1 //===- GlobalOpt.cpp - Optimize Global Variables --------------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by the LLVM research group and is distributed under
6 // the University of Illinois Open Source License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This pass transforms simple global variables that never have their address
11 // taken. If obviously true, it marks read/write globals as constant, deletes
12 // variables only stored to, etc.
14 //===----------------------------------------------------------------------===//
16 #define DEBUG_TYPE "globalopt"
17 #include "llvm/Transforms/IPO.h"
18 #include "llvm/Constants.h"
19 #include "llvm/DerivedTypes.h"
20 #include "llvm/Instructions.h"
21 #include "llvm/Module.h"
22 #include "llvm/Pass.h"
23 #include "llvm/Support/Debug.h"
24 #include "llvm/Target/TargetData.h"
25 #include "llvm/Transforms/Utils/Local.h"
26 #include "llvm/ADT/Statistic.h"
27 #include "llvm/ADT/StringExtras.h"
33 Statistic<> NumMarked ("globalopt", "Number of globals marked constant");
34 Statistic<> NumSRA ("globalopt", "Number of aggregate globals broken "
36 Statistic<> NumSubstitute("globalopt",
37 "Number of globals with initializers stored into them");
38 Statistic<> NumDeleted ("globalopt", "Number of globals deleted");
39 Statistic<> NumFnDeleted("globalopt", "Number of functions deleted");
40 Statistic<> NumGlobUses ("globalopt", "Number of global uses devirtualized");
41 Statistic<> NumShrunkToBool("globalopt",
42 "Number of global vars shrunk to booleans");
44 struct GlobalOpt : public ModulePass {
45 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
46 AU.addRequired<TargetData>();
49 bool runOnModule(Module &M);
52 bool ProcessInternalGlobal(GlobalVariable *GV, Module::giterator &GVI);
55 RegisterOpt<GlobalOpt> X("globalopt", "Global Variable Optimizer");
58 ModulePass *llvm::createGlobalOptimizerPass() { return new GlobalOpt(); }
60 /// GlobalStatus - As we analyze each global, keep track of some information
61 /// about it. If we find out that the address of the global is taken, none of
62 /// this info will be accurate.
64 /// isLoaded - True if the global is ever loaded. If the global isn't ever
65 /// loaded it can be deleted.
68 /// StoredType - Keep track of what stores to the global look like.
71 /// NotStored - There is no store to this global. It can thus be marked
75 /// isInitializerStored - This global is stored to, but the only thing
76 /// stored is the constant it was initialized with. This is only tracked
77 /// for scalar globals.
80 /// isStoredOnce - This global is stored to, but only its initializer and
81 /// one other value is ever stored to it. If this global isStoredOnce, we
82 /// track the value stored to it in StoredOnceValue below. This is only
83 /// tracked for scalar globals.
86 /// isStored - This global is stored to by multiple values or something else
87 /// that we cannot track.
91 /// StoredOnceValue - If only one value (besides the initializer constant) is
92 /// ever stored to this global, keep track of what value it is.
93 Value *StoredOnceValue;
95 /// isNotSuitableForSRA - Keep track of whether any SRA preventing users of
96 /// the global exist. Such users include GEP instruction with variable
97 /// indexes, and non-gep/load/store users like constant expr casts.
98 bool isNotSuitableForSRA;
100 GlobalStatus() : isLoaded(false), StoredType(NotStored), StoredOnceValue(0),
101 isNotSuitableForSRA(false) {}
106 /// ConstantIsDead - Return true if the specified constant is (transitively)
107 /// dead. The constant may be used by other constants (e.g. constant arrays and
108 /// constant exprs) as long as they are dead, but it cannot be used by anything
110 static bool ConstantIsDead(Constant *C) {
111 if (isa<GlobalValue>(C)) return false;
113 for (Value::use_iterator UI = C->use_begin(), E = C->use_end(); UI != E; ++UI)
114 if (Constant *CU = dyn_cast<Constant>(*UI)) {
115 if (!ConstantIsDead(CU)) return false;
122 /// AnalyzeGlobal - Look at all uses of the global and fill in the GlobalStatus
123 /// structure. If the global has its address taken, return true to indicate we
124 /// can't do anything with it.
126 static bool AnalyzeGlobal(Value *V, GlobalStatus &GS,
127 std::set<PHINode*> &PHIUsers) {
128 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; ++UI)
129 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(*UI)) {
130 if (AnalyzeGlobal(CE, GS, PHIUsers)) return true;
131 if (CE->getOpcode() != Instruction::GetElementPtr)
132 GS.isNotSuitableForSRA = true;
133 else if (!GS.isNotSuitableForSRA) {
134 // Check to see if this ConstantExpr GEP is SRA'able. In particular, we
135 // don't like < 3 operand CE's, and we don't like non-constant integer
137 if (CE->getNumOperands() < 3 || !CE->getOperand(1)->isNullValue())
138 GS.isNotSuitableForSRA = true;
140 for (unsigned i = 1, e = CE->getNumOperands(); i != e; ++i)
141 if (!isa<ConstantInt>(CE->getOperand(i))) {
142 GS.isNotSuitableForSRA = true;
148 } else if (Instruction *I = dyn_cast<Instruction>(*UI)) {
149 if (isa<LoadInst>(I)) {
151 } else if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
152 // Don't allow a store OF the address, only stores TO the address.
