1 //===- SCCP.cpp - Sparse Conditional Constant Propagation -----------------===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by the LLVM research group and is distributed under
6 // the University of Illinois Open Source License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements sparse conditional constant propagation and merging:
12 // Specifically, this:
13 // * Assumes values are constant unless proven otherwise
14 // * Assumes BasicBlocks are dead unless proven otherwise
15 // * Proves values to be constant, and replaces them with constants
16 // * Proves conditional branches to be unconditional
19 // * This pass has a habit of making definitions be dead. It is a good idea
20 // to to run a DCE pass sometime after running this pass.
22 //===----------------------------------------------------------------------===//
24 #define DEBUG_TYPE "sccp"
25 #include "llvm/Transforms/Scalar.h"
26 #include "llvm/Transforms/IPO.h"
27 #include "llvm/Constants.h"
28 #include "llvm/DerivedTypes.h"
29 #include "llvm/Instructions.h"
30 #include "llvm/Pass.h"
31 #include "llvm/Support/InstVisitor.h"
32 #include "llvm/Transforms/Utils/Local.h"
33 #include "llvm/Support/CallSite.h"
34 #include "llvm/Support/Debug.h"
35 #include "llvm/ADT/hash_map"
36 #include "llvm/ADT/Statistic.h"
37 #include "llvm/ADT/STLExtras.h"
42 // LatticeVal class - This class represents the different lattice values that an
43 // instruction may occupy. It is a simple class with value semantics.
49 undefined, // This instruction has no known value
50 constant, // This instruction has a constant value
51 overdefined // This instruction has an unknown value
52 } LatticeValue; // The current lattice position
53 Constant *ConstantVal; // If Constant value, the current value
55 inline LatticeVal() : LatticeValue(undefined), ConstantVal(0) {}
57 // markOverdefined - Return true if this is a new status to be in...
58 inline bool markOverdefined() {
59 if (LatticeValue != overdefined) {
60 LatticeValue = overdefined;
66 // markConstant - Return true if this is a new status for us...
67 inline bool markConstant(Constant *V) {
68 if (LatticeValue != constant) {
69 LatticeValue = constant;
73 assert(ConstantVal == V && "Marking constant with different value");
78 inline bool isUndefined() const { return LatticeValue == undefined; }
79 inline bool isConstant() const { return LatticeValue == constant; }
80 inline bool isOverdefined() const { return LatticeValue == overdefined; }
82 inline Constant *getConstant() const {
83 assert(isConstant() && "Cannot get the constant of a non-constant!");
88 } // end anonymous namespace
91 //===----------------------------------------------------------------------===//
93 /// SCCPSolver - This class is a general purpose solver for Sparse Conditional
94 /// Constant Propagation.
96 class SCCPSolver : public InstVisitor<SCCPSolver> {
97 std::set<BasicBlock*> BBExecutable;// The basic blocks that are executable
98 hash_map<Value*, LatticeVal> ValueState; // The state each value is in...
100 /// GlobalValue - If we are tracking any values for the contents of a global
101 /// variable, we keep a mapping from the constant accessor to the element of
102 /// the global, to the currently known value. If the value becomes
103 /// overdefined, it's entry is simply removed from this map.
104 hash_map<GlobalVariable*, LatticeVal> TrackedGlobals;
106 /// TrackedFunctionRetVals - If we are tracking arguments into and the return
107 /// value out of a function, it will have an entry in this map, indicating
108 /// what the known return value for the function is.
109 hash_map<Function*, LatticeVal> TrackedFunctionRetVals;
111 // The reason for two worklists is that overdefined is the lowest state
112 // on the lattice, and moving things to overdefined as fast as possible
113 // makes SCCP converge much faster.
114 // By having a separate worklist, we accomplish this because everything
115 // possibly overdefined will become overdefined at the soonest possible
117 std::vector<Value*> OverdefinedInstWorkList;
118 std::vector<Value*> InstWorkList;
121 std::vector<BasicBlock*> BBWorkList; // The BasicBlock work list
123 /// UsersOfOverdefinedPHIs - Keep track of any users of PHI nodes that are not
124 /// overdefined, despite the fact that the PHI node is overdefined.
125 std::multimap<PHINode*, Instruction*> UsersOfOverdefinedPHIs;
127 /// KnownFeasibleEdges - Entries in this set are edges which have already had
128 /// PHI nodes retriggered.
129 typedef std::pair<BasicBlock*,BasicBlock*> Edge;
130 std::set<Edge> KnownFeasibleEdges;
133 /// MarkBlockExecutable - This method can be used by clients to mark all of
134 /// the blocks that are known to be intrinsically live in the processed unit.
135 void MarkBlockExecutable(BasicBlock *BB) {
136 DEBUG(std::cerr << "Marking Block Executable: " << BB->getName() << "\n");
137 BBExecutable.insert(BB); // Basic block is executable!
138 BBWorkList.push_back(BB); // Add the block to the work list!
141 /// TrackValueOfGlobalVariable - Clients can use this method to
142 /// inform the SCCPSolver that it should track loads and stores to the
143 /// specified global variable if it can. This is only legal to call if
144 /// performing Interprocedural SCCP.
145 void TrackValueOfGlobalVariable(GlobalVariable *GV) {
146 const Type *ElTy = GV->getType()->getElementType();
147 if (ElTy->isFirstClassType()) {
148 LatticeVal &IV = TrackedGlobals[GV];
149 if (!isa<UndefValue>(GV->getInitializer()))
150 IV.markConstant(GV->getInitializer());
154 /// AddTrackedFunction - If the SCCP solver is supposed to track calls into
155 /// and out of the specified function (which cannot have its address taken),
156 /// this method must be called.
157 void AddTrackedFunction(Function *F) {
158 assert(F->hasInternalLinkage() && "Can only track internal functions!");
159 // Add an entry, F -> undef.
160 TrackedFunctionRetVals[F];
163 /// Solve - Solve for constants and executable blocks.
167 /// ResolveBranchesIn - While solving the dataflow for a function, we assume
168 /// that branches on undef values cannot reach any of their successors.
