1 //===- SCCP.cpp - Sparse Conditional Constant Propagation -----------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements sparse conditional constant propagation and merging:
12 // Specifically, this:
13 // * Assumes values are constant unless proven otherwise
14 // * Assumes BasicBlocks are dead unless proven otherwise
15 // * Proves values to be constant, and replaces them with constants
16 // * Proves conditional branches to be unconditional
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/Analysis/ConstantFolding.h"
32 #include "llvm/Transforms/Utils/Local.h"
33 #include "llvm/Support/CallSite.h"
34 #include "llvm/Support/Compiler.h"
35 #include "llvm/Support/Debug.h"
36 #include "llvm/Support/InstVisitor.h"
37 #include "llvm/ADT/DenseMap.h"
38 #include "llvm/ADT/SmallSet.h"
39 #include "llvm/ADT/SmallVector.h"
40 #include "llvm/ADT/Statistic.h"
41 #include "llvm/ADT/STLExtras.h"
45 STATISTIC(NumInstRemoved, "Number of instructions removed");
46 STATISTIC(NumDeadBlocks , "Number of basic blocks unreachable");
48 STATISTIC(IPNumInstRemoved, "Number of instructions removed by IPSCCP");
49 STATISTIC(IPNumDeadBlocks , "Number of basic blocks unreachable by IPSCCP");
50 STATISTIC(IPNumArgsElimed ,"Number of arguments constant propagated by IPSCCP");
51 STATISTIC(IPNumGlobalConst, "Number of globals found to be constant by IPSCCP");
54 /// LatticeVal class - This class represents the different lattice values that
55 /// an LLVM value may occupy. It is a simple class with value semantics.
57 class VISIBILITY_HIDDEN LatticeVal {
59 /// undefined - This LLVM Value has no known value yet.
62 /// constant - This LLVM Value has a specific constant value.
65 /// forcedconstant - This LLVM Value was thought to be undef until
66 /// ResolvedUndefsIn. This is treated just like 'constant', but if merged
67 /// with another (different) constant, it goes to overdefined, instead of
71 /// overdefined - This instruction is not known to be constant, and we know
74 } LatticeValue; // The current lattice position
76 Constant *ConstantVal; // If Constant value, the current value
78 inline LatticeVal() : LatticeValue(undefined), ConstantVal(0) {}
80 // markOverdefined - Return true if this is a new status to be in...
81 inline bool markOverdefined() {
82 if (LatticeValue != overdefined) {
83 LatticeValue = overdefined;
89 // markConstant - Return true if this is a new status for us.
90 inline bool markConstant(Constant *V) {
91 if (LatticeValue != constant) {
92 if (LatticeValue == undefined) {
93 LatticeValue = constant;
94 assert(V && "Marking constant with NULL");
97 assert(LatticeValue == forcedconstant &&
98 "Cannot move from overdefined to constant!");
99 // Stay at forcedconstant if the constant is the same.
100 if (V == ConstantVal) return false;
102 // Otherwise, we go to overdefined. Assumptions made based on the
103 // forced value are possibly wrong. Assuming this is another constant
104 // could expose a contradiction.
105 LatticeValue = overdefined;
109 assert(ConstantVal == V && "Marking constant with different value");
114 inline void markForcedConstant(Constant *V) {
115 assert(LatticeValue == undefined && "Can't force a defined value!");
116 LatticeValue = forcedconstant;
120 inline bool isUndefined() const { return LatticeValue == undefined; }
121 inline bool isConstant() const {
122 return LatticeValue == constant || LatticeValue == forcedconstant;
124 inline bool isOverdefined() const { return LatticeValue == overdefined; }
126 inline Constant *getConstant() const {
127 assert(isConstant() && "Cannot get the constant of a non-constant!");
132 /// LatticeValIndex - LatticeVal and associated Index. This is used
133 /// to track individual operand Lattice values for multi value ret instructions.
134 class VISIBILITY_HIDDEN LatticeValIndexed {
136 LatticeValIndexed(unsigned I = 0) { Index = I; }
137 LatticeVal &getLatticeVal() { return LV; }
138 unsigned getIndex() const { return Index; }
140 void setLatticeVal(LatticeVal &L) { LV = L; }
141 void setIndex(unsigned I) { Index = I; }
147 //===----------------------------------------------------------------------===//
149 /// SCCPSolver - This class is a general purpose solver for Sparse Conditional
150 /// Constant Propagation.
152 class SCCPSolver : public InstVisitor<SCCPSolver> {
153 SmallSet<BasicBlock*, 16> BBExecutable;// The basic blocks that are executable
154 std::map<Value*, LatticeVal> ValueState; // The state each value is in.
156 /// GlobalValue - If we are tracking any values for the contents of a global
157 /// variable, we keep a mapping from the constant accessor to the element of
158 /// the global, to the currently known value. If the value becomes
159 /// overdefined, it's entry is simply removed from this map.
160 DenseMap<GlobalVariable*, LatticeVal> TrackedGlobals;
162 /// TrackedRetVals - If we are tracking arguments into and the return
163 /// value out of a function, it will have an entry in this map, indicating
164 /// what the known return value for the function is.
165 DenseMap<Function*, LatticeVal> TrackedRetVals;
167 /// TrackedMultipleRetVals - Same as TrackedRetVals, but used for functions
168 /// that return multiple values.
169 std::multimap<Function*, LatticeValIndexed> TrackedMultipleRetVals;
171 // The reason for two worklists is that overdefined is the lowest state
172 // on the lattice, and moving things to overdefined as fast as possible
173 // makes SCCP converge much faster.
174 // By having a separate worklist, we accomplish this because everything
175 // possibly overdefined will become overdefined at the soonest possible
177 std::vector<Value*> OverdefinedInstWorkList;
178 std::vector<Value*> InstWorkList;
181 std::vector<BasicBlock*> BBWorkList; // The BasicBlock work list
183 /// UsersOfOverdefinedPHIs - Keep track of any users of PHI nodes that are not
184 /// overdefined, despite the fact that the PHI node is overdefined.
185 std::multimap<PHINode*, Instruction*> UsersOfOverdefinedPHIs;
187 /// KnownFeasibleEdges - Entries in this set are edges which have already had
188 /// PHI nodes retriggered.
189 typedef std::pair<BasicBlock*,BasicBlock*> Edge;
190 std::set<Edge> KnownFeasibleEdges;
193 /// MarkBlockExecutable - This method can be used by clients to mark all of
194 /// the blocks that are known to be intrinsically live in the processed unit.
195 void MarkBlockExecutable(BasicBlock *BB) {
196 DOUT << "Marking Block Executable: " << BB->getName() << "\n";
197 BBExecutable.insert(BB); // Basic block is executable!
198 BBWorkList.push_back(BB); // Add the block to the work list!
201 /// TrackValueOfGlobalVariable - Clients can use this method to
202 /// inform the SCCPSolver that it should track loads and stores to the
203 /// specified global variable if it can. This is only legal to call if
204 /// performing Interprocedural SCCP.
205 void TrackValueOfGlobalVariable(GlobalVariable *GV) {
206 const Type *ElTy = GV->getType()->getElementType();
207 if (ElTy->isFirstClassType()) {
208 LatticeVal &IV = TrackedGlobals[GV];
209 if (!isa<UndefValue>(GV->getInitializer()))
210 IV.markConstant(GV->getInitializer());
214 /// AddTrackedFunction - If the SCCP solver is supposed to track calls into
215 /// and out of the specified function (which cannot have its address taken),
216 /// this method must be called.
217 void AddTrackedFunction(Function *F) {
218 assert(F->hasInternalLinkage() && "Can only track internal functions!");
219 // Add an entry, F -> undef.
220 if (const StructType *STy = dyn_cast<StructType>(F->getReturnType())) {
221 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
222 TrackedMultipleRetVals.insert(std::pair<Function *, LatticeValIndexed>
223 (F, LatticeValIndexed(i)));
229 /// Solve - Solve for constants and executable blocks.
233 /// ResolvedUndefsIn - While solving the dataflow for a function, we assume
234 /// that branches on undef values cannot reach any of their successors.
