
1451 // Check to see if we have a branch or switch on an undefined value. If so
1452 // we force the branch to go one way or the other to make the successor
1453 // values live. It doesn't really matter which way we force it.
1454 TerminatorInst *TI = BB->getTerminator();
1455 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
1456 if (!BI->isConditional()) continue;
1457 if (!getValueState(BI->getCondition()).isUndefined())
1460 // If the input to SCCP is actually branch on undef, fix the undef to
1462 if (isa<UndefValue>(BI->getCondition())) {
1463 BI->setCondition(ConstantInt::getFalse(BI->getContext()));
1464 markEdgeExecutable(BB, TI->getSuccessor(1));
1468 // Otherwise, it is a branch on a symbolic value which is currently
1469 // considered to be undef. Handle this by forcing the input value to the
1471 markForcedConstant(BI->getCondition(),
1472 ConstantInt::getFalse(TI->getContext()));
1476 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
1477 if (!SI->getNumCases())
1479 if (!getValueState(SI->getCondition()).isUndefined())
1482 // If the input to SCCP is actually switch on undef, fix the undef to
1483 // the first constant.
1484 if (isa<UndefValue>(SI->getCondition())) {
1485 SI->setCondition(SI->case_begin().getCaseValue());
1486 markEdgeExecutable(BB, SI->case_begin().getCaseSuccessor());
1490 markForcedConstant(SI->getCondition(), SI->case_begin().getCaseValue());
1500 //===--------------------------------------------------------------------===//
1502 /// SCCP Class - This class uses the SCCPSolver to implement a per-function
1503 /// Sparse Conditional Constant Propagator.
1505 struct SCCP : public FunctionPass {
1506 void getAnalysisUsage(AnalysisUsage &AU) const override {
1507 AU.addRequired<TargetLibraryInfoWrapperPass>();
1509 static char ID; // Pass identification, replacement for typeid
1510 SCCP() : FunctionPass(ID) {
1511 initializeSCCPPass(*PassRegistry::getPassRegistry());
1514 // runOnFunction - Run the Sparse Conditional Constant Propagation
1515 // algorithm, and return true if the function was modified.
1517 bool runOnFunction(Function &F) override;
1519 } // end anonymous namespace
1522 INITIALIZE_PASS(SCCP, "sccp",
1523 "Sparse Conditional Constant Propagation", false, false)
1525 // createSCCPPass - This is the public interface to this file.
1526 FunctionPass *llvm::createSCCPPass() {
1530 static void DeleteInstructionInBlock(BasicBlock *BB) {
1531 DEBUG(dbgs() << " BasicBlock Dead:" << *BB);
1534 // Check to see if there are non-terminating instructions to delete.
1535 if (isa<TerminatorInst>(BB->begin()))
1538 // Delete the instructions backwards, as it has a reduced likelihood of having
1539 // to update as many def-use and use-def chains.
1540 Instruction *EndInst = BB->getTerminator(); // Last not to be deleted.
1541 while (EndInst != BB->begin()) {
1542 // Delete the next to last instruction.
1543 BasicBlock::iterator I = EndInst;
1544 Instruction *Inst = --I;
1545 if (!Inst->use_empty())
1546 Inst->replaceAllUsesWith(UndefValue::get(Inst->getType()));
1547 if (isa<LandingPadInst>(Inst)) {
1551 BB->getInstList().erase(Inst);
1556 // runOnFunction() - Run the Sparse Conditional Constant Propagation algorithm,
1557 // and return true if the function was modified.
1559 bool SCCP::runOnFunction(Function &F) {
1560 if (skipOptnoneFunction(F))
1563 DEBUG(dbgs() << "SCCP on function '" << F.getName() << "'\n");
1564 const DataLayout &DL = F.getParent()->getDataLayout();
1565 const TargetLibraryInfo *TLI =
1566 &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
1567 SCCPSolver Solver(DL, TLI);
1569 // Mark the first block of the function as being executable.
1570 Solver.MarkBlockExecutable(F.begin());
1572 // Mark all arguments to the function as being overdefined.
1573 for (Function::arg_iterator AI = F.arg_begin(), E = F.arg_end(); AI != E;++AI)
1574 Solver.markAnythingOverdefined(AI);
1576 // Solve for constants.
