1 //===- SCCP.cpp - Sparse Conditional Constant Propagation -----------------===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by the LLVM research group and is distributed under
6 // the University of Illinois Open Source License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements sparse conditional constant propagation and merging:
12 // Specifically, this:
13 // * Assumes values are constant unless proven otherwise
14 // * Assumes BasicBlocks are dead unless proven otherwise
15 // * Proves values to be constant, and replaces them with constants
16 // * Proves conditional branches to be unconditional
19 // * This pass has a habit of making definitions be dead. It is a good idea
20 // to to run a DCE pass sometime after running this pass.
22 //===----------------------------------------------------------------------===//
24 #define DEBUG_TYPE "sccp"
25 #include "llvm/Transforms/Scalar.h"
26 #include "llvm/Transforms/IPO.h"
27 #include "llvm/Constants.h"
28 #include "llvm/DerivedTypes.h"
29 #include "llvm/Instructions.h"
30 #include "llvm/Pass.h"
31 #include "llvm/Support/InstVisitor.h"
32 #include "llvm/Transforms/Utils/Local.h"
33 #include "llvm/Support/CallSite.h"
34 #include "llvm/Support/Debug.h"
35 #include "llvm/ADT/hash_map"
36 #include "llvm/ADT/Statistic.h"
37 #include "llvm/ADT/STLExtras.h"
42 STATISTIC(NumInstRemoved, "Number of instructions removed");
43 STATISTIC(NumDeadBlocks , "Number of basic blocks unreachable");
45 STATISTIC(IPNumInstRemoved, "Number ofinstructions removed by IPSCCP");
46 STATISTIC(IPNumDeadBlocks , "Number of basic blocks unreachable by IPSCCP");
47 STATISTIC(IPNumArgsElimed ,"Number of arguments constant propagated by IPSCCP");
48 STATISTIC(IPNumGlobalConst, "Number of globals found to be constant by IPSCCP");
51 /// LatticeVal class - This class represents the different lattice values that
52 /// an LLVM value may occupy. It is a simple class with value semantics.
56 /// undefined - This LLVM Value has no known value yet.
59 /// constant - This LLVM Value has a specific constant value.
62 /// forcedconstant - This LLVM Value was thought to be undef until
63 /// ResolvedUndefsIn. This is treated just like 'constant', but if merged
64 /// with another (different) constant, it goes to overdefined, instead of
68 /// overdefined - This instruction is not known to be constant, and we know
71 } LatticeValue; // The current lattice position
73 Constant *ConstantVal; // If Constant value, the current value
75 inline LatticeVal() : LatticeValue(undefined), ConstantVal(0) {}
77 // markOverdefined - Return true if this is a new status to be in...
78 inline bool markOverdefined() {
79 if (LatticeValue != overdefined) {
80 LatticeValue = overdefined;
86 // markConstant - Return true if this is a new status for us.
87 inline bool markConstant(Constant *V) {
88 if (LatticeValue != constant) {
89 if (LatticeValue == undefined) {
90 LatticeValue = constant;
91 assert(V && "Marking constant with NULL");
94 assert(LatticeValue == forcedconstant &&
95 "Cannot move from overdefined to constant!");
96 // Stay at forcedconstant if the constant is the same.
97 if (V == ConstantVal) return false;
99 // Otherwise, we go to overdefined. Assumptions made based on the
100 // forced value are possibly wrong. Assuming this is another constant
101 // could expose a contradiction.
102 LatticeValue = overdefined;
106 assert(ConstantVal == V && "Marking constant with different value");
111 inline void markForcedConstant(Constant *V) {
112 assert(LatticeValue == undefined && "Can't force a defined value!");
113 LatticeValue = forcedconstant;
117 inline bool isUndefined() const { return LatticeValue == undefined; }
118 inline bool isConstant() const {
119 return LatticeValue == constant || LatticeValue == forcedconstant;
121 inline bool isOverdefined() const { return LatticeValue == overdefined; }
123 inline Constant *getConstant() const {
124 assert(isConstant() && "Cannot get the constant of a non-constant!");
129 } // end anonymous namespace
132 //===----------------------------------------------------------------------===//
134 /// SCCPSolver - This class is a general purpose solver for Sparse Conditional
135 /// Constant Propagation.
137 class SCCPSolver : public InstVisitor<SCCPSolver> {
138 std::set<BasicBlock*> BBExecutable;// The basic blocks that are executable
139 hash_map<Value*, LatticeVal> ValueState; // The state each value is in...
141 /// GlobalValue - If we are tracking any values for the contents of a global
142 /// variable, we keep a mapping from the constant accessor to the element of
143 /// the global, to the currently known value. If the value becomes
144 /// overdefined, it's entry is simply removed from this map.
145 hash_map<GlobalVariable*, LatticeVal> TrackedGlobals;
147 /// TrackedFunctionRetVals - If we are tracking arguments into and the return
148 /// value out of a function, it will have an entry in this map, indicating
149 /// what the known return value for the function is.
150 hash_map<Function*, LatticeVal> TrackedFunctionRetVals;
152 // The reason for two worklists is that overdefined is the lowest state
153 // on the lattice, and moving things to overdefined as fast as possible
154 // makes SCCP converge much faster.
155 // By having a separate worklist, we accomplish this because everything
156 // possibly overdefined will become overdefined at the soonest possible
158 std::vector<Value*> OverdefinedInstWorkList;
159 std::vector<Value*> InstWorkList;
162 std::vector<BasicBlock*> BBWorkList; // The BasicBlock work list
164 /// UsersOfOverdefinedPHIs - Keep track of any users of PHI nodes that are not
165 /// overdefined, despite the fact that the PHI node is overdefined.
166 std::multimap<PHINode*, Instruction*> UsersOfOverdefinedPHIs;
168 /// KnownFeasibleEdges - Entries in this set are edges which have already had
169 /// PHI nodes retriggered.
170 typedef std::pair<BasicBlock*,BasicBlock*> Edge;
171 std::set<Edge> KnownFeasibleEdges;
174 /// MarkBlockExecutable - This method can be used by clients to mark all of
175 /// the blocks that are known to be intrinsically live in the processed unit.
176 void MarkBlockExecutable(BasicBlock *BB) {
177 DOUT << "Marking Block Executable: " << BB->getName() << "\n";
178 BBExecutable.insert(BB); // Basic block is executable!
179 BBWorkList.push_back(BB); // Add the block to the work list!
182 /// TrackValueOfGlobalVariable - Clients can use this method to
183 /// inform the SCCPSolver that it should track loads and stores to the
184 /// specified global variable if it can. This is only legal to call if
185 /// performing Interprocedural SCCP.
186 void TrackValueOfGlobalVariable(GlobalVariable *GV) {
187 const Type *ElTy = GV->getType()->getElementType();
188 if (ElTy->isFirstClassType()) {
189 LatticeVal &IV = TrackedGlobals[GV];
190 if (!isa<UndefValue>(GV->getInitializer()))
191 IV.markConstant(GV->getInitializer());
195 /// AddTrackedFunction - If the SCCP solver is supposed to track calls into
196 /// and out of the specified function (which cannot have its address taken),
197 /// this method must be called.
198 void AddTrackedFunction(Function *F) {
199 assert(F->hasInternalLinkage() && "Can only track internal functions!");
200 // Add an entry, F -> undef.
201 TrackedFunctionRetVals[F];
204 /// Solve - Solve for constants and executable blocks.
208 /// ResolvedUndefsIn - While solving the dataflow for a function, we assume
209 /// that branches on undef values cannot reach any of their successors.