235 /// However, this is not a safe assumption. After we solve dataflow, this
236 /// method should be use to handle this. If this returns true, the solver
238 bool ResolvedUndefsIn(Function &F);
240 /// getExecutableBlocks - Once we have solved for constants, return the set of
241 /// blocks that is known to be executable.
242 SmallSet<BasicBlock*, 16> &getExecutableBlocks() {
246 /// getValueMapping - Once we have solved for constants, return the mapping of
247 /// LLVM values to LatticeVals.
248 std::map<Value*, LatticeVal> &getValueMapping() {
252 /// getTrackedRetVals - Get the inferred return value map.
254 const DenseMap<Function*, LatticeVal> &getTrackedRetVals() {
255 return TrackedRetVals;
258 /// getTrackedGlobals - Get and return the set of inferred initializers for
259 /// global variables.
260 const DenseMap<GlobalVariable*, LatticeVal> &getTrackedGlobals() {
261 return TrackedGlobals;
264 inline void markOverdefined(Value *V) {
265 markOverdefined(ValueState[V], V);
269 // markConstant - Make a value be marked as "constant". If the value
270 // is not already a constant, add it to the instruction work list so that
271 // the users of the instruction are updated later.
273 inline void markConstant(LatticeVal &IV, Value *V, Constant *C) {
274 if (IV.markConstant(C)) {
275 DOUT << "markConstant: " << *C << ": " << *V;
276 InstWorkList.push_back(V);
280 inline void markForcedConstant(LatticeVal &IV, Value *V, Constant *C) {
281 IV.markForcedConstant(C);
282 DOUT << "markForcedConstant: " << *C << ": " << *V;
283 InstWorkList.push_back(V);
286 inline void markConstant(Value *V, Constant *C) {
287 markConstant(ValueState[V], V, C);
290 // markOverdefined - Make a value be marked as "overdefined". If the
291 // value is not already overdefined, add it to the overdefined instruction
292 // work list so that the users of the instruction are updated later.
294 inline void markOverdefined(LatticeVal &IV, Value *V) {
295 if (IV.markOverdefined()) {
296 DEBUG(DOUT << "markOverdefined: ";
297 if (Function *F = dyn_cast<Function>(V))
298 DOUT << "Function '" << F->getName() << "'\n";
301 // Only instructions go on the work list
302 OverdefinedInstWorkList.push_back(V);
306 inline void mergeInValue(LatticeVal &IV, Value *V, LatticeVal &MergeWithV) {
307 if (IV.isOverdefined() || MergeWithV.isUndefined())
309 if (MergeWithV.isOverdefined())
310 markOverdefined(IV, V);
311 else if (IV.isUndefined())
312 markConstant(IV, V, MergeWithV.getConstant());
313 else if (IV.getConstant() != MergeWithV.getConstant())
314 markOverdefined(IV, V);
317 inline void mergeInValue(Value *V, LatticeVal &MergeWithV) {
318 return mergeInValue(ValueState[V], V, MergeWithV);
322 // getValueState - Return the LatticeVal object that corresponds to the value.
323 // This function is necessary because not all values should start out in the
324 // underdefined state... Argument's should be overdefined, and
325 // constants should be marked as constants. If a value is not known to be an
326 // Instruction object, then use this accessor to get its value from the map.
328 inline LatticeVal &getValueState(Value *V) {
329 std::map<Value*, LatticeVal>::iterator I = ValueState.find(V);
330 if (I != ValueState.end()) return I->second; // Common case, in the map
332 if (Constant *C = dyn_cast<Constant>(V)) {
333 if (isa<UndefValue>(V)) {
334 // Nothing to do, remain undefined.
336 LatticeVal &LV = ValueState[C];
337 LV.markConstant(C); // Constants are constant
341 // All others are underdefined by default...
342 return ValueState[V];
345 // markEdgeExecutable - Mark a basic block as executable, adding it to the BB
346 // work list if it is not already executable...
348 void markEdgeExecutable(BasicBlock *Source, BasicBlock *Dest) {
349 if (!KnownFeasibleEdges.insert(Edge(Source, Dest)).second)
350 return; // This edge is already known to be executable!
352 if (BBExecutable.count(Dest)) {
353 DOUT << "Marking Edge Executable: " << Source->getName()
354 << " -> " << Dest->getName() << "\n";
356 // The destination is already executable, but we just made an edge
357 // feasible that wasn't before. Revisit the PHI nodes in the block
358 // because they have potentially new operands.
359 for (BasicBlock::iterator I = Dest->begin(); isa<PHINode>(I); ++I)
360 visitPHINode(*cast<PHINode>(I));
363 MarkBlockExecutable(Dest);
367 // getFeasibleSuccessors - Return a vector of booleans to indicate which
368 // successors are reachable from a given terminator instruction.
370 void getFeasibleSuccessors(TerminatorInst &TI, SmallVector<bool, 16> &Succs);
372 // isEdgeFeasible - Return true if the control flow edge from the 'From' basic
373 // block to the 'To' basic block is currently feasible...
375 bool isEdgeFeasible(BasicBlock *From, BasicBlock *To);
377 // OperandChangedState - This method is invoked on all of the users of an
378 // instruction that was just changed state somehow.... Based on this
379 // information, we need to update the specified user of this instruction.
381 void OperandChangedState(User *U) {
382 // Only instructions use other variable values!
383 Instruction &I = cast<Instruction>(*U);
384 if (BBExecutable.count(I.getParent())) // Inst is executable?
389 friend class InstVisitor<SCCPSolver>;
391 // visit implementations - Something changed in this instruction... Either an
392 // operand made a transition, or the instruction is newly executable. Change
393 // the value type of I to reflect these changes if appropriate.
395 void visitPHINode(PHINode &I);
398 void visitReturnInst(ReturnInst &I);
399 void visitTerminatorInst(TerminatorInst &TI);
401 void visitCastInst(CastInst &I);
402 void visitGetResultInst(GetResultInst &GRI);
403 void visitSelectInst(SelectInst &I);
404 void visitBinaryOperator(Instruction &I);
405 void visitCmpInst(CmpInst &I);
406 void visitExtractElementInst(ExtractElementInst &I);
407 void visitInsertElementInst(InsertElementInst &I);
408 void visitShuffleVectorInst(ShuffleVectorInst &I);
410 // Instructions that cannot be folded away...
411 void visitStoreInst (Instruction &I);
412 void visitLoadInst (LoadInst &I);
413 void visitGetElementPtrInst(GetElementPtrInst &I);
414 void visitCallInst (CallInst &I) { visitCallSite(CallSite::get(&I)); }
415 void visitInvokeInst (InvokeInst &II) {
416 visitCallSite(CallSite::get(&II));
417 visitTerminatorInst(II);
419 void visitCallSite (CallSite CS);
420 void visitUnwindInst (TerminatorInst &I) { /*returns void*/ }
421 void visitUnreachableInst(TerminatorInst &I) { /*returns void*/ }
422 void visitAllocationInst(Instruction &I) { markOverdefined(&I); }
423 void visitVANextInst (Instruction &I) { markOverdefined(&I); }
424 void visitVAArgInst (Instruction &I) { markOverdefined(&I); }
425 void visitFreeInst (Instruction &I) { /*returns void*/ }
427 void visitInstruction(Instruction &I) {
428 // If a new instruction is added to LLVM that we don't handle...
429 cerr << "SCCP: Don't know how to handle: " << I;
430 markOverdefined(&I); // Just in case
434 } // end anonymous namespace
437 // getFeasibleSuccessors - Return a vector of booleans to indicate which
438 // successors are reachable from a given terminator instruction.
440 void SCCPSolver::getFeasibleSuccessors(TerminatorInst &TI,
441 SmallVector<bool, 16> &Succs) {
442 Succs.resize(TI.getNumSuccessors());
443 if (BranchInst *BI = dyn_cast<BranchInst>(&TI)) {
444 if (BI->isUnconditional()) {
447 LatticeVal &BCValue = getValueState(BI->getCondition());
448 if (BCValue.isOverdefined() ||
449 (BCValue.isConstant() && !isa<ConstantInt>(BCValue.getConstant()))) {
450 // Overdefined condition variables, and branches on unfoldable constant
451 // conditions, mean the branch could go either way.