153 if (SI->getOperand(0) == V) return true;
155 // If this is a direct store to the global (i.e., the global is a scalar
156 // value, not an aggregate), keep more specific information about
158 if (GS.StoredType != GlobalStatus::isStored)
159 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(SI->getOperand(1))){
160 Value *StoredVal = SI->getOperand(0);
161 if (StoredVal == GV->getInitializer()) {
162 if (GS.StoredType < GlobalStatus::isInitializerStored)
163 GS.StoredType = GlobalStatus::isInitializerStored;
164 } else if (isa<LoadInst>(StoredVal) &&
165 cast<LoadInst>(StoredVal)->getOperand(0) == GV) {
167 if (GS.StoredType < GlobalStatus::isInitializerStored)
168 GS.StoredType = GlobalStatus::isInitializerStored;
169 } else if (GS.StoredType < GlobalStatus::isStoredOnce) {
170 GS.StoredType = GlobalStatus::isStoredOnce;
171 GS.StoredOnceValue = StoredVal;
172 } else if (GS.StoredType == GlobalStatus::isStoredOnce &&
173 GS.StoredOnceValue == StoredVal) {
176 GS.StoredType = GlobalStatus::isStored;
179 GS.StoredType = GlobalStatus::isStored;
181 } else if (I->getOpcode() == Instruction::GetElementPtr) {
182 if (AnalyzeGlobal(I, GS, PHIUsers)) return true;
184 // If the first two indices are constants, this can be SRA'd.
185 if (isa<GlobalVariable>(I->getOperand(0))) {
186 if (I->getNumOperands() < 3 || !isa<Constant>(I->getOperand(1)) ||
187 !cast<Constant>(I->getOperand(1))->isNullValue() ||
188 !isa<ConstantInt>(I->getOperand(2)))
189 GS.isNotSuitableForSRA = true;
190 } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(I->getOperand(0))){
191 if (CE->getOpcode() != Instruction::GetElementPtr ||
192 CE->getNumOperands() < 3 || I->getNumOperands() < 2 ||
193 !isa<Constant>(I->getOperand(0)) ||
194 !cast<Constant>(I->getOperand(0))->isNullValue())
195 GS.isNotSuitableForSRA = true;
197 GS.isNotSuitableForSRA = true;
199 } else if (I->getOpcode() == Instruction::Select) {
200 if (AnalyzeGlobal(I, GS, PHIUsers)) return true;
201 GS.isNotSuitableForSRA = true;
202 } else if (PHINode *PN = dyn_cast<PHINode>(I)) {
203 // PHI nodes we can check just like select or GEP instructions, but we
204 // have to be careful about infinite recursion.
205 if (PHIUsers.insert(PN).second) // Not already visited.
206 if (AnalyzeGlobal(I, GS, PHIUsers)) return true;
207 GS.isNotSuitableForSRA = true;
208 } else if (isa<SetCondInst>(I)) {
209 GS.isNotSuitableForSRA = true;
211 return true; // Any other non-load instruction might take address!
213 } else if (Constant *C = dyn_cast<Constant>(*UI)) {
214 // We might have a dead and dangling constant hanging off of here.
215 if (!ConstantIsDead(C))
218 // Otherwise must be a global or some other user.
225 static Constant *getAggregateConstantElement(Constant *Agg, Constant *Idx) {
226 ConstantInt *CI = dyn_cast<ConstantInt>(Idx);
228 unsigned IdxV = (unsigned)CI->getRawValue();
230 if (ConstantStruct *CS = dyn_cast<ConstantStruct>(Agg)) {
231 if (IdxV < CS->getNumOperands()) return CS->getOperand(IdxV);
232 } else if (ConstantArray *CA = dyn_cast<ConstantArray>(Agg)) {
233 if (IdxV < CA->getNumOperands()) return CA->getOperand(IdxV);
234 } else if (ConstantPacked *CP = dyn_cast<ConstantPacked>(Agg)) {
235 if (IdxV < CP->getNumOperands()) return CP->getOperand(IdxV);
236 } else if (isa<ConstantAggregateZero>(Agg)) {
237 if (const StructType *STy = dyn_cast<StructType>(Agg->getType())) {
238 if (IdxV < STy->getNumElements())
239 return Constant::getNullValue(STy->getElementType(IdxV));
240 } else if (const SequentialType *STy =
241 dyn_cast<SequentialType>(Agg->getType())) {
242 return Constant::getNullValue(STy->getElementType());
244 } else if (isa<UndefValue>(Agg)) {
245 if (const StructType *STy = dyn_cast<StructType>(Agg->getType())) {
246 if (IdxV < STy->getNumElements())
247 return UndefValue::get(STy->getElementType(IdxV));
248 } else if (const SequentialType *STy =
249 dyn_cast<SequentialType>(Agg->getType())) {
250 return UndefValue::get(STy->getElementType());
256 static Constant *TraverseGEPInitializer(User *GEP, Constant *Init) {
257 if (GEP->getNumOperands() == 1 ||
258 !isa<Constant>(GEP->getOperand(1)) ||
259 !cast<Constant>(GEP->getOperand(1))->isNullValue())
262 for (unsigned i = 2, e = GEP->getNumOperands(); i != e; ++i) {
263 ConstantInt *Idx = dyn_cast<ConstantInt>(GEP->getOperand(i));
265 Init = getAggregateConstantElement(Init, Idx);
266 if (Init == 0) return 0;
271 /// CleanupConstantGlobalUsers - We just marked GV constant. Loop over all
272 /// users of the global, cleaning up the obvious ones. This is largely just a
273 /// quick scan over the use list to clean up the easy and obvious cruft. This
274 /// returns true if it made a change.