210 /// However, this is not a safe assumption. After we solve dataflow, this
211 /// method should be use to handle this. If this returns true, the solver
213 bool ResolvedUndefsIn(Function &F);
215 /// getExecutableBlocks - Once we have solved for constants, return the set of
216 /// blocks that is known to be executable.
217 std::set<BasicBlock*> &getExecutableBlocks() {
221 /// getValueMapping - Once we have solved for constants, return the mapping of
222 /// LLVM values to LatticeVals.
223 hash_map<Value*, LatticeVal> &getValueMapping() {
227 /// getTrackedFunctionRetVals - Get the inferred return value map.
229 const hash_map<Function*, LatticeVal> &getTrackedFunctionRetVals() {
230 return TrackedFunctionRetVals;
233 /// getTrackedGlobals - Get and return the set of inferred initializers for
234 /// global variables.
235 const hash_map<GlobalVariable*, LatticeVal> &getTrackedGlobals() {
236 return TrackedGlobals;
241 // markConstant - Make a value be marked as "constant". If the value
242 // is not already a constant, add it to the instruction work list so that
243 // the users of the instruction are updated later.
245 inline void markConstant(LatticeVal &IV, Value *V, Constant *C) {
246 if (IV.markConstant(C)) {
247 DOUT << "markConstant: " << *C << ": " << *V;
248 InstWorkList.push_back(V);
252 inline void markForcedConstant(LatticeVal &IV, Value *V, Constant *C) {
253 IV.markForcedConstant(C);
254 DOUT << "markForcedConstant: " << *C << ": " << *V;
255 InstWorkList.push_back(V);
258 inline void markConstant(Value *V, Constant *C) {
259 markConstant(ValueState[V], V, C);
262 // markOverdefined - Make a value be marked as "overdefined". If the
263 // value is not already overdefined, add it to the overdefined instruction
264 // work list so that the users of the instruction are updated later.
266 inline void markOverdefined(LatticeVal &IV, Value *V) {
267 if (IV.markOverdefined()) {
268 DEBUG(DOUT << "markOverdefined: ";
269 if (Function *F = dyn_cast<Function>(V))
270 DOUT << "Function '" << F->getName() << "'\n";
273 // Only instructions go on the work list
274 OverdefinedInstWorkList.push_back(V);
277 inline void markOverdefined(Value *V) {
278 markOverdefined(ValueState[V], V);
281 inline void mergeInValue(LatticeVal &IV, Value *V, LatticeVal &MergeWithV) {
282 if (IV.isOverdefined() || MergeWithV.isUndefined())
284 if (MergeWithV.isOverdefined())
285 markOverdefined(IV, V);
286 else if (IV.isUndefined())
287 markConstant(IV, V, MergeWithV.getConstant());
288 else if (IV.getConstant() != MergeWithV.getConstant())
289 markOverdefined(IV, V);
292 inline void mergeInValue(Value *V, LatticeVal &MergeWithV) {
293 return mergeInValue(ValueState[V], V, MergeWithV);
297 // getValueState - Return the LatticeVal object that corresponds to the value.
298 // This function is necessary because not all values should start out in the
299 // underdefined state... Argument's should be overdefined, and
300 // constants should be marked as constants. If a value is not known to be an
301 // Instruction object, then use this accessor to get its value from the map.
303 inline LatticeVal &getValueState(Value *V) {
304 hash_map<Value*, LatticeVal>::iterator I = ValueState.find(V);
305 if (I != ValueState.end()) return I->second; // Common case, in the map
307 if (Constant *C = dyn_cast<Constant>(V)) {
308 if (isa<UndefValue>(V)) {
309 // Nothing to do, remain undefined.
311 ValueState[C].markConstant(C); // Constants are constant
314 // All others are underdefined by default...
315 return ValueState[V];
318 // markEdgeExecutable - Mark a basic block as executable, adding it to the BB
319 // work list if it is not already executable...
321 void markEdgeExecutable(BasicBlock *Source, BasicBlock *Dest) {
322 if (!KnownFeasibleEdges.insert(Edge(Source, Dest)).second)
323 return; // This edge is already known to be executable!
325 if (BBExecutable.count(Dest)) {
326 DOUT << "Marking Edge Executable: " << Source->getName()
327 << " -> " << Dest->getName() << "\n";
329 // The destination is already executable, but we just made an edge
330 // feasible that wasn't before. Revisit the PHI nodes in the block
331 // because they have potentially new operands.
332 for (BasicBlock::iterator I = Dest->begin(); isa<PHINode>(I); ++I)
333 visitPHINode(*cast<PHINode>(I));
336 MarkBlockExecutable(Dest);
340 // getFeasibleSuccessors - Return a vector of booleans to indicate which
341 // successors are reachable from a given terminator instruction.
343 void getFeasibleSuccessors(TerminatorInst &TI, std::vector<bool> &Succs);
345 // isEdgeFeasible - Return true if the control flow edge from the 'From' basic
346 // block to the 'To' basic block is currently feasible...
348 bool isEdgeFeasible(BasicBlock *From, BasicBlock *To);
350 // OperandChangedState - This method is invoked on all of the users of an
351 // instruction that was just changed state somehow.... Based on this
352 // information, we need to update the specified user of this instruction.
354 void OperandChangedState(User *U) {
355 // Only instructions use other variable values!
356 Instruction &I = cast<Instruction>(*U);
357 if (BBExecutable.count(I.getParent())) // Inst is executable?
362 friend class InstVisitor<SCCPSolver>;
364 // visit implementations - Something changed in this instruction... Either an
365 // operand made a transition, or the instruction is newly executable. Change
366 // the value type of I to reflect these changes if appropriate.
368 void visitPHINode(PHINode &I);
371 void visitReturnInst(ReturnInst &I);
372 void visitTerminatorInst(TerminatorInst &TI);
374 void visitCastInst(CastInst &I);
375 void visitSelectInst(SelectInst &I);
376 void visitBinaryOperator(Instruction &I);
377 void visitCmpInst(CmpInst &I);
378 void visitShiftInst(ShiftInst &I) { visitBinaryOperator(I); }
379 void visitExtractElementInst(ExtractElementInst &I);
380 void visitInsertElementInst(InsertElementInst &I);
381 void visitShuffleVectorInst(ShuffleVectorInst &I);
383 // Instructions that cannot be folded away...
384 void visitStoreInst (Instruction &I);
385 void visitLoadInst (LoadInst &I);
386 void visitGetElementPtrInst(GetElementPtrInst &I);
387 void visitCallInst (CallInst &I) { visitCallSite(CallSite::get(&I)); }
388 void visitInvokeInst (InvokeInst &II) {
389 visitCallSite(CallSite::get(&II));
390 visitTerminatorInst(II);
392 void visitCallSite (CallSite CS);
393 void visitUnwindInst (TerminatorInst &I) { /*returns void*/ }
394 void visitUnreachableInst(TerminatorInst &I) { /*returns void*/ }
395 void visitAllocationInst(Instruction &I) { markOverdefined(&I); }
396 void visitVANextInst (Instruction &I) { markOverdefined(&I); }
397 void visitVAArgInst (Instruction &I) { markOverdefined(&I); }
398 void visitFreeInst (Instruction &I) { /*returns void*/ }
400 void visitInstruction(Instruction &I) {
401 // If a new instruction is added to LLVM that we don't handle...
402 cerr << "SCCP: Don't know how to handle: " << I;
403 markOverdefined(&I); // Just in case
407 // getFeasibleSuccessors - Return a vector of booleans to indicate which
408 // successors are reachable from a given terminator instruction.