452 Succs[0] = Succs[1] = true;
453 } else if (BCValue.isConstant()) {
454 // Constant condition variables mean the branch can only go a single way
455 Succs[BCValue.getConstant() == ConstantInt::getFalse()] = true;
458 } else if (isa<InvokeInst>(&TI)) {
459 // Invoke instructions successors are always executable.
460 Succs[0] = Succs[1] = true;
461 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(&TI)) {
462 LatticeVal &SCValue = getValueState(SI->getCondition());
463 if (SCValue.isOverdefined() || // Overdefined condition?
464 (SCValue.isConstant() && !isa<ConstantInt>(SCValue.getConstant()))) {
465 // All destinations are executable!
466 Succs.assign(TI.getNumSuccessors(), true);
467 } else if (SCValue.isConstant()) {
468 Constant *CPV = SCValue.getConstant();
469 // Make sure to skip the "default value" which isn't a value
470 for (unsigned i = 1, E = SI->getNumSuccessors(); i != E; ++i) {
471 if (SI->getSuccessorValue(i) == CPV) {// Found the right branch...
477 // Constant value not equal to any of the branches... must execute
478 // default branch then...
482 assert(0 && "SCCP: Don't know how to handle this terminator!");
487 // isEdgeFeasible - Return true if the control flow edge from the 'From' basic
488 // block to the 'To' basic block is currently feasible...
490 bool SCCPSolver::isEdgeFeasible(BasicBlock *From, BasicBlock *To) {
491 assert(BBExecutable.count(To) && "Dest should always be alive!");
493 // Make sure the source basic block is executable!!
494 if (!BBExecutable.count(From)) return false;
496 // Check to make sure this edge itself is actually feasible now...
497 TerminatorInst *TI = From->getTerminator();
498 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
499 if (BI->isUnconditional())
502 LatticeVal &BCValue = getValueState(BI->getCondition());
503 if (BCValue.isOverdefined()) {
504 // Overdefined condition variables mean the branch could go either way.
506 } else if (BCValue.isConstant()) {
507 // Not branching on an evaluatable constant?
508 if (!isa<ConstantInt>(BCValue.getConstant())) return true;
510 // Constant condition variables mean the branch can only go a single way
511 return BI->getSuccessor(BCValue.getConstant() ==
512 ConstantInt::getFalse()) == To;
516 } else if (isa<InvokeInst>(TI)) {
517 // Invoke instructions successors are always executable.
519 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
520 LatticeVal &SCValue = getValueState(SI->getCondition());
521 if (SCValue.isOverdefined()) { // Overdefined condition?
522 // All destinations are executable!
524 } else if (SCValue.isConstant()) {
525 Constant *CPV = SCValue.getConstant();
526 if (!isa<ConstantInt>(CPV))
527 return true; // not a foldable constant?
529 // Make sure to skip the "default value" which isn't a value
530 for (unsigned i = 1, E = SI->getNumSuccessors(); i != E; ++i)
531 if (SI->getSuccessorValue(i) == CPV) // Found the taken branch...
532 return SI->getSuccessor(i) == To;
534 // Constant value not equal to any of the branches... must execute
535 // default branch then...
536 return SI->getDefaultDest() == To;
540 cerr << "Unknown terminator instruction: " << *TI;
545 // visit Implementations - Something changed in this instruction... Either an
546 // operand made a transition, or the instruction is newly executable. Change
547 // the value type of I to reflect these changes if appropriate. This method
548 // makes sure to do the following actions:
550 // 1. If a phi node merges two constants in, and has conflicting value coming
551 // from different branches, or if the PHI node merges in an overdefined
552 // value, then the PHI node becomes overdefined.
553 // 2. If a phi node merges only constants in, and they all agree on value, the
554 // PHI node becomes a constant value equal to that.
555 // 3. If V <- x (op) y && isConstant(x) && isConstant(y) V = Constant
556 // 4. If V <- x (op) y && (isOverdefined(x) || isOverdefined(y)) V = Overdefined
557 // 5. If V <- MEM or V <- CALL or V <- (unknown) then V = Overdefined
558 // 6. If a conditional branch has a value that is constant, make the selected
559 // destination executable
560 // 7. If a conditional branch has a value that is overdefined, make all
561 // successors executable.
563 void SCCPSolver::visitPHINode(PHINode &PN) {
564 LatticeVal &PNIV = getValueState(&PN);
565 if (PNIV.isOverdefined()) {
566 // There may be instructions using this PHI node that are not overdefined
567 // themselves. If so, make sure that they know that the PHI node operand
569 std::multimap<PHINode*, Instruction*>::iterator I, E;
570 tie(I, E) = UsersOfOverdefinedPHIs.equal_range(&PN);
572 SmallVector<Instruction*, 16> Users;
573 for (; I != E; ++I) Users.push_back(I->second);
574 while (!Users.empty()) {
579 return; // Quick exit
582 // Super-extra-high-degree PHI nodes are unlikely to ever be marked constant,
583 // and slow us down a lot. Just mark them overdefined.
584 if (PN.getNumIncomingValues() > 64) {
585 markOverdefined(PNIV, &PN);
589 // Look at all of the executable operands of the PHI node. If any of them
590 // are overdefined, the PHI becomes overdefined as well. If they are all
591 // constant, and they agree with each other, the PHI becomes the identical
592 // constant. If they are constant and don't agree, the PHI is overdefined.
593 // If there are no executable operands, the PHI remains undefined.
595 Constant *OperandVal = 0;
596 for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) {
597 LatticeVal &IV = getValueState(PN.getIncomingValue(i));
598 if (IV.isUndefined()) continue; // Doesn't influence PHI node.
600 if (isEdgeFeasible(PN.getIncomingBlock(i), PN.getParent())) {
601 if (IV.isOverdefined()) { // PHI node becomes overdefined!
602 markOverdefined(PNIV, &PN);
606 if (OperandVal == 0) { // Grab the first value...
607 OperandVal = IV.getConstant();
608 } else { // Another value is being merged in!
609 // There is already a reachable operand. If we conflict with it,
610 // then the PHI node becomes overdefined. If we agree with it, we
613 // Check to see if there are two different constants merging...
614 if (IV.getConstant() != OperandVal) {
615 // Yes there is. This means the PHI node is not constant.
616 // You must be overdefined poor PHI.
618 markOverdefined(PNIV, &PN); // The PHI node now becomes overdefined
619 return; // I'm done analyzing you
625 // If we exited the loop, this means that the PHI node only has constant
626 // arguments that agree with each other(and OperandVal is the constant) or
627 // OperandVal is null because there are no defined incoming arguments. If
628 // this is the case, the PHI remains undefined.
631 markConstant(PNIV, &PN, OperandVal); // Acquire operand value
634 void SCCPSolver::visitReturnInst(ReturnInst &I) {
635 if (I.getNumOperands() == 0) return; // Ret void
637 Function *F = I.getParent()->getParent();
638 // If we are tracking the return value of this function, merge it in.
639 if (!F->hasInternalLinkage())
642 if (!TrackedRetVals.empty()) {
643 DenseMap<Function*, LatticeVal>::iterator TFRVI =
644 TrackedRetVals.find(F);
645 if (TFRVI != TrackedRetVals.end() &&
646 !TFRVI->second.isOverdefined()) {
647 LatticeVal &IV = getValueState(I.getOperand(0));
648 mergeInValue(TFRVI->second, F, IV);
653 // Handle function that returns multiple values.
654 std::multimap<Function*, LatticeValIndexed>::iterator It, E;
655 tie(It, E) = TrackedMultipleRetVals.equal_range(F);
657 for (; It != E; ++It) {
658 LatticeValIndexed &LV = It->second;
659 unsigned Idx = LV.getIndex();
660 Value *V = I.getOperand(Idx);
661 mergeInValue(LV.getLatticeVal(), V, getValueState(V));
666 void SCCPSolver::visitTerminatorInst(TerminatorInst &TI) {
667 SmallVector<bool, 16> SuccFeasible;
668 getFeasibleSuccessors(TI, SuccFeasible);
670 BasicBlock *BB = TI.getParent();
672 // Mark all feasible successors executable...
