1 //===- SCCP.cpp - Sparse Conditional Constant Propagation -----------------===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file implements sparse conditional constant propagation and merging:
11 //
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
17 //
18 //===----------------------------------------------------------------------===//
19
20 #include "llvm/Transforms/Scalar.h"
21 #include "llvm/ADT/DenseMap.h"
22 #include "llvm/ADT/DenseSet.h"
23 #include "llvm/ADT/PointerIntPair.h"
24 #include "llvm/ADT/SmallPtrSet.h"
25 #include "llvm/ADT/SmallVector.h"
26 #include "llvm/ADT/Statistic.h"
27 #include "llvm/Analysis/GlobalsModRef.h"
28 #include "llvm/Analysis/ConstantFolding.h"
29 #include "llvm/Analysis/TargetLibraryInfo.h"
30 #include "llvm/IR/CallSite.h"
31 #include "llvm/IR/Constants.h"
32 #include "llvm/IR/DataLayout.h"
33 #include "llvm/IR/DerivedTypes.h"
34 #include "llvm/IR/InstVisitor.h"
35 #include "llvm/IR/Instructions.h"
36 #include "llvm/Pass.h"
37 #include "llvm/Support/Debug.h"
38 #include "llvm/Support/ErrorHandling.h"
39 #include "llvm/Support/raw_ostream.h"
40 #include "llvm/Transforms/IPO.h"
41 #include "llvm/Transforms/Utils/Local.h"
42 #include <algorithm>
43 using namespace llvm;
44
45 #define DEBUG_TYPE "sccp"
46
47 STATISTIC(NumInstRemoved, "Number of instructions removed");
48 STATISTIC(NumDeadBlocks , "Number of basic blocks unreachable");
49
50 STATISTIC(IPNumInstRemoved, "Number of instructions removed by IPSCCP");
51 STATISTIC(IPNumArgsElimed ,"Number of arguments constant propagated by IPSCCP");
52 STATISTIC(IPNumGlobalConst, "Number of globals found to be constant by IPSCCP");
53
54 namespace {
55 /// LatticeVal class - This class represents the different lattice values that
56 /// an LLVM value may occupy. It is a simple class with value semantics.
57 ///
58 class LatticeVal {
59 enum LatticeValueTy {
60 /// undefined - This LLVM Value has no known value yet.
61 undefined,
62
63 /// constant - This LLVM Value has a specific constant value.
64 constant,
65
66 /// forcedconstant - This LLVM Value was thought to be undef until
67 /// ResolvedUndefsIn. This is treated just like 'constant', but if merged
68 /// with another (different) constant, it goes to overdefined, instead of
69 /// asserting.
70 forcedconstant,
71
72 /// overdefined - This instruction is not known to be constant, and we know
73 /// it has a value.
74 overdefined
75 };
76
77 /// Val: This stores the current lattice value along with the Constant* for
78 /// the constant if this is a 'constant' or 'forcedconstant' value.
79 PointerIntPair<Constant *, 2, LatticeValueTy> Val;
80
getLatticeValue() const81 LatticeValueTy getLatticeValue() const {
82 return Val.getInt();
83 }
84
85 public:
LatticeVal()86 LatticeVal() : Val(nullptr, undefined) {}
87
isUndefined() const88 bool isUndefined() const { return getLatticeValue() == undefined; }
isConstant() const89 bool isConstant() const {
90 return getLatticeValue() == constant || getLatticeValue() == forcedconstant;
91 }
isOverdefined() const92 bool isOverdefined() const { return getLatticeValue() == overdefined; }
93
getConstant() const94 Constant *getConstant() const {
95 assert(isConstant() && "Cannot get the constant of a non-constant!");
96 return Val.getPointer();
97 }
98
99 /// markOverdefined - Return true if this is a change in status.
markOverdefined()100 bool markOverdefined() {
101 if (isOverdefined())
102 return false;
103
104 Val.setInt(overdefined);
105 return true;
106 }
107
108 /// markConstant - Return true if this is a change in status.
markConstant(Constant * V)109 bool markConstant(Constant *V) {
110 if (getLatticeValue() == constant) { // Constant but not forcedconstant.
111 assert(getConstant() == V && "Marking constant with different value");
112 return false;
113 }
114
115 if (isUndefined()) {
116 Val.setInt(constant);
117 assert(V && "Marking constant with NULL");
118 Val.setPointer(V);
119 } else {
120 assert(getLatticeValue() == forcedconstant &&
121 "Cannot move from overdefined to constant!");
122 // Stay at forcedconstant if the constant is the same.
123 if (V == getConstant()) return false;
124
125 // Otherwise, we go to overdefined. Assumptions made based on the
126 // forced value are possibly wrong. Assuming this is another constant
127 // could expose a contradiction.
128 Val.setInt(overdefined);
129 }
130 return true;
131 }
132
133 /// getConstantInt - If this is a constant with a ConstantInt value, return it
134 /// otherwise return null.
getConstantInt() const135 ConstantInt *getConstantInt() const {
136 if (isConstant())
137 return dyn_cast<ConstantInt>(getConstant());
138 return nullptr;
139 }
140
markForcedConstant(Constant * V)141 void markForcedConstant(Constant *V) {
142 assert(isUndefined() && "Can't force a defined value!");
143 Val.setInt(forcedconstant);
144 Val.setPointer(V);
145 }
146 };
147 } // end anonymous namespace.
148
149
150 namespace {
151
152 //===----------------------------------------------------------------------===//
153 //
154 /// SCCPSolver - This class is a general purpose solver for Sparse Conditional
155 /// Constant Propagation.
156 ///
157 class SCCPSolver : public InstVisitor<SCCPSolver> {
158 const DataLayout &DL;
159 const TargetLibraryInfo *TLI;
160 SmallPtrSet<BasicBlock*, 8> BBExecutable; // The BBs that are executable.
161 DenseMap<Value*, LatticeVal> ValueState; // The state each value is in.
162
163 /// StructValueState - This maintains ValueState for values that have
164 /// StructType, for example for formal arguments, calls, insertelement, etc.
165 ///
166 DenseMap<std::pair<Value*, unsigned>, LatticeVal> StructValueState;
167
168 /// GlobalValue - If we are tracking any values for the contents of a global
169 /// variable, we keep a mapping from the constant accessor to the element of
170 /// the global, to the currently known value. If the value becomes
171 /// overdefined, it's entry is simply removed from this map.
172 DenseMap<GlobalVariable*, LatticeVal> TrackedGlobals;
173
174 /// TrackedRetVals - If we are tracking arguments into and the return
175 /// value out of a function, it will have an entry in this map, indicating
176 /// what the known return value for the function is.
177 DenseMap<Function*, LatticeVal> TrackedRetVals;
178
179 /// TrackedMultipleRetVals - Same as TrackedRetVals, but used for functions
180 /// that return multiple values.
181 DenseMap<std::pair<Function*, unsigned>, LatticeVal> TrackedMultipleRetVals;
182
183 /// MRVFunctionsTracked - Each function in TrackedMultipleRetVals is
184 /// represented here for efficient lookup.
185 SmallPtrSet<Function*, 16> MRVFunctionsTracked;
186
187 /// TrackingIncomingArguments - This is the set of functions for whose
188 /// arguments we make optimistic assumptions about and try to prove as
189 /// constants.
190 SmallPtrSet<Function*, 16> TrackingIncomingArguments;
191
192 /// The reason for two worklists is that overdefined is the lowest state
193 /// on the lattice, and moving things to overdefined as fast as possible
194 /// makes SCCP converge much faster.
195 ///
196 /// By having a separate worklist, we accomplish this because everything
197 /// possibly overdefined will become overdefined at the soonest possible
198 /// point.
199 SmallVector<Value*, 64> OverdefinedInstWorkList;
200 SmallVector<Value*, 64> InstWorkList;
201
202
203 SmallVector<BasicBlock*, 64> BBWorkList; // The BasicBlock work list
204
205 /// KnownFeasibleEdges - Entries in this set are edges which have already had
206 /// PHI nodes retriggered.
207 typedef std::pair<BasicBlock*, BasicBlock*> Edge;
208 DenseSet<Edge> KnownFeasibleEdges;
209 public:
SCCPSolver(const DataLayout & DL,const TargetLibraryInfo * tli)210 SCCPSolver(const DataLayout &DL, const TargetLibraryInfo *tli)
211 : DL(DL), TLI(tli) {}
212
213 /// MarkBlockExecutable - This method can be used by clients to mark all of
214 /// the blocks that are known to be intrinsically live in the processed unit.
215 ///
216 /// This returns true if the block was not considered live before.
MarkBlockExecutable(BasicBlock * BB)217 bool MarkBlockExecutable(BasicBlock *BB) {
218 if (!BBExecutable.insert(BB).second)
219 return false;
220 DEBUG(dbgs() << "Marking Block Executable: " << BB->getName() << '\n');
221 BBWorkList.push_back(BB); // Add the block to the work list!
222 return true;
223 }
224
225 /// TrackValueOfGlobalVariable - Clients can use this method to
226 /// inform the SCCPSolver that it should track loads and stores to the
227 /// specified global variable if it can. This is only legal to call if
228 /// performing Interprocedural SCCP.
TrackValueOfGlobalVariable(GlobalVariable * GV)229 void TrackValueOfGlobalVariable(GlobalVariable *GV) {
230 // We only track the contents of scalar globals.
231 if (GV->getType()->getElementType()->isSingleValueType()) {
232 LatticeVal &IV = TrackedGlobals[GV];
233 if (!isa<UndefValue>(GV->getInitializer()))
234 IV.markConstant(GV->getInitializer());
235 }
236 }
237
238 /// AddTrackedFunction - If the SCCP solver is supposed to track calls into
239 /// and out of the specified function (which cannot have its address taken),
240 /// this method must be called.
AddTrackedFunction(Function * F)241 void AddTrackedFunction(Function *F) {
242 // Add an entry, F -> undef.
243 if (StructType *STy = dyn_cast<StructType>(F->getReturnType())) {
244 MRVFunctionsTracked.insert(F);
245 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
246 TrackedMultipleRetVals.insert(std::make_pair(std::make_pair(F, i),
247 LatticeVal()));
248 } else
249 TrackedRetVals.insert(std::make_pair(F, LatticeVal()));
250 }
251
AddArgumentTrackedFunction(Function * F)252 void AddArgumentTrackedFunction(Function *F) {
253 TrackingIncomingArguments.insert(F);
254 }
255
256 /// Solve - Solve for constants and executable blocks.