169 /// However, this is not a safe assumption. After we solve dataflow, this
170 /// method should be use to handle this. If this returns true, the solver
172 bool ResolveBranchesIn(Function &F);
174 /// getExecutableBlocks - Once we have solved for constants, return the set of
175 /// blocks that is known to be executable.
176 std::set<BasicBlock*> &getExecutableBlocks() {
180 /// getValueMapping - Once we have solved for constants, return the mapping of
181 /// LLVM values to LatticeVals.
182 hash_map<Value*, LatticeVal> &getValueMapping() {
186 /// getTrackedFunctionRetVals - Get the inferred return value map.
188 const hash_map<Function*, LatticeVal> &getTrackedFunctionRetVals() {
189 return TrackedFunctionRetVals;
192 /// getTrackedGlobals - Get and return the set of inferred initializers for
193 /// global variables.
194 const hash_map<GlobalVariable*, LatticeVal> &getTrackedGlobals() {
195 return TrackedGlobals;
200 // markConstant - Make a value be marked as "constant". If the value
201 // is not already a constant, add it to the instruction work list so that
202 // the users of the instruction are updated later.
204 inline void markConstant(LatticeVal &IV, Value *V, Constant *C) {
205 if (IV.markConstant(C)) {
206 DEBUG(std::cerr << "markConstant: " << *C << ": " << *V);
207 InstWorkList.push_back(V);
210 inline void markConstant(Value *V, Constant *C) {
211 markConstant(ValueState[V], V, C);
214 // markOverdefined - Make a value be marked as "overdefined". If the
215 // value is not already overdefined, add it to the overdefined instruction
216 // work list so that the users of the instruction are updated later.
218 inline void markOverdefined(LatticeVal &IV, Value *V) {
219 if (IV.markOverdefined()) {
220 DEBUG(std::cerr << "markOverdefined: ";
221 if (Function *F = dyn_cast<Function>(V))
222 std::cerr << "Function '" << F->getName() << "'\n";
225 // Only instructions go on the work list
226 OverdefinedInstWorkList.push_back(V);
229 inline void markOverdefined(Value *V) {
230 markOverdefined(ValueState[V], V);
233 inline void mergeInValue(LatticeVal &IV, Value *V, LatticeVal &MergeWithV) {
234 if (IV.isOverdefined() || MergeWithV.isUndefined())
236 if (MergeWithV.isOverdefined())
237 markOverdefined(IV, V);
238 else if (IV.isUndefined())
239 markConstant(IV, V, MergeWithV.getConstant());
240 else if (IV.getConstant() != MergeWithV.getConstant())
241 markOverdefined(IV, V);
244 // getValueState - Return the LatticeVal object that corresponds to the value.
245 // This function is necessary because not all values should start out in the
246 // underdefined state... Argument's should be overdefined, and
247 // constants should be marked as constants. If a value is not known to be an
248 // Instruction object, then use this accessor to get its value from the map.
250 inline LatticeVal &getValueState(Value *V) {
251 hash_map<Value*, LatticeVal>::iterator I = ValueState.find(V);
252 if (I != ValueState.end()) return I->second; // Common case, in the map
254 if (Constant *CPV = dyn_cast<Constant>(V)) {
255 if (isa<UndefValue>(V)) {
256 // Nothing to do, remain undefined.
258 ValueState[CPV].markConstant(CPV); // Constants are constant
261 // All others are underdefined by default...
262 return ValueState[V];
265 // markEdgeExecutable - Mark a basic block as executable, adding it to the BB
266 // work list if it is not already executable...
268 void markEdgeExecutable(BasicBlock *Source, BasicBlock *Dest) {
269 if (!KnownFeasibleEdges.insert(Edge(Source, Dest)).second)
270 return; // This edge is already known to be executable!
272 if (BBExecutable.count(Dest)) {
273 DEBUG(std::cerr << "Marking Edge Executable: " << Source->getName()
274 << " -> " << Dest->getName() << "\n");
276 // The destination is already executable, but we just made an edge
277 // feasible that wasn't before. Revisit the PHI nodes in the block
278 // because they have potentially new operands.
279 for (BasicBlock::iterator I = Dest->begin(); isa<PHINode>(I); ++I)
280 visitPHINode(*cast<PHINode>(I));
283 MarkBlockExecutable(Dest);
287 // getFeasibleSuccessors - Return a vector of booleans to indicate which
288 // successors are reachable from a given terminator instruction.
290 void getFeasibleSuccessors(TerminatorInst &TI, std::vector<bool> &Succs);
292 // isEdgeFeasible - Return true if the control flow edge from the 'From' basic
293 // block to the 'To' basic block is currently feasible...
295 bool isEdgeFeasible(BasicBlock *From, BasicBlock *To);
297 // OperandChangedState - This method is invoked on all of the users of an
298 // instruction that was just changed state somehow.... Based on this
299 // information, we need to update the specified user of this instruction.
301 void OperandChangedState(User *U) {
302 // Only instructions use other variable values!
303 Instruction &I = cast<Instruction>(*U);
304 if (BBExecutable.count(I.getParent())) // Inst is executable?
309 friend class InstVisitor<SCCPSolver>;
311 // visit implementations - Something changed in this instruction... Either an
312 // operand made a transition, or the instruction is newly executable. Change
313 // the value type of I to reflect these changes if appropriate.
315 void visitPHINode(PHINode &I);
318 void visitReturnInst(ReturnInst &I);
319 void visitTerminatorInst(TerminatorInst &TI);
321 void visitCastInst(CastInst &I);
322 void visitSelectInst(SelectInst &I);
323 void visitBinaryOperator(Instruction &I);
324 void visitShiftInst(ShiftInst &I) { visitBinaryOperator(I); }
325 void visitExtractElementInst(ExtractElementInst &I);
327 // Instructions that cannot be folded away...