275 static bool CleanupConstantGlobalUsers(Value *V, Constant *Init) {
276 bool Changed = false;
277 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;) {
280 if (LoadInst *LI = dyn_cast<LoadInst>(U)) {
281 // Replace the load with the initializer.
282 LI->replaceAllUsesWith(Init);
283 LI->eraseFromParent();
285 } else if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
286 // Store must be unreachable or storing Init into the global.
287 SI->eraseFromParent();
289 } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(U)) {
290 if (CE->getOpcode() == Instruction::GetElementPtr) {
291 if (Constant *SubInit = TraverseGEPInitializer(CE, Init))
292 Changed |= CleanupConstantGlobalUsers(CE, SubInit);
293 if (CE->use_empty()) {
294 CE->destroyConstant();
298 } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(U)) {
299 if (Constant *SubInit = TraverseGEPInitializer(GEP, Init))
300 Changed |= CleanupConstantGlobalUsers(GEP, SubInit);
302 // If this GEP has variable indexes, we should still be able to delete
303 // any stores through it.
304 for (Value::use_iterator GUI = GEP->use_begin(), E = GEP->use_end();
306 if (StoreInst *SI = dyn_cast<StoreInst>(*GUI++)) {
307 SI->eraseFromParent();
312 if (GEP->use_empty()) {
313 GEP->eraseFromParent();
316 } else if (Constant *C = dyn_cast<Constant>(U)) {
317 // If we have a chain of dead constantexprs or other things dangling from
318 // us, and if they are all dead, nuke them without remorse.
319 if (ConstantIsDead(C)) {
320 C->destroyConstant();
321 // This could have incalidated UI, start over from scratch.x
322 CleanupConstantGlobalUsers(V, Init);
330 /// SRAGlobal - Perform scalar replacement of aggregates on the specified global
331 /// variable. This opens the door for other optimizations by exposing the
332 /// behavior of the program in a more fine-grained way. We have determined that
333 /// this transformation is safe already. We return the first global variable we
334 /// insert so that the caller can reprocess it.
335 static GlobalVariable *SRAGlobal(GlobalVariable *GV) {
336 assert(GV->hasInternalLinkage() && !GV->isConstant());
337 Constant *Init = GV->getInitializer();
338 const Type *Ty = Init->getType();
340 std::vector<GlobalVariable*> NewGlobals;
341 Module::GlobalListType &Globals = GV->getParent()->getGlobalList();
343 if (const StructType *STy = dyn_cast<StructType>(Ty)) {
344 NewGlobals.reserve(STy->getNumElements());
345 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
346 Constant *In = getAggregateConstantElement(Init,
347 ConstantUInt::get(Type::UIntTy, i));
348 assert(In && "Couldn't get element of initializer?");
349 GlobalVariable *NGV = new GlobalVariable(STy->getElementType(i), false,
350 GlobalVariable::InternalLinkage,
351 In, GV->getName()+"."+utostr(i));
352 Globals.insert(GV, NGV);
353 NewGlobals.push_back(NGV);
355 } else if (const SequentialType *STy = dyn_cast<SequentialType>(Ty)) {
356 unsigned NumElements = 0;
357 if (const ArrayType *ATy = dyn_cast<ArrayType>(STy))
358 NumElements = ATy->getNumElements();
359 else if (const PackedType *PTy = dyn_cast<PackedType>(STy))
360 NumElements = PTy->getNumElements();
362 assert(0 && "Unknown aggregate sequential type!");
364 if (NumElements > 16 && GV->use_size() > 16) return 0; // It's not worth it.
365 NewGlobals.reserve(NumElements);
366 for (unsigned i = 0, e = NumElements; i != e; ++i) {
367 Constant *In = getAggregateConstantElement(Init,
368 ConstantUInt::get(Type::UIntTy, i));
369 assert(In && "Couldn't get element of initializer?");
371 GlobalVariable *NGV = new GlobalVariable(STy->getElementType(), false,
372 GlobalVariable::InternalLinkage,
373 In, GV->getName()+"."+utostr(i));
374 Globals.insert(GV, NGV);
375 NewGlobals.push_back(NGV);
379 if (NewGlobals.empty())
382 DEBUG(std::cerr << "PERFORMING GLOBAL SRA ON: " << *GV);
384 Constant *NullInt = Constant::getNullValue(Type::IntTy);
386 // Loop over all of the uses of the global, replacing the constantexpr geps,
387 // with smaller constantexpr geps or direct references.