257 ///
258 void Solve();
259
260 /// ResolvedUndefsIn - While solving the dataflow for a function, we assume
261 /// that branches on undef values cannot reach any of their successors.
262 /// However, this is not a safe assumption. After we solve dataflow, this
263 /// method should be use to handle this. If this returns true, the solver
264 /// should be rerun.
265 bool ResolvedUndefsIn(Function &F);
266
isBlockExecutable(BasicBlock * BB) const267 bool isBlockExecutable(BasicBlock *BB) const {
268 return BBExecutable.count(BB);
269 }
270
getLatticeValueFor(Value * V) const271 LatticeVal getLatticeValueFor(Value *V) const {
272 DenseMap<Value*, LatticeVal>::const_iterator I = ValueState.find(V);
273 assert(I != ValueState.end() && "V is not in valuemap!");
274 return I->second;
275 }
276
277 /// getTrackedRetVals - Get the inferred return value map.
278 ///
getTrackedRetVals()279 const DenseMap<Function*, LatticeVal> &getTrackedRetVals() {
280 return TrackedRetVals;
281 }
282
283 /// getTrackedGlobals - Get and return the set of inferred initializers for
284 /// global variables.
getTrackedGlobals()285 const DenseMap<GlobalVariable*, LatticeVal> &getTrackedGlobals() {
286 return TrackedGlobals;
287 }
288
markOverdefined(Value * V)289 void markOverdefined(Value *V) {
290 assert(!V->getType()->isStructTy() && "Should use other method");
291 markOverdefined(ValueState[V], V);
292 }
293
294 /// markAnythingOverdefined - Mark the specified value overdefined. This
295 /// works with both scalars and structs.
markAnythingOverdefined(Value * V)296 void markAnythingOverdefined(Value *V) {
297 if (StructType *STy = dyn_cast<StructType>(V->getType()))
298 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
299 markOverdefined(getStructValueState(V, i), V);
300 else
301 markOverdefined(V);
302 }
303
304 private:
305 // markConstant - Make a value be marked as "constant". If the value
306 // is not already a constant, add it to the instruction work list so that
307 // the users of the instruction are updated later.
308 //
markConstant(LatticeVal & IV,Value * V,Constant * C)309 void markConstant(LatticeVal &IV, Value *V, Constant *C) {
310 if (!IV.markConstant(C)) return;
311 DEBUG(dbgs() << "markConstant: " << *C << ": " << *V << '\n');
312 if (IV.isOverdefined())
313 OverdefinedInstWorkList.push_back(V);
314 else
315 InstWorkList.push_back(V);
316 }
317
markConstant(Value * V,Constant * C)318 void markConstant(Value *V, Constant *C) {
319 assert(!V->getType()->isStructTy() && "Should use other method");
320 markConstant(ValueState[V], V, C);
321 }
322
markForcedConstant(Value * V,Constant * C)323 void markForcedConstant(Value *V, Constant *C) {
324 assert(!V->getType()->isStructTy() && "Should use other method");
325 LatticeVal &IV = ValueState[V];
326 IV.markForcedConstant(C);
327 DEBUG(dbgs() << "markForcedConstant: " << *C << ": " << *V << '\n');
328 if (IV.isOverdefined())
329 OverdefinedInstWorkList.push_back(V);
330 else
331 InstWorkList.push_back(V);
332 }
333
334
335 // markOverdefined - Make a value be marked as "overdefined". If the
336 // value is not already overdefined, add it to the overdefined instruction
337 // work list so that the users of the instruction are updated later.
markOverdefined(LatticeVal & IV,Value * V)338 void markOverdefined(LatticeVal &IV, Value *V) {
339 if (!IV.markOverdefined()) return;
340
341 DEBUG(dbgs() << "markOverdefined: ";
342 if (Function *F = dyn_cast<Function>(V))
343 dbgs() << "Function '" << F->getName() << "'\n";
344 else
345 dbgs() << *V << '\n');
346 // Only instructions go on the work list
347 OverdefinedInstWorkList.push_back(V);
348 }
349
mergeInValue(LatticeVal & IV,Value * V,LatticeVal MergeWithV)350 void mergeInValue(LatticeVal &IV, Value *V, LatticeVal MergeWithV) {
351 if (IV.isOverdefined() || MergeWithV.isUndefined())
352 return; // Noop.
353 if (MergeWithV.isOverdefined())
354 markOverdefined(IV, V);
355 else if (IV.isUndefined())
356 markConstant(IV, V, MergeWithV.getConstant());
357 else if (IV.getConstant() != MergeWithV.getConstant())
358 markOverdefined(IV, V);
359 }
360
mergeInValue(Value * V,LatticeVal MergeWithV)361 void mergeInValue(Value *V, LatticeVal MergeWithV) {
362 assert(!V->getType()->isStructTy() && "Should use other method");
363 mergeInValue(ValueState[V], V, MergeWithV);
364 }
365
366
367 /// getValueState - Return the LatticeVal object that corresponds to the
368 /// value. This function handles the case when the value hasn't been seen yet
369 /// by properly seeding constants etc.
getValueState(Value * V)370 LatticeVal &getValueState(Value *V) {
371 assert(!V->getType()->isStructTy() && "Should use getStructValueState");
372
373 std::pair<DenseMap<Value*, LatticeVal>::iterator, bool> I =
374 ValueState.insert(std::make_pair(V, LatticeVal()));
375 LatticeVal &LV = I.first->second;
376
377 if (!I.second)
378 return LV; // Common case, already in the map.
379
380 if (Constant *C = dyn_cast<Constant>(V)) {
381 // Undef values remain undefined.
382 if (!isa<UndefValue>(V))
383 LV.markConstant(C); // Constants are constant
384 }
385
386 // All others are underdefined by default.
387 return LV;
388 }
389
390 /// getStructValueState - Return the LatticeVal object that corresponds to the
391 /// value/field pair. This function handles the case when the value hasn't
392 /// been seen yet by properly seeding constants etc.
getStructValueState(Value * V,unsigned i)393 LatticeVal &getStructValueState(Value *V, unsigned i) {
394 assert(V->getType()->isStructTy() && "Should use getValueState");
395 assert(i < cast<StructType>(V->getType())->getNumElements() &&
396 "Invalid element #");
397
398 std::pair<DenseMap<std::pair<Value*, unsigned>, LatticeVal>::iterator,
399 bool> I = StructValueState.insert(
400 std::make_pair(std::make_pair(V, i), LatticeVal()));
401 LatticeVal &LV = I.first->second;
402
403 if (!I.second)
404 return LV; // Common case, already in the map.
405
406 if (Constant *C = dyn_cast<Constant>(V)) {
407 Constant *Elt = C->getAggregateElement(i);
408
409 if (!Elt)
410 LV.markOverdefined(); // Unknown sort of constant.
411 else if (isa<UndefValue>(Elt))
412 ; // Undef values remain undefined.
413 else
414 LV.markConstant(Elt); // Constants are constant.
415 }
416
417 // All others are underdefined by default.
418 return LV;
419 }
420
421
422 /// markEdgeExecutable - Mark a basic block as executable, adding it to the BB
423 /// work list if it is not already executable.
markEdgeExecutable(BasicBlock * Source,BasicBlock * Dest)424 void markEdgeExecutable(BasicBlock *Source, BasicBlock *Dest) {
425 if (!KnownFeasibleEdges.insert(Edge(Source, Dest)).second)
426 return; // This edge is already known to be executable!
427
428 if (!MarkBlockExecutable(Dest)) {
429 // If the destination is already executable, we just made an *edge*
430 // feasible that wasn't before. Revisit the PHI nodes in the block
431 // because they have potentially new operands.
432 DEBUG(dbgs() << "Marking Edge Executable: " << Source->getName()
433 << " -> " << Dest->getName() << '\n');
434
435 PHINode *PN;
436 for (BasicBlock::iterator I = Dest->begin();
437 (PN = dyn_cast<PHINode>(I)); ++I)
438 visitPHINode(*PN);
439 }
440 }
441
442 // getFeasibleSuccessors - Return a vector of booleans to indicate which
443 // successors are reachable from a given terminator instruction.
444 //
445 void getFeasibleSuccessors(TerminatorInst &TI, SmallVectorImpl<bool> &Succs);
446
447 // isEdgeFeasible - Return true if the control flow edge from the 'From' basic
448 // block to the 'To' basic block is currently feasible.
449 //
450 bool isEdgeFeasible(BasicBlock *From, BasicBlock *To);
451
452 // OperandChangedState - This method is invoked on all of the users of an
453 // instruction that was just changed state somehow. Based on this
454 // information, we need to update the specified user of this instruction.
455 //
OperandChangedState(Instruction * I)456 void OperandChangedState(Instruction *I) {
457 if (BBExecutable.count(I->getParent())) // Inst is executable?
458 visit(*I);
459 }
460
461 private:
462 friend class InstVisitor<SCCPSolver>;
463
464 // visit implementations - Something changed in this instruction. Either an
465 // operand made a transition, or the instruction is newly executable. Change
466 // the value type of I to reflect these changes if appropriate.
467 void visitPHINode(PHINode &I);
468
469 // Terminators
470 void visitReturnInst(ReturnInst &I);
471 void visitTerminatorInst(TerminatorInst &TI);
472
473 void visitCastInst(CastInst &I);
474 void visitSelectInst(SelectInst &I);
475 void visitBinaryOperator(Instruction &I);
476 void visitCmpInst(CmpInst &I);
477 void visitExtractElementInst(ExtractElementInst &I);
478 void visitInsertElementInst(InsertElementInst &I);
479 void visitShuffleVectorInst(ShuffleVectorInst &I);
480 void visitExtractValueInst(ExtractValueInst &EVI);
481 void visitInsertValueInst(InsertValueInst &IVI);
visitLandingPadInst(LandingPadInst & I)482 void visitLandingPadInst(LandingPadInst &I) { markAnythingOverdefined(&I); }
visitFuncletPadInst(FuncletPadInst & FPI)483 void visitFuncletPadInst(FuncletPadInst &FPI) {
484 markAnythingOverdefined(&FPI);
485 }
visitCatchSwitchInst(CatchSwitchInst & CPI)486 void visitCatchSwitchInst(CatchSwitchInst &CPI) {
487 markAnythingOverdefined(&CPI);
488 visitTerminatorInst(CPI);
489 }
490
491 // Instructions that cannot be folded away.
