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* Pull out the meat of runOnModule into another function for clarity.
* Do not lead dangling dead constants prevent optimization * Iterate global optimization while we're making progress. These changes allow us to be more aggressive, handling cases like GlobalOpt/iterate.llx without a problem (turning it into 'ret int 0'). git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@16857 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -87,6 +87,24 @@ struct GlobalStatus {
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isNotSuitableForSRA(false) {}
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};
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/// ConstantIsDead - Return true if the specified constant is (transitively)
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/// dead. The constant may be used by other constants (e.g. constant arrays and
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/// constant exprs) as long as they are dead, but it cannot be used by anything
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/// else.
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static bool ConstantIsDead(Constant *C) {
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if (isa<GlobalValue>(C)) return false;
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for (Value::use_iterator UI = C->use_begin(), E = C->use_end(); UI != E; ++UI)
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if (Constant *CU = dyn_cast<Constant>(*UI)) {
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if (!ConstantIsDead(CU)) return false;
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} else
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return false;
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return true;
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}
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/// AnalyzeGlobal - Look at all uses of the global and fill in the GlobalStatus
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/// structure. If the global has its address taken, return true to indicate we
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/// can't do anything with it.
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@ -160,6 +178,10 @@ static bool AnalyzeGlobal(Value *V, GlobalStatus &GS,
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} else {
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return true; // Any other non-load instruction might take address!
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}
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} else if (Constant *C = dyn_cast<Constant>(*UI)) {
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// We might have a dead and dangling constant hanging off of here.
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if (!ConstantIsDead(C))
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return true;
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} else {
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// Otherwise must be a global or some other user.
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return true;
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@ -232,6 +254,15 @@ static void CleanupConstantGlobalUsers(Value *V, Constant *Init) {
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CleanupConstantGlobalUsers(GEP, SubInit);
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if (GEP->use_empty())
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GEP->getParent()->getInstList().erase(GEP);
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} else if (Constant *C = dyn_cast<Constant>(U)) {
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// If we have a chain of dead constantexprs or other things dangling from
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// us, and if they are all dead, nuke them without remorse.
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if (ConstantIsDead(C)) {
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C->destroyConstant();
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// This could have incalidated UI, start over from scratch.x
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CleanupConstantGlobalUsers(V, Init);
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return;
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}
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}
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}
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}
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@ -322,6 +353,67 @@ static GlobalVariable *SRAGlobal(GlobalVariable *GV) {
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return NewGlobals[0];
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}
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/// ProcessInternalGlobal - Analyze the specified global variable and optimize
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/// it if possible. If we make a change, return true.
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static bool ProcessInternalGlobal(GlobalVariable *GV, Module::giterator &GVI) {
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std::set<PHINode*> PHIUsers;
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GlobalStatus GS;
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PHIUsers.clear();
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GV->removeDeadConstantUsers();
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if (GV->use_empty()) {
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DEBUG(std::cerr << "GLOBAL DEAD: " << *GV);
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++NumDeleted;
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return true;
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}
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if (!AnalyzeGlobal(GV, GS, PHIUsers)) {
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// If the global is never loaded (but may be stored to), it is dead.
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// Delete it now.
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if (!GS.isLoaded) {
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DEBUG(std::cerr << "GLOBAL NEVER LOADED: " << *GV);
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// Delete any stores we can find to the global. We may not be able to
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// make it completely dead though.
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CleanupConstantGlobalUsers(GV, GV->getInitializer());
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// If the global is dead now, delete it.
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if (GV->use_empty()) {
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GV->getParent()->getGlobalList().erase(GV);
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++NumDeleted;
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}
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return true;
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} else if (GS.StoredType <= GlobalStatus::isInitializerStored) {
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DEBUG(std::cerr << "MARKING CONSTANT: " << *GV);
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GV->setConstant(true);
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// Clean up any obviously simplifiable users now.
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CleanupConstantGlobalUsers(GV, GV->getInitializer());
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// If the global is dead now, just nuke it.
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if (GV->use_empty()) {
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DEBUG(std::cerr << " *** Marking constant allowed us to simplify "
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"all users and delete global!\n");
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GV->getParent()->getGlobalList().erase(GV);
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++NumDeleted;
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}
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++NumMarked;
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return true;
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} else if (!GS.isNotSuitableForSRA &&
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!GV->getInitializer()->getType()->isFirstClassType()) {
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DEBUG(std::cerr << "PERFORMING GLOBAL SRA ON: " << *GV);
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if (GlobalVariable *FirstNewGV = SRAGlobal(GV)) {
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GVI = FirstNewGV; // Don't skip the newly produced globals!
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return true;
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}
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}
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}
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return false;
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}
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bool GlobalOpt::runOnModule(Module &M) {
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bool Changed = false;
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@ -341,52 +433,16 @@ bool GlobalOpt::runOnModule(Module &M) {
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Changed |= LocalChange;
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}
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std::set<PHINode*> PHIUsers;
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for (Module::giterator GVI = M.gbegin(), E = M.gend(); GVI != E;) {
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GlobalVariable *GV = GVI++;
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if (!GV->isConstant() && GV->hasInternalLinkage() && GV->hasInitializer()) {
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GlobalStatus GS;
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PHIUsers.clear();
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GV->removeDeadConstantUsers();
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if (!AnalyzeGlobal(GV, GS, PHIUsers)) {
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// If the global is never loaded (but may be stored to), it is dead.
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// Delete it now.
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if (!GS.isLoaded) {
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DEBUG(std::cerr << "GLOBAL NEVER LOADED: " << *GV);
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// Delete any stores we can find to the global. We may not be able to
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// make it completely dead though.
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CleanupConstantGlobalUsers(GV, GV->getInitializer());
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// If the global is dead now, delete it.
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if (GV->use_empty()) {
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M.getGlobalList().erase(GV);
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++NumDeleted;
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}
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Changed = true;
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} else if (GS.StoredType <= GlobalStatus::isInitializerStored) {
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DEBUG(std::cerr << "MARKING CONSTANT: " << *GV);
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GV->setConstant(true);
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// Clean up any obviously simplifiable users now.
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CleanupConstantGlobalUsers(GV, GV->getInitializer());
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// If the global is dead now, just nuke it.
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if (GV->use_empty()) {
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M.getGlobalList().erase(GV);
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++NumDeleted;
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}
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++NumMarked;
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Changed = true;
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} else if (!GS.isNotSuitableForSRA &&
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!GV->getInitializer()->getType()->isFirstClassType()) {
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DEBUG(std::cerr << "PERFORMING GLOBAL SRA ON: " << *GV);
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if (GlobalVariable *FirstNewGV = SRAGlobal(GV))
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GVI = FirstNewGV; // Don't skip the newly produced globals!
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}
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}
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LocalChange = true;
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while (LocalChange) {
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LocalChange = false;
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for (Module::giterator GVI = M.gbegin(), E = M.gend(); GVI != E;) {
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GlobalVariable *GV = GVI++;
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if (!GV->isConstant() && GV->hasInternalLinkage() &&
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GV->hasInitializer())
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LocalChange |= ProcessInternalGlobal(GV, GVI);
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}
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Changed |= LocalChange;
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}
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return Changed;
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}
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