388 while (!GV->use_empty()) {
389 User *GEP = GV->use_back();
390 assert(((isa<ConstantExpr>(GEP) &&
391 cast<ConstantExpr>(GEP)->getOpcode()==Instruction::GetElementPtr)||
392 isa<GetElementPtrInst>(GEP)) && "NonGEP CE's are not SRAable!");
394 // Ignore the 1th operand, which has to be zero or else the program is quite
395 // broken (undefined). Get the 2nd operand, which is the structure or array
398 (unsigned)cast<ConstantInt>(GEP->getOperand(2))->getRawValue();
399 if (Val >= NewGlobals.size()) Val = 0; // Out of bound array access.
401 Value *NewPtr = NewGlobals[Val];
403 // Form a shorter GEP if needed.
404 if (GEP->getNumOperands() > 3)
405 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(GEP)) {
406 std::vector<Constant*> Idxs;
407 Idxs.push_back(NullInt);
408 for (unsigned i = 3, e = CE->getNumOperands(); i != e; ++i)
409 Idxs.push_back(CE->getOperand(i));
410 NewPtr = ConstantExpr::getGetElementPtr(cast<Constant>(NewPtr), Idxs);
412 GetElementPtrInst *GEPI = cast<GetElementPtrInst>(GEP);
413 std::vector<Value*> Idxs;
414 Idxs.push_back(NullInt);
415 for (unsigned i = 3, e = GEPI->getNumOperands(); i != e; ++i)
416 Idxs.push_back(GEPI->getOperand(i));
417 NewPtr = new GetElementPtrInst(NewPtr, Idxs,
418 GEPI->getName()+"."+utostr(Val), GEPI);
420 GEP->replaceAllUsesWith(NewPtr);
422 if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(GEP))
423 GEPI->eraseFromParent();
425 cast<ConstantExpr>(GEP)->destroyConstant();
428 // Delete the old global, now that it is dead.
432 // Loop over the new globals array deleting any globals that are obviously
433 // dead. This can arise due to scalarization of a structure or an array that
434 // has elements that are dead.
435 unsigned FirstGlobal = 0;
436 for (unsigned i = 0, e = NewGlobals.size(); i != e; ++i)
437 if (NewGlobals[i]->use_empty()) {
438 Globals.erase(NewGlobals[i]);
439 if (FirstGlobal == i) ++FirstGlobal;
442 return FirstGlobal != NewGlobals.size() ? NewGlobals[FirstGlobal] : 0;
445 /// AllUsesOfValueWillTrapIfNull - Return true if all users of the specified
446 /// value will trap if the value is dynamically null.
447 static bool AllUsesOfValueWillTrapIfNull(Value *V) {
448 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; ++UI)
449 if (isa<LoadInst>(*UI)) {
451 } else if (StoreInst *SI = dyn_cast<StoreInst>(*UI)) {
452 if (SI->getOperand(0) == V) {
453 //std::cerr << "NONTRAPPING USE: " << **UI;
454 return false; // Storing the value.
456 } else if (CallInst *CI = dyn_cast<CallInst>(*UI)) {
457 if (CI->getOperand(0) != V) {
458 //std::cerr << "NONTRAPPING USE: " << **UI;
459 return false; // Not calling the ptr
461 } else if (InvokeInst *II = dyn_cast<InvokeInst>(*UI)) {
462 if (II->getOperand(0) != V) {
463 //std::cerr << "NONTRAPPING USE: " << **UI;
464 return false; // Not calling the ptr
466 } else if (CastInst *CI = dyn_cast<CastInst>(*UI)) {
467 if (!AllUsesOfValueWillTrapIfNull(CI)) return false;
468 } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(*UI)) {
469 if (!AllUsesOfValueWillTrapIfNull(GEPI)) return false;
470 } else if (isa<SetCondInst>(*UI) &&
471 isa<ConstantPointerNull>(UI->getOperand(1))) {
472 // Ignore setcc X, null
474 //std::cerr << "NONTRAPPING USE: " << **UI;
480 /// AllUsesOfLoadedValueWillTrapIfNull - Return true if all uses of any loads
481 /// from GV will trap if the loaded value is null. Note that this also permits
482 /// comparisons of the loaded value against null, as a special case.
483 static bool AllUsesOfLoadedValueWillTrapIfNull(GlobalVariable *GV) {
484 for (Value::use_iterator UI = GV->use_begin(), E = GV->use_end(); UI!=E; ++UI)
485 if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) {
486 if (!AllUsesOfValueWillTrapIfNull(LI))
488 } else if (isa<StoreInst>(*UI)) {
489 // Ignore stores to the global.
491 // We don't know or understand this user, bail out.