673 for (unsigned i = 0, e = SuccFeasible.size(); i != e; ++i)
675 markEdgeExecutable(BB, TI.getSuccessor(i));
678 void SCCPSolver::visitCastInst(CastInst &I) {
679 Value *V = I.getOperand(0);
680 LatticeVal &VState = getValueState(V);
681 if (VState.isOverdefined()) // Inherit overdefinedness of operand
683 else if (VState.isConstant()) // Propagate constant value
684 markConstant(&I, ConstantExpr::getCast(I.getOpcode(),
685 VState.getConstant(), I.getType()));
688 void SCCPSolver::visitGetResultInst(GetResultInst &GRI) {
689 unsigned Idx = GRI.getIndex();
690 Value *Aggr = GRI.getOperand(0);
692 if (CallInst *CI = dyn_cast<CallInst>(Aggr))
693 F = CI->getCalledFunction();
694 else if (InvokeInst *II = dyn_cast<InvokeInst>(Aggr))
695 F = II->getCalledFunction();
697 assert (F && "Invalid GetResultInst operands!");
699 std::multimap<Function*, LatticeValIndexed>::iterator It, E;
700 tie(It, E) = TrackedMultipleRetVals.equal_range(F);
704 for (; It != E; ++It) {
705 LatticeValIndexed &LIV = It->second;
706 if (LIV.getIndex() == Idx) {
707 mergeInValue(&GRI, LIV.getLatticeVal());
712 void SCCPSolver::visitSelectInst(SelectInst &I) {
713 LatticeVal &CondValue = getValueState(I.getCondition());
714 if (CondValue.isUndefined())
716 if (CondValue.isConstant()) {
717 if (ConstantInt *CondCB = dyn_cast<ConstantInt>(CondValue.getConstant())){
718 mergeInValue(&I, getValueState(CondCB->getZExtValue() ? I.getTrueValue()
719 : I.getFalseValue()));
724 // Otherwise, the condition is overdefined or a constant we can't evaluate.
725 // See if we can produce something better than overdefined based on the T/F
727 LatticeVal &TVal = getValueState(I.getTrueValue());
728 LatticeVal &FVal = getValueState(I.getFalseValue());
730 // select ?, C, C -> C.
731 if (TVal.isConstant() && FVal.isConstant() &&
732 TVal.getConstant() == FVal.getConstant()) {
733 markConstant(&I, FVal.getConstant());
737 if (TVal.isUndefined()) { // select ?, undef, X -> X.
738 mergeInValue(&I, FVal);
739 } else if (FVal.isUndefined()) { // select ?, X, undef -> X.
740 mergeInValue(&I, TVal);
746 // Handle BinaryOperators and Shift Instructions...
747 void SCCPSolver::visitBinaryOperator(Instruction &I) {
748 LatticeVal &IV = ValueState[&I];
749 if (IV.isOverdefined()) return;
751 LatticeVal &V1State = getValueState(I.getOperand(0));
752 LatticeVal &V2State = getValueState(I.getOperand(1));
754 if (V1State.isOverdefined() || V2State.isOverdefined()) {
755 // If this is an AND or OR with 0 or -1, it doesn't matter that the other
756 // operand is overdefined.
757 if (I.getOpcode() == Instruction::And || I.getOpcode() == Instruction::Or) {
758 LatticeVal *NonOverdefVal = 0;
759 if (!V1State.isOverdefined()) {
760 NonOverdefVal = &V1State;
761 } else if (!V2State.isOverdefined()) {
762 NonOverdefVal = &V2State;
766 if (NonOverdefVal->isUndefined()) {
767 // Could annihilate value.
768 if (I.getOpcode() == Instruction::And)
769 markConstant(IV, &I, Constant::getNullValue(I.getType()));
770 else if (const VectorType *PT = dyn_cast<VectorType>(I.getType()))
771 markConstant(IV, &I, ConstantVector::getAllOnesValue(PT));
773 markConstant(IV, &I, ConstantInt::getAllOnesValue(I.getType()));
776 if (I.getOpcode() == Instruction::And) {
777 if (NonOverdefVal->getConstant()->isNullValue()) {
778 markConstant(IV, &I, NonOverdefVal->getConstant());
779 return; // X and 0 = 0
782 if (ConstantInt *CI =
783 dyn_cast<ConstantInt>(NonOverdefVal->getConstant()))
784 if (CI->isAllOnesValue()) {
785 markConstant(IV, &I, NonOverdefVal->getConstant());
786 return; // X or -1 = -1
794 // If both operands are PHI nodes, it is possible that this instruction has
795 // a constant value, despite the fact that the PHI node doesn't. Check for
796 // this condition now.
797 if (PHINode *PN1 = dyn_cast<PHINode>(I.getOperand(0)))
798 if (PHINode *PN2 = dyn_cast<PHINode>(I.getOperand(1)))
799 if (PN1->getParent() == PN2->getParent()) {
800 // Since the two PHI nodes are in the same basic block, they must have
801 // entries for the same predecessors. Walk the predecessor list, and
802 // if all of the incoming values are constants, and the result of
803 // evaluating this expression with all incoming value pairs is the
804 // same, then this expression is a constant even though the PHI node
805 // is not a constant!
807 for (unsigned i = 0, e = PN1->getNumIncomingValues(); i != e; ++i) {
808 LatticeVal &In1 = getValueState(PN1->getIncomingValue(i));
809 BasicBlock *InBlock = PN1->getIncomingBlock(i);
811 getValueState(PN2->getIncomingValueForBlock(InBlock));
813 if (In1.isOverdefined() || In2.isOverdefined()) {
814 Result.markOverdefined();
815 break; // Cannot fold this operation over the PHI nodes!
816 } else if (In1.isConstant() && In2.isConstant()) {
817 Constant *V = ConstantExpr::get(I.getOpcode(), In1.getConstant(),
819 if (Result.isUndefined())
820 Result.markConstant(V);
821 else if (Result.isConstant() && Result.getConstant() != V) {
822 Result.markOverdefined();
828 // If we found a constant value here, then we know the instruction is
829 // constant despite the fact that the PHI nodes are overdefined.
830 if (Result.isConstant()) {
831 markConstant(IV, &I, Result.getConstant());
832 // Remember that this instruction is virtually using the PHI node
834 UsersOfOverdefinedPHIs.insert(std::make_pair(PN1, &I));
835 UsersOfOverdefinedPHIs.insert(std::make_pair(PN2, &I));
837 } else if (Result.isUndefined()) {
841 // Okay, this really is overdefined now. Since we might have
842 // speculatively thought that this was not overdefined before, and
843 // added ourselves to the UsersOfOverdefinedPHIs list for the PHIs,
844 // make sure to clean out any entries that we put there, for
846 std::multimap<PHINode*, Instruction*>::iterator It, E;
847 tie(It, E) = UsersOfOverdefinedPHIs.equal_range(PN1);
849 if (It->second == &I) {
850 UsersOfOverdefinedPHIs.erase(It++);
854 tie(It, E) = UsersOfOverdefinedPHIs.equal_range(PN2);
856 if (It->second == &I) {
857 UsersOfOverdefinedPHIs.erase(It++);
863 markOverdefined(IV, &I);
864 } else if (V1State.isConstant() && V2State.isConstant()) {
865 markConstant(IV, &I, ConstantExpr::get(I.getOpcode(), V1State.getConstant(),
866 V2State.getConstant()));
870 // Handle ICmpInst instruction...
871 void SCCPSolver::visitCmpInst(CmpInst &I) {
872 LatticeVal &IV = ValueState[&I];
873 if (IV.isOverdefined()) return;
875 LatticeVal &V1State = getValueState(I.getOperand(0));
876 LatticeVal &V2State = getValueState(I.getOperand(1));
878 if (V1State.isOverdefined() || V2State.isOverdefined()) {
879 // If both operands are PHI nodes, it is possible that this instruction has
880 // a constant value, despite the fact that the PHI node doesn't. Check for
881 // this condition now.