492 void visitStoreInst (StoreInst &I);
493 void visitLoadInst (LoadInst &I);
494 void visitGetElementPtrInst(GetElementPtrInst &I);
visitCallInst(CallInst & I)495 void visitCallInst (CallInst &I) {
496 visitCallSite(&I);
497 }
visitInvokeInst(InvokeInst & II)498 void visitInvokeInst (InvokeInst &II) {
499 visitCallSite(&II);
500 visitTerminatorInst(II);
501 }
502 void visitCallSite (CallSite CS);
visitResumeInst(TerminatorInst & I)503 void visitResumeInst (TerminatorInst &I) { /*returns void*/ }
visitUnreachableInst(TerminatorInst & I)504 void visitUnreachableInst(TerminatorInst &I) { /*returns void*/ }
visitFenceInst(FenceInst & I)505 void visitFenceInst (FenceInst &I) { /*returns void*/ }
visitAtomicCmpXchgInst(AtomicCmpXchgInst & I)506 void visitAtomicCmpXchgInst(AtomicCmpXchgInst &I) {
507 markAnythingOverdefined(&I);
508 }
visitAtomicRMWInst(AtomicRMWInst & I)509 void visitAtomicRMWInst (AtomicRMWInst &I) { markOverdefined(&I); }
visitAllocaInst(Instruction & I)510 void visitAllocaInst (Instruction &I) { markOverdefined(&I); }
visitVAArgInst(Instruction & I)511 void visitVAArgInst (Instruction &I) { markAnythingOverdefined(&I); }
512
visitInstruction(Instruction & I)513 void visitInstruction(Instruction &I) {
514 // If a new instruction is added to LLVM that we don't handle.
515 dbgs() << "SCCP: Don't know how to handle: " << I << '\n';
516 markAnythingOverdefined(&I); // Just in case
517 }
518 };
519
520 } // end anonymous namespace
521
522
523 // getFeasibleSuccessors - Return a vector of booleans to indicate which
524 // successors are reachable from a given terminator instruction.
525 //
getFeasibleSuccessors(TerminatorInst & TI,SmallVectorImpl<bool> & Succs)526 void SCCPSolver::getFeasibleSuccessors(TerminatorInst &TI,
527 SmallVectorImpl<bool> &Succs) {
528 Succs.resize(TI.getNumSuccessors());
529 if (BranchInst *BI = dyn_cast<BranchInst>(&TI)) {
530 if (BI->isUnconditional()) {
531 Succs[0] = true;
532 return;
533 }
534
535 LatticeVal BCValue = getValueState(BI->getCondition());
536 ConstantInt *CI = BCValue.getConstantInt();
537 if (!CI) {
538 // Overdefined condition variables, and branches on unfoldable constant
539 // conditions, mean the branch could go either way.
540 if (!BCValue.isUndefined())
541 Succs[0] = Succs[1] = true;
542 return;
543 }
544
545 // Constant condition variables mean the branch can only go a single way.
546 Succs[CI->isZero()] = true;
547 return;
548 }
549
550 // Unwinding instructions successors are always executable.
551 if (TI.isExceptional()) {
552 Succs.assign(TI.getNumSuccessors(), true);
553 return;
554 }
555
556 if (SwitchInst *SI = dyn_cast<SwitchInst>(&TI)) {
557 if (!SI->getNumCases()) {
558 Succs[0] = true;
559 return;
560 }
561 LatticeVal SCValue = getValueState(SI->getCondition());
562 ConstantInt *CI = SCValue.getConstantInt();
563
564 if (!CI) { // Overdefined or undefined condition?
565 // All destinations are executable!
566 if (!SCValue.isUndefined())
567 Succs.assign(TI.getNumSuccessors(), true);
568 return;
569 }
570
571 Succs[SI->findCaseValue(CI).getSuccessorIndex()] = true;
572 return;
573 }
574
575 // TODO: This could be improved if the operand is a [cast of a] BlockAddress.
576 if (isa<IndirectBrInst>(&TI)) {
577 // Just mark all destinations executable!
578 Succs.assign(TI.getNumSuccessors(), true);
579 return;
580 }
581
582 #ifndef NDEBUG
583 dbgs() << "Unknown terminator instruction: " << TI << '\n';
584 #endif
585 llvm_unreachable("SCCP: Don't know how to handle this terminator!");
586 }
587
588
589 // isEdgeFeasible - Return true if the control flow edge from the 'From' basic
590 // block to the 'To' basic block is currently feasible.
591 //
isEdgeFeasible(BasicBlock * From,BasicBlock * To)592 bool SCCPSolver::isEdgeFeasible(BasicBlock *From, BasicBlock *To) {
593 assert(BBExecutable.count(To) && "Dest should always be alive!");
594
595 // Make sure the source basic block is executable!!
596 if (!BBExecutable.count(From)) return false;
597
598 // Check to make sure this edge itself is actually feasible now.
599 TerminatorInst *TI = From->getTerminator();
600 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
601 if (BI->isUnconditional())
602 return true;
603
604 LatticeVal BCValue = getValueState(BI->getCondition());
605
606 // Overdefined condition variables mean the branch could go either way,
607 // undef conditions mean that neither edge is feasible yet.
608 ConstantInt *CI = BCValue.getConstantInt();
609 if (!CI)
610 return !BCValue.isUndefined();
611
612 // Constant condition variables mean the branch can only go a single way.
613 return BI->getSuccessor(CI->isZero()) == To;
614 }
615
616 // Unwinding instructions successors are always executable.
617 if (TI->isExceptional())
618 return true;
619
620 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
621 if (SI->getNumCases() < 1)
622 return true;
623
624 LatticeVal SCValue = getValueState(SI->getCondition());
625 ConstantInt *CI = SCValue.getConstantInt();
626
627 if (!CI)
628 return !SCValue.isUndefined();
629
630 return SI->findCaseValue(CI).getCaseSuccessor() == To;
631 }
632
633 // Just mark all destinations executable!
634 // TODO: This could be improved if the operand is a [cast of a] BlockAddress.
635 if (isa<IndirectBrInst>(TI))
636 return true;
637
638 #ifndef NDEBUG
639 dbgs() << "Unknown terminator instruction: " << *TI << '\n';
640 #endif
641 llvm_unreachable("SCCP: Don't know how to handle this terminator!");
642 }
643
644 // visit Implementations - Something changed in this instruction, either an
645 // operand made a transition, or the instruction is newly executable. Change
646 // the value type of I to reflect these changes if appropriate. This method
647 // makes sure to do the following actions:
648 //
649 // 1. If a phi node merges two constants in, and has conflicting value coming
650 // from different branches, or if the PHI node merges in an overdefined
651 // value, then the PHI node becomes overdefined.
652 // 2. If a phi node merges only constants in, and they all agree on value, the
653 // PHI node becomes a constant value equal to that.
654 // 3. If V <- x (op) y && isConstant(x) && isConstant(y) V = Constant
655 // 4. If V <- x (op) y && (isOverdefined(x) || isOverdefined(y)) V = Overdefined
656 // 5. If V <- MEM or V <- CALL or V <- (unknown) then V = Overdefined
657 // 6. If a conditional branch has a value that is constant, make the selected
658 // destination executable
659 // 7. If a conditional branch has a value that is overdefined, make all
660 // successors executable.
661 //
visitPHINode(PHINode & PN)662 void SCCPSolver::visitPHINode(PHINode &PN) {
663 // If this PN returns a struct, just mark the result overdefined.
664 // TODO: We could do a lot better than this if code actually uses this.
665 if (PN.getType()->isStructTy())
666 return markAnythingOverdefined(&PN);
667
668 if (getValueState(&PN).isOverdefined())
669 return; // Quick exit
670
671 // Super-extra-high-degree PHI nodes are unlikely to ever be marked constant,
672 // and slow us down a lot. Just mark them overdefined.
673 if (PN.getNumIncomingValues() > 64)
674 return markOverdefined(&PN);
675
676 // Look at all of the executable operands of the PHI node. If any of them
677 // are overdefined, the PHI becomes overdefined as well. If they are all
678 // constant, and they agree with each other, the PHI becomes the identical
679 // constant. If they are constant and don't agree, the PHI is overdefined.
680 // If there are no executable operands, the PHI remains undefined.
681 //
682 Constant *OperandVal = nullptr;
683 for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) {
684 LatticeVal IV = getValueState(PN.getIncomingValue(i));
685 if (IV.isUndefined()) continue; // Doesn't influence PHI node.
686
687 if (!isEdgeFeasible(PN.getIncomingBlock(i), PN.getParent()))
688 continue;
689
690 if (IV.isOverdefined()) // PHI node becomes overdefined!
691 return markOverdefined(&PN);
692
693 if (!OperandVal) { // Grab the first value.
694 OperandVal = IV.getConstant();
695 continue;
696 }
697
698 // There is already a reachable operand. If we conflict with it,
699 // then the PHI node becomes overdefined. If we agree with it, we
700 // can continue on.
701
702 // Check to see if there are two different constants merging, if so, the PHI
703 // node is overdefined.
704 if (IV.getConstant() != OperandVal)
705 return markOverdefined(&PN);
706 }
707
708 // If we exited the loop, this means that the PHI node only has constant
709 // arguments that agree with each other(and OperandVal is the constant) or
710 // OperandVal is null because there are no defined incoming arguments. If
711 // this is the case, the PHI remains undefined.
712 //
713 if (OperandVal)
714 markConstant(&PN, OperandVal); // Acquire operand value
715 }
716
visitReturnInst(ReturnInst & I)717 void SCCPSolver::visitReturnInst(ReturnInst &I) {
718 if (I.getNumOperands() == 0) return; // ret void
719
720 Function *F = I.getParent()->getParent();
721 Value *ResultOp = I.getOperand(0);
722
723 // If we are tracking the return value of this function, merge it in.