328 void visitStoreInst (Instruction &I);
329 void visitLoadInst (LoadInst &I);
330 void visitGetElementPtrInst(GetElementPtrInst &I);
331 void visitCallInst (CallInst &I) { visitCallSite(CallSite::get(&I)); }
332 void visitInvokeInst (InvokeInst &II) {
333 visitCallSite(CallSite::get(&II));
334 visitTerminatorInst(II);
336 void visitCallSite (CallSite CS);
337 void visitUnwindInst (TerminatorInst &I) { /*returns void*/ }
338 void visitUnreachableInst(TerminatorInst &I) { /*returns void*/ }
339 void visitAllocationInst(Instruction &I) { markOverdefined(&I); }
340 void visitVANextInst (Instruction &I) { markOverdefined(&I); }
341 void visitVAArgInst (Instruction &I) { markOverdefined(&I); }
342 void visitFreeInst (Instruction &I) { /*returns void*/ }
344 void visitInstruction(Instruction &I) {
345 // If a new instruction is added to LLVM that we don't handle...
346 std::cerr << "SCCP: Don't know how to handle: " << I;
347 markOverdefined(&I); // Just in case
351 // getFeasibleSuccessors - Return a vector of booleans to indicate which
352 // successors are reachable from a given terminator instruction.
354 void SCCPSolver::getFeasibleSuccessors(TerminatorInst &TI,
355 std::vector<bool> &Succs) {
356 Succs.resize(TI.getNumSuccessors());
357 if (BranchInst *BI = dyn_cast<BranchInst>(&TI)) {
358 if (BI->isUnconditional()) {
361 LatticeVal &BCValue = getValueState(BI->getCondition());
362 if (BCValue.isOverdefined() ||
363 (BCValue.isConstant() && !isa<ConstantBool>(BCValue.getConstant()))) {
364 // Overdefined condition variables, and branches on unfoldable constant
365 // conditions, mean the branch could go either way.
366 Succs[0] = Succs[1] = true;
367 } else if (BCValue.isConstant()) {
368 // Constant condition variables mean the branch can only go a single way
369 Succs[BCValue.getConstant() == ConstantBool::False] = true;
372 } else if (InvokeInst *II = dyn_cast<InvokeInst>(&TI)) {
373 // Invoke instructions successors are always executable.
374 Succs[0] = Succs[1] = true;
375 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(&TI)) {
376 LatticeVal &SCValue = getValueState(SI->getCondition());
377 if (SCValue.isOverdefined() || // Overdefined condition?
378 (SCValue.isConstant() && !isa<ConstantInt>(SCValue.getConstant()))) {
379 // All destinations are executable!
380 Succs.assign(TI.getNumSuccessors(), true);
381 } else if (SCValue.isConstant()) {
382 Constant *CPV = SCValue.getConstant();
383 // Make sure to skip the "default value" which isn't a value
384 for (unsigned i = 1, E = SI->getNumSuccessors(); i != E; ++i) {
385 if (SI->getSuccessorValue(i) == CPV) {// Found the right branch...
391 // Constant value not equal to any of the branches... must execute
392 // default branch then...
396 std::cerr << "SCCP: Don't know how to handle: " << TI;
397 Succs.assign(TI.getNumSuccessors(), true);
402 // isEdgeFeasible - Return true if the control flow edge from the 'From' basic
403 // block to the 'To' basic block is currently feasible...
405 bool SCCPSolver::isEdgeFeasible(BasicBlock *From, BasicBlock *To) {
406 assert(BBExecutable.count(To) && "Dest should always be alive!");
408 // Make sure the source basic block is executable!!
409 if (!BBExecutable.count(From)) return false;
411 // Check to make sure this edge itself is actually feasible now...
412 TerminatorInst *TI = From->getTerminator();
413 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
414 if (BI->isUnconditional())
417 LatticeVal &BCValue = getValueState(BI->getCondition());
418 if (BCValue.isOverdefined()) {
419 // Overdefined condition variables mean the branch could go either way.
421 } else if (BCValue.isConstant()) {
422 // Not branching on an evaluatable constant?
423 if (!isa<ConstantBool>(BCValue.getConstant())) return true;
425 // Constant condition variables mean the branch can only go a single way
426 return BI->getSuccessor(BCValue.getConstant() ==
427 ConstantBool::False) == To;
431 } else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) {
432 // Invoke instructions successors are always executable.
434 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
435 LatticeVal &SCValue = getValueState(SI->getCondition());
436 if (SCValue.isOverdefined()) { // Overdefined condition?
437 // All destinations are executable!
439 } else if (SCValue.isConstant()) {
440 Constant *CPV = SCValue.getConstant();
441 if (!isa<ConstantInt>(CPV))
442 return true; // not a foldable constant?
444 // Make sure to skip the "default value" which isn't a value
445 for (unsigned i = 1, E = SI->getNumSuccessors(); i != E; ++i)
446 if (SI->getSuccessorValue(i) == CPV) // Found the taken branch...
447 return SI->getSuccessor(i) == To;
449 // Constant value not equal to any of the branches... must execute
450 // default branch then...
451 return SI->getDefaultDest() == To;
455 std::cerr << "Unknown terminator instruction: " << *TI;
460 // visit Implementations - Something changed in this instruction... Either an
461 // operand made a transition, or the instruction is newly executable. Change
462 // the value type of I to reflect these changes if appropriate. This method
463 // makes sure to do the following actions:
465 // 1. If a phi node merges two constants in, and has conflicting value coming
466 // from different branches, or if the PHI node merges in an overdefined
467 // value, then the PHI node becomes overdefined.
468 // 2. If a phi node merges only constants in, and they all agree on value, the
469 // PHI node becomes a constant value equal to that.
470 // 3. If V <- x (op) y && isConstant(x) && isConstant(y) V = Constant
471 // 4. If V <- x (op) y && (isOverdefined(x) || isOverdefined(y)) V = Overdefined
472 // 5. If V <- MEM or V <- CALL or V <- (unknown) then V = Overdefined
473 // 6. If a conditional branch has a value that is constant, make the selected
474 // destination executable
475 // 7. If a conditional branch has a value that is overdefined, make all
476 // successors executable.