492 //std::cerr << "UNKNOWN USER OF GLOBAL!: " << **UI;
499 static bool OptimizeAwayTrappingUsesOfValue(Value *V, Constant *NewV) {
500 bool Changed = false;
501 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; ) {
502 Instruction *I = cast<Instruction>(*UI++);
503 if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
504 LI->setOperand(0, NewV);
506 } else if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
507 if (SI->getOperand(1) == V) {
508 SI->setOperand(1, NewV);
511 } else if (isa<CallInst>(I) || isa<InvokeInst>(I)) {
512 if (I->getOperand(0) == V) {
513 // Calling through the pointer! Turn into a direct call, but be careful
514 // that the pointer is not also being passed as an argument.
515 I->setOperand(0, NewV);
517 bool PassedAsArg = false;
518 for (unsigned i = 1, e = I->getNumOperands(); i != e; ++i)
519 if (I->getOperand(i) == V) {
521 I->setOperand(i, NewV);
525 // Being passed as an argument also. Be careful to not invalidate UI!
529 } else if (CastInst *CI = dyn_cast<CastInst>(I)) {
530 Changed |= OptimizeAwayTrappingUsesOfValue(CI,
531 ConstantExpr::getCast(NewV, CI->getType()));
532 if (CI->use_empty()) {
534 CI->eraseFromParent();
536 } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(I)) {
537 // Should handle GEP here.
538 std::vector<Constant*> Indices;
539 Indices.reserve(GEPI->getNumOperands()-1);
540 for (unsigned i = 1, e = GEPI->getNumOperands(); i != e; ++i)
541 if (Constant *C = dyn_cast<Constant>(GEPI->getOperand(i)))
542 Indices.push_back(C);
545 if (Indices.size() == GEPI->getNumOperands()-1)
546 Changed |= OptimizeAwayTrappingUsesOfValue(GEPI,
547 ConstantExpr::getGetElementPtr(NewV, Indices));
548 if (GEPI->use_empty()) {
550 GEPI->eraseFromParent();
559 /// OptimizeAwayTrappingUsesOfLoads - The specified global has only one non-null
560 /// value stored into it. If there are uses of the loaded value that would trap
561 /// if the loaded value is dynamically null, then we know that they cannot be
562 /// reachable with a null optimize away the load.
563 static bool OptimizeAwayTrappingUsesOfLoads(GlobalVariable *GV, Constant *LV) {
564 std::vector<LoadInst*> Loads;
565 bool Changed = false;
567 // Replace all uses of loads with uses of uses of the stored value.
568 for (Value::use_iterator GUI = GV->use_begin(), E = GV->use_end();
570 if (LoadInst *LI = dyn_cast<LoadInst>(*GUI)) {
572 Changed |= OptimizeAwayTrappingUsesOfValue(LI, LV);
574 assert(isa<StoreInst>(*GUI) && "Only expect load and stores!");
578 DEBUG(std::cerr << "OPTIMIZED LOADS FROM STORED ONCE POINTER: " << *GV);
582 // Delete all of the loads we can, keeping track of whether we nuked them all!
583 bool AllLoadsGone = true;
584 while (!Loads.empty()) {
585 LoadInst *L = Loads.back();
586 if (L->use_empty()) {
587 L->eraseFromParent();
590 AllLoadsGone = false;
595 // If we nuked all of the loads, then none of the stores are needed either,
596 // nor is the global.
598 DEBUG(std::cerr << " *** GLOBAL NOW DEAD!\n");
599 CleanupConstantGlobalUsers(GV, 0);
600 if (GV->use_empty()) {
601 GV->eraseFromParent();
609 /// ConstantPropUsersOf - Walk the use list of V, constant folding all of the
610 /// instructions that are foldable.
611 static void ConstantPropUsersOf(Value *V) {
612 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; )
613 if (Instruction *I = dyn_cast<Instruction>(*UI++))
614 if (Constant *NewC = ConstantFoldInstruction(I)) {
615 I->replaceAllUsesWith(NewC);
617 // Back up UI to avoid invalidating it!
618 bool AtBegin = false;
619 if (UI == V->use_begin())
623 I->eraseFromParent();
631 /// OptimizeGlobalAddressOfMalloc - This function takes the specified global
632 /// variable, and transforms the program as if it always contained the result of
633 /// the specified malloc. Because it is always the result of the specified
634 /// malloc, there is no reason to actually DO the malloc. Instead, turn the
635 /// malloc into a global, and any laods of GV as uses of the new global.
636 static GlobalVariable *OptimizeGlobalAddressOfMalloc(GlobalVariable *GV,
638 DEBUG(std::cerr << "PROMOTING MALLOC GLOBAL: " << *GV << " MALLOC = " <<*MI);
639 ConstantInt *NElements = cast<ConstantInt>(MI->getArraySize());
641 if (NElements->getRawValue() != 1) {
642 // If we have an array allocation, transform it to a single element
643 // allocation to make the code below simpler.