724 if (!TrackedRetVals.empty() && !ResultOp->getType()->isStructTy()) {
725 DenseMap<Function*, LatticeVal>::iterator TFRVI =
726 TrackedRetVals.find(F);
727 if (TFRVI != TrackedRetVals.end()) {
728 mergeInValue(TFRVI->second, F, getValueState(ResultOp));
729 return;
730 }
731 }
732
733 // Handle functions that return multiple values.
734 if (!TrackedMultipleRetVals.empty()) {
735 if (StructType *STy = dyn_cast<StructType>(ResultOp->getType()))
736 if (MRVFunctionsTracked.count(F))
737 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
738 mergeInValue(TrackedMultipleRetVals[std::make_pair(F, i)], F,
739 getStructValueState(ResultOp, i));
740
741 }
742 }
743
visitTerminatorInst(TerminatorInst & TI)744 void SCCPSolver::visitTerminatorInst(TerminatorInst &TI) {
745 SmallVector<bool, 16> SuccFeasible;
746 getFeasibleSuccessors(TI, SuccFeasible);
747
748 BasicBlock *BB = TI.getParent();
749
750 // Mark all feasible successors executable.
751 for (unsigned i = 0, e = SuccFeasible.size(); i != e; ++i)
752 if (SuccFeasible[i])
753 markEdgeExecutable(BB, TI.getSuccessor(i));
754 }
755
visitCastInst(CastInst & I)756 void SCCPSolver::visitCastInst(CastInst &I) {
757 LatticeVal OpSt = getValueState(I.getOperand(0));
758 if (OpSt.isOverdefined()) // Inherit overdefinedness of operand
759 markOverdefined(&I);
760 else if (OpSt.isConstant()) // Propagate constant value
761 markConstant(&I, ConstantExpr::getCast(I.getOpcode(),
762 OpSt.getConstant(), I.getType()));
763 }
764
765
visitExtractValueInst(ExtractValueInst & EVI)766 void SCCPSolver::visitExtractValueInst(ExtractValueInst &EVI) {
767 // If this returns a struct, mark all elements over defined, we don't track
768 // structs in structs.
769 if (EVI.getType()->isStructTy())
770 return markAnythingOverdefined(&EVI);
771
772 // If this is extracting from more than one level of struct, we don't know.
773 if (EVI.getNumIndices() != 1)
774 return markOverdefined(&EVI);
775
776 Value *AggVal = EVI.getAggregateOperand();
777 if (AggVal->getType()->isStructTy()) {
778 unsigned i = *EVI.idx_begin();
779 LatticeVal EltVal = getStructValueState(AggVal, i);
780 mergeInValue(getValueState(&EVI), &EVI, EltVal);
781 } else {
782 // Otherwise, must be extracting from an array.
783 return markOverdefined(&EVI);
784 }
785 }
786
visitInsertValueInst(InsertValueInst & IVI)787 void SCCPSolver::visitInsertValueInst(InsertValueInst &IVI) {
788 StructType *STy = dyn_cast<StructType>(IVI.getType());
789 if (!STy)
790 return markOverdefined(&IVI);
791
792 // If this has more than one index, we can't handle it, drive all results to
793 // undef.
794 if (IVI.getNumIndices() != 1)
795 return markAnythingOverdefined(&IVI);
796
797 Value *Aggr = IVI.getAggregateOperand();
798 unsigned Idx = *IVI.idx_begin();
799
800 // Compute the result based on what we're inserting.
801 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
802 // This passes through all values that aren't the inserted element.
803 if (i != Idx) {
804 LatticeVal EltVal = getStructValueState(Aggr, i);
805 mergeInValue(getStructValueState(&IVI, i), &IVI, EltVal);
806 continue;
807 }
808
809 Value *Val = IVI.getInsertedValueOperand();
810 if (Val->getType()->isStructTy())
811 // We don't track structs in structs.
812 markOverdefined(getStructValueState(&IVI, i), &IVI);
813 else {
814 LatticeVal InVal = getValueState(Val);
815 mergeInValue(getStructValueState(&IVI, i), &IVI, InVal);
816 }
817 }
818 }
819
visitSelectInst(SelectInst & I)820 void SCCPSolver::visitSelectInst(SelectInst &I) {
821 // If this select returns a struct, just mark the result overdefined.
822 // TODO: We could do a lot better than this if code actually uses this.
823 if (I.getType()->isStructTy())
824 return markAnythingOverdefined(&I);
825
826 LatticeVal CondValue = getValueState(I.getCondition());
827 if (CondValue.isUndefined())
828 return;
829
830 if (ConstantInt *CondCB = CondValue.getConstantInt()) {
831 Value *OpVal = CondCB->isZero() ? I.getFalseValue() : I.getTrueValue();
832 mergeInValue(&I, getValueState(OpVal));
833 return;
834 }
835
836 // Otherwise, the condition is overdefined or a constant we can't evaluate.
837 // See if we can produce something better than overdefined based on the T/F
838 // value.
839 LatticeVal TVal = getValueState(I.getTrueValue());
840 LatticeVal FVal = getValueState(I.getFalseValue());
841
842 // select ?, C, C -> C.
843 if (TVal.isConstant() && FVal.isConstant() &&
844 TVal.getConstant() == FVal.getConstant())
845 return markConstant(&I, FVal.getConstant());
846
847 if (TVal.isUndefined()) // select ?, undef, X -> X.
848 return mergeInValue(&I, FVal);
849 if (FVal.isUndefined()) // select ?, X, undef -> X.
850 return mergeInValue(&I, TVal);
851 markOverdefined(&I);
852 }
853
854 // Handle Binary Operators.
visitBinaryOperator(Instruction & I)855 void SCCPSolver::visitBinaryOperator(Instruction &I) {
856 LatticeVal V1State = getValueState(I.getOperand(0));
857 LatticeVal V2State = getValueState(I.getOperand(1));
858
859 LatticeVal &IV = ValueState[&I];
860 if (IV.isOverdefined()) return;
861
862 if (V1State.isConstant() && V2State.isConstant())
863 return markConstant(IV, &I,
864 ConstantExpr::get(I.getOpcode(), V1State.getConstant(),
865 V2State.getConstant()));
866
867 // If something is undef, wait for it to resolve.
868 if (!V1State.isOverdefined() && !V2State.isOverdefined())
869 return;
870
871 // Otherwise, one of our operands is overdefined. Try to produce something
872 // better than overdefined with some tricks.
873
874 // If this is an AND or OR with 0 or -1, it doesn't matter that the other
875 // operand is overdefined.
876 if (I.getOpcode() == Instruction::And || I.getOpcode() == Instruction::Or) {
877 LatticeVal *NonOverdefVal = nullptr;
878 if (!V1State.isOverdefined())
879 NonOverdefVal = &V1State;
880 else if (!V2State.isOverdefined())
881 NonOverdefVal = &V2State;
882
883 if (NonOverdefVal) {
884 if (NonOverdefVal->isUndefined()) {
885 // Could annihilate value.
886 if (I.getOpcode() == Instruction::And)
887 markConstant(IV, &I, Constant::getNullValue(I.getType()));
888 else if (VectorType *PT = dyn_cast<VectorType>(I.getType()))
889 markConstant(IV, &I, Constant::getAllOnesValue(PT));
890 else
891 markConstant(IV, &I,
892 Constant::getAllOnesValue(I.getType()));
893 return;
894 }
895
896 if (I.getOpcode() == Instruction::And) {
897 // X and 0 = 0
898 if (NonOverdefVal->getConstant()->isNullValue())
899 return markConstant(IV, &I, NonOverdefVal->getConstant());
900 } else {
901 if (ConstantInt *CI = NonOverdefVal->getConstantInt())
902 if (CI->isAllOnesValue()) // X or -1 = -1
903 return markConstant(IV, &I, NonOverdefVal->getConstant());
904 }
905 }
906 }
907
908
909 markOverdefined(&I);
910 }
911
912 // Handle ICmpInst instruction.
visitCmpInst(CmpInst & I)913 void SCCPSolver::visitCmpInst(CmpInst &I) {
914 LatticeVal V1State = getValueState(I.getOperand(0));
915 LatticeVal V2State = getValueState(I.getOperand(1));
916
917 LatticeVal &IV = ValueState[&I];
918 if (IV.isOverdefined()) return;
919
920 if (V1State.isConstant() && V2State.isConstant())
921 return markConstant(IV, &I, ConstantExpr::getCompare(I.getPredicate(),
922 V1State.getConstant(),
923 V2State.getConstant()));
924
925 // If operands are still undefined, wait for it to resolve.
926 if (!V1State.isOverdefined() && !V2State.isOverdefined())
927 return;
928
929 markOverdefined(&I);
930 }
931
visitExtractElementInst(ExtractElementInst & I)932 void SCCPSolver::visitExtractElementInst(ExtractElementInst &I) {
933 // TODO : SCCP does not handle vectors properly.
934 return markOverdefined(&I);
935
936 #if 0
937 LatticeVal &ValState = getValueState(I.getOperand(0));
938 LatticeVal &IdxState = getValueState(I.getOperand(1));
939
940 if (ValState.isOverdefined() || IdxState.isOverdefined())
941 markOverdefined(&I);
942 else if(ValState.isConstant() && IdxState.isConstant())
943 markConstant(&I, ConstantExpr::getExtractElement(ValState.getConstant(),
944 IdxState.getConstant()));
945 #endif
946 }
947
visitInsertElementInst(InsertElementInst & I)948 void SCCPSolver::visitInsertElementInst(InsertElementInst &I) {
949 // TODO : SCCP does not handle vectors properly.
950 return markOverdefined(&I);
951 #if 0
952 LatticeVal &ValState = getValueState(I.getOperand(0));
953 LatticeVal &EltState = getValueState(I.getOperand(1));
954 LatticeVal &IdxState = getValueState(I.getOperand(2));
955
956 if (ValState.isOverdefined() || EltState.isOverdefined() ||
957 IdxState.isOverdefined())
958 markOverdefined(&I);
959 else if(ValState.isConstant() && EltState.isConstant() &&
960 IdxState.isConstant())
961 markConstant(&I, ConstantExpr::getInsertElement(ValState.getConstant(),
962 EltState.getConstant(),
963 IdxState.getConstant()));
964 else if (ValState.isUndefined() && EltState.isConstant() &&
965 IdxState.isConstant())
966 markConstant(&I,ConstantExpr::getInsertElement(UndefValue::get(I.getType()),
967 EltState.getConstant(),
968 IdxState.getConstant()));
969 #endif
970 }
971
visitShuffleVectorInst(ShuffleVectorInst & I)972 void SCCPSolver::visitShuffleVectorInst(ShuffleVectorInst &I) {
973 // TODO : SCCP does not handle vectors properly.