478 void SCCPSolver::visitPHINode(PHINode &PN) {
479 LatticeVal &PNIV = getValueState(&PN);
480 if (PNIV.isOverdefined()) {
481 // There may be instructions using this PHI node that are not overdefined
482 // themselves. If so, make sure that they know that the PHI node operand
484 std::multimap<PHINode*, Instruction*>::iterator I, E;
485 tie(I, E) = UsersOfOverdefinedPHIs.equal_range(&PN);
487 std::vector<Instruction*> Users;
488 Users.reserve(std::distance(I, E));
489 for (; I != E; ++I) Users.push_back(I->second);
490 while (!Users.empty()) {
495 return; // Quick exit
498 // Super-extra-high-degree PHI nodes are unlikely to ever be marked constant,
499 // and slow us down a lot. Just mark them overdefined.
500 if (PN.getNumIncomingValues() > 64) {
501 markOverdefined(PNIV, &PN);
505 // Look at all of the executable operands of the PHI node. If any of them
506 // are overdefined, the PHI becomes overdefined as well. If they are all
507 // constant, and they agree with each other, the PHI becomes the identical
508 // constant. If they are constant and don't agree, the PHI is overdefined.
509 // If there are no executable operands, the PHI remains undefined.
511 Constant *OperandVal = 0;
512 for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) {
513 LatticeVal &IV = getValueState(PN.getIncomingValue(i));
514 if (IV.isUndefined()) continue; // Doesn't influence PHI node.
516 if (isEdgeFeasible(PN.getIncomingBlock(i), PN.getParent())) {
517 if (IV.isOverdefined()) { // PHI node becomes overdefined!
518 markOverdefined(PNIV, &PN);
522 if (OperandVal == 0) { // Grab the first value...
523 OperandVal = IV.getConstant();
524 } else { // Another value is being merged in!
525 // There is already a reachable operand. If we conflict with it,
526 // then the PHI node becomes overdefined. If we agree with it, we
529 // Check to see if there are two different constants merging...
530 if (IV.getConstant() != OperandVal) {
531 // Yes there is. This means the PHI node is not constant.
532 // You must be overdefined poor PHI.
534 markOverdefined(PNIV, &PN); // The PHI node now becomes overdefined
535 return; // I'm done analyzing you
541 // If we exited the loop, this means that the PHI node only has constant
542 // arguments that agree with each other(and OperandVal is the constant) or
543 // OperandVal is null because there are no defined incoming arguments. If
544 // this is the case, the PHI remains undefined.
547 markConstant(PNIV, &PN, OperandVal); // Acquire operand value
550 void SCCPSolver::visitReturnInst(ReturnInst &I) {
551 if (I.getNumOperands() == 0) return; // Ret void
553 // If we are tracking the return value of this function, merge it in.
554 Function *F = I.getParent()->getParent();
555 if (F->hasInternalLinkage() && !TrackedFunctionRetVals.empty()) {
556 hash_map<Function*, LatticeVal>::iterator TFRVI =
557 TrackedFunctionRetVals.find(F);
558 if (TFRVI != TrackedFunctionRetVals.end() &&
559 !TFRVI->second.isOverdefined()) {
560 LatticeVal &IV = getValueState(I.getOperand(0));
561 mergeInValue(TFRVI->second, F, IV);
567 void SCCPSolver::visitTerminatorInst(TerminatorInst &TI) {
568 std::vector<bool> SuccFeasible;
569 getFeasibleSuccessors(TI, SuccFeasible);
571 BasicBlock *BB = TI.getParent();
573 // Mark all feasible successors executable...
574 for (unsigned i = 0, e = SuccFeasible.size(); i != e; ++i)
576 markEdgeExecutable(BB, TI.getSuccessor(i));
579 void SCCPSolver::visitCastInst(CastInst &I) {
580 Value *V = I.getOperand(0);
581 LatticeVal &VState = getValueState(V);
582 if (VState.isOverdefined()) // Inherit overdefinedness of operand
584 else if (VState.isConstant()) // Propagate constant value
585 markConstant(&I, ConstantExpr::getCast(VState.getConstant(), I.getType()));
588 void SCCPSolver::visitSelectInst(SelectInst &I) {
589 LatticeVal &CondValue = getValueState(I.getCondition());
590 if (CondValue.isOverdefined())
592 else if (CondValue.isConstant()) {
593 if (CondValue.getConstant() == ConstantBool::True) {
594 LatticeVal &Val = getValueState(I.getTrueValue());
595 if (Val.isOverdefined())
597 else if (Val.isConstant())
598 markConstant(&I, Val.getConstant());
599 } else if (CondValue.getConstant() == ConstantBool::False) {
600 LatticeVal &Val = getValueState(I.getFalseValue());
601 if (Val.isOverdefined())
603 else if (Val.isConstant())
604 markConstant(&I, Val.getConstant());
610 // Handle BinaryOperators and Shift Instructions...
611 void SCCPSolver::visitBinaryOperator(Instruction &I) {
612 LatticeVal &IV = ValueState[&I];
613 if (IV.isOverdefined()) return;
615 LatticeVal &V1State = getValueState(I.getOperand(0));
616 LatticeVal &V2State = getValueState(I.getOperand(1));
618 if (V1State.isOverdefined() || V2State.isOverdefined()) {
619 // If this is an AND or OR with 0 or -1, it doesn't matter that the other
620 // operand is overdefined.
621 if (I.getOpcode() == Instruction::And || I.getOpcode() == Instruction::Or) {
622 LatticeVal *NonOverdefVal = 0;
623 if (!V1State.isOverdefined()) {
624 NonOverdefVal = &V1State;
625 } else if (!V2State.isOverdefined()) {
626 NonOverdefVal = &V2State;
630 if (NonOverdefVal->isUndefined()) {
631 // Could annihilate value.