1577 bool ResolvedUndefs = true;
1578 while (ResolvedUndefs) {
1580 DEBUG(dbgs() << "RESOLVING UNDEFs\n");
1581 ResolvedUndefs = Solver.ResolvedUndefsIn(F);
1584 bool MadeChanges = false;
1586 // If we decided that there are basic blocks that are dead in this function,
1587 // delete their contents now. Note that we cannot actually delete the blocks,
1588 // as we cannot modify the CFG of the function.
1590 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
1591 if (!Solver.isBlockExecutable(BB)) {
1592 DeleteInstructionInBlock(BB);
1597 // Iterate over all of the instructions in a function, replacing them with
1598 // constants if we have found them to be of constant values.
1600 for (BasicBlock::iterator BI = BB->begin(), E = BB->end(); BI != E; ) {
1601 Instruction *Inst = BI++;
1602 if (Inst->getType()->isVoidTy() || isa<TerminatorInst>(Inst))
1605 // TODO: Reconstruct structs from their elements.
1606 if (Inst->getType()->isStructTy())
1609 LatticeVal IV = Solver.getLatticeValueFor(Inst);
1610 if (IV.isOverdefined())
1613 Constant *Const = IV.isConstant()
1614 ? IV.getConstant() : UndefValue::get(Inst->getType());
1615 DEBUG(dbgs() << " Constant: " << *Const << " = " << *Inst << '\n');
1617 // Replaces all of the uses of a variable with uses of the constant.
1618 Inst->replaceAllUsesWith(Const);
1620 // Delete the instruction.
1621 Inst->eraseFromParent();
1623 // Hey, we just changed something!
1633 //===--------------------------------------------------------------------===//
1635 /// IPSCCP Class - This class implements interprocedural Sparse Conditional
1636 /// Constant Propagation.
1638 struct IPSCCP : public ModulePass {
1639 void getAnalysisUsage(AnalysisUsage &AU) const override {
1640 AU.addRequired<TargetLibraryInfoWrapperPass>();
1643 IPSCCP() : ModulePass(ID) {
1644 initializeIPSCCPPass(*PassRegistry::getPassRegistry());
1646 bool runOnModule(Module &M) override;
1648 } // end anonymous namespace
1650 char IPSCCP::ID = 0;
1651 INITIALIZE_PASS_BEGIN(IPSCCP, "ipsccp",
1652 "Interprocedural Sparse Conditional Constant Propagation",
1654 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
1655 INITIALIZE_PASS_END(IPSCCP, "ipsccp",
1656 "Interprocedural Sparse Conditional Constant Propagation",
1659 // createIPSCCPPass - This is the public interface to this file.
1660 ModulePass *llvm::createIPSCCPPass() {
1661 return new IPSCCP();
1665 static bool AddressIsTaken(const GlobalValue *GV) {
1666 // Delete any dead constantexpr klingons.
1667 GV->removeDeadConstantUsers();
1669 for (const Use &U : GV->uses()) {
1670 const User *UR = U.getUser();
1671 if (const StoreInst *SI = dyn_cast<StoreInst>(UR)) {
1672 if (SI->getOperand(0) == GV || SI->isVolatile())
1673 return true; // Storing addr of GV.
1674 } else if (isa<InvokeInst>(UR) || isa<CallInst>(UR)) {
1675 // Make sure we are calling the function, not passing the address.
1676 ImmutableCallSite CS(cast<Instruction>(UR));
1677 if (!CS.isCallee(&U))
1679 } else if (const LoadInst *LI = dyn_cast<LoadInst>(UR)) {
1680 if (LI->isVolatile())
1682 } else if (isa<BlockAddress>(UR)) {
1683 // blockaddress doesn't take the address of the function, it takes addr
1692 bool IPSCCP::runOnModule(Module &M) {
1693 const DataLayout &DL = M.getDataLayout();
1694 const TargetLibraryInfo *TLI =
1695 &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
1696 SCCPSolver Solver(DL, TLI);
1698 // AddressTakenFunctions - This set keeps track of the address-taken functions
1699 // that are in the input. As IPSCCP runs through and simplifies code,
1700 // functions that were address taken can end up losing their
1701 // address-taken-ness. Because of this, we keep track of their addresses from
1702 // the first pass so we can use them for the later simplification pass.
1703 SmallPtrSet<Function*, 32> AddressTakenFunctions;
1705 // Loop over all functions, marking arguments to those with their addresses
1706 // taken or that are external as overdefined.