410 void SCCPSolver::getFeasibleSuccessors(TerminatorInst &TI,
411 std::vector<bool> &Succs) {
412 Succs.resize(TI.getNumSuccessors());
413 if (BranchInst *BI = dyn_cast<BranchInst>(&TI)) {
414 if (BI->isUnconditional()) {
417 LatticeVal &BCValue = getValueState(BI->getCondition());
418 if (BCValue.isOverdefined() ||
419 (BCValue.isConstant() && !isa<ConstantBool>(BCValue.getConstant()))) {
420 // Overdefined condition variables, and branches on unfoldable constant
421 // conditions, mean the branch could go either way.
422 Succs[0] = Succs[1] = true;
423 } else if (BCValue.isConstant()) {
424 // Constant condition variables mean the branch can only go a single way
425 Succs[BCValue.getConstant() == ConstantBool::getFalse()] = true;
428 } else if (isa<InvokeInst>(&TI)) {
429 // Invoke instructions successors are always executable.
430 Succs[0] = Succs[1] = true;
431 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(&TI)) {
432 LatticeVal &SCValue = getValueState(SI->getCondition());
433 if (SCValue.isOverdefined() || // Overdefined condition?
434 (SCValue.isConstant() && !isa<ConstantInt>(SCValue.getConstant()))) {
435 // All destinations are executable!
436 Succs.assign(TI.getNumSuccessors(), true);
437 } else if (SCValue.isConstant()) {
438 Constant *CPV = SCValue.getConstant();
439 // Make sure to skip the "default value" which isn't a value
440 for (unsigned i = 1, E = SI->getNumSuccessors(); i != E; ++i) {
441 if (SI->getSuccessorValue(i) == CPV) {// Found the right branch...
447 // Constant value not equal to any of the branches... must execute
448 // default branch then...
452 cerr << "SCCP: Don't know how to handle: " << TI;
453 Succs.assign(TI.getNumSuccessors(), true);
458 // isEdgeFeasible - Return true if the control flow edge from the 'From' basic
459 // block to the 'To' basic block is currently feasible...
461 bool SCCPSolver::isEdgeFeasible(BasicBlock *From, BasicBlock *To) {
462 assert(BBExecutable.count(To) && "Dest should always be alive!");
464 // Make sure the source basic block is executable!!
465 if (!BBExecutable.count(From)) return false;
467 // Check to make sure this edge itself is actually feasible now...
468 TerminatorInst *TI = From->getTerminator();
469 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
470 if (BI->isUnconditional())
473 LatticeVal &BCValue = getValueState(BI->getCondition());
474 if (BCValue.isOverdefined()) {
475 // Overdefined condition variables mean the branch could go either way.
477 } else if (BCValue.isConstant()) {
478 // Not branching on an evaluatable constant?
479 if (!isa<ConstantBool>(BCValue.getConstant())) return true;
481 // Constant condition variables mean the branch can only go a single way
482 return BI->getSuccessor(BCValue.getConstant() ==
483 ConstantBool::getFalse()) == To;
487 } else if (isa<InvokeInst>(TI)) {
488 // Invoke instructions successors are always executable.
490 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
491 LatticeVal &SCValue = getValueState(SI->getCondition());
492 if (SCValue.isOverdefined()) { // Overdefined condition?
493 // All destinations are executable!
495 } else if (SCValue.isConstant()) {
496 Constant *CPV = SCValue.getConstant();
497 if (!isa<ConstantInt>(CPV))
498 return true; // not a foldable constant?
500 // Make sure to skip the "default value" which isn't a value
501 for (unsigned i = 1, E = SI->getNumSuccessors(); i != E; ++i)
502 if (SI->getSuccessorValue(i) == CPV) // Found the taken branch...
503 return SI->getSuccessor(i) == To;
505 // Constant value not equal to any of the branches... must execute
506 // default branch then...
507 return SI->getDefaultDest() == To;
511 cerr << "Unknown terminator instruction: " << *TI;
516 // visit Implementations - Something changed in this instruction... Either an
517 // operand made a transition, or the instruction is newly executable. Change
518 // the value type of I to reflect these changes if appropriate. This method
519 // makes sure to do the following actions:
521 // 1. If a phi node merges two constants in, and has conflicting value coming
522 // from different branches, or if the PHI node merges in an overdefined
523 // value, then the PHI node becomes overdefined.
524 // 2. If a phi node merges only constants in, and they all agree on value, the
525 // PHI node becomes a constant value equal to that.
526 // 3. If V <- x (op) y && isConstant(x) && isConstant(y) V = Constant
527 // 4. If V <- x (op) y && (isOverdefined(x) || isOverdefined(y)) V = Overdefined
528 // 5. If V <- MEM or V <- CALL or V <- (unknown) then V = Overdefined
529 // 6. If a conditional branch has a value that is constant, make the selected
530 // destination executable
531 // 7. If a conditional branch has a value that is overdefined, make all
532 // successors executable.
534 void SCCPSolver::visitPHINode(PHINode &PN) {
535 LatticeVal &PNIV = getValueState(&PN);
536 if (PNIV.isOverdefined()) {
537 // There may be instructions using this PHI node that are not overdefined
538 // themselves. If so, make sure that they know that the PHI node operand
540 std::multimap<PHINode*, Instruction*>::iterator I, E;
541 tie(I, E) = UsersOfOverdefinedPHIs.equal_range(&PN);
543 std::vector<Instruction*> Users;
544 Users.reserve(std::distance(I, E));
545 for (; I != E; ++I) Users.push_back(I->second);
546 while (!Users.empty()) {
551 return; // Quick exit
554 // Super-extra-high-degree PHI nodes are unlikely to ever be marked constant,
555 // and slow us down a lot. Just mark them overdefined.
556 if (PN.getNumIncomingValues() > 64) {
557 markOverdefined(PNIV, &PN);
561 // Look at all of the executable operands of the PHI node. If any of them
562 // are overdefined, the PHI becomes overdefined as well. If they are all
563 // constant, and they agree with each other, the PHI becomes the identical
564 // constant. If they are constant and don't agree, the PHI is overdefined.
565 // If there are no executable operands, the PHI remains undefined.
567 Constant *OperandVal = 0;
568 for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) {
569 LatticeVal &IV = getValueState(PN.getIncomingValue(i));
570 if (IV.isUndefined()) continue; // Doesn't influence PHI node.
572 if (isEdgeFeasible(PN.getIncomingBlock(i), PN.getParent())) {
573 if (IV.isOverdefined()) { // PHI node becomes overdefined!
574 markOverdefined(PNIV, &PN);
578 if (OperandVal == 0) { // Grab the first value...
579 OperandVal = IV.getConstant();
580 } else { // Another value is being merged in!
581 // There is already a reachable operand. If we conflict with it,
582 // then the PHI node becomes overdefined. If we agree with it, we
585 // Check to see if there are two different constants merging...
586 if (IV.getConstant() != OperandVal) {
587 // Yes there is. This means the PHI node is not constant.
588 // You must be overdefined poor PHI.
590 markOverdefined(PNIV, &PN); // The PHI node now becomes overdefined
591 return; // I'm done analyzing you
597 // If we exited the loop, this means that the PHI node only has constant
598 // arguments that agree with each other(and OperandVal is the constant) or
599 // OperandVal is null because there are no defined incoming arguments. If
600 // this is the case, the PHI remains undefined.
603 markConstant(PNIV, &PN, OperandVal); // Acquire operand value
606 void SCCPSolver::visitReturnInst(ReturnInst &I) {
607 if (I.getNumOperands() == 0) return; // Ret void
609 // If we are tracking the return value of this function, merge it in.