632 if (I.getOpcode() == Instruction::And)
633 markConstant(IV, &I, Constant::getNullValue(I.getType()));
635 markConstant(IV, &I, ConstantInt::getAllOnesValue(I.getType()));
638 if (I.getOpcode() == Instruction::And) {
639 if (NonOverdefVal->getConstant()->isNullValue()) {
640 markConstant(IV, &I, NonOverdefVal->getConstant());
641 return; // X or 0 = -1
644 if (ConstantIntegral *CI =
645 dyn_cast<ConstantIntegral>(NonOverdefVal->getConstant()))
646 if (CI->isAllOnesValue()) {
647 markConstant(IV, &I, NonOverdefVal->getConstant());
648 return; // X or -1 = -1
656 // If both operands are PHI nodes, it is possible that this instruction has
657 // a constant value, despite the fact that the PHI node doesn't. Check for
658 // this condition now.
659 if (PHINode *PN1 = dyn_cast<PHINode>(I.getOperand(0)))
660 if (PHINode *PN2 = dyn_cast<PHINode>(I.getOperand(1)))
661 if (PN1->getParent() == PN2->getParent()) {
662 // Since the two PHI nodes are in the same basic block, they must have
663 // entries for the same predecessors. Walk the predecessor list, and
664 // if all of the incoming values are constants, and the result of
665 // evaluating this expression with all incoming value pairs is the
666 // same, then this expression is a constant even though the PHI node
667 // is not a constant!
669 for (unsigned i = 0, e = PN1->getNumIncomingValues(); i != e; ++i) {
670 LatticeVal &In1 = getValueState(PN1->getIncomingValue(i));
671 BasicBlock *InBlock = PN1->getIncomingBlock(i);
673 getValueState(PN2->getIncomingValueForBlock(InBlock));
675 if (In1.isOverdefined() || In2.isOverdefined()) {
676 Result.markOverdefined();
677 break; // Cannot fold this operation over the PHI nodes!
678 } else if (In1.isConstant() && In2.isConstant()) {
679 Constant *V = ConstantExpr::get(I.getOpcode(), In1.getConstant(),
681 if (Result.isUndefined())
682 Result.markConstant(V);
683 else if (Result.isConstant() && Result.getConstant() != V) {
684 Result.markOverdefined();
690 // If we found a constant value here, then we know the instruction is
691 // constant despite the fact that the PHI nodes are overdefined.
692 if (Result.isConstant()) {
693 markConstant(IV, &I, Result.getConstant());
694 // Remember that this instruction is virtually using the PHI node
696 UsersOfOverdefinedPHIs.insert(std::make_pair(PN1, &I));
697 UsersOfOverdefinedPHIs.insert(std::make_pair(PN2, &I));
699 } else if (Result.isUndefined()) {
703 // Okay, this really is overdefined now. Since we might have
704 // speculatively thought that this was not overdefined before, and
705 // added ourselves to the UsersOfOverdefinedPHIs list for the PHIs,
706 // make sure to clean out any entries that we put there, for
708 std::multimap<PHINode*, Instruction*>::iterator It, E;
709 tie(It, E) = UsersOfOverdefinedPHIs.equal_range(PN1);
711 if (It->second == &I) {
712 UsersOfOverdefinedPHIs.erase(It++);
716 tie(It, E) = UsersOfOverdefinedPHIs.equal_range(PN2);
718 if (It->second == &I) {
719 UsersOfOverdefinedPHIs.erase(It++);
725 markOverdefined(IV, &I);
726 } else if (V1State.isConstant() && V2State.isConstant()) {
727 markConstant(IV, &I, ConstantExpr::get(I.getOpcode(), V1State.getConstant(),
728 V2State.getConstant()));
732 void SCCPSolver::visitExtractElementInst(ExtractElementInst &I) {
733 LatticeVal &ValState = getValueState(I.getOperand(0));
734 LatticeVal &IdxState = getValueState(I.getOperand(1));
736 if (ValState.isOverdefined() || IdxState.isOverdefined())
738 else if(ValState.isConstant() && IdxState.isConstant())
739 markConstant(&I, ConstantExpr::getExtractElement(ValState.getConstant(),
740 IdxState.getConstant()));
743 // Handle getelementptr instructions... if all operands are constants then we
744 // can turn this into a getelementptr ConstantExpr.
746 void SCCPSolver::visitGetElementPtrInst(GetElementPtrInst &I) {
747 LatticeVal &IV = ValueState[&I];
748 if (IV.isOverdefined()) return;
750 std::vector<Constant*> Operands;
751 Operands.reserve(I.getNumOperands());
753 for (unsigned i = 0, e = I.getNumOperands(); i != e; ++i) {
754 LatticeVal &State = getValueState(I.getOperand(i));
755 if (State.isUndefined())
756 return; // Operands are not resolved yet...
757 else if (State.isOverdefined()) {
758 markOverdefined(IV, &I);
761 assert(State.isConstant() && "Unknown state!");
762 Operands.push_back(State.getConstant());
765 Constant *Ptr = Operands[0];
766 Operands.erase(Operands.begin()); // Erase the pointer from idx list...
768 markConstant(IV, &I, ConstantExpr::getGetElementPtr(Ptr, Operands));
771 void SCCPSolver::visitStoreInst(Instruction &SI) {
772 if (TrackedGlobals.empty() || !isa<GlobalVariable>(SI.getOperand(1)))
774 GlobalVariable *GV = cast<GlobalVariable>(SI.getOperand(1));
775 hash_map<GlobalVariable*, LatticeVal>::iterator I = TrackedGlobals.find(GV);
776 if (I == TrackedGlobals.end() || I->second.isOverdefined()) return;
778 // Get the value we are storing into the global.
779 LatticeVal &PtrVal = getValueState(SI.getOperand(0));
781 mergeInValue(I->second, GV, PtrVal);
782 if (I->second.isOverdefined())
783 TrackedGlobals.erase(I); // No need to keep tracking this!
787 // Handle load instructions. If the operand is a constant pointer to a constant
788 // global, we can replace the load with the loaded constant value!
789 void SCCPSolver::visitLoadInst(LoadInst &I) {
790 LatticeVal &IV = ValueState[&I];
791 if (IV.isOverdefined()) return;
793 LatticeVal &PtrVal = getValueState(I.getOperand(0));
794 if (PtrVal.isUndefined()) return; // The pointer is not resolved yet!