974 return markOverdefined(&I);
975 #if 0
976 LatticeVal &V1State = getValueState(I.getOperand(0));
977 LatticeVal &V2State = getValueState(I.getOperand(1));
978 LatticeVal &MaskState = getValueState(I.getOperand(2));
979
980 if (MaskState.isUndefined() ||
981 (V1State.isUndefined() && V2State.isUndefined()))
982 return; // Undefined output if mask or both inputs undefined.
983
984 if (V1State.isOverdefined() || V2State.isOverdefined() ||
985 MaskState.isOverdefined()) {
986 markOverdefined(&I);
987 } else {
988 // A mix of constant/undef inputs.
989 Constant *V1 = V1State.isConstant() ?
990 V1State.getConstant() : UndefValue::get(I.getType());
991 Constant *V2 = V2State.isConstant() ?
992 V2State.getConstant() : UndefValue::get(I.getType());
993 Constant *Mask = MaskState.isConstant() ?
994 MaskState.getConstant() : UndefValue::get(I.getOperand(2)->getType());
995 markConstant(&I, ConstantExpr::getShuffleVector(V1, V2, Mask));
996 }
997 #endif
998 }
999
1000 // Handle getelementptr instructions. If all operands are constants then we
1001 // can turn this into a getelementptr ConstantExpr.
1002 //
visitGetElementPtrInst(GetElementPtrInst & I)1003 void SCCPSolver::visitGetElementPtrInst(GetElementPtrInst &I) {
1004 if (ValueState[&I].isOverdefined()) return;
1005
1006 SmallVector<Constant*, 8> Operands;
1007 Operands.reserve(I.getNumOperands());
1008
1009 for (unsigned i = 0, e = I.getNumOperands(); i != e; ++i) {
1010 LatticeVal State = getValueState(I.getOperand(i));
1011 if (State.isUndefined())
1012 return; // Operands are not resolved yet.
1013
1014 if (State.isOverdefined())
1015 return markOverdefined(&I);
1016
1017 assert(State.isConstant() && "Unknown state!");
1018 Operands.push_back(State.getConstant());
1019 }
1020
1021 Constant *Ptr = Operands[0];
1022 auto Indices = makeArrayRef(Operands.begin() + 1, Operands.end());
1023 markConstant(&I, ConstantExpr::getGetElementPtr(I.getSourceElementType(), Ptr,
1024 Indices));
1025 }
1026
visitStoreInst(StoreInst & SI)1027 void SCCPSolver::visitStoreInst(StoreInst &SI) {
1028 // If this store is of a struct, ignore it.
1029 if (SI.getOperand(0)->getType()->isStructTy())
1030 return;
1031
1032 if (TrackedGlobals.empty() || !isa<GlobalVariable>(SI.getOperand(1)))
1033 return;
1034
1035 GlobalVariable *GV = cast<GlobalVariable>(SI.getOperand(1));
1036 DenseMap<GlobalVariable*, LatticeVal>::iterator I = TrackedGlobals.find(GV);
1037 if (I == TrackedGlobals.end() || I->second.isOverdefined()) return;
1038
1039 // Get the value we are storing into the global, then merge it.
1040 mergeInValue(I->second, GV, getValueState(SI.getOperand(0)));
1041 if (I->second.isOverdefined())
1042 TrackedGlobals.erase(I); // No need to keep tracking this!
1043 }
1044
1045
1046 // Handle load instructions. If the operand is a constant pointer to a constant
1047 // global, we can replace the load with the loaded constant value!
visitLoadInst(LoadInst & I)1048 void SCCPSolver::visitLoadInst(LoadInst &I) {
1049 // If this load is of a struct, just mark the result overdefined.
1050 if (I.getType()->isStructTy())
1051 return markAnythingOverdefined(&I);
1052
1053 LatticeVal PtrVal = getValueState(I.getOperand(0));
1054 if (PtrVal.isUndefined()) return; // The pointer is not resolved yet!
1055
1056 LatticeVal &IV = ValueState[&I];
1057 if (IV.isOverdefined()) return;
1058
1059 if (!PtrVal.isConstant() || I.isVolatile())
1060 return markOverdefined(IV, &I);
1061
1062 Constant *Ptr = PtrVal.getConstant();
1063
1064 // load null -> null
1065 if (isa<ConstantPointerNull>(Ptr) && I.getPointerAddressSpace() == 0)
1066 return markConstant(IV, &I, UndefValue::get(I.getType()));
1067
1068 // Transform load (constant global) into the value loaded.
1069 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Ptr)) {
1070 if (!TrackedGlobals.empty()) {
1071 // If we are tracking this global, merge in the known value for it.
1072 DenseMap<GlobalVariable*, LatticeVal>::iterator It =
1073 TrackedGlobals.find(GV);
1074 if (It != TrackedGlobals.end()) {
1075 mergeInValue(IV, &I, It->second);
1076 return;
1077 }
1078 }
1079 }
1080
1081 // Transform load from a constant into a constant if possible.
1082 if (Constant *C = ConstantFoldLoadFromConstPtr(Ptr, DL))
1083 return markConstant(IV, &I, C);
1084
1085 // Otherwise we cannot say for certain what value this load will produce.
1086 // Bail out.
1087 markOverdefined(IV, &I);
1088 }
1089
visitCallSite(CallSite CS)1090 void SCCPSolver::visitCallSite(CallSite CS) {
1091 Function *F = CS.getCalledFunction();
1092 Instruction *I = CS.getInstruction();
1093
1094 // The common case is that we aren't tracking the callee, either because we
1095 // are not doing interprocedural analysis or the callee is indirect, or is
1096 // external. Handle these cases first.
1097 if (!F || F->isDeclaration()) {
1098 CallOverdefined:
1099 // Void return and not tracking callee, just bail.
1100 if (I->getType()->isVoidTy()) return;
1101
1102 // Otherwise, if we have a single return value case, and if the function is
1103 // a declaration, maybe we can constant fold it.
1104 if (F && F->isDeclaration() && !I->getType()->isStructTy() &&
1105 canConstantFoldCallTo(F)) {
1106
1107 SmallVector<Constant*, 8> Operands;
1108 for (CallSite::arg_iterator AI = CS.arg_begin(), E = CS.arg_end();
1109 AI != E; ++AI) {
1110 LatticeVal State = getValueState(*AI);
1111
1112 if (State.isUndefined())
1113 return; // Operands are not resolved yet.
1114 if (State.isOverdefined())
1115 return markOverdefined(I);
1116 assert(State.isConstant() && "Unknown state!");
1117 Operands.push_back(State.getConstant());
1118 }
1119
1120 if (getValueState(I).isOverdefined())
1121 return;
1122
1123 // If we can constant fold this, mark the result of the call as a
1124 // constant.
1125 if (Constant *C = ConstantFoldCall(F, Operands, TLI))
1126 return markConstant(I, C);
1127 }
1128
1129 // Otherwise, we don't know anything about this call, mark it overdefined.
1130 return markAnythingOverdefined(I);
1131 }
1132
1133 // If this is a local function that doesn't have its address taken, mark its
1134 // entry block executable and merge in the actual arguments to the call into
1135 // the formal arguments of the function.
1136 if (!TrackingIncomingArguments.empty() && TrackingIncomingArguments.count(F)){
1137 MarkBlockExecutable(&F->front());
1138
1139 // Propagate information from this call site into the callee.
1140 CallSite::arg_iterator CAI = CS.arg_begin();
1141 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
1142 AI != E; ++AI, ++CAI) {
1143 // If this argument is byval, and if the function is not readonly, there
1144 // will be an implicit copy formed of the input aggregate.
1145 if (AI->hasByValAttr() && !F->onlyReadsMemory()) {
1146 markOverdefined(&*AI);
1147 continue;
1148 }
1149
1150 if (StructType *STy = dyn_cast<StructType>(AI->getType())) {
1151 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
1152 LatticeVal CallArg = getStructValueState(*CAI, i);
1153 mergeInValue(getStructValueState(&*AI, i), &*AI, CallArg);
1154 }
1155 } else {
1156 mergeInValue(&*AI, getValueState(*CAI));
1157 }
1158 }
1159 }
1160
1161 // If this is a single/zero retval case, see if we're tracking the function.
1162 if (StructType *STy = dyn_cast<StructType>(F->getReturnType())) {
1163 if (!MRVFunctionsTracked.count(F))
1164 goto CallOverdefined; // Not tracking this callee.
1165
1166 // If we are tracking this callee, propagate the result of the function
1167 // into this call site.
1168 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
1169 mergeInValue(getStructValueState(I, i), I,
1170 TrackedMultipleRetVals[std::make_pair(F, i)]);
1171 } else {
1172 DenseMap<Function*, LatticeVal>::iterator TFRVI = TrackedRetVals.find(F);
1173 if (TFRVI == TrackedRetVals.end())
1174 goto CallOverdefined; // Not tracking this callee.
1175
1176 // If so, propagate the return value of the callee into this call result.
1177 mergeInValue(I, TFRVI->second);
1178 }
1179 }
1180
Solve()1181 void SCCPSolver::Solve() {
1182 // Process the work lists until they are empty!
1183 while (!BBWorkList.empty() || !InstWorkList.empty() ||
1184 !OverdefinedInstWorkList.empty()) {
1185 // Process the overdefined instruction's work list first, which drives other
1186 // things to overdefined more quickly.
1187 while (!OverdefinedInstWorkList.empty()) {
1188 Value *I = OverdefinedInstWorkList.pop_back_val();
1189
1190 DEBUG(dbgs() << "\nPopped off OI-WL: " << *I << '\n');
1191
1192 // "I" got into the work list because it either made the transition from
1193 // bottom to constant, or to overdefined.
1194 //
1195 // Anything on this worklist that is overdefined need not be visited
1196 // since all of its users will have already been marked as overdefined
1197 // Update all of the users of this instruction's value.