610 Function *F = I.getParent()->getParent();
611 if (F->hasInternalLinkage() && !TrackedFunctionRetVals.empty()) {
612 hash_map<Function*, LatticeVal>::iterator TFRVI =
613 TrackedFunctionRetVals.find(F);
614 if (TFRVI != TrackedFunctionRetVals.end() &&
615 !TFRVI->second.isOverdefined()) {
616 LatticeVal &IV = getValueState(I.getOperand(0));
617 mergeInValue(TFRVI->second, F, IV);
623 void SCCPSolver::visitTerminatorInst(TerminatorInst &TI) {
624 std::vector<bool> SuccFeasible;
625 getFeasibleSuccessors(TI, SuccFeasible);
627 BasicBlock *BB = TI.getParent();
629 // Mark all feasible successors executable...
630 for (unsigned i = 0, e = SuccFeasible.size(); i != e; ++i)
632 markEdgeExecutable(BB, TI.getSuccessor(i));
635 void SCCPSolver::visitCastInst(CastInst &I) {
636 Value *V = I.getOperand(0);
637 LatticeVal &VState = getValueState(V);
638 if (VState.isOverdefined()) // Inherit overdefinedness of operand
640 else if (VState.isConstant()) // Propagate constant value
641 markConstant(&I, ConstantExpr::getCast(I.getOpcode(),
642 VState.getConstant(), I.getType()));
645 void SCCPSolver::visitSelectInst(SelectInst &I) {
646 LatticeVal &CondValue = getValueState(I.getCondition());
647 if (CondValue.isUndefined())
649 if (CondValue.isConstant()) {
650 if (ConstantBool *CondCB = dyn_cast<ConstantBool>(CondValue.getConstant())){
651 mergeInValue(&I, getValueState(CondCB->getValue() ? I.getTrueValue()
652 : I.getFalseValue()));
657 // Otherwise, the condition is overdefined or a constant we can't evaluate.
658 // See if we can produce something better than overdefined based on the T/F
660 LatticeVal &TVal = getValueState(I.getTrueValue());
661 LatticeVal &FVal = getValueState(I.getFalseValue());
663 // select ?, C, C -> C.
664 if (TVal.isConstant() && FVal.isConstant() &&
665 TVal.getConstant() == FVal.getConstant()) {
666 markConstant(&I, FVal.getConstant());
670 if (TVal.isUndefined()) { // select ?, undef, X -> X.
671 mergeInValue(&I, FVal);
672 } else if (FVal.isUndefined()) { // select ?, X, undef -> X.
673 mergeInValue(&I, TVal);
679 // Handle BinaryOperators and Shift Instructions...
680 void SCCPSolver::visitBinaryOperator(Instruction &I) {
681 LatticeVal &IV = ValueState[&I];
682 if (IV.isOverdefined()) return;
684 LatticeVal &V1State = getValueState(I.getOperand(0));
685 LatticeVal &V2State = getValueState(I.getOperand(1));
687 if (V1State.isOverdefined() || V2State.isOverdefined()) {
688 // If this is an AND or OR with 0 or -1, it doesn't matter that the other
689 // operand is overdefined.
690 if (I.getOpcode() == Instruction::And || I.getOpcode() == Instruction::Or) {
691 LatticeVal *NonOverdefVal = 0;
692 if (!V1State.isOverdefined()) {
693 NonOverdefVal = &V1State;
694 } else if (!V2State.isOverdefined()) {
695 NonOverdefVal = &V2State;
699 if (NonOverdefVal->isUndefined()) {
700 // Could annihilate value.
701 if (I.getOpcode() == Instruction::And)
702 markConstant(IV, &I, Constant::getNullValue(I.getType()));
703 else if (Constant *Ones = ConstantInt::getAllOnesValue(I.getType())) {
704 markConstant(IV, &I, Ones);
708 if (I.getOpcode() == Instruction::And) {
709 if (NonOverdefVal->getConstant()->isNullValue()) {
710 markConstant(IV, &I, NonOverdefVal->getConstant());
711 return; // X and 0 = 0
714 if (ConstantIntegral *CI =
715 dyn_cast<ConstantIntegral>(NonOverdefVal->getConstant()))
716 if (CI->isAllOnesValue()) {
717 markConstant(IV, &I, NonOverdefVal->getConstant());
718 return; // X or -1 = -1
726 // If both operands are PHI nodes, it is possible that this instruction has
727 // a constant value, despite the fact that the PHI node doesn't. Check for
728 // this condition now.
729 if (PHINode *PN1 = dyn_cast<PHINode>(I.getOperand(0)))
730 if (PHINode *PN2 = dyn_cast<PHINode>(I.getOperand(1)))
731 if (PN1->getParent() == PN2->getParent()) {
732 // Since the two PHI nodes are in the same basic block, they must have
733 // entries for the same predecessors. Walk the predecessor list, and
734 // if all of the incoming values are constants, and the result of
735 // evaluating this expression with all incoming value pairs is the
736 // same, then this expression is a constant even though the PHI node
737 // is not a constant!
739 for (unsigned i = 0, e = PN1->getNumIncomingValues(); i != e; ++i) {
740 LatticeVal &In1 = getValueState(PN1->getIncomingValue(i));
741 BasicBlock *InBlock = PN1->getIncomingBlock(i);
743 getValueState(PN2->getIncomingValueForBlock(InBlock));
745 if (In1.isOverdefined() || In2.isOverdefined()) {
746 Result.markOverdefined();
747 break; // Cannot fold this operation over the PHI nodes!
748 } else if (In1.isConstant() && In2.isConstant()) {
749 Constant *V = ConstantExpr::get(I.getOpcode(), In1.getConstant(),
751 if (Result.isUndefined())
752 Result.markConstant(V);
753 else if (Result.isConstant() && Result.getConstant() != V) {
754 Result.markOverdefined();
760 // If we found a constant value here, then we know the instruction is
761 // constant despite the fact that the PHI nodes are overdefined.
762 if (Result.isConstant()) {
763 markConstant(IV, &I, Result.getConstant());
764 // Remember that this instruction is virtually using the PHI node
766 UsersOfOverdefinedPHIs.insert(std::make_pair(PN1, &I));
767 UsersOfOverdefinedPHIs.insert(std::make_pair(PN2, &I));
769 } else if (Result.isUndefined()) {
773 // Okay, this really is overdefined now. Since we might have
774 // speculatively thought that this was not overdefined before, and
775 // added ourselves to the UsersOfOverdefinedPHIs list for the PHIs,
776 // make sure to clean out any entries that we put there, for
778 std::multimap<PHINode*, Instruction*>::iterator It, E;
779 tie(It, E) = UsersOfOverdefinedPHIs.equal_range(PN1);
781 if (It->second == &I) {
782 UsersOfOverdefinedPHIs.erase(It++);
786 tie(It, E) = UsersOfOverdefinedPHIs.equal_range(PN2);
788 if (It->second == &I) {
789 UsersOfOverdefinedPHIs.erase(It++);
795 markOverdefined(IV, &I);
796 } else if (V1State.isConstant() && V2State.isConstant()) {
797 markConstant(IV, &I, ConstantExpr::get(I.getOpcode(), V1State.getConstant(),
798 V2State.getConstant()));
802 // Handle ICmpInst instruction...
803 void SCCPSolver::visitCmpInst(CmpInst &I) {
804 LatticeVal &IV = ValueState[&I];
805 if (IV.isOverdefined()) return;
807 LatticeVal &V1State = getValueState(I.getOperand(0));
808 LatticeVal &V2State = getValueState(I.getOperand(1));
810 if (V1State.isOverdefined() || V2State.isOverdefined()) {
811 // If both operands are PHI nodes, it is possible that this instruction has
812 // a constant value, despite the fact that the PHI node doesn't. Check for
813 // this condition now.