795 if (PtrVal.isConstant() && !I.isVolatile()) {
796 Value *Ptr = PtrVal.getConstant();
797 if (isa<ConstantPointerNull>(Ptr)) {
799 markConstant(IV, &I, Constant::getNullValue(I.getType()));
803 // Transform load (constant global) into the value loaded.
804 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Ptr)) {
805 if (GV->isConstant()) {
806 if (!GV->isExternal()) {
807 markConstant(IV, &I, GV->getInitializer());
810 } else if (!TrackedGlobals.empty()) {
811 // If we are tracking this global, merge in the known value for it.
812 hash_map<GlobalVariable*, LatticeVal>::iterator It =
813 TrackedGlobals.find(GV);
814 if (It != TrackedGlobals.end()) {
815 mergeInValue(IV, &I, It->second);
821 // Transform load (constantexpr_GEP global, 0, ...) into the value loaded.
822 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr))
823 if (CE->getOpcode() == Instruction::GetElementPtr)
824 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(CE->getOperand(0)))
825 if (GV->isConstant() && !GV->isExternal())
827 ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE)) {
828 markConstant(IV, &I, V);
833 // Otherwise we cannot say for certain what value this load will produce.
835 markOverdefined(IV, &I);
838 void SCCPSolver::visitCallSite(CallSite CS) {
839 Function *F = CS.getCalledFunction();
841 // If we are tracking this function, we must make sure to bind arguments as
843 hash_map<Function*, LatticeVal>::iterator TFRVI =TrackedFunctionRetVals.end();
844 if (F && F->hasInternalLinkage())
845 TFRVI = TrackedFunctionRetVals.find(F);
847 if (TFRVI != TrackedFunctionRetVals.end()) {
848 // If this is the first call to the function hit, mark its entry block
850 if (!BBExecutable.count(F->begin()))
851 MarkBlockExecutable(F->begin());
853 CallSite::arg_iterator CAI = CS.arg_begin();
854 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
855 AI != E; ++AI, ++CAI) {
856 LatticeVal &IV = ValueState[AI];
857 if (!IV.isOverdefined())
858 mergeInValue(IV, AI, getValueState(*CAI));
861 Instruction *I = CS.getInstruction();
862 if (I->getType() == Type::VoidTy) return;
864 LatticeVal &IV = ValueState[I];
865 if (IV.isOverdefined()) return;
867 // Propagate the return value of the function to the value of the instruction.
868 if (TFRVI != TrackedFunctionRetVals.end()) {
869 mergeInValue(IV, I, TFRVI->second);
873 if (F == 0 || !F->isExternal() || !canConstantFoldCallTo(F)) {
874 markOverdefined(IV, I);
878 std::vector<Constant*> Operands;
879 Operands.reserve(I->getNumOperands()-1);
881 for (CallSite::arg_iterator AI = CS.arg_begin(), E = CS.arg_end();
883 LatticeVal &State = getValueState(*AI);
884 if (State.isUndefined())
885 return; // Operands are not resolved yet...
886 else if (State.isOverdefined()) {
887 markOverdefined(IV, I);
890 assert(State.isConstant() && "Unknown state!");
891 Operands.push_back(State.getConstant());
894 if (Constant *C = ConstantFoldCall(F, Operands))
895 markConstant(IV, I, C);
897 markOverdefined(IV, I);
901 void SCCPSolver::Solve() {
902 // Process the work lists until they are empty!
903 while (!BBWorkList.empty() || !InstWorkList.empty() ||
904 !OverdefinedInstWorkList.empty()) {
905 // Process the instruction work list...
906 while (!OverdefinedInstWorkList.empty()) {
907 Value *I = OverdefinedInstWorkList.back();
908 OverdefinedInstWorkList.pop_back();
910 DEBUG(std::cerr << "\nPopped off OI-WL: " << *I);
912 // "I" got into the work list because it either made the transition from
913 // bottom to constant
915 // Anything on this worklist that is overdefined need not be visited
916 // since all of its users will have already been marked as overdefined
917 // Update all of the users of this instruction's value...
919 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
921 OperandChangedState(*UI);
923 // Process the instruction work list...
924 while (!InstWorkList.empty()) {
925 Value *I = InstWorkList.back();
926 InstWorkList.pop_back();
928 DEBUG(std::cerr << "\nPopped off I-WL: " << *I);
930 // "I" got into the work list because it either made the transition from
931 // bottom to constant
933 // Anything on this worklist that is overdefined need not be visited
934 // since all of its users will have already been marked as overdefined.
935 // Update all of the users of this instruction's value...
937 if (!getValueState(I).isOverdefined())
938 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
940 OperandChangedState(*UI);
943 // Process the basic block work list...
944 while (!BBWorkList.empty()) {
945 BasicBlock *BB = BBWorkList.back();
946 BBWorkList.pop_back();
948 DEBUG(std::cerr << "\nPopped off BBWL: " << *BB);
950 // Notify all instructions in this basic block that they are newly
957 /// ResolveBranchesIn - While solving the dataflow for a function, we assume
958 /// that branches on undef values cannot reach any of their successors.
959 /// However, this is not a safe assumption. After we solve dataflow, this
960 /// method should be use to handle this. If this returns true, the solver
962 bool SCCPSolver::ResolveBranchesIn(Function &F) {
963 bool BranchesResolved = false;
964 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
965 if (BBExecutable.count(BB)) {
966 TerminatorInst *TI = BB->getTerminator();
967 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
968 if (BI->isConditional()) {
969 LatticeVal &BCValue = getValueState(BI->getCondition());
970 if (BCValue.isUndefined()) {
971 BI->setCondition(ConstantBool::True);
972 BranchesResolved = true;
976 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
977 LatticeVal &SCValue = getValueState(SI->getCondition());
978 if (SCValue.isUndefined()) {
979 const Type *CondTy = SI->getCondition()->getType();
980 SI->setCondition(Constant::getNullValue(CondTy));
981 BranchesResolved = true;
987 return BranchesResolved;
992 Statistic<> NumInstRemoved("sccp", "Number of instructions removed");
993 Statistic<> NumDeadBlocks ("sccp", "Number of basic blocks unreachable");
995 //===--------------------------------------------------------------------===//
997 /// SCCP Class - This class uses the SCCPSolver to implement a per-function
998 /// Sparse Conditional COnstant Propagator.