1198 //
1199 for (User *U : I->users())
1200 if (Instruction *UI = dyn_cast<Instruction>(U))
1201 OperandChangedState(UI);
1202 }
1203
1204 // Process the instruction work list.
1205 while (!InstWorkList.empty()) {
1206 Value *I = InstWorkList.pop_back_val();
1207
1208 DEBUG(dbgs() << "\nPopped off I-WL: " << *I << '\n');
1209
1210 // "I" got into the work list because it made the transition from undef to
1211 // constant.
1212 //
1213 // Anything on this worklist that is overdefined need not be visited
1214 // since all of its users will have already been marked as overdefined.
1215 // Update all of the users of this instruction's value.
1216 //
1217 if (I->getType()->isStructTy() || !getValueState(I).isOverdefined())
1218 for (User *U : I->users())
1219 if (Instruction *UI = dyn_cast<Instruction>(U))
1220 OperandChangedState(UI);
1221 }
1222
1223 // Process the basic block work list.
1224 while (!BBWorkList.empty()) {
1225 BasicBlock *BB = BBWorkList.back();
1226 BBWorkList.pop_back();
1227
1228 DEBUG(dbgs() << "\nPopped off BBWL: " << *BB << '\n');
1229
1230 // Notify all instructions in this basic block that they are newly
1231 // executable.
1232 visit(BB);
1233 }
1234 }
1235 }
1236
1237 /// ResolvedUndefsIn - While solving the dataflow for a function, we assume
1238 /// that branches on undef values cannot reach any of their successors.
1239 /// However, this is not a safe assumption. After we solve dataflow, this
1240 /// method should be use to handle this. If this returns true, the solver
1241 /// should be rerun.
1242 ///
1243 /// This method handles this by finding an unresolved branch and marking it one
1244 /// of the edges from the block as being feasible, even though the condition
1245 /// doesn't say it would otherwise be. This allows SCCP to find the rest of the
1246 /// CFG and only slightly pessimizes the analysis results (by marking one,
1247 /// potentially infeasible, edge feasible). This cannot usefully modify the
1248 /// constraints on the condition of the branch, as that would impact other users
1249 /// of the value.
1250 ///
1251 /// This scan also checks for values that use undefs, whose results are actually
1252 /// defined. For example, 'zext i8 undef to i32' should produce all zeros
1253 /// conservatively, as "(zext i8 X -> i32) & 0xFF00" must always return zero,
1254 /// even if X isn't defined.
ResolvedUndefsIn(Function & F)1255 bool SCCPSolver::ResolvedUndefsIn(Function &F) {
1256 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
1257 if (!BBExecutable.count(&*BB))
1258 continue;
1259
1260 for (Instruction &I : *BB) {
1261 // Look for instructions which produce undef values.
1262 if (I.getType()->isVoidTy()) continue;
1263
1264 if (StructType *STy = dyn_cast<StructType>(I.getType())) {
1265 // Only a few things that can be structs matter for undef.
1266
1267 // Tracked calls must never be marked overdefined in ResolvedUndefsIn.
1268 if (CallSite CS = CallSite(&I))
1269 if (Function *F = CS.getCalledFunction())
1270 if (MRVFunctionsTracked.count(F))
1271 continue;
1272
1273 // extractvalue and insertvalue don't need to be marked; they are
1274 // tracked as precisely as their operands.
1275 if (isa<ExtractValueInst>(I) || isa<InsertValueInst>(I))
1276 continue;
1277
1278 // Send the results of everything else to overdefined. We could be
1279 // more precise than this but it isn't worth bothering.
1280 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
1281 LatticeVal &LV = getStructValueState(&I, i);
1282 if (LV.isUndefined())
1283 markOverdefined(LV, &I);
1284 }
1285 continue;
1286 }
1287
1288 LatticeVal &LV = getValueState(&I);
1289 if (!LV.isUndefined()) continue;
1290
1291 // extractvalue is safe; check here because the argument is a struct.
1292 if (isa<ExtractValueInst>(I))
1293 continue;
1294
1295 // Compute the operand LatticeVals, for convenience below.
1296 // Anything taking a struct is conservatively assumed to require
1297 // overdefined markings.
1298 if (I.getOperand(0)->getType()->isStructTy()) {
1299 markOverdefined(&I);
1300 return true;
1301 }
1302 LatticeVal Op0LV = getValueState(I.getOperand(0));
1303 LatticeVal Op1LV;
1304 if (I.getNumOperands() == 2) {
1305 if (I.getOperand(1)->getType()->isStructTy()) {
1306 markOverdefined(&I);
1307 return true;
1308 }
1309
1310 Op1LV = getValueState(I.getOperand(1));
1311 }
1312 // If this is an instructions whose result is defined even if the input is
1313 // not fully defined, propagate the information.
1314 Type *ITy = I.getType();
1315 switch (I.getOpcode()) {
1316 case Instruction::Add:
1317 case Instruction::Sub:
1318 case Instruction::Trunc:
1319 case Instruction::FPTrunc:
1320 case Instruction::BitCast:
1321 break; // Any undef -> undef
1322 case Instruction::FSub:
1323 case Instruction::FAdd:
1324 case Instruction::FMul:
1325 case Instruction::FDiv:
1326 case Instruction::FRem:
1327 // Floating-point binary operation: be conservative.
1328 if (Op0LV.isUndefined() && Op1LV.isUndefined())
1329 markForcedConstant(&I, Constant::getNullValue(ITy));
1330 else
1331 markOverdefined(&I);
1332 return true;
1333 case Instruction::ZExt:
1334 case Instruction::SExt:
1335 case Instruction::FPToUI:
1336 case Instruction::FPToSI:
1337 case Instruction::FPExt:
1338 case Instruction::PtrToInt:
1339 case Instruction::IntToPtr:
1340 case Instruction::SIToFP:
1341 case Instruction::UIToFP:
1342 // undef -> 0; some outputs are impossible
1343 markForcedConstant(&I, Constant::getNullValue(ITy));
1344 return true;
1345 case Instruction::Mul:
1346 case Instruction::And:
1347 // Both operands undef -> undef
1348 if (Op0LV.isUndefined() && Op1LV.isUndefined())
1349 break;
1350 // undef * X -> 0. X could be zero.
1351 // undef & X -> 0. X could be zero.
1352 markForcedConstant(&I, Constant::getNullValue(ITy));
1353 return true;
1354
1355 case Instruction::Or:
1356 // Both operands undef -> undef
1357 if (Op0LV.isUndefined() && Op1LV.isUndefined())
1358 break;
1359 // undef | X -> -1. X could be -1.
1360 markForcedConstant(&I, Constant::getAllOnesValue(ITy));
1361 return true;
1362
1363 case Instruction::Xor:
1364 // undef ^ undef -> 0; strictly speaking, this is not strictly
1365 // necessary, but we try to be nice to people who expect this
1366 // behavior in simple cases
1367 if (Op0LV.isUndefined() && Op1LV.isUndefined()) {
1368 markForcedConstant(&I, Constant::getNullValue(ITy));
1369 return true;
1370 }
1371 // undef ^ X -> undef
1372 break;
1373
1374 case Instruction::SDiv:
1375 case Instruction::UDiv:
1376 case Instruction::SRem:
1377 case Instruction::URem:
1378 // X / undef -> undef. No change.
1379 // X % undef -> undef. No change.
1380 if (Op1LV.isUndefined()) break;
1381
1382 // undef / X -> 0. X could be maxint.
1383 // undef % X -> 0. X could be 1.
1384 markForcedConstant(&I, Constant::getNullValue(ITy));
1385 return true;
1386
1387 case Instruction::AShr:
1388 // X >>a undef -> undef.
1389 if (Op1LV.isUndefined()) break;
1390
1391 // undef >>a X -> all ones
1392 markForcedConstant(&I, Constant::getAllOnesValue(ITy));
1393 return true;
1394 case Instruction::LShr:
1395 case Instruction::Shl:
1396 // X << undef -> undef.
1397 // X >> undef -> undef.
1398 if (Op1LV.isUndefined()) break;
1399
1400 // undef << X -> 0
1401 // undef >> X -> 0
1402 markForcedConstant(&I, Constant::getNullValue(ITy));
1403 return true;
1404 case Instruction::Select:
1405 Op1LV = getValueState(I.getOperand(1));
1406 // undef ? X : Y -> X or Y. There could be commonality between X/Y.
1407 if (Op0LV.isUndefined()) {
1408 if (!Op1LV.isConstant()) // Pick the constant one if there is any.
1409 Op1LV = getValueState(I.getOperand(2));
1410 } else if (Op1LV.isUndefined()) {
1411 // c ? undef : undef -> undef. No change.
1412 Op1LV = getValueState(I.getOperand(2));
1413 if (Op1LV.isUndefined())
1414 break;
1415 // Otherwise, c ? undef : x -> x.
1416 } else {
1417 // Leave Op1LV as Operand(1)'s LatticeValue.
1418 }
1419
1420 if (Op1LV.isConstant())
1421 markForcedConstant(&I, Op1LV.getConstant());
1422 else
1423 markOverdefined(&I);
1424 return true;
1425 case Instruction::Load:
1426 // A load here means one of two things: a load of undef from a global,
1427 // a load from an unknown pointer. Either way, having it return undef
1428 // is okay.
1429 break;
1430 case Instruction::ICmp:
1431 // X == undef -> undef. Other comparisons get more complicated.
1432 if (cast<ICmpInst>(&I)->isEquality())
1433 break;
1434 markOverdefined(&I);
1435 return true;
1436 case Instruction::Call:
1437 case Instruction::Invoke: {
1438 // There are two reasons a call can have an undef result
1439 // 1. It could be tracked.
1440 // 2. It could be constant-foldable.
1441 // Because of the way we solve return values, tracked calls must
1442 // never be marked overdefined in ResolvedUndefsIn.
1443 if (Function *F = CallSite(&I).getCalledFunction())
1444 if (TrackedRetVals.count(F))
1445 break;
1446
1447 // If the call is constant-foldable, we mark it overdefined because
1448 // we do not know what return values are valid.
1449 markOverdefined(&I);
1450 return true;
1451 }
1452 default:
1453 // If we don't know what should happen here, conservatively mark it
1454 // overdefined.