814 if (PHINode *PN1 = dyn_cast<PHINode>(I.getOperand(0)))
815 if (PHINode *PN2 = dyn_cast<PHINode>(I.getOperand(1)))
816 if (PN1->getParent() == PN2->getParent()) {
817 // Since the two PHI nodes are in the same basic block, they must have
818 // entries for the same predecessors. Walk the predecessor list, and
819 // if all of the incoming values are constants, and the result of
820 // evaluating this expression with all incoming value pairs is the
821 // same, then this expression is a constant even though the PHI node
822 // is not a constant!
824 for (unsigned i = 0, e = PN1->getNumIncomingValues(); i != e; ++i) {
825 LatticeVal &In1 = getValueState(PN1->getIncomingValue(i));
826 BasicBlock *InBlock = PN1->getIncomingBlock(i);
828 getValueState(PN2->getIncomingValueForBlock(InBlock));
830 if (In1.isOverdefined() || In2.isOverdefined()) {
831 Result.markOverdefined();
832 break; // Cannot fold this operation over the PHI nodes!
833 } else if (In1.isConstant() && In2.isConstant()) {
834 Constant *V = ConstantExpr::getCompare(I.getPredicate(),
837 if (Result.isUndefined())
838 Result.markConstant(V);
839 else if (Result.isConstant() && Result.getConstant() != V) {
840 Result.markOverdefined();
846 // If we found a constant value here, then we know the instruction is
847 // constant despite the fact that the PHI nodes are overdefined.
848 if (Result.isConstant()) {
849 markConstant(IV, &I, Result.getConstant());
850 // Remember that this instruction is virtually using the PHI node
852 UsersOfOverdefinedPHIs.insert(std::make_pair(PN1, &I));
853 UsersOfOverdefinedPHIs.insert(std::make_pair(PN2, &I));
855 } else if (Result.isUndefined()) {
859 // Okay, this really is overdefined now. Since we might have
860 // speculatively thought that this was not overdefined before, and
861 // added ourselves to the UsersOfOverdefinedPHIs list for the PHIs,
862 // make sure to clean out any entries that we put there, for
864 std::multimap<PHINode*, Instruction*>::iterator It, E;
865 tie(It, E) = UsersOfOverdefinedPHIs.equal_range(PN1);
867 if (It->second == &I) {
868 UsersOfOverdefinedPHIs.erase(It++);
872 tie(It, E) = UsersOfOverdefinedPHIs.equal_range(PN2);
874 if (It->second == &I) {
875 UsersOfOverdefinedPHIs.erase(It++);
881 markOverdefined(IV, &I);
882 } else if (V1State.isConstant() && V2State.isConstant()) {
883 markConstant(IV, &I, ConstantExpr::getCompare(I.getPredicate(),
884 V1State.getConstant(),
885 V2State.getConstant()));
889 void SCCPSolver::visitExtractElementInst(ExtractElementInst &I) {
890 // FIXME : SCCP does not handle vectors properly.
895 LatticeVal &ValState = getValueState(I.getOperand(0));
896 LatticeVal &IdxState = getValueState(I.getOperand(1));
898 if (ValState.isOverdefined() || IdxState.isOverdefined())
900 else if(ValState.isConstant() && IdxState.isConstant())
901 markConstant(&I, ConstantExpr::getExtractElement(ValState.getConstant(),
902 IdxState.getConstant()));
906 void SCCPSolver::visitInsertElementInst(InsertElementInst &I) {
907 // FIXME : SCCP does not handle vectors properly.
911 LatticeVal &ValState = getValueState(I.getOperand(0));
912 LatticeVal &EltState = getValueState(I.getOperand(1));
913 LatticeVal &IdxState = getValueState(I.getOperand(2));
915 if (ValState.isOverdefined() || EltState.isOverdefined() ||
916 IdxState.isOverdefined())
918 else if(ValState.isConstant() && EltState.isConstant() &&
919 IdxState.isConstant())
920 markConstant(&I, ConstantExpr::getInsertElement(ValState.getConstant(),
921 EltState.getConstant(),
922 IdxState.getConstant()));
923 else if (ValState.isUndefined() && EltState.isConstant() &&
924 IdxState.isConstant())
925 markConstant(&I, ConstantExpr::getInsertElement(UndefValue::get(I.getType()),
926 EltState.getConstant(),
927 IdxState.getConstant()));
931 void SCCPSolver::visitShuffleVectorInst(ShuffleVectorInst &I) {
932 // FIXME : SCCP does not handle vectors properly.
936 LatticeVal &V1State = getValueState(I.getOperand(0));
937 LatticeVal &V2State = getValueState(I.getOperand(1));
938 LatticeVal &MaskState = getValueState(I.getOperand(2));
940 if (MaskState.isUndefined() ||
941 (V1State.isUndefined() && V2State.isUndefined()))
942 return; // Undefined output if mask or both inputs undefined.
944 if (V1State.isOverdefined() || V2State.isOverdefined() ||
945 MaskState.isOverdefined()) {
948 // A mix of constant/undef inputs.
949 Constant *V1 = V1State.isConstant() ?
950 V1State.getConstant() : UndefValue::get(I.getType());
951 Constant *V2 = V2State.isConstant() ?
952 V2State.getConstant() : UndefValue::get(I.getType());
953 Constant *Mask = MaskState.isConstant() ?
954 MaskState.getConstant() : UndefValue::get(I.getOperand(2)->getType());
955 markConstant(&I, ConstantExpr::getShuffleVector(V1, V2, Mask));
960 // Handle getelementptr instructions... if all operands are constants then we
961 // can turn this into a getelementptr ConstantExpr.
963 void SCCPSolver::visitGetElementPtrInst(GetElementPtrInst &I) {
964 LatticeVal &IV = ValueState[&I];
965 if (IV.isOverdefined()) return;
967 std::vector<Constant*> Operands;
968 Operands.reserve(I.getNumOperands());
970 for (unsigned i = 0, e = I.getNumOperands(); i != e; ++i) {
971 LatticeVal &State = getValueState(I.getOperand(i));
972 if (State.isUndefined())
973 return; // Operands are not resolved yet...
974 else if (State.isOverdefined()) {
975 markOverdefined(IV, &I);
978 assert(State.isConstant() && "Unknown state!");
979 Operands.push_back(State.getConstant());
982 Constant *Ptr = Operands[0];
983 Operands.erase(Operands.begin()); // Erase the pointer from idx list...
985 markConstant(IV, &I, ConstantExpr::getGetElementPtr(Ptr, Operands));
988 void SCCPSolver::visitStoreInst(Instruction &SI) {
989 if (TrackedGlobals.empty() || !isa<GlobalVariable>(SI.getOperand(1)))
991 GlobalVariable *GV = cast<GlobalVariable>(SI.getOperand(1));
992 hash_map<GlobalVariable*, LatticeVal>::iterator I = TrackedGlobals.find(GV);
993 if (I == TrackedGlobals.end() || I->second.isOverdefined()) return;
995 // Get the value we are storing into the global.
996 LatticeVal &PtrVal = getValueState(SI.getOperand(0));
998 mergeInValue(I->second, GV, PtrVal);
999 if (I->second.isOverdefined())
1000 TrackedGlobals.erase(I); // No need to keep tracking this!
1004 // Handle load instructions. If the operand is a constant pointer to a constant
1005 // global, we can replace the load with the loaded constant value!
1006 void SCCPSolver::visitLoadInst(LoadInst &I) {
1007 LatticeVal &IV = ValueState[&I];
1008 if (IV.isOverdefined()) return;
1010 LatticeVal &PtrVal = getValueState(I.getOperand(0));
1011 if (PtrVal.isUndefined()) return; // The pointer is not resolved yet!