1000 struct SCCP : public FunctionPass {
1001 // runOnFunction - Run the Sparse Conditional Constant Propagation
1002 // algorithm, and return true if the function was modified.
1004 bool runOnFunction(Function &F);
1006 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
1007 AU.setPreservesCFG();
1011 RegisterOpt<SCCP> X("sccp", "Sparse Conditional Constant Propagation");
1012 } // end anonymous namespace
1015 // createSCCPPass - This is the public interface to this file...
1016 FunctionPass *llvm::createSCCPPass() {
1021 // runOnFunction() - Run the Sparse Conditional Constant Propagation algorithm,
1022 // and return true if the function was modified.
1024 bool SCCP::runOnFunction(Function &F) {
1025 DEBUG(std::cerr << "SCCP on function '" << F.getName() << "'\n");
1028 // Mark the first block of the function as being executable.
1029 Solver.MarkBlockExecutable(F.begin());
1031 // Mark all arguments to the function as being overdefined.
1032 hash_map<Value*, LatticeVal> &Values = Solver.getValueMapping();
1033 for (Function::arg_iterator AI = F.arg_begin(), E = F.arg_end(); AI != E; ++AI)
1034 Values[AI].markOverdefined();
1036 // Solve for constants.
1037 bool ResolvedBranches = true;
1038 while (ResolvedBranches) {
1040 DEBUG(std::cerr << "RESOLVING UNDEF BRANCHES\n");
1041 ResolvedBranches = Solver.ResolveBranchesIn(F);
1044 bool MadeChanges = false;
1046 // If we decided that there are basic blocks that are dead in this function,
1047 // delete their contents now. Note that we cannot actually delete the blocks,
1048 // as we cannot modify the CFG of the function.
1050 std::set<BasicBlock*> &ExecutableBBs = Solver.getExecutableBlocks();
1051 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
1052 if (!ExecutableBBs.count(BB)) {
1053 DEBUG(std::cerr << " BasicBlock Dead:" << *BB);
1056 // Delete the instructions backwards, as it has a reduced likelihood of
1057 // having to update as many def-use and use-def chains.
1058 std::vector<Instruction*> Insts;
1059 for (BasicBlock::iterator I = BB->begin(), E = BB->getTerminator();
1062 while (!Insts.empty()) {
1063 Instruction *I = Insts.back();
1065 if (!I->use_empty())
1066 I->replaceAllUsesWith(UndefValue::get(I->getType()));
1067 BB->getInstList().erase(I);
1072 // Iterate over all of the instructions in a function, replacing them with
1073 // constants if we have found them to be of constant values.
1075 for (BasicBlock::iterator BI = BB->begin(), E = BB->end(); BI != E; ) {
1076 Instruction *Inst = BI++;
1077 if (Inst->getType() != Type::VoidTy) {
1078 LatticeVal &IV = Values[Inst];
1079 if (IV.isConstant() || IV.isUndefined() &&
1080 !isa<TerminatorInst>(Inst)) {
1081 Constant *Const = IV.isConstant()
1082 ? IV.getConstant() : UndefValue::get(Inst->getType());
1083 DEBUG(std::cerr << " Constant: " << *Const << " = " << *Inst);
1085 // Replaces all of the uses of a variable with uses of the constant.
1086 Inst->replaceAllUsesWith(Const);
1088 // Delete the instruction.
1089 BB->getInstList().erase(Inst);
1091 // Hey, we just changed something!
1103 Statistic<> IPNumInstRemoved("ipsccp", "Number of instructions removed");
1104 Statistic<> IPNumDeadBlocks ("ipsccp", "Number of basic blocks unreachable");
1105 Statistic<> IPNumArgsElimed ("ipsccp",
1106 "Number of arguments constant propagated");
1107 Statistic<> IPNumGlobalConst("ipsccp",
1108 "Number of globals found to be constant");
1110 //===--------------------------------------------------------------------===//
1112 /// IPSCCP Class - This class implements interprocedural Sparse Conditional
1113 /// Constant Propagation.
1115 struct IPSCCP : public ModulePass {
1116 bool runOnModule(Module &M);
1120 Y("ipsccp", "Interprocedural Sparse Conditional Constant Propagation");
1121 } // end anonymous namespace
1123 // createIPSCCPPass - This is the public interface to this file...
1124 ModulePass *llvm::createIPSCCPPass() {
1125 return new IPSCCP();
1129 static bool AddressIsTaken(GlobalValue *GV) {
1130 // Delete any dead constantexpr klingons.
1131 GV->removeDeadConstantUsers();
1133 for (Value::use_iterator UI = GV->use_begin(), E = GV->use_end();
1135 if (StoreInst *SI = dyn_cast<StoreInst>(*UI)) {
1136 if (SI->getOperand(0) == GV || SI->isVolatile())
1137 return true; // Storing addr of GV.
1138 } else if (isa<InvokeInst>(*UI) || isa<CallInst>(*UI)) {
1139 // Make sure we are calling the function, not passing the address.
1140 CallSite CS = CallSite::get(cast<Instruction>(*UI));
1141 for (CallSite::arg_iterator AI = CS.arg_begin(),
1142 E = CS.arg_end(); AI != E; ++AI)
1145 } else if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) {
1146 if (LI->isVolatile())
1154 bool IPSCCP::runOnModule(Module &M) {
1157 // Loop over all functions, marking arguments to those with their addresses
1158 // taken or that are external as overdefined.
1160 hash_map<Value*, LatticeVal> &Values = Solver.getValueMapping();
1161 for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F)
1162 if (!F->hasInternalLinkage() || AddressIsTaken(F)) {
1163 if (!F->isExternal())
1164 Solver.MarkBlockExecutable(F->begin());
1165 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
1167 Values[AI].markOverdefined();
1169 Solver.AddTrackedFunction(F);
1172 // Loop over global variables. We inform the solver about any internal global
1173 // variables that do not have their 'addresses taken'. If they don't have
1174 // their addresses taken, we can propagate constants through them.