644 Type *NewTy = ArrayType::get(MI->getAllocatedType(),
645 (unsigned)NElements->getRawValue());
647 new MallocInst(NewTy, Constant::getNullValue(Type::UIntTy),
649 std::vector<Value*> Indices;
650 Indices.push_back(Constant::getNullValue(Type::IntTy));
651 Indices.push_back(Indices[0]);
652 Value *NewGEP = new GetElementPtrInst(NewMI, Indices,
653 NewMI->getName()+".el0", MI);
654 MI->replaceAllUsesWith(NewGEP);
655 MI->eraseFromParent();
659 // Create the new global variable. The contents of the malloc'd memory is
660 // undefined, so initialize with an undef value.
661 Constant *Init = UndefValue::get(MI->getAllocatedType());
662 GlobalVariable *NewGV = new GlobalVariable(MI->getAllocatedType(), false,
663 GlobalValue::InternalLinkage, Init,
664 GV->getName()+".body");
665 GV->getParent()->getGlobalList().insert(GV, NewGV);
667 // Anything that used the malloc now uses the global directly.
668 MI->replaceAllUsesWith(NewGV);
670 Constant *RepValue = NewGV;
671 if (NewGV->getType() != GV->getType()->getElementType())
672 RepValue = ConstantExpr::getCast(RepValue, GV->getType()->getElementType());
674 // If there is a comparison against null, we will insert a global bool to
675 // keep track of whether the global was initialized yet or not.
676 GlobalVariable *InitBool =
677 new GlobalVariable(Type::BoolTy, false, GlobalValue::InternalLinkage,
678 ConstantBool::False, GV->getName()+".init");
679 bool InitBoolUsed = false;
681 // Loop over all uses of GV, processing them in turn.
682 std::vector<StoreInst*> Stores;
683 while (!GV->use_empty())
684 if (LoadInst *LI = dyn_cast<LoadInst>(GV->use_back())) {
685 while (!LI->use_empty()) {
686 // FIXME: the iterator should expose a getUse() method.
687 Use &LoadUse = *(const iplist<Use>::iterator&)LI->use_begin();
688 if (!isa<SetCondInst>(LoadUse.getUser()))
691 // Replace the setcc X, 0 with a use of the bool value.
692 SetCondInst *SCI = cast<SetCondInst>(LoadUse.getUser());
693 Value *LV = new LoadInst(InitBool, InitBool->getName()+".val", SCI);
695 switch (SCI->getOpcode()) {
696 default: assert(0 && "Unknown opcode!");
697 case Instruction::SetLT:
698 LV = ConstantBool::False; // X < null -> always false
700 case Instruction::SetEQ:
701 case Instruction::SetLE:
702 LV = BinaryOperator::createNot(LV, "notinit", SCI);
704 case Instruction::SetNE:
705 case Instruction::SetGE:
706 case Instruction::SetGT:
709 SCI->replaceAllUsesWith(LV);
710 SCI->eraseFromParent();
713 LI->eraseFromParent();
715 StoreInst *SI = cast<StoreInst>(GV->use_back());
716 // The global is initialized when the store to it occurs.
717 new StoreInst(ConstantBool::True, InitBool, SI);
718 SI->eraseFromParent();
721 // If the initialization boolean was used, insert it, otherwise delete it.
723 while (!InitBool->use_empty()) // Delete initializations
724 cast<Instruction>(InitBool->use_back())->eraseFromParent();
727 GV->getParent()->getGlobalList().insert(GV, InitBool);
730 // Now the GV is dead, nuke it and the malloc.
731 GV->eraseFromParent();
732 MI->eraseFromParent();
734 // To further other optimizations, loop over all users of NewGV and try to
735 // constant prop them. This will promote GEP instructions with constant
736 // indices into GEP constant-exprs, which will allow global-opt to hack on it.
737 ConstantPropUsersOf(NewGV);
738 if (RepValue != NewGV)
739 ConstantPropUsersOf(RepValue);
744 /// ValueIsOnlyUsedLocallyOrStoredToOneGlobal - Scan the use-list of V checking
745 /// to make sure that there are no complex uses of V. We permit simple things
746 /// like dereferencing the pointer, but not storing through the address, unless
747 /// it is to the specified global.
748 static bool ValueIsOnlyUsedLocallyOrStoredToOneGlobal(Instruction *V,
749 GlobalVariable *GV) {
750 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;++UI)
751 if (isa<LoadInst>(*UI) || isa<SetCondInst>(*UI)) {
753 } else if (StoreInst *SI = dyn_cast<StoreInst>(*UI)) {
754 if (SI->getOperand(0) == V && SI->getOperand(1) != GV)
755 return false; // Storing the pointer itself... bad.
756 // Otherwise, storing through it, or storing into GV... fine.
757 } else if (isa<GetElementPtrInst>(*UI) || isa<SelectInst>(*UI)) {
758 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(cast<Instruction>(*UI),GV))
767 // OptimizeOnceStoredGlobal - Try to optimize globals based on the knowledge
768 // that only one value (besides its initializer) is ever stored to the global.