1455 markOverdefined(&I);
1456 return true;
1457 }
1458 }
1459
1460 // Check to see if we have a branch or switch on an undefined value. If so
1461 // we force the branch to go one way or the other to make the successor
1462 // values live. It doesn't really matter which way we force it.
1463 TerminatorInst *TI = BB->getTerminator();
1464 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
1465 if (!BI->isConditional()) continue;
1466 if (!getValueState(BI->getCondition()).isUndefined())
1467 continue;
1468
1469 // If the input to SCCP is actually branch on undef, fix the undef to
1470 // false.
1471 if (isa<UndefValue>(BI->getCondition())) {
1472 BI->setCondition(ConstantInt::getFalse(BI->getContext()));
1473 markEdgeExecutable(&*BB, TI->getSuccessor(1));
1474 return true;
1475 }
1476
1477 // Otherwise, it is a branch on a symbolic value which is currently
1478 // considered to be undef. Handle this by forcing the input value to the
1479 // branch to false.
1480 markForcedConstant(BI->getCondition(),
1481 ConstantInt::getFalse(TI->getContext()));
1482 return true;
1483 }
1484
1485 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
1486 if (!SI->getNumCases())
1487 continue;
1488 if (!getValueState(SI->getCondition()).isUndefined())
1489 continue;
1490
1491 // If the input to SCCP is actually switch on undef, fix the undef to
1492 // the first constant.
1493 if (isa<UndefValue>(SI->getCondition())) {
1494 SI->setCondition(SI->case_begin().getCaseValue());
1495 markEdgeExecutable(&*BB, SI->case_begin().getCaseSuccessor());
1496 return true;
1497 }
1498
1499 markForcedConstant(SI->getCondition(), SI->case_begin().getCaseValue());
1500 return true;
1501 }
1502 }
1503
1504 return false;
1505 }
1506
1507
1508 namespace {
1509 //===--------------------------------------------------------------------===//
1510 //
1511 /// SCCP Class - This class uses the SCCPSolver to implement a per-function
1512 /// Sparse Conditional Constant Propagator.
1513 ///
1514 struct SCCP : public FunctionPass {
getAnalysisUsage__anon10360b9e0311::SCCP1515 void getAnalysisUsage(AnalysisUsage &AU) const override {
1516 AU.addRequired<TargetLibraryInfoWrapperPass>();
1517 AU.addPreserved<GlobalsAAWrapperPass>();
1518 }
1519 static char ID; // Pass identification, replacement for typeid
SCCP__anon10360b9e0311::SCCP1520 SCCP() : FunctionPass(ID) {
1521 initializeSCCPPass(*PassRegistry::getPassRegistry());
1522 }
1523
1524 // runOnFunction - Run the Sparse Conditional Constant Propagation
1525 // algorithm, and return true if the function was modified.
1526 //
1527 bool runOnFunction(Function &F) override;
1528 };
1529 } // end anonymous namespace
1530
1531 char SCCP::ID = 0;
1532 INITIALIZE_PASS(SCCP, "sccp",
1533 "Sparse Conditional Constant Propagation", false, false)
1534
1535 // createSCCPPass - This is the public interface to this file.
createSCCPPass()1536 FunctionPass *llvm::createSCCPPass() {
1537 return new SCCP();
1538 }
1539
DeleteInstructionInBlock(BasicBlock * BB)1540 static void DeleteInstructionInBlock(BasicBlock *BB) {
1541 DEBUG(dbgs() << " BasicBlock Dead:" << *BB);
1542 ++NumDeadBlocks;
1543
1544 // Check to see if there are non-terminating instructions to delete.
1545 if (isa<TerminatorInst>(BB->begin()))
1546 return;
1547
1548 // Delete the instructions backwards, as it has a reduced likelihood of having
1549 // to update as many def-use and use-def chains.
1550 Instruction *EndInst = BB->getTerminator(); // Last not to be deleted.
1551 while (EndInst != BB->begin()) {
1552 // Delete the next to last instruction.
1553 Instruction *Inst = &*--EndInst->getIterator();
1554 if (!Inst->use_empty())
1555 Inst->replaceAllUsesWith(UndefValue::get(Inst->getType()));
1556 if (Inst->isEHPad()) {
1557 EndInst = Inst;
1558 continue;
1559 }
1560 BB->getInstList().erase(Inst);
1561 ++NumInstRemoved;
1562 }
1563 }
1564
1565 // runOnFunction() - Run the Sparse Conditional Constant Propagation algorithm,
1566 // and return true if the function was modified.
1567 //
runOnFunction(Function & F)1568 bool SCCP::runOnFunction(Function &F) {
1569 if (skipOptnoneFunction(F))
1570 return false;
1571
1572 DEBUG(dbgs() << "SCCP on function '" << F.getName() << "'\n");
1573 const DataLayout &DL = F.getParent()->getDataLayout();
1574 const TargetLibraryInfo *TLI =
1575 &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
1576 SCCPSolver Solver(DL, TLI);
1577
1578 // Mark the first block of the function as being executable.
1579 Solver.MarkBlockExecutable(&F.front());
1580
1581 // Mark all arguments to the function as being overdefined.
1582 for (Argument &AI : F.args())
1583 Solver.markAnythingOverdefined(&AI);
1584
1585 // Solve for constants.
1586 bool ResolvedUndefs = true;
1587 while (ResolvedUndefs) {
1588 Solver.Solve();
1589 DEBUG(dbgs() << "RESOLVING UNDEFs\n");
1590 ResolvedUndefs = Solver.ResolvedUndefsIn(F);
1591 }
1592
1593 bool MadeChanges = false;
1594
1595 // If we decided that there are basic blocks that are dead in this function,
1596 // delete their contents now. Note that we cannot actually delete the blocks,
1597 // as we cannot modify the CFG of the function.
1598
1599 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
1600 if (!Solver.isBlockExecutable(&*BB)) {
1601 DeleteInstructionInBlock(&*BB);
1602 MadeChanges = true;
1603 continue;
1604 }
1605
1606 // Iterate over all of the instructions in a function, replacing them with
1607 // constants if we have found them to be of constant values.
1608 //
1609 for (BasicBlock::iterator BI = BB->begin(), E = BB->end(); BI != E; ) {
1610 Instruction *Inst = &*BI++;
1611 if (Inst->getType()->isVoidTy() || isa<TerminatorInst>(Inst))
1612 continue;
1613
1614 // TODO: Reconstruct structs from their elements.
1615 if (Inst->getType()->isStructTy())
1616 continue;
1617
1618 LatticeVal IV = Solver.getLatticeValueFor(Inst);
1619 if (IV.isOverdefined())
1620 continue;
1621
1622 Constant *Const = IV.isConstant()
1623 ? IV.getConstant() : UndefValue::get(Inst->getType());
1624 DEBUG(dbgs() << " Constant: " << *Const << " = " << *Inst << '\n');
1625
1626 // Replaces all of the uses of a variable with uses of the constant.
1627 Inst->replaceAllUsesWith(Const);
1628
1629 // Delete the instruction.
1630 Inst->eraseFromParent();
1631
1632 // Hey, we just changed something!
1633 MadeChanges = true;
1634 ++NumInstRemoved;
1635 }
1636 }
1637
1638 return MadeChanges;
1639 }
1640
1641 namespace {
1642 //===--------------------------------------------------------------------===//
1643 //
1644 /// IPSCCP Class - This class implements interprocedural Sparse Conditional
1645 /// Constant Propagation.
1646 ///
1647 struct IPSCCP : public ModulePass {
getAnalysisUsage__anon10360b9e0411::IPSCCP1648 void getAnalysisUsage(AnalysisUsage &AU) const override {
1649 AU.addRequired<TargetLibraryInfoWrapperPass>();
1650 }
1651 static char ID;
IPSCCP__anon10360b9e0411::IPSCCP1652 IPSCCP() : ModulePass(ID) {
1653 initializeIPSCCPPass(*PassRegistry::getPassRegistry());
1654 }
1655 bool runOnModule(Module &M) override;
1656 };
1657 } // end anonymous namespace
1658
1659 char IPSCCP::ID = 0;
1660 INITIALIZE_PASS_BEGIN(IPSCCP, "ipsccp",
1661 "Interprocedural Sparse Conditional Constant Propagation",
1662 false, false)
INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)1663 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
1664 INITIALIZE_PASS_END(IPSCCP, "ipsccp",
1665 "Interprocedural Sparse Conditional Constant Propagation",
1666 false, false)
1667
1668 // createIPSCCPPass - This is the public interface to this file.
1669 ModulePass *llvm::createIPSCCPPass() {
1670 return new IPSCCP();
1671 }
1672
1673
AddressIsTaken(const GlobalValue * GV)1674 static bool AddressIsTaken(const GlobalValue *GV) {
1675 // Delete any dead constantexpr klingons.
1676 GV->removeDeadConstantUsers();
1677
1678 for (const Use &U : GV->uses()) {
1679 const User *UR = U.getUser();
1680 if (const StoreInst *SI = dyn_cast<StoreInst>(UR)) {
1681 if (SI->getOperand(0) == GV || SI->isVolatile())
1682 return true; // Storing addr of GV.
1683 } else if (isa<InvokeInst>(UR) || isa<CallInst>(UR)) {
1684 // Make sure we are calling the function, not passing the address.
1685 ImmutableCallSite CS(cast<Instruction>(UR));
1686 if (!CS.isCallee(&U))
1687 return true;
1688 } else if (const LoadInst *LI = dyn_cast<LoadInst>(UR)) {
1689 if (LI->isVolatile())
1690 return true;
1691 } else if (isa<BlockAddress>(UR)) {
1692 // blockaddress doesn't take the address of the function, it takes addr
1693 // of label.
1694 } else {
1695 return true;
1696 }
1697 }
1698 return false;
1699 }
1700
runOnModule(Module & M)1701 bool IPSCCP::runOnModule(Module &M) {
1702 const DataLayout &DL = M.getDataLayout();
1703 const TargetLibraryInfo *TLI =
1704 &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
1705 SCCPSolver Solver(DL, TLI);
1706
1707 // AddressTakenFunctions - This set keeps track of the address-taken functions
1708 // that are in the input. As IPSCCP runs through and simplifies code,
1709 // functions that were address taken can end up losing their
1710 // address-taken-ness. Because of this, we keep track of their addresses from
1711 // the first pass so we can use them for the later simplification pass.