882 if (PHINode *PN1 = dyn_cast<PHINode>(I.getOperand(0)))
883 if (PHINode *PN2 = dyn_cast<PHINode>(I.getOperand(1)))
884 if (PN1->getParent() == PN2->getParent()) {
885 // Since the two PHI nodes are in the same basic block, they must have
886 // entries for the same predecessors. Walk the predecessor list, and
887 // if all of the incoming values are constants, and the result of
888 // evaluating this expression with all incoming value pairs is the
889 // same, then this expression is a constant even though the PHI node
890 // is not a constant!
892 for (unsigned i = 0, e = PN1->getNumIncomingValues(); i != e; ++i) {
893 LatticeVal &In1 = getValueState(PN1->getIncomingValue(i));
894 BasicBlock *InBlock = PN1->getIncomingBlock(i);
896 getValueState(PN2->getIncomingValueForBlock(InBlock));
898 if (In1.isOverdefined() || In2.isOverdefined()) {
899 Result.markOverdefined();
900 break; // Cannot fold this operation over the PHI nodes!
901 } else if (In1.isConstant() && In2.isConstant()) {
902 Constant *V = ConstantExpr::getCompare(I.getPredicate(),
905 if (Result.isUndefined())
906 Result.markConstant(V);
907 else if (Result.isConstant() && Result.getConstant() != V) {
908 Result.markOverdefined();
914 // If we found a constant value here, then we know the instruction is
915 // constant despite the fact that the PHI nodes are overdefined.
916 if (Result.isConstant()) {
917 markConstant(IV, &I, Result.getConstant());
918 // Remember that this instruction is virtually using the PHI node
920 UsersOfOverdefinedPHIs.insert(std::make_pair(PN1, &I));
921 UsersOfOverdefinedPHIs.insert(std::make_pair(PN2, &I));
923 } else if (Result.isUndefined()) {
927 // Okay, this really is overdefined now. Since we might have
928 // speculatively thought that this was not overdefined before, and
929 // added ourselves to the UsersOfOverdefinedPHIs list for the PHIs,
930 // make sure to clean out any entries that we put there, for
932 std::multimap<PHINode*, Instruction*>::iterator It, E;
933 tie(It, E) = UsersOfOverdefinedPHIs.equal_range(PN1);
935 if (It->second == &I) {
936 UsersOfOverdefinedPHIs.erase(It++);
940 tie(It, E) = UsersOfOverdefinedPHIs.equal_range(PN2);
942 if (It->second == &I) {
943 UsersOfOverdefinedPHIs.erase(It++);
949 markOverdefined(IV, &I);
950 } else if (V1State.isConstant() && V2State.isConstant()) {
951 markConstant(IV, &I, ConstantExpr::getCompare(I.getPredicate(),
952 V1State.getConstant(),
953 V2State.getConstant()));
957 void SCCPSolver::visitExtractElementInst(ExtractElementInst &I) {
958 // FIXME : SCCP does not handle vectors properly.
963 LatticeVal &ValState = getValueState(I.getOperand(0));
964 LatticeVal &IdxState = getValueState(I.getOperand(1));
966 if (ValState.isOverdefined() || IdxState.isOverdefined())
968 else if(ValState.isConstant() && IdxState.isConstant())
969 markConstant(&I, ConstantExpr::getExtractElement(ValState.getConstant(),
970 IdxState.getConstant()));
974 void SCCPSolver::visitInsertElementInst(InsertElementInst &I) {
975 // FIXME : SCCP does not handle vectors properly.
979 LatticeVal &ValState = getValueState(I.getOperand(0));
980 LatticeVal &EltState = getValueState(I.getOperand(1));
981 LatticeVal &IdxState = getValueState(I.getOperand(2));
983 if (ValState.isOverdefined() || EltState.isOverdefined() ||
984 IdxState.isOverdefined())
986 else if(ValState.isConstant() && EltState.isConstant() &&
987 IdxState.isConstant())
988 markConstant(&I, ConstantExpr::getInsertElement(ValState.getConstant(),
989 EltState.getConstant(),
990 IdxState.getConstant()));
991 else if (ValState.isUndefined() && EltState.isConstant() &&
992 IdxState.isConstant())
993 markConstant(&I,ConstantExpr::getInsertElement(UndefValue::get(I.getType()),
994 EltState.getConstant(),
995 IdxState.getConstant()));
999 void SCCPSolver::visitShuffleVectorInst(ShuffleVectorInst &I) {
1000 // FIXME : SCCP does not handle vectors properly.
1001 markOverdefined(&I);
1004 LatticeVal &V1State = getValueState(I.getOperand(0));
1005 LatticeVal &V2State = getValueState(I.getOperand(1));
1006 LatticeVal &MaskState = getValueState(I.getOperand(2));
1008 if (MaskState.isUndefined() ||
1009 (V1State.isUndefined() && V2State.isUndefined()))
1010 return; // Undefined output if mask or both inputs undefined.
1012 if (V1State.isOverdefined() || V2State.isOverdefined() ||
1013 MaskState.isOverdefined()) {
1014 markOverdefined(&I);
1016 // A mix of constant/undef inputs.
1017 Constant *V1 = V1State.isConstant() ?
1018 V1State.getConstant() : UndefValue::get(I.getType());
1019 Constant *V2 = V2State.isConstant() ?
1020 V2State.getConstant() : UndefValue::get(I.getType());
1021 Constant *Mask = MaskState.isConstant() ?
1022 MaskState.getConstant() : UndefValue::get(I.getOperand(2)->getType());
1023 markConstant(&I, ConstantExpr::getShuffleVector(V1, V2, Mask));
1028 // Handle getelementptr instructions... if all operands are constants then we
1029 // can turn this into a getelementptr ConstantExpr.
1031 void SCCPSolver::visitGetElementPtrInst(GetElementPtrInst &I) {
1032 LatticeVal &IV = ValueState[&I];
1033 if (IV.isOverdefined()) return;
1035 SmallVector<Constant*, 8> Operands;
1036 Operands.reserve(I.getNumOperands());
1038 for (unsigned i = 0, e = I.getNumOperands(); i != e; ++i) {
1039 LatticeVal &State = getValueState(I.getOperand(i));
1040 if (State.isUndefined())
1041 return; // Operands are not resolved yet...
1042 else if (State.isOverdefined()) {
1043 markOverdefined(IV, &I);
1046 assert(State.isConstant() && "Unknown state!");
1047 Operands.push_back(State.getConstant());
1050 Constant *Ptr = Operands[0];
1051 Operands.erase(Operands.begin()); // Erase the pointer from idx list...
1053 markConstant(IV, &I, ConstantExpr::getGetElementPtr(Ptr, &Operands[0],
1057 void SCCPSolver::visitStoreInst(Instruction &SI) {
1058 if (TrackedGlobals.empty() || !isa<GlobalVariable>(SI.getOperand(1)))
1060 GlobalVariable *GV = cast<GlobalVariable>(SI.getOperand(1));
1061 DenseMap<GlobalVariable*, LatticeVal>::iterator I = TrackedGlobals.find(GV);
1062 if (I == TrackedGlobals.end() || I->second.isOverdefined()) return;
1064 // Get the value we are storing into the global.
1065 LatticeVal &PtrVal = getValueState(SI.getOperand(0));
1067 mergeInValue(I->second, GV, PtrVal);
1068 if (I->second.isOverdefined())
1069 TrackedGlobals.erase(I); // No need to keep tracking this!
1073 // Handle load instructions. If the operand is a constant pointer to a constant
1074 // global, we can replace the load with the loaded constant value!
1075 void SCCPSolver::visitLoadInst(LoadInst &I) {
1076 LatticeVal &IV = ValueState[&I];
1077 if (IV.isOverdefined()) return;
1079 LatticeVal &PtrVal = getValueState(I.getOperand(0));
1080 if (PtrVal.isUndefined()) return; // The pointer is not resolved yet!
1081 if (PtrVal.isConstant() && !I.isVolatile()) {
1082 Value *Ptr = PtrVal.getConstant();
1083 // TODO: Consider a target hook for valid address spaces for this xform.
1084 if (isa<ConstantPointerNull>(Ptr) &&
1085 cast<PointerType>(Ptr->getType())->getAddressSpace() == 0) {
1086 // load null -> null
1087 markConstant(IV, &I, Constant::getNullValue(I.getType()));
1091 // Transform load (constant global) into the value loaded.