769 static bool OptimizeOnceStoredGlobal(GlobalVariable *GV, Value *StoredOnceVal,
770 Module::giterator &GVI, TargetData &TD) {
771 if (CastInst *CI = dyn_cast<CastInst>(StoredOnceVal))
772 StoredOnceVal = CI->getOperand(0);
773 else if (GetElementPtrInst *GEPI =dyn_cast<GetElementPtrInst>(StoredOnceVal)){
774 // "getelementptr Ptr, 0, 0, 0" is really just a cast.
775 bool IsJustACast = true;
776 for (unsigned i = 1, e = GEPI->getNumOperands(); i != e; ++i)
777 if (!isa<Constant>(GEPI->getOperand(i)) ||
778 !cast<Constant>(GEPI->getOperand(i))->isNullValue()) {
783 StoredOnceVal = GEPI->getOperand(0);
786 // If we are dealing with a pointer global that is initialized to null and
787 // only has one (non-null) value stored into it, then we can optimize any
788 // users of the loaded value (often calls and loads) that would trap if the
790 if (isa<PointerType>(GV->getInitializer()->getType()) &&
791 GV->getInitializer()->isNullValue()) {
792 if (Constant *SOVC = dyn_cast<Constant>(StoredOnceVal)) {
793 if (GV->getInitializer()->getType() != SOVC->getType())
794 SOVC = ConstantExpr::getCast(SOVC, GV->getInitializer()->getType());
796 // Optimize away any trapping uses of the loaded value.
797 if (OptimizeAwayTrappingUsesOfLoads(GV, SOVC))
799 } else if (MallocInst *MI = dyn_cast<MallocInst>(StoredOnceVal)) {
800 // If we have a global that is only initialized with a fixed size malloc,
801 // and if all users of the malloc trap, and if the malloc'd address is not
802 // put anywhere else, transform the program to use global memory instead
803 // of malloc'd memory. This eliminates dynamic allocation (good) and
804 // exposes the resultant global to further GlobalOpt (even better). Note
805 // that we restrict this transformation to only working on small
806 // allocations (2048 bytes currently), as we don't want to introduce a 16M
807 // global or something.
808 if (ConstantInt *NElements = dyn_cast<ConstantInt>(MI->getArraySize()))
809 if (MI->getAllocatedType()->isSized() &&
810 NElements->getRawValue()*
811 TD.getTypeSize(MI->getAllocatedType()) < 2048 &&
812 AllUsesOfLoadedValueWillTrapIfNull(GV) &&
813 ValueIsOnlyUsedLocallyOrStoredToOneGlobal(MI, GV)) {
814 GVI = OptimizeGlobalAddressOfMalloc(GV, MI);
823 /// ShrinkGlobalToBoolean - At this point, we have learned that the only two
824 /// values ever stored into GV are its initializer and OtherVal.
825 static void ShrinkGlobalToBoolean(GlobalVariable *GV, Constant *OtherVal) {
826 // Create the new global, initializing it to false.
827 GlobalVariable *NewGV = new GlobalVariable(Type::BoolTy, false,
828 GlobalValue::InternalLinkage, ConstantBool::False, GV->getName()+".b");
829 GV->getParent()->getGlobalList().insert(GV, NewGV);
831 Constant *InitVal = GV->getInitializer();
832 assert(InitVal->getType() != Type::BoolTy && "No reason to shrink to bool!");
834 // If initialized to zero and storing one into the global, we can use a cast
835 // instead of a select to synthesize the desired value.
836 bool IsOneZero = false;
837 if (ConstantInt *CI = dyn_cast<ConstantInt>(OtherVal))
838 IsOneZero = InitVal->isNullValue() && CI->equalsInt(1);
840 while (!GV->use_empty()) {
841 Instruction *UI = cast<Instruction>(GV->use_back());
842 if (StoreInst *SI = dyn_cast<StoreInst>(UI)) {
843 // Change the store into a boolean store.
844 bool StoringOther = SI->getOperand(0) == OtherVal;
845 // Only do this if we weren't storing a loaded value.
847 if (StoringOther || SI->getOperand(0) == InitVal)
848 StoreVal = ConstantBool::get(StoringOther);
850 // Otherwise, we are storing a previously loaded copy. To do this,
851 // change the copy from copying the original value to just copying the
853 Instruction *StoredVal = cast<Instruction>(SI->getOperand(0));
855 // If we're already replaced the input, StoredVal will be a cast or
856 // select instruction. If not, it will be a load of the original
858 if (LoadInst *LI = dyn_cast<LoadInst>(StoredVal)) {
859 assert(LI->getOperand(0) == GV && "Not a copy!");
860 // Insert a new load, to preserve the saved value.
861 StoreVal = new LoadInst(NewGV, LI->getName()+".b", LI);
863 assert((isa<CastInst>(StoredVal) || isa<SelectInst>(StoredVal)) &&
864 "This is not a form that we understand!");
865 StoreVal = StoredVal->getOperand(0);
866 assert(isa<LoadInst>(StoreVal) && "Not a load of NewGV!");
869 new StoreInst(StoreVal, NewGV, SI);
870 } else if (!UI->use_empty()) {
871 // Change the load into a load of bool then a select.