1712 SmallPtrSet<Function*, 32> AddressTakenFunctions;
1713
1714 // Loop over all functions, marking arguments to those with their addresses
1715 // taken or that are external as overdefined.
1716 //
1717 for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) {
1718 if (F->isDeclaration())
1719 continue;
1720
1721 // If this is a strong or ODR definition of this function, then we can
1722 // propagate information about its result into callsites of it.
1723 if (!F->mayBeOverridden())
1724 Solver.AddTrackedFunction(&*F);
1725
1726 // If this function only has direct calls that we can see, we can track its
1727 // arguments and return value aggressively, and can assume it is not called
1728 // unless we see evidence to the contrary.
1729 if (F->hasLocalLinkage()) {
1730 if (AddressIsTaken(&*F))
1731 AddressTakenFunctions.insert(&*F);
1732 else {
1733 Solver.AddArgumentTrackedFunction(&*F);
1734 continue;
1735 }
1736 }
1737
1738 // Assume the function is called.
1739 Solver.MarkBlockExecutable(&F->front());
1740
1741 // Assume nothing about the incoming arguments.
1742 for (Argument &AI : F->args())
1743 Solver.markAnythingOverdefined(&AI);
1744 }
1745
1746 // Loop over global variables. We inform the solver about any internal global
1747 // variables that do not have their 'addresses taken'. If they don't have
1748 // their addresses taken, we can propagate constants through them.
1749 for (GlobalVariable &G : M.globals())
1750 if (!G.isConstant() && G.hasLocalLinkage() && !AddressIsTaken(&G))
1751 Solver.TrackValueOfGlobalVariable(&G);
1752
1753 // Solve for constants.
1754 bool ResolvedUndefs = true;
1755 while (ResolvedUndefs) {
1756 Solver.Solve();
1757
1758 DEBUG(dbgs() << "RESOLVING UNDEFS\n");
1759 ResolvedUndefs = false;
1760 for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F)
1761 ResolvedUndefs |= Solver.ResolvedUndefsIn(*F);
1762 }
1763
1764 bool MadeChanges = false;
1765
1766 // Iterate over all of the instructions in the module, replacing them with
1767 // constants if we have found them to be of constant values.
1768 //
1769 SmallVector<BasicBlock*, 512> BlocksToErase;
1770
1771 for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) {
1772 if (F->isDeclaration())
1773 continue;
1774
1775 if (Solver.isBlockExecutable(&F->front())) {
1776 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
1777 AI != E; ++AI) {
1778 if (AI->use_empty() || AI->getType()->isStructTy()) continue;
1779
1780 // TODO: Could use getStructLatticeValueFor to find out if the entire
1781 // result is a constant and replace it entirely if so.
1782
1783 LatticeVal IV = Solver.getLatticeValueFor(&*AI);
1784 if (IV.isOverdefined()) continue;
1785
1786 Constant *CST = IV.isConstant() ?
1787 IV.getConstant() : UndefValue::get(AI->getType());
1788 DEBUG(dbgs() << "*** Arg " << *AI << " = " << *CST <<"\n");
1789
1790 // Replaces all of the uses of a variable with uses of the
1791 // constant.
1792 AI->replaceAllUsesWith(CST);
1793 ++IPNumArgsElimed;
1794 }
1795 }
1796
1797 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB) {
1798 if (!Solver.isBlockExecutable(&*BB)) {
1799 DeleteInstructionInBlock(&*BB);
1800 MadeChanges = true;
1801
1802 TerminatorInst *TI = BB->getTerminator();
1803 for (BasicBlock *Succ : TI->successors()) {
1804 if (!Succ->empty() && isa<PHINode>(Succ->begin()))
1805 Succ->removePredecessor(&*BB);
1806 }
1807 if (!TI->use_empty())
1808 TI->replaceAllUsesWith(UndefValue::get(TI->getType()));
1809 TI->eraseFromParent();
1810 new UnreachableInst(M.getContext(), &*BB);
1811
1812 if (&*BB != &F->front())
1813 BlocksToErase.push_back(&*BB);
1814 continue;
1815 }
1816
1817 for (BasicBlock::iterator BI = BB->begin(), E = BB->end(); BI != E; ) {
1818 Instruction *Inst = &*BI++;
1819 if (Inst->getType()->isVoidTy() || Inst->getType()->isStructTy())
1820 continue;
1821
1822 // TODO: Could use getStructLatticeValueFor to find out if the entire
1823 // result is a constant and replace it entirely if so.
1824
1825 LatticeVal IV = Solver.getLatticeValueFor(Inst);
1826 if (IV.isOverdefined())
1827 continue;
1828
1829 Constant *Const = IV.isConstant()
1830 ? IV.getConstant() : UndefValue::get(Inst->getType());
1831 DEBUG(dbgs() << " Constant: " << *Const << " = " << *Inst << '\n');
1832
1833 // Replaces all of the uses of a variable with uses of the
1834 // constant.
1835 Inst->replaceAllUsesWith(Const);
1836
1837 // Delete the instruction.
1838 if (!isa<CallInst>(Inst) && !isa<TerminatorInst>(Inst))
1839 Inst->eraseFromParent();
1840
1841 // Hey, we just changed something!
1842 MadeChanges = true;
1843 ++IPNumInstRemoved;
1844 }
1845 }
1846
1847 // Now that all instructions in the function are constant folded, erase dead
1848 // blocks, because we can now use ConstantFoldTerminator to get rid of
1849 // in-edges.
1850 for (unsigned i = 0, e = BlocksToErase.size(); i != e; ++i) {
1851 // If there are any PHI nodes in this successor, drop entries for BB now.
1852 BasicBlock *DeadBB = BlocksToErase[i];
1853 for (Value::user_iterator UI = DeadBB->user_begin(),
1854 UE = DeadBB->user_end();
1855 UI != UE;) {
1856 // Grab the user and then increment the iterator early, as the user
1857 // will be deleted. Step past all adjacent uses from the same user.
1858 Instruction *I = dyn_cast<Instruction>(*UI);
1859 do { ++UI; } while (UI != UE && *UI == I);
1860
1861 // Ignore blockaddress users; BasicBlock's dtor will handle them.
1862 if (!I) continue;
1863
1864 bool Folded = ConstantFoldTerminator(I->getParent());
1865 if (!Folded) {
1866 // The constant folder may not have been able to fold the terminator
1867 // if this is a branch or switch on undef. Fold it manually as a
1868 // branch to the first successor.
1869 #ifndef NDEBUG
1870 if (BranchInst *BI = dyn_cast<BranchInst>(I)) {
1871 assert(BI->isConditional() && isa<UndefValue>(BI->getCondition()) &&
1872 "Branch should be foldable!");
1873 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(I)) {
1874 assert(isa<UndefValue>(SI->getCondition()) && "Switch should fold");
1875 } else {
1876 llvm_unreachable("Didn't fold away reference to block!");
1877 }
1878 #endif
1879
1880 // Make this an uncond branch to the first successor.
1881 TerminatorInst *TI = I->getParent()->getTerminator();
1882 BranchInst::Create(TI->getSuccessor(0), TI);
1883
1884 // Remove entries in successor phi nodes to remove edges.
1885 for (unsigned i = 1, e = TI->getNumSuccessors(); i != e; ++i)
1886 TI->getSuccessor(i)->removePredecessor(TI->getParent());
1887
1888 // Remove the old terminator.
1889 TI->eraseFromParent();
1890 }
1891 }
1892
1893 // Finally, delete the basic block.
1894 F->getBasicBlockList().erase(DeadBB);
1895 }
1896 BlocksToErase.clear();
1897 }
1898
1899 // If we inferred constant or undef return values for a function, we replaced
1900 // all call uses with the inferred value. This means we don't need to bother
1901 // actually returning anything from the function. Replace all return
1902 // instructions with return undef.
1903 //
1904 // Do this in two stages: first identify the functions we should process, then
1905 // actually zap their returns. This is important because we can only do this
1906 // if the address of the function isn't taken. In cases where a return is the
1907 // last use of a function, the order of processing functions would affect
1908 // whether other functions are optimizable.
1909 SmallVector<ReturnInst*, 8> ReturnsToZap;
1910
1911 // TODO: Process multiple value ret instructions also.
1912 const DenseMap<Function*, LatticeVal> &RV = Solver.getTrackedRetVals();
1913 for (DenseMap<Function*, LatticeVal>::const_iterator I = RV.begin(),
1914 E = RV.end(); I != E; ++I) {
1915 Function *F = I->first;
1916 if (I->second.isOverdefined() || F->getReturnType()->isVoidTy())
1917 continue;
1918
1919 // We can only do this if we know that nothing else can call the function.
1920 if (!F->hasLocalLinkage() || AddressTakenFunctions.count(F))
1921 continue;
1922
1923 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
1924 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator()))
1925 if (!isa<UndefValue>(RI->getOperand(0)))
1926 ReturnsToZap.push_back(RI);
1927 }
1928
1929 // Zap all returns which we've identified as zap to change.
1930 for (unsigned i = 0, e = ReturnsToZap.size(); i != e; ++i) {
1931 Function *F = ReturnsToZap[i]->getParent()->getParent();
1932 ReturnsToZap[i]->setOperand(0, UndefValue::get(F->getReturnType()));
1933 }
1934
1935 // If we inferred constant or undef values for globals variables, we can
1936 // delete the global and any stores that remain to it.
1937 const DenseMap<GlobalVariable*, LatticeVal> &TG = Solver.getTrackedGlobals();
1938 for (DenseMap<GlobalVariable*, LatticeVal>::const_iterator I = TG.begin(),
1939 E = TG.end(); I != E; ++I) {
1940 GlobalVariable *GV = I->first;
1941 assert(!I->second.isOverdefined() &&
1942 "Overdefined values should have been taken out of the map!");
1943 DEBUG(dbgs() << "Found that GV '" << GV->getName() << "' is constant!\n");
1944 while (!GV->use_empty()) {
1945 StoreInst *SI = cast<StoreInst>(GV->user_back());
1946 SI->eraseFromParent();
1947 }
1948 M.getGlobalList().erase(GV);
1949 ++IPNumGlobalConst;
1950 }
1951
1952 return MadeChanges;
1953 }
1954