1012 if (PtrVal.isConstant() && !I.isVolatile()) {
1013 Value *Ptr = PtrVal.getConstant();
1014 if (isa<ConstantPointerNull>(Ptr)) {
1015 // load null -> null
1016 markConstant(IV, &I, Constant::getNullValue(I.getType()));
1020 // Transform load (constant global) into the value loaded.
1021 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Ptr)) {
1022 if (GV->isConstant()) {
1023 if (!GV->isExternal()) {
1024 markConstant(IV, &I, GV->getInitializer());
1027 } else if (!TrackedGlobals.empty()) {
1028 // If we are tracking this global, merge in the known value for it.
1029 hash_map<GlobalVariable*, LatticeVal>::iterator It =
1030 TrackedGlobals.find(GV);
1031 if (It != TrackedGlobals.end()) {
1032 mergeInValue(IV, &I, It->second);
1038 // Transform load (constantexpr_GEP global, 0, ...) into the value loaded.
1039 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr))
1040 if (CE->getOpcode() == Instruction::GetElementPtr)
1041 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(CE->getOperand(0)))
1042 if (GV->isConstant() && !GV->isExternal())
1044 ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE)) {
1045 markConstant(IV, &I, V);
1050 // Otherwise we cannot say for certain what value this load will produce.
1052 markOverdefined(IV, &I);
1055 void SCCPSolver::visitCallSite(CallSite CS) {
1056 Function *F = CS.getCalledFunction();
1058 // If we are tracking this function, we must make sure to bind arguments as
1060 hash_map<Function*, LatticeVal>::iterator TFRVI =TrackedFunctionRetVals.end();
1061 if (F && F->hasInternalLinkage())
1062 TFRVI = TrackedFunctionRetVals.find(F);
1064 if (TFRVI != TrackedFunctionRetVals.end()) {
1065 // If this is the first call to the function hit, mark its entry block
1067 if (!BBExecutable.count(F->begin()))
1068 MarkBlockExecutable(F->begin());
1070 CallSite::arg_iterator CAI = CS.arg_begin();
1071 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
1072 AI != E; ++AI, ++CAI) {
1073 LatticeVal &IV = ValueState[AI];
1074 if (!IV.isOverdefined())
1075 mergeInValue(IV, AI, getValueState(*CAI));
1078 Instruction *I = CS.getInstruction();
1079 if (I->getType() == Type::VoidTy) return;
1081 LatticeVal &IV = ValueState[I];
1082 if (IV.isOverdefined()) return;
1084 // Propagate the return value of the function to the value of the instruction.
1085 if (TFRVI != TrackedFunctionRetVals.end()) {
1086 mergeInValue(IV, I, TFRVI->second);
1090 if (F == 0 || !F->isExternal() || !canConstantFoldCallTo(F)) {
1091 markOverdefined(IV, I);
1095 std::vector<Constant*> Operands;
1096 Operands.reserve(I->getNumOperands()-1);
1098 for (CallSite::arg_iterator AI = CS.arg_begin(), E = CS.arg_end();
1100 LatticeVal &State = getValueState(*AI);
1101 if (State.isUndefined())
1102 return; // Operands are not resolved yet...
1103 else if (State.isOverdefined()) {
1104 markOverdefined(IV, I);
1107 assert(State.isConstant() && "Unknown state!");
1108 Operands.push_back(State.getConstant());
1111 if (Constant *C = ConstantFoldCall(F, Operands))
1112 markConstant(IV, I, C);
1114 markOverdefined(IV, I);
1118 void SCCPSolver::Solve() {
1119 // Process the work lists until they are empty!
1120 while (!BBWorkList.empty() || !InstWorkList.empty() ||
1121 !OverdefinedInstWorkList.empty()) {
1122 // Process the instruction work list...
1123 while (!OverdefinedInstWorkList.empty()) {
1124 Value *I = OverdefinedInstWorkList.back();
1125 OverdefinedInstWorkList.pop_back();
1127 DOUT << "\nPopped off OI-WL: " << *I;
1129 // "I" got into the work list because it either made the transition from
1130 // bottom to constant
1132 // Anything on this worklist that is overdefined need not be visited
1133 // since all of its users will have already been marked as overdefined
1134 // Update all of the users of this instruction's value...
1136 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
1138 OperandChangedState(*UI);
1140 // Process the instruction work list...
1141 while (!InstWorkList.empty()) {
1142 Value *I = InstWorkList.back();
1143 InstWorkList.pop_back();
1145 DOUT << "\nPopped off I-WL: " << *I;
1147 // "I" got into the work list because it either made the transition from
1148 // bottom to constant
1150 // Anything on this worklist that is overdefined need not be visited
1151 // since all of its users will have already been marked as overdefined.
1152 // Update all of the users of this instruction's value...
1154 if (!getValueState(I).isOverdefined())
1155 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
1157 OperandChangedState(*UI);
1160 // Process the basic block work list...
1161 while (!BBWorkList.empty()) {
1162 BasicBlock *BB = BBWorkList.back();
1163 BBWorkList.pop_back();
1165 DOUT << "\nPopped off BBWL: " << *BB;
1167 // Notify all instructions in this basic block that they are newly
1174 /// ResolvedUndefsIn - While solving the dataflow for a function, we assume
1175 /// that branches on undef values cannot reach any of their successors.
1176 /// However, this is not a safe assumption. After we solve dataflow, this
1177 /// method should be use to handle this. If this returns true, the solver
1178 /// should be rerun.
1180 /// This method handles this by finding an unresolved branch and marking it one
1181 /// of the edges from the block as being feasible, even though the condition
1182 /// doesn't say it would otherwise be. This allows SCCP to find the rest of the
1183 /// CFG and only slightly pessimizes the analysis results (by marking one,
1184 /// potentially infeasible, edge feasible). This cannot usefully modify the
1185 /// constraints on the condition of the branch, as that would impact other users
1188 /// This scan also checks for values that use undefs, whose results are actually
1189 /// defined. For example, 'zext i8 undef to i32' should produce all zeros
1190 /// conservatively, as "(zext i8 X -> i32) & 0xFF00" must always return zero,
1191 /// even if X isn't defined.
1192 bool SCCPSolver::ResolvedUndefsIn(Function &F) {
1193 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
1194 if (!BBExecutable.count(BB))
1197 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
1198 // Look for instructions which produce undef values.
1199 if (I->getType() == Type::VoidTy) continue;
1201 LatticeVal &LV = getValueState(I);
1202 if (!LV.isUndefined()) continue;
1204 // Get the lattice values of the first two operands for use below.
1205 LatticeVal &Op0LV = getValueState(I->getOperand(0));
1207 if (I->getNumOperands() == 2) {
1208 // If this is a two-operand instruction, and if both operands are
1209 // undefs, the result stays undef.
1210 Op1LV = getValueState(I->getOperand(1));
1211 if (Op0LV.isUndefined() && Op1LV.isUndefined())
1215 // If this is an instructions whose result is defined even if the input is
1216 // not fully defined, propagate the information.
1217 const Type *ITy = I->getType();
1218 switch (I->getOpcode()) {
1219 default: break; // Leave the instruction as an undef.
1220 case Instruction::ZExt:
1221 // After a zero extend, we know the top part is zero. SExt doesn't have
1222 // to be handled here, because we don't know whether the top part is 1's
1224 assert(Op0LV.isUndefined());
1225 markForcedConstant(LV, I, Constant::getNullValue(ITy));
1227 case Instruction::Mul:
1228 case Instruction::And:
1229 // undef * X -> 0. X could be zero.
1230 // undef & X -> 0. X could be zero.
1231 markForcedConstant(LV, I, Constant::getNullValue(ITy));
1234 case Instruction::Or:
1235 // undef | X -> -1. X could be -1.
