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* Pull out the meat of runOnModule into another function for clarity.

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* 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
This commit is contained in:
Chris Lattner 2004-10-08 20:59:28 +00:00
parent 508540321b
commit a4be1dc0a1
1 changed files with 101 additions and 45 deletions
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142
lib/Transforms/IPO/GlobalOpt.cpp
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@ -87,6 +87,24 @@ struct GlobalStatus {
isNotSuitableForSRA(false) {}
};
/// ConstantIsDead - Return true if the specified constant is (transitively)
/// dead. The constant may be used by other constants (e.g. constant arrays and
/// constant exprs) as long as they are dead, but it cannot be used by anything
/// else.
static bool ConstantIsDead(Constant *C) {
if (isa<GlobalValue>(C)) return false;
for (Value::use_iterator UI = C->use_begin(), E = C->use_end(); UI != E; ++UI)
if (Constant *CU = dyn_cast<Constant>(*UI)) {
if (!ConstantIsDead(CU)) return false;
} else
return false;
return true;
}
/// AnalyzeGlobal - Look at all uses of the global and fill in the GlobalStatus
/// structure. If the global has its address taken, return true to indicate we
/// can't do anything with it.
@ -160,6 +178,10 @@ static bool AnalyzeGlobal(Value *V, GlobalStatus &GS,
} else {
return true; // Any other non-load instruction might take address!
}
} else if (Constant *C = dyn_cast<Constant>(*UI)) {
// We might have a dead and dangling constant hanging off of here.
if (!ConstantIsDead(C))
return true;
} else {
// Otherwise must be a global or some other user.
return true;
@ -232,6 +254,15 @@ static void CleanupConstantGlobalUsers(Value *V, Constant *Init) {
CleanupConstantGlobalUsers(GEP, SubInit);
if (GEP->use_empty())
GEP->getParent()->getInstList().erase(GEP);
} else if (Constant *C = dyn_cast<Constant>(U)) {
// If we have a chain of dead constantexprs or other things dangling from
// us, and if they are all dead, nuke them without remorse.
if (ConstantIsDead(C)) {
C->destroyConstant();
// This could have incalidated UI, start over from scratch.x
CleanupConstantGlobalUsers(V, Init);
return;
}
}
}
}
@ -322,6 +353,67 @@ static GlobalVariable *SRAGlobal(GlobalVariable *GV) {
return NewGlobals[0];
}
/// ProcessInternalGlobal - Analyze the specified global variable and optimize
/// it if possible. If we make a change, return true.
static bool ProcessInternalGlobal(GlobalVariable *GV, Module::giterator &GVI) {
std::set<PHINode*> PHIUsers;
GlobalStatus GS;
PHIUsers.clear();
GV->removeDeadConstantUsers();
if (GV->use_empty()) {
DEBUG(std::cerr << "GLOBAL DEAD: " << *GV);
++NumDeleted;
return true;
}
if (!AnalyzeGlobal(GV, GS, PHIUsers)) {
// If the global is never loaded (but may be stored to), it is dead.
// Delete it now.
if (!GS.isLoaded) {
DEBUG(std::cerr << "GLOBAL NEVER LOADED: " << *GV);
// Delete any stores we can find to the global. We may not be able to
// make it completely dead though.
CleanupConstantGlobalUsers(GV, GV->getInitializer());
// If the global is dead now, delete it.
if (GV->use_empty()) {
GV->getParent()->getGlobalList().erase(GV);
++NumDeleted;
}
return true;
} else if (GS.StoredType <= GlobalStatus::isInitializerStored) {
DEBUG(std::cerr << "MARKING CONSTANT: " << *GV);
GV->setConstant(true);
// Clean up any obviously simplifiable users now.
CleanupConstantGlobalUsers(GV, GV->getInitializer());
// If the global is dead now, just nuke it.
if (GV->use_empty()) {
DEBUG(std::cerr << " *** Marking constant allowed us to simplify "
"all users and delete global!\n");
GV->getParent()->getGlobalList().erase(GV);
++NumDeleted;
}
++NumMarked;
return true;
} else if (!GS.isNotSuitableForSRA &&
!GV->getInitializer()->getType()->isFirstClassType()) {
DEBUG(std::cerr << "PERFORMING GLOBAL SRA ON: " << *GV);
if (GlobalVariable *FirstNewGV = SRAGlobal(GV)) {
GVI = FirstNewGV; // Don't skip the newly produced globals!
return true;
}
}
}
return false;
}
bool GlobalOpt::runOnModule(Module &M) {
bool Changed = false;
@ -341,52 +433,16 @@ bool GlobalOpt::runOnModule(Module &M) {
Changed |= LocalChange;
}
std::set<PHINode*> PHIUsers;
LocalChange = true;
while (LocalChange) {
LocalChange = false;
for (Module::giterator GVI = M.gbegin(), E = M.gend(); GVI != E;) {
GlobalVariable *GV = GVI++;
if (!GV->isConstant() && GV->hasInternalLinkage() && GV->hasInitializer()) {
GlobalStatus GS;
PHIUsers.clear();
GV->removeDeadConstantUsers();
if (!AnalyzeGlobal(GV, GS, PHIUsers)) {
// If the global is never loaded (but may be stored to), it is dead.
// Delete it now.
if (!GS.isLoaded) {
DEBUG(std::cerr << "GLOBAL NEVER LOADED: " << *GV);
// Delete any stores we can find to the global. We may not be able to
// make it completely dead though.
CleanupConstantGlobalUsers(GV, GV->getInitializer());
// If the global is dead now, delete it.
if (GV->use_empty()) {
M.getGlobalList().erase(GV);
++NumDeleted;
}
Changed = true;
} else if (GS.StoredType <= GlobalStatus::isInitializerStored) {
DEBUG(std::cerr << "MARKING CONSTANT: " << *GV);
GV->setConstant(true);
// Clean up any obviously simplifiable users now.
CleanupConstantGlobalUsers(GV, GV->getInitializer());
// If the global is dead now, just nuke it.
if (GV->use_empty()) {
M.getGlobalList().erase(GV);
++NumDeleted;
}
++NumMarked;
Changed = true;
} else if (!GS.isNotSuitableForSRA &&
!GV->getInitializer()->getType()->isFirstClassType()) {
DEBUG(std::cerr << "PERFORMING GLOBAL SRA ON: " << *GV);
if (GlobalVariable *FirstNewGV = SRAGlobal(GV))
GVI = FirstNewGV; // Don't skip the newly produced globals!
}
}
if (!GV->isConstant() && GV->hasInternalLinkage() &&
GV->hasInitializer())
LocalChange |= ProcessInternalGlobal(GV, GVI);
}
Changed |= LocalChange;
}
return Changed;
}