1175 for (Module::global_iterator G = M.global_begin(), E = M.global_end();
1177 if (!G->isConstant() && G->hasInternalLinkage() && !AddressIsTaken(G))
1178 Solver.TrackValueOfGlobalVariable(G);
1180 // Solve for constants.
1181 bool ResolvedBranches = true;
1182 while (ResolvedBranches) {
1185 DEBUG(std::cerr << "RESOLVING UNDEF BRANCHES\n");
1186 ResolvedBranches = false;
1187 for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F)
1188 ResolvedBranches |= Solver.ResolveBranchesIn(*F);
1191 bool MadeChanges = false;
1193 // Iterate over all of the instructions in the module, replacing them with
1194 // constants if we have found them to be of constant values.
1196 std::set<BasicBlock*> &ExecutableBBs = Solver.getExecutableBlocks();
1197 for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) {
1198 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
1200 if (!AI->use_empty()) {
1201 LatticeVal &IV = Values[AI];
1202 if (IV.isConstant() || IV.isUndefined()) {
1203 Constant *CST = IV.isConstant() ?
1204 IV.getConstant() : UndefValue::get(AI->getType());
1205 DEBUG(std::cerr << "*** Arg " << *AI << " = " << *CST <<"\n");
1207 // Replaces all of the uses of a variable with uses of the
1209 AI->replaceAllUsesWith(CST);
1214 std::vector<BasicBlock*> BlocksToErase;
1215 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
1216 if (!ExecutableBBs.count(BB)) {
1217 DEBUG(std::cerr << " BasicBlock Dead:" << *BB);
1220 // Delete the instructions backwards, as it has a reduced likelihood of
1221 // having to update as many def-use and use-def chains.
1222 std::vector<Instruction*> Insts;
1223 TerminatorInst *TI = BB->getTerminator();
1224 for (BasicBlock::iterator I = BB->begin(), E = TI; I != E; ++I)
1227 while (!Insts.empty()) {
1228 Instruction *I = Insts.back();
1230 if (!I->use_empty())
1231 I->replaceAllUsesWith(UndefValue::get(I->getType()));
1232 BB->getInstList().erase(I);
1237 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) {
1238 BasicBlock *Succ = TI->getSuccessor(i);
1239 if (Succ->begin() != Succ->end() && isa<PHINode>(Succ->begin()))
1240 TI->getSuccessor(i)->removePredecessor(BB);
1242 if (!TI->use_empty())
1243 TI->replaceAllUsesWith(UndefValue::get(TI->getType()));
1244 BB->getInstList().erase(TI);
1246 if (&*BB != &F->front())
1247 BlocksToErase.push_back(BB);
1249 new UnreachableInst(BB);
1252 for (BasicBlock::iterator BI = BB->begin(), E = BB->end(); BI != E; ) {
1253 Instruction *Inst = BI++;
1254 if (Inst->getType() != Type::VoidTy) {
1255 LatticeVal &IV = Values[Inst];
1256 if (IV.isConstant() || IV.isUndefined() &&
1257 !isa<TerminatorInst>(Inst)) {
1258 Constant *Const = IV.isConstant()
1259 ? IV.getConstant() : UndefValue::get(Inst->getType());
1260 DEBUG(std::cerr << " Constant: " << *Const << " = " << *Inst);
1262 // Replaces all of the uses of a variable with uses of the
1264 Inst->replaceAllUsesWith(Const);
1266 // Delete the instruction.
1267 if (!isa<TerminatorInst>(Inst) && !isa<CallInst>(Inst))
1268 BB->getInstList().erase(Inst);
1270 // Hey, we just changed something!
1278 // Now that all instructions in the function are constant folded, erase dead
1279 // blocks, because we can now use ConstantFoldTerminator to get rid of
1281 for (unsigned i = 0, e = BlocksToErase.size(); i != e; ++i) {
1282 // If there are any PHI nodes in this successor, drop entries for BB now.
1283 BasicBlock *DeadBB = BlocksToErase[i];
1284 while (!DeadBB->use_empty()) {
1285 Instruction *I = cast<Instruction>(DeadBB->use_back());
1286 bool Folded = ConstantFoldTerminator(I->getParent());
1287 assert(Folded && "Didn't fold away reference to block!");
1290 // Finally, delete the basic block.
1291 F->getBasicBlockList().erase(DeadBB);
1295 // If we inferred constant or undef return values for a function, we replaced
1296 // all call uses with the inferred value. This means we don't need to bother
1297 // actually returning anything from the function. Replace all return
1298 // instructions with return undef.
1299 const hash_map<Function*, LatticeVal> &RV =Solver.getTrackedFunctionRetVals();
1300 for (hash_map<Function*, LatticeVal>::const_iterator I = RV.begin(),
1301 E = RV.end(); I != E; ++I)
1302 if (!I->second.isOverdefined() &&
1303 I->first->getReturnType() != Type::VoidTy) {
1304 Function *F = I->first;
1305 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
1306 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator()))
1307 if (!isa<UndefValue>(RI->getOperand(0)))
1308 RI->setOperand(0, UndefValue::get(F->getReturnType()));
1311 // If we infered constant or undef values for globals variables, we can delete
1312 // the global and any stores that remain to it.
1313 const hash_map<GlobalVariable*, LatticeVal> &TG = Solver.getTrackedGlobals();
1314 for (hash_map<GlobalVariable*, LatticeVal>::const_iterator I = TG.begin(),
1315 E = TG.end(); I != E; ++I) {
1316 GlobalVariable *GV = I->first;
1317 assert(!I->second.isOverdefined() &&
1318 "Overdefined values should have been taken out of the map!");
1319 DEBUG(std::cerr << "Found that GV '" << GV->getName()<< "' is constant!\n");
1320 while (!GV->use_empty()) {
1321 StoreInst *SI = cast<StoreInst>(GV->use_back());
1322 SI->eraseFromParent();
1324 M.getGlobalList().erase(GV);