1236 if (Constant *Ones = ConstantInt::getAllOnesValue(ITy)) {
1237 markForcedConstant(LV, I, Ones);
1242 case Instruction::SDiv:
1243 case Instruction::UDiv:
1244 case Instruction::SRem:
1245 case Instruction::URem:
1246 // X / undef -> undef. No change.
1247 // X % undef -> undef. No change.
1248 if (Op1LV.isUndefined()) break;
1250 // undef / X -> 0. X could be maxint.
1251 // undef % X -> 0. X could be 1.
1252 markForcedConstant(LV, I, Constant::getNullValue(ITy));
1255 case Instruction::AShr:
1256 // undef >>s X -> undef. No change.
1257 if (Op0LV.isUndefined()) break;
1259 // X >>s undef -> X. X could be 0, X could have the high-bit known set.
1260 if (Op0LV.isConstant())
1261 markForcedConstant(LV, I, Op0LV.getConstant());
1263 markOverdefined(LV, I);
1265 case Instruction::LShr:
1266 case Instruction::Shl:
1267 // undef >> X -> undef. No change.
1268 // undef << X -> undef. No change.
1269 if (Op0LV.isUndefined()) break;
1271 // X >> undef -> 0. X could be 0.
1272 // X << undef -> 0. X could be 0.
1273 markForcedConstant(LV, I, Constant::getNullValue(ITy));
1275 case Instruction::Select:
1276 // undef ? X : Y -> X or Y. There could be commonality between X/Y.
1277 if (Op0LV.isUndefined()) {
1278 if (!Op1LV.isConstant()) // Pick the constant one if there is any.
1279 Op1LV = getValueState(I->getOperand(2));
1280 } else if (Op1LV.isUndefined()) {
1281 // c ? undef : undef -> undef. No change.
1282 Op1LV = getValueState(I->getOperand(2));
1283 if (Op1LV.isUndefined())
1285 // Otherwise, c ? undef : x -> x.
1287 // Leave Op1LV as Operand(1)'s LatticeValue.
1290 if (Op1LV.isConstant())
1291 markForcedConstant(LV, I, Op1LV.getConstant());
1293 markOverdefined(LV, I);
1298 TerminatorInst *TI = BB->getTerminator();
1299 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
1300 if (!BI->isConditional()) continue;
1301 if (!getValueState(BI->getCondition()).isUndefined())
1303 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
1304 if (!getValueState(SI->getCondition()).isUndefined())
1310 // If the edge to the first successor isn't thought to be feasible yet, mark
1312 if (KnownFeasibleEdges.count(Edge(BB, TI->getSuccessor(0))))
1315 // Otherwise, it isn't already thought to be feasible. Mark it as such now
1316 // and return. This will make other blocks reachable, which will allow new
1317 // values to be discovered and existing ones to be moved in the lattice.
1318 markEdgeExecutable(BB, TI->getSuccessor(0));
1327 //===--------------------------------------------------------------------===//
1329 /// SCCP Class - This class uses the SCCPSolver to implement a per-function
1330 /// Sparse Conditional Constant Propagator.
1332 struct SCCP : public FunctionPass {
1333 // runOnFunction - Run the Sparse Conditional Constant Propagation
1334 // algorithm, and return true if the function was modified.
1336 bool runOnFunction(Function &F);
1338 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
1339 AU.setPreservesCFG();
1343 RegisterPass<SCCP> X("sccp", "Sparse Conditional Constant Propagation");
1344 } // end anonymous namespace
1347 // createSCCPPass - This is the public interface to this file...
1348 FunctionPass *llvm::createSCCPPass() {
1353 // runOnFunction() - Run the Sparse Conditional Constant Propagation algorithm,
1354 // and return true if the function was modified.
1356 bool SCCP::runOnFunction(Function &F) {
1357 DOUT << "SCCP on function '" << F.getName() << "'\n";
1360 // Mark the first block of the function as being executable.
1361 Solver.MarkBlockExecutable(F.begin());
1363 // Mark all arguments to the function as being overdefined.
1364 hash_map<Value*, LatticeVal> &Values = Solver.getValueMapping();
1365 for (Function::arg_iterator AI = F.arg_begin(), E = F.arg_end(); AI != E; ++AI)
1366 Values[AI].markOverdefined();
1368 // Solve for constants.
1369 bool ResolvedUndefs = true;
1370 while (ResolvedUndefs) {
1372 DOUT << "RESOLVING UNDEFs\n";
1373 ResolvedUndefs = Solver.ResolvedUndefsIn(F);
1376 bool MadeChanges = false;
1378 // If we decided that there are basic blocks that are dead in this function,
1379 // delete their contents now. Note that we cannot actually delete the blocks,
1380 // as we cannot modify the CFG of the function.
1382 std::set<BasicBlock*> &ExecutableBBs = Solver.getExecutableBlocks();
1383 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
1384 if (!ExecutableBBs.count(BB)) {
1385 DOUT << " BasicBlock Dead:" << *BB;
1388 // Delete the instructions backwards, as it has a reduced likelihood of
1389 // having to update as many def-use and use-def chains.
1390 std::vector<Instruction*> Insts;
1391 for (BasicBlock::iterator I = BB->begin(), E = BB->getTerminator();
1394 while (!Insts.empty()) {
1395 Instruction *I = Insts.back();
1397 if (!I->use_empty())
1398 I->replaceAllUsesWith(UndefValue::get(I->getType()));
1399 BB->getInstList().erase(I);
1404 // Iterate over all of the instructions in a function, replacing them with
1405 // constants if we have found them to be of constant values.
1407 for (BasicBlock::iterator BI = BB->begin(), E = BB->end(); BI != E; ) {
1408 Instruction *Inst = BI++;
1409 if (Inst->getType() != Type::VoidTy) {
1410 LatticeVal &IV = Values[Inst];
1411 if (IV.isConstant() || IV.isUndefined() &&
1412 !isa<TerminatorInst>(Inst)) {
1413 Constant *Const = IV.isConstant()
1414 ? IV.getConstant() : UndefValue::get(Inst->getType());
1415 DOUT << " Constant: " << *Const << " = " << *Inst;
1417 // Replaces all of the uses of a variable with uses of the constant.
1418 Inst->replaceAllUsesWith(Const);
1420 // Delete the instruction.
1421 BB->getInstList().erase(Inst);
1423 // Hey, we just changed something!
1435 //===--------------------------------------------------------------------===//
1437 /// IPSCCP Class - This class implements interprocedural Sparse Conditional
1438 /// Constant Propagation.
1440 struct IPSCCP : public ModulePass {
1441 bool runOnModule(Module &M);
1444 RegisterPass<IPSCCP>
1445 Y("ipsccp", "Interprocedural Sparse Conditional Constant Propagation");
1446 } // end anonymous namespace
1448 // createIPSCCPPass - This is the public interface to this file...
1449 ModulePass *llvm::createIPSCCPPass() {
1450 return new IPSCCP();
1454 static bool AddressIsTaken(GlobalValue *GV) {
1455 // Delete any dead constantexpr klingons.
1456 GV->removeDeadConstantUsers();
1458 for (Value::use_iterator UI = GV->use_begin(), E = GV->use_end();
1460 if (StoreInst *SI = dyn_cast<StoreInst>(*UI)) {
1461 if (SI->getOperand(0) == GV || SI->isVolatile())
1462 return true; // Storing addr of GV.
1463 } else if (isa<InvokeInst>(*UI) || isa<CallInst>(*UI)) {
1464 // Make sure we are calling the function, not passing the address.