1708 for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) {
1709 if (F->isDeclaration())
1712 // If this is a strong or ODR definition of this function, then we can
1713 // propagate information about its result into callsites of it.
1714 if (!F->mayBeOverridden())
1715 Solver.AddTrackedFunction(F);
1717 // If this function only has direct calls that we can see, we can track its
1718 // arguments and return value aggressively, and can assume it is not called
1719 // unless we see evidence to the contrary.
1720 if (F->hasLocalLinkage()) {
1721 if (AddressIsTaken(F))
1722 AddressTakenFunctions.insert(F);
1724 Solver.AddArgumentTrackedFunction(F);
1729 // Assume the function is called.
1730 Solver.MarkBlockExecutable(F->begin());
1732 // Assume nothing about the incoming arguments.
1733 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
1735 Solver.markAnythingOverdefined(AI);
1738 // Loop over global variables. We inform the solver about any internal global
1739 // variables that do not have their 'addresses taken'. If they don't have
1740 // their addresses taken, we can propagate constants through them.
1741 for (Module::global_iterator G = M.global_begin(), E = M.global_end();
1743 if (!G->isConstant() && G->hasLocalLinkage() && !AddressIsTaken(G))
1744 Solver.TrackValueOfGlobalVariable(G);
1746 // Solve for constants.
1747 bool ResolvedUndefs = true;
1748 while (ResolvedUndefs) {
1751 DEBUG(dbgs() << "RESOLVING UNDEFS\n");
1752 ResolvedUndefs = false;
1753 for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F)
1754 ResolvedUndefs |= Solver.ResolvedUndefsIn(*F);
1757 bool MadeChanges = false;
1759 // Iterate over all of the instructions in the module, replacing them with
1760 // constants if we have found them to be of constant values.
1762 SmallVector<BasicBlock*, 512> BlocksToErase;
1764 for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) {
1765 if (Solver.isBlockExecutable(F->begin())) {
1766 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
1768 if (AI->use_empty() || AI->getType()->isStructTy()) continue;
1770 // TODO: Could use getStructLatticeValueFor to find out if the entire
1771 // result is a constant and replace it entirely if so.
1773 LatticeVal IV = Solver.getLatticeValueFor(AI);
1774 if (IV.isOverdefined()) continue;
1776 Constant *CST = IV.isConstant() ?
1777 IV.getConstant() : UndefValue::get(AI->getType());
1778 DEBUG(dbgs() << "*** Arg " << *AI << " = " << *CST <<"\n");
1780 // Replaces all of the uses of a variable with uses of the
1782 AI->replaceAllUsesWith(CST);
1787 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB) {
1788 if (!Solver.isBlockExecutable(BB)) {
1789 DeleteInstructionInBlock(BB);
1792 TerminatorInst *TI = BB->getTerminator();
1793 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) {
1794 BasicBlock *Succ = TI->getSuccessor(i);
1795 if (!Succ->empty() && isa<PHINode>(Succ->begin()))
1796 TI->getSuccessor(i)->removePredecessor(BB);
1798 if (!TI->use_empty())
1799 TI->replaceAllUsesWith(UndefValue::get(TI->getType()));
1800 TI->eraseFromParent();
1802 if (&*BB != &F->front())
1803 BlocksToErase.push_back(BB);
1805 new UnreachableInst(M.getContext(), BB);
1809 for (BasicBlock::iterator BI = BB->begin(), E = BB->end(); BI != E; ) {
1810 Instruction *Inst = BI++;
1811 if (Inst->getType()->isVoidTy() || Inst->getType()->isStructTy())
1814 // TODO: Could use getStructLatticeValueFor to find out if the entire
1815 // result is a constant and replace it entirely if so.
1817 LatticeVal IV = Solver.getLatticeValueFor(Inst);
1818 if (IV.isOverdefined())
1821 Constant *Const = IV.isConstant()
1822 ? IV.getConstant() : UndefValue::get(Inst->getType());
1823 DEBUG(dbgs() << " Constant: " << *Const << " = " << *Inst << '\n');
1825 // Replaces all of the uses of a variable with uses of the
1827 Inst->replaceAllUsesWith(Const);
1829 // Delete the instruction.
1830 if (!isa<CallInst>(Inst) && !isa<TerminatorInst>(Inst))
1831 Inst->eraseFromParent();
1833 // Hey, we just changed something!