1092 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Ptr)) {
1093 if (GV->isConstant()) {
1094 if (!GV->isDeclaration()) {
1095 markConstant(IV, &I, GV->getInitializer());
1098 } else if (!TrackedGlobals.empty()) {
1099 // If we are tracking this global, merge in the known value for it.
1100 DenseMap<GlobalVariable*, LatticeVal>::iterator It =
1101 TrackedGlobals.find(GV);
1102 if (It != TrackedGlobals.end()) {
1103 mergeInValue(IV, &I, It->second);
1109 // Transform load (constantexpr_GEP global, 0, ...) into the value loaded.
1110 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr))
1111 if (CE->getOpcode() == Instruction::GetElementPtr)
1112 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(CE->getOperand(0)))
1113 if (GV->isConstant() && !GV->isDeclaration())
1115 ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE)) {
1116 markConstant(IV, &I, V);
1121 // Otherwise we cannot say for certain what value this load will produce.
1123 markOverdefined(IV, &I);
1126 void SCCPSolver::visitCallSite(CallSite CS) {
1127 Function *F = CS.getCalledFunction();
1129 DenseMap<Function*, LatticeVal>::iterator TFRVI =TrackedRetVals.end();
1130 // If we are tracking this function, we must make sure to bind arguments as
1132 bool FirstCall = false;
1133 if (F && F->hasInternalLinkage()) {
1134 TFRVI = TrackedRetVals.find(F);
1135 if (TFRVI != TrackedRetVals.end())
1138 std::multimap<Function*, LatticeValIndexed>::iterator It, E;
1139 tie(It, E) = TrackedMultipleRetVals.equal_range(F);
1146 // If this is the first call to the function hit, mark its entry block
1148 if (!BBExecutable.count(F->begin()))
1149 MarkBlockExecutable(F->begin());
1151 CallSite::arg_iterator CAI = CS.arg_begin();
1152 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
1153 AI != E; ++AI, ++CAI) {
1154 LatticeVal &IV = ValueState[AI];
1155 if (!IV.isOverdefined())
1156 mergeInValue(IV, AI, getValueState(*CAI));
1159 Instruction *I = CS.getInstruction();
1161 if (!CS.doesNotThrow() && I->getParent()->getUnwindDest())
1162 markEdgeExecutable(I->getParent(), I->getParent()->getUnwindDest());
1164 if (I->getType() == Type::VoidTy) return;
1166 LatticeVal &IV = ValueState[I];
1167 if (IV.isOverdefined()) return;
1169 // Propagate the single return value of the function to the value of the
1171 if (TFRVI != TrackedRetVals.end()) {
1172 mergeInValue(IV, I, TFRVI->second);
1176 if (F == 0 || !F->isDeclaration() || !canConstantFoldCallTo(F)) {
1177 markOverdefined(IV, I);
1181 SmallVector<Constant*, 8> Operands;
1182 Operands.reserve(I->getNumOperands()-1);
1184 for (CallSite::arg_iterator AI = CS.arg_begin(), E = CS.arg_end();
1186 LatticeVal &State = getValueState(*AI);
1187 if (State.isUndefined())
1188 return; // Operands are not resolved yet...
1189 else if (State.isOverdefined()) {
1190 markOverdefined(IV, I);
1193 assert(State.isConstant() && "Unknown state!");
1194 Operands.push_back(State.getConstant());
1197 if (Constant *C = ConstantFoldCall(F, &Operands[0], Operands.size()))
1198 markConstant(IV, I, C);
1200 markOverdefined(IV, I);
1204 void SCCPSolver::Solve() {
1205 // Process the work lists until they are empty!
1206 while (!BBWorkList.empty() || !InstWorkList.empty() ||
1207 !OverdefinedInstWorkList.empty()) {
1208 // Process the instruction work list...
1209 while (!OverdefinedInstWorkList.empty()) {
1210 Value *I = OverdefinedInstWorkList.back();
1211 OverdefinedInstWorkList.pop_back();
1213 DOUT << "\nPopped off OI-WL: " << *I;
1215 // "I" got into the work list because it either made the transition from
1216 // bottom to constant
1218 // Anything on this worklist that is overdefined need not be visited
1219 // since all of its users will have already been marked as overdefined
1220 // Update all of the users of this instruction's value...
1222 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
1224 OperandChangedState(*UI);
1226 // Process the instruction work list...
1227 while (!InstWorkList.empty()) {
1228 Value *I = InstWorkList.back();
1229 InstWorkList.pop_back();
1231 DOUT << "\nPopped off I-WL: " << *I;
1233 // "I" got into the work list because it either made the transition from
1234 // bottom to constant
1236 // Anything on this worklist that is overdefined need not be visited
1237 // since all of its users will have already been marked as overdefined.
1238 // Update all of the users of this instruction's value...
1240 if (!getValueState(I).isOverdefined())
1241 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
1243 OperandChangedState(*UI);
1246 // Process the basic block work list...
1247 while (!BBWorkList.empty()) {
1248 BasicBlock *BB = BBWorkList.back();
1249 BBWorkList.pop_back();
1251 DOUT << "\nPopped off BBWL: " << *BB;
1253 // Notify all instructions in this basic block that they are newly
1260 /// ResolvedUndefsIn - While solving the dataflow for a function, we assume
1261 /// that branches on undef values cannot reach any of their successors.
1262 /// However, this is not a safe assumption. After we solve dataflow, this
1263 /// method should be use to handle this. If this returns true, the solver
1264 /// should be rerun.
1266 /// This method handles this by finding an unresolved branch and marking it one
1267 /// of the edges from the block as being feasible, even though the condition
1268 /// doesn't say it would otherwise be. This allows SCCP to find the rest of the
1269 /// CFG and only slightly pessimizes the analysis results (by marking one,
1270 /// potentially infeasible, edge feasible). This cannot usefully modify the
1271 /// constraints on the condition of the branch, as that would impact other users
1274 /// This scan also checks for values that use undefs, whose results are actually
1275 /// defined. For example, 'zext i8 undef to i32' should produce all zeros
1276 /// conservatively, as "(zext i8 X -> i32) & 0xFF00" must always return zero,
1277 /// even if X isn't defined.
1278 bool SCCPSolver::ResolvedUndefsIn(Function &F) {
1279 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
1280 if (!BBExecutable.count(BB))
1283 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
1284 // Look for instructions which produce undef values.
1285 if (I->getType() == Type::VoidTy) continue;
1287 LatticeVal &LV = getValueState(I);
1288 if (!LV.isUndefined()) continue;
1290 // Get the lattice values of the first two operands for use below.
1291 LatticeVal &Op0LV = getValueState(I->getOperand(0));
1293 if (I->getNumOperands() == 2) {
1294 // If this is a two-operand instruction, and if both operands are
1295 // undefs, the result stays undef.
1296 Op1LV = getValueState(I->getOperand(1));
1297 if (Op0LV.isUndefined() && Op1LV.isUndefined())
1301 // If this is an instructions whose result is defined even if the input is
1302 // not fully defined, propagate the information.
1303 const Type *ITy = I->getType();
1304 switch (I->getOpcode()) {
1305 default: break; // Leave the instruction as an undef.
1306 case Instruction::ZExt:
1307 // After a zero extend, we know the top part is zero. SExt doesn't have
1308 // to be handled here, because we don't know whether the top part is 1's
1310 assert(Op0LV.isUndefined());
1311 markForcedConstant(LV, I, Constant::getNullValue(ITy));
1313 case Instruction::Mul:
1314 case Instruction::And:
1315 // undef * X -> 0. X could be zero.
1316 // undef & X -> 0. X could be zero.
1317 markForcedConstant(LV, I, Constant::getNullValue(ITy));
1320 case Instruction::Or:
1321 // undef | X -> -1. X could be -1.
1322 if (const VectorType *PTy = dyn_cast<VectorType>(ITy))
1323 markForcedConstant(LV, I, ConstantVector::getAllOnesValue(PTy));
1325 markForcedConstant(LV, I, ConstantInt::getAllOnesValue(ITy));
1328 case Instruction::SDiv:
1329 case Instruction::UDiv:
1330 case Instruction::SRem:
1331 case Instruction::URem:
1332 // X / undef -> undef. No change.