872 LoadInst *LI = cast<LoadInst>(UI);
874 std::string Name = LI->getName(); LI->setName("");
875 LoadInst *NLI = new LoadInst(NewGV, Name+".b", LI);
878 NSI = new CastInst(NLI, LI->getType(), Name, LI);
880 NSI = new SelectInst(NLI, OtherVal, InitVal, Name, LI);
881 LI->replaceAllUsesWith(NSI);
883 UI->eraseFromParent();
886 GV->eraseFromParent();
890 /// ProcessInternalGlobal - Analyze the specified global variable and optimize
891 /// it if possible. If we make a change, return true.
892 bool GlobalOpt::ProcessInternalGlobal(GlobalVariable *GV,
893 Module::giterator &GVI) {
894 std::set<PHINode*> PHIUsers;
897 GV->removeDeadConstantUsers();
899 if (GV->use_empty()) {
900 DEBUG(std::cerr << "GLOBAL DEAD: " << *GV);
901 GV->eraseFromParent();
906 if (!AnalyzeGlobal(GV, GS, PHIUsers)) {
907 // If the global is never loaded (but may be stored to), it is dead.
910 DEBUG(std::cerr << "GLOBAL NEVER LOADED: " << *GV);
912 // Delete any stores we can find to the global. We may not be able to
913 // make it completely dead though.
914 bool Changed = CleanupConstantGlobalUsers(GV, GV->getInitializer());
916 // If the global is dead now, delete it.
917 if (GV->use_empty()) {
918 GV->eraseFromParent();
924 } else if (GS.StoredType <= GlobalStatus::isInitializerStored) {
925 DEBUG(std::cerr << "MARKING CONSTANT: " << *GV);
926 GV->setConstant(true);
928 // Clean up any obviously simplifiable users now.
929 CleanupConstantGlobalUsers(GV, GV->getInitializer());
931 // If the global is dead now, just nuke it.
932 if (GV->use_empty()) {
933 DEBUG(std::cerr << " *** Marking constant allowed us to simplify "
934 "all users and delete global!\n");
935 GV->eraseFromParent();
941 } else if (!GS.isNotSuitableForSRA &&
942 !GV->getInitializer()->getType()->isFirstClassType()) {
943 if (GlobalVariable *FirstNewGV = SRAGlobal(GV)) {
944 GVI = FirstNewGV; // Don't skip the newly produced globals!
947 } else if (GS.StoredType == GlobalStatus::isStoredOnce) {
948 // If the initial value for the global was an undef value, and if only
949 // one other value was stored into it, we can just change the
950 // initializer to be an undef value, then delete all stores to the
951 // global. This allows us to mark it constant.
952 if (Constant *SOVConstant = dyn_cast<Constant>(GS.StoredOnceValue))
953 if (isa<UndefValue>(GV->getInitializer())) {
954 // Change the initial value here.
955 GV->setInitializer(SOVConstant);
957 // Clean up any obviously simplifiable users now.
958 CleanupConstantGlobalUsers(GV, GV->getInitializer());
960 if (GV->use_empty()) {
961 DEBUG(std::cerr << " *** Substituting initializer allowed us to "
962 "simplify all users and delete global!\n");
963 GV->eraseFromParent();
972 // Try to optimize globals based on the knowledge that only one value
973 // (besides its initializer) is ever stored to the global.
974 if (OptimizeOnceStoredGlobal(GV, GS.StoredOnceValue, GVI,
975 getAnalysis<TargetData>()))
978 // Otherwise, if the global was not a boolean, we can shrink it to be a
980 if (Constant *SOVConstant = dyn_cast<Constant>(GS.StoredOnceValue))
981 if (GV->getType()->getElementType() != Type::BoolTy &&
982 !GV->getType()->getElementType()->isFloatingPoint()) {
983 DEBUG(std::cerr << " *** SHRINKING TO BOOL: " << *GV);
984 ShrinkGlobalToBoolean(GV, SOVConstant);
994 bool GlobalOpt::runOnModule(Module &M) {
995 bool Changed = false;
997 // As a prepass, delete functions that are trivially dead.
998 bool LocalChange = true;
999 while (LocalChange) {
1000 LocalChange = false;
1001 for (Module::iterator FI = M.begin(), E = M.end(); FI != E; ) {
1003 F->removeDeadConstantUsers();
1004 if (F->use_empty() && (F->hasInternalLinkage() ||
1005 F->hasLinkOnceLinkage())) {
1006 M.getFunctionList().erase(F);
1011 Changed |= LocalChange;
1015 while (LocalChange) {
1016 LocalChange = false;
1017 for (Module::giterator GVI = M.gbegin(), E = M.gend(); GVI != E;) {
1018 GlobalVariable *GV = GVI++;
1019 if (!GV->isConstant() && GV->hasInternalLinkage() &&
1020 GV->hasInitializer())
1021 LocalChange |= ProcessInternalGlobal(GV, GVI);
1023 Changed |= LocalChange;