1839 // Now that all instructions in the function are constant folded, erase dead
1840 // blocks, because we can now use ConstantFoldTerminator to get rid of
1842 for (unsigned i = 0, e = BlocksToErase.size(); i != e; ++i) {
1843 // If there are any PHI nodes in this successor, drop entries for BB now.
1844 BasicBlock *DeadBB = BlocksToErase[i];
1845 for (Value::user_iterator UI = DeadBB->user_begin(),
1846 UE = DeadBB->user_end();
1848 // Grab the user and then increment the iterator early, as the user
1849 // will be deleted. Step past all adjacent uses from the same user.
1850 Instruction *I = dyn_cast<Instruction>(*UI);
1851 do { ++UI; } while (UI != UE && *UI == I);
1853 // Ignore blockaddress users; BasicBlock's dtor will handle them.
1856 bool Folded = ConstantFoldTerminator(I->getParent());
1858 // The constant folder may not have been able to fold the terminator
1859 // if this is a branch or switch on undef. Fold it manually as a
1860 // branch to the first successor.
1862 if (BranchInst *BI = dyn_cast<BranchInst>(I)) {
1863 assert(BI->isConditional() && isa<UndefValue>(BI->getCondition()) &&
1864 "Branch should be foldable!");
1865 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(I)) {
1866 assert(isa<UndefValue>(SI->getCondition()) && "Switch should fold");
1868 llvm_unreachable("Didn't fold away reference to block!");
1872 // Make this an uncond branch to the first successor.
1873 TerminatorInst *TI = I->getParent()->getTerminator();
1874 BranchInst::Create(TI->getSuccessor(0), TI);
1876 // Remove entries in successor phi nodes to remove edges.
1877 for (unsigned i = 1, e = TI->getNumSuccessors(); i != e; ++i)
1878 TI->getSuccessor(i)->removePredecessor(TI->getParent());
1880 // Remove the old terminator.
1881 TI->eraseFromParent();
1885 // Finally, delete the basic block.
1886 F->getBasicBlockList().erase(DeadBB);
1888 BlocksToErase.clear();
1891 // If we inferred constant or undef return values for a function, we replaced
1892 // all call uses with the inferred value. This means we don't need to bother
1893 // actually returning anything from the function. Replace all return
1894 // instructions with return undef.
1896 // Do this in two stages: first identify the functions we should process, then
1897 // actually zap their returns. This is important because we can only do this
1898 // if the address of the function isn't taken. In cases where a return is the
1899 // last use of a function, the order of processing functions would affect
1900 // whether other functions are optimizable.
1901 SmallVector<ReturnInst*, 8> ReturnsToZap;
1903 // TODO: Process multiple value ret instructions also.
1904 const DenseMap<Function*, LatticeVal> &RV = Solver.getTrackedRetVals();
1905 for (DenseMap<Function*, LatticeVal>::const_iterator I = RV.begin(),
1906 E = RV.end(); I != E; ++I) {
1907 Function *F = I->first;
1908 if (I->second.isOverdefined() || F->getReturnType()->isVoidTy())
1911 // We can only do this if we know that nothing else can call the function.
1912 if (!F->hasLocalLinkage() || AddressTakenFunctions.count(F))
1915 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
1916 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator()))
1917 if (!isa<UndefValue>(RI->getOperand(0)))
1918 ReturnsToZap.push_back(RI);
1921 // Zap all returns which we've identified as zap to change.
1922 for (unsigned i = 0, e = ReturnsToZap.size(); i != e; ++i) {
1923 Function *F = ReturnsToZap[i]->getParent()->getParent();
1924 ReturnsToZap[i]->setOperand(0, UndefValue::get(F->getReturnType()));
1927 // If we inferred constant or undef values for globals variables, we can
1928 // delete the global and any stores that remain to it.
1929 const DenseMap<GlobalVariable*, LatticeVal> &TG = Solver.getTrackedGlobals();
1930 for (DenseMap<GlobalVariable*, LatticeVal>::const_iterator I = TG.begin(),
1931 E = TG.end(); I != E; ++I) {
1932 GlobalVariable *GV = I->first;
1933 assert(!I->second.isOverdefined() &&
1934 "Overdefined values should have been taken out of the map!");
1935 DEBUG(dbgs() << "Found that GV '" << GV->getName() << "' is constant!\n");
1936 while (!GV->use_empty()) {
1937 StoreInst *SI = cast<StoreInst>(GV->user_back());
1938 SI->eraseFromParent();
1940 M.getGlobalList().erase(GV);