1333 // X % undef -> undef. No change.
1334 if (Op1LV.isUndefined()) break;
1336 // undef / X -> 0. X could be maxint.
1337 // undef % X -> 0. X could be 1.
1338 markForcedConstant(LV, I, Constant::getNullValue(ITy));
1341 case Instruction::AShr:
1342 // undef >>s X -> undef. No change.
1343 if (Op0LV.isUndefined()) break;
1345 // X >>s undef -> X. X could be 0, X could have the high-bit known set.
1346 if (Op0LV.isConstant())
1347 markForcedConstant(LV, I, Op0LV.getConstant());
1349 markOverdefined(LV, I);
1351 case Instruction::LShr:
1352 case Instruction::Shl:
1353 // undef >> X -> undef. No change.
1354 // undef << X -> undef. No change.
1355 if (Op0LV.isUndefined()) break;
1357 // X >> undef -> 0. X could be 0.
1358 // X << undef -> 0. X could be 0.
1359 markForcedConstant(LV, I, Constant::getNullValue(ITy));
1361 case Instruction::Select:
1362 // undef ? X : Y -> X or Y. There could be commonality between X/Y.
1363 if (Op0LV.isUndefined()) {
1364 if (!Op1LV.isConstant()) // Pick the constant one if there is any.
1365 Op1LV = getValueState(I->getOperand(2));
1366 } else if (Op1LV.isUndefined()) {
1367 // c ? undef : undef -> undef. No change.
1368 Op1LV = getValueState(I->getOperand(2));
1369 if (Op1LV.isUndefined())
1371 // Otherwise, c ? undef : x -> x.
1373 // Leave Op1LV as Operand(1)'s LatticeValue.
1376 if (Op1LV.isConstant())
1377 markForcedConstant(LV, I, Op1LV.getConstant());
1379 markOverdefined(LV, I);
1384 TerminatorInst *TI = BB->getTerminator();
1385 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
1386 if (!BI->isConditional()) continue;
1387 if (!getValueState(BI->getCondition()).isUndefined())
1389 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
1390 if (!getValueState(SI->getCondition()).isUndefined())
1396 // If the edge to the second successor isn't thought to be feasible yet,
1397 // mark it so now. We pick the second one so that this goes to some
1398 // enumerated value in a switch instead of going to the default destination.
1399 if (KnownFeasibleEdges.count(Edge(BB, TI->getSuccessor(1))))
1402 // Otherwise, it isn't already thought to be feasible. Mark it as such now
1403 // and return. This will make other blocks reachable, which will allow new
1404 // values to be discovered and existing ones to be moved in the lattice.
1405 markEdgeExecutable(BB, TI->getSuccessor(1));
1407 // This must be a conditional branch of switch on undef. At this point,
1408 // force the old terminator to branch to the first successor. This is
1409 // required because we are now influencing the dataflow of the function with
1410 // the assumption that this edge is taken. If we leave the branch condition
1411 // as undef, then further analysis could think the undef went another way
1412 // leading to an inconsistent set of conclusions.
1413 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
1414 BI->setCondition(ConstantInt::getFalse());
1416 SwitchInst *SI = cast<SwitchInst>(TI);
1417 SI->setCondition(SI->getCaseValue(1));
1428 //===--------------------------------------------------------------------===//
1430 /// SCCP Class - This class uses the SCCPSolver to implement a per-function
1431 /// Sparse Conditional Constant Propagator.
1433 struct VISIBILITY_HIDDEN SCCP : public FunctionPass {
1434 static char ID; // Pass identification, replacement for typeid
1435 SCCP() : FunctionPass((intptr_t)&ID) {}
1437 // runOnFunction - Run the Sparse Conditional Constant Propagation
1438 // algorithm, and return true if the function was modified.
1440 bool runOnFunction(Function &F);
1442 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
1443 AU.setPreservesCFG();
1448 RegisterPass<SCCP> X("sccp", "Sparse Conditional Constant Propagation");
1449 } // end anonymous namespace
1452 // createSCCPPass - This is the public interface to this file...
1453 FunctionPass *llvm::createSCCPPass() {
1458 // runOnFunction() - Run the Sparse Conditional Constant Propagation algorithm,
1459 // and return true if the function was modified.
1461 bool SCCP::runOnFunction(Function &F) {
1462 DOUT << "SCCP on function '" << F.getName() << "'\n";
1465 // Mark the first block of the function as being executable.
1466 Solver.MarkBlockExecutable(F.begin());
1468 // Mark all arguments to the function as being overdefined.
1469 for (Function::arg_iterator AI = F.arg_begin(), E = F.arg_end(); AI != E;++AI)
1470 Solver.markOverdefined(AI);
1472 // Solve for constants.
1473 bool ResolvedUndefs = true;
1474 while (ResolvedUndefs) {
1476 DOUT << "RESOLVING UNDEFs\n";
1477 ResolvedUndefs = Solver.ResolvedUndefsIn(F);
1480 bool MadeChanges = false;
1482 // If we decided that there are basic blocks that are dead in this function,
1483 // delete their contents now. Note that we cannot actually delete the blocks,
1484 // as we cannot modify the CFG of the function.
1486 SmallSet<BasicBlock*, 16> &ExecutableBBs = Solver.getExecutableBlocks();
1487 SmallVector<Instruction*, 32> Insts;
1488 std::map<Value*, LatticeVal> &Values = Solver.getValueMapping();
1490 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
1491 if (!ExecutableBBs.count(BB)) {
1492 DOUT << " BasicBlock Dead:" << *BB;
1495 // Delete the instructions backwards, as it has a reduced likelihood of
1496 // having to update as many def-use and use-def chains.
1497 for (BasicBlock::iterator I = BB->begin(), E = BB->getTerminator();
1500 while (!Insts.empty()) {
1501 Instruction *I = Insts.back();
1503 if (!I->use_empty())
1504 I->replaceAllUsesWith(UndefValue::get(I->getType()));
1505 BB->getInstList().erase(I);
1510 // Iterate over all of the instructions in a function, replacing them with
1511 // constants if we have found them to be of constant values.
1513 for (BasicBlock::iterator BI = BB->begin(), E = BB->end(); BI != E; ) {
1514 Instruction *Inst = BI++;
1515 if (Inst->getType() != Type::VoidTy) {
1516 LatticeVal &IV = Values[Inst];
1517 if ((IV.isConstant() || IV.isUndefined()) &&
1518 !isa<TerminatorInst>(Inst)) {
1519 Constant *Const = IV.isConstant()
1520 ? IV.getConstant() : UndefValue::get(Inst->getType());
1521 DOUT << " Constant: " << *Const << " = " << *Inst;
1523 // Replaces all of the uses of a variable with uses of the constant.
1524 Inst->replaceAllUsesWith(Const);
1526 // Delete the instruction.
1527 BB->getInstList().erase(Inst);
1529 // Hey, we just changed something!
1541 //===--------------------------------------------------------------------===//
1543 /// IPSCCP Class - This class implements interprocedural Sparse Conditional
1544 /// Constant Propagation.
1546 struct VISIBILITY_HIDDEN IPSCCP : public ModulePass {
1548 IPSCCP() : ModulePass((intptr_t)&ID) {}
1549 bool runOnModule(Module &M);
1552 char IPSCCP::ID = 0;
1553 RegisterPass<IPSCCP>
1554 Y("ipsccp", "Interprocedural Sparse Conditional Constant Propagation");
1555 } // end anonymous namespace
1557 // createIPSCCPPass - This is the public interface to this file...
1558 ModulePass *llvm::createIPSCCPPass() {
1559 return new IPSCCP();
1563 static bool AddressIsTaken(GlobalValue *GV) {
1564 // Delete any dead constantexpr klingons.
1565 GV->removeDeadConstantUsers();
1567 for (Value::use_iterator UI = GV->use_begin(), E = GV->use_end();
1569 if (StoreInst *SI = dyn_cast<StoreInst>(*UI)) {
1570 if (SI->getOperand(0) == GV || SI->isVolatile())
1571 return true; // Storing addr of GV.