1465 CallSite CS = CallSite::get(cast<Instruction>(*UI));
1466 for (CallSite::arg_iterator AI = CS.arg_begin(),
1467 E = CS.arg_end(); AI != E; ++AI)
1470 } else if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) {
1471 if (LI->isVolatile())
1479 bool IPSCCP::runOnModule(Module &M) {
1482 // Loop over all functions, marking arguments to those with their addresses
1483 // taken or that are external as overdefined.
1485 hash_map<Value*, LatticeVal> &Values = Solver.getValueMapping();
1486 for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F)
1487 if (!F->hasInternalLinkage() || AddressIsTaken(F)) {
1488 if (!F->isExternal())
1489 Solver.MarkBlockExecutable(F->begin());
1490 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
1492 Values[AI].markOverdefined();
1494 Solver.AddTrackedFunction(F);
1497 // Loop over global variables. We inform the solver about any internal global
1498 // variables that do not have their 'addresses taken'. If they don't have
1499 // their addresses taken, we can propagate constants through them.
1500 for (Module::global_iterator G = M.global_begin(), E = M.global_end();
1502 if (!G->isConstant() && G->hasInternalLinkage() && !AddressIsTaken(G))
1503 Solver.TrackValueOfGlobalVariable(G);
1505 // Solve for constants.
1506 bool ResolvedUndefs = true;
1507 while (ResolvedUndefs) {
1510 DOUT << "RESOLVING UNDEFS\n";
1511 ResolvedUndefs = false;
1512 for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F)
1513 ResolvedUndefs |= Solver.ResolvedUndefsIn(*F);
1516 bool MadeChanges = false;
1518 // Iterate over all of the instructions in the module, replacing them with
1519 // constants if we have found them to be of constant values.
1521 std::set<BasicBlock*> &ExecutableBBs = Solver.getExecutableBlocks();
1522 for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) {
1523 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
1525 if (!AI->use_empty()) {
1526 LatticeVal &IV = Values[AI];
1527 if (IV.isConstant() || IV.isUndefined()) {
1528 Constant *CST = IV.isConstant() ?
1529 IV.getConstant() : UndefValue::get(AI->getType());
1530 DOUT << "*** Arg " << *AI << " = " << *CST <<"\n";
1532 // Replaces all of the uses of a variable with uses of the
1534 AI->replaceAllUsesWith(CST);
1539 std::vector<BasicBlock*> BlocksToErase;
1540 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
1541 if (!ExecutableBBs.count(BB)) {
1542 DOUT << " BasicBlock Dead:" << *BB;
1545 // Delete the instructions backwards, as it has a reduced likelihood of
1546 // having to update as many def-use and use-def chains.
1547 std::vector<Instruction*> Insts;
1548 TerminatorInst *TI = BB->getTerminator();
1549 for (BasicBlock::iterator I = BB->begin(), E = TI; I != E; ++I)
1552 while (!Insts.empty()) {
1553 Instruction *I = Insts.back();
1555 if (!I->use_empty())
1556 I->replaceAllUsesWith(UndefValue::get(I->getType()));
1557 BB->getInstList().erase(I);
1562 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) {
1563 BasicBlock *Succ = TI->getSuccessor(i);
1564 if (Succ->begin() != Succ->end() && isa<PHINode>(Succ->begin()))
1565 TI->getSuccessor(i)->removePredecessor(BB);
1567 if (!TI->use_empty())
1568 TI->replaceAllUsesWith(UndefValue::get(TI->getType()));
1569 BB->getInstList().erase(TI);
1571 if (&*BB != &F->front())
1572 BlocksToErase.push_back(BB);
1574 new UnreachableInst(BB);
1577 for (BasicBlock::iterator BI = BB->begin(), E = BB->end(); BI != E; ) {
1578 Instruction *Inst = BI++;
1579 if (Inst->getType() != Type::VoidTy) {
1580 LatticeVal &IV = Values[Inst];
1581 if (IV.isConstant() || IV.isUndefined() &&
1582 !isa<TerminatorInst>(Inst)) {
1583 Constant *Const = IV.isConstant()
1584 ? IV.getConstant() : UndefValue::get(Inst->getType());
1585 DOUT << " Constant: " << *Const << " = " << *Inst;
1587 // Replaces all of the uses of a variable with uses of the
1589 Inst->replaceAllUsesWith(Const);
1591 // Delete the instruction.
1592 if (!isa<TerminatorInst>(Inst) && !isa<CallInst>(Inst))
1593 BB->getInstList().erase(Inst);
1595 // Hey, we just changed something!
1603 // Now that all instructions in the function are constant folded, erase dead
1604 // blocks, because we can now use ConstantFoldTerminator to get rid of
1606 for (unsigned i = 0, e = BlocksToErase.size(); i != e; ++i) {
1607 // If there are any PHI nodes in this successor, drop entries for BB now.
1608 BasicBlock *DeadBB = BlocksToErase[i];
1609 while (!DeadBB->use_empty()) {
1610 Instruction *I = cast<Instruction>(DeadBB->use_back());
1611 bool Folded = ConstantFoldTerminator(I->getParent());
1613 // The constant folder may not have been able to fold the termiantor
1614 // if this is a branch or switch on undef. Fold it manually as a
1615 // branch to the first successor.
1616 if (BranchInst *BI = dyn_cast<BranchInst>(I)) {
1617 assert(BI->isConditional() && isa<UndefValue>(BI->getCondition()) &&
1618 "Branch should be foldable!");
1619 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(I)) {
1620 assert(isa<UndefValue>(SI->getCondition()) && "Switch should fold");
1622 assert(0 && "Didn't fold away reference to block!");
1625 // Make this an uncond branch to the first successor.
1626 TerminatorInst *TI = I->getParent()->getTerminator();
1627 new BranchInst(TI->getSuccessor(0), TI);
1629 // Remove entries in successor phi nodes to remove edges.
1630 for (unsigned i = 1, e = TI->getNumSuccessors(); i != e; ++i)
1631 TI->getSuccessor(i)->removePredecessor(TI->getParent());
1633 // Remove the old terminator.
1634 TI->eraseFromParent();
1638 // Finally, delete the basic block.
1639 F->getBasicBlockList().erase(DeadBB);
1643 // If we inferred constant or undef return values for a function, we replaced
1644 // all call uses with the inferred value. This means we don't need to bother
1645 // actually returning anything from the function. Replace all return
1646 // instructions with return undef.
1647 const hash_map<Function*, LatticeVal> &RV =Solver.getTrackedFunctionRetVals();
1648 for (hash_map<Function*, LatticeVal>::const_iterator I = RV.begin(),
1649 E = RV.end(); I != E; ++I)
1650 if (!I->second.isOverdefined() &&
1651 I->first->getReturnType() != Type::VoidTy) {
1652 Function *F = I->first;
1653 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
1654 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator()))
1655 if (!isa<UndefValue>(RI->getOperand(0)))
1656 RI->setOperand(0, UndefValue::get(F->getReturnType()));
1659 // If we infered constant or undef values for globals variables, we can delete
1660 // the global and any stores that remain to it.
1661 const hash_map<GlobalVariable*, LatticeVal> &TG = Solver.getTrackedGlobals();
1662 for (hash_map<GlobalVariable*, LatticeVal>::const_iterator I = TG.begin(),
1663 E = TG.end(); I != E; ++I) {
1664 GlobalVariable *GV = I->first;
1665 assert(!I->second.isOverdefined() &&
1666 "Overdefined values should have been taken out of the map!");
1667 DOUT << "Found that GV '" << GV->getName()<< "' is constant!\n";
1668 while (!GV->use_empty()) {
1669 StoreInst *SI = cast<StoreInst>(GV->use_back());
1670 SI->eraseFromParent();
1672 M.getGlobalList().erase(GV);