1572 } else if (isa<InvokeInst>(*UI) || isa<CallInst>(*UI)) {
1573 // Make sure we are calling the function, not passing the address.
1574 CallSite CS = CallSite::get(cast<Instruction>(*UI));
1575 for (CallSite::arg_iterator AI = CS.arg_begin(),
1576 E = CS.arg_end(); AI != E; ++AI)
1579 } else if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) {
1580 if (LI->isVolatile())
1588 bool IPSCCP::runOnModule(Module &M) {
1591 // Loop over all functions, marking arguments to those with their addresses
1592 // taken or that are external as overdefined.
1594 for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F)
1595 if (!F->hasInternalLinkage() || AddressIsTaken(F)) {
1596 if (!F->isDeclaration())
1597 Solver.MarkBlockExecutable(F->begin());
1598 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
1600 Solver.markOverdefined(AI);
1602 Solver.AddTrackedFunction(F);
1605 // Loop over global variables. We inform the solver about any internal global
1606 // variables that do not have their 'addresses taken'. If they don't have
1607 // their addresses taken, we can propagate constants through them.
1608 for (Module::global_iterator G = M.global_begin(), E = M.global_end();
1610 if (!G->isConstant() && G->hasInternalLinkage() && !AddressIsTaken(G))
1611 Solver.TrackValueOfGlobalVariable(G);
1613 // Solve for constants.
1614 bool ResolvedUndefs = true;
1615 while (ResolvedUndefs) {
1618 DOUT << "RESOLVING UNDEFS\n";
1619 ResolvedUndefs = false;
1620 for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F)
1621 ResolvedUndefs |= Solver.ResolvedUndefsIn(*F);
1624 bool MadeChanges = false;
1626 // Iterate over all of the instructions in the module, replacing them with
1627 // constants if we have found them to be of constant values.
1629 SmallSet<BasicBlock*, 16> &ExecutableBBs = Solver.getExecutableBlocks();
1630 SmallVector<Instruction*, 32> Insts;
1631 SmallVector<BasicBlock*, 32> BlocksToErase;
1632 std::map<Value*, LatticeVal> &Values = Solver.getValueMapping();
1634 for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) {
1635 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
1637 if (!AI->use_empty()) {
1638 LatticeVal &IV = Values[AI];
1639 if (IV.isConstant() || IV.isUndefined()) {
1640 Constant *CST = IV.isConstant() ?
1641 IV.getConstant() : UndefValue::get(AI->getType());
1642 DOUT << "*** Arg " << *AI << " = " << *CST <<"\n";
1644 // Replaces all of the uses of a variable with uses of the
1646 AI->replaceAllUsesWith(CST);
1651 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
1652 if (!ExecutableBBs.count(BB)) {
1653 DOUT << " BasicBlock Dead:" << *BB;
1656 // Delete the instructions backwards, as it has a reduced likelihood of
1657 // having to update as many def-use and use-def chains.
1658 TerminatorInst *TI = BB->getTerminator();
1659 for (BasicBlock::iterator I = BB->begin(), E = TI; I != E; ++I)
1662 while (!Insts.empty()) {
1663 Instruction *I = Insts.back();
1665 if (!I->use_empty())
1666 I->replaceAllUsesWith(UndefValue::get(I->getType()));
1667 BB->getInstList().erase(I);
1672 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) {
1673 BasicBlock *Succ = TI->getSuccessor(i);
1674 if (!Succ->empty() && isa<PHINode>(Succ->begin()))
1675 TI->getSuccessor(i)->removePredecessor(BB);
1677 if (!TI->use_empty())
1678 TI->replaceAllUsesWith(UndefValue::get(TI->getType()));
1679 BB->getInstList().erase(TI);
1681 if (&*BB != &F->front())
1682 BlocksToErase.push_back(BB);
1684 new UnreachableInst(BB);
1687 for (BasicBlock::iterator BI = BB->begin(), E = BB->end(); BI != E; ) {
1688 Instruction *Inst = BI++;
1689 if (Inst->getType() != Type::VoidTy) {
1690 LatticeVal &IV = Values[Inst];
1691 if (IV.isConstant() ||
1692 (IV.isUndefined() && !isa<TerminatorInst>(Inst))) {
1693 Constant *Const = IV.isConstant()
1694 ? IV.getConstant() : UndefValue::get(Inst->getType());
1695 DOUT << " Constant: " << *Const << " = " << *Inst;
1697 // Replaces all of the uses of a variable with uses of the
1699 Inst->replaceAllUsesWith(Const);
1701 // Delete the instruction.
1702 if (!isa<TerminatorInst>(Inst) && !isa<CallInst>(Inst))
1703 BB->getInstList().erase(Inst);
1705 // Hey, we just changed something!
1713 // Now that all instructions in the function are constant folded, erase dead
1714 // blocks, because we can now use ConstantFoldTerminator to get rid of
1716 for (unsigned i = 0, e = BlocksToErase.size(); i != e; ++i) {
1717 // If there are any PHI nodes in this successor, drop entries for BB now.
1718 BasicBlock *DeadBB = BlocksToErase[i];
1719 while (!DeadBB->use_empty()) {
1720 if (BasicBlock *PredBB = dyn_cast<BasicBlock>(DeadBB->use_back())) {
1721 PredBB->setUnwindDest(NULL);
1725 Instruction *I = cast<Instruction>(DeadBB->use_back());
1726 bool Folded = ConstantFoldTerminator(I->getParent());
1728 // The constant folder may not have been able to fold the terminator
1729 // if this is a branch or switch on undef. Fold it manually as a
1730 // branch to the first successor.
1731 if (BranchInst *BI = dyn_cast<BranchInst>(I)) {
1732 assert(BI->isConditional() && isa<UndefValue>(BI->getCondition()) &&
1733 "Branch should be foldable!");
1734 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(I)) {
1735 assert(isa<UndefValue>(SI->getCondition()) && "Switch should fold");
1737 assert(0 && "Didn't fold away reference to block!");
1740 // Make this an uncond branch to the first successor.
1741 TerminatorInst *TI = I->getParent()->getTerminator();
1742 new BranchInst(TI->getSuccessor(0), TI);
1744 // Remove entries in successor phi nodes to remove edges.
1745 for (unsigned i = 1, e = TI->getNumSuccessors(); i != e; ++i)
1746 TI->getSuccessor(i)->removePredecessor(TI->getParent());
1748 // Remove the old terminator.
1749 TI->eraseFromParent();
1753 // Finally, delete the basic block.
1754 F->getBasicBlockList().erase(DeadBB);
1756 BlocksToErase.clear();
1759 // If we inferred constant or undef return values for a function, we replaced
1760 // all call uses with the inferred value. This means we don't need to bother
1761 // actually returning anything from the function. Replace all return
1762 // instructions with return undef.
1763 // TODO: Process multiple value ret instructions also.
1764 const DenseMap<Function*, LatticeVal> &RV = Solver.getTrackedRetVals();
1765 for (DenseMap<Function*, LatticeVal>::const_iterator I = RV.begin(),
1766 E = RV.end(); I != E; ++I)
1767 if (!I->second.isOverdefined() &&
1768 I->first->getReturnType() != Type::VoidTy) {
1769 Function *F = I->first;
1770 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
1771 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator()))
1772 if (!isa<UndefValue>(RI->getOperand(0)))
1773 RI->setOperand(0, UndefValue::get(F->getReturnType()));
1776 // If we infered constant or undef values for globals variables, we can delete
1777 // the global and any stores that remain to it.
1778 const DenseMap<GlobalVariable*, LatticeVal> &TG = Solver.getTrackedGlobals();
1779 for (DenseMap<GlobalVariable*, LatticeVal>::const_iterator I = TG.begin(),
1780 E = TG.end(); I != E; ++I) {
1781 GlobalVariable *GV = I->first;
1782 assert(!I->second.isOverdefined() &&
1783 "Overdefined values should have been taken out of the map!");
1784 DOUT << "Found that GV '" << GV->getName()<< "' is constant!\n";
1785 while (!GV->use_empty()) {
1786 StoreInst *SI = cast<StoreInst>(GV->use_back());
1787 SI->eraseFromParent();
1789 M.getGlobalList().erase(GV);